FEMA

Risk Management Series

Design Guide

for Improving Hospital Safety 

in Earthquakes, Floods, and High Winds

FEMA 577 / June 2007 
Olive View Hospital After the 1971 Magnitude 6.7 San Fernando 

Earthquake

Photo Credit: E.V. Leyendecker, U.S. Geological Survey 

About the Cover

Olive View Hospital Replacement Fares Well In 1994 Quake

The new Olive View hospital building shown on the cover performed well during the 1994 

Northridge earthquake. This quake, of the same magnitude as the 1971 San Fernando Earthquake 

that nearly collapsed the original building, 

caused no serious damage. Built in 1970, the 

Medical Treatment and Care Building of the 

Olive View Hospital complex was designed to 

meet the earthquake provisions of building 

codes in place at that time. The hospital 

incurred heavy damage (at left) during 

the 1971 earthquake and was subsequently 

rebuilt to stricter design and construction 

standards.
Risk Management Series

Design Guide for 

Improving Hospital Safety 

in Earthquakes, Floods, 

and High Winds

Providing Protection to People and Buildings

FEMA 577 / June 2007
Any opinions, findings, conclusions, or recommendations 

expressed in this publication do not necessarily reflect the views of 

FEMA. Additionally, neither FEMA nor any of its employees makes 

any warranty, expressed or implied, or assumes any legal liability 

or responsibility for the accuracy, completeness, or usefulness of 

any information, product, or process included in this publication. 

Users of information from this publication assume all liability 

arising from such use.
FOREWORD AND ACKNOWLEDGMENTS 

FOREWORD AND ACKNOWLEDGMENTS

BACKGROUND

T he United States is currently in the middle of the biggest hospital 

construction boom in more than 50 years. According to data from 

the U.S. Census Bureau, spending for construction of new hospitals and other medical facilities increased 65 percent between 2000 and 

2006. New scientific and technological innovations, as well as advancements in medical practice and the organization of health care, demand 

a physical environment different from the hospitals of the past. This demand is being met by the increasing use of evidence-based design, which 

relies on a combination of scientifically proven research and the evaluation of completed projects to make design and construction decisions that 

improve the safety and functionality of hospital buildings. 

Architects and engineers now look at credible research related not just 

to structural and mechanical engineering, but also to clinical outcomes, 

behavioral science, the environment, and technology. New building designs are now seen as important components that can improve medical 

outcomes, patient safety, employee satisfaction, and even financial performance. The effective use of evidence-based design requires continuous 

and timely updates of the information that affects hospital design. As part 

of this effort, the Federal Emergency Management Agency (FEMA) has 

developed this Design Guide to provide the designers of new hospitals 

and retrofits to existing ones with the latest information and research results on the best practices to reduce the risks from natural hazards. 

This publication is the latest addition to FEMA’s Risk Management Series, 

which provides guidelines for mitigating the risks associated with multiple hazards. The series emphasizes mitigation best practices for specific 
ii FOREWORD AND ACKNOWLEDGMENTS

building uses and occupancies, such as schools, critical facilities, commercial buildings, and multi-family dwellings.

OBJECTIVE AND SCOPE

The objective of the “Design Guide for Improving Hospital Safety in 

Earthquakes, Floods, and High Winds” is to inform and assist design professionals, hospital administrators, and facility managers in implementing 

sound mitigation measures that will decrease the vulnerability of hospitals to disruptions caused by natural hazard events. The intent of the 

Design Guide is to provide its audience with state-of-the-art knowledge on 

the variety of vulnerabilities faced by hospitals exposed to earthquakes, 

flooding, and high-winds risks, as well as the best ways to mitigate the risk 

of damage and disruption of hospital operations caused by these events. 

The information presented in this publication provides an exhaustive review of mitigation measures and design solutions that can improve the 

safety of hospitals in natural hazard events. However, this publication is 

not intended to be a comprehensive mitigation design manual that the 

reader can use to develop actual plans and specifications. It is intended 

as an introduction to the fundamental principles of natural hazard risk 

reduction, with an emphasis on mitigation planning and the design of 

hospital buildings. The information presented here is intended to help 

design professionals, hospital administrators, and facility managers understand the broad aspects of risk reduction methods and strategies, and 

integrate them into hospital designs. 

ORGANIZATION AND CONTENT

The Design Guide is organized around three specific natural hazards: 

earthquakes, floods, and high winds. It comprises four main chapters.

Chapter 1 presents an overview of the principal considerations determining hospital design, from standard industry requirements to new 

developments that are transforming both hospital operations and organization of the physical environment. It highlights the known vulnerabilities 

of hospitals and the repercussions of damage caused by natural hazard 

events that frequently interfere with the operation of these facilities. The 

chapter concludes with a look at the multi-hazard approach to hospital 

design, and provides basic guidelines on the interaction between the responses of building components to various natural hazard risks.

Chapter 2 examines potential earthquake damage to hospitals, and how 

these facilities can most efficiently improve their performance. The 
FOREWORD AND ACKNOWLEDGMENTS iii

chapter opens with an introductory discussion on the nature and probability of earthquakes, and procedures for determining seismic risk to 

specific locations. Typical seismic damages, and the possible resulting effects on building functions or risk to occupants, are described and related 

to the standard damage states currently used in performance-based earthquake engineering design. The chapter ends with a review of the best 

practices in seismic design and seismic retrofit of hospital facilities.

Chapter 3 discusses the nature of flood forces and their effects on buildings. It outlines the procedures for risk assessment and describes the 

current mitigation measures for reducing flood damage. It emphasizes 

the benefits of avoiding construction of new hospitals in high-risk areas, 

describes regulatory design requirements that help reduce the exposure 

of hospitals that must be located in flood hazard areas, and encourages 

the application of appropriate mitigation measures to existing hospitals at 

risk of flooding. 

Chapter 4 discusses the effects of wind forces on hospitals’ structural and 

nonstructural building components. By reviewing numerous examples of 

wind-induced damage to these facilities, this chapter highlights the best 

mitigation practices for new hospital design and construction, and for the 

rehabilitation of existing facilities. It concentrates on the building components that are the most critical for maintaining uninterrupted operation 

of hospitals, and provides detailed guidelines for improving their design 

and construction.

At the end are Appendix A, which contains a list of acronyms, and Appendix B, which contains a glossary of terms that appear in the Design 

Guide.

ACKNOWLEDGMENTS

Principal Authors:

Christopher Arnold, Building Systems Development, Inc.

William B. Holmes, Rutherford and Chekene

Rebecca C. Quinn, RCQuinn Consulting, Inc.

Thomas L. Smith, TLSmith Consulting

Bogdan Srdanovic, URS Corporation

Wilbur Tussler, Consultant
iv FOREWORD AND ACKNOWLEDGMENTS

Contributors:

Milagros Nanita Kennett, FEMA, Project Officer, Risk Management Series 

Publications

Eric Letvin, URS Corporation, Project Manager

Susan Patton, URS Corporation

Rob Fernandez, URS Corporation

Ivy Porpotage, URS Corporation

Wanda Rizer, design4impact

Project Advisory Panel:

Amar Chaker (AEI), American Society of Civil Engineers (ASCE) 

Ken Dickerman, AIA Academy of Architecture and Health 

Skip Gregory, Florida Agency for Health Care Administration

Mike Kuechenmeister, American Society of Healthcare Engineering

Jim Rossberg (SEI), American Society of Civil Engineers (ASCE) 

John Sullivan, Portland Cement Association

This manual will be revised periodically, and FEMA welcomes comments and suggestions for improvements in future editions. Please send 

your comments and suggestions via e-mail to: 

RiskManagementSeriesPubs@dhs.gov
TABLE OF CONTENTS

TABLE OF CONTENTS 

FOREWORD AND ACknowledgments.......................................................................i

Background.................................................................................................................................i

Objective and Scope................................................................................................................ii

Organization and Contents....................................................................................................ii

Acknowledgements................................................................................................................iii

1 HOSPITAL DESIGN CONSIDERATIONS............................................................. 1-1

1.1	 Introduction......................................................................................................................... 1-1

1.2	 Health Care Industry............................................................................................................. 1-3

1.2.1 Ambulatory Care..................................................................................................... 1-3

1.2.2 Patient Volume........................................................................................................ 1-4

1.2.3 Aging Facilities........................................................................................................ 1-5

1.2.4 Healing Environments........................................................................................... 1-5

1.2.5 Technological Advances......................................................................................... 1-6

1.3	 Hazard Mitigation................................................................................................................. 1-8

1.3.1 Assessing Risk.......................................................................................................... 1-9

1.3.2 Evacuation Considerations................................................................................... 1-10

1.3.3 Potential Vulnerabilities....................................................................................... 1-11
vi TABLE OF CONTENTS

1.3.3.1 Structural Vulnerability..................................................................... 1-12

1.3.3.2 Nonstructural Vulnerability.............................................................. 1-12

1.3.3.3 Spatial and Other Organizational Vulnerabilities........................... 1-15

1.4 	 Hospital Design and Construction.......................................................................................... 1-17

1.4.1 Building Codes...................................................................................................... 1-18

1.5 	 Multi-Hazard Design Considerations...................................................................................... 1-20

1.5.1 The Need for a Multi-Hazard Approach ............................................................ 1-21

1.5.2 Multi-Hazard Design Matrix................................................................................ 1-22

1.6 	 References......................................................................................................................... 1-32

2 MAKING HOSPITALS SAFE FROM EARTHQUAKES.................................. 2-1

2.1	 Introduction......................................................................................................................... 2-1

2.1.1 The Nature and Probability of Earthquakes......................................................... 2-1

2.1.2 Earthquake Effects.................................................................................................. 2-2

2.1.3 Measuring Earthquake Effects............................................................................... 2-3

2.1.3.1 Measuring Seismic Ground Motion................................................... 2-5

2.1.3.2 Measuring Potential for Liquefaction................................................ 2-7

2.1.3.3 Measuring Potential for Landslide..................................................... 2-7

2.1.3.4 Measuring Potential for Tsunami and Seiche................................... 2-8

2.1.4 Earthquakes: A National Problem........................................................................ 2-8

2.2	 Seismic Building Design ....................................................................................................... 2-11

2.2.1 The Equivalent Lateral Force (ELF) Analysis Methodology............................. 2-12

2.2.1.1 Acceleration....................................................................................... 2-13

2.2.1.2 Amplification and Soil Type............................................................. 2-14

2.2.1.3 Building Period.................................................................................. 2-15

2.2.2 Critical Building Characteristics ......................................................................... 2-16

2.2.2.1 Period and Resonance...................................................................... 2-16

2.2.2.2 Damping............................................................................................. 2-16

2.2.2.3 Nonlinear Behavior........................................................................... 2-17
TABLE OF CONTENTS vii

2.2.2.4 Ductility.............................................................................................. 2-17

2.2.2.5 Strength and Stiffness....................................................................... 2-18

2.2.2.6 Drift.................................................................................................... 2-19

2.2.2.7 Configuration: Size and Shape........................................................ 2-20

2.2.2.8 Stress Concentrations........................................................................ 2-20

2.2.2.9 Torsional Forces................................................................................. 2-21

2.2.3 Specifications for Performance-Based Seismic Design...................................... 2-24

2.2.3.1 Performance Levels........................................................................... 2-24

2.2.3.2 New Developments in Performance-Based Design......................... 2-27

2.3	 Earthquake Damage to Hospitals........................................................................................... 2-29

2.3.1 Types of Structural Damage................................................................................. 2-31

2.3.1.1 The Case of the Olive View Medical Center.................................... 2-32

2.3.2 Nonstructural Damage......................................................................................... 2-35

2.3.2.1 The Case of New Olive View Medical Center.................................. 2-39

2.3.2.2 The Case of Kona Community Hospital, Hawaii ........................... 2-42

2.3.3 Consequences of Building Damage ................................................................... 2-48

2.3.4 Seismic Vulnerability of Hospitals ...................................................................... 2-49

2.3.4.1 Seismic Vulnerability of Hospitals Based on

Historical Performance in California.............................................. 2-50

2.3.4.2 Vulnerability Assessment of Hospital Buildings.............................. 2-52

2.3.4.3 Comparability of Hospital Buildings................................................ 2-53

2.4	 Risk Reduction Measures..................................................................................................... 2-57

2.4.1 Site Selection Basics.............................................................................................. 2-57

2.4.2 Seismic Design Basics........................................................................................... 2-58

2.4.3 Structural Systems................................................................................................. 2-59

2.4.3.1 Basic Types of Lateral Force Resisting Systems............................... 2-59

2.4.3.2 Innovative Structural Systems........................................................... 2-62

2.4.3.3 Structural Systems Selection............................................................. 2-63

2.4.4 Nonstructural Components and Systems............................................................ 2-64

2.4.4.1 Code Regulated Nonstructural Systems........................................... 2-65

2.4.4.2 Interstitial Space for Utility Installations......................................... 2-67
viii TABLE OF CONTENTS

2.4.5 Mitigation Measures for New Buildings.............................................................. 2-68

2.4.5.1 The Case of Loma Linda Veterans Hospital.................................... 2-68

2.4.6 Mitigation Measures for Existing Buildings........................................................ 2-72

2.4.6.1 Procedures and Design Strategies for Rehabilitation

of Structural Systems......................................................................... 2-72

2.4.6.2 The Case of Naval Hospital Bremerton........................................... 2-73

2.4.6.3 Procedures and Design Strategies for Rehabilitation

of Nonstructural Systems.................................................................. 2-77

2.4.6.4 Summary of Risk Reduction Measures for Existing

Buildings............................................................................................ 2-77

2.5	 Checklist for Seismic Vulnerability of Hospitals........................................................................ 2-80

2.6	 References and Sources of Additional Information.................................................................... 2-84

3 MAKING HOSPITALS SAFE FROM FLO0DING............................................ 3-1

3.1	 General Design Considerations................................................................................................ 3-1

3.1.1 The Nature of Flooding......................................................................................... 3-1

3.1.2 Probability of Occurrence or Frequency.............................................................. 3-4

3.1.3 Flood Characteristics and Loads............................................................................ 3-7

3.1.3.1 Hydrostatic Loads................................................................................ 3-9

3.1.3.2 Hydrodynamic Loads........................................................................ 3-10

3.1.3.3 Debris Impact Loads......................................................................... 3-12

3.1.3.4 Erosion and Local Scour .................................................................. 3-13

3.1.4 Design Parameters................................................................................................ 3-14

3.1.4.1 Flood Depth ...................................................................................... 3-14

3.1.4.2 Design Flood Elevation .................................................................... 3-17

3.1.4.3 Flood Velocity—Riverine.................................................................. 3-17

3.1.4.4 Flood Velocity—Coastal.................................................................... 3-18

3.1.5 Flood Hazard Maps and Zones............................................................................ 3-19

3.1.5.1 NFIP Flood Maps............................................................................... 3-20

3.1.5.2 NFIP Flood Zones.............................................................................. 3-21

3.1.5.3 Coastal A Zones ................................................................................ 3-24
TABLE OF CONTENTS ix

3.1.6 Floodplain Management Requirements and Building Codes .......................... 3-26

3.1.6.1 Overview of the NFIP........................................................................ 3-26

3.1.6.2 Summary of the NFIP Minimum Requirements ............................ 3-28

3.1.6.3 Executive Order 11988 and Critical Facilities ................................ 3-29

3.1.6.4 Scope of Model Building Codes and Standards ............................. 3-30

3.2	 Hospitals Exposed to Flooding ............................................................................................. 3-33

3.2.1 Identifying Flood Hazards at Existing Hospitals................................................ 3-33

3.2.2 Vulnerability: What Flooding Can Do to Existing Hospitals............................ 3-33

3.2.2.1 Site Damage....................................................................................... 3-34

3.2.2.2 Structural Damage............................................................................. 3-36

3.2.2.3 Nonstructural Damage...................................................................... 3-38

3.2.2.4 Medical Equipment........................................................................... 3-41

3.2.2.5 Utility System Damage....................................................................... 3-41

3.2.2.6 Contents Damage.............................................................................. 3-44

3.3	 Requirements and Best Practices in Flood Hazard Areas............................................................ 3-47

3.3.1 Evaluating Risk and Avoiding Flood Hazards..................................................... 3-47

3.3.2 Benefits and Costs: Determining Acceptable Risk............................................ 3-48

3.3.3 Site Modifications................................................................................................. 3-50

3.3.4 Elevation Considerations..................................................................................... 3-53

3.3.4.1 The Case of Boulder Community Foothills Hospital,

Boulder, Colorado ............................................................................ 3-58

3.3.5 Dry Floodproofing Considerations .................................................................... 3-63

3.3.6 Flood-Resistant Materials .................................................................................... 3-66

3.3.7 Access Roads ......................................................................................................... 3-68

3.3.8 Utility Installations ............................................................................................... 3-69

3.3.9 Potable Water and Wastewater Systems............................................................... 3-71

3.3.10 Storage Tank Installations ................................................................................... 3-71

3.3.11 Accessory Structures ............................................................................................ 3-72

3.4	 Risk Reduction for Existing Hospitals..................................................................................... 3-73

3.4.1 Introduction.......................................................................................................... 3-73
TABLE OF CONTENTS

3.4.2 Site Modifications ................................................................................................ 3-73

3.4.3 Additions .............................................................................................................. 3-75

3.4.4 Repairs, Renovations, and Upgrades.................................................................. 3-77

3.4.5 Retrofit Dry Floodproofing ................................................................................. 3-78

3.4.5.1 The Case of Pungo District Hospital, Belhaven, North

Carolina.............................................................................................. 3-79

3.4.6 Utility Installations ............................................................................................... 3-84

3.4.7 Potable Water and Wastewater Systems............................................................... 3-86

3.4.8 Other Damage Reduction Measures .................................................................. 3-87

3.4.9 Emergency Measures............................................................................................ 3-88

3.5	 Checklist for Building Vulnerability of Flood-Prone Hospitals...................................................... 3-90

3.6	 References and Sources of Additional Information.................................................................... 3-98

4 MAKING HOSPITALS SAFE FROM HIGH WIND................................ 4-1

4.1	 General Design Considerations................................................................................................ 4-1

4.1.1 Nature of High Winds............................................................................................ 4-3

4.1.2 Probability of Occurrence...................................................................................... 4-3

4.1.3 Wind/Building Interactions.................................................................................. 4-5

4.1.4 Building Codes........................................................................................................ 4-9

4.1.4.1 Scope of Building Codes..................................................................... 4-9

4.1.4.2 Effectiveness and Limitations of Building Codes............................ 4-10

4.2 	 Hospitals Exposed to High Winds.......................................................................................... 4-13

4.2.1 Vulnerability: What High Winds Can Do to Hospitals...................................... 4-13

4.2.1.1 Types of Building Damage................................................................ 4-13

4.2.1.2 Ramifications of Damage.................................................................. 4-16

4.2.1.3 The Case of West Florida Hospital, Pensacola, Florida.................. 4-17

4.2.2 Evaluating Hospitals for Risk From High Winds................................................ 4-24

4.2.2.1 New Buildings.................................................................................... 4-24

4.2.2.2 Existing Buildings.............................................................................. 4-25
TABLE OF CONTENTS xi

4.3 	 Requirements and Best Practices In High-Wind Regions ........................................................... 4-26

4.3.1 General Hospital Design Considerations............................................................ 4-26

4.3.1.1 Site ..................................................................................................... 4-28

4.3.1.2 Building Design ................................................................................ 4-29

4.3.1.3 Construction Contract Administration............................................ 4-34

4.3.1.4 Post-Occupancy Inspections, Periodic

Maintenance, Repair, and Replacement.......................................... 4-35

4.3.1.5 Site and General Design Considerations in

Hurricane-Prone Regions................................................................. 4-36

4.3.2 Structural Systems ............................................................................................... 4-37

4.3.2.1 Structural Systems in Hurricane-Prone Regions............................. 4-41

4.3.3 Building Envelope ............................................................................................... 4-42

4.3.3.1 Exterior Doors................................................................................... 4-42

4.3.3.2 Exterior Doors in Hurricane-Prone Regions................................... 4-46

4.3.3.3 Windows and Skylights...................................................................... 4-47

4.3.3.4 Windows and Skylights in Hurricane-Prone Regions .................... 4-49

4.3.3.5 Non-Load-Bearing Walls, Wall Coverings, and Soffits.................... 4-52

4.3.3.6 Non-Load-Bearing Walls, Wall Coverings, and Soffits

in Hurricane-Prone Regions ............................................................ 4-64

4.3.3.7 Roof Systems...................................................................................... 4-65

4.3.3.8 Roof Systems in Hurricane-Prone Regions...................................... 4-74

4.3.3.9 The Case of DeSoto Memorial Hospital, Arcadia, Florida............. 4-81

4.3.4 Nonstructural Systems And Equipment.............................................................. 4-85

4.3.4.1 Exterior-Mounted Mechanical Equipment..................................... 4-86

4.3.4.2 Nonstructural Systems and Mechanical Equipment

in Hurricane-Prone Regions............................................................ 4-94

4.3.4.3 Exterior-Mounted Electrical and Communications

Equipment......................................................................................... 4-94

4.3.4.4 Lightning Protection Systems (LPS) in HurricaneProne Regions.................................................................................... 4-97

4.3.4.5 The Case of Martin Memorial Medical Center, Stuart,

Florida.............................................................................................. 4-102
xii TABLE OF CONTENTS

4.3.5 Municipal Utilities in Hurricane-prone Regions.............................................. 4-104

4.3.5.1 Electrical Power .............................................................................. 4-104

4.3.5.2 Water Service .................................................................................. 4-105

4.3.5.3 Sewer Service .................................................................................. 4-106

4.3.6 Post-design Considerations In Hurricane-Prone Regions............................... 4-106

4.3.6.1 Construction Contract Administration ......................................... 4-106

4.3.6.2 Periodic Inspections, Maintenance, and Repair .......................... 4-106

4.4	 Remedial Work on Existing Facilities.................................................................................... 4-107

4.4.1 Structural Systems............................................................................................... 4-109

4.4.2 Building Envelope ............................................................................................. 4-111

4.4.2.1 Sectional and Rolling Doors........................................................... 4-111

4.4.2.2 Windows and Skylights.................................................................... 4-112

4.4.2.3 Roof Coverings................................................................................ 4-115

4.4.3 Exterior-Mounted Equipment........................................................................... 4-117

4.4.3.1 Antenna (Communications Mast)................................................. 4-117

4.4.3.2 Lightning Protection Systems......................................................... 4-118

4.4.4 The Case of Baptist Hospital, Pensacola, Florida............................................. 4-118

4.5 	 Best Practices in Tornado-Prone Regions............................................................................... 4-122

4.5.1 The case of Kiowa County Memorial Hospital,

Greensburg, Kansas............................................................................................ 4-126

4.5.2 The case of Sumter Regional Hospital, Americus, Georgia............................ 4-135

4.6 	 Checklist for Building Vulnerability of Hospitals Exposed to High Winds .................................... 4-141

4.7 	 References and Sources of Additional Information.................................................................. 4-147

APPENDICES

Appendix A	 Acronyms................................................................................................................A-1

Appendix B	 Glossary of Terms....................................................................................................B-1
HOSPITAL DESIGN CONSIDERATIONS 1-1

HOSPITAL DESIGN CONSIDERATIONS 1

1.1 INTRODUCTION

Most Americans are accustomed to receiving sophisticated and prompt medical attention after an injury or a medical problem occurs, anytime and anywhere in the 

country, without traveling great distances. Such expectations are even 

greater during mass emergencies that require immediate care for a 

large number of casualties. In circumstances in which hospital operations are disrupted or completely disabled, the adverse effects of such 

disasters can be quickly compounded, frequently with catastrophic results. A recent report from the Congressional Research Service (CRS),

Hurricane Katrina: the Public Health and Medical Response, examined the 

performance of the public health system during this devastating event. 

According to the CRS report, Hurricane Katrina pushed some of the 

most critical health care delivery systems to their limits, for the first time 

in recent memory (Lister, 2005). Therefore, the importance of uninterrupted hospital operations and ready access to, and availability of, 

immediate medical care cannot be exaggerated.

The intent of this publication is to provide guidelines for planning, design, and construction of new hospitals and rehabilitation of existing 

ones, for the purpose of improving their performance during, and in the 

immediate aftermath of, seismic, flooding, and high-wind events. It is important to acknowledge that there are no universal design guidelines 

to protect buildings from all such events. Different natural phenomena 

present different challenges, and each hazard requires a different approach and a different set of recommendations. When communities face 

more than one of these hazards, the design team must select the mitigation measures most appropriate for achieving the desired performance 

level, regardless of the immediate cause for the potential losses.
1-2 HOSPITAL DESIGN CONSIDERATIONS

For instance, flooding is a more site-specific hazard than others. The preferred approach for new facilities is to select a site that is not subject to 

flooding. When that is not feasible, site modifications or other site-specific 

building design features that mitigate anticipated flood hazard will reduce 

the potential for damage. When it comes to seismic and high-wind events, 

however, in addition to carefully selecting the site, it is necessary to design 

the buildings to be resistant to the variety of forces associated with these 

phenomena. The protection against seismic forces requires that both 

structural and non-structural building components have sufficient resistance. For high winds, protection efforts focus mainly on the exposed 

building components and systems.

This chapter addresses the general issues that influence the operations 

and hospital building designs. Typically, the design of hospital facilities is 

driven by their function and the type of services they provide to the community. These services are constantly evolving in response to trends in the 

health care industry and changing expectations of health care customers. 

Some of these health care trends have been the logical result of advances 

in medical science and technology, while the others, driven by social and 

economic conditions, represent new approaches to management of medical care. Additionally, hospital design has been greatly influenced by the 

recognition that physical environment has a measurable influence on 

human well-being. A growing body of evidence has been accumulated 

that shows how appropriate hospital designs can create the healing environments that improve patient treatment outcomes and patient care in 

general. Increasingly, hospital designers are expected to use this new evidence-based design approach when designing new hospitals.

In order to design effective medical facilities for the future, designers 

must be familiar with the latest industry developments, building requirements stemming from these trends, and the latest research findings on 

the impact of building designs on hospital operations, staff and patient 

morale, and patient care. It is the purpose of this Design Guide to add 

to these general considerations the issues of buildings’ resistance to natural hazards and recommended hazard mitigation measures for risk 

reduction.
HOSPITAL DESIGN CONSIDERATIONS 1-3

1.2 HEALTH CARE INDUSTRY

1.2.1 Ambulatory Care

I

n the last 30 years or so, the health care industry has increasingly 

been moving toward greater emphasis on ambulatory care. The increasing availability of procedures that can be successfully completed 

without an overnight stay in the hospital has led to a proliferation of freestanding ambulatory care centers. Many of these centers are performing 

sophisticated surgeries and complicated diagnostic procedures. Frequently, these centers are not affiliated, or are only loosely affiliated with, 

other hospitals in the community. 

The emphasis on the ambulatory care had a profound effect on the 

healthcare industry, leading to the reduction in the number of hospital 

beds and, in many cases, closing of hospitals because of the reduced demand for overnight stays. At the same time, hospitals had to increase their 

own role in ambulatory care to remain competitive. As the freestanding 

ambulatory facilities took an ever-increasing market share, many hospitals had to downsize, and in some cases, scale back even their surgical 

capacity. In many respects, this development has diminished the capacity 

of medical facilities to care for the casualties in the event of a disaster, because most of the freestanding ambulatory care centers are not suitable 

for post-disaster emergency care. There are several reasons for this:

m They do not have dedicated emergency departments or adequate 

facilities and equipment to deal with trauma patients.

m They are not available or staffed on a 24-hour, 7 days-a-week basis.

m They are not adequately equipped with emergency communications 

systems.

m The staff is not experienced or well trained to care for the types of 

patients and injuries expected in post-disaster emergencies.
1-4 HOSPITAL DESIGN CONSIDERATIONS

m These facilities are not considered essential and are sometimes built 

to a lower building code standard than hospitals, which makes them 

more vulnerable to disruption resulting from building damage.

On the other hand, hospital-based ambulatory care (outpatient) departments can easily be converted for post-disaster care during an emergency, 

assuming the hospital itself remains operational. Hospital-based ambulatory surgeries are often contiguous to surgery for inpatients. Clinic space 

can be used for triage or emergency treatment rooms, and the ambulatory diagnostic equipment is suitable for use in an emergency. The key to 

having hospital-based ambulatory capacity available in the aftermath of 

major disasters is thoughtful planning, so that the emergency department 

can remain the command center, coordinating other areas of the hospital 

where post-disaster patients might be transferred and treated.

1.2.2 Patient Volume

Hospital emergency rooms have become the primary source of medical 

care for millions of people. Unlike other medical facilities, hospitals are 

required to treat anyone who walks in, or is brought in, irrespective of 

their insurance status or ability to pay. This trend puts an enormous pressure on emergency departments, not only because it increases the patient 

load, but also because it expands their functions beyond the treatment of 

emergency and trauma cases.

As a result, many hospitals have enlarged and better equipped their emergency departments to accommodate the ever-increasing patient load, 

which had a positive influence on their capacity to deal with disaster-related emergencies. Additionally, hospital emergency departments are well 

trained in triage that involves prioritization of cases according to the level 

of medical urgency. Patients who are most in need of immediate treatment are treated first, while the others who can wait without harm are 

treated later. Emergency department staff members also go through extensive disaster drills, and in most cases are well trained to respond to 

mass emergencies.

Despite current hospital construction boom, the trend towards reduced 

inpatient capacity in the past decades has adversely affected hospitals’ 

readiness for emergencies. In 1990, the national average was 372 hospital 

beds per 100,000 people, whereas in 2004 there were only 275 beds. The 

number of hospitals in the country1 dropped from 5,384 in 1990 to 4,919 

in 2004. This has reduced the number of hospital beds in many commu1 Data from Trendwatch Chartbook 2006, by the American Hospital Association and the Lewin Group.
HOSPITAL DESIGN CONSIDERATIONS 1-5

nities to the point where some rural communities were left without any 

acute inpatient capacity. 

As a result of hospital closures and inpatient capacity reduction, occupancy rates in the remaining hospitals have increased. The increase 

means that most hospitals are operating at near-maximum inpatient capacity on a regular basis, making it difficult to accommodate a potential 

influx of casualties in a disaster emergency. Some reports, especially those 

that analyzed the response to Hurricane Katrina, singled out the limited 

surge capacity for health care emergencies as one of the most pressing 

problems of the Nation’s health care system (see Lister, 2005).

1.2.3 Aging Facilities

Renovation and replacement of health facilities have been at record 

highs in recent years. Still, a majority of hospital buildings throughout the 

country are of considerable age. A great many of them were built in the 

1950s and 1960s, particularly in rural areas, with Federal funding assistance provided by the Hill-Burton Act passed by Congress following World 

War II. In the 1960s and 1970s, this grant program was also used for replacement and renovation of urban hospitals. As a consequence, a large 

number of hospitals were built in a short period of time. Many of these 

hospitals are now nearing the end of their useful life. Even with periodic 

renovations, there are limits to the value of continued investment in older 

facilities to be used for acute care.

Hospitals are constantly renovating, whether they are just adding electrical outlets or communications cables, or engaging in more complex 

projects that involve moving functions and building additions to the existing structures. This kind of change is a result of many factors: changing 

personnel, new technologies, and competitive pressure. Some changes, 

however, may affect the use of spaces or facilities originally planned and 

built for emergency operations. For instance, renovation may inadvertently upset bracing for piping and communications conduits, making 

them more vulnerable to hazards like earthquakes or high winds. Similarly, functional reorganization of a hospital that makes some critical 

functions and services more accessible by placing them on the ground 

floor increases the risks from flooding to these facilities.

1.2.4 Healing Environments

Since the advent of the hospital “birthing unit” in the late 1970s, the 

health industry has shown an increasing interest in the ability of the 

physical environment to contribute to healing. The growing evidence in-
1-6 HOSPITAL DESIGN CONSIDERATIONS

dicates that a pleasant and comfortable environment reduces stress and 

provides a sense of well-being, both of which are important preconditions 

for successful recovery. Additionally, patient satisfaction with hospital 

services today extends beyond medical care and encompasses a whole hospital experience. To be able to compete successfully with the increasing 

number of outpatient and other alternative healthcare providers, hospitals have started to pay greater attention to providing a “hospitable” and 

“healing environment,” in addition to medical expertise, new technology, 

and advanced procedures. 

This trend manifests itself in building designs that introduce the spirit of 

nature into the hospital environment: more natural light, views of nature 

and direct access to the outdoors from many more areas of the hospital, 

and increased use of courtyards and gardens. Hospital gardens have been 

found to provide not only the restorative and calming nature views, but 

also help reduce stress by providing opportunities for escape from clinical settings, and by fostering greater social interaction among patients 

and staff. The social aspect is particularly important for patients who 

might feel isolated in a sterile hospital environment without the support 

of their families and friends. Considering the significance of social support for patients’ successful recovery, hospitals are planning for greater 

involvement of the family in the care of their patients by requiring singlebed rooms for all newly built acute care hospitals. Additionally, hospitals 

are providing more public spaces that facilitate social interaction, such as 

lounges, atria, and interior streets with shops and restaurants that were 

not part of the traditional hospital environment.

The advent of new hospital architecture, especially the new physical 

arrangements designed to assist in healing have, in many respects, increased the exposure of hospital buildings to natural hazards. The 

emphasis on natural light, the use of single-patient rooms, and a greater 

variety of public spaces usually produces complex building designs with 

greater exterior perimeter and a greater number of doors and windows 

that frequently increase building’s vulnerability to wind and windborne 

debris damage. 

1.2.5 Technological Advances

New and emerging technologies ranging from new electronic devices, 

such as nanoscale sensors, to new wireless communication networks are 

rapidly changing patient treatment practices as well as the organization of 

hospitals. These innovative medical technologies help empower the physicians, nurses, and patients with tools that enable faster diagnosis and 

better treatment of diseases. Most diagnostic practices and procedural 

functions in clinics and surgeries are dependent on modern instruments, 
HOSPITAL DESIGN CONSIDERATIONS 1-7

tools, and laboratory equipment. Today’s hospitals are in the process of 

replacing all analog-based instruments with digital ones. New hospital organization is now based on an IT architecture that maximizes the flow 

of diagnostic and monitoring data from these instruments through new 

communications networks and makes them available to hospital staff in 

making treatment decisions.

Digitized X-rays and other images are being transmitted electronically 

to all parts of the hospital and to doctors’ offices. Clinical laboratory 

test results, prescriptions, and most forms of medical data are now instantly available to medical practitioners. There is a national movement to 

adopt a universal electronic medical record, which would make patient’s 

medical history and other information almost instantly available to the 

treating physician. 

These technological innovations substantially changed not only the medical practice, but also turned this new electronic and IT infrastructure 

into an essential and indispensable backbone of all hospital operations. 

Therein lays the grave vulnerability of hospitals in cases where this sensitive infrastructure can be disrupted, as was seen in many hospitals 

affected by Hurricane Katrina. When a disaster, such as Hurricane Katrina, disables or impairs the functioning of electronic equipment and 

data transmission systems, or even the hospital voice communications systems, the ability of the medical staff to care for their patients is 

significantly reduced.

Emergency power systems, therefore, become 

the critical component for maintaining hospital’s functions. The dependence on electrical 

power generators is increasing as the hospitals 

rely more and more on energy-intensive equipment and procedures. Even if the hospital is 

designed to continue to care for patients after 

a disaster, its ability to function is limited by 

the emergency power supply capacity, the extent of coverage by emergency power systems, and the ability to remain operational for extended 

periods of time.

A U.S. Department of Energy (DOE) 2002 

report ranked healthcare facilities second 

only to food-service facilities in the intensity 

of energy use, defined as the amount of 

energy consumed per square foot of space.
1-8 HOSPITAL DESIGN CONSIDERATIONS

1.3 HAZARD MITIGATION

Mitigation is defined as any sustained action taken to reduce 

or eliminate long-term risk to life and property from hazard 

events. The goal is to save lives and reduce property damage 

in ways that are cost-effective and environmentally sound. Hazard 

mitigation measures should be integrated into the process of planning 

and design because they reduce casualties and damage resulting from 

building failures during hazard events. The effects of a disaster on 

a hospital, however, are never restricted to the physical damage or 

the distress among the staff and patients as a result of such damage. 

Consequences frequently include partial or total loss of the ability to 

provide services and meet the demand for health care when it is most 

needed. Incorporating mitigation measures in the design of hospitals is 

therefore especially important because they minimize the disruption of 

hospital operations and protect the uninterrupted provision of critical 

health services. 

Advances in building science and technology, and changes in design 

philosophy and quality assurance techniques for the construction and 

maintenance of medical infrastructure, now make it possible to limit the 

damage during seismic, flooding, and high-wind events. The advent of 

performance-based design allows the use of different levels of protection 

for different types of infrastructure and operations that frequently exceed the minimum requirements of currently applicable codes. However, 

it is not always possible to achieve the protection levels one might desire, 

owing to a variety of factors. Natural or technical barriers may exist, or 

the funding may be insufficient. Even though financial resources may be 

limited, and other circumstances may impose technical barriers to the fulfillment of performance objectives, a detailed assessment is still required 

in order to ensure the optimal utilization of available resources. 

The starting point for such an assessment should be a general review of 

the existing hospital network in the area—its operational characteristics, 

geographical distribution, the degree to which it is able to meet health 
HOSPITAL DESIGN CONSIDERATIONS 1-9

care needs and expectations, the epidemiological and demographic profile of the population served, and the natural hazards that threaten the 

provision of medical services. The effective functional capacity of all existing hospitals should be taken into account, considering as fully as 

possible all factual information on the natural hazards they face and their 

current level of vulnerability. Once the actual characteristics of this network and the potential hazards have been identified, and the need to 

build a new hospital in a specific location has been established, it is still 

necessary to define the role that the new facility will play, both in normal 

times and during emergencies of various kinds and intensities. Based on 

all this information, the level of overall functional performance should be 

set for the new facility. The process of determination of the performance 

level must address the questions of the importance of continued and 

uninterrupted operation of the facility, as well as the feasibility and cost-effectiveness of such a performance objective. 

All this will be influenced by the characteristics of the site, the specifics of 

the infrastructure to be built, and the basic services it can realistically be 

expected to provide based on different disaster scenarios. In considering 

disaster mitigation, the goal should be to provide the community with access to health care in a reasonable period of time, within reasonable travel 

distances, and to have essential services available to treat patients who 

sustained injuries as a result of the disaster. At the same time, a hospital 

needs to continue to care for their pre-disaster patients and ensure that 

no harm comes to them. 

Much of the procedure for a new building described above can apply to 

hazard mitigation in an existing building as well, with obvious limitations.

1.3.1 Assessing Risk

Beyond the building codes in existence at the time a hospital is designed 

or slated for renovation, the leadership of the facility and the design 

consultants must address key questions to establish the adequacy of the 

building’s performance in the event of a disaster. Hospitals are under 

enormous financial pressure. Any funds invested in making a hospital facility safer for patients and staff, more resistant to damage, or capable of 

continued operations in a post-disaster situation must consider the following questions:

m What types and magnitudes of hazard events are anticipated at the site?

m What are the vulnerabilities of the site or existing building to natural 

hazards?
1-10 HOSPITAL DESIGN CONSIDERATIONS

m What are the anticipated frequencies of hazard events?

m What level of loss/damage/injury/death, if any, is acceptable?

m What might be the financial impact of extended downtime on the 

institution?

m What is the impact to the community if the hospital cannot maintain 

operations in the aftermath of a disaster?

It is not possible to protect against every conceivable event, or to be 

100 percent safe and free of damage in a major disaster. The level of 

acceptable risk must be decided on an individual facility basis by those responsible for the institution and its mission.

1.3.2 Evacuation Considerations

In anticipation of high winds or flooding, timely evacuation of some 

or all of the hospital patients to facilities out of the disaster area may 

sometimes be a prudent choice for patient welfare. The risks of transferring acutely ill patients must be taken into consideration, as pointed 

out by the General Accounting Office (GAO) report to Congress dated 

February 16, 2006, titled, Disaster Preparedness: Preliminary Observations on the Evacuation of Hospitals and Nursing Homes Due to Hurricanes.

It stated: “Administrators consider several issues when deciding to 

evacuate or to shelter in place, including the availability of adequate 

resources to shelter in place, the risks to patients in deciding when to 

evacuate, the availability of transportation to move patients and of receiving facilities to accept patients, and the destruction of the facility’s 

or community’s infrastructure.”

Many patients have limited mobility and some are on critical life support, oxygen or other medical gasses, ventilators, or IV pumps. Moving 

these patients to evacuate the hospital is difficult and requires highly 

trained staff.

In each geographical area, acute care facility managers must evaluate 

the likely time that they would need to hold patients, how many additional patients might arrive seeking care, and what services would be 

needed and for what period of time. In the case of Hurricane Katrina, 

some hospitals evacuated their Neonatal Intensive Care Unit, bariatric 

patients, and dialysis patients before the storm landfall, which proved 

both prudent and beneficial. For hospitals planning to retain their dialysis patients, it is essential to assure a constant supply of electricity to 

power the equipment needed for these patients.
HOSPITAL DESIGN CONSIDERATIONS 1-11

Most hospitals plan to “shelter in place” and weather the storms, rather 

than evacuate. In order to do this, they must take care of their existing 

patients, many of whom are critically ill, and in addition, be prepared 

to accommodate the casualties as well as the increased number of outpatients. In order to accomplish this, there are a wide variety of services 

that must remain functional. Often municipal utility services will be cut 

off during a disaster, so alternative power, water, and waste disposal services need to be provided onsite whenever possible. Communication 

systems are often cut off, so redundancy is a key factor in maintaining 

links to the outside world as well as internal communications within 

the hospital. FEMA publications 361 and 543 both address the specific 

needs of structures to be used as disaster shelters. Sheltering in place 

can be challenging, but in most cases it is the preferred option for most 

acutely ill patients. 

If there is a plan to evacuate patients, or a probability that patients will 

need to be evacuated, regional planning with other hospitals in the area 

and coordination of resources is essential. Agreements and appropriate 

provisions need to be put in place so that space and staff are available to 

accommodate evacuated patients. The State of Florida has put in place 

an evacuation tracking system for all evacuated patients. This might be 

a useful model for other States to follow.

1.3.3 Potential Vulnerabilities

Hospitals provide services that are essential for protecting and safeguarding the health and well-being of a community. The continued 

provision of these services is even more critical during and in the immediate aftermath of disasters. Considering the complexity of hospital 

operations, even the smallest breakdown in one of its building or equipment systems can cause serious disruption of hospital functions. This 

makes the hospitals extremely vulnerable to a variety of natural hazards. 

Hospitals usually have high levels of occupancy, with patients, staff, and 

many visitors present 24 hours a day. Many patients require constant attention, and in many cases continuous specialized care and the use of 

sophisticated medical instruments or other equipment. Hospital operations also depend on a steady supply of medical and other types of 

material, as well as public services or lifelines. In addition, hospital vulnerability is aggravated by the presence of hazardous substances that may be 

spilled or released in a hazard event. 

Given the importance of hospital services for response and recovery following emergencies, and the need for uninterrupted operation of these 

facilities, hospital administrators and designers must consider all aspects 
1-12 HOSPITAL DESIGN CONSIDERATIONS

of their vulnerability. Three main aspects of hospital vulnerability must be 

taken into account:

m Structural

m Nonstructural

m Organizational

1.3.3.1 Structural Vulnerability

Structural vulnerability is related to potential damage to structural components of a building. They include foundations, bearing walls, columns 

and beams, staircases, floors and roof decks, or other types of structural 

components that help support the building. The level of vulnerability of 

these components depends on the following factors:

m The level to which the design of the structural system has addressed 

the hazard forces

m The quality of building materials, construction, and maintenance

m The architectural and structural form or configuration of a building

The aspects of adequate design and construction in most hazard-prone 

areas are regulated by building codes and other regulations. The main 

purpose of these regulations is to protect the safety of occupants. They 

are usually prescriptive in nature, i.e. they establish minimum requirements that are occasionally updated based on newly acquired knowledge. 

The building regulations alone, however, cannot guarantee uninterrupted operation of a hospital, because a great many other factors affect 

hospital functions. 

1.3.3.2 Nonstructural Vulnerability

The experience of hospital evacuations and other types of disruption 

during recent hazard events (many of which are described in greater 

detail in later chapters) has heightened the awareness that hospital functions could be seriously impaired or interrupted, even when the facilities 

did not sustain significant structural damage. The effects of damage to 

nonstructural building components and equipment, as well as the effects 

of breakdowns in public services (lifelines), transportation, re-supply, or 

other organizational aspects of hospital operations, can be as disruptive, 

and as dangerous for the safety of patients, as any structural damage. 
HOSPITAL DESIGN CONSIDERATIONS 1-13

Architectural Components

Nonstructural vulnerabilities that can affect hospital functions and the 

safety of occupants include the potential failures of architectural components, both on the exterior and the interior of buildings. 

Damage to roof coverings, facades, or windows can make way for water 

penetration that can damage sensitive equipment and shut down many 

hospital functions. When roofing material is disturbed by wind, the 

roof may start to leak and the moisture can knock out vital equipment, 

disrupt patient care, and penetrate walls and other concealed spaces, 

allowing mold to build up over time. Window breakage resulting from 

high winds, earthquakes, and even flooding frequently requires patient 

evacuation from affected areas. Patients in critical care and acute care 

units are particularly vulnerable because the move separates them from 

medical gas outlets, monitors, lighting, and other essential support 

services.

Non-load bearing and partition walls and ceilings, for instance, are 

rarely designed and constructed to the same standards of hazard resistance as the structural elements. Collapse of these components has 

caused a number of evacuations and closures of hospitals following a 

hazard event. 

Installations

Hospitals are extremely complex building systems that depend on an 

extensive network of mechanical, electrical, and piping installations. 

The air and ventilation system is one of the most important ones because it is responsible for maintaining an appropriate environment in 

different parts of the hospital. Isolation rooms usually have negative 

pressure so that harmful airborne organisms do not migrate outside the 

patient’s room and infect others. Likewise, wards housing patients with 

immune system deficiencies require a positive pressure differential, 

so that harmful organisms do not enter the patient room and needlessly infect them. The malfunction in any one part of this ventilation 

system could create a risk of infection to patients and staff. This system 

is extremely vulnerable to disruption as a result of indirect building 

damage. Winds habitually overturn improperly attached roof-mounted 

ventilation and air-conditioning equipment, while the ductwork is very 

susceptible to collapse in earthquakes. Additionally, strong winds may 

change the airflow from ventilation exhaust outlets, potentially causing 

harmful discharges from patient care areas and the clinical laboratory to be sucked back into the fresh air intakes. Airborne debris from 

windstorms could quickly clog the air filtration systems, making them 

inoperable or impaired. 
1-14 HOSPITAL DESIGN CONSIDERATIONS

Hospitals depend on several essential piping systems. Medical gasses are 

among the most important, along with water, steam, and fire sprinkler systems. Physicians and nurses depend on oxygen and other gasses required 

for patient care. Unless properly secured and braced, these installations 

can be easily dislodged or broken, causing dangerous leakage and potential additional damage. 

In floods and earthquakes particularly, sewers are apt to overflow, back 

up, or break down. Waste disposal is essential for any hospital, because 

when the toilets back up, or sterilizers, dishwashers, and other automated 

cleaning equipment cannot be discharged, patient care is immediately 

affected. Retention ponds or holding tanks coupled with backflow and diversion valves can be employed to solve this problem; however, in many 

hospitals, this issue has not been adequately addressed. 

Elevator service is vulnerable not only to power outage, but also to 

direct damage to elevator installations. Wind and windborne debris can 

damage elevator penthouses, opening a path for water penetration that 

can disable elevator motors and controls, as has happened in numerous 

hurricanes in recent years. In the event of an earthquake, elevator shafts 

and other equipment can be damaged or dislodged, effectively shutting 

down the building. Flooding of elevator pits was a common problem 

during Hurricane Katrina, and responsible for the loss of elevator service.

The emergency power supply system is probably the most critical element 

in this group. Together with fuel supply and storage facilities, this system 

enables all the other hospital installations and equipment that have not 

sustained direct physical damage to function normally in any disaster. 

However, uninterrupted operation of a hospital during a power outage is 

possible only if adequate electrical wiring is installed in all the areas that 

require uninterrupted power supply. Since extra wiring and additional circuits for emergency power increase the initial construction costs of the 

building, the decision on the emergency power coverage requires a thorough evaluation of the relative vulnerability of various functions to power 

outage. As patients become more critically ill and the nature of diagnosis 

and treatment becomes more dependent on computers, monitors, and 

other electrical equipment, the need for emergency power will continue 

to grow.

The experience of Hurricane Katrina has demonstrated the need for 

emergency power coverage even for services that typically have not been 

regarded as critical, such as climate control and air-conditioning systems. 

Extreme heat caused a number of hospitals to evacuate their patients and 

staff when the conditions became unbearable.
HOSPITAL DESIGN CONSIDERATIONS 1-15

Equipment and Furnishings

There are many types of internal hazards that might occur as the result of a disaster. In the past, bottles in clinical laboratories have fallen 

and started fires. Earthquakes have catapulted filing cabinet drawers and 

ventilators across rooms at high speed, with the potential of causing considerable injury to personnel. Any wheeled equipment is vulnerable to 

displacement and has the potential to cause injury. 

Electronic communication systems

Hospitals use and depend on many types of communication systems. For 

communications with emergency vehicles or first response agencies, hospitals depend on radio equipment that is frequently mounted on roofs 

and exposed to high winds and windborne debris impact. Satellite dishes, 

communication masts, antennae, and other equipment can be blown off 

the roof or be severely damaged, leaving the hospital without this vital service at a critical time. 

1.3.3.3 Spatial and Other Organizational 

Vulnerabilities

Most hospitals have disaster mitigation or emergency operation plans, but 

not all of them provide organizational alternatives in the event of disruption of the normal movement of staff, patients, equipment, and supplies 

that characterizes everyday hospital operations. The critical nature and 

interdependence of these processes represent a separate category of vulnerabilities that need careful attention. Spatial distribution of hospital 

functions and their inter-relationship determines the extent hospital operations are affected when normal movement and communication of 

people, materials, and waste are disrupted. The disruption by natural 

hazard events of administrative services such as contracting, procurement, 

maintenance, as well as allocation of resources, can impair hospital functions almost as much as any physical damage.

Just-in-time delivery: Many hospitals have currently eliminated, or greatly 

reduced, onsite storage for linen, supplies, food, and other materials essential to normal operations. Any prolonged isolation or blockage of 

streets serving the hospital could lead to a need to ration supplies and 

triage patients for treatment, due to the limited supplies stored on site. 

During Hurricane Katrina, many hospitals were isolated by floodwaters 

for 5 or more days and, in many cases, could not replenish critical supplies, which in some instances contributed to the decision to evacuate 

the facility. 
1-16 HOSPITAL DESIGN CONSIDERATIONS

Evacuation: Evacuation of patients is a measure of last resort, but occasionally necessary, especially in extreme situations. Many different conditions 

or vulnerabilities mentioned above can cause the evacuation of a hospital, 

but the process of evacuation itself can also be vulnerable to disruption 

that can seriously aggravate the health and safety of patients. Frequently, a 

flood, earthquake, or a windstorm can cause blockage of access roads, cut 

ting off a hospital from normal evacuation routes, as happened during 

Hurricane Katrina. Surface escape routes were under water and unusable, and even air evacuation was impaired because many ground level 

helicopter landing pads were under water. Elevated helipads located on 

roof tops or elevated parking structures proved invaluable features in this 

type of an emergency. The spatial relationship to the hospital building 

was another aspect that greatly influenced the evacuation and reduced 

the risk of aggravating patients’ condition. Helipads physically connected 

to the hospital were most useful, because patients could be transported directly and very rapidly from the upper levels of the hospital to the helipad 

without interference from other hospital functions. 
HOSPITAL DESIGN CONSIDERATIONS 1-17

1.4 HOSPITAL DESIGN AND 

CONSTRUCTION

Permanent high occupancy and the need for uninterrupted 

operation are the most important characteristics of hospital 

facilities. They determine most of the building design 

requirements and pose the greatest challenge in the design of 

mitigation measures. Contemporary hospitals must accommodate both 

critically ill patients and a high volume of ambulatory patients. Length 

of stay for inpatients may be as short as one day, but usually averages 

around 5 to 6 days in most hospitals. Acute care patients often have 

visitors on a daily basis, while emergency departments are routinely 

crowded with patients and their families, particularly at peak times 

during the day.

It is not uncommon that some building designs that are otherwise suitable for the complex requirements of hospital operations can impair 

these operations in emergency conditions. This is particularly true of 

many older hospitals that were not designed to maintain their performance level in all conditions. Older emergency departments are 

generally not large enough and are often overcrowded. Many of the 

older hospitals would not have been designed to adjust their operations 

and their physical space to the conditions of mass post-disaster care.

Similarly, larger hospitals typically have greater flexibility to cope with the 

emergencies and large numbers of casualties than smaller hospitals. This, 

however, can be a liability, especially in dense urban areas where hospitals 

buildings are frequently 10 or more stories high. Large, tall hospital buildings, with greater than usual floor-to-floor height, are almost completely 

dependent on elevators for vertical communication, which exposes them 

to serious disruption in case of electrical or mechanical failures common 

during hazard events. Such difficulties are further compounded if an 

evacuation is necessary. When the elevators are rendered inoperable, the 

patients must be carried up or down long stairwells, which can be an overwhelming task for the staff of any large hospital. 
1-18 HOSPITAL DESIGN CONSIDERATIONS

Since the development of effective ventilation systems, most hospitals 

were designed as “thick” buildings, where many areas do not have natural 

light and depend on mechanical ventilation to be usable. Generally, the 

larger the hospital, the more functions and areas depend on mechanical 

ventilation and artificial light. This is another important aspect of hospital 

vulnerability in situations where normal power supply is disrupted. Hospital closures and evacuations caused by nonfunctioning air-conditioning 

systems in the wake of Hurricane Katrina stand as stark examples of the 

need to protect these systems much more effectively. 

Hospitals usually do not occupy just one building. In most cases a hospital 

is located on campus that comprises a number of different buildings, each 

housing a separate function. In addition to an acute care hospital, which 

might be composed of several wings of varying ages, there might also be 

a separate power plant, medical office building, ambulatory surgery and 

procedures building, behavioral health building, fitness center, dialysis 

center, or cancer center. Since all of these buildings have a different type 

and level of occupancy, from the perspective of patient safety and that of 

uninterrupted hospital operations, they do not need the same level of disaster-resistant construction. 

1.4.1 Building Codes

Most States have adopted one of the model building codes, frequently 

with modifications and local additions. Building codes address minimum 

requirements for building resistance to major hazards based on historical 

experience. Recent disaster experience, however, indicates that current 

code requirements are not always adequate, especially not for essential facilities such as hospitals. To make things worse, many existing hospitals 

were built to older codes that frequently did not have any provisions for 

protection against natural hazards. 

Most essential facilities require special attention, in addition to compliance with building code requirements, in order to be able to sustain their 

operations after a major disaster. Some States, like Florida or California, 

for example, have amended their codes to address the need for adequate 

protection of hospitals and other critical facilities from prevailing local 

hazards. California has adopted legislation for seismic design based on the 

principle that hospitals should be able to function at least at a basic level 

after an earthquake of moderate to large magnitude. This new standard 

has resulted in the closure of many hospitals that could not comply with 

the new requirements in a cost-effective manner. The implementation of 

this standard was significant because it established the new criterion for 

post-disaster functionality that should serve as a model for hazard-prone 

regions. This and similar standards have expanded the narrow, prescrip-
HOSPITAL DESIGN CONSIDERATIONS 1-19

tive nature of most building codes, by defining the performance goals 

that hospitals must achieve. This Design Guide fully supports the trend toward performance-based codes for design and construction of hospitals.

In addition to local building codes, various organizations and agencies, 

like the U.S. Department of Veterans Affairs (VA), have developed their 

internal building design and construction regulations to address the three 

major hazards: flood, wind and earthquake. The VA standard “Natural Disasters Non-Structural Resistive Design (formerly CD-54)” together with this 

publication, is a valuable resource for information on new hospital construction and renovation of existing hospitals.
1-20 HOSPITAL DESIGN CONSIDERATIONS

1.5 MULTI-HAZARD DESIGN 

CONSIDERATIONS

A comprehensive hazard risk reduction design strategy that considers all the risks to which a facility may be subject is an evolving concept that is still in its infancy. Multi-hazard design is an approach that aims to integrate risk reduction with the building design 

process, rather than pursuing a traditional tendency towards fragmented 

risk reduction efforts. 

Chapters 2, 3, and 4 outline the characteristics of the three natural hazards that are the subject of this publication, in terms of their geographical 

locations, intensity, and frequency. In addition, methods used to mitigate 

the risks and issues relating to building codes and regulations are also discussed. However, each hazard is discussed separately, without reference 

to the others. Many building locations are vulnerable to more than one 

hazard, requiring the application of appropriate design solutions that 

would mitigate each relevant hazard.

This section looks at the interaction between various building design features and mitigation measures used to protect buildings against specific 

hazards, by comparing their effects for each individual hazard. The similarities and differences in the ways that hazards affect buildings, and how 

to guard against them, demand an integrated approach to building design that would be resistant to natural hazards. This, in turn, must be 

pursued as part of a larger, integrated approach to the whole building design process.

Of the many hazards that can endanger a hospital and impair the services 

it provides to a community, fire is the most prevalent. Every hospital is at 

risk from fire, which makes this hazard much more pervasive than any of 

the natural hazards noted above. However, fire protection measures have 

been present in building codes for a long time, in the form of approved 

materials, fire-resistant assemblies, exiting requirements, the minimum 

number and capacity of emergency exit routes, and many other specifications. For that reason, fire hazards are not addressed in this publication as 
HOSPITAL DESIGN CONSIDERATIONS 1-21

a stand-alone hazard. However, the mitigation measures used to protect 

the buildings against high winds, floods, and earthquakes may interact favorably or unfavorably with the need for fire protection. For this reason, 

fire is included as a hazard in the table of system interactions at the end of 

this chapter.

1.5.1 The Need for a Multi-hazard

Approach

The need to embrace a multi-hazard approach when designing or retrofitting a hospital is essential for their protection, especially when they 

are located in areas that are exposed to a variety of natural and manmade hazards. A multi-hazard approach can help identify potentially 

conflicting effects of certain mitigation measures and help to avoid aggravating the vulnerability of many hospital building components and 

systems. A comprehensive evaluation and application of hazard mitigation in building design serves to improve the overall effectiveness of 

mitigation measures that protect the continuity of hospital functions 

and operations. The importance of this practice has become increasingly evident following the catastrophic disasters that have occurred in 

the recent past.

The aim should be to anticipate and coordinate how the building and its systems interact, 

how mitigation of the risk from one hazard can 

influence the building’s vulnerability to others, 

and how undesirable conditions and conflicts 

may be avoided or resolved. Through the application of a multi-hazard and multi-disciplinary 

approach, cost savings, efficiency, and better 

performance can be achieved in programming and planning new buildings and retrofitting existing ones.

The design team should be able to take an all-hazard viewpoint, and 

understand how the structure and systems interact under extreme conditions imposed by natural hazards. Thus, an important aspect of 

multi-hazard design should be to investigate the extent to which the 

methods used for mitigation of one hazard may reinforce or conflict with 

design elements necessary for protection against other possible hazards. 

When the design methods reinforce one another, the costs of multihazard design may be reduced and the performance improved, but where 

they conflict, costs may be increased in order to satisfy the requirements 

for resistance to all relevant hazards. 

A multi-hazard risk reduction approach 

requires a multidisciplinary design team. 

This ensures that the project design benefits 

from an appropriate professional expertise 

and a thorough discussion of project issues 

from start to finish.

A multi-hazard risk reduction approach 

requires a multidisciplinary design team. 

This ensures that the project design benefits 

from an appropriate professional expertise 

and a thorough discussion of project issues 

from start to finish.
1-22 HOSPITAL DESIGN CONSIDERATIONS

1.5.2 Multi-Hazard Design Matrix

The Multi-hazard Design System Interaction Matrix highlights the interaction between a particular hazard and a building design component or 

system. Table 1-1 presents this system interaction matrix in a graphic form 

by adding small illustrations for each site or building characteristic listed. 

For each entry the matrix provides a description; a sample illustration; 

positive, negative, or neutral characterization of the interaction; and an 

explanation of the nature of interaction.

The explanations are general statements intended more to provoke 

thought and further analysis towards design integration, rather than to 

provide definite restrictions or recommendations. It is possible to overcome conflicts by sound, coordinated design between the consultants, 

starting at the inception of design. General cautions, such as the relationship between building weight and seismic forces, for example, are 

intended only as reminders of basic physical facts. 

In order to facilitate comparison between hazards, the following convention has been used in Table 1-1.

4 Indicates a desirable condition or beneficial interaction between the 

designated component/system and a given hazard 

6 Indicates an undesirable condition or the increased vulnerability of a 

designated component/system to a given hazard 

0 Indicates little or no significant interaction between the designated 

component/system and a given hazard
HOSPITAL DESIGN CONSIDERATIONS 1-23

Table 1-1: Multi-hazard Design Matrix System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

1 SITE

1A

Site-specific and 

building specific 

all-hazard

analysis.

4 4 4 4 Beneficial for all 

hazards.

1B

Two or more 

means of access 

to the site

4 4 4 4 Beneficial for all 

hazards.

1C

Site modification 

to elevate 

building on 

engineered fill.

Stress Concentration

6 4 0 0

Highly beneficial for 

flood, needs very 

careful site engineering 

for earthquakes. Not 

significant for fire. 

Probably not significant 

for wind but depends 

on topography.

2 ARCHITECTURAL

2A CONFIGURATION

2A-1 

Re-entrant corner 

plan forms

6 0 6 0

May cause stress 

concentrations and 

torsional forces in 

earthquakes, and 

contribute to localized 

high-wind pressures.

2A-2 

Enclosed 

courtyard plan 

forms

6 0 0 0

May cause stress 

concentrations and 

torsional forces in 

earthquakes.
1-24 HOSPITAL DESIGN CONSIDERATIONS System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

2 ARCHITECTURAL (continued)

2A CONFIGURATION (continued)

2A-3 

Very irregular 

threedimensional 

building forms

6 0 6 6

May create indirect 

load paths, stress 

concentrations, and 

torsional forces in 

earthquakes. May 

contribute to localized 

high wind pressures, 

and aggravate 

evacuation during fire 

emergencies.

2A-4 

Large roof 

overhangs

6 0 6 0

Vulnerable to vertical 

earthquake and wind 

forces, needs careful 

engineering.

2B CEILINGS

2B-1 

Hung ceilings 4 0 0 4

If properly attached 

to structural 

components using 

diagonal braces, 

reduce damage from 

earthquakes. 

2C PARTITIONS

2C-1 

Unreinforced 

CMU or hollow 

clay tile, used 

as partitions or 

infill between 

structural 

framing 

6 6 6 4

High vulnerability 

to seismic and wind 

forces, but desirable 

against fire if not 

in seismic zone. If 

exposed, vulnerable to 

flood forces.

Table 1-1: Multi-hazard Design Matrix (continued)
HOSPITAL DESIGN CONSIDERATIONS 1-25

Table 1-1: Multi-hazard Design Matrix (continued) System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

2 ARCHITECTURAL (continued)

2C PARTITIONS (continued)

2C-2 

Non-rigid (ductile) 

connections for 

attachment of 

interior non-loadbearing walls to 

structures including 

extra-high and 

-heavy gypsum 

board walls

4 0 0 6

Beneficial for 

earthquakes but gaps 

between components 

may threaten fire 

resistance. Not 

significant for flood 

and wind.

2C-3 

Gypsum wall 

board partitions

4 6 0 4

Gypsum partitions 

properly braced to 

structure beneficial 

in seismic zones. 

Susceptible to flood 

damage, but good for 

fire if proper resistance 

is specified. Not 

significant for wind.

2D OTHER ELEMENTS

2D-1 

Tile roofs 6 0 6 4

Undesirable in seismic 

zones unless properly 

attached. On light 

structures, may cause 

poor seismic response. 

Good fire protection 

against external 

fire (wildfires) but 

undesirable in hurricaneand tornado-prone 

regions.

2D-2 

Parapets 4 0 0 4

Properly engineered 

parapet beneficial 

in seismic zones, 

but unbraced URM 

very dangerous in 

earthquake and wind. 

High parapets ( >3 ft.) 

beneficial for wind. 

May assist in reducing 

fire spread to adjacent 

buildings. 
1-26 HOSPITAL DESIGN CONSIDERATIONS System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

3 STRUCTURAL SYSTEM

3-1 

Base isolation 

and/or energy 

dissipating 

dampers

4 6 0 0 

Beneficial for 

earthquake, but 

base isolation in 

basement should be 

dry floodproofed to 

reduce vulnerability 

to flood damage. Not 

significant for wind 

and fire.

3-2 

Wood frame 

structure, used 

for small hospitals 

and ancillary and 

service buildings

4 6 0 0 

Light weight beneficial 

in seismic zones 

provided adequate 

connections and shear 

walls are used.

Lightness and lack of 

moisture resistance a 

disadvantage in floods.

3-3 

Heavy structure 

with concrete floors, 

reinforced concrete 

moment frame, or 

frame with reinforced 

concrete or masonry 

shear walls.

4 4 4 4

Although weight 

increases seismic 

forces it is not a 

design problem. 

Requires special nonductile detailing for 

large building frames. 

Generally beneficial 

for all other hazards.

3-4 

Reinforced 

concrete or 

reinforced CMU 

structural walls 

with concrete 

floors and roof 

deck

4 4 4 4

Very beneficial 

for wind, good 

performance for 

earthquake, flood, 

and fire when 

correctly designed 

and constructed.

3-5 

Steel structural 

frame

4 4 4 6

Lighter than concrete, 

needs properly detailed 

moment frame, steel 

braces, or shear walls 

in seismic and highwind zones. Good 

in flood with proper 

detailing, especially 

for elevated structure. 

Vulnerable to fire.

Table 1-1: Multi-hazard Design Matrix (continued)
HOSPITAL DESIGN CONSIDERATIONS 1-27 System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

3 STRUCTURAL SYSTEM (continued)

3-6 

Unreinforced 

masonry loadbearing walls

6 6 6 0 

Very poor 

performance in 

earthquakes and high 

winds. Undesirable for 

all hazards because of 

possibility of collapse.

3-7 

Steel or concrete 

frame structure 

with open first 

floor

0 4 0 0 

Very beneficial for 

flood. Requires careful 

design for earthquake, 

wind, and fire.

3-8

Indirect vertical 

load path

Discontinuity at third floor

6 0 6 6

Undesirable for 

seismic and wind 

hazards because poor 

structural integrity 

increases likelihood 

of collapse. Fire 

may further weaken 

structure.

3-9 

Large seismic 

separation joints 

in structure

4 0 6 6

Improves seismic 

response, but creates 

possible path for 

toxic gases during 

fire. (Cause of deaths 

in Las Vegas MGM 

Grand fire.) Needs 

careful protection 

against wind-driven 

rain.

3-10 

Ductile detailing 

of steel and RC 

structure and 

connections

4 0 4 0 

Provides better 

nonlinear response 

and a structure that 

is more resistant to 

collapse.

Table 1-1: Multi-hazard Design Matrix (continued)
1-28 HOSPITAL DESIGN CONSIDERATIONS System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

3 STRUCTURAL SYSTEM (continued)

3-11 

Reinforced 

concrete or 

reinforced CMU 

around exit ways 

and exit stairs

6 0 4 4

Properly designed, will 

preserve evacuation 

routes in event of fire.

May create torsional 

response and stress 

concentrations in 

earthquakes unless 

isolated. If fully encloses 

staircases beneficial as 

wind shelter.

4 BUILDING ENVELOPE

4A EXTERIOR WALL CLADDING

4A-1 

Brick veneer on 

exterior walls

6 6 6 0 

In earthquakes, winds, 

and floods material 

may detach and cause 

costly damage and 

injury. Careful detailing 

and quality control 

necessary for good 

performance.

4A-2 

Lightweight 

insulated cladding 

and EIFS

4 0 6 0 

Light weight reduces 

structural response 

in earthquakes, 

but needs very 

careful engineering 

and application to 

prevent leakage 

and detachment in 

winds. Vulnerable 

to windborne debris 

impact. Not significant 

in floods or fire.

4A-3 

Precast concrete 

panels

6 0 4 0 

Requires special 

detailing with ductile 

connections to structure 

in high seismic zones.

Good for winds if well 

attached and joints are 

protected against winddriven rain.

Table 1-1: Multi-hazard Design Matrix (continued)
HOSPITAL DESIGN CONSIDERATIONS 1-29 System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

4 BUILDING ENVELOPE (continued)

4B GLAZING

4B-1 

Metal/glass 

curtain wall

4 0 6 6

Light weight reduces 

seismic forces, but needs 

special design and 

installation to prevent 

failure in earthquakes. 

Fire can spread upward 

behind curtain wall if 

not properly fireproofed. 

Vulnerable to windborne 

debris.

4B-2 

Impact-resistant 

glazing

0 0 4 6

Can cause problems 

during fire rescue 

operations, limiting 

smoke ventilation and 

access. Good against 

wind-borne debris 

but not significant for 

earthquake or flood.

5 UTILITIES

5-1 

Anchorage/

bracing of system 

components

Chiller Support

4 4 4 0 

Essential for 

earthquake and wind 

(especially exterior 

mounted), beneficial 

for flood, not 

significant for fire.

5-2 

Location of system 

components above 

flood level

6 4 0 0 

Very beneficial for 

flood, if in upper 

floors may be subject 

to greater forces 

in earthquake, not 

significant for wind 

or fire.

Table 1-1: Multi-hazard Design Matrix (continued)
1-30 HOSPITAL DESIGN CONSIDERATIONS System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

6 MECHANICAL

6-1 

Anchorage/

bracing of system 

components

4 4 4 0 

Essential for 

earthquake and wind 

(exterior-mounted), 

beneficial for flood.

6-2 

Vibration-isolated 

equipment 

designed for 

seismic and wind 

forces: snubbers 

prevent 

equipment 

from falling off 

isolators Isolators with “snubbers” 

and provisions for wind 

uplift

4 0 0 0 

Very beneficial for 

earthquake, not 

significant for flood or 

fire. If not designed to 

resist uplift inadequate 

for wind.

6-3 

Anchorage 

of rooftop 

equipment

4 0 4 0 

Very beneficial for 

wind and earthquake 

(with seismic designed 

isolators where 

necessary), not 

significant for floods 

and fire.

7 PLUMBING

7-1 

Anchorage/

bracing of system 

components

4 0 4 4

Essential for 

earthquake and wind 

(for exterior-mounted 

systems), beneficial 

for fire.

Table 1-1: Multi-hazard Design Matrix (continued)
HOSPITAL DESIGN CONSIDERATIONS 1-31 System ID

Site and 

Building 

Characteristics

Examples of Site

and Building Characteristics

THE HAZARDS

Seismic

Flood

Wind

Fire

Explanation of Interaction

8 ELECTRICAL AND COMMUNICATIONS SYSTEM

8-1 

Anchorage/

bracing of system 

components

Unbraced electrical 

cabinets

4 0 4 4

Essential for 

earthquake and wind 

(for exterior-mounted 

systems), beneficial 

for fire.

8-2 

Emergency 

power supply 

adequate for 

essential services 

and equipment 

securely braced

Braced emergency 

batteries

4 4 4 4 Essential for seismic, 

flood, wind, and fire.

Table 1-1: Multi-hazard Design Matrix (continued)
1-32 HOSPITAL DESIGN CONSIDERATIONS

1.6 References

S. A. Lister, “Hurricane Katrina: The Public Health and Medical Response,” 

Congressional Research Service, 21 September 2005.

US Department of Energy (DOE). 2002. Buildings for the 21st Century. 

Office of Building Technology, State and Community Programs 

Newsletter. Washington, DC. DOE/GO-102002-1518. Winter 2002.

World Health Organization. 2006. Health Facility Seismic Vulnerability 

Evaluation. World Health Organization Regional Office of Europe, 

Copenhagen, Denmark.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-1

MAKING HOSPITALS SAFE FROM EARTHQUAKES 2

2.1 INTRODUCTION

T his chapter examines potential earthquake damage to hospitals 

and how these facilities can most efficiently improve their expected performance. An explanation of the nature and probability 

of earthquakes is provided, together with procedures for determining 

the approximate earthquake threat to specific locations. Typical seismic 

damages and the possible resulting effects on building function or risk to 

occupants are described and related to standard damage states currently 

used in performance-based earthquake engineering design.

The enhanced performance normally expected from hospitals is discussed, specifically as it relates to protection of inpatients and provision 

of care for the injured and other outpatients. Since many older buildings 

may not have been designed for seismic forces, particularly for enhanced 

performance, estimation of the actual expected performance is critical 

for adequate emergency planning.

The case studies in this chapter illustrate the performance of hospital 

buildings in earthquakes, and look at the enhancements made in the existing seismic protection of the structural and nonstructural systems to 

improve performance. The chapter ends with a review of best practices in 

seismic design and seismic retrofit of hospital facilities.

2.1.1 The Nature and Probability of

Earthquakes

Although earthquakes cannot be prevented, modern science and 

engineering provide tools that can be used to reduce their effects. 
2-2 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Firstly, science can now identify where earthquakes are likely to occur, 

at what magnitude, and determine the relative likelihood of a range of 

ground shaking levels. This information is readily available to architects, 

engineers, code writers, planners, and to the general public. Secondly, 

seismic researchers and structural engineers with experience in seismic 

design have sufficient understanding of the effects of earthquake shaking 

on buildings to create designs that will be safe for various intensities of 

shaking. Modern building codes incorporate all of this information and 

require buildings to have seismic designs appropriate for each region.

However, earthquakes are complex phenomena, and the exact nature 

of ground shaking, and a building’s response to that shaking, are still 

shrouded in considerable uncertainty. The primary intent of the seismic 

provisions of building codes is to provide buildings that will be safe in the 

expected earthquake. Current buildings designed to modern codes are 

extremely unlikely to sustain serious structural damage or partial collapse 

in a design earthquake. However, subtle changes in shaking from site to 

site, the wide range of building types and configurations, and the variation in skill and thoroughness with which any one building is designed 

and constructed can result in a wide range of damage levels in any given 

earthquake. Perhaps more importantly, many older hospital buildings 

were designed and built without seismic design features, or at best outdated ones. These buildings cannot be expected to perform well enough 

to serve their intended roles after an earthquake event. Lastly, it is now 

well known that the nonstructural systems of essential buildings are extremely important in maintaining post-earthquake functionality. Until 

very recently these systems, in general, have not been designed and installed with adequate seismic protection.

2.1.2 Earthquake Effects

Fractures and movements within the earth’s crust generate earthquake 

ground motion by sending waves through the rocks and soil outward 

from the source. Most commonly, these sources are known faults, defined 

as cracks or weakened planes in the earth’s crust most likely to “break” 

as a result of global tectonic movements. The propagation of the waves 

through the crust produces movement of the earth’s surface. Any one location on the surface will move in every direction simultaneously, back 

and forth, side to side, and up and down, creating the shaking effect that 

is both strange and frightening. The shaking effect, or seismic ground motion, is felt in all directions from the epicenter—the location where the 

fracture started—and diminishes with distance from the epicenter. Buildings, bridges, transmission towers, and other structures supported by, and 

attached to, the ground will also be shaken. If the intensity of shaking is 

high, most structures will sustain some damage. The criteria used to de-
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-3

termine the capacity of the ground motion to inflict damage on the built 

environment are somewhat intuitive: large displacements of the ground 

(3 feet versus 3 inches), rapid changes in the movement (measured in 

units of acceleration), or the duration of shaking.

Although seismic ground motion is most often identified with earthquakes, it is not the only phenomenon that causes damage. Earthquakes 

involve movements of large portions of the earth’s crust, and the resulting 

shaking can produce other geologic hazards:

Surface Fault Rupture affects a small strip at the ground when the movement on a fault deep within the earth breaks through to the surface. The 

relative displacement of the ground on each side of the rupture may be 

several feet or more, and structures straddling this zone are likely to be severely damaged. 

Liquefaction occurs when the behavior of loose granular soils and sand in 

the presence of water changes temporarily from that of a solid to that of a 

liquid material when subjected to ground shaking. This condition occurs 

mainly at sites located near rivers, lakes, and bays.

Landslides occur when the top layers of soil and rock slip on sloping 

ground, triggered by earthquake ground motion.

Tsunamis are earthquake-caused wave movements in the ocean that travel 

at high speed and may result in large coastal waves of 30 feet or more. 

They are sometimes, and incorrectly, called tidal waves.

Seiches are waves similar to tsunamis. They can be triggered by earthquakes 

and generated by sloshing in closed lakes or bays; they have the potential 

to cause serious damage, although such occurrences are very rare.

2.1.3 Measuring Earthquake Effects

Earthquakes vary in many respects, but the resulting shaking depends 

mainly on the magnitude of the earthquake and the distance from the 

epicenter. The potential risk to manmade structures is determined on the 

basis of frequency of occurrence of earthquakes at a given site, and measurements of a number of physical characteristics of ground shaking. The 

following section discusses the measurements used for this purpose, and 

their role as damage parameters.

Perhaps the most familiar measure of earthquakes is the Richter Magnitude, devised by Professor Charles Richter of the California Institute 

of Technology in 1935. Richter’s scale is based on the maximum ampli-
2-4 MAKING HOSPITALS SAFE FROM EARTHQUAKES

tude of certain seismic waves recorded on a standard seismograph at 

a distance of 100 kilometers (km) from the earthquake epicenter. Because the instruments are unlikely to be exactly 100 km from the source, 

Richter devised a method to allow for the diminishing of wave amplitude 

with increased distance. The Richter scale is logarithmic, and each unit 

of magnitude indicates a ten-fold increase in wave amplitude. The energy level is multiplied approximately by 31 for a unit increase in Ritcher 

magnitude scale. The scale is open-ended, but a magnitude of about 9.5 

represents the largest earthquake scientists now expect within the current understanding of movement in the earth’s crust.

Among scientists, Richter Magnitude has been replaced by Moment 

Magnitude, a similar measure of energy that is based on the physical characteristics of the fault rupture, which is a more useful measure for large 

events. The Moment Magnitude scale has been set to produce values 

similar to the Richter scale, and for damaging earthquakes, values are normally in the 5.5 to 8.0 range, although magnitudes over 9.0 also occur.

The level of damage is often measured by intensity scales, and the most 

common scale used in the United States is the Modified Mercalli Intensity (MMI) scale, reported in Roman Numerals from I to XII. MMI is 

often incorrectly used to measure the size of an earthquake. In fact, the 

MMI is assigned to small areas, like zip codes, based on the local damage 

to structures or movements of soil. Many MMIs 

can be associated with a single earthquake because the shaking, and therefore the damage, 

diminishes as the distance to the epicenter increases. Although the MMI is useful for the 

purpose of comparing damage from one event 

to another (particularly events for which little 

or no instrumental measurements are available), it is very subjective, and scientists and 

engineers prefer instrumental measurements 

of the ground shaking to measure intensity.

Scientists and engineers need measures of the damaging characteristics 

of earthquakes to compare the inherent risk at different locations, and 

to develop design solutions to limit damage to acceptable levels. The universal characteristic of earthquakes, and the one that can be measured 

most precisely, is the ground motion. Extensive networks of instruments 

are now employed on the ground and in manmade structures to record 

continuously the motions during an earthquake. The ever-growing database of earthquake recordings can be analyzed in various ways to develop 

appropriate measures of intensity that best predict potential damage to 

buildings and other structures, and the possibility of liquefaction and 

landslides. Tsunamis and seiches are normally not caused by the traveling 

It is important to understand that magnitude 

is not a measure of damage, but a physical 

characteristic of an earthquake. An 

earthquake with magnitude 6.7 that occurs 

in a remote area may cause no damage to 

manmade structures, but one with the same 

magnitude can cause considerable damage 

if it occurs close to an urban area.

It is important to understand that magnitude 

is not a measure of damage, but a physical 

characteristic of an earthquake. An 

earthquake with magnitude 6.7 that occurs 

in a remote area may cause no damage to 

manmade structures, but one with the same 

magnitude can cause considerable damage 

if it occurs close to an urban area.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-5

seismic waves, but by large, single movements of land under water as part 

of the fault movement or resulting large landslides.

2.1.3.1 Measuring Seismic Ground Motion

Acceleration is a measure of velocity changes over time, and is commonly 

experienced when our heads snap back when a car starts off rapidly. Similarly, acceleration causes a building to “snap back” as a result of sudden 

large ground movement. This movement within the building or other 

structure, which becomes very complex when caused by 20 seconds or 

more of ongoing, rapidly changing accelerations, is what causes direct 

shaking damage. Consequently, it is common to describe earthquake motion using the largest acceleration that occurred during the event, or peak 

ground acceleration (PGA).

Although PGA is useful as a simple way to measure and compare ground 

motions, it is not the most comprehensive one. From studies of ground 

motions and structural responses to ground motions, engineers and researchers have developed parameters that consider the characteristics 

of the entire motion, rather than the one instant when the PGA occurs. 

This characterization of the ground motion is called a response spectrum

and measures the extent of shaking different structures will experience, based on their natural period of vibration, when subjected to a 

given ground motion (see section 2.2.2.1). The maximum response to 

a specific ground motion of a structure with a given period is called the 

spectral ordinate. The full response spectrum simply represents the suite of 

spectral ordinates for a wide range of structures—from periods of about 

0.2 seconds (short, very stiff buildings) to periods of about 4.0 seconds 

(tall, very flexible buildings).

Response spectra can be calculated for the entire database of recorded 

ground motions, and trends analyzed. For example, it has been determined that the response spectrum for most earthquake shaking has a 

similar shape, and that this shape has subtle changes based on the soil on 

which it was recorded. Figure 2-1 shows the typical shape of earthquake 

ground motion spectra and the variations that will be caused, on average, 

by different site soils. Like PGA, higher spectral ordinates typically mean 

more intense and potentially damaging motions. By studying the location 

of potential earthquake sources and the probability of them generating 

an earthquake in any given time period, scientists can develop a response 

spectrum for earthquake shaking likely to occur at that site. This has 

been done by the U.S. Geological Survey (USGS) for the entire United 

States, and is the basis for seismic design requirements in building codes. 

This information is presented on maps. For simplicity, only two spectral 

ordinates are mapped, for periods of 0.2 second and 1.0 second. Exam-
2-6 MAKING HOSPITALS SAFE FROM EARTHQUAKES

ples of these maps are shown in Figure 2-2. Rules in the building codes 

allow engineers to calculate the appropriate spectral ordinate for all periods, as shown in Figure 2-1, based on the mapped values. Site classes 

in the figure are also defined in the building codes, Class A being hard 

rock, and Class E being a very soft site with potential soil failure.

Figure 2-1:

Representative shapes 

of building code (or 

design) response 

spectra for different 

soils

Figure 2-1:

Representative shapes 

of building code (or 

design) response 

spectra for different 

soils

Figure 2-2: Example of national seismic hazard maps
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-7

2.1.3.2 Measuring Potential for Liquefaction

Soils that are loose, not well graded, and saturated with water are prone to 

liquefaction. These conditions often occur near waterways, but not always. 

In addition to the soil type, the probability of liquefaction also depends 

on the depth from the surface to the layer, and the intensity of ground 

motion. Further, the results of liquefaction can vary from a small, uniform settlement across a site, to loss of foundation bearing, resulting in 

extreme settlement and horizontal movement of tens of feet (called lateral spreading). Lastly, the risk of liquefaction is directly dependent on 

the earthquake risk. Due to this complex set of conditions, damage potential from liquefaction is difficult to map. For all but the smallest projects, 

many building jurisdictions in seismic areas require identification of liquefaction potential in the geotechnical report, particularly in areas of known 

potential vulnerability. On sites where liquefaction is more than a remote 

possibility, the likely results of liquefaction at the ground surface or at the 

building foundations will also be estimated. Small settlements may be tolerated without mitigation. Larger potential settlements can be prevented 

by site remediation measures, if economically justified. In some cases of 

potential massive liquefaction and lateral spreading, using the site for 

structures may not be cost effective. Officials in some regions of high seismicity have developed maps of local areas that are potentially susceptible 

to liquefaction and require site-specific investigation.

2.1.3.3 Measuring Potential for Landslide

The shaking from earthquakes can also cause landslides, depending on 

the slope, type, and configuration of soil stratum. Landslides can cause 

damage to improvements built within the slide area or near the top of 

the slide, ranging from complete destruction to distortion from relatively 

small vertical or lateral movements. Sites can also be threatened by landslides occurring uphill, sometimes completely offsite and quite a distance 

away. Similar to liquefaction, accurate probability of land sliding is difficult to map on a regional or national scale, and this threat is normally 

identified in site-specific geologic hazard studies. Also similar to liquefaction, the largest portion of the risk may be a triggering event. In some 

cases, it is possible and cost effective to stabilize small areas at risk of potential landslides. Stabilizing larger areas at risk of landslides may not 

be feasible. Some regions of high seismicity have developed maps of the 

areas susceptible to landslides based on average slopes, geologic soil types, 

and the past history of sliding. Sites within these susceptible zones require 

site-specific investigation.
2-8 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.1.3.4 Measuring Potential for Tsunami and Seiche

Researchers have studied tsunamis and seiches for many years, but the 

tragic tsunami in the Indian Ocean in December 2004 highlighted the 

need for better measurement of the threat in terms of magnitude and location. Obviously, only sites near large bodies of water are susceptible, 

and normally at elevations 50 feet or less above the water surface, although bays and narrow canyons can amplify the wave height. Although 

similar to storm surge, the height and the potential velocity of a tsunami 

wave represent a separate risk and must be mapped separately. In addition to dependence on local conditions, quantification of the risk from 

tsunamis and seiches is made more difficult because not every earthquake generates such a wave. Studies are required that consider the 

individual characteristics of the site and the facility, to establish the risk 

and identify possible mitigating measures.

2.1.4 Earthquakes: A National Problem

Most people now know that although most frequent in California and 

Alaska, earthquakes are not restricted to just a few areas in the United 

States. In fact, two of the greatest earthquakes in U.S. history occurred not 

in California, but near New Madrid, MO, in 

1811 and 1812. In the International Building 

Code (IBC), the most common model building 

code in use in the United States and its territories, buildings on sites with a low enough 

seismic risk that specific design for seismic 

forces is not required are classified as Seismic 

Design Category (SDC) A. As shown in Figure 

2-3, 37 of 50 States have regions with sufficient 

seismic risk to require designs more stringent 

than SDC A. The likelihood of a damaging 

earthquake occurring west of the Rocky Mountains—and particularly in 

California, Alaska, Oregon, Washington, and Utah—is much greater than 

it is in the East, Midwest, or South. However, the New Madrid and 

Charleston, SC, regions are subject to potentially more severe earthquakes, although with a lower probability, than most regions of the 

western United States. According to the IBC design maps and the USGS 

hazard maps upon which they are based, other locations should also plan 

for intermediate ground motions.

The U.S. Congress recognized earthquakes 

as a national problem by passing 

legislation authorizing the National 

Earthquake Hazards Reduction Program 

(NEHRP) in 1977. NEHRP has since 

supported numerous research and hazard 

mitigation efforts. 

The U.S. Congress recognized earthquakes 

as a national problem by passing 

legislation authorizing the National 

Earthquake Hazards Reduction Program 

(NEHRP) in 1977. NEHRP has since 

supported numerous research and hazard 

mitigation efforts. 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-9

Figure 2-3: States with seismic risk

Records show that some seismic zones in the United States experience potentially damaging earthquakes approximately every 50 to 70 years, while 

other areas have “recurrence intervals” for the same size earthquake of 

about 200 to 400 years. These frequencies of occurrence are simply statistical probabilities, and one or several earthquakes could occur in a much 

shorter than average period. With current knowledge, there is no practical alternative for those responsible for healthcare facilities located in 

earthquake-prone regions but to assume that the design earthquake, specified in the building code for the local area, could occur at any time, and 

that appropriate planning for that event should be undertaken.

Moderate and even very large earthquakes are inevitable, although very 

infrequent, in some areas of normally low seismicity. Consequently, in 

these regions, most buildings in the past were not designed to deal with 

an earthquake threat; they are extremely vulnerable. In other places, however, the earthquake threat is quite familiar. Medical facilities in many 

areas of California and Alaska will be shaken by an earthquake, perhaps 

two or three times a year, and some level of “earthquake-resistant” design 

has been accepted as a way of life since the early 20th century.

Nationally, the areas where earthquakes are likely to occur have been 

identified, and scientists have a broad statistical knowledge of the po-
2-10 MAKING HOSPITALS SAFE FROM EARTHQUAKES

tential magnitude of these earthquakes and the likelihood of their 

occurrence. However, it is not yet possible to predict the near-term occurrence of a damaging earthquake. Therefore, it makes sense to take 

the minimum precautionary measures and conform to local seismic 

building code requirements for new buildings. U.S. seismic building 

code provisions focus on requiring the minimum measures necessary to 

prevent building collapse, because most lives are lost in earthquakes as 

a result of building collapse. The code provisions for essential buildings 

intended to remain functional after a major earthquake have not yet 

been thoroughly tested.

If a healthcare facility or community desires to obtain more detailed information on the seismic 

hazard than is shown on the code maps, or if the location does not enforce a seismic code but 

there is concern about seismicity, the USGS Web page at www.USGS.gov, Earthquake Hazards 

Program, is an excellent resource. The USGS provides more detailed earthquake hazard maps 

for general regions such as the Western, Central, and Eastern United States. Local building or 

planning departments, fire departments, or other local emergency management agencies should 

be consulted for the availability of mapping for liquefaction, landslide, tsunami, and seiche. 

For even more localized information, the USGS provides seismicity information for any location 

in the United States on the basis of latitude and longitude or zip code. This information 

can be obtained by referring to the Seismic Hazard listings on the USGS Web page, and 

opening “Hazards by Latitude and Longitude,” or “Hazards by Zip Code.” These listings show 

information on the expected maximum shaking that is estimated for the location. The information 

and terminology are quite technical, and may need to be interpreted by qualified staff at the 

responsible local code office, a structural engineer, or other knowledgeable seismic professional.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-11

2.2 SEISMIC BUILDING DESIGN 

Seismic design is highly developed, complex, and strictly regulated 

by codes and standards. Seismic codes present criteria for the design and construction of new structures subject to earthquake 

ground motions in order to minimize the hazard to life and to improve 

the capability of essential facilities to function after an earthquake. To 

these ends, current building codes provide the minimum requirements 

necessary for reasonable and prudent life safety. 

More basic information about seismic design of buildings can be found in 

FEMA 454, Designing for Earthquakes (FEMA, 2007)

Seismic code requirements cover:

m A methodology for establishing the design ground motion at any site 

based on seismicity and soil type

Building design codes for cities, States, or other jurisdictions throughout the United States 

are typically based on the adoption, sometimes with more restrictive local modification, of 

a model building code. Up until the mid-1990s, there were three primary model building 

code organizations: Building Officials and Code Administrators International, Inc. (BOCA), 

International Conference of Building Officials (ICBO), and Southern Building Code Congress 

International, Inc. (SBCCI). In 1994, these three organizations united to found the International 

Code Council (ICC), a nonprofit organization dedicated to developing a single set of 

comprehensive and coordinated national model construction codes. The first code published by 

ICC was the 2000 International Building Code (IBC; ICC, 2000) and was based on the NERHP 

Provisions. The IBC now references ASCE 7, Minimum Design Loads for Buildings and Other 

Structures (ASCE, 2005) for its seismic provisions. Some jurisdictions in the country may still be 

using the Uniform Building Code (UBC) seismic provisions (its final update was in 1997), while 

most have adopted or are preparing to adopt the IBC. In this document, code references are to 

the IBC Code and to its seismic standard, ASCE 7.

Building design codes for cities, States, or other jurisdictions throughout the United States 

are typically based on the adoption, sometimes with more restrictive local modification, of 

a model building code. Up until the mid-1990s, there were three primary model building 

code organizations: Building Officials and Code Administrators International, Inc. (BOCA), 

International Conference of Building Officials (ICBO), and Southern Building Code Congress 

International, Inc. (SBCCI). In 1994, these three organizations united to found the International 

Code Council (ICC), a nonprofit organization dedicated to developing a single set of 

comprehensive and coordinated national model construction codes. The first code published by 

ICC was the 2000 International Building Code (IBC; ICC, 2000) and was based on the NERHP 

Provisions. The IBC now references ASCE 7, Minimum Design Loads for Buildings and Other 

Structures (ASCE, 2005) for its seismic provisions. Some jurisdictions in the country may still be 

using the Uniform Building Code (UBC) seismic provisions (its final update was in 1997), while 

most have adopted or are preparing to adopt the IBC. In this document, code references are to 

the IBC Code and to its seismic standard, ASCE 7.
2-12 MAKING HOSPITALS SAFE FROM EARTHQUAKES

m Procedures for the seismic analysis of the building structure and key 

nonstructural components and systems

m Some detailed design requirements for materials, systems, and 

components

m Definitions of irregular building configurations and limitations on 

their use

m Building height limitations related to structural type and level of 

seismicity

Current codes and seismic design practices have evolved rapidly as the 

result of intensive research and development in the United States and 

elsewhere during the second half of the twentieth century. The advances 

in the development of the code during this period are illustrated by the 

fact that the 1961 Earthquake Provisions of the Uniform Building Code 

took seven pages, eight equations, and one map of the United States. The 

current provisions in the IBC cover about 80 pages, 96 equations, and 22 

maps of the United States. 

2.2.1 The Equivalent Lateral Force (ELF) 

Analysis Methodology

Of the 96 equations in the IBC, the Equivalent Lateral Force (ELF) 

equation is the key element in the most-used code methodology for determining seismic forces. This force is termed the equivalent force because it 

represents, in greatly simplified and reduced form, the complex to-andfro, multidirectional earthquake forces with a single static force applied at 

the base of the building. Once this force is determined, all the structural 

components of the building (walls, beams, columns, etc.) can be analyzed 

through other code-prescribed procedures to determine what proportion 

of this force must be assigned to each of them. This general methodology 

is characteristic of all seismic codes throughout the world. 

The ELF equation is derived from Newton’s Second Law of Motion, which 

defines inertial force as the product of mass and acceleration. The ELF 

equation replaces Newton’s acceleration with an acceleration coefficient 

that incorporates some of the other factors necessary to represent more 

accurately the acceleration of the mass of the building, which is generally higher than the ground acceleration. To determine this coefficient, 

the code provides another equation and additional coefficients that encompass most of the characteristics that affect the building’s seismic 

performance. The ELF procedure is used for the great majority of build-
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-13

ings. Buildings of unusual form, or with other special features or site conditions, may be required to use more complex analytical methods.

Hospitals are classified in the building code as Occupancy Category IV—

“essential for post-earthquake response and recovery”—and therefore 

have special design requirements intended to improve performance. Designers should use 50 percent greater earthquake forces for design of 

Category IV buildings than for normal buildings, which will provide an 

additional safety factor and reduce potential structural damage. In addition, design rules for Category IV buildings allow less movement between 

floors during earthquake shaking, reducing nonstructural damage to windows, walls, stairways, and elevators. Lastly, these buildings are required 

to incorporate more complete and stronger anchorage and bracing of 

nonstructural components and systems than normal buildings.

2.2.1.1 Acceleration

The most common and widespread cause of earthquake damage is 

ground shaking caused by the seismic waves that radiate out from the 

focus of the earthquake. The waves begin like ripples in a still pond when 

a pebble is thrown into it, but rapidly become more complex. There are 

four main wave types, of which “body” waves, within the earth, are most 

important for seismic design purposes. First to arrive at a given site is the 

P or Primary wave: this wave successively pushes and pulls the ground 

along the wave front as it moves forward. The effect is felt as a sharp 

punch—it feels as if a truck has hit the building. The P wave is followed 

by S, the secondary or shear wave, which is a lateral motion, back and forth, 

but perpendicular to the wave front.

The nature of the waves and their interactions are such that actual movement of the ground will be random: predominantly horizontal, often with 

considerable directional emphasis and sometimes with a considerable vertical component. Because of the random nature of the shaking, structures 

must be designed on the assumption that earthquake forces will come from 

all directions in very rapid succession, often fractions of a second apart.

The inertial forces inside the building, generated by ground shaking, depend on the building’s mass and acceleration.1 The seismic code provides 

22 maps that provide values for spectral acceleration (the acceleration to be 

experienced by structures of different periods). These values, with some 

1 Acceleration is the change of velocity (or speed) in a certain direction over time, and is a function of the 

earthquake characteristics: acceleration is measured in “g,” which is the acceleration of a falling body due to 

gravity. 
2-14 MAKING HOSPITALS SAFE FROM EARTHQUAKES

additional operations, are inserted into the ELF equation and provide the 

acceleration value and eventually the base shear value for the structure. 

Figure 2-4 shows an example of a portion of map from the IBC, showing 

contour lines of spectral acceleration. The numbers are the acceleration 

values to be used in the equation, based on the project location.

2.2.1.2 Amplification and Soil Type

As seismic vibrations propagate towards the earth’s surface, they may 

be amplified depending on the intensity of the shaking, the nature of 

the rock and, above all, by the surface soil type and depth. Earthquake 

shaking tends to be more severe on soft ground than in stiff soil or rock, 

which produces greater building damage in areas of soft soils. This amplification is most pronounced for shaking at longer periods and may not 

be significant at short periods. Studies after the 1989 Loma Prieta Earthquake showed that shaking in the soft ground was 2.5 to 3.5 times that of 

shaking in rock.

Figure 2-4:

Portion of an 

earthquake ground 

motion map used in 

the seismic code

Figure 2-4:

Portion of an 

earthquake ground 

motion map used in 

the seismic code
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-15

The ELF equation deals with soil amplification by introducing a soil type 

coefficient in the process of determining the acceleration coefficient. The 

code defines six soil types, ranging from hard rock to very soft soil, and 

provides varying coefficients that relate soil type to building period, because the amplification is also modified by building period.

2.2.1.3 Building Period

All objects have a natural or fundamental period. This is the rate at which 

they will vibrate if they are given a horizontal push. When a building begins to vibrate as a result of ground motion, it will tend to sway back and 

forth at its natural period (Figure 2-5).

More complex structures will oscillate at several different periods, the longest one (greatest amount of time to complete one cycle) often being 

called the fundamental period. The fundamental periods of structures 

vary from about 0.05 second for a piece of equipment anchored to the 

ground to about 0.10 second for a one-story building. Taller buildings between 10 to 20 stories will oscillate in the fundamental mode at periods 

of between 1 and 2 seconds. The building height is normally the main determinant of building period (Figure 2-6), although more technically, the 

period is based on the mass and stiffness characteristics of the structure.

Acceleration within the building is influenced by its period, and diminishes as the period increases (the motion changes from abrupt shocks to a 

gentler swaying) as explained in Section 2.1.3.1.

Figure 2-5:

Natural period
2-16 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.2.2 Critical Building Characteristics

2.2.2.1 Period and Resonance

As described in Section 2.1.3.1, the natural period of a building measures the time it takes to vibrate one full cycle. This basic characteristic of 

the structure will determine to a large degree how a building responds to 

earthquake ground shaking. Short, stiff buildings will have a short period 

and will shake with sharp, jerky movements (high accelerations), which 

will tend to cause contents such as equipment or furniture to slide around 

and possibly overturn. Taller, more flexible buildings will have longer 

periods and “shake” slower and smoother, but with larger “to and fro” 

movement than short buildings. The larger movements may create more 

relative displacement between floors and cause damage to walls, stairs, 

and elevators connected to multiple floors. In rare cases, buildings with 

periods over about 1.5 seconds on soft sites may match the vibration patterns of the site and resonate, causing large amplifications of the motions 

within the buildings.

2.2.2.2 Damping

A pendulum—or a child’s swing—is a very effective oscillator, and will 

continue to swing for many minutes after a push, although the extent of 

the swinging, or amplitude, will gradually diminish. Buildings and other 

objects do not oscillate as effectively because the vibration is damped, or 

reduced. The extent of damping in a building depends on the structural 

system, materials of construction; how the structural components are connected; and on the type and quantity of architectural elements such as 

Figure 2-6:

Period (in seconds) 

and building height
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-17

partitions, ceilings, and exterior walls. A high level of damping, in which 

the vibration of the building will rapidly diminish, is a desirable feature.

2.2.2.3 Nonlinear Behavior

It is generally not cost-effective to design buildings to be completely undamaged in strong earthquake motion. Building codes require designers 

to base their designs on forces that are not as great as the shaking can 

generate, on the assumption that the building’s structure will deform and 

absorb part of the energy, thus limiting the forces that can be generated. 

These severe deformations represent “nonlinear behavior” and structural 

damage, ranging from minor (that can be left alone) to more serious 

(that will require repair). The building code has been “tuned” over the 

last 5 or 6 decades by adjusting code requirements according to the results of detailed observations of the behavior of buildings. Nonlinear 

deformations are expected in hospitals and other critical buildings, but to 

a lesser extent than normal buildings. The intent is to minimize structural 

damage to enable the buildings to remain occupied after the shaking.

Some materials and structural systems can accept nonlinear behavior 

better than others and are thus considered superior seismic systems.

2.2.2.4 Ductility

Ductility is the characteristic of certain materials—steel in particular—

that fail only after considerable distortion or deformation has occurred. 

This is why it is more difficult to break a metal spoon by bending it than 

one made of plastic. The metal object will remain whole, though distorted, while the plastic spoon will break suddenly without warning 

(Figure 2-7). This property of materials is used to ensure that a building 

may adequately resist more than its design ground motion.

Figure 2-7:

Ductility
2-18 MAKING HOSPITALS SAFE FROM EARTHQUAKES

The deformation of metal, even in the spoon, absorbs energy and defers 

absolute failure of the structure. Brittle materials, such as unreinforced 

masonry or ceramic tile, fail suddenly with a minimum of distortion. 

Ductility is an important characteristic of the structural system. Thus, 

buildings with appropriate seismic designs are either designed so that 

the materials and connections will distort but not break, in case they are 

subjected to forces higher than those required by the code, or they are designed for very large forces. Some structural materials, like masonry and 

concrete, are brittle on their own, but when properly combined with steel 

reinforcing bars, can exhibit high ductility. This characteristic of the structural system is also considered in the ELF methodology.

2.2.2.5 Strength and Stiffness

Strength and stiffness are the two of most important seismic characteristics of any structure. Two structural beams may be equally strong (or safe) 

in supporting a load, but may vary in their stiffness—the extent to which 

they bend or deflect in doing so. Stiffness is a material property but is also 

dependent on shape. For vertical forces this is usually the only aspect of 

stiffness that is of concern. When floor joists are designed for a house, for 

instance, their deflection rather than strength is what often dictates their 

size. Typically, an unacceptable amount of deflection will occur well before the members are stressed to the point at which they break. 

In seismic design, there is another very important aspect to stiffness. The 

problem of determining the overall lateral force on the building by multiplying its weight by its acceleration has already been discussed. But how 

is this force distributed among the various structural members so that the 

engineer can design each one appropriately? Relative stiffness enters into 

this issue because the applied forces are “attracted to” and concentrated 

at the stiffer elements of the structure—in engineering terms, the forces 

are distributed in proportion to the stiffness of the resisting elements. Mathematically, the stiffness of a structural member varies approximately as 

the cube of its length: thus one column that is half the length of another 

will be eight times stiffer (23) and will be subject to eight times the horizontal load of the long column. This concept has serious implications 

for structures with lateral members of varying lengths, and in designing 

such a structure the engineer tries to equalize the stiffness of the resisting 

elements so that no one member or small group of members takes a disproportionate amount of the overall load (Figure 2-8).

Short columns represent a problem that emphasizes the need for good 

structural seismic design. Columns in this category may not even be part 

of the lateral force resisting system. Nevertheless, if the structural and 

nonstructural components create such a condition, these columns are 

likely to be severely damaged during strong ground shaking. 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-19

2.2.2.6 Drift

Drift is the term used in seismic design to describe the horizontal deflection of structural members in response to seismic forces. In the seismic 

code, limits are set on the amount of drift permitted. This is done to ensure that the structure will not be designed to be so flexible, even if 

structurally sound, that its nonstructural components will be unacceptably damaged. Drift is limited on a story basis. The allowable story drift is 

limited to floor-to-floor height times 0.010 (1 percent of the floor height) 

for essential buildings and 0.015 (1.5 percent of the floor height) if the 

nonstructural components have been designed to accommodate drift. A 

story drift of 0.010 is equivalent to a deflection of 1-1/2 inches for a floorto-floor height of 12 feet 6 inches (Figure 2-9).

Figure 2-9:

Allowable story drift

Figure 2-8:

The short column 

problem
2-20 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.2.2.7 Configuration: Size and Shape

Experience has shown that the architectural form of a building has a 

major influence on its performance during ground motion. This influence is the result of the three-dimensional interaction of all the structural 

systems and all architectural components when subjected to earthquake 

forces. For certain architectural forms, the response of the building can become very complex and the earthquake forces can become concentrated 

and distributed in undesirable ways. The term building configuration is used 

in seismic design to determine the architectural form of the building.

The kinds of unusual conditions that warrant concern are a result of early 

architectural decisions that determine the configuration of the building. 

In making these decisions, the architect plays a major role in determining 

the seismic performance of the building and can make it easy or difficult 

for an engineer to develop an efficient and cost-effective structural design. For seismic design purposes, configuration can be defined as building 

size and shape; the size and location of the structural elements; and the nature, size, 

and location of nonstructural elements that may affect structural performance. The 

latter include such elements as heavy and/or stiff nonstructural walls, staircases and elevator shafts, exterior wall panels, and heavy equipment items.

The seismic significance of the building configuration is that it determines both the way forces are distributed throughout the structure and 

the relative magnitude of those forces. Seismic codes distinguish between 

regular and irregular configurations, and it is the latter that may have a 

detrimental influence on the effectiveness of the seismic engineering and 

on building seismic performance. Configuration irregularity results in two 

main undesirable conditions—stress concentrations and torsional forces.

2.2.2.8 Stress Concentrations

Irregularities tend to create abrupt changes in strength or stiffness that 

may concentrate forces in an undesirable way. Stress concentration means 

that an undue proportion of the overall forces is concentrated at one or 

a few points of the structure, such as a particular set of beams, columns, 

or walls. Those few members may fail, and by chain reaction bring down 

the whole building. Stress concentration can also be created by vertical irregularity. The most serious condition of vertical irregularity occurs when 

a building has a soft or weak story, usually the ground floor, which is significantly weaker or more flexible than those above. This design creates a 

major stress concentration at the points of discontinuity, and in extreme 

cases may lead to collapse unless adequate design is provided for such 

points. Figure 2-10 shows some types of soft story design, and Figure 2-11 

shows the collapse mechanism that is created.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-21

The severe damage to Olive View Hospital in 1971, described in Section 

2.3.1.1, was largely the result of a soft first story design. Such soft or weak 

stories are not permitted in current seismic designs. 

2.2.2.9 Torsional Forces

Irregularities in building configuration may 

produce torsional forces, which complicates 

the analysis of building resistance. Torsion 

is created by a lack of balance between the 

location of the resisting elements and the arrangement of the building mass. Engineers 

refer to this as eccentricity between the center 

of mass and the center of resistance, which 

tends to make the building rotate around the 

latter and create torsion within the resisting 

elements.

The IBC lists a dozen conditions of 

irregularity (six horizontal and six vertical) 

for which special design requirements 

apply. These special requirements either 

restrict the level of irregularity, amplify 

forces to account for it, or require more 

sophisticated analysis. A severe soft first 

story is specifically prohibited, although it 

is often encountered in existing buildings.

The IBC lists a dozen conditions of 

irregularity (six horizontal and six vertical) 

for which special design requirements 

apply. These special requirements either 

restrict the level of irregularity, amplify 

forces to account for it, or require more 

sophisticated analysis. A severe soft first 

story is specifically prohibited, although it 

is often encountered in existing buildings.

Figure 2-10:

Types of soft and weak 

story structures

Figure 2-11:

Soft story collapse 

mechanism
2-22 MAKING HOSPITALS SAFE FROM EARTHQUAKES

As explained in Section 2.2.1.1, the weight of the floors, walls, and roof 

contributes to the main lateral forces exerted on the structure through the 

center of mass, usually the geometric center of the floor plan. If the resistance provided by the building components is exerted through this same 

point (the center of resistance), then there is no torsion and balance is 

maintained. As shown in Figure 2-12, conditions of eccentricity—when the 

centers of mass and resistance are offset—produce torsional forces.

One building configuration that is most likely to produce torsion features 

re-entrant corners (buildings shaped in plan like an “L” or a “T,” for example). The wings of such buildings tend to twist and result in torsion 

and stress concentration at the “notch” where the wings meet, also called 

a re-entrant corner (Figure 2-13).

Figure 2-12:

Torsion

Figure 2-13:

The re-entrant corner 

building
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-23

Buildings that have large variations in their perimeter resistance on 

different facades of the building also tend to produce torsion. Such variations often occur when some facades have large areas of glazing while the 

others have solid walls.

Irregular configurations generally arise because of functional planning 

and programming requirements, or sometimes because of the architect’s 

or owner’s desire to create an original or striking architectural form.

Hospitals often have irregular and complicated configurations as a result of their functional complexity. Broadly speaking, smaller hospitals 

are usually planned in one or two stories with horizontal-planned layouts; large hospitals often have a vertical tower for patient rooms elevated 

above horizontally planned floors for the diagnostic, treatment, and administrative services. Emergency services are generally placed at the 

ground floor level, with direct access for emergency vehicles. However, 

new developments in hospital design (see Section 1.2.4) represent a radical departure from this traditional hospital morphology. The new designs 

are based on decentralization of functions, and the introduction of natural environment into hospital buildings. New hospital buildings have 

even more complex configurations consisting of fragmented blocks interspersed with courtyards and gardens, where different blocks frequently 

have not only different shapes, but different structural systems as well.

The structural design for a hospital, however, should still focus on reducing configuration irregularities to the greatest extent possible and 

ensuring direct load paths. Framing systems need careful design to 

provide the great variety of spatial types necessary without introducing localized irregularities (Figure 2-14). 

Figure 2-14:

Complex footprint of 

a large community 

hospital. Shaded 

areas represent open 

courtyards.

Figure 2-14:

Complex footprint of 

a large community 

hospital. Shaded 

areas represent open 

courtyards.
2-24 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.2.3 Specifications for PerformanceBased Seismic Design

Beginning with the 1989 Loma Prieta earthquake in the San Francisco Bay 

Area, the importance of the consequences of damage, other than endangering life safety, has been increasingly recognized, not only in hospitals 

and other critical facilities, but in all buildings. A major effort to develop 

guidelines for seismic rehabilitation of buildings was funded by FEMA in 

1992, and published as FEMA 273 (1997). Subsequently, this guideline was 

improved and republished as FEMA 356 (2000), and in 2007 was made a 

standard by the American Society of Civil Engineers (ASCE 41).

2.2.3.1 Performance Levels

As a result of the high cost of retrofit and the growing interest in understanding the various performance levels of buildings in earthquakes, 

FEMA 273 described a variety of seismic performances for both structural and nonstructural systems that could be targeted in design. These 

performances were summarized in a matrix (see Table 2-1) that allowed 

specification of a given performance level by combining the desired structural performance with a desired nonstructural performance. Four overall 

performances levels from that table were highlighted as discussed below. 

These performance levels were developed to be applicable to any building 

with any occupancy, as appropriate.

Table 2-1: Combinations of Structural and Nonstructural Seismic Performance

Nonstructural 

Performance 

Levels

Structural Performance Levels and Ranges

S-1

Immediate 

Occupancy

S-2

Damage Control 

Range

S-3

Life 

Safety

S-4

Limited Safety 

Range

S-5

Collapse 

Prevention

S-6

Not 

Considered

N-A 

Operational

Operational 

1-A 2-A Not recommended

Not 

recommended

Not 

recommended

Not 

recommended

N-B 

Immediate Occupancy

Immediate 

Occupancy 

1-B

2-B 3-B Not 

recommended

Not 

recommended

Not 

recommended

N-C

Life Safety 1-C 2-C Life Safety 

3-C 4-C 5-C 6-C

N-D

Hazards Reduced

Not 

recommended 2-D 3-D 4-D 5-D 6-D

N-E

Not Considered

Not 

recommended

Not 

recommended

Not 

recommended 4-E Collapse Prevention 5-E

No 

rehabilitation
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-25

Operational Building Performance Level (1-A)

Buildings meeting this target building performance level are expected to 

sustain minimal or no damage to their structural and nonstructural components. The building would be able to continue its normal operations, 

possibly with only slight adjustments, mainly with respect to power, water, 

and other utilities that may need to be provided from emergency sources. 

Under low levels of earthquake ground motion, most hospitals should be 

able to meet or exceed this target building performance level. However, 

it would not be cost-effective to design buildings for this target building 

performance level under very rare, intense ground shaking, except for 

buildings that offer unique services or that contain exceptionally hazardous material.

Full functionality is normally considered difficult to achieve in the immediate aftermath of strong earthquake shaking. Offsite issues, such as staff 

availability and potential loss of utilities that are not under the control 

of the facility, may impair operations. In addition, relatively minor onsite 

damage to key components can significantly affect overall functionality. 

A single anchorage failure of the emergency generator, or a leak in one 

of the many pressurized water systems, can significantly disrupt hospital 

operations. 

Immediate Occupancy Building Performance Level (1-B)

Buildings meeting this target building performance level are expected 

to sustain minimal damage to their structural elements and only minor 

damage to their nonstructural components. While it would be safe to 

reoccupy a building meeting this target building performance level immediately following a major earthquake, nonstructural systems may not 

function, either because of the lack of electrical power or damage to 

fragile equipment. Therefore, although immediate occupancy is possible, it may be necessary to perform some cleanup and repair and await 

the restoration of utility services before the building can function in a 

normal mode. The risk of casualties at this target building performance 

level is very low.

Many building owners may wish to achieve this level of performance 

when the building is subjected to moderate earthquake ground motion. In addition, some owners may desire such performance for very 

important buildings under severe earthquake ground shaking. This 

level provides most of the protection obtained under the Operational 

Building Performance Level, without the cost of providing full standby 

utilities and performing rigorous seismic qualification of equipment 

performance.
2-26 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Immediate Occupancy is more realistic than the Operational performance level for most buildings, and at a minimum, should be the goal of 

all new hospital buildings. However, since even the smallest disruption of 

non-structural systems may be too detrimental for continued operation 

of a hospital, the owners and designers should consider a higher level of 

protection for critical hospital functions. For instance, it is recommended 

that provisions be made for independent operation of critical utilities 

for a minimum of 4 days. Critical utilities usually include electric power; 

water; the sanitary sewer; and, depending on the local weather conditions, 

fuel for heating and cooling.

Life Safety Building Performance Level (3-C)

Buildings meeting this performance level may experience extensive 

damage to structural and nonstructural components. Repairs may be required before re-occupancy of the building is allowed, although in some 

cases the repair may not be deemed cost-effective. The risk of casualties in 

buildings meeting this target building performance level is low.

This target building performance level entails somewhat more extensive 

damage than anticipated for new buildings that have been properly designed and constructed for seismic resistance. 

The Life Safety level should prevent significant casualties among ablebodied hospital occupants, but may not protect bed-ridden patients. In 

these circumstances, life safety level of protection is not appropriate for 

new hospitals.

Collapse Prevention Building Performance Level (5-E)

Although buildings meeting this target building performance level 

may pose a significant hazard to life safety resulting from failure of 

nonstructural components, significant loss of life may be avoided by preventing collapse of the entire building. Many buildings meeting this 

performance level may, however, be complete economic losses.

This level has been sometimes selected as the basis for mandatory seismic 

rehabilitation ordinances enacted by municipalities, as it results in mitigation of the most severe life-safety hazards at the lowest cost. Collapse 

Prevention is intended to prevent only the most egregious structural 

failures, and includes no consideration for continued occupancy and 

functionality of a hospital, the economics of damage repair, or damage to 

nonstructural components. 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-27

2.2.3.2 New Developments in Performance-Based 

Design

Although developed for use in the process of seismic rehabilitation of 

older buildings, the aforementioned damage descriptions have filled a 

void and have become an interim standard for describing seismic performance of both new and existing buildings.

The goal of performance-based earthquake engineering has thus become 

the development of methods to predict the expected losses adequately, 

measured by the risk of casualties, the cost of damage repair, and the 

length of building downtime. These losses are to be calculated on a cumulative and probabilistic basis, allowing communication with stakeholders 

based on losses in a given scenario earthquake, the losses due to a probabilistically determined event, or the average annual losses over a given 

time period.

Since the publication of FEMA 273, performance-based earthquake 

engineering has continued to develop, particularly through research performed at the Pacific Earthquake Engineering Research Center, one of 

three major earthquake research centers funded by the National Science 

Foundation, and through the FEMA funded project, Next Generation Performance-Based Seismic Design Guidelines, FEMA 445 (2006). When this 

work is completed, the global performance states used by FEMA 356 will 

be redefined better to reflect current knowledge and to communicate the 

potential losses to stakeholders more effectively.

The example of California shows how earthquake damage affects legislation. The 1971 San 

Fernando earthquake was particularly damaging to hospital buildings, most notably the Olive 

View Medical Center, a brand new facility that was damaged so badly that it was eventually 

demolished. Based on similar experiences with schools, the legislature passed the Hospital Seismic 

Safety Act (HSSA) in 1972. The intent of the law was both to protect acute care patients and 

to provide post-earthquake medical care. The law was patterned after the Field Act covering 

schools in California, specifying the same State review agency, and stipulating design by specially 

experienced and approved “Structural Engineers.” It covered new buildings only and provided for 

a “Building Safety Board” of industry design professionals and facility experts, appointed by the 

Director of Health Services, to advise the State on implementation of requirements.

The law and regulations included four main considerations:

m Geologic hazard studies for sites

m Structural design forces in excess of those used for “normal” buildings (initially a “K-factor” of 

3.0; later, an importance factor, I, of 1.5)
2-28 MAKING HOSPITALS SAFE FROM EARTHQUAKES

(continued)

m Specific design requirements for nonstructural elements

m Strict review of design and inspection of construction

Surprisingly, only 23 years after the San Fernando earthquake, another damaging event occurred 

in almost the same spot. In January of 1994, the Northridge earthquake produced very large 

ground motions in the San Fernando Valley just north of Los Angeles. Just as the San Fernando 

event, the Northridge earthquake had a profound effect on hospital design in California. 

Although there were no failures in hospitals comparable to the Olive View disaster, several 

hospitals required evacuation as a result of failures of both structural and nonstructural systems. 

These high-profile evacuations once again put the hospital building inventory in the spotlight. 

Analysis and comparison of the performance of buildings in Northridge built before and after the 

HSSA clearly indicated its effectiveness. This analysis also indicated that further improvements 

were needed in the performance of nonstructural systems.

Senate Bill 1953, which introduced a plan to bring all pre-Act hospital buildings into compliance 

with the HSSA by the year 2030, was signed into law by the governor of California in September, 

1994. Standards and regulations needed to implement the law included:

m Definition of structural vulnerabilities and evaluation standards

m Definition of nonstructural vulnerabilities and evaluation standards

m Standards for retrofit

m Building evaluations and facility compliance plans shall be submitted to the Office of 

Statewide Health Planning and Development (OSHPD) by January 1, 2001; Facility owners, 

60 days after approval by OSHPD, shall submit building performance categories to local 

emergency service agencies and use the performance information to improve emergency 

training, response, and recovery plans

m Hospital buildings with a high risk of collapse cannot be used for acute care purposes after 

January 1, 2008. These buildings must be retrofit (to a “life safe” performance), demolished, 

or abandoned for acute care use by that date

m High-risk nonstructural systems (pre- and post-Act) shall be mitigated in accordance with 

priorities and timelines to be set in regulation by OSHPD, in consultation with the Hospital 

Building Safety Board

m All facilities shall be in substantial compliance with the intent of the HSSA by January 1, 2030
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-29

2.3 EARTHQUAKE DAMAGE TO 

HOSPITALS

Although earthquakes damage most manmade structures in similar ways, to understand the true consequences of damage to buildings with special occupancies and functions requires a 

much more detailed and accurate damage description than may be 

needed for other buildings. The effects of earthquake damage on hospital 

operations and the safety of occupants have been described below based 

on the experiences of hospitals in the United States and around the world.

Historically, buildings have been engineered to provide adequate life 

safety to occupants and passers-by from earthquake hazards. For most 

buildings, life safety is primarily threatened by building collapse or the debris falling into the street and neighboring buildings. A higher level of 

performance is required to address the life safety issues of hospitals, since 

patients often have limited mobility and are dependant on caregivers or 

specialized medical equipment. 

Figure 2-15a:

Structural and 

nonstructural elements 

of a building

Figure 2-15a:

Structural and 

nonstructural elements 

of a building

Building Structure
2-30 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Figure 2-15 shows typical building components and systems present in 

hospital facilities. The structural elements consist of the foundations, 

columns, beams and slabs, walls, and braces that hold the building up 

against vertical gravity forces and horizontal wind and earthquake forces. 

The nonstructural elements include building service systems, such as 

electricity and lighting, heating and cooling, plumbing, and interior architectural systems, such as ceilings, floors, partitions, and other interior 

components. The building envelope includes the systems that separate 

the interior spaces from the exterior, both structural and nonstructural. 

It includes exterior walls and cladding, roof systems, doors and windows, 

and floors or slabs that separate the building interior from the ground. 

Contents and equipment are completely dependent on the type of occupancy and the function of the space, and range from items such as 

furniture encountered in a lobby or a waiting room, to highly technical 

equipment commonly present in treatment rooms. In addition, laboratories, pharmacies, bulk storage areas, and large central energy plants have 

highly specialized and frequently very sensitive equipment.

In general, both the building service systems and the contents of hospitals rank among the most complex and expensive of any building type. 

Furthermore, both the structural system and most of the nonstructural 

systems are required to perform without interruption after an earthquake 

to enable adequate functionality. 

Figure 2-15b: Structural and nonstructural elements of a building
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-31

2.3.1 Types of Structural Damage

When the ground shakes in an earthquake, the shaking is transferred 

to the building, potentially causing structural damage. The damage can 

consist of cracks in structural walls, bent or broken braces, or damage to 

columns and beams. Damage can range from minor (a few cracks), to 

major (parts of the structure rendered ineffective and potentially unsafe), 

to complete collapse. See Figures 2-16, 2-17, 2-18, and 2-19 for examples 

of structural damage.

Figure 2-16:

This concrete building 

suffered severe 

damage to the 

columns at the second 

floor level. It was 

deemed unsafe by the 

local jurisdiction and 

later demolished.

Figure 2-17:

A steel frame building with a post-earthquake 

“lean” to the right, seen particularly at the first 

floor. Severe damage was found in its beamcolumn joints and it was later demolished.
2-32 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.3.1.1	 The Case of the Olive View Medical Center

The Olive View Hospital in the northern San Fernando Valley, owned 

by Los Angeles County in Southern California, was severely damaged 

on February 9, 1971, when the San Fernando earthquake damaged the 

almost-new facility so severely that it was later demolished. Over 500 patients were evacuated immediately after this event. 

The 850-bed Olive View Hospital campus comprised over 30 buildings of 

various ages, but most notably featured a complex of buildings completed 

Figure 2-18:

Severe damage to 

a poorly reinforced 

masonry wall on a 

steam plant

Figure 2-19:

Damage to an exterior 

concrete wall. This 

hospital building was 

evacuated.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-33

in 1970, only months before the 1971 San Fernando earthquake. These 

“new” buildings included the five-story Medical Care Facility, the twostory Psychiatric Unit, the Heat and Refrigeration Plant, and several 

other smaller ancillary buildings such as a warehouse, assembly building, 

walkway canopy, and ambulance canopy. The 1970 buildings were all 

made of reinforced concrete and designed under the 1965 Los Angeles 

Building Code, which included seismic provisions. However, neither 

of these buildings had any special seismic protection features. In fact, 

the poor performance of this facility was one of the prime reasons for 

passage of California’s Hospital Seismic Safety Act (HSSA). The shaking 

experienced in the 1971 San Fernando earthquake was extreme; however, 

structural performance of these buildings was worse than the engineering 

community had expected. Subsequent investigations indicated that the 

buildings technically met the requirements of the code, but included 

features that made them particularly vulnerable to earthquake damage. 

Seismic codes were subsequently refined to prevent this type of 

vulnerability in future buildings.

The damage to Olive View Hospital buildings was nearly catastrophic. 

The first story of the medical treatment and care unit was over 15 inches 

out of plumb and near collapse (Figure 2-20). Three of the four exterior 

stair towers pulled away from the main building or collapsed completely, 

rendering them useless for egress (Figure 2-21). The Ambulance Canopy 

collapsed onto the parked ambulances and destroyed them. The first 

story of the Psychiatric Unit collapsed, but all the occupants were on the 

second floor at the time.

Almost immediately after the event, the patients in the Psychiatric Unit 

began assembling in a parking lot adjacent to their facility. The need to 

evacuate was obvious, and the second floor wards were only feet from the 

ground after the first floor collapse (see Figure 2-22). Controlling and 

tracking these patients was nearly impossible, particularly in the first few 

hours. Within 5 hours, evacuation was underway in the main building 

using interior stairwells. The building had no power and therefore no 

elevators or lights. The nurses evacuated their own units, ambulatory 

patients first, and, when sufficient assistance was available, non-ambulatory patients. By that time, a network of ambulances and helicopters 

had been set up for transfer to other facilities (Arnold, 1983; Lew, 1971; 

NOAA, 1973).

Subsequent analysis of the effects of this earthquake on the hospital 

noted, as particularly troublesome, the lack of functioning communications, either internal or external, the lack of an effective evacuation plan 

or identified assembly area, and the lack of any control or tracking of 

medical records. 
2-34 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Figure 2-20:

Aerial view of 1971 

Olive View Hospital

Source: NOAA, 1973

Figure 2-21:

Collapsed stair tower 

in main building of 

Olive View Hospital
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-35

2.3.2 Nonstructural Damage

When the ground shakes the structure, the structure shakes everything 

that is in it or on it, including the building envelope and components of 

the interior nonstructural systems. This shaking can damage most components directly. Indirect damage, resulting from structural deformation 

between floors, can cause damage to all the systems connected to these 

structural components.

Damage to architectural systems consists of broken windows and cracked 

exterior walls and interior partitions. In extreme cases, exterior walls and 

partitions topple completely. Ceilings are also vulnerable to damage and 

can break into small pieces or fall to the floor (see Figure 2-23).

Figure 2-23:

A damaged exit 

corridor—dark and 

barely passable

Figure 2-23:

A damaged exit 

corridor—dark and 

barely passable

Figure 2-22:

Completely collapsed 

first level (not visible) 

of Psychiatric Unit
2-36 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Damage to the building service systems can consist of sliding or overturning of equipment like boilers, generators, and fans, or swaying and 

possible fracture of mechanical ducts, pipes, and electrical conduit (see 

Figures 2-24, 2-25, and 2-26).

Figure 2-24:

Vibration isolation 

bearing assemblies on 

mechanical equipment 

collapsed due to 

seismic shaking—such 

movement breaks 

pipe or electrical 

connections to the 

equipment.

Figure 2-24:

Vibration isolation 

bearing assemblies on 

mechanical equipment 

collapsed due to 

seismic shaking—such 

movement breaks 

pipe or electrical 

connections to the 

equipment.

Figure 2-25:

A heavy transformer 

that moved several 

feet, breaking all 

connections

Figure 2-25:

A heavy transformer 

that moved several 

feet, breaking all 

connections
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-37

Because of the wide variation of contents and equipment in a typical hospital, the type of damage experienced by these systems varies widely. For 

example, medical equipment, such as operating tables and lights, radiation and x-ray units, sterilizers, and patient monitors, is often heavy and 

Figure 2-26:

A large chiller almost tipped over. 

Figure 2-27:

Damaged radiology 

equipment that not 

only will not function, 

but has become a lifesafety risk
2-38 MAKING HOSPITALS SAFE FROM EARTHQUAKES

not well anchored to the structure (see Figure 2-27). Offices and storage 

rooms, such as the areas used to store critical supplies, medicine, medical records, chemicals, and fuel, can also be severely damaged by shaking 

(see Figures 2-28, 2-29, and 2-30).

Figure 2-28:

Chaos in a storage 

area similar to central 

storage or medical 

records

Figure 2-28:

Chaos in a storage 

area similar to central 

storage or medical 

records

Figure 2-29:

Jumbled contents of a 

typical office
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-39

2.3.2.1 The Case of New Olive View Medical Center

Nearly 15 years after the 1971 earthquake event that destroyed the Olive 

View Medical Center (see Section 2.3.1.1), a new hospital was opened on 

the same site in 1986 (see Figure 2-31). Built even stronger than required 

under the HSSA of 1972, the building has no basement and features a 

seismic system of concrete shear walls and steel plate shear panels. The 

building was also equipped with instruments to record its response in future earthquakes. 

Figure 2-31:

Aerial view of “new” 

Olive View Hospital 

(1986)

Figure 2-31:

Aerial view of “new” 

Olive View Hospital 

(1986)

Figure 2-30:

Overturned tank 

similar to medical gas 

storage
2-40 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Early in the morning of February 17, 1994, a Magnitude 6.7 earthquake 

occurred on a little known fault not generally considered dangerous, located near Northridge, about 10 miles from the hospital. The recorders 

captured exceptionally high accelerations of 0.82 g at the first floor and 

1.7 g at the roof. The structure suffered little or no structural damage, but 

its stiffness and strength contributed to the transfer of unprecedented accelerations through the building, in some cases overwhelming the seismic 

anchorage and bracing provided for the building’s nonstructural systems. 

Some of these components and systems were not considered sufficiently 

vulnerable to require special bracing.

Damage included the following (see Figures 2-25, 2-26, and 2-27):

m Shifting, and in some cases, failure, of anchorages of equipment at 

the roof level, where accelerations were the highest. This movement 

broke one or more chiller water lines, causing flooding in the top 

floors (see Figure 2-32).

m Excessive movement and failure of wall-mounted television brackets, 

causing some television units to fall.

m Extensive damage to suspended panelized ceilings, some exacerbated 

by leaks from water pipes from above.

m Excessive movement and interaction between gypsum board and 

other fire-rated ceilings and sprinkler lines, causing additional leaks.

m Movement at the copper tube reheat coils in the ceiling spaces, 

almost universally at the third through the sixth floor, causing leaks 

(see Figures 2-33 and 2-34).

Figure 2-32:

Anchor bolts 

stretched by large 

seismic accelerations 

at roof level

Figure 2-32:

Anchor bolts 

stretched by large 

seismic accelerations 

at roof level
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-41

m Damage to some equipment anchorage in the Central Plant and at 

the bulk oxygen tank.

m Damage to elevators, seven of which were temporarily out of service. 

Four had sustained severe damage as a result of derailed and bent 

counterweight frames. 

Right after the earthquake event, administrators planned a partial evacuation of 79 patients, but by the afternoon, they decided to transfer all 

377 patients to other facilities, despite the dangers associated with such 

a move. The evacuation was prompted primarily by water damage and 

lasted 41 hours (EERI, 1995; LACDHS, 1994; URS, 1996).

Figure 2-33:

Damage to ceiling and 

fixtures from sprinkler 

breaks

Figure 2-34:

Detail of water 

damage to ceiling
2-42 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Despite vastly improved structural performance and compliance with 

the requirements for anchorage and bracing of nonstructural components and systems compared to the conditions in 1971, the hospital’s 

operations were severely compromised. It was not ready to accept local 

casualties, but actually increased the load of neighboring facilities by requiring evacuation. The unexpectedly poor performance was caused 

by extraordinary ground motions, probably made more damaging to 

nonstructural systems and contents by the very stiff and strong structure 

of the hospital.

2.3.2.2 The Case of Kona Community Hospital, Hawaii 

The Kona Community Hospital (KCH) is located in Kealakekua, Kona, on 

the central west coast of the Big Island of Hawaii. It was originally a county 

hospital but became part of the State-owned Hawaii Health Systems Corporation in 1996. KCH is a full service medical center and is the primary 

health care facility serving West Hawaii. The facility has 33 acute medical-surgical beds, a 9-bed intensive care unit, 7 obstetric beds, an 11-bed 

behavioral health unit, and a 34-bed skilled nursing/long term care wing.

The KCH campus includes several buildings, but the primary medical facility occupies a three-story L-shaped building that consists of the original 

60,500-square-foot block built in 1972, and an 18,300-square foot addition built in 1989. Both structures are concrete, rectangular in plan, and 

each forms one leg of the L shape. The site slopes east to west creating 

two stories above grade and one basement floor on the east, and three 

stories above grade on the west face. The lateral force (wind and earthquake) resisting system of the original building consists of concrete pier 

shear walls that are part of the exterior wall and concrete walls around 

the elevators and stairs. The lateral force resisting system of the addition 

is a ductile concrete frame, which consists of the beams and columns rigidly tied together in a manner that resists lateral motion. The addition is 

notable in that the two bays of the western end are open at the ground 

floor and serve as a drive-through to the back of the campus and as an 

ambulance entrance. 

Seismic Characteristics of the Facility

A technical evaluation of the facility, performed in 1993 by the Hawaii 

State Earthquake Advisory Board, identified several seismic deficiencies. 

It was found that the layout of the lateral-force-resisting shear walls in the 

original 1972 building and the outdated pattern of column reinforcement 

were of the type that previously contributed to unacceptable levels of 

damage in similar buildings. Conditions that presented potential seismic 

deficiencies were also found in the 1989 addition, including:
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-43

m The eccentric location of the stair and elevator core, which could 

potentially create torsional response 

m Inadequate connection of the floor slabs to the core, which could 

cause moderate damage 

m The potential for nonstructural plaster cracks in the upper floors,

m The potential for local damage at the connection between new and 

original wings during shaking 

As part of the evaluation, the torsion issue (related to the stair and elevator) was checked and found not to represent a significant problem. No 

specific recommendations related to the other problems were included in 

the evaluation. The structural evaluation concluded with a recommendation to retain a local structural engineer to review the seismic adequacy of 

KCH in more detail. The evaluation also covered the seismic protection 

of nonstructural systems and equipment, but included no specific recommendations for KCH.

The evaluation categorized nonstructural components and systems as:

m Systems and elements which are essential to hospital operations and 

without which the hospital cannot function (Essential) 

m Nonessential elements whose failure could compromise hospital 

operations (Nonessential) 

In fact, when considering seismic preparedness of hospital facilities, there 

is little consensus about the types of nonstructural systems that should be 

considered essential. These classifications vary from facility to facility and 

are closely tied to elements of the emergency response plan. For example, 

unbraced, suspended panelized ceiling systems typically used in hospitals on the island were noted as a deficiency, but consistent with standard 

seismic evaluation procedures for hospitals, these systems were classified 

as nonessential. However, as described below, damage to these ceilings 

proved critical when a real event struck.

Most of the larger equipment categorized as “essential” in the evaluation, 

including the emergency generator, the bulk oxygen tank, the chiller, and 

the rooftop cooling tower were seismically anchored and continued to 

function during the earthquake.
2-44 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Damage

The Hawaii Earthquake of October 15, 2006, had a magnitude 6.7 and 

was centered about 35 miles north of the KCH. It was followed by a 

second shock of magnitude 6.0. The shaking caused moderate damage 

over much of the Big Island and was felt as far away as Oahu. Shaking on 

the island of Hawaii, as recorded on several instruments installed by the 

USGS, featured relatively high accelerations, but the energy was restricted 

to very high frequency (short period), which proved damaging to stiff, 

brittle structures. Several unreinforced masonry buildings suffered severe 

damage, many ungrouted stone masonry fences and walls partially collapsed, and landslides and rockslides were common, which is consistent 

with this kind of motion. 

The Special Services Building at KCH (seen in Figure 2-35 behind the 

small single-story building on the left) contained such an instrument. The 

response spectrum for one component of motion is shown in Figure 2-

36 in blue. Note the rapid decline of spectral acceleration values for very 

short periods, much less than 0.5 seconds. The orange curve shows a spectral shape that might be expected in association with such high ground 

accelerations, and is included in building codes. High values of spectral acceleration between the periods of 0.5 seconds and 2.0 seconds, as 

shown in this standard curve, are usually associated with much greater 

building damage.

Figure 2-35:

Kona Community 

Hospital. Addition 

(1989) supported 

on isolated columns 

in the foreground. 

The original building 

(1972) is in the left 

background.

Figure 2-35:

Kona Community 

Hospital. Addition 

(1989) supported 

on isolated columns 

in the foreground. 

The original building 

(1972) is in the left 

background.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-45

The high acceleration motion caused the unbraced, suspended panelized ceilings (see Figure 2-37), found almost everywhere at KCH, to strike 

partitions that demarcated rooms and corridors. The partitions were constructed of steel studs and gypsum board, and the studs run from the 

structural floor to the underside of the structure above, making them very 

strong and stiff. The impact of the panelized ceilings caused the lightweight support tees either to buckle or pull off of a typical perimeter 

trim angle (Figure 2-38). In the absence of vertical support wire, the tees 

collapsed, allowing the ceiling tiles to fall. Many of the florescent light fixtures, also supported on the tees, became dangerously unstable, though 

few fell to the floor. This type of damage was concentrated at the perimeter of rooms, adjacent to the partition walls, but it was not completely 

limited to these locations (see Figures 2-39). When ceiling tiles became 

dislodged, decades of accumulated dust on the top of the tiles came 

down, adding to the general disarray and threatening the health of patients and other occupants. 

Figure 2-36:

Response spectra for 

one of the orthogonal 

components recorded 

at the site of the KCH. 

The blue line is for the 

recorded motion. The 

orange line represents 

the spectral shape 

more commonly 

expected and 

contained in building 

codes.

(Graph courtesy of

www.Cosmos-eg.org)

Figure 2-37: Typical suspended panelized ceiling system showing seismic bracing (according to the 1993 

seismic evaluation report, this system was not used in the hospitals reviewed at that time).
2-46 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Almost simultaneously with the first shock, the power went out. The emergency generator was seismically protected and provided power for the 

emergency circuits. Eight minutes after the main shock, about the time 

some semblance of order was being restored, the second shock hit. With 

equipment and contents as well as ceiling tiles and metal tees littering the 

floor or hanging precariously over patients’ beds, a decision was made to 

evacuate the most disrupted areas.

At the time of the earthquake KCH had 69 patients, including 31 in the 

long-term care unit. These 31 long-term care patients were taken to a 

local hotel; 27 patients were discharged; 5 were airlifted to an acute care 

Figure 2-38:

Typical damage at the 

perimeter of a room 

from loss of support 

from the partitionmounted perimeter 

angles to the ceiling 

system tees or from 

contact with the 

ceiling system and the 

partitions.

Figure 2-39:

Ceiling damage in the 

operating room. The 

round operating lights 

on the right were not 

damaged.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-47

facility in Hilo, and one was transported to a local long-term care facility. 

The remaining five patients were more difficult to move and were placed 

in usable rooms in the obstetrics or the intensive care unit (ICU) on site.

The potential torsional response of the building addition, identified in 

the 1993 evaluation, proved prophetic, as the column-supported west 

end attempted to rotate around the stiffly supported east end. As shown 

in Figure 2-40, the two beam connections tending to restrain the motion 

spalled. Similarly, in the partially enclosed penthouse, the embedded connection of a steel beam spanning between two exterior concrete walls 

pulled out due to a stiffness incompatibility. This damage was not considered serious enough for the structure and did not affect the occupancy 

status.

Figure 2-40: Spalling at beam connections

Exterior and interior nonstructural plaster or stucco walls had many 

cracks, especially around some door frames. This damage was costly, but 

did not affect operations.

Emergency generators and medical gas storage were seismically anchored 

and survived the tremor undamaged. The communications were disrupted 

for the first hour or so, because the telephone main switching equipment, 

which was not anchored, failed. The radio-repeater mast on the roof fell 

over and dislodged the coaxial cable, limiting the use of that system. The 

hospital has subsequently decided that their radio system does not have 

sufficient channels for emergency use and intends to upgrade the system. 

Ham radio was also available on the site but was not used. 

The hydraulic elevators, which are not as susceptible to damage as the 

traction elevators used in taller buildings, sustained no major damage 

but were not functional as a result of power outage. Elevators can be very 

valuable after earthquakes for moving bed-ridden patients, provided spe-
2-48 MAKING HOSPITALS SAFE FROM EARTHQUAKES

cial seismic anchorage and controls are installed and emergency power is 

available. The pressurized water systems (including sprinklers, domestic, 

and chilled water), considered by many the most likely to break or leak 

and disrupt operations, suffered no damage.

The experience of KCH highlighted the vulnerability of unbraced suspended panelized ceilings, which are often given a low retrofit priority 

because they are not considered a serious life safety hazard. It was also 

thought that the benefits of bracing do not warrant the extreme disruption that such a retrofit usually causes for hospital operations. It is very 

likely that lessons from Kona Community Hospital’s experience will help 

change this view.

2.3.3 Consequences of Building Damage

The uninterrupted operation of hospitals is crucial in the aftermath of an 

earthquake, because of a potentially large number of casualties. Damage 

to these facilities and a possible need for an evacuation not only hampers the emergency response but can also 

compound the disaster by adding casualties. 

The most obvious risk to life safety is serious 

structural failure of a hospital, similar to the experience of the original Olive View hospital. 

In the aftermath of an earthquake the local 

building authority typically determines which 

buildings are unsafe for use based on the level 

of damage. For this purpose, a simple “tagging” 

procedure has been developed in California 

that uses colored placards or “tags” affixed 

to buildings that show that the building has 

been inspected and indicate the level of safety. 

The evacuation is inevitable when the hospital buildings are “red tagged,” i.e. when the 

building is in imminent danger of collapse in 

an aftershock. In such circumstances, a hospital 

becomes unavailable for emergency services 

and the staff can only provide medical care in 

parking lots or other ancillary facilities, as has 

happened in the past.

Even in cases where hospitals have avoided 

major damage, their operations may be 

sufficiently disrupted to require complete evacuation, which can be very dangerous for many 

patients. Failures in nonstructural systems, such 

TAGGING

A red tag indicates UNSAFE: 

Extreme hazard, may collapse. 

Imminent danger of collapse 

from an aftershock. Unsafe for 

occupancy or entry, except by 

authorities.

A yellow tag indicates LIMITED 

ENTRY: Dangerous condition 

believed to be present. Entry 

by owner permitted only for 

emergency purposes and only 

at own risk. No usage on a 

continuous basis. Entry by public 

not permitted. Possible major 

aftershock hazard.

A green tag indicates 

INSPECTED: No apparent 

hazard found, although repairs 

may be required. Original lateral 

load capacity not significantly 

decreased. No restriction on use 

or occupancy.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-49

as broken pipes that cause extensive flooding, failed emergency generators, lack of water, or general chaos created by contents that have been 

thrown about have all created conditions that have forced hospital administrators or local jurisdictions to order an evacuation. Minor nonstructural 

damage, especially if essential equipment or other contents are affected, 

can still cause considerable disruption in hospital operation, even if 

global evacuation is not deemed necessary.

Finally, almost all hospitals have financial constraints. The cost of repairs 

and/or the partial loss of capacity will affect the financial well-being of 

any facility and must be considered as a significant potential consequence 

of earthquake damage.

2.3.4 Seismic Vulnerability of Hospitals

Seismic vulnerability of a hospital facility is a measure of the damage a 

building is likely to experience when subjected to ground shaking of a 

specified intensity. The response of a structure to ground shaking is very 

complex and depends on a number of interrelated parameters that are 

often very difficult, if not impossible, to predict precisely. These include: 

the exact character of the ground shaking the building will experience; 

the extent to which the structure will respond to the ground shaking; the 

strength of the materials in the building; the quality of construction, the 

condition of individual structural elements and of the whole structure; 

the interaction between structural and nonstructural elements; and the 

live load in the building at the time of the earthquake.

Frequently, seismic activity causes insignificant damage to the structure of 

a hospital, yet its operations are impaired or disrupted because of damage 

to nonstructural elements. Even a low-magnitude seismic event can affect 

vital functions of a hospital and cause its evacuation and closure. This was 

evident in some recent earthquakes, whereby structures designed in accordance with modern seismic resistance criteria performed well, while 

the poor performance of the nonstructural elements caused serious disruption of hospital operations. 

A variety of methods for assessing seismic vulnerability of buildings exist 

that differ in cost and precision. The type of method to be used depends 

on the objective of the assessment and the availability of data and appropriate technology. Typically, quicker and less sophisticated methods, like 

the commonly used rapid visual screening, are used for larger areas and 

large number of buildings. They often form the first phase of a multiphase procedure for identifying hazardous buildings, which must then be 

analyzed in more detail to determine upgrading strategies. Detailed assessment procedures use computer models and various forms of engineering 
2-50 MAKING HOSPITALS SAFE FROM EARTHQUAKES

analysis that are time consuming and expensive and require a high degree 

of analytical expertise to obtain reliable results. Consequently, they are 

used for detailed verification of the safety of structural and nonstructural 

elements, including proposals for specific mitigation measures.

A simple preliminary vulnerability assessment of existing hospitals can be performed using the results of the historical study of hospital performance in a 

variety of seismic events. This method is described below in greater detail.

2.3.4.1 Seismic Vulnerability of Hospitals Based on 

Historical Performance in California

A recently completed study on “Seismic Vulnerability of Hospitals Based on 

Historical Performance in California,” (Holmes and Burkett, 2006) analyzed 

the historical record of losses to hospitals damaged in major California 

earthquakes since 1971. The data base contained two hundred eighteen 

cases, each representing a hospital (potentially one or more buildings) that experienced earthquake ground shaking in the earthquakes 

of San Fernando (1971), Imperial Valley (1979), Coalinga (1983), Whittier (1987), Loma Prieta (1989), Sierra Madre (1991), and Northridge 

(1994). Damage reports varied from brief, one-paragraph summaries to 

elaborate narratives of the damage patterns and the consequences. Evacuations or shut-downs of facilities were always noted. These descriptions 

were used to categorize hospital damage into one of the structural and 

nonstructural performance categories shown in Table 2-2.

Table 2-2: The description of performance categories in terms of structural and nonstructural building damage

Performance category 

(damage level) Type of Structural Damage Type of Nonstructural damage

None

Minor Minor structural damage (light 

concrete cracking, etc.)

Minor damage to nonstructural components 

or systems (plaster cracking, ceiling damage, 

some equipment shaken off supports)

Affecting hospital operations Damage requiring immediate 

evacuation due to dangerous 

conditions or concern for 

collapse in an aftershock

Nonstructural damage that prevents full 

functioning of the hospital (loss of emergency 

generator, local pipe breaks and causes 

flooding, computer system down)

At least temporary closure Closure could be temporary or 

permanent

Temporary Closure based on major 

nonstructural damage (long-term power or 

water outage, extensive ceiling and light fixture 

damage, major flooding)
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-51

The study related the recorded levels of damage experienced by hospitals 

and ground motion data for each seismic event, determined on the basis 

of recorded ground motion at the site during the earthquake and USGS 

data. The intensity of ground motion was represented by spectral acceleration at short periods (SDS), measured in units of the acceleration of 

gravity “g” in order to match building code information that can be obtained locally (see Section 2.2.2.1). In this study, the spectral acceleration 

at short periods for each case in the historical record was labeled SHS, 

which stands for historical short period spectral acceleration. By matching 

spectral acceleration data with performance categories, a relationship was 

established between the damage (and the consequences of damage) and 

the ground motion intensity that caused it. All buildings were divided into 

two groups according to the level and quality of seismic design and construction. The adoption of the HSSA in 1972 was used as a divide between 

pre-Act buildings and post-Act buildings. The results of this study presented the differences in performance of hospital buildings in California 

in graphic form on Figures 2-41 for pre-Act buildings and in Figure 2-42 

for post-Act buildings. 

The measure of ground motion intensity is different in the two figures. 

For pre-Act buildings, SHS represents accelerations recorded at the time, 

while post-Act building performance was categorized according to ground 

motion expressed as the percentage of SDS typically used in California 

for seismic design in the post-Act period. Post-Act buildings in the database were designed for the higher seismic zones of California, typically 

with an SDS of about 1.0. To use this data to estimate potential damage to 

newer buildings in other parts of the country that have incorporated thorough seismic design with other values of SDS, it is necessary to normalize 

the data to an SDS of 1.0. The ground motion in Figure 2-42 is thus represented as a percentage of the SDS used to design the building. “SHS = 

0.25–0.50 of SDS” shows expected damage to a relatively new building 

when it is shaken with an intensity of 25 to 50 percent of its code design, 

as measured by SDS. Since damage occurs even at levels considerably 

below the code earthquake, the data is still very useful for planning purposes. The probability of occurrence of shaking different from the code 

level can be estimated by local seismologists or engineers.

This study, based on past damages, provided a clearer picture of the vulnerability of hospitals and established a benchmark for vulnerability 

assessments of all the existing hospitals. Among other things, the analysis 

indicated that the threshold for potentially significant seismic damage coincided with the current, lower-bound ground motion intensity requiring 

seismic design for new buildings (SDS greater than 0.167 g). The pre-Act 

charts indicated a slight possibility of significant structural damage, but a 

strong possibility of nonstructural damage at low shaking levels. It should 

be noted however, that structural damage requiring building closure has 
2-52 MAKING HOSPITALS SAFE FROM EARTHQUAKES

been recorded even at the SDS level just above 0.4 g. The analysis of the 

post-Act data indicated that hospital buildings built in accordance with 

the 2000 IBC (or later edition) are unlikely to suffer serious structural 

damage for events up to, and including, the intensity of the code earthquake. However, as previously discussed, new hospital buildings may not 

perform as well as indicated on the post-Act charts, since most regions 

of the country do not have as strict design and construction codes and 

code enforcement as California. Nonstructural damage, which can reduce 

hospital effectiveness or even cause evacuation, remains a significant vulnerability, even in new buildings.

2.3.4.2 Vulnerability Assessment of Hospital Buildings

Although the above-mentioned study was based on data from California, where the ground motions have slightly different characteristics 

than in other parts of the country, the vulnerability to damage for certain building types at given levels of ground motion is comparable to 

any location. Prior to obtaining the detailed site-specific seismic evaluations, the expected damage from a given ground motion can be 

estimated on the basis of historical data. The results of the study, therefore, can be used effectively to make preliminary assessments of the 

vulnerability of hospitals in any seismic region of the country. While 

this type of analysis will not take the place of a formal seismic building 

evaluation performed by experienced design professionals, it can be 

very helpful in raising the awareness of potential earthquake risks, in 

determining whether a more detailed study of vulnerability is justified, 

and whether to incorporate more realistic damage projections in a disaster plan or emergency exercise.

For example, a hypothetical hospital near Charleston, SC, may determine from the local building code that the seismic spectral acceleration 

value for short periods at the site is 0.8 g. If one or more of their buildings are 20 or more years old and were designed without seismic 

provisions or with out-of-date seismic provisions, the pre-Act columns of 

Figure 2-41 should be consulted. The chart on Figure 2-41 for the range 

of SDS between 0.6-0.8 g shows that, unless building-specific studies are 

done to prove otherwise, it should be assumed that a code earthquake 

will cause sufficient damage to hinder the full operations (about a 33 

percent chance) or require closure of a building (about a 13 percent 

chance). Perhaps more importantly, the right column of Figure 2-41 indicates a high probability that hospital operations will be interrupted by 

nonstructural damage. In fact, for such a facility, even very low shaking 

levels of SDS 0.2 g to 0.4 g could be expected to cause nonstructural 

damage resulting in significant disruption of hospital operations.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-53

In contrast, a brand new hospital in northern Utah, on a site with SDS of 

about 0.7 g, is unlikely to suffer significant structural damage (as shown 

on the post-Act charts, left column of Figure 2-42). However, if such a hospital was not constructed according to the best design and construction 

standards, it can be expected to suffer a more significant nonstructural 

damage than the post-Act data shown in Figure 2-42. A prudent disaster 

plan would in such a case consider the possibility that nonstructural 

damage could cause a temporary closure.

2.3.4.3 Comparability of Hospital Buildings

The structural performance of hospital buildings built anywhere in the 

country without any seismic design provisions is most likely comparable to 

the performance of pre-Act buildings as shown on Figure 2-41. All buildings in the pre-Act group were either constructed with no seismic design, 

or with the archaic seismic design rules of the 1960s or earlier. Most of 

these buildings were constructed with concrete, steel, reinforced masonry, 

or wood construction. Unreinforced masonry buildings are rare in California because most of these buildings have either been abandoned or 

retrofitted. However, it should be assumed that older buildings of unreinforced masonry bearing wall construction, that are still common in other 

parts of the country, would perform at the low end of the ranges recorded 

for pre-Act buildings. 

Buildings with seismic designs completed in the 1970s and 1980s can be 

expected to perform somewhere between pre- and post-Act levels, but 

probably closer to the pre-Act data. Buildings classified as post-Act are exceptionally strong, because the designs were thoroughly checked and 

the construction monitored in detail. Due to the State-of-California-mandated scrutiny given design and construction, there are few hospital 

buildings outside of that area that would be equivalent to the post-Act category. However, the structural performance of hospitals built since the 

early 1990s that incorporated full seismic design, including an importance 

factor of 1.5, can be compared to the post-Act category. 

The vulnerability assessment of existing hospitals with respect to 

nonstructural building components is different from the assessment of 

potential structural damage. Unless a significant emphasis was placed on 

the design and installation of nonstructural anchorage and bracing, and 

unless the construction was monitored and inspected regularly, the potential for damage to ceilings, partitions, pipes, ducts, equipment, and other 

nonstructural systems should be estimated using the pre-Act column and 

charts. Since it is unlikely that nonstructural systems have been adequately 

protected in areas outside of California, it is recommended to assume that 
2-54 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Figure 2-41: Charts showing performance categories for pre-Act buildings for various ground motions
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-55

Figure 2-42: Charts showing performance categories for post-Act buildings for various ground motions 
2-56 MAKING HOSPITALS SAFE FROM EARTHQUAKES

substantial damage to these systems would be a certainty in moderate to 

high levels of shaking. Even with the extraordinary measures taken in California to assure thorough seismic protection of nonstructural systems, 

the level of nonstructural damage recorded indicates that the potential 

disruption of hospital operations can happen at shaking of about 50 percent SDS. The shaking above 80 percent SDS would most likely result in 

nonstructural damage that would require immediate closure and total 

evacuation of the hospital.

This type of vulnerability analysis should be used for preliminary assessments or for the purpose of awareness training or emergency planning. 

It cannot replace a formal seismic building evaluation performed by experienced design professionals. The type and the extent of seismic risk 

exposure for hospitals can only be identified by expert analysis.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-57

2.4 RISK REDUCTION MEASURES

T his section outlines some of the basic approaches and techniques 

of mitigating earthquake hazards. Since the theory and practice of 

seismic design are well established and have largely been incorporated into the current model building codes, this section starts with the 

review of basic steps in the process of planning and design of hospitals. It 

also highlights some of the well-established seismic design and construction techniques and specialized building systems designed specifically to 

address the seismic forces. Although the general principles of design are 

similar for new and existing hospitals, this section highlights the differences in code requirements and overall project delivery processes that 

reflect the opportunities and constraints of seismic design for new and existing buildings. 

2.4.1 Site Selection Basics

The first priority for owners of existing hospitals and planners and designers of new facilities is to understand the seismic hazard risk. The 

location and the physical characteristics of the site determine the extent of seismic hazards, which include the potential intensity of ground 

shaking, the possibility of liquefaction, earthquake induced landslide, or 

more rarely, the potential of a tsunami or seiche. If ground motion is the 

only or predominant hazard, site seismicity can be determined from the 

local building code by a local structural engineer or a building department official. More detailed information can be obtained from the USGS 

Web site, which provides seismological information for any zip code in the 

nation. When hazards in addition to ground motion exist, seismic experts 

are needed to determine the probability and extent of these risks and possible mitigation techniques.

The selection of hospital sites is generally based more on factors associated with availability of land, proximity to service area, cost, convenience 

of access for patients, visitors, and staff, or general demographic con-
2-58 MAKING HOSPITALS SAFE FROM EARTHQUAKES

cerns than on the exposure of these sites to natural hazards, particularly 

earthquakes. Careful site selection, however, is a critical first step in risk 

reduction, because the potential ground motion from a single earthquake 

may vary considerably depending on the nature of the soil and the distance of the site from known earthquake faults. A large medical center 

that is developing a plan for new multi-building facility should include 

comprehensive analysis of the site characteristics and its exposure to natural hazard as an important factor in evaluating alternative sites. 

m Consider seismic constraints in site selection. Although it would be 

very rare for a hospital district to make a site selection decision based 

solely on seismic risk, moving a hospital even a few miles in some 

cases can make a big difference to its exposure to seismic hazard. 

An example is locating a hospital 5 to 10 miles away from a major 

earthquake fault, rather than locating it within 1 mile of the fault.

m Locate the building on a soil type that reduces the risk. Local soil profiles can be highly variable, especially near water, on sloped surfaces, 

or close to faults. In an extreme case, siting on poor soils can lead to 

damage from liquefaction, land sliding, or lateral spreading of the soil. 

m Since hospitals should be designed to performance-based criteria that 

include minimum disruption and continued operation, the location 

of the site within the region may play a critical role in achieving the 

required performance. The definition of “site” becomes the region 

within which the facility is located, and assessments should be made 

with respect to its access to materials, personnel, and utilities, as well 

as its position in the regional transportation grid. 

In most cases, however, it is probable that a site with optimal characteristics (other than seismic considerations) will be selected and that seismic 

issues will be mitigated as part of planning and design of the facility. A 

proposed construction site located directly over a fault is probably the 

only location characteristic that would lead to rejection of an otherwise 

suitable site. 

2.4.2 Seismic Design Basics

Minimum standards and criteria for seismic design are defined in the 

seismic section of building codes. The codes provide maps that show 

whether the location is subject to earthquakes and, if so, the probability 

of occurrence, expressed by varying levels of seismic forces for which a 

building must be designed. The seismic provisions in building codes are 

adopted by State or local authorities, so it is possible for a seismicallyprone region to be exempt from seismic building code regulations if the 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-59

local community decides that the adoption of such provisions is not required. Hospital board officials and designers should not ignore seismic 

design requirements irrespective of whether local communities have adopted seismic code regulations or not.

Budgeting extra costs for seismic design is a difficult issue, because 

although the risk may appear to be minimal, the effects could be catastrophic if a significant event were to occur. The very fact that such an 

event is rare means that the community may have no history of designing 

for earthquakes, and the building stock in general would be especially vulnerable. Hospital buildings are an important community resource (along 

with other essential buildings, such as schools and fire and police stations) 

that must be protected as much as possible.

2.4.3 Structural Systems

Health care facilities occupy buildings of different sizes, configurations, 

and structural systems. Additionally, hospitals differ in the level of services 

they provide. Some hospitals are distinguished by high occupancies, while 

others emphasize outpatient services. The mixture of functions and services is such that hospitals frequently require building systems that can 

accommodate very diverse functions. These can vary from acute care with 

many diagnostic, laboratory, and treatment areas requiring high-tech facilities and services to support functions such as laundry, food service, 

receiving, storage, and distribution. 

Smaller healthcare facilities may encompass one or more of these functions, such as predominantly longer residential care, or specialized 

treatment such as physical rehabilitation or dialysis. This functional variety may influence some structural choices, but the structure, as in all 

buildings, plays a primary role in providing a safe and secure support for 

the facility activities. Since continued operation is the preferred performance objective, structural design that goes beyond life safety standards is 

necessary, which requires special attention.

2.4.3.1 Basic Types of Lateral Force Resisting Systems

Figure 2-43 shows the basic types of structural lateral force resisting systems. These systems compose the three basic alternatives for providing 

lateral resistance: shear walls, braced frames, and moment-resistant 

frames. Each of these has specific characteristics, such as stiffness, relationship to spatial requirements, and cost-effectiveness that must be 

evaluated for each project. Diaphragms connect horizontal and vertical elements and transfer the seismic loads to the lateral force resisting 
2-60 MAKING HOSPITALS SAFE FROM EARTHQUAKES

system. This concept is shown in Figure 2-43. Structural material alternatives—steel, reinforced concrete, reinforced concrete masonry, and wood, 

provide further options that must be evaluated. Figures 2-44, 2-45, and 2-

46 show the three systems and materials that can be used to resist seismic 

forces in more detail. 

Figure 2-43: Basic types of lateral force resisting systems

SOURCE: BSSC: PRESENTATIONS TO THE ARCHITECTURAL COMMUNITY, 2001, CHRIS ARNOLD AND TONY ALEXANDER

Figure 2-44:

Reinforced concrete 

shear wall structure
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-61

Figure 2-45:

Steel braced frame 

structure

Figure 2-46:

Steel moment resistant 

frame
2-62 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Many variations of these types are possible, together with other structural 

types such as wood frame, light steel, reinforced masonry, and tilt-up reinforced concrete. The seismic codes expand these three basic systems into 

six categories by the addition of two categories of dual systems (composite 

steel and reinforced concrete) and inverted pendulum systems (such as 

cantilevered water tanks). 

For each of the three basic systems, four coefficients and factors are provided, of which the most unique is the response modification, or “R” 

factor. This is a coefficient related to the overall behavior and ductility 

of the structural system. R has values from 1.25 to 8, and is a divisor that 

modifies the base shear value obtained in the ELF procedure by reducing 

the design forces. The higher the number assigned to R, the greater the 

reduction. Thus, the highly ductile and better-understood moment resisting frame has a value of 8, while an unreinforced masonry structure 

has a value of 1.5. Using the R reduction is justified because experience 

and research confirm the expected performance of these systems and 

their ability to accept overloads.

2.4.3.2 Innovative Structural Systems

In recent years, a number of new approaches to the seismic protection of 

buildings have been developed that are now seeing increased use. These 

systems depend on modifying either the seismic loads that are transmitted 

from the ground to the building, or the building response. In both instances, the strategy is to let the building “ride with the punch,” rather 

than relying on resistance alone to protect the building.

Seismic isolation, generally referred to as base isolation, is a design concept that reduces the earthquake motions in the building superstructure 

by isolating the building from ground motions. This is accomplished by 

supporting the building on bearings that greatly reduce the transmission of ground motion (see Figure 2-47). Both the structure and the 

nonstructural systems are subjected to reduced shaking levels, so the 

system is well suited for essential facilities, like hospitals that need to remain functional following an earthquake. Many emergency management 

centers and a few hospitals in the United States have employed this technique. It has also been used by private industry on buildings of high 

importance, and as a retrofit technique, mostly for significant historic 

buildings.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-63

Passive energy dissipation is another concept in which the earthquake 

forces in the building are reduced by the introduction of devices that 

are designed to dissipate the earthquake energy in a controlled manner 

using friction, hydraulics, or deformation of material specially placed for 

this purpose (see Figure 2-52). These devices usually take the form of a 

bracing system that connects the vertical structural members together. 

These devices also increase the damping of the structure and reduce the 

drift. The Bremerton Naval Hospital provides an example of successful rehabilitation that used these devices (see Section 2.4.6.2).

2.4.3.3 Structural Systems Selection

The seismic code prescribes the analysis procedures for a number of different types of structural systems. The engineer, however, must choose the 

system that is appropriate for the type of building and its use. Structural 

systems vary greatly in their performance attributes, even though they 

may all meet the requirements of the seismic code if correctly designed 

and constructed. 

The critical initial step in selecting a structural system is to establish 

performance goals for the project. Because hospitals are classified as essential buildings, the seismic code requirements imply a requirement 

for a certain level of performance. An informed performance-based design procedure is necessary. This procedure should involve the owner, the 

full design team, and any other stakeholders. The process should cover 

all steps, from determining performance goals to the detailed design and 

construction of the project. 

On the technical side, the most important measure of good earthquakeresistant design is the effect on the structure after the earth has stopped 

Figure 2-47:

Seismic isolation
2-64 MAKING HOSPITALS SAFE FROM EARTHQUAKES

shaking. With little building damage, there is a good chance that the 

building will be functional and repair costs will be low. With significant 

damage, it is unlikely that the building would be functional and repair or 

replacement costs would be high. The measure of success in seismic design of a hospital is the extent to which a building can avoid significant 

damage and retain a reasonable level of functionality without the need 

to evacuate patients. The behavior of each structural system and building 

configuration differs with earthquake ground motions, soil types, duration of strong shaking, etc., but past observations of damage can inform 

the decisions about the most appropriate systems.

The best performing structural systems will do the following:

m Possess stable cyclic behavior. Will not be prone to sudden structural 

failure or collapse

m Control lateral drift. Will keep drift (lateral distortion between 

floors) to reasonable dimensions to reduce damage to nonstructural 

components, such as glazing, partitions, and cladding

m Dissipate seismic energy without failing. Absorb the earthquake 

energy in a controlled manner without causing structural members to 

fail 

m Create a good chance of functionality and a low post-earthquake 

repair cost

2.4.4 Nonstructural Components and

Systems

For a long time, seismic building codes focused exclusively on the structural components of building. Although this focus still remains dominant, 

experience in recent earthquakes has shown that damage to nonstructural 

components and systems is also of great concern. Continued hospital operation is increasingly dependent on nonstructural components and 

systems, including medical and building equipment. Hospital operations 

also depend on specialized services, some of which involve storing of hazardous substances, such as pharmaceuticals, toxic chemicals, oxygen, 

and other gases, that must be protected against spilling. Distribution systems for hazardous gases must be well supported and braced. Unlike most 

buildings, hospitals require a very extensive plumbing network to supply 

water throughout the building, and an adequate piping network to supply 

water for fire sprinklers, which increases the risk of secondary water 

damage in case of failure of these systems during earthquakes.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-65

In a typical hospital, not only do the nonstructural components play a major 

role in operations, they also account for large share of the cost. Typically, for 

a medium-size hospital, the structure accounts for around 15 percent of the 

total cost, and the nonstructural components for the remaining 85 percent. 

Of the latter, the mechanical, electrical, and plumbing systems alone account for approximately 35 percent of the total building cost.

Even though the building structure may be relatively undamaged after 

an earthquake, excessive structural motion and drift may cause damage 

to ceilings, partitions, light fixtures, service piping, and exterior walls and 

glazing. In addition, storage units, medical equipment, and filing cabinets may topple and cause injuries if not properly anchored or braced. 

Excessive drift and motion may also lead to damage to rooftop equipment, and localized damage to water systems and fire suppression piping 

and sprinklers. Heavy equipment, such as shop machinery, kilns, and 

heavy mechanical and electrical equipment, may also be displaced and 

become non-functional. 

2.4.4.1 Code Regulated Nonstructural Systems

The seismic code categorizes nonstructural components as architectural 

components or mechanical and electrical components. Many of the hospital contents, such as furnishings and specialized equipment, which may 

be critical to hospital function, are not subject to regulation.

Table 2-3 shows the list of nonstructural components and systems that are 

subject to code regulation. 

Table 2-3: Code Regulated Architectural, Mechanical, and Electrical Components 

Architectural Components Mechanical and Electrical Components

Interior Nonstructural Partitions General Mechanical

 Plain unreinforced masonry Boilers and furnaces

 Other walls and partitions Pressure vessels

Cantilever Elements, Unbraced Stacks

 Parapets Cantilevered chimneys

 Chimneys and stacks Other

Cantilever Elements, Braced Manufacturing And Process Machinery

 Parapets General

 Chimneys and stacks Conveyors (non-personnel)

Exterior Nonstructural Wall Elements Piping Systems 

 Wall elements High deformability

 Body of panel connections Limited deformability

 Fasteners of connecting systems Low deformability
2-66 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Architectural Components Mechanical and Electrical Components

Veneer HVAC System Equipment

 Limited deformability Vibration isolated

 Low deformability Non-vibration isolated

Penthouses, Not Part of Main Structure Mounted in-line with ductwork

Ceilings Other

Cabinets Elevator Components 

 Storage cabinets and lab equipment Escalator Components

Access Floors Trussed Towers (Free-standing or Guyed)

 Special access floors General Electrical

 All others Lighting Fixtures

Appendages and Ornamentation

Signs and Billboards

Other Rigid Components

 High deformability elements

 Limited deformability elements

 Low deformability elements

Other Flexible Components

 High deformability elements 

 Limited deformability elements

 Low deformability elements

Figure 2-48 is an example of a cable tray with a braced support system designed in conformance with the seismic code.

Figure 2-48:

Seismically braced 

cable tray support

Table 2-3: Code Regulated Architectural, Mechanical, and Electrical Components (continued)
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-67

2.4.4.2 Interstitial Space for Utility Installations

Developments in medical technology frequently require hospitals to add 

or re-route utility and medical services infrastructure and add electrical 

capacity to various parts of the building, often with consequent disruption of the operations and difficulties caused by limited available space 

above the ceiling. In response to these problems, a number of hospitals 

have been designed with interstitial service space. In some designs, the 

interstitial floor is a nonstructural floor hung from the structural floor 

above (Figure 2-49).

The interstitial space concept provided a full floor above the functional 

space where service personnel can work to add or modify installations 

without disturbing the space below, or disrupting hospital operations. 

The main structural effect of an interstitial floor is to increase the floor-tofloor height of the occupied floors and the building as a whole, with some 

increase in the amount of structural material. Any of the common steel 

and concrete frame systems can be used to provide the interstitial floor 

arrangement. The interstitial space concept was used in the Loma Linda 

Veterans Hospital (see Section 2.4.5.1)

Figure 2-49:

Interstitial floor system 

hung from the floor 

above

Figure 2-49:

Interstitial floor system 

hung from the floor 

above
2-68 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.4.5 Mitigation Measures for New 

Buildings

If mitigation measures are instituted in the planning stage, a high level of 

seismic protection can be achieved in a new building with the following steps:

m Assure that the latest model building code is used, using the 

appropriate importance factor.

m Include provisions in the design to allow the facility to function on 

its own for 4 days. This would require storage of sufficient fuel for 

emergency standby power supply system, reserve water supply, and 

provisions for waste water storage. Assure that access to the site will 

not be impaired by earthquake damage.

m Although seismic isolation should be considered for all buildings that 

are intended to be functional after an earthquake, this measure should 

be considered as a realistic alternative only for sites with SDS over 0.8 g.

m Consider a peer review of the structural design, particularly in 

jurisdictions that do not require a thorough plan check to obtain 

a building permit. A peer review is essential if innovative structural 

systems, such as isolation or structural dampers, are used.

m Assure that the seismic design for nonstructural elements and 

systems regulated by the building code are the responsibility of the 

design team. A list of such responsibilities is given in FEMA 356. 

One method of gaining such assurance is to create the position of a 

Nonstructural Seismic Coordinator (NSC), whose responsibility is to 

review the specifications, drawings, or other methods proposed to 

attain adequate seismic anchoring and bracing of all systems. Further, 

the NSC will follow the submittals and construction processes to 

assure appropriate implementation.

m Put in place a comprehensive system to monitor construction quality 

and to track significant change orders that might imply subtle 

reductions in structural or nonstructural seismic performance.

2.4.5.1 The Case of Loma Linda Veterans Hospital

The 500-bed Veterans Administration Hospital in Loma Linda, CA, 

opened in September 1977. Designed as a replacement facility for the Veterans Administration Hospital lost in the 1971 San Fernando earthquake, 

it was built in the area of extremely high seismicity, and represents an interesting case of careful seismic design.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-69

The project was remarkable because of the extent to which the configuration of a large and complex building was influenced by seismic design 

concerns. At the same time, the project provides a lesson in showing 

that early recognition of seismic design determinants by the whole design team, and a serious interdis­ciplinary approach from the inception of 

design, can enable requirements of both seismic design and hospital planning and economy to be achieved with equal effectiveness.

The San Bernardino Valley is seismically very active, and the final site selected for the new hospital had 11 known active faults within a 65-mile 

radius, including the San Jacinto fault and two segments of the San Andreas fault. The potentially active Loma Linda fault was also believed to 

be located near the site, and after intensive studies, it was concluded that 

the most likely location of the fault was 200 to 400 feet southwest of the 

site, but that surface rupture at the site was not likely. The risk of soil amplification was significant.

The consultants recommended that design earthquakes of magnitude 8+ 

and duration of 35–40 seconds on the San Andreas fault, and magnitude 

6.5–7.25 and duration of 20 seconds on the San Jacinto fault, should be 

consid­ered. The building structure was to be designed for a peak acceleration of 0.5 g, while the essential and potentially damaging nonstructural 

components were to be designed for an acceleration of 2.0 g. 

Some of the design force determinants evaluated were dependent on a 

building configuration concept. 

1. Site geometry: The large 40-acre site enabled the designers to consider a freestanding building unconstrained by site geometry. The site 

area was sufficiently large to allow consideration of a relatively low, 

horizontally planned building.

2. Design Program: Research studies on hospital organization and 

plan­ning had estab­lished some general benefits of horizontal 

planning—defined as plans in which clinical and diagnostic areas 

are placed on the same floor as nursing areas, rather than being 

concentrated into a base structure with a vertical connection to the 

bed-related functions. Experience in vertically planned hospitals 

had indicated some prob­lems in ensuring adequate circulation, 

since the concentration of vertical circulation into a single tower 

tended to result in over- or under-capacity, depending on the time 

of the day. There were also indications of a general preference by 

staff for horizontal movement over vertical, and an indication that 

a reduction of vertical circulation for severely ill patients would be 

desirable.
2-70 MAKING HOSPITALS SAFE FROM EARTHQUAKES

3. Aesthetics: The design of hospitals tends to be dominated by the solution of very complex planning, service, and equipment problems, 

and appearance tends to be a secondary concern. The city of Loma 

Linda was anxious that the setting of the hospital should be “parklike.” In response to this desire, and to the generally small scale of 

the immediate site surroundings, the image of a low, nonassertive 

building, placed toward the center of the site, seemed appropriate. 

Although very large in size, the building’s relatively low height and 

the considerable size of the site was to help reduce the visual effect of 

the building on the neighboring community

4. Building system: The Loma Linda Hospital was intended as a 

demonstration of the Veterans Administration Hospital Building 

System, which had been developed over a period of several years 

by the same team that was respon­sible for the hospital design. The 

building system consisted of a carefully conceived set of design 

concepts intended to rationalize and organize the preliminary 

hospital design.

The structural design comprised moderate-span simple post and beam 

shallow floor framing system, large floor-to-floor heights, and lateral force 

resistance elements concentrated in the service tower at the end of each 

of the service modules. The planning and aesthetic requirements of a low, 

deep plan building coincided well with a stiff seismic design that would 

minimize story drift; consequent architectural, mechanical, electrical, and 

contents damage; and loss of operational capability. In addition, the low, 

stiff building would have a shorter period and possibly a lower response 

than the projected response spectra peaks of 0.3 and 0.8 seconds from the 

two nearby faults. The only way of moving the building response well away 

from the ground response would be to develop a flexible high-rise structure that would be undesirable from all the other viewpoints considered.

The chosen configuration was the simplest of all those studied: a simple 

block, almost square in plan, with no basement and with a symmetrical 

pattern of four courtyards within the block. The courtyards were relatively 

small. The plan had an even distribution of shear walls throughout, running uninterrupted from roof to foundation and having direct continuity 

in plan with the structural framing members.

The planning and circulation of the building were carefully related to 

shear wall layout to achieve minimum shear wall penetration with clearly 

defined, highly accessible public and departmental planning. The eight 

service towers (four at each end) provided a location for major shear 

walls. Each tower pro­vided two shear walls in the east-west direction and 

one in the north-south direction. 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-71

The general lateral resisting system used concrete shear walls and a ductile moment-resistant “backup” frame. The stiff primary shear wall system 

was designed for a high force level, so that the structure will tend to have 

low lateral deflections for the design earthquakes described earlier. The 

calculated maximum story-to-story drift was well within presently accepted 

desirable ranges for hospitals.

The backup frame was intended to form a stable and reliable backup 

system for lateral force resistance and redistribution of forces should one 

or more of the shear walls become seriously damaged. The chances of the 

backup frame being forced to work to its full capacity were considered 

small, but considering the size and importance of the facility, and the uncertainties of estimating the nature of ground motion, the possibility 

could not be ignored.

Shear walls were always placed at the perimeter of service modules to 

mini­mize interference. Interior girders were dropped below the beams 

to minimize interference with plumbing service and to allow beam continuity across the module. As a result of the service organization, all beams 

and girders are free of penetrations. These framing characteristics were 

the product of the research study that determined the system’s design.

The shear walls are collocated with frame lines. The advantages of this arrangement were:

m Beams or girders were always parallel and lined up with the walls, to 

serve as lateral force collectors.

m The continuation of these members through the wall allowed direct 

transfer of forces from the diaphragm to the wall.

m The columns at the end of walls formed the required ductile flange 

members.

m Frame members were in the correct position to provide vertical 

support for shear wall dead loads.

Complete calculations and designs were completed for all nonstructural 

components and systems. The bracing of utility distribution systems, ceilings, partitions, and lights was made easier and less expensive by the 

presence of the interstitial floor system shown in Figure 2-49.
2-72 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.4.6 MITIGATION MEASURES FOR EXISTING 

BUILDINGS

Engineering of structural and nonstructural risk reduction measures 

is similar for new and existing hospitals. New hospital design offers the 

possibility to minimize the risk by selecting a site subject to less ground 

motion, with better soil conditions, or located farther from a fault. It can 

be designed with the most appropriate structural system, using known 

and tested materials and a good building configuration. These possibilities are not available when retrofitting an existing hospital. The existing 

building may have been designed to an obsolete seismic code or no code 

at all, its materials may be questionable, or the building configuration and 

structural system may be inappropriate. Therefore, protecting an existing 

hospital must start with a detailed evaluation of its vulnerability, because 

seismic retrofitting is both disruptive and expensive, and should not be 

implemented without careful study.

2.4.6.1 Procedures and Design Strategies for 

Rehabilitation of Structural Systems

Additions to an existing hospital must meet all the code requirements for 

a new building. With the exception of California, there are currently no 

seismic codes that apply to the retrofit of existing hospitals. Typically, the 

standards to be applied are derived from the code for new buildings and 

negotiated with the applicable building department. It is generally recognized that it is difficult, or almost impossible, to bring an existing structure 

to full compliance with a current code, and so some compromises have to 

be made. There is, however, no general agreement as to how the code for 

new buildings shoul be applied to the retrofit design of existing ones.

FEMA has developed many such documents and several have been adopted by ASCE as standards suitable for adoption by building codes (see 

ASCE 31 and ASCE 41). The planning process for retrofits should begin 

with an evaluation procedure, such as Tier 1 of the ASCE 31 Seismic Evaluation of Existing Buildings (ASCE, 2003). If the evaluation results require a 

retrofit of an existing building, ASCE 41, Seismic Rehabilitation of Buildings 

(ASCE, 2007) is the authoritative source document and can be used to 

help a hospital design team select seismic protection criteria. The architect and engineer can also use the document for the design and analysis 

of the seismic rehabilitation project. 

ASCE 41 provides methods and design criteria for several different levels 

of seismic performance. The document also recommends a thorough and 

systematic procedure for performance-based seismic design, intended to 

produce a design responsive to the owner’s level of acceptable risk and 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-73

available resources. This process starts with a requirement to select specific 

performance goals (Rehabilitation Objectives) as a basis for design. In this 

way, users can directly determine the effect of different performance goals 

on the design requirements, including their complexity and cost. See Section 2.2.3 for a further description of performance-based seismic design.

Typical basic design concepts for improving the structural seismic performance of an existing hospital include:

m Modifying and improving local components or materials, such as 

beam/column connections. This involves retrofitting connections 

and strengthening structural members by such methods as adding, 

reinforcing, or replacing them with new components.

m Adding new lateral force resisting elements, such as shear walls or 

braced frames. 

m Removing or reducing configuration irregularities. This involves 

providing seismic separations in irregular configurations, or adding 

shear walls or bracing to reduce torsional effects. Mass can also be 

removed by removing stories.

m Modifying the basic seismic response of a structure by adding 

dampers or installing seismic isolation systems.

2.4.6.2 The Case of Naval Hospital Bremerton

Naval Hospital Bremerton, located in Bremerton, WA, not only serves military personnel and their families in the area—up to 60,000 people—but 

could also be called on to serve more than 250,000 people on Washington’s Kitsap Peninsula after a major earthquake. The facility is spread 

over 40 acres, and includes 20 buildings, some of which are 70 years old. 

Being one of only two major hospitals in the region, the Navy was concerned about its response capability to moderate-to-strong seismic ground 

shaking expected at the site (Wilson, 2005).

To obtain a broad understanding of the vulnerability of the facility and the 

relative risk among the many buildings, a rapid visual screening was completed by the Navy’s consultant, Reid Middleton, using FEMA 154 (FEMA, 

2002), which considers structural type, basic seismic characteristics, 

building use, and occupancy load. This relatively modest effort provided 

an overview of the seismic risk at the campus, as well as a preliminary relative ranking among buildings. It made it obvious that the main hospital 

building, a nine-story, 250,000-square-foot building that housed most of 

the essential medical functions, should be a priority (see Figure 2-50).
2-74 MAKING HOSPITALS SAFE FROM EARTHQUAKES

The building is a steel moment frame, constructed in the 1960s, that employed welded beam-to-column connections, now known to be prone 

to cracking when subjected to large seismic deformations. A more detailed structural analysis and evaluation was performed using FEMA 356 

(FEMA, 2000). It was found that although the frame does not pose a significant threat of collapse, the building’s ability to function after an 

earthquake could be severely limited by damage to structural joints, and 

by nonstructural damage. 

In February 2001, while the Navy and the design team were considering 

their options, the Magnitude 6.8 Nisqually earthquake struck the area. 

The earthquake occurred deep below the surface and approximately 30 

miles from the site. The ground motions at the site were below the design shaking for the site, but nevertheless caused significant nonstructural 

damage—particularly in the upper floors (see Figure 2-51). Such 

nonstructural damage always causes concern about the integrity of the 

structure—and often requires destructive exploration to verify. Based on 

preliminary structural inspections, aided by recordings of the response 

from instruments in the building, the Navy decided to stay in the building 

while more extensive exploration and analysis were performed. It took 

several months before nonstructural repairs were completed and the 

building returned to full use. Subsequent structural review indicated no 

structural damage.

Figure 2-50:

The main building 

at Naval Hospital 

Bremerton 

Source: Reid Middleton, 

Inc.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-75

The data on the response of the building to the Nisqually earthquake provided an opportunity to simulate, by computer analysis, a design event. 

This simulation revealed that shaking at the design level could cause unacceptable damage, both to the beam-column joints and to nonstructural 

systems. The team found that traditional, code-based retrofits, such as 

local modification of the 1,550 beam-column connections, or introduction of braced frames to meet current standards, were too costly and 

disruptive. Solutions were investigated using the more finely tuned, 

performance-based design methodologies of FEMA 356, and a more innovative scheme, based on the introduction of supplemental seismic 

dampers, appeared feasible.

Several styles of dampers are available for use in buildings, including 

those employing controlled yielding of steel elements, those based on friction (similar to a brake shoe), and more sophisticated hydraulic dampers 

(similar to a shock absorber). Dampers are normally placed in a building 

in a configuration similar to diagonal braces, and work against the movement between floors (see Figure 2-52). This action reduces inter-story 

drift and, to a lesser extent, reduces floor accelerations that cause sliding 

and overturning of equipment and contents. Although dampers should 

be evenly distributed throughout the building, they allow greater flexFigure 2-51:

Disruption in the upper floors at Naval Hospital 

Bremerton from the Nisqually earthquake

Source: Reid Middleton, Inc.
2-76 MAKING HOSPITALS SAFE FROM EARTHQUAKES

ibility in placement than braced frames or other standard lateral force 

resisting systems. The flexibility in placement of the dampers means that 

critical locations, those that would reduce usefulness of the intended 

space or cause operational shutdowns during installation, can be avoided. 

Using performance-based design concepts, the team set the target structural performance levels for Immediate Occupancy (see Section 2.2.3.1) 

for the design earthquake shaking, and Collapse Prevention for a reasonable estimate of the worst shaking expected at the site. Structural analysis 

indicated that adding a total of 88 fluid viscous dampers, spread through 

the facility, would deliver the desired performance within the bounds of 

the current analysis and prediction capability. The cost of the structural 

retrofit was projected to be less than 10 percent of the replacement cost, 

a value that would yield a favorable life cycle cost (from damage avoided) 

on most sites in the country.

In parallel with the retrofit design, the team developed an inexpensive 

and innovative program (called REACH—Rapid Evaluation and Assessment CHecklist) to improve the speed and effectiveness of future building 

safety evaluation following a seismic event. For many structural types, 

the seismic structural damage is covered and not obvious; concern about 

the extent of structural damage can sometimes delay decisions about 

building safety, or even cause an unneeded evacuation. The building-specific REACH program incorporates real-time data from the building’s 

seismograph network. Threshold values for acceleration and displacement are pre-determined by the design team, and actual building motion 

is then compared with these threshold values to allow more accurate and 

informed decisionmaking regarding the ability of the building to sustain 

the safe delivery of medical services after earthquakes. The REACH checklist contains additional information, such as a description of the structural 

Figure 2-52:

Installation of dampers 

at Naval Hospital 

Bremerton. The 

configuration is similar 

to steel braced frames.

Source Reid Middleton, 

Inc.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-77

system, structural drawings, recommended structural inspection sites, 

and other information of use to the facility engineer and building inspectors. The REACH documents are stored in the facility department’s 

disaster response locker, and are reviewed by facility staff during routine 

emergency drills.

Recognizing the significant effect that damage to nonstructural systems 

can have on post earthquake functionality, the facility has begun retrofit 

of nonstructural elements, including bracing of acoustic tile ceiling and 

light grids, mechanical system piping, as well as cabinetry and furniture. 

Future analysis and reinforcement of bracing for critical equipment (such 

as radiology and laboratory) is planned.

2.4.6.3 Procedures and Design Strategies for 

Rehabilitation of Nonstructural Systems

Complete, nonstructural seismic rehabilitation of an existing hospital in 

operation is disruptive and very expensive. However, it is relatively easy to 

incorporate seismic bracing and anchoring during ongoing renovation or 

rehabilitation work. A more active and aggressive program requires developing databases of components and systems, and developing a process for 

prioritizing. Priorities can be set by considering importance to life safety, 

importance to overall functionality, associated cost and disruption, component vulnerability, or by cost-benefit considerations (see FEMA 274 for 

more information). 

Components commonly found to be of high priority because of their 

importance, high level of vulnerability, and relatively low cost include anchorage of standby generators, medical gas storage, pressurized piping, 

and communications systems. Although not normally considered a dangerous or high-priority system, damage to lightweight suspended panelized 

ceiling and light systems can disrupt hospital operations, as happened 

in Hawaii where such damage forced the KCH to evacuate (see Section 

2.3.2.2). It is important that the key vulnerabilities of each facility be identified and considered in emergency planning and mitigation programs.

2.4.6.4 Summary of Risk Reduction Measures for 

Existing Buildings

Achieving cost-effective improvements in seismic performance of existing 

facilities is far more complex than improving expected performance for 

proposed new buildings in the planning and design stage. First, and most 

obvious, it is always far less expensive to include relatively small changes 

in a new design to create seismically resistant structural and nonstructural 
2-78 MAKING HOSPITALS SAFE FROM EARTHQUAKES

systems than it is to retrofit—or sometimes replace—existing systems. 

The complexity and expense of retrofitting is exacerbated when such 

work is not done in conjunction with complete renovation—that is, if the 

building has to remain mostly occupied and operational. 

Following the recommended seismic evaluations, careful analysis is 

needed to identify significant life safety risks from potential structural 

collapse; to identify and achieve short-term, high benefit-cost mitigation 

measures; and to plan for longer-term overall mitigation. The following 

steps are recommended:

m Engage a structural engineer experienced in seismic evaluation and 

design to perform a seismic structural evaluation of existing buildings 

on the campus that contribute to the hospital function. The primary 

purpose of such an analysis is to quickly identify buildings that may 

be seriously damaged or even collapse in a code-level earthquake. 

A secondary purpose is to gain an understanding of the probable 

performance of the structural and nonstructural systems of each 

building by using the data charted in Figures 2-41 and 2-42.

m Engage an architect, mechanical and electrical engineer, and 

structural engineer, as needed, to evaluate the probable seismic 

performance of nonstructural components and systems.

m Update the emergency response plan, considering the results of the 

seismic evaluations.

m If significant life safety risks are identified from review of either 

structural or nonstructural systems, make plans to minimize 

occupancy of the building, replace the building, or retrofit to an 

acceptable level of performance.

m In most cases, shaking of less than code intensity, which may cause 

minor or no structural damage, can cause serious nonstructural 

damage. The most vulnerable elements that can affect the functions 

of the hospital have been identified from past earthquakes. They are 

the emergency generator, the bulk oxygen storage tank, the internal 

and external emergency communication systems, and the patient 

elevators. These elements, other than the elevators, normally can be 

anchored and braced against seismic damage rather inexpensively 

and quickly. The elevators may require extensive retrofit to assure 

operation after strong shaking. However, to assure safe patient 

relocation immediately after an event, it is recommended that one 

patient elevator serving each floor be retrofitted to at least the 

capacity of the structural system and to current standards for essential 

facilities. Automatic seismic switches that demobilize elevators at low 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-79

shaking levels should be used with caution, as the switch may defeat 

the purpose of the strengthened elevator.

m Mechanical equipment on vibration isolators that are not designed 

for seismic forces are extremely vulnerable to seismic damage. This 

equipment should be identified and fitted with appropriate antiseismic isolators, or seismic snubbers, as soon as possible.

m Nonstructural elements affected by or exposed by normal renovation 

should be upgraded to current standards.

m The expected seismic structural performance of all buildings on the 

campus should be considered as part of master planning. Planning 

should also consider opportunities to provide 4 days of self reliance, 

(See Section 2.4.5).

m Vulnerable medical buildings that can lose full functionality after 

a code earthquake should be studied for retrofit or replacement. 

Improvements in seismic structural performance can often be 

combined with major renovations. Adjacent additions can sometimes 

be made sufficiently strong to buttress an existing building.

m Incremental seismic rehabilitation, as described in FEMA 396 (2003), 

should also be considered for applicability. 

m An emergency plan that considers the care of the patients and staff 

of the facility, as well as the surrounding community, should be kept 

up to date and should include a realistic estimation of the seismic 

performance of the structural and nonstructural systems in each 

building, and on the site in general.

m The Hospital Seismic Safety Evaluation Checklist (Table 2.4) should 

be applied.
2-80 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.5 CHECKLIST FOR SEISMIC 

VULNERABILITY OF HOSPITALS

T he Checklist for Seismic Vulnerability of Hospitals (Table 2-4) is a 

tool that can be used to help assess site-specific seismic hazards and 

building vulnerability. The checklist is useful during site selection, 

preliminary design of a new building, or when considering rehabilitation of an existing facility. In addition to examining building design issues 

that affect vulnerability, the checklist also helps users to examine the functionality of the crit­ical and emergency systems upon which most hospitals 

depend. The checklist is organized into separate sections, so that each 

section can be assigned to a subject expert for greater accu­racy of the examination. The results should be integrated into a master vulnerability 

assessment to guide the design process and the choice of appropriate mitigation measures.

Table 2-4: Hospital Seismic Safety Evaluation Checklist

Vulnerability Sections Guidance Observations

Site Condition

Is there an active fault on or 

adjacent to the site?

If suspected, site-specific geologic 

investigations should be performed. 

Consult local building department, 

State geologist, local university, or local 

geotechnical expert.

Does the site consist of soft, stiff, 

or dense soil or rock?

If the presence of softer soil that can lead 

to force amplification or liquefaction 

is suspected, site-specific geologic 

investigations should be performed.

Are post-earthquake site egress 

and access secured?

Alternative routes—unlikely to be blocked 

by falling buildings, power lines, etc.—are 

desirable.

Are utility and communications 

lifelines vulnerable to disruption 

and failure?

Security of the entire utility and 

communications network is the issue: the 

facility may be affected by offsite failures.
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-81

Vulnerability Sections Guidance Observations

Site Condition (continued)

Are there alternate or backup 

sources for vital utilities such as 

water and power?

Redundant systems increase the probability 

of the hospital remaining functional after 

an event.

Architectural

Is the architectural/structural 

configuration irregular?

Irregular vertical and horizontal 

configurations, such as set backs, open 

first stories, or L- or T-shaped plans, may 

lead to significant stress concentrations.

Is the building cladding attached 

to structural frames so that it can 

accommodate drift?

Frames are flexible, and cladding must 

be detailed to accommodate calculated 

drifts and deformations. If waterproofing 

of these systems is compromised, rain 

following an earthquake could cause parts 

of the building to be closed.

Are heavy veneers, such as brick 

or stone, securely attached to the 

structural walls?

Shear wall structures are very stiff and 

carry large earthquake forces; heavy 

attachments must be securely attached.

Are glazing and other panels 

attached so that they can 

accommodate drift?

Glazing must be installed with sufficient 

bite and adequate space between glass 

and metal to accommodate drift

Are light, suspended grid ceilings 

and lights braced and correctly 

attached at walls?

Suspended ceilings, if not braced, easily 

distort (particularly in light and flexible 

frame structures), thus causing ceiling 

panels to fall out.

Are heavy plaster suspended 

ceilings securely supported and 

braced?

Heavy lath and plaster ceilings in older 

facilities are very dangerous if poorly 

supported.

Are partitions that terminate at 

a hung ceiling braced to the 

structure above?

Partitions need support for out-of-plane 

forces, and attachment to a suspended 

ceiling grid only is inadequate.

Are masonry or hollow tile 

partitions reinforced, particularly 

those surrounding exit stairs?

Heavy partitions attract strong earthquake 

forces because of their stiffness and mass, 

and are prone to damage. They are particularly dangerous around stairs and exit ways.

Are parapets and other 

appendages securely braced and 

attached to the building structure?

Unreinforced masonry parapets are 

especially vulnerable. Brace items such as 

cornices, signs, and large antennas.

Structural System

When was the existing structure 

designed?

Buildings with no, or outdated, seismic 

design are unlikely to perform adequately 

in strong shaking. Verify that the 

Importance Factor was used in design.

Table 2-4: Hospital Seismic Safety Evaluation Checklist (continued)
2-82 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Vulnerability Sections Guidance Observations

Structural System (continued)

Has the local seismic zoning 

changed significantly since the 

building was designed?

Local expectation of shaking intensity can 

change as scientific knowledge increases

Is there a continuous load path 

from all components of the 

building to the foundation?

A continuous load path assures that the 

structure will act together as a whole when 

shaken. Connections from walls to floors and 

roofs should also form part of this load path.

Is all load-bearing structural 

masonry reinforced according to 

code?

Older unreinforced masonry has proven 

very vulnerable in strong shaking.

Are horizontal diaphragms 

correctly designed and 

constructed with necessary chords 

and collectors?

Large diaphragm openings and the edges 

of diaphragms need careful design to 

ensure forces are properly transmitted to 

walls and frames.

Nonstructural Systems

Are there backups for critical 

municipal utilities?

Municipal utilities such as water, power, 

and gas, are often disrupted in strong 

shaking. Onsite backups should provide 

48 hours of use.

Are ducts, piping, conduit, fire 

alarm wiring, and communication 

systems that pass through seismic 

joints provided with flexible 

connections?

Differential movement between sections of 

the building can cause breakage and leaks 

in pipes and ducts if no provision is made 

for movement. If walls at joint are firewalls, 

penetrations should be fireproofed.

Is heavy mechanical equipment 

adequately secured?

Heavy equipment may slide and break 

utility connections.

Are vibration isolators for 

vibrating equipment designed for 

seismic forces?

Equipment may jump off very loose 

isolators and may break restraints 

designed for wind only.

Is the piping properly braced and 

provided with expansion joints?

See Section 2.4.4.

Is ductwork properly supported 

and braced?

See Section 2.4.4.

Are boilers and other tanks 

securely braced?

Gas heaters or tanks with flammable or 

hazardous materials must be secured 

against toppling or sliding.

Are plumbing lines adequately 

supported and braced?

Leaks in pressure pipes can cause damage 

over a large area. Protection of joints is 

especially important. See Section 2.4.4.

Is fire protection piping correctly 

installed and braced?

See Section 2.4.4.

Table 2-4: Hospital Seismic Safety Evaluation Checklist (continued)
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-83

Vulnerability Sections Guidance Observations

Nonstructural Systems (continued)

Is heavy electrical equipment 

adequately secured?

Switch gear and transformers are heavy 

and sliding or movement failure can shut 

down the electrical system. See Section 

2.4.4.

Is emergency generator and 

associated equipment secured 

against movement?

The generator, muffler, batteries, day tank, 

and other electrical equipment may be 

necessary for emergency operation. See 

Section 2.4.4.

Are suspended lighting fixtures 

securely attached, braced, or 

designed to sway safely?

Older suspended lighting fixtures have 

performed badly in earthquakes, and are 

an injury hazard. See Section 2.4.4.

Are light fixtures supported in an 

integrated ceiling, braced, and 

provided with safety wires?

Light fixtures within a grid often fall when 

the grid is distorted, unless the fixtures 

are secured with safety wires. See Section 

2.4.4.

Are the elevator cars, 

counterweights, and equipment 

anchored for seismic forces?

Elevators are important for patient 

movement, particularly in an emergency. 

After strong shaking, elevators and shafts 

should be checked for safety before use. 

See Section 2.4.4.

Is at least one elevator in each 

wing connected to the emergency 

power system?

Even if properly anchored and 

undamaged, the elevator needs power 

to enable vertical patient movement. See 

2.4.4.

Is the bulk oxygen tank and 

associated equipment secured?

The legs, anchorage, and foundations 

of large tanks need to be checked for 

adequacy.

Is nitrogen storage secured? Loose tanks may fall and break 

connections.

Are small natural gas lines to 

laboratories or small equipment 

vulnerable?

Incompatibility of large and small lines 

and equipment movement can cause 

dangerous leaks.

Is the fire alarm system connected 

to a secondary power supply?

This is also necessary to support daily 

operational needs, including lighting, 

heating, communications, etc.

Is significant fire alarm equipment 

secured against movement?

Equipment can slide or topple, breaking 

connections. See FEMA 74.

Communications and IT Systems

Are communications components, 

including antennas, adequately 

braced and supported?

Post-event communications are vital for 

post-earthquake operations. See FEMA 74.

Are plans in place for emergency 

communication systems, both 

within the facility and to outside 

facilities?

Planning must consider likely postearthquake conditions at the site and 

offsite.

Table 2-4: Hospital Seismic Safety Evaluation Checklist (continued)
2-84 MAKING HOSPITALS SAFE FROM EARTHQUAKES

2.6 References and Sources of

Additional Information

Note: FEMA publications may be obtained at no cost by calling (800) 

480-2520, faxing a request to (301) 497-6378, or downloading from the library/publications section online at http://www.fema.gov.

ASCE, 2003, Seismic Evaluation of Existing Buildings, ASCE Standard ASCE31, American Society of Civil Engineers, Reston, VA.

ASCE, 2005, Minimum Design Loads for Buildings and Other Structures,

ASCE Standard ASCE-7-05, American Society of Civil Engineers, Reston, 

VA.

ASCE, 2007, Seismic Rehabilitation of Buildings, ASCE Standard ASCE-41, 

Reston, VA.

Arnold, Christopher, and Michael Durkin, 1983, Hospitals and the San Fernando Earthquake, August 1983, Building Systems Development, Inc., Palo 

Alto, CA.

Behr, R.A., 2004, “Design of Architectural Glazing to Resist Earthquakes,” 

Proceeding, 13th World Conference on Earthquake Engineering, Vancouver, BC, August 2004.

Earthquake Engineering Research Institute (EERI), John F. Hall, Technical Editor, 1995, “Chapter 11, Nonstructural Damage, Northridge 

Earthquake of January 17, 1994 Reconnaissance Report,” Volume 1, 

Earthquake Spectra, Supplement C to Volume 11, April 1995, Earthquake Engineering Research Institute, Oakland, CA.

Federal Emergency Management Agency (FEMA), 1997a, NEHRP 

Guidelines for the Seismic Rehabilitation of Buildings, FEMA 273, Federal 

Emergency Management Agency, Washington, DC. 
MAKING HOSPITALS SAFE FROM EARTHQUAKES 2-85

FEMA, 1997b, NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings, FEMA 274, Federal Emergency Management Agency, 

Washington, DC. 

FEMA, 2000, Prestandard and Commentary for the Seismic Rehabilitation of 

Buildings, FEMA 356, Federal Emergency Management Agency, Washington, DC. 

FEMA, 2002, Rapid Visual Screening of Buildings for Potential Seismic Hazards, A Handbook, FEMA 154, Federal Emergency Management Agency, 

Washington, DC. 

FEMA, 2003, Incremental Seismic Rehabilitation of Hospital Buildings, FEMA 

396, Federal Emergency Management Agency, Washington, DC. 

FEMA, 2007, Designing for Earthquakes, A Manual for Architects, FEMA 454, 

Federal Emergency Management Agency, Washington, DC. 

Holmes, William T., 2002, “Background and History of the Seismic Hospital Program in California,” Proceedings, 7th U.S. National Conference 

on Earthquake Engineering, July 21-25, 2005, Boston, MA, Earthquake 

Engineering Research Institute, Oakland, CA.

Holmes, William T. and Lawrence Burkett, 2006, “Seismic Vulnerability of 

Hospitals Based on Historical Performance in California,” Proceedings, 

8th U. S. National Conference on Earthquake Engineering, April 18-22, 

2006, San Francisco, CA, Earthquake Engineering Research Institute, 

Oakland, CA.

Lew, H. S., E. V. Leyendecker, and R. D. Dikkers, 1971, Engineering Aspects 

of the 1971 San Fernando Earthquake, Building Science Series 40, U. S. Department of Commerce, National Bureau of Standards, Washington, DC.

Los Angeles County, Department of Health Services (LACDHS), 1994, 

Report to the California Hospital Building Safety Board’s Special Forum on 

Damage to Health Facilities in the January 17, 1994 Northridge Earthquake,

Minutes of the California State Hospital Building Safety Board, April 

12, 1994, Office of Statewide Health Planning and Development, Sacramento, CA.

National Oceanic and Atmospheric Administration (NOAA), Leonard 

Murphy, Scientific Coordinator, 1973, San Fernando, California Earthquake 

of February 9, Volume 1, Part A, U.S. Department of Commerce, NOAA, 

Washington, DC.
2-86 MAKING HOSPITALS SAFE FROM EARTHQUAKES

Precast/Prestressed Concrete Institute (PCI), 1989, Architectural Precast 

Concrete, 2nd. Edition, PCI, Chicago, IL.

URS Consultants (URS), 1996, Northridge Earthquake Study of Seismic Design 

Factors for Hospital Non-Structural Components, Office of Statewide Health 

Planning and Development, Sacramento, CA.

Wang, M.L., 1987, “Cladding Performance on a Full-Scale Test Frame,” 

Earthquake Spectra, EERI, Vol. 3, No. 1, pp. 119-173, February 1987.

Wilson, Douglas, Kent Russell, Stephen Stanek, and David Swanson, 

2005, “Strong Medicine” pp 26-29, Modern Steel Construction, Volume 45, 

Number 2, American Institute of Steel Construction, Chicago, IL.

Whole Building Design Guide, Seismic Design of the Building Envelope, National Institute of Building Sciences, Washington, DC, 2006.
MAKING HOSPITALS SAFE FROM FLOODING 3-1

MAKING HOSPITALS SAFE FROM FLO0DING 3

3.1 GENERAL DESIGN CONSIDERATIONS

T his chapter introduces the physical nature and mechanics of floods 

and explains how flood probabilities are determined and how 

flood hazard areas are identified. It describes the types of flood 

damage that can result when hospitals are located in flood hazard areas 

or are affected by flooding. A series of requirements and best practices 

are introduced that facility owners, planners, and designers should consider for reducing the risks from flooding to new hospitals and to existing 

facilities located in areas prone to flooding.

This chapter demonstrates why avoidance of flood hazard areas is the 

most effective way to minimize the life-safety risk to patients, staff, and the 

citizens who rely on these facilities, as well as to minimize the potential for 

damage to buildings and other elements of hospitals. When an existing facility is ex­posed to flooding, or if a new facility is proposed to be located 

in a flood hazard area, steps need to be taken to minimize the risks. A 

well-planned, designed, constructed, and maintained hospital should be 

able to withstand damage and remain functional after a flooding event, 

even one of low probability. 

3.1.1 The Nature of Flooding

Flooding is the most common natural hazard in the United States, affecting more than 20,000 local jurisdictions and representing more than 

70 percent of Presidential disaster declarations. Several evaluations have 

estimated that 7 to 10 percent of the Nation’s land area is subject to 

flooding. Some communities have very little flood risk; others lie entirely 

within the floodplain.
3-2 MAKING HOSPITALS SAFE FROM FLOODING

Flooding is a natural process that may occur in a variety of forms: longduration flooding along rivers that drain large watersheds; flash floods 

that send a devastating wall of water down a mountain canyon; and coastal 

flooding that accompanies high tides and onshore winds, hurricanes, 

and nor’easters. When this natural process does not affect human activity, 

flooding is not a problem. In fact, many species of plants and animals 

that live adjacent to bodies of water are adapted to a regimen of periodic 

flooding. 

Flooding is only considered a problem when human development is located in areas prone to flooding. Such development exposes people to 

potentially life-threatening situations and makes property vulnerable to 

serious damage or destruction. It also can disrupt the natural surface flow, 

redirecting water onto lands not normally subject to flooding. 

Flooding along waterways normally occurs as a result of excessive rainfall or snowmelt that exceeds the capacity of channels. Flooding along 

shorelines is usually a result of coastal storms that generate storm surges 

or waves above normal tidal fluctuations. Factors that can affect the frequency and severity of flooding and the resulting damage include:

m Channel obstructions caused by fallen trees, accumulated debris, and 

ice jams

m Channel obstructions caused by road and rail crossings where the 

bridge or culvert openings are insufficient to convey floodwaters

m Erosion of shorelines and stream banks, often with episodic collapse 

of large areas of land

m Deposition of sediment that settles out of floodwaters or is carried 

inland by wave action

m Increased upland development of impervious surfaces and manmade 

drainage improvements that increase runoff volumes

m Land subsidence, which increases flood depths

m Failure of dams (resulting from seismic activity, lack of maintenance, 

flows that exceed the design, or destructive acts), which may suddenly 

and unexpectedly release large volumes of water

m Failure of levees (associated with flows that exceed the design, 

weakening by seismic activity, lack of maintenance, or destructive acts), 

which may result in sudden flooding of areas behind levees
MAKING HOSPITALS SAFE FROM FLOODING 3-3

m Failure of seawalls, revetments, bulkheads, or similar coastal structures, 

which can lead to rapid erosion and increased flooding and wave 

damage during storms

Each type of flooding has characteristics that represent important aspects 

of the hazard. These characteristics should be considered in the selection 

of hospital sites, the design of new facilities, and the expansion or rehabilitation of existing flood-prone facilities.

Riverine flooding results from the accumulation of runoff from rainfall or 

snowmelt, such that the volume of water exceeds the capacity of waterway 

channels and spreads out over the adjacent land. Riverine flooding flows 

downstream under the force of gravity. Its depth, duration, and velocity 

are functions of many factors, including watershed size and slope, degree 

of upstream development, soil types and nature of vegetation, topography, 

and characteristics of storms (or depth of snowpack and rate of melting). 

Figure 3-1 illustrates a cross-section of a generic riverine floodplain.

Coastal flooding is experienced along the Atlantic, Gulf, and Pacific 

coasts, and the Great Lakes. Coastal flooding is influenced by storm 

surges associated with tropical cyclonic weather systems (hurricanes, tropical storms, tropical depressions, typhoons), extratropical systems 

(nor’easters and other large low-pressure systems), seiches and tsunamis 

(surges induced by seismic activity). Coastal flooding is characterized by 

wind-driven waves which also may affect areas along the Great Lakes 

shorelines; winds blowing across the broad expanses of water generate 

waves that can rival those experienced along ocean shorelines. Some 

Great Lakes shorelines experience coastal erosion, in part because the 

erosion is associated with fluctuations in water levels. Figure 3-2 is a schematic of a generic coastal floodplain.

Figure 3-1:

The riverine floodplain

* Floodway is defined in Section 3.1.5.2 

*
3-4 MAKING HOSPITALS SAFE FROM FLOODING

3.1.2 Probability of Occurrence or

Frequency

The probability of occurrence, or frequency, is a statement of the likelihood that an event of a certain magnitude will occur in a given period 

of time. For many decades, floodplain management has been based on 

the flood that has a 1 percent chance of occurring in any given year, 

commonly called the “100-year flood.” For certain critical actions and 

decisions, such as planning or constructing hospitals and emergency operations centers, the basis of risk decisions should be the flood that has a 

0.2 percent probability of occurring in any given year, commonly called 

the “500-year flood.” In most locations, the benefits of added protection 

to the 500-year level are greater than the added costs.

The term “100-year flood” is often misunderstood because it conveys the 

impression that a flood of that magnitude will occur only once every 100 

years. Actually, the 1-percent-annual-chance flood has one chance in 100 

of occurring in any given year. The fact that a 1-percent-annual-chance 

flood is experienced at a specific location does not alter the probability 

that a flood of the same or greater magnitude could occur at the same 

location in the next year, or even multiple times in a single year. As the 

length of time considered increases, so does the probability that a flood 

of a specific magnitude or greater will occur. For example, Figure 3-3 illustrates the probability that a 100-year flood will occur is 26 percent in a 

* Defined in Section 3.1.5.2

**Defined in Section 3.1.5.3

* ** *

Figure 3-2: The floodplain along an open coast
MAKING HOSPITALS SAFE FROM FLOODING 3-5

30-year period. And during a 70-year period (the potential useful life of 

many buildings), the probability increases to 50 percent. Similarly, a 500-

year flood has a 0.2-percent probability of being equaled or exceeded in 

any given year, a 6 percent probability of occurrence in a 30-year period, 

and an 18 percent probability of occurrence during a 70-year period. 

The assigned frequency of a flood (e.g., 100-year) is independent of the 

number of years between actual occurrences. Hurricane Camille hit the 

Mississippi coast in 1969 with storm surge flooding that far exceeded 

previous events, and Hurricane Katrina affected much the same area. 

Although just 36 years apart, both storms produced flood levels that 

were significantly higher than the predicted 100-year flood. Similarly, the 

Mississippi River flooded large areas in Missouri in 1993 with flooding 

that exceeded the predicted 100-year flood levels. Just two years later, 

many of the same areas were flooded again. 

Regardless of the flood selected for design purposes (the “design flood”), 

the designer must determine specific characteristics associated with that 

flood. Determining a flood with a specific probability of occurrence is 

done in a multi-step process that typically involves using computer models 

that are in the public domain. If a sufficiently long record of flood information exists, the design flood may be determined by applying statistical 

tools to the data. Alternatively, water resource engineers sometimes apply 

Figure 3-3:

Probability and 

magnitude 

SOURCE: U.S. Geological

Survey, Guidelines for 

Determining Flood Flow 

Frequency, Bulletin 17B 

(Appendix D).

Figure 3-3:

Probability and 

magnitude 

SOURCE: U.S. Geological

Survey, Guidelines for 

Determining Flood Flow 

Frequency, Bulletin 17B 

(Appendix D).
3-6 MAKING HOSPITALS SAFE FROM FLOODING

computer models to simulate different rainfall events over watersheds, to 

predict how much water will run off and accumulate in channels. Other 

computer models are used to characterize the flow of water down the watershed and predict how high the floodwaters will rise. 

Flood frequency analyses are performed using historical records, and the 

results are influenced by the length of the record. Such analyses do not 

account for recent changes to the land (upland development or subsidence) or future changes (additional development, greater subsidence, or 

climatic variations).

For coastal areas, both historical storms and simulated storm surge 

models can be used to predict the probability that floodwaters will rise 

to a certain level and be accompanied by waves of certain heights. Many 

coastal storms will produce storm surge flooding that, depending on local 

topography, may extend inland significantly farther than anticipated for 

a 1-percent-annual-chance flood. Statistically, such extreme storm surges 

occur less frequently than the 1-percent or 0.2-percent-annual-chance 

floods, but their consequences can be catastrophic.

The Saffir-Simpson Hurricane Scale categorizes hurricanes based on sustained wind speeds (see Chapter 4). Storm surge, though suggested by the 

Scale, is not always well correlated with the storm category because other 

factors influence surge elevations, notably forward speed of the storm, 

tide cycle, offshore bathymetry, and land topography.

Planners and designers should research the relationship between flood 

levels for different frequency events, including extreme events, especially 

in hurricane-prone communities. The difference in flood levels may be 

extreme in some situations, depending on local conditions and the source 

of flooding. In other areas flood levels of lower probability floods might 

not be much higher than a 1-percent-annual-chance flood.

The National Flood Insurance Program (NFIP) is a Federal program that 

encourages communities to regulate flood hazard areas and, in return, offers property owners insurance protection against losses from flooding 

(see Sections 3.1.6.1 and 3.1.6.2). The NFIP uses the 1-per­cent-annualchance flood as the basis for flood hazard maps, for setting insurance 

rates, and for application of regulations in order to minimize future flood 

damage. The 1-percent-annual-chance flood is also used as the standard 

for examination of older buildings to determine the measures to apply in 

order to reduce future damage.

Satisfying the minimum requirements of the NFIP does not provide adequate protection for hospitals that need to be functional even after 

low-probability events. Nearly every year, a very low probability flood 
MAKING HOSPITALS SAFE FROM FLOODING 3-7

occurs somewhere in the United States, often with catastrophic consequences. Therefore, for planning and design of hospitals, use of a lower 

probability flood (at least the 500-year) is strongly recommended (and 

may be required by some States and local jurisdictions). As noted in Section 3.1.6.3, the 500-year level of protection is required if Federal funds 

are involved in constructing facilities that are vital for emergency response 

and rapid recovery, including hospitals, emergency operations centers, 

emergency shelters, and other buildings that support vital services. This 

reinforces the importance of protecting both the functionality and financial investment in a hospital with stricter standards than those applied to 

other buildings.

3.1.3 Flood Characteristics and Loads

A number of factors associated with riverine and coastal flooding are important in the selection of sites for hospitals, in site design, and in the 

determination of flood loads which must be considered as part of architectural and engineering design. 

Depth:  The most apparent characteristic of any flood is the depth of the 

water. Depending on many factors, such as the shape of a river valley or 

the presence of obstructing bridges, riverine flooding may rise just a few 

feet or tens of feet above normal levels. The depth of coastal flooding is 

influenced by such factors as the tidal cycle, the duration of the storm, 

the elevation of the land, offshore bathymetry, and the presence of 

waves. Depth is a critical factor in building design because the hydrostatic forces on a vertical surface (such as a foundation wall) are directly 

related to depth, and because costs associated with protecting buildings 

from flooding increase with depth. Under certain conditions, hurricanes 

can produce storm surge flooding that is 20 to 30 feet above mean sea 

level or, in extreme cases along the Gulf Coast, as much as 35 feet above 

mean sea level.

Duration:  Duration is the measure of how long the water remains above 

normal levels. The duration of riverine flooding is primarily a function 

of watershed size and the longitudinal slope of the valley (which influences how fast water drains away). Small watersheds are more likely to 

be “flashy,” a characteristic that refers to the rapidity with which floodwaters rise and fall. Areas adjacent to large rivers may be flooded for weeks 

or months. Most coastal flooding is influenced by the normal tidal cycle, 

as well as how fast coastal storms move through the region. Areas subject to coastal flooding can experience long periods of flooding where 

drainage is poor or slow as a result of topography or the presence of flood 

control structures. For example, water may be trapped in depressions in 

the land or behind a floodwall or levee with inadequate drainage. More 
3-8 MAKING HOSPITALS SAFE FROM FLOODING

commonly, coastal flooding is of shorter duration, on the order of 12 to 

24 hours, especially if storms move rapidly. Flooding of large lakes, including those behind dams, can be of very long duration because the 

large volume of water takes longer to drain. For building design, duration 

is important because it affects access, building usability, and saturation 

and stability of soils and building materials. Information about flood duration is sometimes available as part of a flood study, or could be developed 

by a qualified engineer.

Local drainage problems create ponding and local flooding that is often 

not directly associated with a body of water such as a creek or river. Although such flooding is relatively shallow and not characterized by high 

velocity flows, considerable damage may result. Areas with poor drainage 

frequently experience repetitive damage. Some local drainage problems 

are exacerbated by old or undersized drainage system infrastructure. 

Flooding caused by drainage problems typically occurs as sheetflow or 

along waterways with small drainage areas. This type of flooding is often 

not mapped or regulated.

Velocity:  The velocity of floodwaters ranges from extremely high (associated with flash floods or storm surge) to very low or nearly stagnant 

(in backwater areas and expansive floodplains). Velocity is important 

in site planning because of the potential for erosion. In structural design, velocity is a factor in determining the hydrodynamic loads and 

impact loads. Even shallow, high-velocity water can threaten the lives of 

pedestrians and motorists. Accurate estimates of velocities are difficult 

to make, although information about mean velocities may be found in 

some floodplain studies.

Wave action:  Waves contribute to erosion and scour, and also contribute 

significantly to design loads on buildings. The magnitude of wave forces 

can be 10 to more than 100 times greater than wind and other design 

loads, and thus may control many design parameters. Waves must be accounted for in site planning along coastal shorelines, in flood hazard 

areas that are inland of open coasts, and other areas where waves occur, 

including areas with sufficient fetch that winds can generate waves (such 

as lakes and expansive riverine floodplains). Waves on top of storm 

surges may be as much as 50 percent higher than the stillwater depth of 

the surge. 

Impacts from debris and ice:  Floating debris and ice contribute to the 

loads that must be accounted for in structural design. The methods and 

models used to predict and delineate flood hazard areas do not specifically incorporate the effects of debris. Thus, there are few sources to 

determine the potential effects of debris impact loads, other than past 

observations and judgment. 
MAKING HOSPITALS SAFE FROM FLOODING 3-9

Erosion and scour:  In coastal areas, erosion refers to the lowering of the 

ground surface as a result of a flood event, or the gradual recession of a 

shoreline as a result of long-term coastal processes. Along riverine waterways, erosion refers to undermining of channel banks, lateral movement 

of the channel, or cutting of new channels. Scour refers to a localized lowering of the ground surface due to the interaction of currents and/or waves 

with structural elements, such as pilings. Soil characteristics influence an 

area’s susceptibility to scour. Erosion and scour may affect the stability of 

foundations and earthen-filled areas, and may cause extensive site damage. 

3.1.3.1 Hydrostatic Loads

Hydrostatic loads occur when water comes into contact with a building or 

building component, both above and below the ground level. They act as 

lateral pressure or vertical pressure (buoyancy). Hydrostatic loads on inclined or irregular surfaces may be resolved into lateral and vertical loads 

based on the surface geometry and the distribution of hydrostatic pressure. 

Lateral hydrostatic loads are a direct function of water depth (see Figure 

3-4). These loads can cause severe deflection or displacement of buildings or building components if there is a substantial difference in water 

levels on opposite sides of the component (or inside and outside of the 

building). Hydrostatic loads are balanced on foundation elements of 

elevated buildings, such as piers and columns, because the element is surrounded by water. If not oriented parallel to the flow of water, shearwalls 

may experience hydrostatic loads due to a difference of water depth on either side of the wall. To reduce excessive pressure from standing water, 

floodplain management requirements in A Zones call for openings in 

walls that enclose areas below the flood elevation (see description of continuous perimeter wall foundation in Section 3.4.4).

Figure 3-4: Hydrostatic loads on buildings 
3-10 MAKING HOSPITALS SAFE FROM FLOODING

Buoyancy force resulting from the displacement of water is also of concern, especially for dry floodproofed buildings and aboveground and 

underground tanks. Buoyancy force is resisted by the dead load of the 

building or the weight of the tank. When determining buoyancy force, 

the weight of occupants or other live loads (such as the contents of a 

tank) should not be considered. If the building or tank does not weigh 

enough “empty,” then additional stabilizing measures need to be taken to 

avoid flotation. This becomes a significant consideration for designs intended to dry floodproof a building. Buoyancy force is slightly larger in 

saltwater, because saltwater weighs slightly more than fresh water.

3.1.3.2 Hydrodynamic Loads

Water flowing around a building or a structural element that extends 

below the flood level imposes hydrodynamic loads. The loads, which 

are a function of flow velocity and structure geometry, include frontal 

impact on the upstream face, drag along the sides, and suction on the 

downstream side (see Figure 3-5). Ways to determine or estimate flood velocities are described in Section 3.1.4.3 and Section 3.1.4.4.

The most common computation methods for hydrodynamic loads are 

outlined in the design standard ASCE 7, Minimum Design Loads for Buildings and Other Structures, produced by the American Society of Civil 

Engineers’ Structural Engineers Institute (ASCE/SEI, 2005). Those 

methods assume that the flood velocity is constant (i.e., steady state flow) 

and that the dynamic load imposed by floodwaters moving at less than 10 

feet per second can be converted to an equivalent hydro­static load. This 

conversion is accomplished by adding an equivalent surcharge depth to 

Figure 3-5: Hydrodynamic loads on a building or building element
MAKING HOSPITALS SAFE FROM FLOODING 3-11

the depth of water on the upstream side. The equivalent surcharge depth 

is a function of the velocity. Loads imposed by floodwaters with velocities 

greater than 10 feet per second cannot be converted to equivalent hydrostatic loads. Instead, they must be determined according to the principles 

of fluid mechanics or hydraulic models. 

Hydrodynamic loads become important when flow reaches moderate velocities of 5 feet per second. The components of hydrodynamic loads 

are laterally imposed, caused by the impact of the mass of water against 

the building, and drag forces along the wetted surfaces. Drag coefficients for common building elements, such as columns and piers, can be 

found in a number of sources. ASCE 7 recommends values for a variety of 

conditions. 

Wave loads are another important component of hydrodynamic loads. 

As described in ASCE 7, “design and construction of buildings and 

other structures subject to wave loads shall account for the following 

loads: waves breaking on any portion of the building or structure; uplift 

forces caused by shoaling waves beneath a building or structure, or portion thereof; wave runup striking any portion of the building or structure; 

wave-induced drag and inertia forces; and wave-induced scour at the base 

of a building or structure, or its foundation.” 

Wave forces striking buildings and building elements can range from 10 

to more than 100 times wind or other forces. Forces of this magnitude can 

be substantial, even when acting over the relatively small surface area of 

the supporting structure of elevated buildings. Post-storm damage inspections show that breaking wave loads overwhelm virtually all wood-frame 

and unreinforced masonry walls below the wave crest elevation. Only 

engineered or massive structural elements are capable of consistently 

withstanding breaking wave loads. 

The magnitude of wave forces is the rationale behind the floodplain management requirement for the bottom of the lowest horizontal structural 

member to be at or above the design flood elevation in environments 

where high-velocity wave action from storms or seismic sources is possible (called V Zones, also referred to as Coastal High Hazard Areas). In 

V Zones, breaking wave heights or wave runup depths are predicted to be 

3 feet or higher. Because breaking waves as small as 1.5 feet in height can 

impose considerable loads, there is a growing awareness of the value of accounting for waves in areas immediately landward of V Zones, which are 

referred to as “Coastal A Zones” (see Section 3.1.5.3). 

Of the variety of wave forces described in ASCE 7—breaking waves, uplift, 

wave runup, wave-induced drag and inertia, and scour—breaking waves 

constitute the greatest hazard. Designers should therefore use breaking 
3-12 MAKING HOSPITALS SAFE FROM FLOODING

wave forces as the basis of the design load. Computation of breaking wave 

loads depends on the determination of wave height. For further information on how wave heights can be estimated, see Section 3.1.4.1. Designers 

should refer to ASCE 7 for detailed discussion and computation procedures for determining breaking wave loads.

Breaking wave loads on vertical walls or supporting structural members 

reach a maximum when the direction of wave approach is perpendicular 

to the wall. It is common to assume that the direction of approach will be 

perpendicular to the shoreline, in which case the orientation of the wall 

to the shoreline will influence the direction of approach used in load calculations. ASCE 7 provides a method for reducing breaking wave loads 

on vertical walls for waves that approach a building from a direction other 

than straight on. 

Breaking wave forces are much higher than typical wind pressures, even 

wind pressures that occur during a hurricane or typhoon. However, the 

duration of individual loads is brief, with peak pressures probably occurring within 0.1 to 0.3 seconds after the wave breaks. Structures are 

to be designed for repetitive impact loads that occur over the duration 

of a storm. Some storms may last just a few hours, as hurricanes move 

through the area, or several days, as during some winter coastal storms 

(nor’easters) that affect the Mid-Atlantic and northeastern States. 

3.1.3.3 Debris Impact Loads

Debris impact loads on a building or building element are caused by objects carried by moving water. Objects commonly carried by floodwaters 

include trees, dislodged tanks, and remnants of manmade structures such 

as docks and buildings. Extreme impact loads result from less common 

sources, such as shipping containers, boats, and barges. The magnitude 

of these loads is very difficult to predict, yet some reasonable allowance 

should be made during the design process. 

Impact loads are influenced by the location of the building in the potential debris stream. The potential for debris impacts is significant if a 

building is located immediately adjacent to, or downstream from, other 

buildings, among closely spaced buildings, or downstream from large floatable objects. While these conditions may be observable in coastal areas, it is 

more difficult to estimate the potential for debris in riverine flood hazard 

areas. Any riverine waterway, whether a large river or smaller urban stream, 

can carry large quantities of debris, especially uprooted trees and trash. 

The basic equation for estimating the magnitude of impact loads depends 

on several variables that must be selected by the designer. These variables 
MAKING HOSPITALS SAFE FROM FLOODING 3-13

include several coefficients, building or building element stiffness, debris 

weight, debris velocity, and duration of impact. The latter three variables, 

described in more detail in ASCE 7, are briefly described below.

Debris weight:  Debris weight is one of the more difficult variables to 

estimate. Unless otherwise indicated by field conditions, ASCE 7 recommends using an average object weight of 1,000 pounds. This weight 

corresponds to a 30-foot long log that is 1 foot in diameter, which is relatively small compared to large trees that may be uprooted during a flood. 

In coastal areas, expected debris weights depend on the nature of the 

debris. In the Pacific Northwest, large trees and logs are common, with 

weights in excess of 4,000 pounds. In areas where piers and pilings are 

likely to become debris, 1,000 pounds is reasonable. In areas where most 

debris is likely to result from building damage (failed decks, steps, failed 

walls, propane tanks), the average debris weight may be less than 500 

pounds.

Debris velocity:  The velocity of the debris when it strikes a building depends on the nature of the debris and the velocity of floodwaters. For 

the impact load computation, the velocity of the water-borne object is assumed to be the same as the flood velocity. Although this assumption 

is reasonable for smaller objects, it is considered conservative for large 

objects.

Debris impact duration:  Duration of impact is the elapsed time during 

which the impact load acts on the building or building element. The duration of impact is influenced primarily by the natural frequency1 of the 

building or element, which is a function of the building’s stiffness. Stiffness is determined by the properties of the material, the number of 

supporting members (columns or piles), the height of the building above 

the ground, and the height at which the element is struck. Despite all the 

variables that may influence duration of impact, early assumptions suggested 1-second duration. A review of results from several laboratory tests 

that measured impacts yielded much briefer periods, and ASCE 7 currently recommends the duration of 0.03 second. 

3.1.3.4 Erosion and Local Scour 

Strictly speaking, erosion and scour are not loads; however, they must be 

considered during site evaluation and load calculations because they increase the local flood depth, which in turn influences load calculations. 

1 Natural frequency is the frequency at which an object will vibrate freely when set in motion.
3-14 MAKING HOSPITALS SAFE FROM FLOODING

Erosion may occur in riverine and coastal flood hazard areas. In coastal 

areas, storms can erode or completely remove sand dunes, which act as 

barriers to flooding and damaging waves. Erosion may also lower the 

ground surface or cause a short-term or long-term recession of the shoreline. In areas subject to gradual erosion of the ground surface, additional 

foundation embedment depth can mitigate the effects. However, where 

waterways are prone to changing channels and where shoreline erosion is 

significant, engineered solutions are unlikely to be effective. Avoidance of 

sites in areas subject to active erosion usually is the safest and most cost-effective course of action.

Local scour results from turbulence at the ground level around foundation elements. Scour occurs in both riverine and coastal flood hazard 

areas, especially in areas with erodible soils. Determining potential scour 

is critical in the design of foundations, to ensure that the bearing capacity 

or anchoring resistance of the soil around posts, piles, piers, columns, 

footings, or walls is not compromised. Scour determinations require 

knowledge of the flood depth, velocity, waves, soil characteristics, and 

foundation type. 

At some locations, soil at or below the ground surface can be resistant 

to local scour, and calculated scour depths based on unconsolidated 

surface soils below will be excessive. In instances where the designer believes the underlying soil at a site will be scour-resistant, the assistance 

of a geotechnical engineer or geologist should be sought to verify that 

assumption. 

3.1.4 Design Parameters

Flood hazards and characteristics of flooding must be identified to 

evaluate the impact of site development and to determine the design 

parameters necessary to calculate flood loads, to design floodproofing 

measures, and to identify and prioritize retrofit measures for existing hospitals. Table 3-3 in Section 3.6 outlines a series of questions to facilitate 

this objective.

3.1.4.1 Flood Depth 

Flood depth is the most important factor required to compute flood loads 

because almost every other flood load calculation depends directly or indirectly on this factor. The first step in determining flood depth at a specific 

site is to identify the flood that is specified by governing authorities’ regulations. The most common flood used for design is the “base flood” (see 

Section 3.1.4.2). The second step is to determine the expected elevation 
MAKING HOSPITALS SAFE FROM FLOODING 3-15

of the ground at the site. This expected ground elevation must account 

for any erosion, scour, subsidence, or other ground eroding condition that 

occurs over time. Flood depth is computed by subtracting the ground elevation from the flood elevation. Since these data usually are obtained from 

different sources, it is important to determine whether they are based on 

the same datum. If not, standard corrections must be applied.

In riverine areas, the flood elevations shown on flood hazard maps rarely 

account for waves. Fast moving water usually has an undulating surface 

that is referred to as “standing waves,” which do not break as do waves 

in coastal areas. Standing waves may rise higher than the flood elevation 

specified on maps used for regulatory purposes, thus increasing flood 

depth. This increase should be taken into account when determining 

flood loads by increasing the flood depth used for design purposes. 

In coastal areas, the flood elevations shown on FEMA flood maps account 

for stillwater flooding plus local wave effects, including wave heights, wave 

runup, or wave overtopping over vertical walls. As shown in Figure 3-6, 

subtracting the ground elevation from the FEMA flood map elevation will 

provide a flood depth comprised of the stillwater component and the predicted wave contribution. 

For design purposes, it is important to know that wave forces on buildings cause the most damage. FEMA has identified V Zones (velocity 

zones) on coastal flood maps, where wave heights or wave runup depths 

are predicted to be 3 feet or greater (see Section 3.1.5.2). However, postdisaster assessments and laboratory studies have shown that waves as 

small as 1.5 feet in height can also cause significant damage. While FEMA 

flood maps do not specifically designate flood hazard areas subject to 1.5- 

to 3-foot waves, referred to as “Coastal A Zones” (see Section 3.1.5.3). It is 

important to consider these smaller waves and their potential damaging 

effects on buildings. 

Figure 3-6 illustrates the two main principles that are used to estimate 

wave heights at a particular site. Equations for wave height are based 

on the concept that waves are depth-limited, that is, waves propagating 

into shallow water will break when the wave height reaches a certain proportion of the underlying stillwater depth. For modeling wave heights 

during the base flood, FEMA utilizes the proportion determined by the 

National Academy of Sciences (1977): the total wave height will reach a 

maximum of 78 percent of stillwater depth before breaking. At any given 

site, this proportion may be reduced because of obstructions between 

open water and the site, such as dense stands of vegetation or unelevated 

buildings. In V Zones, 3-foot waves can be supported in only 4 feet of 

stillwater and the smaller “Coastal A Zone” waves of 1.5 feet can be supported in only 2 feet of stillwater. The second principle is that the wave 
3-16 MAKING HOSPITALS SAFE FROM FLOODING

height extends from the trough, which is below the stillwater elevation to 

the crest ,which is above the stillwater elevation, and is equal to 55 percent of this stillwater depth. 

Using these two principles, some general rules of thumb are available to 

estimate wave heights. If the only information available is the base flood 

depth (i.e., the depth calculated using the FEMA flood map elevation 

minus the ground elevation), assume that flood depths between 3 and 6 

feet can have an added wave-height component between 1.5 and 3 feet, 

while flood depths of 6 feet or more will likely have wave heights in excess 

of 3 feet. If only the stillwater flood depth is known (from an alternative 

surge map or other data source), the maximum flood depth (including 

wave height) will be approximately 1.5 times the stillwater depth. 

In any area with erodible soils, whether coastal or inland site, designers 

need to consider the effects of erosion where floodwaters lower the 

ground surface or cause local scour around 

foundation elements. The flood depth determined using flood elevation and ground 

elevation should be increased to account for 

changes in conditions during a flood event. 

Not only does lowering the ground surface effectively result in deeper water against the 

foundation, it may also remove supporting soil 

from the foundation, which must be accounted 

for in the foundation design. 

Waves and storm-induced erosion are most 

common in coastal areas. However, wide 

rivers and lakes may experience winddriven waves and erodible soils are found 

throughout the United States. For more 

information about waves and erosion, 

refer to FEMA 55, Coastal Construction 

Manual. 

Waves and storm-induced erosion are most 

common in coastal areas. However, wide 

rivers and lakes may experience winddriven waves and erodible soils are found 

throughout the United States. For more 

information about waves and erosion, 

refer to FEMA 55, Coastal Construction 

Manual. 

Figure 3-6:

Definition sketch 

– coastal wave height 

and stillwater depth
MAKING HOSPITALS SAFE FROM FLOODING 3-17

3.1.4.2 Design Flood Elevation 

The design flood elevation (DFE) establishes 

the minimum level of flood protection that 

must be provided. The DFE, as used in the 

model building codes, is defined as either the 

base flood elevation (BFE) determined by the 

NFIP and shown on FIRMs, or the elevation of 

a design flood designated by the community, 

whichever is higher. The DFE will always be 

at least as high as the BFE. Communities may 

use a design flood that is higher than the base 

flood for a number of reasons. For example, a design flood may be used 

to account for future upland development, to recognize a historic flood, 

or to incorporate a factor of safety, known as freeboard. 

Facility owners, planners, and designers should check with the appropriate regulatory authority to determine the minimum flood elevation to 

be used in site planning and building design. Although the NFIP minimum is the BFE, State or local regulations commonly cite the 

0.2-percent-annual-chance flood (500-year flood) as the de­sign requirement for hospitals, or the regulations may call for added freeboard above 

the minimum flood elevation. Even if there is no specific requirement to 

use the 0.2-percent-annual-chance flood for siting and design purposes, it 

is strongly recommended that decisionmakers take into consideration the 

flood conditions associated with this lower probability event.

If significant flood events have occurred 

since the effective date of the FIRM, these 

events may change the statistical analyses, 

which might prompt an update of the flood 

maps and produce revised elevations for 

the 1-percent-annual-chance flood. Hospital owners, planners, and designers should 

contact community officials to determine 

whether there have been any significant 

flood events or other changes that may affect 

flood hazards since the effective date of the 

FIRM. The best available information should 

be used at all times. 

3.1.4.3 Flood Velocity—Riverine

There are few sources of information that are readily available for estimating flood velocities at specific locations along riverine bodies of water. 

“Freeboard” is a factor of safety usually 

expressed in feet above a flood level. 

Freeboard compensates for the many 

unknown factors that could contribute 

to flood heights, such as wave action, 

constricting bridge openings, and the 

hydrological effect of urbanization of the 

watershed. A freeboard of 1 to 3 feet is 

often applied to hospitals.

“Freeboard” is a factor of safety usually 

expressed in feet above a flood level. 

Freeboard compensates for the many 

unknown factors that could contribute 

to flood heights, such as wave action, 

constricting bridge openings, and the 

hydrological effect of urbanization of the 

watershed. A freeboard of 1 to 3 feet is 

often applied to hospitals.

After Hurricane Katrina in 2005, FEMA 

expedited development of Flood Recovery 

Maps and Advisory Base Flood Elevations 

for the Mississippi coast; the new maps 

were delivered less than 3 months after the 

storm. 

In 2004, after widespread wildfires in 

California changed runoff characteristics, 

FEMA developed recovery maps to show 

increased riverine flood hazards.

After Hurricane Katrina in 2005, FEMA 

expedited development of Flood Recovery 

Maps and Advisory Base Flood Elevations 

for the Mississippi coast; the new maps 

were delivered less than 3 months after the 

storm. 

In 2004, after widespread wildfires in 

California changed runoff characteristics, 

FEMA developed recovery maps to show 

increased riverine flood hazards.
3-18 MAKING HOSPITALS SAFE FROM FLOODING

If a riverine source has been studied using detailed hydraulic methods, 

some information may be available in summary form in published studies. 

Studies prepared for the NFIP contain tables of data for waterways for 

which floodways were delineated (see Section 3.1.5.2). For specified 

cross-sections along the waterway, the Floodway Data Table includes a 

mean velocity expressed in feet per second. This value is the average of 

all velocities across the floodway. Generally, velocities in the flood fringe 

(landward of the floodway) will be lower than in the floodway. 

For waterways without detailed studies, methods that are commonly used 

in civil engineering for estimating open channel flow velocities can be 

applied. 

3.1.4.4 Flood Velocity—Coastal

Estimating flood velocities in coastal flood hazard areas involves considerable uncertainty and there is little reliable historical information or 

measurements from actual coastal flood events. In this context, velocity 

does not refer to the motion associated with breaking waves, but the 

speed of the mass movement of floodwater over an area.

The direction and velocity of floodwaters can vary significantly 

throughout a coastal flood event. Floodwaters can approach a site from 

one direction as a storm approaches, then shift to another direction (or 

through several directions) as the storm moves through the area. Floodwaters can inundate some low-lying coastal sites from both the front (e.g., 

ocean) and the back (e.g., bay, sound, or river). In a similar manner, at 

any given site, flow velocities can vary from close to zero to very high. For 

these reasons, when determining flood loads for building design, velocities should be estimated conservatively, and it should be assumed that 

floodwaters can approach from the most critical direction. 

Despite the uncertainties, there are methods to approximate coastal flood 

velocities. One common method is based on the stillwater depth (flood 

depth without waves). Designers should consider the topography, the distance from the source of flooding, and the 

proximity to other buildings and obstructions 

before selecting the flood velocity for design. 

Those factors can direct and confine floodwaters, with a resulting acceleration of velocities. 

This increase in velocities is described as the 

“expected upper bound.” The “expected lower 

bound” velocities are experienced in areas 

where those factors are not expected to influence the direction and velocity of floodwaters. 

Upper bound velocities caused by 

Hurricane Katrina along the Mississippi 

coast, where storm surge depths neared 

25 feet deep (with waves, total flood 

depths approached 35 feet), have been 

estimated at nearly 30 feet per second (20 

miles per hour).

Upper bound velocities caused by 

Hurricane Katrina along the Mississippi 

coast, where storm surge depths neared 

25 feet deep (with waves, total flood 

depths approached 35 feet), have been 

estimated at nearly 30 feet per second (20 

miles per hour).
MAKING HOSPITALS SAFE FROM FLOODING 3-19

Figure 3-7 shows the general relationship between velocity and stillwater 

depth. For design purposes, actual flood velocities are assumed to lie between the upper and lower bounds. Conservative designs will use the 

upper bound velocities.

3.1.5 Flood Hazard Maps and Zones

Flood hazard maps identify areas of the landscape that are subject to 

flooding, usually flooding by the 1-percent-annual-chance flood. Maps 

prepared by the NFIP are the minimum basis of State and local floodplain 

regulatory programs. Some States and communities have prepared maps 

of a floodplain based on the assumption that the upper watershed area 

is fully developed according to existing zoning. Some communities base 

their regulations on a flood of record or a historically significant flood 

that exceeds the base flood shown on the NFIP maps.

The flood hazard maps used by the appropriate regulatory authority 

should be consulted during planning and site selection, site design, and 

architectural and engineering design (whether for the design of new 

buildings or rehabilitation of existing buildings). Regardless of the flood 

hazard data required for regulatory purposes, additional research should 

be conducted on past major floods and other factors that could lead to 

more severe flooding.

Figure 3-7:

Velocity as a function 

of stillwater flood 

depth

Figure 3-7:

Velocity as a function 

of stillwater flood 

depth
3-20 MAKING HOSPITALS SAFE FROM FLOODING

3.1.5.1 NFIP Flood Maps

The NFIP produces Flood Insurance Rate Maps (FIRMs) for more than 

20,000 communities nationwide. FIRMs are prepared for each local jurisdiction that has been determined to have some degree of flood risk. The 

current effective maps are typically avail­able for viewing in community 

planning or permit offices.2 It is important to use the most recent flood 

hazard map when deter­mining site-specific flood hazard characteristics. Although many FIRMs are more than 15 years old, often one or more panels 

or portions of a map panel have been revised and republished. Communities must adopt revised maps to continue participating in the NFIP. 

Some FIRMs do not show the 0.2-percent-annual-chance flood hazard 

area (500-year floodplain), and many FIRMs do not provide detailed information about predicted flood elevations 

along every body of water, especially smaller 

streams and tributaries. Determining the 500-

year flood is especially difficult when records of 

past flood events are limited. When existing 

data are insufficient, additional statistical 

methods and engineering analyses are necessary to determine the flood-prone areas and 

the appropriate characteristics of flooding required for site layout and building design. If a 

proposed hospital site or existing hospital is affected by flooding, a site-specific topographic 

survey is critical to delineate the land that is 

below the flood elevation used for planning 

purposes. If detailed flood elevation information is not available, a floodplain study may be 

required to identify the important flood characteristics and data required for sound design. 

However, having flood hazard areas delineated 

on a map conveys a degree of precision that may be misleading. Flood 

maps have a number of limitations that should be taken into consideration, especially during site selection and building design. Some of the 

well-known limitations are:

m Flood hazard areas are approximations based on probabilities; the 

flood elevations shown and the areas delineated should not be 

taken as absolutes, in part because they are based on numerical 

approximations of the real world. 

2 Flood maps may also be viewed at FEMA’s Map Service Center at http://msc.fema.gov. For a fee, copies may 

be ordered online or by calling (800) 358-9616. The Flood Insurance Study (FIS) and engineering analyses 

used to determine the flood hazard area may be ordered through the FEMA Web site.

It is important to note that the number of 

revised and updated FIRMs is increasing 

rapidly. During the last few years FEMA, 

in partnership with many States and 

communities, has been implementing 

an ini­tiative to modernize and update 

all maps that are determined to be out 

of date. The modernization process 

may involve an exam­ination of flood 

experience in the period since the original 

flood studies were prepared, use of more 

detailed topographic and base maps, recomputation of flood discharges and flood 

heights, and re-delineation of flood hazard 

area boundaries.

It is important to note that the number of 

revised and updated FIRMs is increasing 

rapidly. During the last few years FEMA, 

in partnership with many States and 

communities, has been implementing 

an ini­tiative to modernize and update 

all maps that are determined to be out 

of date. The modernization process 

may involve an exam­ination of flood 

experience in the period since the original 

flood studies were prepared, use of more 

detailed topographic and base maps, recomputation of flood discharges and flood 

heights, and re-delineation of flood hazard 

area boundaries.
MAKING HOSPITALS SAFE FROM FLOODING 3-21

m For the most part, floodplains along smaller streams and drainage 

areas (less than 1 square mile) are not shown.

m Especially for older maps, the topography used to delineate the flood 

boundary may have had contour intervals of 5, 10, or even 20 feet, 

which significantly affects the precision with which the boundary is 

determined. The actual elevation of the ground relative to the flood 

elevation is critical, as opposed to whether an area is shown as being in 

or out of the mapped flood hazard area. 

m Maps are based on the data available at the time they were prepared, 

and, therefore, do not account for subsequent upland development 

that increases rainfall-runoff, which may increase flooding. 

m The scale of the maps may impede precise determinations (many 

older maps are 1 inch = 2,000 feet).

m The land surface of the floodplain may have been altered by 

modifications after the maps were prepared, including fills, 

excavations, or levees.

m Local conditions are not reflected, especially conditions that change 

regularly, such as stream bank erosion and shoreline erosion.

m Areas exposed to very low probability flooding are not shown, such as 

flooding from extreme hurricane storm surges, extreme riverine 

flooding, dam failures, or overtopping or failure of levees.

3.1.5.2 NFIP Flood Zones

The flood hazard maps prepared by the NFIP show different flood zones 

to delineate different floodplain characteristics (see Figures 3-8, 3-9, and 

In communities along the Gulf and Atlantic coasts, facility owners, planners, and designers should 

check with emergency management offices for maps that estimate storm surge flooding from 

hurricanes. Local planning or engineering offices may have post-disaster advisory flood maps and 

documentation of past storm surge events. The FIRMs and regulatory design flood elevations (DFEs) 

do not reflect low probability/high magnitude flooding that may result from a hurricane making 

landfall at a specific location. 

Be aware that most storm surge maps report stillwater flood elevations only; local wave heights or 

wave runup are seldom included. If necessary, local wave effects should be estimated and added 

to the stillwater elevation when determining flood depths for design purposes (see Section 3.1.4.1). 

In communities along the Gulf and Atlantic coasts, facility owners, planners, and designers should 

check with emergency management offices for maps that estimate storm surge flooding from 

hurricanes. Local planning or engineering offices may have post-disaster advisory flood maps and 

documentation of past storm surge events. The FIRMs and regulatory design flood elevations (DFEs) 

do not reflect low probability/high magnitude flooding that may result from a hurricane making 

landfall at a specific location. 

Be aware that most storm surge maps report stillwater flood elevations only; local wave heights or 

wave runup are seldom included. If necessary, local wave effects should be estimated and added 

to the stillwater elevation when determining flood depths for design purposes (see Section 3.1.4.1). 
3-22 MAKING HOSPITALS SAFE FROM FLOODING

3-10). The flood zones shown on the NFIP maps, and some other designations, are described below.

A Zones:  Also called “unnumbered A Zones” or “approximate A Zones,” 

this designation is used for flood hazard areas where engineering studies 

have not been performed to develop detailed flood elevations. BFEs are 

not provided. Additional engineering analyses 

and site-specific assessments usually are required to determine the DFE.

AE Zones or A1-A30 Zones:  Also called “numbered A Zones,” these designations are used for 

flood hazard areas where engineering analyses 

have produced detailed flood elevations and 

boundaries for the base flood (1-percent-annual-chance flood). BFEs are provided. For riverine waterways with these 

zones, FISs include longitudinal profiles showing water surface elevations 

for different frequency flood events.

Floodways:  The floodway includes the waterway channel and adjacent 

land areas that must be reserved in order to convey the discharge of the 

base flood without cumulatively increasing the water surface elevation 

above a designated height. Floodways are designated for most waterways 

that have AE Zones or numbered A Zones. FISs include data on floodway 

widths and mean floodway velocities. 

AO and AH Zones:  These zones include areas of shallow flooding and are 

generally shown where the flood depth averages from 1 to 3 feet, where 

a clearly defined channel does not exist, where the path of flooding is 

unpredictable, and where velocity flow may be evident. These zones are 

characterized by ponding or sheetflow. BFEs may be provided for AH 

Zones; flood depths may be specified in AO Zones.

Shaded X (or B) Zones:  This zone shows areas of the 500-year flood (0.2-

percent-annual-chance flood), or areas protected by flood control levees. 

This zone is not shown on many NFIP maps, and its absence does not 

imply that flooding of this frequency will not occur. 

Unshaded X (or C) Zones:  These zones are all land areas not mapped as 

flood hazard areas that are outside of the floodplain that is designated 

for the purposes of regulating development pursuant to the NFIP. These 

zones may still be subject to small stream flooding and flooding from 

local drainage problems.

V Zones (V, VE, and V1-V30):  Also known as Coastal High Hazard Areas 

or special flood hazard areas subject to high-velocity wave action. V Zones 

“Base flood elevation” (BFE) is the elevation 

above a datum to which floodwaters are 

predicted to rise during the 1-percentannual-chance flood (also called the “base 

flood” or the 100-year flood).
MAKING HOSPITALS SAFE FROM FLOODING 3-23

are relatively narrow areas along open coastlines and some large lake 

shores that are subject to high-velocity wave action from storms or seismic 

sources. V Zones extend from offshore to the inland limit of a primary 

frontal dune, or to an inland limit where the predicted breaking wave 

height or wave runup depth drops below 3 feet.

Zone C (or Zone X) is all other areas, considered low-risk.

Figure 3-8: Riverine flood hazard zones 

Figure 3-9: Coastal flood hazard zones
3-24 MAKING HOSPITALS SAFE FROM FLOODING

3.1.5.3 Coastal A Zones 

As shown in Figure 3-9, coastal floodplains can be subdivided into A 

Zones and, where Primary Frontal Dunes occur or wave heights or runup 

depths exceed 3 feet, V Zones. NFIP maps do not currently differentiate 

which portions of the A Zone will experience wave heights between 1.5 

and 3 feet, which are capable of causing structural damage to buildings. 

These areas of special concern, called Coastal A Zones, can be identified 

through assessment of coastal flood hazard data (see Figure 3-11). 

Coastal A Zones are present where two conditions exist: where the expected stillwater flood depth is sufficient to support breaking waves 1.5 

to 3 feet high, and where such waves can actually occur. The first condition occurs where stillwater depths (vertical distance between the 

stillwater elevation and the ground) are more than 2 feet deep. The 

second condition occurs where there are few obstructions between the 

shoreline and the site. In these areas, the principal sources of flooding 

are tides, storm surges, seiches, or tsunamis, 

not riverine flooding.

The stillwater depth requirement is 

necessary, but is not sufficient by itself to 

warrant designation as a Coastal A Zone. 

This is because obstructions in the area may 

The current editions of the model building 

codes refer to ASCE 7 and ASCE 24; both 

design standards include requirements for 

Coastal A Zones.

Figure 3-10: Sample digital FIRM format used for modernized maps

ZONE

X

114

113

112

110

ZONE

X
MAKING HOSPITALS SAFE FROM FLOODING 3-25

block wind (limiting the initial growth of waves) or cause friction that 

attenuates wave energy. Obstructions can include buildings, locally high 

ground, and dense, continuous stands of vegetation (trees, shrubs, etc.). 

Designers should determine whether Coastal A Zone conditions are 

likely to occur at a hospital site because of the anticipated wave action 

and loads. This determination is based on an examination of the site 

and its surroundings, the actual surveyed ground elevations, and the 

estimated wave heights (calculated using predicted stillwater elevations 

found in the FIS or derived from elevations shown on the FEMA flood 

map; see Section 3.1.4.1).

When a decision is made to build a hospital in a Coastal A Zone, the 

characteristics of the site and the nature of the flood hazards must be examined prior to making important design decisions. Field observations 

and laboratory research have determined that flooding with breaking 

waves between 1.5 and 3 feet high pro­duces more damage than flooding 

of similar depths without waves. Therefore, ASCE 24, Flood Resistant 

Design and Construction, produced by the American Society of Civil Engineers’ Structural Engineers Institute (ASCE/SEI, 2005) specifically 

requires application of the NFIP’s V Zone design requirements in Coastal 

A Zones. The designers are advised to pay special attention to two additional considerations:

m Debris loads may be significant in Coastal A Zones landward of V 

Zones where damaged buildings, piers, and boardwalks can produce 

battering debris. Damage caused by debris can be minimized if 

foundations are designed to account for debris impact loads.

m Especially in high-wind regions, designers must pay special attention to 

the entire roof-to-foundation load path when designing and specifying 

Figure 3-11: Flood 

hazard zones in 

coastal areas
3-26 MAKING HOSPITALS SAFE FROM FLOODING

connections. To meet V Zone requirements, designs for buildings 

in Coastal A Zones should account for simultaneous wind and flood 

forces. Corrosion-resistant connections are especially important for 

the long-term integrity of the structure.

3.1.6 Floodplain Management

Requirements and Building Codes

The NFIP is the basis for the minimum requirements included in model 

building codes and standards for design and construction methods to resist flood damage. The original authorizing legislation for the NFIP is the 

National Flood Insurance Act of 1968 (42 U.S.C. 4001 et seq.). In that 

act, Congress expressly found that “a program of flood insurance can promote the public interest by encouraging sound land use by minimizing 

exposure of property to flood losses...” 

The most convincing evidence of the effectiveness of the NFIP minimum requirements is found in flood insurance claim payment statistics. 

Buildings that pre-date the NFIP requirements are, by and large, not constructed to resist flood damage. Buildings that post-date the NFIP (i.e., 

those that were constructed after a community joined the program and 

began applying the minimum requirements) are designed to resist flood 

damage. The NFIP reports that aggregate loss data indicate that buildings 

that meet the minimum requirements experience 70 percent less damage 

than buildings that pre-date the NFIP. There is ample evidence that buildings designed to exceed the minimum requirements are even less likely to 

sustain damage. 

3.1.6.1 Overview of the NFIP

The NFIP is based on the premise that the Federal government will make 

flood insurance available in communities that agree to recognize and incorporate flood hazards in land use and development decisions. In some 

States and communities, this is achieved by guiding development to areas 

with a lower risk. When decisions result in development within flood 

hazard areas, application of the criteria set forth in Federal regulation 

44 CFR Part 60.3 are intended to minimize exposure and flood-related 

damage. State and local governments are responsible for applying the 

provisions of the NFIP through the regulatory permitting processes. At 

the Federal level, the NFIP is managed by FEMA and has three main 

elements:

m Hazard identification and mapping, under which engineering studies 

are conducted and flood maps are prepared in partnership with States 
MAKING HOSPITALS SAFE FROM FLOODING 3-27

and communities. These maps delineate areas that are predicted to be 

subject to flooding under certain conditions. 

m Floodplain management criteria for development establish the 

minimum requirements to be applied to development within mapped 

flood hazard areas. The intent is to recognize flood hazards in the 

entire land development process. 

m Flood insurance, which provides some financial protection for 

property owners to cover flood-related damage to buildings and 

contents.

Federal flood insurance is intended to shift 

some of the costs of flood disasters away from 

the taxpayer by providing property owners an 

alternative to disaster assistance and disaster 

loans. Disaster assistance provides limited 

funding for repair and cleanup, and is available 

only after the President signs a major disaster 

declaration for the area. NFIP flood insurance 

claims are paid any time damage from a qualifying flood event3 occurs, regardless of whether 

a major disaster is declared. Community officials should be aware that public buildings 

may be subject to a mandated reduction in disaster assistance payments if the building is in 

a mapped flood hazard area and is not covered 

by flood insurance. 

Another important objective of the NFIP is to break the cycle of flood 

damage. Many buildings have been flooded, repaired or rebuilt, and 

flooded again. Before the NFIP, in some parts of the country this cycle was 

repeated every couple of years, with reconstruction taking place in the 

same flood-prone areas, using the same construction techniques that did 

not adequately resist flood damage. NFIP provisions guide development 

to lower-risk areas by requiring compliance with performance measures 

to minimize exposure of new buildings and buildings that undergo major 

renovation or expansion (called “substantial improvement” or repair of 

“substantial damage”). This achieves the long-term objective of building 

disaster-resistant communities. 

3 For the purpose of adjusting claims for flood damage, the NFIP defines a flood as “a general and temporary 

condition of partial or complete inundation of two or more acres of normally dry land area or of two or more 

properties (at least one of which is the policyholder’s property) from: overflow of inland or tidal waters; unusual 

and rapid accumulation or runoff of surface waters from any source; mudflow; or collapse or subsidence of land 

along the shore of a lake or similar body of water as a result of erosion or undermining caused by waves or 

currents of water exceeding anticipated cyclical levels that result in a flood as defined above.”

“Substantial damage” is damage of any 

origin sustained by a structure whereby 

the cost of restoring the structure to its 

condition before the damage would 

equal or exceed 50 percent of the market 

value of the structure before the damage 

occurred. 

“Substantial improvement” is any repair, 

reconstruction, rehabilitation, addition, 

or improvement of a building, the cost 

of which exceeds 50 percent of the 

market value of the building before the 

improvement or repair is started (certain 

historic structures may be excluded). 

“Substantial damage” is damage of any 

origin sustained by a structure whereby 

the cost of restoring the structure to its 

condition before the damage would 

equal or exceed 50 percent of the market 

value of the structure before the damage 

occurred. 

“Substantial improvement” is any repair, 

reconstruction, rehabilitation, addition, 

or improvement of a building, the cost 

of which exceeds 50 percent of the 

market value of the building before the 

improvement or repair is started (certain 

historic structures may be excluded). 
3-28 MAKING HOSPITALS SAFE FROM FLOODING

3.1.6.2 Summary of the NFIP Minimum Requirements 

The performance requirements of the NFIP are set forth in Federal regulation 44 CFR Part 60. The requirements apply to all development, which 

the NFIP broadly defines to include buildings and structures, site work, 

roads and bridges, and other activities. Buildings must be designed and 

constructed to resist flood damage, which is primarily achieved through 

elevation (or floodproofing). Additional specific requirements apply to 

existing development, especially existing buildings. Existing buildings 

that are proposed for substantial improvement, including restoration following substantial damage, are subject to the regulations. 

Although the NFIP regulations primarily focus on how to build structures, 

one of the long-term objectives of the program is to guide development 

to less hazardous locations. Preparing flood hazard maps and making the 

information available to the public is fundamental in satisfying that objective. With that information, people can make informed decisions about 

where to build, how to use site design to minimize exposure to flooding, 

and how to design buildings that will resist flood damage.

The NFIP’s broad performance standards for site work in flood hazard 

areas include the following requirements.

m Building sites shall be reasonably safe from flooding.

m Adequate site drainage shall be provided to reduce exposure to 

flooding. 

m New and replacement sanitary sewage systems shall be designed to 

minimize or eliminate infiltration of floodwaters into the systems and 

discharges from the systems into floodwaters.

m Development in floodways shall be prohibited, unless engineering 

analyses show that there will be no increases in flood levels. 

The NFIP’s broad performance standards for new buildings proposed for 

flood hazard areas (and substantial improvement of existing flood-prone 

buildings) include the following requirements.

m Buildings shall be designed and adequately anchored to prevent 

flotation, collapse, or lateral movement resulting from hydrodynamic 

and hydrostatic loads, including the effects of buoyancy.

m Building materials used below the DFE shall be resistant to flood 

damage.
MAKING HOSPITALS SAFE FROM FLOODING 3-29

m Buildings shall be constructed by methods and practices that minimize 

flood damage (primarily by elevating to or above the base flood level, 

or by specially designed and certified floodproofing measures).

m Buildings shall be constructed with electrical, heating, ventilation, 

plumbing, and air conditioning equipment and other service facilities 

that are designed and/or located so as to prevent water from entering 

or accumulating within the components.

Owners, planners, and designers should determine if there are any applicable State-specific requirements for floodplain development. Some 

States require that local jurisdictions apply standards that exceed the minimum requirements 

of the NFIP. In particular, some States require 

that hospitals be located outside of the floodplain (including the 500-year floodplain) or 

they are to be designed and constructed to resist 

conditions associated with the 500-year flood. 

Some States have regulations that impose other 

higher standards, while some States have direct 

permitting authority over certain types of construction or certain types of applicants. 

As participants in the NFIP, States are required 

to ensure that development not subject to 

local regulations, such as the development of 

State-owned properties, satisfies the same performance requirements. 

If hospitals are exempt from local permits, this may be accomplished 

through a State permit, a governor’s executive order, or other mechanisms that apply to entities not subject to local authorities.

3.1.6.3 Executive Order 11988 and Critical Facilities 

When Federal funding is provided for the planning, design, and construction of new critical facilities (including hospitals), or for the repair of 

existing critical facilities that are located within the 500-year floodplain, 

the funding agency is required to address additional considerations. Executive Order 11988, Floodplain Management, requires Federal agencies 

to apply a decisionmaking process to avoid, to the extent possible, the 

long- and short-term adverse impacts associated with the occupancy and 

modification of floodplains, and to avoid the direct or indirect support 

of floodplain development whenever there is a practicable alternative. If 

there is no practicable alternative, the Federal agency must take steps to 

minimize any adverse impacts to life, property, and the natural and beneficial functions of floodplains. 

States often use governors’ executive 

orders to influence State-constructed and 

State-funded critical facilities, requiring 

location outside of the 500-year floodplain 

where feasible, or protection to the 500-

year flood level if avoiding the floodplain 

is not practical. In 2004, a review of 

State and local floodplain management 

programs determined that Alabama, Illinois, 

Michigan, New York, North Carolina, 

Ohio, and Virginia have requirements for 

critical facilities (ASFPM 2004). 

States often use governors’ executive 

orders to influence State-constructed and 

State-funded critical facilities, requiring 

location outside of the 500-year floodplain 

where feasible, or protection to the 500-

year flood level if avoiding the floodplain 

is not practical. In 2004, a review of 

State and local floodplain management 

programs determined that Alabama, Illinois, 

Michigan, New York, North Carolina, 

Ohio, and Virginia have requirements for 

critical facilities (ASFPM 2004). 
3-30 MAKING HOSPITALS SAFE FROM FLOODING

The executive order establishes the BFE as the minimum standard for all 

Federal agencies. Implementation guidance specifically addresses “critical 

actions,” which are described as those actions for which even a slight 

chance of flooding would be too great. The construction or repair of 

critical facilities, such as hospitals and clinics, fire stations, emergency 

operations centers, and facilities for storage of hazardous wastes or 

storage of critical records, are examples of critical actions. 

After determining that a site is in a mapped flood hazard area, and after 

giving public notice, the Federal funding agency is required to identify 

and evaluate practicable alternatives to locating a hospital in a 500-year 

floodplain. If the Federal agency has determined that the only practicable alternative is 

to proceed, then the impacts of the proposed 

action must be identified. If the identified impacts are harmful to people, property, and 

the natural and beneficial functions of the 

floodplain, the Federal agency is required to 

minimize the adverse effects on the floodplain 

and the funded activity.

Having identified the impacts of the proposed action and the methods 

to minimize these impacts, the Federal agency is required to re-evaluate 

the proposed action. The re-evaluation must consider whether the action 

is still feasible, whether the action can be modified to relocate the facility 

or eliminate or reduce identified impacts, or if a “no action” alternative 

should be chosen. If the finding results in a determination that there is 

no practicable alternative to locating a critical facility in the floodplain, 

or otherwise affecting the floodplain, then a statement of findings and a 

public explanation must be provided. 

3.1.6.4 Scope of Model Building Codes and Standards 

The International Building Code (IBC) and the Building Construction and 

Safety Code (NFPA 5000) were the first model codes to include comprehensive provisions that addressed flood hazards. Both codes are 

consistent with the minimum provisions of the NFIP that pertain to the 

de­sign and construction of buildings. The NFIP requirements that pertain to site development, floodways, coastal setback lines, ero­sion-prone 

areas, and other environmental constraints are found in other local 

ordinances. The codes require designers to identify and design for anticipated environmental loads and load com­binations, including wind, 

seismic, snow, and flood loads, as well as the soil conditions.

FEMA’s eight-step decisionmaking process 

for complying with Executive Order 11988 

must be applied before Federal disaster 

assistance is used to repair, rehabilitate, 

or reconstruct damaged existing critical 

facilities in the 500-year floodplain.

FEMA’s eight-step decisionmaking process 

for complying with Executive Order 11988 

must be applied before Federal disaster 

assistance is used to repair, rehabilitate, 

or reconstruct damaged existing critical 

facilities in the 500-year floodplain.
MAKING HOSPITALS SAFE FROM FLOODING 3-31

The IBC and NFPA 5000 incorporate, by reference, a number of standards that are developed through a formal or accredited consensus 

process. The best known is ASCE 7. The model building codes require 

that applicable loads be accounted for in the building design. The designer must identify the pertinent, site-specific characteristics and then 

use ASCE 7 to determine the specific loads and load combinations. In effect, it is similar to a local floodplain ordinance that requires 

determination of the environmental condition (in/out of the mapped 

flood hazard area, DFE/depth of water), and then specifies certain conditions that must be met during design and construction. The 1998 edition 

of ASCE 7 was the first version of the standard to include flood loads explicitly, including hydrostatic loads, hydrodynamic loads (velocity and 

waves), and debris impact loads. 

The IBC and NFPA 5000 also incorporate, by reference, a standard that 

was first published by ASCE in 1998 and revised in 2005: ASCE 24. Developed through a consensus process, ASCE 24 

addresses specific topics pertinent to designing 

buildings in flood hazard areas, including 

floodways, coastal high-hazard areas, and other 

high-risk flood hazard areas such as alluvial 

fans, flash flood areas, mudslide areas, erosionprone areas, and high-velocity areas. 

ASCE 7 and the model building codes classify 

structures based on occupancy into four categories, each with different requirements. The 

same categories are used in ASCE 24 and different flood-resistant requirements apply to 

the different categories. Table 3-1 summarizes 

the elevation requirements of ASCE 24 that exceed the NFIP minimum requirements for the 

hospitals and health care facilities addressed 

by this manual (Category III or Category IV 

structures). 

Although most State and local building codes are based on the International Code Series produced by the International Code Council, 

jurisdictions often adopt specific amendments. For example, the State 

of Florida adopted requirements that are specific to nursing homes, new 

hospitals, and additions, alterations, or renovations to existing hospitals 

and all detached outpatient facilities. Such facilities are required to be 

“located above the 100-year flood plain or hurricane Category 3 (SaffirSimpson scale) hurricane surge inundation elevation, whichever requires 

the highest elevation.”

ASCE 7-05 outlines methods to determine 

design loads and load combinations in 

flood hazard areas, including hydrostatic 

loads, hydrodynamic loads, wave loads, 

and debris impact loads. In order to 

compute the loads and load combinations 

the designer must identify site-specific 

characteristics, including flood depths, 

velocities, waves, and the likelihood that 

debris impacts need to be considered. 

ASCE 24-05 addresses design requirements 

for structures in coastal high-hazard areas 

(V Zones) and Coastal A Zones.

ASCE 7-05 outlines methods to determine 

design loads and load combinations in 

flood hazard areas, including hydrostatic 

loads, hydrodynamic loads, wave loads, 

and debris impact loads. In order to 

compute the loads and load combinations 

the designer must identify site-specific 

characteristics, including flood depths, 

velocities, waves, and the likelihood that 

debris impacts need to be considered. 

ASCE 24-05 addresses design requirements 

for structures in coastal high-hazard areas 

(V Zones) and Coastal A Zones.
3-32 MAKING HOSPITALS SAFE FROM FLOODING

Table 3-1: ASCE/SEI 24-05 provisions related to the elevation of hospitals

Category III Category IV

Elevation of Lowest Floor or Bottom of Lowest Horizontal Structural Member

A Zone: elevation of lowest floor BFE +1 ft or DFE, 

whichever is higher

BFE +2 ft or DFE, 

whichever is higher

V Zone and Coastal A Zone: where the lowest horizontal 

structural member is parallel to direction of wave 

approach

BFE +1 ft or DFE, 

whichever is higher

BFE +1 ft or DFE, 

whichever is higher

V Zone and Coastal A Zone: where the lowest horizontal 

structural member is perpendicular to direction of wave 

approach

BFE +2 ft or DFE, 

whichever is higher

BFE +2 ft or DFE, 

whichever is higher

Elevation Below which Flood-Damage-Resistant Materials Shall be Used

A Zone BFE +1 ft or DFE, 

whichever is higher

BFE +2 ft or DFE, 

whichever is higher

V Zone and Coastal A Zone: where the lowest horizontal 

structural member is parallel to direction of wave 

approach

BFE +2 ft or DFE, 

whichever is higher

BFE +2 ft or DFE, 

whichever is higher

V Zone and Coastal A Zone: where the lowest horizontal 

structural member is perpendicular to direction of wave 

approach

BFE +3 ft or DFE, 

whichever is higher

BFE +3 ft or DFE, 

whichever is higher

Minimum Elevation of Utilities and Equipment

A Zone BFE +1 ft or DFE, 

whichever is higher

BFE +2 ft or DFE, 

whichever is higher

V Zone and Coastal A Zone: where the lowest horizontal 

structural member is parallel to direction of wave 

approach

BFE +2 ft or DFE, 

whichever is higher

BFE +2 ft or DFE, 

whichever is higher

V Zone and Coastal A Zone: where the lowest horizontal 

structural member is perpendicular to direction of wave 

approach

BFE +3 ft or DFE, 

whichever is higher

BFE +3 ft or DFE, 

whichever is higher

Dry Floodproofing

A Zone: elevation to which dry floodproofing extends BFE +1 ft or DFE, 

whichever is higher

BFE +2 ft or DFE, 

whichever is higher

V Zone and Coastal A Zone: dry floodproofing not 

allowed Not applicable Not applicable
MAKING HOSPITALS SAFE FROM FLOODING 3-33

3.2 HOSPITALS EXPOSED TO FLOODING 

3.2.1 Identifying Flood Hazards at

Existing Hospitals

Facility owners, planners, and designers of hospitals should investigate site-specific flood hazards and character­istics as part of site selection, guiding the location of a new hospital and other improvements on a site. This same investigation should be undertaken when 

examining existing hospitals and when planning improvements or rehabilitation work. The best available infor­mation should be examined, 

including flood hazard maps, records of historical flooding, storm surge 

maps, and advice from local experts and others who can evaluate flood 

risks. Table 3-3 in Section 3.5 outlines questions that should be answered 

prior to initiating site layout and de­sign work.

3.2.2 Vulnerability: What Flooding Can Do

to Existing Hospitals

Existing flood-prone hospitals are susceptible to damage, the nature 

and severity of which is a function of site-specific flood characteristics. 

Damage may include: site damage, structural and nonstructural building 

damage, destruction or impairment of utility service equipment, and loss 

of contents. 

Regardless of the nature and severity of damage, flooded hospitals typically are not functional while cleanup and repairs are undertaken. The 

length of closure, and thus the impact on the ability of the facility to become operational, depends on the severity of the damage and lingering 

health hazards. Sometimes repairs are put on hold pending a decision 

on whether a hospital should be rebuilt at the flood-prone site. When 

damage is substantial, rehabilitation or reconstruction is allowed only if 

compliance with flood-resistant design requirements is achieved (see Section 3.1.6.2).
3-34 MAKING HOSPITALS SAFE FROM FLOODING

3.2.2.1 Site Damage

The degree of site damage associated with flooding is a function of several 

variables related to the characteristics of the flood, as well as the site itself.

Erosion and scour:  All parts of a site that are subject to flooding by fastmoving water could experience erosion, and local scour could occur 

around any permanent obstructions to flow. Graded areas, filled areas, and 

cut or fill slopes are especially susceptible. Stream and channel bank erosion, and erosion of coastal shorelines, are natural phenomena that may, 

over time, threaten site improvements and buildings (see Figure 3-12). 

Debris and sediment removal:  Even when buildings are not subject to water 

damage, floods can deposit large quantities of debris and sediment that 

can damage a site and be expensive to remove. 

Landscaping:  Grass, trees, and plants suffer after floods, especially longduration flooding that prevents oxygen uptake, and coastal flooding 

that stresses plants that are not salt-tolerant. Fast-moving floodwaters and 

waves also can uproot plants and trees.

Fences:  Some types of fences that are relatively solid can significantly restrict the free flow of floodwaters and trap floating debris. Fences can be 

damaged or knocked down by the pressure of flowing water, or by the 

buildup of debris that may result in significant loads. 

Accessory structures:  Accessory structures can sustain both structural and 

nonstructural damage. In some locations, such structures can be designed 

Figure 3-12:

Riverbank erosion of 

the Genesee River 

during Hurricane 

Agnes flooding in 

1972 eventually led to 

collapse of this wing 

of the Jones Memorial 

Hospital, Wellsville, 

NY. 

Source: Dick Neal

Photography

Figure 3-12:

Riverbank erosion of 

the Genesee River 

during Hurricane 

Agnes flooding in 

1972 eventually led to 

collapse of this wing 

of the Jones Memorial 

Hospital, Wellsville, 

NY. 

Source: Dick Neal

Photography
MAKING HOSPITALS SAFE FROM FLOODING 3-35

and built using techniques that minimize damage potential, without requiring elevation above the DFE. 

Access roads:  Access roads that extend across flood-prone areas may be damaged by erosion, washout of drainage culverts, failure of fill and bedding 

materials, and loss of road surface (see Figure 3-13). Road damage could 

prevent uninterrupted access to a facility and thus impair its functionality. 

Parking lots and parking garages:  Paved parking lots may be damaged 

by failure of bedding materials and loss of driving surface. Vehicles left 

in parking lots and parking garages could also be damaged. Most large 

parking garages are engineered structures that can be designed to allow 

for the flow of water.

Helicopter landing pads:  Helicopters landing pads that are flooded are not 

serviceable when access is critical. Hospitals on flood-prone sites should 

have rooftop landing pads. 

Signage:  Signage on ground that is subject to 

flooding may be damaged. Loss of signage can 

impair ready access, especially by those unfamiliar with the facility or on large medical 

campuses. 

Damage to other site elements such as 

water supply, sewer lines, underground and 

aboveground tanks, and emergency power 

generators, is discussed in Section 3.2.2.5.

Figure 3-13:

Flooding caused the failure of this road bed.

SOURCE: U.S. Army Corps of Engineers
3-36 MAKING HOSPITALS SAFE FROM FLOODING

Stormwater management facilities and site drainage:  Site improvements such 

as swales and stormwater basins may be eroded, filled with sediments, or 

clogged by debris.

3.2.2.2 Structural Damage

Structural damage includes all damage to the load-bearing portions of a 

building. Damage to other components of buildings is described below, 

including nonstructural components (Section 3.2.2.3), medical equipment (Section 3.2.2.4), utility service equipment (Section 3.2.2.5), and 

contents (Section 3.2.2.6). 

Depth:  The hydrostatic load against a wall or foundation is directly related 

to the depth of water. Standard stud and siding, or unreinforced brick veneer walls, may collapse under hydrostatic loads associated with relatively 

shallow water. Reinforced masonry walls perform better than unreinforced masonry walls (see Figure 3-14), although an engineering analysis 

is required to determine performance. Walls and floors of below-grade 

areas (basements) are particularly susceptible to damage by buoyancy 

force. When soils are saturated, pressures against below-grade walls are a 

function of the total depth of water, including the depth below-grade and 

the weight of the saturated soils.

Figure 3-14:

Interior unreinforced 

masonry walls of the 

Port Sulphur High 

School in Louisiana 

were damaged by 

hydrostatic loads 

associated with 

Hurricane Katrina’s 

storm surge (2005).

Figure 3-14:

Interior unreinforced 

masonry walls of the 

Port Sulphur High 

School in Louisiana 

were damaged by 

hydrostatic loads 

associated with 

Hurricane Katrina’s 

storm surge (2005).
MAKING HOSPITALS SAFE FROM FLOODING 3-37

Buoyancy and uplift:  If below-grade areas are essentially watertight, buoyancy 

or uplift forces can float a building out of the ground or rupture concrete 

slabs-on-grade (see Figure 3-15). Buildings that are not adequately anchored can be floated or pushed off foundations. Although rare for large 

and heavy buildings, this is a concern for smaller structures. Buoyancy is 

a significant concern for underground and aboveground tanks, especially 

those used for emergency generator fuel and bulk oxygen.

Duration:  By itself, saturation is unlikely to result in significant structural 

damage to masonry construction. Saturation of soils, a consequence of 

long duration flooding, increases pressure on below-grade foundation 

walls. 

Velocity, wave action, and debris impacts:  Each of these components of dynamic loads can result in structural damage if buildings are not designed 

to resist overturning, repetitive pounding by waves, or short-duration impact loads generated by floating debris (see Figure 3-16).

Erosion and scour:  Structural damage is associated with foundation failure 

when erosion or scour results in partial or complete removal of supporting soil (see Figure 3-17). Erosion of slopes, especially unprotected 

slopes, can lead to slope failures and loss of foundation supporting soil.

Figure 3-15:

Concrete slab ruptured 

by hydrostatic pressure 

(buoyancy) induced 

by the floodwaters 

of Hurricane Katrina 

(2005).

Figure 3-15:

Concrete slab ruptured 

by hydrostatic pressure 

(buoyancy) induced 

by the floodwaters 

of Hurricane Katrina 

(2005).
3-38 MAKING HOSPITALS SAFE FROM FLOODING

3.2.2.3 Nonstructural Damage 

Many flood-prone buildings are exposed to floodwaters that are not fast 

moving, or that may be relatively shallow and not result in structural 

damage. Simple inundation and saturation of the building and finish materials can result in significant and costly damage, including long-term 

health complications associated with mold. Floodwaters often are conFigure 3-16:

The South Cameron 

Memorial Hospital, 

Cameron, LA, was 

damaged by debris 

carried by Hurricane 

Rita’s storm surge 

(2005). 

Source: LSU AG CENTER

Figure 3-16:

The South Cameron 

Memorial Hospital, 

Cameron, LA, was 

damaged by debris 

carried by Hurricane 

Rita’s storm surge 

(2005). 

Source: LSU AG CENTER

Figure 3-17:

Local scour 

undermined the 

footing of this 

exterior stair tower 

(Hurricane Ivan, 

2004). 

Figure 3-17:

Local scour 

undermined the 

footing of this 

exterior stair tower 

(Hurricane Ivan, 

2004). 
MAKING HOSPITALS SAFE FROM FLOODING 3-39

taminated with chemicals, petroleum products, and sewage. Under such 

circumstances, recovery generally involves removal of nonstructural materials and finishes because cleanup and decontamination are expensive 

and time-consuming (see Figure 3-18). Damage to contents is discussed in 

Section 3.2.2.6. 

Saturation damage can vary as a function of the duration of exposure. 

Some materials are not recoverable even after very brief inundation, while 

others remain serviceable if in contact with water for only a few hours. 

Use of water-resistant materials will help to minimize saturation damage 

and reduce the costs of cleanup and restoration to service. (For more 

information, see FEMA Technical Bulletin FIA-TB-2, Flood-Resistant Materials Requirements.)

Wall finishes:  Painted concrete and concrete masonry walls usually resist water damage, provided the type of paint used can be readily cleaned. 

Tiled walls may resist water damage depending on the type of adhesive 

and foundation (gypsum board substrate and wood-framed walls with tile 

typically do not remain stable). 

Flooring:  Many hospitals have durable floors that resist water damage. 

Ground floors are often slab-on-grade and finished with tile or sheet products. Flooring adhesives in use since the early 1990s likely are latex-based 

and tend to break down when saturated (see Figure 3-19). Most carpeting, 

even the indoor-outdoor kind, is difficult to clean. 

Figure 3-18:

Drying out the ground 

floor at Hancock 

Medical Center 

(Hurricane Katrina, 

2005) 

Source: Hancock Medical

Center

Figure 3-18:

Drying out the ground 

floor at Hancock 

Medical Center 

(Hurricane Katrina, 

2005) 

Source: Hancock Medical

Center
3-40 MAKING HOSPITALS SAFE FROM FLOODING

Wall and wood components:  When soaked for long periods of time, some 

materials change composition or shape. Most types of wood swell when 

wet and, if dried too quickly, will crack, split, or warp. Plywood can delaminate and wood door and window frames may swell and become unstable. 

Gypsum wallboard, wood composition panels, other wall materials, and 

wood cabinetry not intended for wet locations can fall apart (see Figure 

3-18). The longer these materials are wet, the more moisture, sediment, 

and pollutants they absorb. Some materials, such as the paper facing on 

gypsum wallboard, “wick” standing water, resulting in damage above the 

actual high-water line (see Figure 3-20). 

Figure 3-20:

The test of the effects of 

flooding on materials 

showed that water 

damage and mold 

growth extended 

above the water line.

Source: Oak Ridge

National Laboratory

Figure 3-20:

The test of the effects of 

flooding on materials 

showed that water 

damage and mold 

growth extended 

above the water line.

Source: Oak Ridge

National Laboratory

Figure 3-19:

Floor damage at West 

Jefferson Medical 

Center (Hurricane 

Katrina, 2005) 
MAKING HOSPITALS SAFE FROM FLOODING 3-41

Metal components:  Metal structural components are unlikely to be permanently damaged by short-term inundation. However, hollow metal 

partitions are particularly susceptible when in contact with water because 

they cannot be thoroughly dried and cleaned. Depending on the degree 

of corrosion protection on the metal, repetitive flooding by saline coastal 

waters may contribute to long-term corrosion.

Metal connectors and fasteners:  Depending on the composition of the 

metal, repetitive flooding, especially by saline coastal waters, may contribute to long-term corrosion. Connectors and fasteners are integral to 

the structural stability of buildings; therefore, failure caused by accelerated corrosion would jeopardize the building. 

3.2.2.4 Medical Equipment

Large medical equipment that is permanently installed usually is considered to be part of the building rather than contents. The nature and 

sensitivity of most medical equipment suggests that post-flood cleaning 

to restore functionality may not be feasible. This limits options for existing hospitals that use such equipment in areas that will be exposed to 

flooding, because temporary relocation of the equipment cannot be part 

of an emergency response plan. 

3.2.2.5 Utility System Damage

Utility system service equipment that is exposed to flooding is vulnerable 

to damage. Damage may result in a total loss, or may require substantial 

cleaning and restoration efforts. The degree of damage varies somewhat 

as a function of the characteristics of flooding. Certain types of equipment and installation measures will help minimize damage and reduce 

the costs of cleanup and restoration to service.

Displacement of equipment and appliances:  Installation below the flood 

level exposes equipment and appliances to flood forces, including drag 

resulting from flowing water and buoyancy. Gas-fired appliances are particularly dangerous: flotation can separate appliances from gas sources, 

resulting in fires and explosive situations. Displaced equipment may dislodge lines from fuel oil tanks, contributing to the threat of fire and 

causing water pollution and environmental damage.

Elevators:  If located in areas subject to flooding, elevator component 

equipment and controls will be damaged, and movement between floors 

will be impaired. In hospitals, maintaining elevator function is important, 

especially if services have to be consolidated to upper floors after a flood.
3-42 MAKING HOSPITALS SAFE FROM FLOODING

Corrosion:  Corrosion related to inundation of equipment and appliances 

may not be apparent immediately, but can increase maintenance demand 

and shorten the useful life of some equipment and appliances. 

Electrical systems and components:  Electrical systems and components, and 

electrical controls of heating, ventilation and air-conditioning systems, 

are subject to damage simply by getting wet, even for short durations. Unless specifically designed for wet locations, switches and other electrical 

components can short out due to deposits of sediment, or otherwise not 

function, even when allowed to dry before operation. Wiring and components that have been submerged may be functional, although generally it 

is more cost-effective to discard flooded outlets, switches, and other lessexpensive components than to attempt thorough cleaning.

Communications infrastructure:  Critical communications infrastructure, such 

as control panels and wiring for warning systems, 911 systems, and regular 

telephone and wireless networks, are most susceptible to failure during 

emergencies if located in below-grade basements. 

Specialized piping:  Unprotected piping for medical gas supply systems may 

be damaged and threaten care that depends on an uninterrupted supply 

of oxygen and other gasses for the treatment of patients.

Ductwork damage:  Ductwork is subject to two flood-related problems. 

Flood forces can displace ductwork, and saturated insulation can overload 

support straps, causing failure.

Mold and dust:  Furnaces, air handlers, and ductwork that have been submerged must be thoroughly cleaned and sanitized. Otherwise, damp 

conditions contribute to the growth of mold and accumulated sediment 

can be circulated throughout the hospital, causing respiratory problems. 

Fiberglass batt or cellulose insulation that has been submerged cannot 

be sanitized and must be replaced. In sensitive environments, ductwork 

should be replaced rather than cleaned.

Gas-fired systems:  Water-borne sediment can impair safe functioning of 

jets and controls in gas-fired furnaces and water heaters, necessitating professional cleaning and inspection prior to restoration of service. Control 

equipment (valves, electrical switches, relays, temperature sensors, circuit 

breakers, and fuses) that have been submerged may pose an explosion 

and fire hazard and should be replaced.

Emergency power generators:  Generators that are installed at-grade are susceptible to inundation and will be out of service after a flood (see Figure 

3-21). Even if fuel tanks are located above flood level, truck access for refueling would be impaired if the site is flooded for any length of time.
MAKING HOSPITALS SAFE FROM FLOODING 3-43

Tanks (underground):  Underground storage tanks are subjected to significant buoyant forces and can be displaced, especially when long-duration 

flooding occurs. Computations of stability should be based on the assumption that the tank is empty in order to maximize safety. Tank inlets, 

fill openings, and vents should be above the DFE, or designed to prevent the inflow of floodwaters or outflow of tank contents during flood 

conditions.

Tanks (aboveground):  Permanently installed aboveground storage tanks 

are subject to buoyant forces and displacement caused by moving water. 

Standard strapping of propane tanks may be inadequate for the anticipated loads. Tank inlets, fill openings, and vents should be above the 

DFE, or designed to prevent the inflow of floodwaters or outflow of tank 

contents during flood conditions. Even temporary storage of tanks can 

be problematic (see Figure 3-22).

Figure 3-21:

Although it was 

anchored and 

not displaced by 

floodwaters,

this generator was out 

of service after being 

submerged (Hurricane 

Katrina, 2005).
3-44 MAKING HOSPITALS SAFE FROM FLOODING

Public Utility Service:  Damage to public utility service (potable water 

supply and wastewater collection) can affect operations and may cause 

damage to hospitals:

m Potable water supply systems may become contaminated if distribution 

lines or treatment facilities are damaged, or if wellheads are submerged.

m During heavy rains, sewers back up from infiltration and inflow of 

stormwater into the sewer lines and manholes, cross connections 

between storm and sanitary sewers, and flooded wastewater treatment 

plants. Sewer backup into a hospital poses a major health hazard. 

Even when the water has receded, exposed building components, 

finish materials, and contents are contaminated, and usually must be 

removed because adequate cleaning is difficult, if not impossible. 

3.2.2.6 Contents Damage

Hospitals contain high-value equipment and contents that can be damaged and unrecoverable when exposed to flooding. For the purpose of 

this discussion, the term “contents” includes items such as furniture, appliances, computers, laboratory equipment and materials, records, and 

specialized moveable machinery. The following types of contents often 

are total losses after flooding.

Furniture:  Porous woods become saturated and swollen, and joints may 

separate. Furniture with coverings or pads generally cannot be restored. 

Metal furniture is difficult to thoroughly dry and clean, is subject to corFigure 3-22:

Oxygen tanks stored 

outside of the Hancock 

Medical Center were 

dislodged by flooding 

(Hurricane Katrina, 

2005).
MAKING HOSPITALS SAFE FROM FLOODING 3-45

rosion, and typically is discarded (see Figure 3-23). Some wood furniture 

may be recoverable after brief inundation.

Computers:  Flood-damaged computers and peripheral equipment cannot 

be restored after inundation, although special recovery procedures may 

be able to recover information on hard drives.

Communications equipment:  Even though some communications 

equipment may be able to be restored with appropriate cleaning, the loss 

of functionality would seriously impair the ability of the facility to provide 

critical services immediately after a flood. Equipment with printed circuit 

boards generally cannot be restored.

Medical records and office files:  Valuable records may be lost if flooded. Although expensive, some recovery of computerized and paper records may 

be possible with special procedures (see Figure 3-24).

Health care equipment and laboratory materials:  Most medical and health 

care equipment cannot be cleaned and restored to safe functioning, and 

would need to be replaced. Depending on the nature of laboratory materials and chemicals, complete disposal or special cleanup procedures may 

be required.

Kitchen equipment and goods:  Floodwaters can dislodge appliances that can 

float and damage other equipment. Stainless steel equipment generally 

Figure 3-23:

The interior of the 

Hancock Medical 

Center required 

extensive cleanup 

following flooding 

(Hurricane Katrina, 

2005). 

Source: Hancock

Medical Center

Figure 3-23:

The interior of the 

Hancock Medical 

Center required 

extensive cleanup 

following flooding 

(Hurricane Katrina, 

2005). 

Source: Hancock

Medical Center
3-46 MAKING HOSPITALS SAFE FROM FLOODING

has cleanable surfaces that can be disinfected and restored to service. Because of contamination, all food stuffs must be discarded. 

Vehicles associated with hospitals: If left in flood-prone areas, vehicles 

must be replaced or cleaned to be serviceable, and may not be functional 

and available for service immediately after a flood.

Figure 3-24: Medical 

records saturated 

by floodwaters 

(Hurricane Katrina, 

2005)

Source: Hancock

Medical Center
MAKING HOSPITALS SAFE FROM FLOODING 3-47

3.3 REQUIREMENTS AND BEST 

PRACTICES IN FLOOD HAZARD 

AREAS

3.3.1 Evaluating Risk and Avoiding Flood

Hazards

Flood hazards are very site-specific. When a flood hazard map is prepared, lines drawn on the map appear to define the hazard area precisely. Land that is on one side of the line is “in” the mapped 

flood hazard area, while the other side of the line is “out.” Although the 

delineation may be an approximation, having hazard areas shown on a 

map facilitates avoiding such areas to the maximum extent practical. If 

such areas are unavoidable, facility owners should carefully evaluate all of 

the benefits and all of the costs in order to determine long-term acceptable risks, and to develop appropriate plans for design and construction 

of new facilities.

Even in communities with expansive floodplains, it should be possible to 

avoid locating new hospitals in floodways and coastal areas subject to significant waves (V Zones).

Section 3.2 describes the damage sustained by existing buildings exposed 

to flood hazards, including site damage, structural and nonstructural 

building damage, destruction or impairment of service equipment, and 

loss of contents. These types of damage, along with loss of function, are 

avoided if hospitals are located away from flood hazard areas. Damage is 

reduced and the ability to sustain function is 

increased when hospitals that must be located 

in flood hazard areas are built to exceed the 

minimum requirements.

Flood hazard areas designated as “V Zones” on 

FIRMs are relatively narrow areas along open 

coasts and lake shores where the base flood 

Construction in V Zones is required to 

meet certain design and construction 

requirements that are different than those 

required in A Zones. This chapter will 

identify these differences. 

Construction in V Zones is required to 

meet certain design and construction 

requirements that are different than those 

required in A Zones. This chapter will 

identify these differences. 
3-48 MAKING HOSPITALS SAFE FROM FLOODING

conditions are expected to produce 3-foot or higher waves. V Zones, 

sometimes called coastal high-hazard areas or special flood hazard areas 

subject to high-velocity wave action, are found on the Pacific, Gulf, and 

Atlantic coasts, and around the Great Lakes. Every effort should be made 

to locate hospitals outside of V Zones, because the destructive nature of 

waves makes it difficult to design a building to be fully functional during 

and after a flood event. This is particularly true in coastal areas subject to 

hurricane surge flooding. 

3.3.2 Benefits and Costs: Determining

Acceptable Risk

Many decisions made with respect to hospitals are, in part, based on a 

determination of acceptable risk. Risk includes the potential losses associated with a hazard. Ideally, risks can be defined in terms of expected 

probability and frequency of the hazard occurring, the people and property exposed, and the potential consequences. Choosing a site that is 

affected by flooding is a decision to accept some degree of risk. Although 

the flood-prone land may have a lower initial cost, the incremental costs 

of construction, plus the likely increased costs of maintenance, repair, 

and replacement, may be significant. Another cost of locating a hospital 

in a flood-prone area is related to access problems if streets and access 

roads are impassable. The building may be elevated and protected, but if 

access is restricted periodically, then the use of the facility is affected (see 

Figure 3-25).

Figure 3-25:

Hurricane Katrina’s 

floodwaters 

surrounded most 

hospitals in New 

Orleans, complicating 

access for evacuation, 

as well as limiting 

treatment options for 

residents.
MAKING HOSPITALS SAFE FROM FLOODING 3-49

In communities with expansive flood hazard areas, there may be no practical alternatives to using a flood-prone site. In these situations, an 

evaluation of acceptable risk should lead to selection of design measures 

that exceed the minimum requirements to 

mitigate the impacts of flooding. 

The building owner and the design team can 

influence the degree of risk (e.g., the frequency and severity of flooding that may affect 

the site). They control it through the selection of the site design and the building design 

measures. Fundamentally, this process is a balancing of the benefits of an acceptable level of 

disaster resistance with the costs of achieving 

that degree of protection. With respect to mitigation of future hazard events:

m Benefits are characterized and measured 

as future damages avoided if the mitigation measures (including 

avoiding flood hazard areas) are implemented.

m Costs are the costs associated with implementing measures to 

eliminate or reduce exposure to hazards. 

Section 3.2 describes typical damage and losses sustained by buildings exposed to flooding. Direct damage includes damage to physical property, 

including the site, the building, building materials, utilities, and building 

contents. Indirect damage that is not listed includes health hazards, loss of 

functionality, emergency response, evacuation, expenses associated with relocating services to another building during repairs, and loss of revenue. 

Benefits other than avoided physical damage are difficult to measure. 

They are associated with future damage that does not occur because of 

the mitigation activity, cleanup that is not required because of the mitigation activity, service that is not interrupted because flooding does not 

affect normal operations, and revenue that is not lost. In addition, benefits accrue over long periods of time, thus making it more difficult to 

make a direct comparison of the benefits with the up-front costs of mitigation. Mitigation costs can be more readily expressed in terms of the 

higher costs of a flood-free site, or the initial capital costs of work designed to resist flood damage. Thus, without full accounting of both 

benefits and costs, decisionmakers may not be able to make fully informed decisions. Some questions that should be answered include:

m If the site is flood-prone and the building is out of the flood hazard 

area or is elevated on fill, what are the average annual cleanup costs 

Extreme hurricane storm surge flooding may 

be a very low-probability event, but the flood 

depths and wave heights may be much more 

severe than the conditions of the base flood 

shown on the FIRMs. The potential impacts 

on a hospital must be carefully considered 

in order to make an informed decision 

regarding acceptable risk and potential 

damage. If possible, it is always best to 

avoid locating hospitals in areas subject to 

extreme storm surge flooding. 

Extreme hurricane storm surge flooding may 

be a very low-probability event, but the flood 

depths and wave heights may be much more 

severe than the conditions of the base flood 

shown on the FIRMs. The potential impacts 

on a hospital must be carefully considered 

in order to make an informed decision 

regarding acceptable risk and potential 

damage. If possible, it is always best to 

avoid locating hospitals in areas subject to 

extreme storm surge flooding. 
3-50 MAKING HOSPITALS SAFE FROM FLOODING

associated with removal of sand, mud, and debris deposited by floods 

of varying frequencies?

m If the facility building is elevated by means other than fill, will periodic 

inundation of the exposed foundation elements cause higher average 

annual maintenance costs?

m If the facility is protected with floodproofing measures, what are the 

costs of annual inspection, periodic maintenance and replacement of 

materials, and staff training and drills?

m If the hospital meets only the minimum elevation requirements, 

what are the average annual damages and cleanup costs over the 

anticipated useful life of the building, including the occurrence of 

floods that exceed the design flood elevation?

m How do long-term costs associated with periodic inundation compare 

to up-front costs of selecting a different site or building to a higher 

level of protection?

m If a site outside of the flood hazard area is available but less than optimal in terms of access by the community, are the trade-offs acceptable?

m If the facility is located in a hurricane-prone community, how should 

the facility design account for low-probability, but high-impact, storm 

surge flooding?

m If access to the facility is periodically restricted by flooding, especially 

long-duration flooding, what are the resulting cost effects? How often 

would an alternate location need to be provided to continue normal 

operations?

3.3.3 Site Modifications

When sites being considered for hospitals are prone to flooding, planners 

and designers may want to evaluate the feasibility of certain site modifications in order to provide an increased level of protection to buildings. 

The eval­uations involve engineering analyses to determine whether the 

desired level of protection is cost-effective, and whether the pro­posed site 

modifications alter the floodplain in ways that could increase flooding. 

The effectiveness of typical site modifications and their ramifications must 

be examined for each specific site. 

Earthen fill:  Fill can be placed in the flood hazard area to elevate an entire 

site above the DFE. If the fill is placed and compacted to be stable during 
MAKING HOSPITALS SAFE FROM FLOODING 3-51

Site modifications are not appropriate 

in floodways along riverine waterways, 

where obstructions to flows can increase 

flood elevations. Engineering analyses are 

required to determine the impact of such 

modifications.

Site modifications are not appropriate 

in floodways along riverine waterways, 

where obstructions to flows can increase 

flood elevations. Engineering analyses are 

required to determine the impact of such 

modifications.

the rise and fall of floodwaters, and if the fill is 

protected from erosion, then modifying a site 

with fill to elevate a facility is preferred over 

other methods of elevation. Not only will buildings be less exposed to flood forces, but, under 

some circumstances (such as long duration 

floods), hospitals may be able to continue to 

function. Whether nonstructural fill is placed 

solely to modify the site, or structural fill is 

placed to elevate buildings, placement of fill can change flooding characteristics, including increased flooding on other properties. Engineering 

analyses can be conducted to determine whether eliminating floodplain 

storage by filling will change the direction of the flow of water, create 

higher flow velocities, or increase the water surface elevation in other 

parts of the floodplain.

In Coastal A Zones, back bays, and along the banks of wide rivers where 

wave action is anticipated, fill is a less-effective site modification method 

because wave action may erode the fill, and adequate armoring or other, 

protection methods can be expensive. 

In V Zones, structural fill is not allowed as a method of elevating buildings. Beachfront areas with sand dunes pose special problems. Manmade 

alterations of sand dunes are not allowed unless analyses indicate that 

such modifications will not increase potential flood damage. 

Excavation:  Excavation on a given parcel of land alone rarely results in 

significant alteration of the floodplain. Excavation that modifies a site is 

more commonly used in conjunction with fill in order to offset or compensate for the adverse impacts of fill.

Earthen levee:  A levee is a specially designed barrier that modifies the 

floodplain by keeping the water away from certain areas (see Figure 3-26). 

Levees are significant structures that require detailed, site-specific geotechnical investigations; engineering analyses to identify whether flooding 

will be made worse on other properties; structural and site design to suit 

existing constraints; design of interior drainage (on the land side); and 

long-term commitment for maintenance, inspection, and repairs. It is important to remember that areas behind levees are protected only up to 

a certain design flood level—once overtopped or breeched, most levees 

fail and catastrophic flooding results. Levees that protect hospitals and 

other critical facilities usually are designed for at least the 0.2-percent-annual-chance flood (500-year) and have freeboard to increase the factor of 

safety. Depending on the site layout and duration of flooding, access for 

vehicles can be problematic. Low levees can be designed with road access; 
3-52 MAKING HOSPITALS SAFE FROM FLOODING

higher levees can be designed with vehicle access points that require special closures when flooding is predicted.

Floodwall:  Floodwalls are similar to levees in that they provide protection 

to certain areas (see Figure 3-26). Failure or overtopping of a floodwall 

can result in catastrophic flooding. A floodwall is a significant structure 

designed to hold back water of a certain depth based on the design flood 

for the site. Generally, floodwalls are most effective in areas with relatively 

shallow flooding and minimal wave action. As with levees, designs must 

accommodate interior drainage on the land side, and maintenance and 

operations are critical for adequate performance. Floodwalls that protect buildings that provide essential services usually are designed for the 

0.2-percent-annual-chance flood (500-year) and have freeboard to increase the factor of safety. If a protected facility is intended to remain 

operational during long-duration flooding, vehicle access to the site and 

pedestrian access to the building are required.

Figure 3-26:

Schematic of typical 

earthen levee and 

permanent floodwall

Figure 3-26:

Schematic of typical 

earthen levee and 

permanent floodwall
MAKING HOSPITALS SAFE FROM FLOODING 3-53

3.3.4 Elevation Considerations

The selection of the appropriate method of elevating a hospital in a special flood hazard area depends on many factors, including type of flood 

zone, costs, level of safety and property protection determined as acceptable risk, and others. 

Another consideration is the elevation of the 

lowest floor relative to the flood elevation. 

Table 3-1 in Section 3.1.6.4 summarizes the elevation requirements in ASCE 24. Given the 

importance of hospitals, elevation of the lowest 

floor to or above the 0.2 percent-annual-chance 

flood (500-year) elevation is crucial. Various 

methods used to elevate buildings in flood 

hazard areas are described below. 

In A Zones, the minimum requirement is that the lowest floor (including 

the basement) must be at or above the DFE (plus freeboard, if desired or 

required). For building elevation methods other than fill, the area under 

elevated buildings in A Zones may be used only for limited 

purposes: parking, building access, and limited storage (crawlspaces are 

treated as enclosures, see below). Owners and designers are cautioned 

that enclosures below the DFE are exposed to flooding and the contents 

will be damaged or destroyed by floodwaters. The walls surrounding an 

enclosure must have flood openings that are intended to equalize interior 

and exterior water levels in changing flood 

conditions, to prevent differential hydrostatic 

pressures leading to structural damage. The enclosed area must not contain utilities and 

equipment (including ductwork) below the required elevation. 

In a V Zone, the minimum requirement is that 

the elevation of the bottom of the lowest horizontal structural member of the lowest floor 

(including basement) must be at or above the 

DFE (plus freeboard, where required). Given 

the importance of hospitals, elevation to or 

above the 0.2-percent-annual-chance flood 

(500-year) elevation is appropriate and strongly 

recommended. The V Zone requirements are 

recommended in Coastal A Zones.

The area under elevated buildings in V Zones 

may be used only for parking, building access, 

and limited storage. The areas may be open 

 “Lowest floor” is the floor of the lowest 

enclosed area (including the basement). 

An unfinished or flood-resistant enclosure, 

usable solely for parking of vehicles, 

building access, or storage in an area 

other than a basement, is not the lowest 

floor, provided the enclosure is built in 

compliance with applicable requirements. 

 “Lowest floor” is the floor of the lowest 

enclosed area (including the basement). 

An unfinished or flood-resistant enclosure, 

usable solely for parking of vehicles, 

building access, or storage in an area 

other than a basement, is not the lowest 

floor, provided the enclosure is built in 

compliance with applicable requirements. 

Communities that participate in the NFIP 

require that a registered professional 

engineer or architect develop or review the 

structural design, specifications, and plans 

of buildings in V Zones, and certify that 

the design and methods of construction to 

be used are in accordance with accepted 

standards of practice. The standards of 

practice require that the foundation and 

structure attached thereto is anchored 

to resist flotation, collapse, and lateral 

movement caused by wind and water 

loads acting simultaneously on all building 

components. Water loading values are 

those associated with the base flood 

conditions, and wind loading values are 

those required by applicable State or local 

building codes and standards. 

Communities that participate in the NFIP 

require that a registered professional 

engineer or architect develop or review the 

structural design, specifications, and plans 

of buildings in V Zones, and certify that 

the design and methods of construction to 

be used are in accordance with accepted 

standards of practice. The standards of 

practice require that the foundation and 

structure attached thereto is anchored 

to resist flotation, collapse, and lateral 

movement caused by wind and water 

loads acting simultaneously on all building 

components. Water loading values are 

those associated with the base flood 

conditions, and wind loading values are 

those required by applicable State or local 

building codes and standards. 
3-54 MAKING HOSPITALS SAFE FROM FLOODING

or enclosed by lattice walls or screening. If areas are enclosed by solid 

walls, the walls must be specifically designed to break away under certain 

flood loads to allow the free passage of floodwaters under the building. 

Breakaway walls are non-load-bearing walls, i.e., they do not provide structural support for the building. They must be designed and constructed to 

collapse under the pressure of floodwaters in such a way that the supporting foundation system and the structure are not affected. 

Coastal communities along the Atlantic and Gulf coasts are subject 

to storm surge flooding generated by hurricanes and tropical storms. 

Depending on a number of variables, storm surge flood depths may significantly exceed the BFE. In addition, waves are likely to be higher than 

predicted for the base flood, and will occur in areas where significant 

wave action during the base flood is not expected. Application of the minimum requirements related to elevation of the lowest floor and foundation 

design does not result in flood resistance for such extreme conditions. 

Foundations for hospitals in areas subject to storm surge should be designed to elevate the building so that the lowest horizontal structural 

members are higher than the minimum required elevation. Additional elevation not only reduces damage that results from lower probability events, 

but the cost of Federal flood insurance is usually lower. Designers and 

owners should plan to use the lowest elevated floor for non-critical uses 

that, even if exposed to flooding more severe than the design flood, will 

not impair critical functioning during post-flood recovery.

Storm surge flooding and waves can cause scour and erosion, even at locations that are some distance from the shoreline. Foundation designs 

for hospitals in coastal communities should account for some erosion and 

local scour of supporting soil during low-probability surge events. Storm 

surge flooding can also produce large quantities of floating debris, even 

at locations that are some distance from the shoreline. Debris can damage 

nonstructural building components and, in some cases of prolonged battering, can lead to structural failure. Foundation designs for hospitals in 

coastal communities should account for debris loads. This is especially 

important where damage to other buildings in the area may generate additional debris, thereby increasing the loads. 

Notes on continuous load path:  In coastal communities and other areas exposed to high winds, designers should pay special attention to the 

entire roof-to-foundation load path when designing and specifying connections. Connections must be capable of withstanding simultaneous 

wind and flood forces. Poorly connected buildings may fail or float off 

foundations when floodwaters and waves are higher than the design 

flood elevation. Corrosion-resistant connections are critical for the 

long-term integrity of the structure, and should be inspected and maintained regularly. 
MAKING HOSPITALS SAFE FROM FLOODING 3-55

Communities may require a registered 

design professional to certify that buildings 

elevated on fill are reasonably safe from 

flooding. The FEMA NFIP Technical Bulletin 

10-01 discusses criteria for this certification.

Slab-on-grade foundation on structural fill:  This is 

considered to be the safest method to elevate 

a building in many flood hazard areas, except 

those where waves and high velocity flows may 

cause erosion. Consequently, this foundation 

type is not allowed in V Zones. Structural fill 

can be placed so that even if water rises up to 

the DFE, the building (see Figure 3-27) and 

building access would still be protected from flooding. The fill must be 

designed to minimize adverse impacts, such as increasing flood elevations on adjacent properties, increasing erosive velocities, and causing 

local drainage problems. To ensure stability, especially as floodwaters 

recede and the soils drain, fill must be designed for the anticipated 

water depths and duration. A geotechnical engineer or soil scientist 

may need to examine underlying soils to determine if the bearing capacity is sufficient to carry the added weight of fill, or if consolidation 

over time may occur. In addition, the effects of long-term compaction 

of the fill should be considered, and may prompt additional elevation as a factor of safety. The horizontal extent of the fill, away from 

the foundation, should be designed to facilitate access by emergency 

vehicles, with a minimum 25-foot width recommended. Engineered 

concrete slabs supported by piers should have sufficient resistance to 

erosion and scour if designed for anticipated flood conditions. Designers are cautioned to avoid excavating a basement into fill without 

added structural protection (and certification that the design meets the 

requirements for dry floodproofing), due to the potential for significant hydrostatic loads and uplift on basement floors.

Figure 3-27:

Structural fill was 

placed to elevate the 

Henrietta Johnson 

Medical Center 

above the shallow 

flood hazard area in 

Wilmington, DE. 

Figure 3-27:

Structural fill was 

placed to elevate the 

Henrietta Johnson 

Medical Center 

above the shallow 

flood hazard area in 

Wilmington, DE. 
3-56 MAKING HOSPITALS SAFE FROM FLOODING

Stem wall foundations:  Stem wall foundations have a continuous perimeter 

grade beam, or perimeter foundation wall, that is backfilled with compacted earth to the underside of the concrete floor slab (see Figure 3-28). 

This foundation type is not allowed in V Zones. Stem wall foundations are 

designed to come in contact with floodwaters on the exterior. They are 

more stable than perimeter wall foundations with crawlspaces, but could 

experience structural damage if undermined by local scour and erosion. 

Designs must account for anticipated debris and ice impacts, and incorporate methods and materials to minimize impact damage.

Columns or shear wall foundations (open foundations):  Open foundations 

consist of vertical load-bearing members (columns, piers, pilings, and 

shear walls) without solid walls connecting the vertical members. Open 

foundations minimize changes to the floodplain and local drainage patterns, and the area under the building can be used for parking or other 

uses (see Figure 3-29). The design of the vertical members must also account for hydrodynamic loads and debris and ice impact loads. Flood 

loads on shear walls are reduced if they are oriented parallel to the anticipated direction of flow. If erodible soils are present and local scour is 

likely, both conditions must be accounted for in determining embedment 

depth. Depending on the total height of the elevated facility, the design 

may need to take into consideration the increased exposure to wind and 

uplift, particularly where loads are expected from breaking waves. 

Figure 3-28:

Typical stem wall 

foundation
MAKING HOSPITALS SAFE FROM FLOODING 3-57

In V Zones, buildings must be elevated using open foundations, which 

consist of vertical load-bearing members (columns, piers, pilings, and 

shear walls) without solid walls connecting the vertical members. The design of the vertical members must also account for hydrodynamic loads 

and debris impact loads. Flood loads on shear walls are reduced if the 

walls are oriented parallel to the anticipated direction of flow. Erodible 

soils may be present and local scour may occur; both must be accounted 

for in designs by extending the load-bearing members and foundation elements well below the expected scour depth. 

Figure 3-29: Tampa General Hospital had its new Emergency Department wing designed to be elevated on 

columns, well above hurricane storm surge flooding elevations. 

Source: Tampa General Hospital

Continuous perimeter walls (enclosed foundations with crawlspace):  Unlike 

stem wall foundations, continuous perimeter walls enclose an open 

area or crawlspace (see Figure 3-30). The perimeter walls must have 

flood openings, also called vents) that are intended to equalize interior and exterior water levels automatically during periods of rising and 

falling flood levels, to prevent differential hydrostatic pressures that 

could lead to structural damage. Flood openings may be engineered 

and certified for the required performance, or they must meet prescriptive requirements (notably, the opening must provide at least 1 

square inch of net open area for each square foot of area enclosed). 

Perimeter wall design must also account for hydrodynamic loads, and 

debris and ice impact loads. Enclosed crawlspaces must not contain 

utilities or equipment (including ductwork) below the required elevation. Designers must provide adequate underfloor ventilation and 

subsurface drainage to minimize moisture problems after flooding. 

This foundation type is not allowed in V Zones.
3-58 MAKING HOSPITALS SAFE FROM FLOODING

Pier supports for manufactured and portable units:  Manufactured buildings 

and portable units must be elevated above the DFE (plus freeboard, if required). Pier supports must account for hydrodynamic loads and debris 

and ice impact loads, and units must be anchored to resist wind loads. Although written specifically for manufactured housing units, FEMA 85, 

Manufactured Home Installation in Flood Hazard Areas, has useful information that is applicable to portable units.

3.3.4.1 The Case of Boulder Community Foothills 

Hospital, Boulder, Colorado 

Located on the east side of the City of Boulder, Colorado, the Boulder 

Community Foothills Hospital (BCFH) is framed by the Flatirons, the first 

of the Rocky Mountains rising steeply above the Front Range plains to 

the east. The new facility, completed in 2003 but not fully occupied until 

2004, is an expansion of the existing Boulder Community Hospital located in the older part of the city. 

The master site plan for complete development of the site is shown in 

Figure 3-31. The primary building on the site incorporates the hospital 

Figure 3-30:

Typical crawlspace 

with flood openings
MAKING HOSPITALS SAFE FROM FLOODING 3-59

and medical building. It consists of a main reception area linking two 

large wings. The hospital wing is cast-in-place concrete with a steel frame 

roof. The medical building wing is steel frame, fireproofed with concrete 

floor slabs. Exteriors are brick veneer on metal studs. The two wings have 

three floors above-grade and one floor below-grade. The original designs 

complied with the 1997 Uniform Building Code for the core and shell; 

clinical spaces and interior designs comply with the 2000 International 

Building Code. Other buildings on the campus include the Table Mesa 

Medical Building, a free-standing parking garage, and the utility plant 

building. The Cancer Care Center and another parking garage are under 

construction. 

BCFH is licensed for a maximum patient capacity of 54 and has approximately 475 employees, of which about 120 are non-medical. Between the 

two wings, 220,000 square feet of space is available for patient care (including in-patient rooms, clinics, operating rooms, and the emergency 

room), and laboratory and administrative uses (including reception, 

waiting areas, and offices). 

In the early planning of the hospital, a search for suitable sites revealed 

that few vacant parcels of sufficient size (16-17 acres) were available within 

the city limits. However, a 39-acre parcel in the county was just over the 

city boundary and could be annexed into the city. The site was entirely 

within the floodplain of Boulder Creek and a tributary, Bear Canyon 

Creek, which come together on the property. Two reservoirs are located 

upstream: Barker Dam on Boulder Creek and Grosse Reservoir on Bear 

Canyon Creek. 

Figure 3-31:

Master site plan of the 

Boulder Community 

Foothills Hospital, 

Boulder, CO. 

SOURCE: CIVITAS, INC. and

OZ ARCHITECTURE

Figure 3-31:

Master site plan of the 

Boulder Community 

Foothills Hospital, 

Boulder, CO. 

SOURCE: CIVITAS, INC. and

OZ ARCHITECTURE
3-60 MAKING HOSPITALS SAFE FROM FLOODING

Design of the hospital and the site began while negotiations for the annexation were underway. As part of the conditions of annexation, the 

city required that the design of the hospital meet the standards of the 

city’s building code and floodplain management ordinance, which include some provisions that are more restrictive than those required by the 

county. The requirements resulted in several measures intended to provide a higher level of protection against flood hazards than is required for 

buildings that do not provide critical services. 

The 17 acres of the site that were needed for the campus, entirely outside 

of the designated floodway, were proposed to be filled to an elevation of 

one-foot above the 100-year flood elevation. The remaining 22 acres were 

placed in conservation easement. Engineering analyses were performed 

to demonstrate that no increase in flood elevations would result. The city 

required approval of a Conditional Letter of Map Revision from FEMA 

prior to approving the plans. The fill was required to be compacted to 95 

percent of the maximum density obtainable with the Standard Proctor 

Test method. The earthen fill is gently sloped to natural grade and various 

landscaping elements and retaining walls provide a pleasing transition 

(Figure 3-32). 

In the BCFH main building, the first floors are used for reception, cafe, 

ambulatory services, the emergency room, and a six-patient Intensive 

Care Unit. All patient rooms are on the second and third floors of the 

three wings, which are built off a single-story connecting reception area. 

In addition to a separate parking garage structure, some parking is provided in a one-level, below-grade parking garage. The three patient wings 

have below-grade floors that are used for offices, laundry, laboratories, 

Figure 3-32:

Boulder Community 

Foothills Hospital 

main entrance, with 

landscaping and 

retaining walls for 

portion of site filled 

to the 500-year flood 

elevation (Boulder 

Creek is behind 

photographer).

Figure 3-32:

Boulder Community 

Foothills Hospital 

main entrance, with 

landscaping and 

retaining walls for 

portion of site filled 

to the 500-year flood 

elevation (Boulder 

Creek is behind 

photographer).
MAKING HOSPITALS SAFE FROM FLOODING 3-61

materials management, and building service and equipment. To provide 

natural light, a portion of these below-grade floors are surrounded by a 

moat (Figure 3-33). Because of anticipated high groundwater and the fact 

that the below-grade areas are constructed into fill that is subject to saturation during flooding, all below-grade areas are designed and certified 

as floodproofed spaces. Floodproofing extends 2 feet above the 100-year 

flood elevation, and 1 foot above the 500-year flood elevation.

Although the risk of flooding is very low, hospital personnel have identified low points where floodwaters that rise higher than the predicted 

500-year flood could begin to affect the facility. The lowest point of entry 

is the ramp to the parking garage, which is more than a foot higher than 

the 500-year water surface elevation (Figure 3-34). A supply of sandbags 

is kept onsite for placement across the ramp. The next most susceptible 

location is the air handler, although its ground elevation is somewhat 

higher than the 500-year flood level (Figure 3-35).

Figure 3-33:

Below-grade office 

spaces provide natural 

light by construction 

of reinforced moat 

designed to provide 

flood protection for a 

foot above the 500-

year flood elevation.

Figure 3-33:

Below-grade office 

spaces provide natural 

light by construction 

of reinforced moat 

designed to provide 

flood protection for a 

foot above the 500-

year flood elevation.
3-62 MAKING HOSPITALS SAFE FROM FLOODING

The City of Boulder has experienced severe flooding of Boulder Creek 

on numerous occasions, and is widely known for its efforts to clear portions of the floodplain for use as a greenway and public open space. 

Prompted by concern about how effectively the city could respond to serious flooding, in early 2006 the city developed a scenario that involved 

catastrophic flooding, bridge failures, and numerous flooded buildings 

and neighborhoods. The drill was organized with partners throughout 

the area, including the Boulder Community Foothills Hospital and other 

health care facilities. 

BCFH, linked to area-wide warnings through NOAA weather radios and 

the county’s emergency management office, had an emergency action 

Figure 3-34:

Ramp entrance to 

below-grade parking 

garage. Note 

retaining walls on 

either side; ramp 

crests at about 16-

inches above the 

500-year flood 

elevation.

Figure 3-35:

The upper floors 

provide patient 

care. The top of the 

retaining wall (on 

right) and the air 

handler (left of center) 

are approximately 

one-foot above the 

500-year flood 

elevation.
MAKING HOSPITALS SAFE FROM FLOODING 3-63

plan, but the participation in the city’s flood drill resulted in a number 

of improvements in communications and protocols for ensuring patient safety. 

The original downtown Boulder Community Hospital, built in the 1940s, is partially affected by the 

500-year floodplain of Goose Creek. The hospital has implemented measures to reduce flooding. 

The side of the building that is susceptible to high water from Goose Creek has two doors that are 

protected by swinging panels permanently mounted in the retaining wall (Figure 3-41). The panels 

are designed with gaskets to create a seal intended to keep water out when they are deployed. 

After consideration of the potential for damage and options for protection, a decision was made 

to leave air-handling equipment at grade in the area that is predicted to flood. The equipment 

provides extra ventilation for office space, a function that would not be impaired if the equipment 

was damaged and not functional for a short period of time.

Although not associated with overflow of the creek during wet weather, subsurface drainage off 

the mountains flows through an abandoned sewer that runs under the building and often overflows 

through a manhole in the center of a courtyard. To protect the building, sandbags are stockpiled 

onsite and deployed at the two doors that lead from the courtyard into the building.

3.3.5 Dry Floodproofing Considerations

Dry floodproofing involves a combination of design and special features that are intended both to prevent water infiltration and resist flood 

forces. According to the NFIP regulations, 

non­residential buildings and nonresidential 

portions of mixed-use buildings in A Zones 

may be dry floodproofed. Areas used for living 

and sleeping purposes in health care facil­ities 

may not be dry floodproofed because of risks 

to occupants. Although floodproofing of the 

nonresidential spaces is allowed, careful consideration must be given to the possible risk to 

occupants and additional physical damage. Dry 

floodproofing is not allowed in V Zones. 

Dry floodproofing typically involves structural 

reinforcement so that exterior walls are sufficiently robust to withstand the loads described 

in Section 3.1.3 (hydrostatic loads, hydrodynamic loads, wave loads, and debris impact 

loads). Exterior walls must also be designed to 

prevent infiltration and seepage of water, 

Communities that participate in the NFIP 

require that a registered professional 

engineer or architect develop or review the 

structural design, specifications, and plans, 

and certify that the dry floodproofing 

design and methods of construction to be 

used are in accordance with accepted 

standards of practice. The standards of 

practice require that the building, together 

with attendant utility and sanitary facilities, 

be designed so that it is watertight, with 

walls substantially impermeable to the 

passage of water and with structural 

components having the capability of 

resisting hydrostatic and hydrodynamic 

loads and effects of buoyancy associated 

with the design flood event.

Communities that participate in the NFIP 

require that a registered professional 

engineer or architect develop or review the 

structural design, specifications, and plans, 

and certify that the dry floodproofing 

design and methods of construction to be 

used are in accordance with accepted 

standards of practice. The standards of 

practice require that the building, together 

with attendant utility and sanitary facilities, 

be designed so that it is watertight, with 

walls substantially impermeable to the 

passage of water and with structural 

components having the capability of 

resisting hydrostatic and hydrodynamic 

loads and effects of buoyancy associated 

with the design flood event.
3-64 MAKING HOSPITALS SAFE FROM FLOODING

whether through the wall or the openings, including the places where 

utility lines penetrate the envelope. Floodproofed buildings constructed 

on permeable soils require additional design attention, because they are 

also susceptible to hydrostatic pressure from below (buoyancy). An alternative to reinforcement of the structure’s walls involves the installation of 

a permanent floodwall that is slightly offset from the exterior of the structure, but designed to be integral to the foundation. 

All flood protection measures are designed for certain flood conditions. 

Considering the possibility that the design conditions can be exceeded 

(i.e., water can rise higher than the protective 

structures) a dry floodproofed building may, 

in such circumstances, sustain catastrophic 

damage. As a general rule, dry floodproofing 

is a poor choice for new hospitals when avoidance of the floodplain or elevation methods to 

raise the building above the flood level can be 

applied. Floodproofing may be acceptable for 

retrofitting existing buildings under certain circumstances (see Section 3.4.5). 

A number of dry floodproofing limitations and requirements are specified in ASCE 24:

m Dry floodproofing is limited to areas where flood velocities at the site 

are less than or equal to 5 feet per second.

m If human intervention is required to deploy measures to protect 

doors and windows, the flood warning time shall be a minimum of 

12 hours unless the community operates a flood warning system and 

implements a notification procedure that provides sufficient time to 

undertake these measures.

m At least one door satisfying building code requirements for an exit 

door or primary means of escape must be provided above the level of 

protection.

m An emergency plan, approved by the community and posted in at least 

two conspicuous locations, is required in floodproofed buildings; the 

plan is intended to specify the location of panels and hardware, 

methods of installation, conditions that activate deployment, a 

schedule for routine maintenance of any aspect that may deteriorate 

over time, and periodic practices and drills. 

Windows and doors that are below the flood level used for dry floodproofing design present significant potential failure points. They must be 

Although dry floodproofing of facilities in 

Coastal A Zones is allowed by the NFIP, 

designs that comply with the IBC must take 

into consideration the additional forces 

associated with wave impacts, which may 

make dry floodproofing a less feasible 

alternative. 

Although dry floodproofing of facilities in 

Coastal A Zones is allowed by the NFIP, 

designs that comply with the IBC must take 

into consideration the additional forces 

associated with wave impacts, which may 

make dry floodproofing a less feasible 

alternative. 
MAKING HOSPITALS SAFE FROM FLOODING 3-65

The following documents provide 

additional information about 

floodproofing: Flood Resistant 

Design and Construction (ASCE 24-

05), Flood Proofing: How to Evaluate 

Your Options (USACE, 1993), Flood 

Proofing Regulations (USACE, 1995), 

Floodproofing Non-Residential 

Structures (FEMA 102), Non-Residential 

Floodproofing – Requirements and 

Certification (FIA-TB-3), Flood Proofing 

Systems & Techniques (USACE, 1984). 

The following documents provide 

additional information about 

floodproofing: Flood Resistant 

Design and Construction (ASCE 24-

05), Flood Proofing: How to Evaluate 

Your Options (USACE, 1993), Flood 

Proofing Regulations (USACE, 1995), 

Floodproofing Non-Residential 

Structures (FEMA 102), Non-Residential 

Floodproofing – Requirements and 

Certification (FIA-TB-3), Flood Proofing 

Systems & Techniques (USACE, 1984). 

specially designed units (see Figure 3-36) or be 

fitted with gasketed, mountable panels that are 

designed for the anticipated flood conditions 

and loads. Generally speaking, it is difficult to 

protect window and door openings from water 

more than a few feet deep. The framing and 

connections must be specifically designed for 

these protective measures, or water pressure 

may cause window and door frames to separate 

from the building. 

Dry floodproofing is required to extend to 1 or 

2 feet above the DFE (see Table 3-1). For the 

purpose of obtaining NFIP flood insurance, 

the floodproofing must extend at least 1 foot 

above the BFE, or the premiums will be very high. A higher level of protection is recommended. 

Figure 3-36: Permanent watertight doors 

designed for deep water

SOURCE: PRESRAY CORPORATION

Floodproofing techniques are considered to be permanent measures if 

they are always in place and do not require any specific human intervening action to be effective. Use of contingent floodproofing measures 

that require installation or activation, such as window shields or inflatable barriers, may significantly reduce the certainty that floodproofing 

will be effective. Rigorous adherence to a periodic maintenance plan is 

critical to ensure proper functioning. The facility must have a formal, 

written plan, and the people responsible for implementing the measures 

must be informed and trained. These measures also depend on the time-
3-66 MAKING HOSPITALS SAFE FROM FLOODING

liness and credibility of the warning. In addition, floodproofing devices 

often rely on flexible seals that require periodic maintenance and that, 

over time, may deteriorate and become ineffective. Therefore, a maintenance plan must be developed and a rigorous annual inspection and 

training must be conducted. 

Safety of occupants is a significant concern with dry floodproofed buildings, because failure or overtopping of the floodproofing barriers is likely 

to cause catastrophic structural damage. When 

human intervention is required for deploying 

of barriers, those responsible for implementing the measures remain at risk, even if 

a credible warning system is in place, because 

of the many uncertainties associated with predicting the onset of flood conditions. 

3.3.6 Flood-Resistant Materials

All structural materials, nonstructural materials, and connectors that are 

used below certain elevations (see Table 3-1) are to be flood-resistant. 

Flood-resistant materials have sufficient strength, rigidity, and durability 

to adequately resist flood loads and damage due to saturation. They are 

building materials that are capable of withstanding direct and prolonged 

contact with floodwaters without sustaining any damage that requires 

more than cosmetic repair. As defined in ASCE 24, the term “prolonged 

contact” means partial or total inundation by floodwaters for 72 hours for 

non-coastal areas (fresh water) or 12 hours for coastal areas. 

In general, materials that are exposed to floodwaters are to be capable of resisting damage, 

deterioration, corrosion, or decay. Typical construction materials range from highly resistant 

to not at all resistant to water damage. FEMA 

NFIP Technical Bulletin FIA-TB-2 contains tables with building materials, classified based on 

flood resistance (Table 3-2).

Dry floodproofed hospitals must not 

be considered completely safe for 

occupancy during periods of high water; 

floodproofing mea­sures are intended only 

to reduce physical damage. 

Dry floodproofed hospitals must not 

be considered completely safe for 

occupancy during periods of high water; 

floodproofing mea­sures are intended only 

to reduce physical damage. 

FEMA NFIP Technical Bulletin FIA-TB-2, 

Flood-Resistant Materials Requirements,

provides some additional information. 

Many types of materials and application 

products are classified by degrees of 

resistance to flood damage. 

FEMA NFIP Technical Bulletin FIA-TB-2, 

Flood-Resistant Materials Requirements,

provides some additional information. 

Many types of materials and application 

products are classified by degrees of 

resistance to flood damage. 
MAKING HOSPITALS SAFE FROM FLOODING 3-67

In coastal areas, airborne salt aerosols and inundation with saline water 

increase the potential for corrosion of some metals. Structural steel and 

other metal components that are exposed to corrosive environments 

should be stainless steel or hot-dipped galvanized after fabrication.

In areas away from the coast, exposed structural steel should be primed, 

coated, plated, or otherwise protected against corrosion. Secondary components such as angles, bars, straps, and anchoring devices, as well as 

other metal components (plates, connectors, screws, bolts, nails angles, 

bars, straps, and the like) should be stainless steel or hot-dipped galvanized after fabrication. 

Concrete and masonry that are designed and constructed in compliance 

with applicable standards are generally considered to be flood-resistant. 

However, masonry facings are undesirable finishes unless extra anchoring 

is added to prevent separation (see Figure 3-37). Wood and timber members exposed to floodwaters should be naturally decay-resistant species, or 

pressure treated with appropriate preservatives. 

Table 3-2: Classes of Flood-Resistant Materials

NFIP Class Class Description Acceptable

5 Highly resistant to floodwater damage. Materials in this class are permitted for 

partially enclosed or outside uses with essentially unmitigated flood exposure.

4

Resistant to floodwater damage. Materials in this class may be exposed to 

and/or submerged in floodwaters in interior spaces and do not require special 

waterproofing protection.

Unacceptable

3 Resistant to clean water damage. Materials in this class may be submerged in 

clean water during periods of intentional flooding.

2 Not resistant to water damage. Materials in this class require essentially dry 

spaces that may be subject to water vapor and slight seepage.

1 Not resistant to water damage. Materials in this class require dry conditions.

Source: From U.S. Army Corps of Engineers, FloodProofing Regulations (1995).
3-68 MAKING HOSPITALS SAFE FROM FLOODING

3.3.7 Access Roads

Roads and entrances leading to hospitals should be designed to provide safe access at all times, to minimize impacts on flood hazard areas, 

to minimize damage to the road itself, and to minimize exposing vehicles to dangerous situations. Even if the hospital is elevated and protected 

from flood damage, when access is impaired, functionality is also impaired. Planners and designers should take the following factors into 

consideration.

Safety factors:  Although a hospital’s access road off the primary surface street may not be required to carry regular traffic like other streets, 

a flood-prone road always presents a degree of risk to public safety. To 

minimize those risks, some State or local regulatory authorities require 

that access roads be designed so that the driving surface is at the DFE, or 

no more than 1 to 2 feet below the DFE. At a minimum, a hospital’s access road should be at least as high as the adjacent public road, so that 

the same level of access is provided during conditions of flooding. To 

maximize evacuation safety, two separate access roads to different feeder 

roads are recommended. In some circumstances, especially long-duration 

flooding where a hospital is built on fill, access roads designed to be above 

flood levels would help the hospital to continue its operations. 

Figure 3-37:

Brick facing separated from masonry wall 

(Hurricane Katrina, 2005).
MAKING HOSPITALS SAFE FROM FLOODING 3-69

Floodplain impacts:  Engineering analyses may be required to determine 

the effects on flood elevations and flow patterns if large volumes of fill are 

required to elevate a road to minimize or eliminate flooding above the 

driving surface.

Drainage structure and road surface design:  The placement of multiple drainage 

culverts, even if not needed for local drainage, can facilitate the passage of 

floodwaters and minimize the potential for a road embankment to act as a 

dam. Alternatively, an access road can be designed with a low section over 

which high water can flow without causing damage. Embankments should 

be designed to remain stable during high water and as waters recede. 

They should be sloped and protected to resist erosion and scour. Similarly, 

the surface and shoulders of roads that are intended to flood should be 

designed to resist erosion. The increased resistance to erosion may be accomplished by increasing the thickness of the road base.

3.3.8 Utility Installations

Utilities associated with new hospitals in flood hazard areas must be protected either by elevation or special designs and installation measures. 

Utilities subject to this provision include all systems, equipment, and fixtures, including mechanical, electrical, plumbing, heating, ventilating, 

and air conditioning. Potable water systems (wellheads and distribution 

lines) and wastewater collection lines are addressed in Section 3.3.9. 

Utility systems and equipment are best protected when elevated above the 

DFE (plus freeboard, if required). Equipment that is required for emergency functioning during or immediately after 

an event, such as emergency generators and 

fuel tanks, is best installed well above the DFE. 

In some cases, equipment can be located inside 

protective floodproofed enclosures, although it 

must be recognized that if flooding exceeded 

the design level of the enclosure, the equipment would be adversely affected (see Figure 

3-38). De­signers should pay particular attention to underfloor utilities and ductwork to ensure that they are properly 

elevated. Plumbing conduits, water supply lines, gas lines, and electric cables that must extend below the DFE should be located, anchored, and 

protected to resist the effects of flooding. Equipment that is outside of elevated building also must be elevated:

m In A Zones, equipment may be affixed to raised support structures or 

mounted on platforms that are attached to or cantilevered from the 

primary structure. 

For more information on utility installations, 

see Protecting Building Utilities from Flood 

Damage: Principles and Practices for 

the Design and Construction of Resistant 

Building Utility Systems (FEMA 348).
3-70 MAKING HOSPITALS SAFE FROM FLOODING

m In V Zones and Coastal A Zones, equipment may be affixed to raised 

support structures designed for the flood conditions (waves, debris 

impact, erosion, and scour) or mounted on platforms that are 

attached to or cantilevered from the primary structure. If an enclosure 

is constructed under the elevated building, the designer must take 

care that utilities and attendant equipment are not mounted on or do 

not pass through walls that are intended to break away. 

Although it is difficult to achieve, the model building codes and NFIP regulations provide an alternative that allows equipment to be located below 

the DFE. This alternative requires that such equipment be designed, 

constructed, and installed to prevent floodwaters from entering or accumulating within the components during flood events. 

Figure 3-38:

Equipment room with 

watertight door

SOURCE: Presray 

Corporation
MAKING HOSPITALS SAFE FROM FLOODING 3-71

3.3.9 Potable Water and Wastewater

Systems

New installations of potable water systems and wastewater collection 

systems are required to resist flood damage, including damage associated with infiltration of floodwaters and discharge of effluent. Health 

concerns arise when water supply systems are exposed to floodwaters. 

Contamination from flooded sewage systems poses additional health and 

environmental risks. Onsite water supply wellheads should be located on 

land elevated from the surrounding landscape to allow contaminated surface water and runoff to drain away. Well casings should extend above the 

DFE, and casings should be sealed with a tight-fitting, floodproof, and 

vermin-proof well cap. The space between the well casing and the side of 

the well must be sealed to minimize infiltration and contamination by surface waters. 

Sewer collection lines should be located and designed to avoid infiltration and backup due to rising floodwaters. Devices designed to prevent 

backup are available and are recommended to provide an added measure 

of protection. 

Onsite sewage systems usually are not used as the primary sewage disposal systems for new hospitals. However, owners, planners and designers 

should consider a backup onsite system if a facility’s functionality can be 

impaired when the public system is affected by flooding. Local or State 

health departments may impose constraints that limit or prevent locating 

septic fields in floodplain soils or within a mapped flood hazard area. If 

allowed, septic fields should be located on the highest available ground 

to minimize inundation and damage by floodwaters. An alternative to a 

septic field is installation of a holding tank that is sized to contain wastewater for a period of time, perhaps a few days, when the municipal system 

is out of service.

3.3.10 Storage Tank Installations

Aboveground and underground storage tanks located in flood hazard 

areas must be designed to resist flotation, collapse, and lateral movement. 

ASCE 24 specifies that aboveground tanks be elevated or constructed, installed, and anchored to resist at least 1.5 times the potential buoyant and 

other flood forces under design flood conditions, assuming the tanks are 

empty. Similarly, underground tanks are to be anchored to resist at least 

1.5 times the potential buoyant forces under design flood conditions, 

assuming the tanks are empty. In all cases, designers are cautioned to address hydrodynamic loads and debris impact loads that may affect tanks 
3-72 MAKING HOSPITALS SAFE FROM FLOODING

that are exposed to floodwaters. Vents and fill openings or cleanouts 

should be elevated above the DFE or designed to prevent the inflow of 

floodwaters or outflow of the contents of tanks. 

3.3.11 Accessory Structures

Depending on the type of accessory structures, full compliance with floodplain management regulations is appropriate and may be required. For 

example, mechanical buildings, storage buildings, and buildings used for 

ancillary purposes, such as medical offices and therapy clinics, are not 

considered to be accessory in nature and must be elevated and protected 

to the same standards as other buildings. 

Some minor accessory structures need not fully comply, but may be “wet 

floodproofed” using techniques that allow them to flood while minimizing damage. Accessory structures must be anchored to resist flotation, 

collapse, and lateral movement. Flood-resistant materials must be used 

and utilities must be elevated above the DFE (plus freeboard, if required). 

In A Zone flood hazard areas, openings in walls must be provided to allow 

the free inflow and outflow of floodwaters to minimize the hydrostatic 

loads that can cause structural damage. Because wet floodproofed accessory buildings are designed to flood, hospital staff must be aware that 

contents will be damaged. 
MAKING HOSPITALS SAFE FROM FLOODING 3-73

3.4 RISK REDUCTION FOR EXISTING 

HOSPITALS

3.4.1 Introduction

Section 3.2 describes the type of damage that can be sustained by 

hospitals that already are located in flood hazard areas. The vulnerability of these facilities can be reduced, if they can be made 

more resistant to flood damage. Decisionmakers may take such action 

when flood hazards are identified and there is a desire to undertake risk 

reduction measures proactively. Interest may be prompted by a flood or 

by the requirement to address flood resistance as part of proposed substantial improvement or an addition. Some questions and guidance 

intended to help identify building characteristics of importance when 

considering risk reduction measures for existing facilities are included in 

the checklist in Section 3.6.

Work on existing buildings and sites is subject 

to codes and regulations, and the appropriate 

regulatory authority with jurisdiction should 

be consulted. With respect to reducing flood 

risks, work generally falls into the categories described in the following subsections.

3.4.2 Site Modifications

Modifying the site of an existing facility that is 

subject to flooding requires careful examination by an experienced professional engineer. 

Determining the suitability of a specific measure requires a complex evaluation of many 

factors, including the nature of flooding and 

the nature of the site. The first part of Table 

3-3 in Section 3.5 identifies elements that influOwners and operators of public and notfor-profit hospitals should be aware of the 

importance of flood insurance coverage 

for facilities that are located in the flood 

hazard areas shown on NFIP maps. If 

not insured for flood peril, the amount of 

flood insurance that should have been in 

place will be deducted from any Federal 

disaster assistance payment that would 

otherwise have been made available. A 

particular facility may have to absorb up 

to $1 million in un-reimbursable flood 

losses per building, because the NFIP 

offers $500,000 in building coverage 

and $500,000 in contents coverage for 

nonresidential buildings (coverage limits as 

of early 2006). 
3-74 MAKING HOSPITALS SAFE FROM FLOODING

ence the choice of mitigation measures applicable to existing sites. Some 

flood characteristics may make it infeasible to apply site modification measures to existing facilities (e.g., depths greater than 3 to 4 feet, very high 

velocities, insufficient warning because of flash flooding or rapid rate of 

rise, and very long duration). In Coastal A Zones, wave conditions must be 

accounted for in design of site modifications. Such modifications are not 

allowed in V Zones. 

A common problem with all site modifications is the matter of access. 

Depending on the topography of the site, construction of barriers to 

floodwaters may require special access points. Access points may be protected with manually installed stop-logs or designed gates that drop in, 

slide, or float into place. Whether activated by automatic systems or manually operated, access protection requires sufficient warning time.

Other significant constraining factors include poor soils and insufficient 

land area, which can make site modifications either infeasible or very 

costly. For any type of barrier, rainfall that collects on the dry side must be 

accounted for in the design, whether through adequately sized stormwater 

storage basins set aside for this purpose, or by providing large-capacity 

pumps to move collected drainage to the water side of the barrier.

Each of these site modification measures described below has limitations, 

including the fact that floods larger than the design flood will exceed the 

level of protection.

Regrading the site (berm):  Regrading of the site, or the construction of an 

earthen berm, may provide adequate protection for situations in which a 

facility is exposed to relatively shallow flooding, and sufficient land area is 

available.

Earthen levee:  Earthen levees are engineered structures that are designed 

to keep water away from certain areas and buildings. Hydraulic analyses 

and geotechnical investigations are required to determine their feasibility 

and effectiveness. The use of earthen levees to protect existing facilities 

is constrained by the availability of land (levees have a large “footprint” 

and require large land areas), cost (including availability of suitable fill 

material and long-term maintenance), and access difficulties. Locating levees and floodwalls within a designated floodway is generally not allowed. 

Rapid onset flooding makes it impractical to design a flood levee with access points that require installation of a closure system. Additionally, high 

velocity flows can cause erosion and reduce the stability of earthen levees. 

Permanent floodwall:  Floodwalls are freestanding, permanent engineered 

structures designed to prevent encroachment of floodwaters. Typically, 

a floodwall is located some distance from a building, so that structural 
MAKING HOSPITALS SAFE FROM FLOODING 3-75

modification of the existing building is not required. Depending on the 

topography of the site, floodwalls may protect only the low side (in which 

case they must “tie” into high ground) or completely surround a site 

(which may affect access because special closure structures are required 

and must be installed before the onset of flooding, see Figure 3-39).

Mobilized floodwall:  This category of flood protection measures includes 

fully engineered flood protection structures that have permanent features 

(foundation and vertical supports) and features that require human intervention when a flood is predicted (horizontal components called planks 

or stop-logs). Mobilized floodwalls have been used to protect entire sites, 

or to tie into permanent floodwalls or high ground. Because of the manpower and time required for proper placement, these measures are better 

suited to conditions that allow long warning times.

3.4.3 Additions

Model building codes generally treat additions as new construction, and 

require hospital additions in flood hazard areas to be elevated or dry 

floodproofed to minimize exposure to flooding. However, full compliance 

with the code and NFIP requirements is only 

required if an addition is a substantial improvement (i.e., the cost of the addition plus all 

other costs associated with the work equal or 

exceed 50 percent of the market value of the 

building, see Section 3.1.6.1 and Section 

Figure 3-39: A masonry 

floodwall with multiple 

engineered openings

in Fargo, ND during 

flooding in 2001.

SOURCE: Flood Central

America, LLC

For more information on additions and 

substantial improvements, see Answers to 

Questions About Substantially Damaged 

Buildings (FEMA 213).
3-76 MAKING HOSPITALS SAFE FROM FLOODING

3.1.6.2). Designers are cautioned that even the existing buildings may be 

required to comply with the flood-resistant provisions of the code or local 

ordinances, if the addition is structurally connected to the existing 

building and is determined to be a substantial improvement. 

Section 3.3.4 outlines foundation methods used to elevate buildings that 

also are applicable to additions. Elevation of an addition on fill may not 

be feasible unless structural fill can be placed adjacent to the existing 

building. Utility service equipment for additions must meet the requirements for new installations (see Section 3.3.7).

If an evaluation determines that dry floodproofing is appropriate, additions may be floodproofed (see Section 3.3.5). To provide adequate 

protection for the addition, floodproofing must be applied to all exterior 

walls and the wall adjoining the existing building. Openings, including 

doors between the addition and existing building, must also be protected.

With respect to code compliance and designing additions to resist flood 

damage, one of the more significant issues to be considered is ease of access. If the lowest floor of the existing facility is below the DFE, steps, 

ramps, or elevators will be required for the transition to the new addition (See Figure 3-40). Some jurisdictions may contemplate allowing 

variances to the requirement for elevation, because alternative means of 

access are available, such as ramps and elevators. Under the regulations 

of the NFIP and FEMA guidance, it is not considered appropriate to 

grant such a variance. 

Figure 3-40:

Tampa General 

Hospital solved 

the problem of 

access to the new 

elevated Emergency 

Department by 

designing a vehicle 

ramp. Visitors and 

ambulatory patients 

take elevators from the 

ground floor. 

Source: Tampa General

Hospital
MAKING HOSPITALS SAFE FROM FLOODING 3-77

3.4.4 Repairs, Renovations, and Upgrades

Every hospital considered for upgrades and renovations, or being repaired after substantial damage from any cause, must be examined for 

structural integrity and stability to determine compatibility with structural 

modifications that may be required to achieve acceptable performance. 

When an existing facility is located in a flood hazard area, that examination should include consideration of measures to improve resistance to 

flood damage and to reduce risks. 

The model building codes and the regulations 

of the NFIP require that work constituting 

“substantial improvement” of an existing 

building be in compliance with the flood-resistant provisions of the code. Non-substantial 

improvements should take into account measures to reduce future flood damage, such 

as those described in Section 3.3, emergency 

measures (see Section 3.4.9), and wet floodproofing measures that allow water to enter the 

building to avoid structural damage. 

Compliance with flood-resistant provisions 

means that the existing building must be elevated or dry floodproofed. Both options can 

be difficult for existing hospitals, given the typical use, size, and complexity of some of these 

buildings. Retrofit dry floodproofing (described in Section 3.4.5) is generally limited to water depths of 3 feet or 

less, provided an assessment by a qualified design professional determines 

that the building is capable of resisting the anticipated loads, or can be 

modified to provide that level of performance. 

Elevating an existing building presents an entirely different set of 

challenges and also requires detailed structural engineering analyses. It 

involves the same equipment and methods used to move other types of 

buildings; expert building movers have successfully moved large, heavy, 

and complex buildings, sometimes by segmenting them. A building that is 

elevated in-place must meet the same performance standards set for new 

construction.

Additional information on rehabilitation 

of existing buildings is provided in: Flood 

Proofing: How to Evaluate Your Options

(USACE, 1993), Floodproofing NonResidential Structures (FEMA 102), 

Floodproofing—Requirements and 

Certification (FIA-TB-3), and Engineering 

Principles and Practices for Retrofitting 

Flood-prone Buildings (FEMA 259). 

Although written primarily for homes, this 

last reference contains very detailed 

checklists and worksheets that can 

be modified. They also provide some 

guidance for evaluating the costs and 

benefits of various measures.
3-78 MAKING HOSPITALS SAFE FROM FLOODING

3.4.5 Retrofit Dry Floodproofing

Modification of an existing building may be required or desired in order 

to address exposure to design flood conditions. Modifications that may be 

considered include construction of a reinforced supplementary wall, measures to counter buoyancy (especially if there is below-grade space), 

installation of special watertight door and window barriers (see Figure 3-

41), and providing watertight seals around the points of entry of utility 

lines. The details of structural investigations and structural design of such 

protection measures are beyond the scope of this manual. 

Because of the tremendous flood loads that may be exerted on a building 

not originally designed to keep water out, detailed structural engineering evaluations are 

required to determine whether an existing 

building can be dry floodproofed. The following elements must be examined:

m The strength of the structural system

m Whether non-load bearing walls can resist anticipated flood loads; 

secondary walls can be constructed immediately adjacent to existing 

walls, with a waterproof membrane, to provide adequate strength

m The effects of hydrostatic pressures on the walls and floors of belowgrade areas

m Effective means to install watertight doors and windows, or mountable 

panels

m Protection where utilities enter the building

m Methods to address seepage, especially where long-duration flooding 

is anticipated

m Whether there is sufficient time for deployment of measures that 

require human intervention, given the availability of official warnings 

of predicted flood conditions

Application of waterproofing products or membranes directly to exterior walls may mini­mize infiltration of water; although there are concerns 

with durability and limitations on use (this measure is most effective for 

shallow, short-duration flooding). Some protection can be achieved using 

emergency measures that are not designed to be integral to the building 

(see Section 3.4.9). 

“Dry floodproofing” refers to measures and 

methods to render a building envelope 

substantially impermeable to floodwater. 
MAKING HOSPITALS SAFE FROM FLOODING 3-79

3.4.5.1 The Case of Pungo District Hospital, Belhaven, 

North Carolina

The Pungo District Hospital has served the waterfront town of Belhaven, 

North Carolina, and the surrounding area for nearly 60 years (Figure 3-

42). The facility is only about 100 feet back from the waters of a canal and 

Pantego Creek, a tidal tributary to the Pungo River in Beaufort County. 

As with the rest of coastal North Carolina, Beaufort County has seen more 

than its share of hurricanes. Notable named storms that affected the area 

in just the past decade include Hurricanes Fran (1996), Dennis (1999), 

Floyd (1999), and Isabel (2003).

Figure 3-42:

Pungo District Hospital 

is situated adjacent to 

a canal and Pantego 

Creek, a tidal tributary 

to the Pungo River in 

eastern North Carolina.

Figure 3-41:

Boulder Community 

Hospital, Boulder, 

CO, installed this 

permanently

mounted floodgate 

in a low floodwall; 

the floodgate swings 

to the left to keep 

water away from the 

mechanical equipment 

room.
3-80 MAKING HOSPITALS SAFE FROM FLOODING

With about 20,000 residents in its service area, Pungo District Hospital 

offers 49 beds for acute care, transitional care, intensive care, and ventilation care services. Outpatient clinics and programs include a cardiology 

clinic, nephrology clinic, pulmonary clinic, EKG/EEG, home health, 

sleep apnea program, speech therapy, laboratory medicine, imaging services, cardio-pulmonary services, nutritional counseling, and patient 

education. The 175 employees (full- and part-time) include 108 medical and 67 non-medical staff. The facility encompasses a total of 57,000 

square feet, of which 84 percent is used for patient care and the remainder is used for administrative and other support services.

The original one-story hospital building was built on piers in 1949, in the 

traditional crawlspace style that typifies older buildings in areas with high 

groundwater and humid conditions. A number of one-story additions 

were constructed in the 1960s and 1970s. The most recent work, started in 

1997, consisted of two additions that expanded the facility and renovation 

of a large portion of the hospital. With the exception of the mechanical 

room, the additions were built to match the original floor elevation using 

masonry block stemwall foundations (perimeter walls with slab-on-structural fill). The floor of the mechanical room is approximately 18-inches 

lower than the main floor elevation, but does not extend below-grade. 

The Town of Belhaven has participated in the NFIP since the mid-1970s, 

administering an ordinance that requires new buildings and substantially 

improved buildings to comply with certain requirements to reduce exposure to flood hazards. The predicted BFE along the waterfront is 8-feet 

above mean sea level. Worst-case hurricane surge flooding is likely to rise 

even higher. Observations in the past decade indicate that flooding may 

last from 12 to 18 hours, largely as a function of the path of a hurricane 

and tidal cycle. 

The ground elevation around the hospital is about 4.5-feet above mean 

sea level, indicating the site would experience 3.5-feet of flooding during 

the base flood. The floor of the main building is nearly 2.5-feet abovegrade; thus, the 100-year flood would reach a level approximately 1-foot 

above the floor. Because the floor of the mechanical room is lower than 

in the main building, the 100-year flood would flood the room with about 

3-feet of water.

In 1997, the City of Belhaven determined that the proposed expansions 

and other work in the main building would be a substantial improvement 

(the cost of the proposed work exceeded 50 percent of the market value 

of the building). This determination triggered compliance with the city’s 

building code and floodplain management ordinance. Two alternatives 

were available to bring the building into compliance: elevating the existing building and additions nearly 18 inches (so the floor level would 
MAKING HOSPITALS SAFE FROM FLOODING 3-81

be at the flood level) or retrofitting the building by dry floodproofing. To 

address this requirement, the hospital hired an engineering company to 

examine the existing building and the proposed new addition, and to design appropriate floodproofing measures. 

The engineer’s examination determined that the exterior walls of the 

existing building were sufficiently strong to resist the flood loads anticipated during the 100-year flood conditions, provided the entrances and 

other openings through the exterior wall were sealed to prevent entry of 

water. The dry floodproofing measures proposed entailed construction 

of low concrete walls in certain areas and installation of specially fabricated frames and metal panels for some doors, floodwall openings, and 

crawlspace ventilation openings (Figures 3-43 and 3-44). The top of the 

concrete wall and the tops of the panels were set about 2 feet higher than 

the BFE, providing 2 feet of freeboard as a factor of safety. To provide additional protection to the new addition, a rubber membrane was installed 

between the brick facing and the block wall. The total cost of the floodproofing measures was $125,000 (1997 dollars). 

Figure 3-43:

A special 

floodproofing panel is 

manually installed in 

this concrete floodwall 

to keep floodwater 

away from the rear 

courtyard and patient 

rooms. 
3-82 MAKING HOSPITALS SAFE FROM FLOODING

The frames that hold the floodproofing panels are permanentlymounted and sealed against the building to prevent seepage. The 

frames are designed with an aluminum cover to keep the channels 

free of dirt and debris. The metal panels that fit into the channels 

have rubber gaskets that are inspected each year as part of the hospital’s routine maintenance program. The manufacturer recently advised 

replacement of the gaskets, as the 10-year anniversary of installation 

nears.

A total of 15 panels of different sizes are stored onsite (Figure 3-45). 

Although the panels can be handled by two people (Figure 3-46), the 

hospital has an on-call agreement with a local rental company to use a 

forklift to facilitate moving them into place. All panels can be installed 

in about 3 hours.

Pungo District Hospital fully recognizes its vulnerability to coastal 

storms and the importance of protecting its patients as well as providing services after a major event. The facilities services director 

monitors weather throughout the hurricane season, coordinating with 

the county emergency services and town officials responsible for issuing 

evacuation notices. 

Figure 3-44:

The ventilation 

openings for the 

original building’s 

crawlspace are 

protected with 

floodproofing panels 

that are bolted in 

place when flooding is 

predicted.
MAKING HOSPITALS SAFE FROM FLOODING 3-83

The detailed evacuation plan was triggered as Hurricane Isabel approached in September 2003. In less than 4 hours all patients, staff, and 

supplies were relocated safely to the Beaufort Memorial Hospital, about 

30 miles inland. Total shutdown of the building, including installation 

of the floodproofing panels, took about 12 hours. An emergency generator, located inside the protected area, was activated in order to run 

four sump pumps to handle groundwater that seeps into the crawlspace 

Figure 3-45:

Large floodproofing 

panels are stored at 

the hospital, ready 

for installation when 

coastal flooding is 

predicted.

Figure 3-46:

Most of the panels can 

be installed by hand. 

Note the protective 

metal strip leaning 

against the building 

on the left; normally 

this strip covers the 

horizontal channel 

into which the panel is 

inserted. 
3-84 MAKING HOSPITALS SAFE FROM FLOODING

of the original building. Isabel’s storm surge produced the highest 

flooding on record in Belhaven, yet the hospital weathered the storm 

without damage.

Reoccupation of the hospital began when the town cleared the streets and 

all systems of the building were brought back online. Municipal water and 

sewer services were not interrupted by flooding.

Despite decades of weathering hurricanes, the Pungo District Hospital has 

not sustained major wind damage. The absence of trees or other buildings between the hospital and the water prevents major wind-borne debris 

damage. Water-borne debris is deposited around the facility every time 

high water crests the bulkhead that lines creek. One corner of the parking 

lot, which extends nearly to the bulkhead, sustained damage as Hurricane 

Isabel’s rising water lifted and displaced the asphalt (Figure 3-47). 

3.4.6 Utility Installations

Some features of utility systems in existing hospitals prone to flooding may 

need to be modified to reduce damage. The effectiveness of such measures 

depends not only on the nature of the flooding, but the type of service 

and the degree of exposure. Table 3-3 in Section 3.5 lists some questions to 

help facility planners and designers examine risk reduction measures. 

Figure 3-47:

High water and waves eroded the slope 

between the parking lot and the bulkhead 

and shifted a portion of the asphalt. 
MAKING HOSPITALS SAFE FROM FLOODING 3-85

Even if a facility is unlikely to sustain extensive structural damage from 

flooding, significant recovery costs and interruption of operations may result if utility systems are damaged. The damage reduction measures 

described below can be applied, whether undertaken as part of large-scale 

retrofits of existing buildings or as separate projects.

Relocate from below-grade areas:  The most vulnerable utility installations are those located 

below grade, and the most effective protection 

measure is to relocate them to higher floors or 

platforms that are at least 2 feet above the DFE. 

The complexity of rerouting pipes, conduits, 

ductwork, electrical service, lines, and connections will depend on building- and site-specific 

factors.

Elevate components:  Whether located inside or outside of the building, 

some components of utility systems can be elevated-in-place on platforms, 

including electric transformers, communication switch boxes, water 

heaters, air-conditioning compressors, generators, furnaces, boilers, and 

heat pumps (see Figure 3-48). 

Additional guidance on improving the 

flood resistance of utility installations in 

existing buildings is found in FEMA 348, 

Protecting Building Utilities From Flood 

Damage: Principles and Practices for the 

Design and Construction of Flood Resistant 

Building Utility Systems.

Figure 3-48:

Elevated utility box
3-86 MAKING HOSPITALS SAFE FROM FLOODING

Anchor tanks and raise openings:  Existing tanks can be elevated or 

anchored, as described in Section 3.4.10. If anchored below the DFE, tank 

inlets, vents, fill pipes, and openings should be elevated above the DFE, or 

fitted with covers designed to prevent the inflow of floodwaters or outflow 

of the tank’s contents.

Protect components:  If utility components cannot be elevated, it may be 

feasible to construct watertight enclosures, or enclosures with watertight 

seals that require human intervention to install when flooding is 

predicted.

Elevate control equipment:  Control panels, gas meters, and electrical panels 

can be elevated, even if the equipment they service cannot be protected.

Separate electrical controls:  Where areas within an existing facility are 

flood-prone, separation of control panels and electrical feeders will 

facilitate shutdown before floodwaters arrive, and help protect workers 

during cleanup.

Protect against electrical surges:  Current fluctuations and service interruptions are common in areas affected by flooding. Equipment and sensitive 

electrical components can be protected by installing surge protection and 

uninterruptible power supplies.

Connections for portable generators:  Prewired portable generator connections allow for quick, failure-free connection and disconnection of the 

generators when needed for continued functionality.

3.4.7 Potable Water and Wastewater

Systems

All plumbing fixtures connected to the potable water system may become 

weak points in the system if they allow floodwaters to contaminate the 

system. Relocating the fixtures and services that require plumbing to elevated floors and removing the fixtures that are below the DFE provides 

protection. Wellheads can be sealed with watertight casings or protected 

within sealed enclosures.

Wastewater system components become sources of contamination during 

floods. Rising floodwaters may force untreated sewage to backup through 

toilets. Specially designed devices that prevent back-flow can be installed, 

or restrooms below the DFE can be provided with overhead piping that 

may require specially designed pumps to operate properly. Septic tanks 

can be sealed and anchored. 
MAKING HOSPITALS SAFE FROM FLOODING 3-87

3.4.8 Other Damage Reduction Measures

A number of steps can be taken to make existing facilities in flood hazard 

areas more resistant to flood damage, which also facilitates rapid recovery, 

cleanup, and timely return to normalcy. Whether these measures are applicable to a specific facility depends, in part, on the characteristics of the 

flood hazard and the characteristics of the building itself. Facility planners 

and designers should consider the following:

m Rehabilitate and retrofit the building envelope with openings 

specifically designed to allow floodwaters to flow in and out to 

minimize hydrostatic pressure on walls (called wet floodproofing). 

Although it allows water to enter the building, this measure minimizes 

the likelihood of major structural damage. Walls that enclose interior 

spaces would also be retrofitted with openings.

m Replace interior walls that have cavities with flood-resistant 

construction or removable panels to facilitate cleanup and drying.

m Abandon the use of below-grade areas (basements) and fill them in to 

prevent structural damage.

m Permanently relocate high-value or sensitive functions that are often 

found on the ground floor of hospitals (e.g., offices, records, libraries, 

and computer laboratories) to higher floors or elevated additions.

m Install backflow devices in sewer lines.

m Preplan actions to move high-value contents from the lower floors to 

higher floors when a flood warning is issued.

m Replace wall, flooring, and finish materials with flood-resistant 

materials. Concrete floors with a sealed, polished, or terrazzo finish 

have few maintenance requirements, but tend to be slippery when wet.

m Use epoxy or other impervious paints on concrete and other 

permeable surfaces to minimize contamination. 

m Install separate electric circuits and ground fault interrupter circuit 

protection in areas that will flood. Emergency measures should 

be provided so that electrical service can be shut down to avoid 

electrocution hazards.

m Relocate chemicals to storage areas not subject to flooding.
3-88 MAKING HOSPITALS SAFE FROM FLOODING

3.4.9 Emergency Measures

Emergency response to flooding is outside the scope of this manual. 

However, it is appropriate to examine feasible emergency measures that 

may provide some protection. The following discussion pertains only 

to emergency measures that have been used to reduce flood damage to 

older buildings that are already located in flood hazard areas. They may 

not provide protection to occupants and they can experience a high 

frequency of failure depending on human factors related to deployment. These measures do not achieve compliance with building and 

life safety codes for new construction. 

Emergency barriers are measures of “last resort,” and should be used 

only when a credible flood warning with adequate lead-time is available and dependable. These measures have varying degrees of success, 

depending on the available manpower, skill required, long-term maintenance of materials and equipment, suitability for site-specific flood 

conditions, and having sufficient advanced warning. Complete evacuation of protected buildings is appropriate, as these measures should not 

be considered adequate protection for occupants. 

Sandbag walls:  Unless emergency placement is planned well in advance 

or under the direction of trained personnel, most sandbag barriers are 

not constructed in accordance with proper practices, leading to leakage 

and failures. Because of the intensive work effort and length of time required for protection even from relatively shallow water, sandbag walls 

are not a reliable protection measure. To be effective, sandbags and 

sand should be stockpiled and checked regularly to ensure that sandbags have not deteriorated. Sandbags have some other drawbacks, 

including high disposal costs and their tendency to absorb pollutants 

from contaminated floodwaters, which necessitates disposal as hazardous waste.

Water-filled barriers:  A number of vendors make water-filled barriers that 

can be assembled with relative ease, depending on the source of water for 

filling. The barriers must be specifically sized for the site. Training and annual drills are important so that personnel know how to place and deploy 

the barriers. Proper storage, including cleaning after deployment, is necessary to protect the materials over long periods of time.

Panels for doors:  For shallow and short-duration flooding, panels of 

sturdy material can be made to fit doorways to minimize the entry of 

floodwaters, although failure is common (see Figure 3-49). Effectiveness is increased significantly if a flexible gasket or sealant is provided, 

and the mounting hardware is designed to apply even pressure. Personnel must know where the materials are stored and be trained in 
MAKING HOSPITALS SAFE FROM FLOODING 3-89

their deployment. A number of vendors make special doors for permanent installation and drop-in panels or barriers that are designed to be 

watertight.

Figure 3-49:

Flooding at Hancock 

Medical Center during 

Hurricane Katrina

Source: Hancock

Medical Center
3-90 MAKING HOSPITALS SAFE FROM FLOODING

3.5 CHECKLIST FOR BUILDING 

VULNERABILITY OF FLOOD-PRONE 

HOSPITALS

T he Checklist for Building Vulnerability of Flood-Prone Hospitals 

(Table 3-3) is a tool that can be used to help assess site-specific 

flood hazards and building vulnerability. The checklist is useful 

during site selection, preliminary design of a new building, or when considering rehabilitation of an existing facility. In addition to examining 

building design issues that affect vulnerability, the checklist also helps 

users to examine the functionality of the crit­ical and emergency systems 

upon which most hospitals depend. The checklist is organized into separate sections, so that each section can be assigned to a subject expert for 

greater accu­racy of the examination. The results should be integrated 

into a master vulnerability assessment to guide the design process and the 

choice of appropriate mitigation measures.

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals

Vulnerability Sections Guidance Observations

Site Conditions

Is the site located near a body of 

water (with or without a mapped 

flood hazard area)? 

Is the site in a flood hazard area 

shown on the community’s map 

(FIRM or other adopted map)? If 

so, what is the flood zone?

Is the site affected by a regulatory 

floodway?

All bodies of water are subject to flooding, 

but not all have been designated as a 

floodplain on FIRMs. 

Flood hazard maps usually are available 

for review in local planning and permit 

offices. Electronic versions of the FIRMs 

may be available online at www.fema.gov. 

Paper maps may be ordered by calling 

(800) 358-9616.

Development in floodways, where 

floodwaters typically are faster and deeper, 

must be supported by engineering analyses 

that demonstrate no rise in flood levels
MAKING HOSPITALS SAFE FROM FLOODING 3-91

Vulnerability Sections Guidance Observations

Site Conditions (continued)

Is the site located in a storm surge 

inundation zone (or tsunami 

inundation area)?

In coastal communities, even sites at some 

distance inland from the shoreline may be 

exposed to extreme storm surge flooding. 

Storm surge maps may be available at State 

or local emergency management offices.

What is the DFE (or does an 

analysis have to be done to 

determine the DFE)? What is the 

minimum protection level required 

by regulatory authorities?

Does the FIS or other study have 

information about the 500-year 

flood hazard area?

Has FEMA issued post-disaster 

advisory flood elevations and 

maps?

What are the expected depths of 

flooding at the site (determined 

using flood elevations and ground 

elevations)?

Reference the FIS for flood profiles and 

data tables. Site-specific analyses should 

be performed by qualified engineers. 

Check with regulatory authorities to 

determine the required level of protection.

If a major flood event has affected the 

community, FEMA may have issued new 

flood hazard information, especially if 

areas not shown on the FIRMs have been 

affected. Sometimes these maps are 

adopted and replace the FIRMs; sometimes 

the new data are advisory only.

Has the site been affected by past 

flood events? What is the flood of 

record? 

Records of actual flooding augment 

studies that predict flooding, especially if 

historic events resulted in deeper or more 

widespread flooding. Information may be 

available from local planning, emergency 

management, and public works agencies, 

or State agencies, the U.S. Army Corps 

of Engineers, or the Natural Resources 

Conservation Service.

The flood of record is often a lower 

probability event (with higher flood 

elevations) than the 100-year flood.

What is the expected velocity of 

floodwaters on the site?

Velocity is a factor in computing loads 

associated with hydrodynamic forces, 

including drag on building surfaces. 

Approximations of velocity may be 

interpolated from data in the FIS Floodway 

Data Table if the waterway was studied 

using detailed methods, application 

of approximation methods based on 

continuity, local observations and sources, 

or site-specific studies. 

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals (continued)
3-92 MAKING HOSPITALS SAFE FROM FLOODING

Vulnerability Sections Guidance Observations

Site Conditions (continued)

Are waves expected to affect the 

site?

Waves can exert considerable dynamic 

forces on buildings and contribute to erosion 

and scour. Wind-driven waves occur in 

areas subject to coastal flooding and where 

unobstructed winds affect wide floodplains 

(large lakes and major rivers). Standing 

waves may occur in riverine floodplains 

where high velocities are present.

Is there information on how quickly 

floodwaters may affect the site?

What is the expected duration of 

flooding?

Warning time is a key factor in the safe 

and orderly evacuation of critical facilities. 

Certain protective measures may require 

adequate warning so that actions can be 

taken by skilled personnel.

Duration has bearing on the stability 

of earthen fills, access to a site and 

emergency response, and durability of 

materials that come into contact with water. 

Records of actual flooding are the best 

indicator of duration as most floodplain 

analyses do not examine duration. 

Is there a history of flood-related 

debris problems or erosion on the 

site?

Site design should account for deposition 

of debris and sediment, as well as the 

potential for erosion-related movement 

of the shoreline or waterway. Buildings 

exposed to debris impact or undermining 

by scour and erosion should be designed 

to account for these conditions. 

Is the site within an area predicted 

to flood if a levee or floodwall fails 

or is overtopped? 

 Is the site in an area predicted to 

be inundated if an upstream dam 

were to fail?

Flood protection works may be distant 

from sites and not readily observable. 

Although a low probability event, failure 

or overtopping can cause unexpected 

and catastrophic damage because the 

protected lands are not regulated as flood 

hazard areas.

The effects of an upstream dam failure 

are not shown on the FIRMs or most flood 

hazard maps prepared locally. Although 

dam failure generally is considered an 

unlikely event, the potential threat should 

be evaluated due to the catastrophic 

consequences. (Note: owners of certain 

dams should have emergency action plans 

geared toward notification and evacuation 

of vulnerable populations and critical 

facilities.)

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals (continued)
MAKING HOSPITALS SAFE FROM FLOODING 3-93

Vulnerability Sections Guidance Observations

Site Conditions (continued)

Does the surrounding topography 

contribute to the flooding at the 

site? Is there a history of local 

surface drainage problems due to 

inadequate site drainage?

If areas with poor local drainage and 

frequent flooding cannot be avoided, 

filling, regrading, and installation of storm 

drainage facilities may be required.

Given the nature of anticipated 

flooding and soils, is scour around 

and under the foundation likely?

Scour-prone sites should be avoided, in 

part due to likely long-term maintenance 

requirements. Flooding that is high 

velocity or accompanied by waves is more 

likely to cause scour, especially on fills, or 

where local soils are unconsolidated and 

subject to erosion.

Has water from other sources 

entered the building (i.e., high 

groundwater, water main breaks, 

sewer backup, etc.)? Is there 

a history of water intrusion 

through floor slabs or wellfloor connections? Are there 

underground utility systems or 

areaways that can contribute to 

basement flooding? Are there 

stormwater sewer manholes 

upslope of window areas 

or openings that allow local 

drainage to enter the basement/

lower floor areas? 

These questions pertain to existing 

facilities that may be impaired by water 

from sources other than the primary source 

of flooding. The entire building envelope, 

including below-grade areas, should 

be examined to identify potential water 

damage.

Is at least one access road to the 

site/building passable during 

flood events? 

Are at-grade parking lots located 

in flood-prone areas?

Are below-grade parking areas 

susceptible to flooding?

Access is increasingly important as the 

duration of flooding increases. For the 

safety of occupants, most critical facilities 

should not be occupied during flood 

events.

Areas where vehicles could be affected 

should have signage to warn users of the 

risk. Emergency response plans should 

include notification of car owners.

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals (continued)
3-94 MAKING HOSPITALS SAFE FROM FLOODING

Vulnerability Sections Guidance Observations

Architectural

Are any critical building functions 

occupying space that is below the 

elevation of the 500-year flood or 

the Design Flood Elevation?

Can critical functions be 

relocated to upper levels that are 

above predicted flood elevations?

If critical functions cannot be 

relocated, is floodproofing 

feasible?

If critical functions must continue 

during a flood event, have power, 

supplies, and access issues been 

addressed?

New critical facilities built in flood hazard 

areas should not have any functions 

occupying flood-prone spaces (other than 

parking, building access, and limited 

storage). 

Existing facilities in floodplains should be 

examined carefully to identify the best 

options for protecting functionality and the 

structure itself.

Have critical contents (files, 

computers, servers, equipment, 

research, and data) been located 

on levels of the facility above the 

flood elevations? 

Are critical records maintained 

offsite?

For existing facilities that are already 

located in flood hazard areas, the nature 

of the facility may require continued use of 

flood-prone space. However, the potential 

for flooding should be recognized and 

steps taken to minimize loss of expensive 

equipment and irreplaceable data. If critical 

contents cannot be permanently located on 

higher floors, a flood response plan should 

take into account the time and attention 

needed to move such contents safely.

Structural Systems

What is the construction type and 

the foundation type and what is 

the load bearing capacity?

Has the foundation been 

designed to resist hydrostatic and 

hydrodynamic flood loads?

If siting in a floodplain is unavoidable, new 

facilities are to be designed to account for 

all loads and load combinations, including 

flood loads. 

If the building has below-grade 

areas (basements), are the lower 

floor slabs subject to cracking 

and uplift?

Below-grade spaces and their contents 

are most vulnerable to flooding and local 

drainage problems. Rapid pump out 

of below-grade spaces can unbalance 

forces if the surrounding soil is saturated, 

leading to structural failure. If belowgrade spaces are intended to be dry 

floodproofed, the design must account for 

buoyant forces.

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals (continued)
MAKING HOSPITALS SAFE FROM FLOODING 3-95

Vulnerability Sections Guidance Observations

Structural Systems (continued)

Building spaces below the design flood level 

can be dry floodproofed, although it must 

be recognized that higher flood levels will 

overtop the protection measures and may 

result in severe damage. Dry floodproofing 

creates large unbalanced forces that can 

jeopardize walls and foundations that are 

not designed to resist the hydrostatic and 

hydrodynamic loads.

Are any portions of the building 

below the Design Flood Elevation?

Has the building been damaged in 

previous floods?

For existing buildings, it is important to 

determine which portions are vulnerable in 

order to evaluate floodproofing options. If 

flood depths are expected to exceed 2 or 3 

feet, dry floodproofing may not be feasible. 

Alternatives include modifying the use of 

flood-prone areas.

If the building is elevated on 

a crawlspace or on an open 

foundation, are there any enclosed 

areas?

New buildings may have enclosures below 

the flood elevation. provided the use of the 

enclosures is limited (crawlspace, parking, 

building access, and limited storage). In 

addition, the enclosures must have flood 

openings to automatically allow for inflow 

and outflow of floodwaters to minimize 

differential hydrostatic pressure. 

Existing buildings that are elevated and 

have enclosures below the flood elevation 

can be retrofit with flood openings.

For an existing building with 

high-value uses below the flood 

elevation, is the building suitable 

for elevation-in-place, or can it be 

relocated to higher ground? 

Elevating a building provides better 

protection than dry floodproofing. 

Depending on the type and soundness of 

the foundation, even large buildings can be 

elevated on a new foundation or moved to 

a site outside of the floodplain.

Building Envelope

Are there existing floodproofing 

measures in place below the 

expected flood elevation? What 

is the nature of these measures 

and what condition are they in? 

Is there an annual inspection and 

maintenance plan?

Is there an “action plan” to implement floodproofing measures when 

flooding is predicted? Do the building 

operators/occupants know what to 

do when a flood warning is issued?

Floodproofing measures are only as 

good as the design and their condition, 

especially if many years have passed 

since initial installation. Floodproofing 

measures that require human intervention 

are entirely dependent on the adequacy of 

advance warning, and the availability and 

ability of personnel to properly install the 

measures. 

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals (continued)
3-96 MAKING HOSPITALS SAFE FROM FLOODING

Vulnerability Sections Guidance Observations

Building Envelope (continued)

For existing buildings, what types 

of openings penetrate the building 

envelope below the 500-year 

flood elevation or the DFE (doors, 

windows, cracks, vent openings, 

plumbing fixtures, floor drains, 

etc.)?

For dry floodproofing to be effective, 

every opening must be identified and 

measures taken to permanently seal 

or to prepare special barriers to resist 

infiltration. Sewage backflow can enter 

through unprotected plumbing fixtures.

Are flood-resistant materials used 

for structural and nonstructural 

components and finishes below 

the 500-year elevation or the DFE?

Flood-resistant materials are capable of 

withstanding direct and prolonged contact 

with floodwaters without sustaining 

damage that requires more than cosmetic 

repair. Contact is considered to be 

prolonged if it is 72 hours or longer in 

freshwater flooding areas, or 12 hours or 

longer in areas subject to coastal flooding.

Utility Systems

Is the potable water supply for the 

facility protected from flooding? If 

served by a well, is the wellhead 

protected? 

Operators of critical facilities that depend 

on fresh water for continued functionality 

should learn about the vulnerability of the 

local water supply system, and the system’s 

plans for recovery of service in the event 

of a flood.

Is the wastewater service for the 

building protected from flooding? 

Are any manholes below the 

DFE? Is infiltration of floodwaters 

into sewer lines a problem? If the 

site is served by an onsite system 

that is located in a flood-prone 

area, have backflow valves been 

installed?

Most waste lines exit buildings at the 

lowest elevation. Even buildings that are 

outside of the floodplain can be affected 

by sewage backups during floods. 

Are there any aboveground or 

underground tanks on the site 

in flood hazard areas? Are they 

installed and anchored to resist 

flotation during the design flood? 

Are tank openings and vents 

elevated above the 500-year 

elevation or the DFE, or otherwise 

protected to prevent entry of 

floodwater or exit of product 

during a flood event?

Dislodged tanks become floating debris 

that pose special hazards during recovery. 

Lost product causes environmental 

damage. Functionality may be impaired 

if tanks for heating fuel, propane, or fuel 

for emergency generators are lost or 

damaged. 

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals (continued)
MAKING HOSPITALS SAFE FROM FLOODING 3-97

Vulnerability Sections Guidance Observations

Mechanical Systems

Are air handlers, HVAC systems, 

ductwork, and other mechanical 

equipment and systems located 

above the 500-year elevation or 

the DFE? Are the vents and inlets 

located above flood level, or sealed 

to prevent entry of floodwater?

In existing buildings, utility equipment 

that is critical for functionality should be 

relocated to higher floors or into elevated 

additions. 

Plumbing and Gas Systems

Are plumbing fixtures and gasfired equipment (meters, pilot light 

devices/burners, etc.) located 

above the 500-year elevation or 

the DFE?

In existing buildings, utility equipment 

that is critical for functionality should be 

relocated to higher floors or into elevated 

additions.

Is plumbing and gas piping 

that extends below flood levels 

installed to minimize damage?

Piping that is exposed could be impacted 

by debris.

Electrical Systems

Are electrical systems, including 

backup power generators, panels, 

and primary service equipment, 

located above the 500-year 

elevation or the DFE? 

Are pieces of electrical standby equipment and generators 

equipped with circuits to turn off 

power?

Are the switches and wiring 

required for safety (minimal 

lighting, door openers) located 

below the flood level designed for 

use in damp locations?

In existing buildings, utility equipment 

that is critical for functionality should be 

relocated to higher floors or into elevated 

additions.

Fire Alarm Systems

Is the fire alarm system located 

above the 500-year elevation or 

the DFE?

In existing buildings, utility equipment 

that is critical for functionality should be 

relocated to higher floors or into elevated 

additions.

Communications and IT Systems

Are the communication/IT systems 

located above the 500-year 

elevation or the DFE? 

Table 3-3: Checklist for Building Vulnerability of Flood-Prone Hospitals (continued)
3-98 MAKING HOSPITALS SAFE FROM FLOODING

3.6 REFERENCES AND SOURCES OF 

ADDITIONAL INFORMATION

Note:  FEMA publications may be obtained at no cost by calling (800) 

480-2520, faxing a request to (301) 497-6378, or downloading from the library/publications section online at http://www.fema.gov. 

American Society of Civil Engineers (ASCE), Structural Engineering Institute, 2005a, Flood Resistant Design and Construction, ASCE/SEI 24-05, 

Reston, VA

American Society of Civil Engineers (ASCE), Structural Engineering 

Institute, 2005b, Minimum Design Loads for Buildings and Other 

Structures, ASCE/SEI 7-05, Reston, VA.

Association of State Floodplain Managers, Inc. (ASFM), 2004, Floodplain 

Management 2003: State and Local Programs, Madison, WI.

Federal Emergency Management Agency (FEMA), 1986, Floodproofing 

Non-Residential Structures, FEMA 102, Washington, DC, May 1986.

Federal Emergency Management Agency (FEMA), 1991, Answers to 

Questions about Substantially Damaged Buildings, FEMA 213, Washington, 

DC, May 1991.

Federal Emergency Management Agency (FEMA), 1995, Engineering 

Principles and Practices for Retrofitting Flood-prone Residential Buildings, 

FEMA 259, Washington, DC, January 1995.

Federal Emergency Management Agency (FEMA), 1999, Protecting 

Building Utilities From Flood Damage: Principles and Practices for the Design 

and Construction of Flood Resistant Building Utility Systems, FEMA 348, 

Washington, DC, November 1999. 
MAKING HOSPITALS SAFE FROM FLOODING 3-99

Federal Emergency Management Agency (FEMA), 2000, Coastal 

Construction Manual, FEMA 55 (3rd Edition), Washington, DC.

Federal Emergency Management Agency (FEMA), 2004, Answers 

to Questions about the National Flood Insurance Program, FEMA F-084, 

Washington, DC, May 2004. 

Federal Emergency Management Agency (FEMA), NFIP Technical 

Bulletins:

m User’s Guide to Technical Bulletins, FIA-TB-0, April 1993. 

m Openings in Foundation Walls, FIA-TB-1, April 1993.

m Flood-Resistant Materials Requirements, FIA-TB-2, April 1993.

m Non-Residential Floodproofing—Requirements and Certification, 

FIA-TB-3, April 1993. 

m Elevator Installation, FIA-TB-4, April 1993. 

m Free-of-Obstruction Requirements, FIA-TB-5, April 1993. 

m Below-Grade Parking Requirements, FIA-TB-6, April 1993.

m Wet Floodproofing Requirements, FIA-TB-7, December 1993.

m Corrosion Protection for Metal Connections in Coastal Areas, FIATB-8, 1996.

m Design and Construction Guidance for Breakaway Walls Below 

Elevated Coastal Buildings, FIA-TB-9, 1999.

m Ensuring That Structures Built on Fill In or Near Special Flood 

Hazard Areas Are Reasonably Safe From Flooding, FIA-TB-10, 2001. 

m Crawlspace Construction for Buildings Located in Special Flood 

Hazard Areas, FIA-TB-11, 2001.

International Code Council, Inc. (ICC), 2006a, ICC Performance Code for 

Buildings and Facilities, Country Club Hills, IL.

International Code Council, Inc. (ICC), 2006b, International Building 

Code, Country Club Hills, IL.
3-100 MAKING HOSPITALS SAFE FROM FLOODING

International Code Council, Inc. (ICC) and Federal Emergency 

Management Agency (FEMA), 2006, Reducing Flood Losses Through the 

International Codes, Meeting the Requirements of the National Flood Insurance 

Program (2006 I-Codes), Country Club Hills, IL.

National Academy of Sciences, 1977, Methodology for Calculating Wave 

Action Effects Associated with Storm Surges. Washington, DC.

National Fire Protection Association (NFPA), 2006, Building Construction 

and Safety Code (NFPA 5000), Quincy, MA. 

U.S. Army Corps of Engineers, 1993, National Flood Proofing Committee, 

Flood Proofing – How To Evaluate Your Options, Washington, DC, July 1993.

U.S. Army Corps of Engineers, 1995, Flood Proofing Regulations, EP 1165-2-

314, Washington, DC. 

U.S. Army Corps of Engineers, 1996, Flood Proofing Programs, Techniques 

and References, Washington, DC.

U.S. Army Corps of Engineers, 1998, Flood Proofing Performance—Successes 

& Failures, Washington, DC.

Organizations and Agencies:

Federal Emergency Management Agency: FEMA’s regional offices can 

be contacted for advice and guidance on NFIP mapping and regulations 

(www.fema.gov). 

NFIP State Coordinating offices help local governments to meet their 

floodplain management obligations, and may provide technical advice 

to others; the offices are listed by the Association of State Floodplain 

Managers, Inc., (www.floods.org/stcoor.htm). 

State agencies that coordinate state funding and or administer regulations 

may have state-specific requirements for hospitals.

U.S. Army Corps of Engineers: District offices offer Flood Plain 

Management Services, (www.usace.army.mil/inet/functions/cw/). 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-1

MAKING HOSPITALS SAFE FROM HIGH WIND 4

4.1 GENERAL DESIGN CONSIDERATIONS

Wind with sufficient speed to cause damage to weak hospitals 

can occur anywhere in the United States and its territories. Even a well-designed, constructed, and maintained 

hospital may be damaged by a wind event much stronger than one the 

building was designed for. However, except for tornado damage, this scenario is a rare occurrence. Rather, most damage occurs because various 

building elements have limited wind resistance due to inadequate design, 

poor installation, or material deterioration. Although the magnitude and 

frequency of strong windstorms vary by locale, all hospitals should be designed, constructed, and maintained to minimize wind damage (other 

than that associated with tornadoes —see Section 4.5). 

This chapter discusses structural, building envelope, and nonstructural 

building systems, and illustrates various types of wind-induced damage 

that affect them. It also presents six case studies. Numerous examples of 

best practices pertaining to new and existing hospitals are presented as 

recommended design guidelines. Incorporating those practices applicable to specific projects will result in greater wind-resistance reliability 

and will, therefore, decrease expenditures for repair of wind-damaged facilities, provide enhanced protection for occupants, and avoid disruption 

of critical services.

The recommendations presented in this manual are based on field 

observation research conducted on 25 hospitals that were struck by 

1 The U.S. territories include American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the U.S. Virgin 

Islands. ASCE 7 provides basic wind speed criteria for all but Northern Mariana Islands.
4-2 MAKING HOSPITALS SAFE FROM HIGH WIND

hurricanes . The recommendations are also based on numerous investigations of other types of critical facilities and other types of buildings 

exposed to hurricanes and tornadoes, and on literature review. Some of 

the 25 hospitals were exposed to extremely high wind speeds, while others 

experienced moderate speeds. Approximately 88 percent of the 25 hospitals experienced roof covering damage (many of which also experienced 

damage to rooftop equipment), and windows were broken on approximately 50 percent of them. Because of wind damage and subsequent 

water leakage, one of the hospitals was totally evacuated after a hurricane (Figure 4-1). Another hospital was also evacuated after a hurricane, 

but evacuation was prompted by flooding. Five other hospitals were partially evacuated after the storm because of interior water damage. None of 

the main hospital buildings on these 25 campuses experienced structural 

failure, although a few auxiliary buildings did collapse.

2 The research on the 25 hospitals was conducted by a team from Texas Tech University (Hurricane Hugo, 

Charleston, South Carolina, 1989), a team under the auspices of the Wind Engineering Research Council—now 

known as the American Association for Wind Engineering (Hurricane Andrew, South Florida, 1992), and teams 

deployed by FEMA (Hurricane Marilyn, U.S. Virgin Islands, 1995; Typhoon Paka, Guam, 1997; Hurricane 

Charley, Port Charlotte, Florida, 2004; Hurricane Frances, east coast of Florida, 2004, Hurricane Ivan, 

Pensacola, Florida, 2004; and Hurricane Katrina, Louisiana and Mississippi, 2005).

Figure 4-1:

Deering Hospital 

was evacuated after 

Hurricane Andrew due 

to water infiltration 

caused by roof 

covering, window, 

and door damage.

Figure 4-1:

Deering Hospital 

was evacuated after 

Hurricane Andrew due 

to water infiltration 

caused by roof 

covering, window, 

and door damage.

The 200-bed Deering Hospital opened shortly before Hurricane Andrew 

struck south Florida in 1992. Aggregate from the hospital’s built-up roofs 

broke several windows, the roof covering was blown off in some areas 

(Figure 4-9), and the entrance doors at the emergency room were blown 

away. Because of extensive interior water damage, the entire hospital 

was evacuated after the storm and remained closed for 9 months.

The 200-bed Deering Hospital opened shortly before Hurricane Andrew 

struck south Florida in 1992. Aggregate from the hospital’s built-up roofs 

broke several windows, the roof covering was blown off in some areas 

(Figure 4-9), and the entrance doors at the emergency room were blown 

away. Because of extensive interior water damage, the entire hospital 

was evacuated after the storm and remained closed for 9 months.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-3

4.1.1 Nature of High Winds

A variety of windstorm types occur in different areas of the United States. 

The characteristics of the types of storms that can affect the site should 

be considered by the design team. The primary storm types are straightline winds, down-slope winds, thunderstorms, downbursts, northeasters 

(nor'easters), hurricanes, and tornadoes. For information on these storm 

types, refer to Section 3.1.1 in FEMA 543, Design Guide for Improving Critical Facility Safety from Flooding and High Winds.

Of all the storm types, hurricanes have the greatest potential for devastating a large geographical area and, hence, affect the greatest number of 

people. See Figure 4-2 for hurricane-prone regions. 

Figure 4-2: Hurricane-prone regions and special wind regions

Source: Adapted from ASCE 7-05

4.1.2 Probability of Occurrence

Via the importance factor, ASCE 7 requires Category III and IV buildings 

to be designed for higher wind loads than Category I and II buildings. 

Hence, hospitals designed in accordance with ASCE 7 have greater 

3 Available at the FEMA Web site. See www.fema.gov/library/viewRecord.do?id=2441

4 The importance factor accounts for the degree of hazard to human life and damage to property. Importance 

factors are given in ASCE 7.
4-4 MAKING HOSPITALS SAFE FROM HIGH WIND

resistance to stronger, rarer storms. When designing a hospital, design 

professionals should consider the following types of winds.

Routine winds: In many locations, winds with low to moderate speeds 

occur daily. Damage is not expected to occur during these events.

Stronger winds: At a given site, stronger winds 

(i.e., winds with a speed in the range of 70 to 

80 mph peak gust, measured at 33 feet in Exposure C—refer to Section 4.1.3) may occur from 

several times a year to only once a year or even 

less frequently. This is the threshold at which 

damage normally begins to occur to building 

elements that have limited wind resistance due 

to problems associated with inadequate design, 

insufficient strength, poor installation, or material deterioration.

Design level winds: Hospitals exposed to design 

level events and events that are somewhat in excess of design level should experience little, if 

any, damage. Actual storm history, however, has 

shown that design level storms frequently cause 

extensive building envelope damage. Structural damage also occurs, but 

less frequently. Damage incurred in design level events is typically associated with inadequate design, poor installation, or material deterioration. 

The exceptions are wind-driven water infiltration and wind-borne debris 

(missiles) damage. Water infiltration is discussed in Sections 4.3.3.1, 

4.3.3.3, and 4.3.3.5. 

Tornadoes: Although more than 1,200 tornadoes typically occur each year in the United 

States, the probability of a tornado occurring 

at any given location is quite small. The probability of occurrence is a function of location. As 

described in Section 4.5, only a few areas of the 

country frequently experience tornadoes, and 

tornadoes are very rare in the west. The Oklahoma City area is the most active location, with 112 recorded tornadoes 

between 1890 and 2003 (www.spc.noaa.gov/faq/tornado/#History). 

Well-designed, constructed, and maintained hospitals should experience 

little if any damage from weak tornadoes, except for window breakage. 

However, weak tornadoes often cause building envelope damage because 

of wind-resistance deficiencies. Most hospitals experience significant 

damage if they are in the path of a strong or violent tornado because they 

Missile damage is very common during 

hurricanes and tornadoes. Missiles can 

puncture roof coverings, many types of 

exterior walls, and glazing. The IBC does 

not address missile-induced damage, 

except for glazing in wind-borne debris 

regions. (Wind-borne debris regions are 

limited to portions of hurricane-prone 

regions.) In hurricane-prone regions, 

significant missile-induced building damage 

should be expected, even during design 

level hurricane events, unless special 

enhancements are incorporated into the 

building’s design (discussed in Section 4.3).

Missile damage is very common during 

hurricanes and tornadoes. Missiles can 

puncture roof coverings, many types of 

exterior walls, and glazing. The IBC does 

not address missile-induced damage, 

except for glazing in wind-borne debris 

regions. (Wind-borne debris regions are 

limited to portions of hurricane-prone 

regions.) In hurricane-prone regions, 

significant missile-induced building damage 

should be expected, even during design 

level hurricane events, unless special 

enhancements are incorporated into the 

building’s design (discussed in Section 4.3).

ASCE 7, Minimum Design Loads for 

Buildings and Other Structures, provides 

guidance for determining wind loads on 

buildings. The IBC and NFPA 5000 refer 

to ASCE 7 for wind load determination.

ASCE 7, Minimum Design Loads for 

Buildings and Other Structures, provides 

guidance for determining wind loads on 

buildings. The IBC and NFPA 5000 refer 

to ASCE 7 for wind load determination.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-5

typically are not designed for this type of storm. See Section 4.5 for recommendations pertaining to tornadoes. 

4.1.3 Wind/Building Interactions

When wind interacts with a building, both positive and negative (i.e., suction) pressures occur simultaneously. Hospitals must have sufficient 

strength to resist the applied loads from these pressures to prevent windinduced building failure. Loads exerted on the building envelope are 

transferred to the structural system, where in turn they must be transferred through the foundation into the ground. The magnitude of the 

pressures is a function of the following primary factors: exposure, basic 

wind speed, topography, building height, internal pressure, and building 

shape. For general information on these factors, refer to Section 3.1.3 in 

FEMA 543, Design Guide for Improving Critical Facility Safety from Flooding 

and High Winds. A description of key issues follows. 

Wind Speed: In the ASCE 7 formula for determining wind pressures, the basic wind speed is 

squared. Therefore, as the wind speed increases, 

the pressures are exponentially increased, as 

illustrated in Figure 4-3. This figure also illustrates the relative difference in pressures 

exerted on the main wind-force resisting system 

(MWFRS) and the components and cladding 

(C&C) elements.

The MWFRS is an assemblage of structural 

elements assigned to provide support and 

stability for the overall structure. The system 

generally receives wind loading from more 

than one surface. The C&C are elements of 

the building envelope that do not qualify as 

part of the main wind-force resisting system.

The MWFRS is an assemblage of structural 

elements assigned to provide support and 

stability for the overall structure. The system 

generally receives wind loading from more 

than one surface. The C&C are elements of 

the building envelope that do not qualify as 

part of the main wind-force resisting system.

Figure 4-3: Wind pressure as a function of wind speed
4-6 MAKING HOSPITALS SAFE FROM HIGH WIND

Building shape: The highest uplift pressures occur at roof corners because 

of building aerodynamics (i.e., the interaction between the wind and the 

building). The roof perimeter has a somewhat lower load compared to 

the corners, and the field of the roof has still lower loads. Exterior walls 

typically have lower loads than the roof. The ends (edges) of walls have 

higher suction loads than the portion of wall between the ends. However, 

when the wall is loaded with positive pressure, the entire wall is uniformly 

loaded. Figure 4-4 illustrates these aerodynamic influences. The negative 

values shown in Figure 4-4 indicate suction pressure acting upward from 

the roof surface and outward from the wall surface. Positive values indicate positive pressure acting inward on the wall surface. 

Figure 4-4:

Relative roof uplift 

pressures as a function 

of roof geometry, roof 

slope, and location 

on roof, and relative 

positive and negative 

wall pressures as a 

function of location 

along the wall
MAKING HOSPITALS SAFE FROM HIGH WIND 4-7

Aerodynamic influences are accounted for by using external pressure 

coefficients in load calculations. The value of the coefficient is a function of the location on the building (e.g., roof corner or field of roof) 

and building shape as discussed below. Positive coefficients represent 

a positive (inward-acting) pressure, and negative coefficients represent 

negative (outward-acting [suction]) pressure. External pressure coefficients for MWFRS and C&C are listed in ASCE 7.

Building shape affects the value of pressure coefficients and, therefore, 

the loads applied to the various building surfaces. For example, the uplift loads on a low-slope roof are larger than the loads on a gable or hip 

roof. The steeper the slope, the lower the uplift load. Pressure coefficients for monoslope (shed) roofs, sawtooth roofs, and domes are all 

different from those for low-slope and gable/hip roofs.

Building irregularities, such as re-entrant corners, bay window projections, a stair tower projecting out from the main wall, dormers, and 

chimneys can cause localized turbulence. Turbulence causes wind 

speed-up, which increases the wind loads in the vicinity of the building 

irregularity, as shown in Figures 4-5 and 4-6. Figure 4-5 shows the aggregate ballast on a hospital’s single-ply membrane roof blown away at the 

re-entrant corner and in the vicinity of the corners of the wall projections 

at the window bays. The irregular wall surface created turbulence, which 

led to wind speed-up and loss of aggregate in the turbulent flow areas.

Figure 4-6 shows a stair tower at a hospital that caused turbulence resulting in wind speed-up. The speed-up increased the suction pressure 

on the base flashing along the parapet behind the stair tower. The 

built-up roof’s base flashing was pulled out from underneath the 

coping because its attachment was insufficient to resist the suction pressure. The base flashing failure propagated and caused a large area of 

the roof membrane to lift and peel. Some of the wall covering on the 

stair tower was also blown away. Had the stair tower not existed, the 

built-up roof would likely not have been damaged. To avoid damage in 

the vicinity of building irregularities, attention needs to be given to the 

attachment of building elements located in turbulent flow areas. 

To avoid the roof membrane damage shown in 

Figure 4-6, it would be prudent to use corner 

uplift loads in lieu of perimeter uplift loads in 

the vicinity of the stair tower, as illustrated in 

Figure 4-7. Wind load increases due to building 

irregularities can be identified by wind tunnel 

studies; however, wind tunnel studies are rarely 

performed for hospitals. Therefore, identification of wind load increases due to building 

Information pertaining to load calculations 

is presented in Section 4.3.1.2. For further 

general information on the nature of 

wind and wind-building interactions, see 

Buildings at Risk: Wind Design Basics for 

Practicing Architects, American Institute of 

Architects, 1997.

Information pertaining to load calculations 

is presented in Section 4.3.1.2. For further 

general information on the nature of 

wind and wind-building interactions, see 

Buildings at Risk: Wind Design Basics for 

Practicing Architects, American Institute of 

Architects, 1997.
4-8 MAKING HOSPITALS SAFE FROM HIGH WIND

irregularities will normally be based on the designer’s professional judgment. Usually load increases will only need to be applied to the building 

envelope, and not to the MWFRS.

Figure 4-5:

Aggregate blowoff associated with 

building irregularities. 

Hurricane Hugo (South 

Carolina, 1989)

Figure 4-5:

Aggregate blowoff associated with 

building irregularities. 

Hurricane Hugo (South 

Carolina, 1989)

Figure 4-6:

The irregularity 

created by the stair 

tower (covered with 

a metal roof) caused 

turbulence resulting 

in wind speed-up 

and roof damage. 

Hurricane Andrew 

(Florida, 1992)

Figure 4-6:

The irregularity 

created by the stair 

tower (covered with 

a metal roof) caused 

turbulence resulting 

in wind speed-up 

and roof damage. 

Hurricane Andrew 

(Florida, 1992)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-9

4.1.4 Building Codes

The IBC is the most extensively used model code. However, in some jurisdictions NFPA 5000 may be used. In other jurisdictions, one of the earlier 

model building codes, or a specially written State or local building code, 

may be used. The specific scope and/or effectiveness and limitations of 

these other building codes will be somewhat different from those of the 

IBC. It is incumbent upon the design professionals to be aware of the specific code (including the edition of the code and local amendments) that 

has been adopted by the authority having jurisdiction over the location of 

the hospital.

4.1.4.1 Scope of Building Codes

With respect to wind performance, the scope of the model building codes 

has greatly expanded since the mid-1980s. Some of the most significant 

improvements are discussed below.

Recognition of increased uplift loads at the roof perimeter and corners: Prior to 

the 1982 edition of the Standard Building Code (SBC), Uniform Building 

Code (UBC), and the 1987 edition of the National Building Code (NBC), 

Figure 4-7:

Plan view of a portion of the building in 

Figure 4-6 showing the use of a corner uplift 

zone in lieu of a perimeter uplift zone on the 

low-slope roof in the vicinity of the stair tower
4-10 MAKING HOSPITALS SAFE FROM HIGH WIND

these model codes did not account for the increased uplift at the roof perimeter and corners. Therefore, hospitals designed in accordance with 

earlier editions of these codes are very susceptible to blow-off of the roof 

deck and/or roof covering.

Adoption of ASCE 7 for design wind loads: Although the SBC, UBC, and 

NBC permitted use of ASCE 7, the 2000 edition of the IBC was the first 

model code to require ASCE 7 for determining wind design loads on all 

buildings. ASCE 7 has been more reflective of the current state of the 

knowledge than the earlier model codes, and use of this procedure typically has resulted in higher design loads. 

Roof coverings: Several performance and prescriptive requirements pertaining to wind 

resistance of roof coverings have been incorporated into the model codes. The majority of 

these additional provisions were added after 

Hurricanes Hugo (1989) and Andrew (1992). 

Poor performance of roof coverings was widespread in both of those storms. Prior to the 

1991 edition of the SBC and UBC, and the 

1990 edition of the NBC, these model codes 

were essentially silent on roof covering wind 

loads and test methods for determining uplift 

resistance. Code improvements continued to 

be made through the 2006 edition of the IBC, 

which added a provision that prohibits aggregate roof surfaces in hurricane-prone regions.

Glazing protection: The 2000 edition of the IBC was the first model code to 

address wind-borne debris requirements for glazing in buildings located 

in hurricane-prone regions (via reference to the 1998 edition of ASCE 7). 

The 1995 edition of ASCE 7 was the first edition to address wind-borne 

debris requirements.

Parapets and rooftop equipment: The 2003 edition of the IBC was the first 

model code to address wind loads on parapets and rooftop equipment 

(via reference to the 2002 edition of ASCE 7, which was the first edition of 

ASCE 7 to address these elements).

4.1.4.2 Effectiveness and Limitations of Building Codes

A key element of an effective building code is for a community to have 

an effective building department. Building safety depends on more than 

the codes and the standards they reference. Building safety results when 

ASCE 7 requires impact-resistant glazing in 

wind-borne debris regions within hurricaneprone regions. Impact-resistant glazing can 

either be laminated glass, polycarbonate, 

or shutters tested in accordance with 

standards specified in ASCE 7. The 

wind-borne debris load criteria were 

developed to minimize property damage 

and to improve building performance. The 

criteria were not developed for occupant 

protection. Where occupant protection is 

a specific criterion, the more conservative 

wind-borne debris criteria given in FEMA 

361, Design and Construction Guidance 

for Community Shelters is recommended.

ASCE 7 requires impact-resistant glazing in 

wind-borne debris regions within hurricaneprone regions. Impact-resistant glazing can 

either be laminated glass, polycarbonate, 

or shutters tested in accordance with 

standards specified in ASCE 7. The 

wind-borne debris load criteria were 

developed to minimize property damage 

and to improve building performance. The 

criteria were not developed for occupant 

protection. Where occupant protection is 

a specific criterion, the more conservative 

wind-borne debris criteria given in FEMA 

361, Design and Construction Guidance 

for Community Shelters is recommended.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-11

trained professionals have the resources and ongoing support they need 

to stay on top of the latest advancements in building safety. An effective 

building safety system provides uniform code interpretations, product 

evaluations, and professional development and certification for inspectors 

and plan reviewers. Local building departments play an important role in 

helping to ensure buildings are designed and constructed in accordance 

with the applicable building codes. Meaningful plan review and inspection by the building department are particularly important for hospitals.

General limitations to building codes include the following:

m Because codes are adopted and enforced on the local or State 

level, the authority having jurisdiction has the power to eliminate 

or modify wind-related provisions of a model code, or write its own 

code instead. In places where important wind-related provisions of 

the current model code are not adopted and enforced, hospitals are 

more susceptible to wind damage. Additionally, a significant time 

lag often exists between the time a model code is updated and the 

time it is implemented by the authority having jurisdiction. Buildings 

designed to the minimum requirements of an outdated code are, 

therefore, not taking advantage of the current state of the knowledge. 

These buildings are prone to poorer wind performance compared to 

buildings designed according to the current model code.

m Adopting the current model code alone does not ensure good 

wind performance. The code is a minimum that should be used by 

knowledgeable design professionals in conjunction with their training, 

skills, professional judgment, and the best practices presented in this 

manual. To achieve good wind performance, in addition to good 

design, the construction work must be effectively executed, and the 

building must be adequately maintained and repaired.

m Hospitals need to perform at a higher level than required by codes 

and standards. 

IBC 2006: The 2006 edition of the IBC is believed to be a relatively effective code, provided that it is properly followed and enforced. Some 

limitations of the 2006 IBC have, however, been identified:

m With respect to hurricanes, the IBC provisions pertaining to building 

envelopes and rooftop equipment do not adequately address the 

special needs of hospitals. For example: (1) they do not account for 

water infiltration due to puncture of the roof membrane by missiles; 

(2) they do not adequately address the vulnerabilities of brittle roof 

coverings (such as tile) to missile-induced damage and subsequent 

progressive failure; (3) they do not adequately address occupant 
4-12 MAKING HOSPITALS SAFE FROM HIGH WIND

protection with respect to missiles; (4) they do not adequately address 

protection of equipment in elevator penthouses; and (5) they do not 

account for interruption of water service or prolonged interruption 

of electrical power. All of these elements are of extreme importance 

for hospitals, which need to remain operational before, during, and 

after a disaster. Guidance to overcome these shortcomings is given in 

Section 4.3 and 4.4.

m The 2000, 2003, and 2006 IBC rely on several referenced standards 

and test methods developed or updated in the 1990s. Prior to 

adoption, most of these standards and test methods had not been 

validated by actual building performance during design level wind 

events. The hurricanes of 2004 and 2005 provided an opportunity 

to evaluate the actual performance of buildings designed and 

constructed to the minimum provisions of the IBC. Building 

performance evaluations conducted by FEMA revealed the need for 

further enhancements to the 2006 IBC pertaining to some of the 

test methods used to assess wind and wind-driven rain resistance of 

building envelope components. For example, there is no test method 

to assess wind resistance of gutters. Further, the test method to 

evaluate the resistance of windows to wind-driven rain is inadequate 

for high wind events. However, before testing limitations can be 

overcome, research needs to be conducted, new test methods need to 

be developed, and some existing test methods need to be modified.

m Except to the extent covered by reference to ASCE 7, the 2006 IBC 

does not address the requirement for continuity, redundancy, or 

energy-dissipating capability (ductility) to limit the effects of local 

collapse, and to prevent or minimize progressive collapse after the loss 

of one or two primary structural members, such as a column. Chapter 

1 of ASCE 7 addresses general structural integrity, and the Chapter 1

Commentary provides some guidance on this issue.

m The 2006 IBC does not account for tornadoes; therefore, except for 

weak tornadoes, it is ineffective for this type of storm. Guidance to 

overcome this shortcoming is given in Section 4.5.

5 Except for glass breakage, code-compliant buildings should not experience significant damage during weak 

tornadoes.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-13

4.2 HOSPITALS EXPOSED TO HIGH 

WINDS

4.2.1 VULNERABILITY: WHAT HIGH WINDS CAN 

DO TO HOSPITALS

This section provides an overview of the common types of wind damage 

and their ramifications.

4.2.1.1 Types of Building Damage

When damaged by wind, hospitals typically experience a variety of 

building component damage. For example, at the hospital shown in 

Figure 4-8, the roof covering was severely damaged, windows were broken, 

and rooftop equipment was blown away. The subsequent water infiltration 

required that most of the hospital be evacuated. The most common types 

of damage are discussed below in descending order of frequency. 

Figure 4-8:

Field military hospital 

in tents set up to 

replace evacuated 

hospital in U.S. Virgin 

Islands following 

Hurricane Marilyn 

(1995)

Figure 4-8:

Field military hospital 

in tents set up to 

replace evacuated 

hospital in U.S. Virgin 

Islands following 

Hurricane Marilyn 

(1995)
4-14 MAKING HOSPITALS SAFE FROM HIGH WIND

Roof: Roof covering damage (including rooftop mechanical, electrical, 

and communications equipment) is the most common type of wind 

damage, as illustrated by Figure 4-9. In addition to blowoff of the roof 

membrane (yellow arrow), ductwork blew away (red circle), a gooseneck 

was blown over (red arrow), and wall panels at an equipment enclosure 

were blown off (blue arrow). The cast-in-place concrete deck kept most of 

the water from entering the hospital. 

Glazing: Exterior glazing damage is very common during hurricanes and tornadoes, but is less common during other storms. The glass shown in Figure 

4-10 was broken by the aggregate from a built-up roof. The inner panes had 

several impact craters. In several of the adjacent windows, both the outer 

and inner panes were broken. The aggregate flew more than 245 feet (the 

estimated wind speed was 104 mph, measured at 33 feet in Exposure C).

Figure 4-9:

Damaged roof 

membrane and rooftop 

equipment. Typhoon 

Paka (1997)

Figure 4-9:

Damaged roof 

membrane and rooftop 

equipment. Typhoon 

Paka (1997)

Figure 4-10:

The outer window 

panes were broken by 

aggregate from a builtup roof. Hurricane 

Hugo (South Carolina, 

1989)

Figure 4-10:

The outer window 

panes were broken by 

aggregate from a builtup roof. Hurricane 

Hugo (South Carolina, 

1989)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-15

Wall coverings, soffits, and large doors: Exterior wall covering, soffit, and large 

door damage is common during hurricanes and tornadoes, but is less 

common during other storms. Wall covering damage is shown at the hospital 

complex described in the West Florida Hospital case study, Section 4.1.3.

Wall collapse: Collapse of non-load-bearing exterior walls is common 

during hurricanes and tornadoes, but is less common during other 

storms. At the hospital shown in Figure 4-11, a portion of the non-loadbearing wall collapsed. Several windows were also broken by aggregate 

ballast blown from the hospital’s roof (see Figure 4-5).

Structural system: Structural damage (e.g., roof deck blow-off, blow-off or 

collapse of the roof structure, collapse of exterior bearing walls, or collapse 

of the entire building or major portions thereof) is the principal type of 

damage that occurs during strong and violent tornadoes (see Figure 4-12)

.

Figure 4-11:

Collapse of non-loadbearing wall (red 

circle) and broken 

glazing from roof 

aggregate (red arrow). 

Hurricane Hugo (South 

Carolina, 1989)

Figure 4-11:

Collapse of non-loadbearing wall (red 

circle) and broken 

glazing from roof 

aggregate (red arrow). 

Hurricane Hugo (South 

Carolina, 1989)

Figure 4-12:

This building in 

Northern Illinois was 

heavily damaged by 

a strong tornado in 

1990.

Figure 4-12:

This building in 

Northern Illinois was 

heavily damaged by 

a strong tornado in 

1990.
4-16 MAKING HOSPITALS SAFE FROM HIGH WIND

4.2.1.2 Ramifications of Damage

The ramifications of building component damage on hospitals are described below.

Property damage: Property damage requires repairing/replacing the damaged components (or replacing the entire facility), and may require 

repairing/replacing interior building components, furniture, and other 

equipment, and mold remediation. As illustrated by Figures 4-1 and 4-8, 

even when damage to the building envelope is limited, such as blow-off of 

a portion of the roof covering or broken glazing, substantial water 

damage frequently occurs because heavy rains often accompany strong 

winds (particularly in the case of thunderstorms, tropical storms, hurricanes, and tornadoes). 

Wind-borne debris such as roof aggregate, gutters, rooftop equipment, 

and siding blown from buildings can damage vehicles and other buildings 

in the vicinity. Debris can travel well over 300 

feet in high-wind events.

Ancillary buildings (such as storage buildings) 

adjacent to hospitals are also vulnerable to 

damage. Although loss of these buildings may 

not be crippling to the operation of the hospital, debris from ancillary buildings may strike 

and damage the hospital. 

Injury or death: Although infrequent, hospital occupants or people outside hospitals may be injured and killed if struck by collapsed building 

components (such as exterior masonry walls or the roof structure) or 

wind-borne debris. The greatest risk of injury or death is during strong 

hurricanes and strong/violent tornadoes. If a hospital, or a portion of a 

hospital, needs to be evacuated due to wind-related damage, patients may 

be exposed to risk of injury or death during their relocation.

Interrupted use: Depending on the magnitude of wind and water damage, 

it can take days, months, or more than a year to repair the damage or 

replace a facility. In addition to the costs associated with repairing/replacing the damage, 

other social and financial costs can be even 

more significant. The repercussions related to 

interrupted use of hospitals can include lack of 

medical care, and the costs to rent temporary 

facilities. These additional costs can be quite 

substantial.

Modest wind speeds can drive rain into 

exterior walls. Unless adequate provisions 

are taken to account for water infiltration 

(see Sections 4.3.3.1 – 4.3.3.6), 

damaging corrosion, dry rot, and mold 

can occur within walls.

Modest wind speeds can drive rain into 

exterior walls. Unless adequate provisions 

are taken to account for water infiltration 

(see Sections 4.3.3.1 – 4.3.3.6), 

damaging corrosion, dry rot, and mold 

can occur within walls.

Although people are not usually outside 

during hurricanes, it is not uncommon 

for people to seek medical care during a 

storm. Missiles, such as roof aggregate or 

tile shedding from a hospital, could injure 

or kill people before they have a chance to 

enter the building.

Although people are not usually outside 

during hurricanes, it is not uncommon 

for people to seek medical care during a 

storm. Missiles, such as roof aggregate or 

tile shedding from a hospital, could injure 

or kill people before they have a chance to 

enter the building.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-17

4.2.1.3 The Case of West Florida Hospital, Pensacola, 

Florida

The case of West Florida Hospital illustrates a variety of building performance problems. The 531-bed West Florida Healthcare facility (also 

called the Pavillion) includes the 400-bed acute tertiary West Florida Hospital, the 58-bed Rehabilitation Institute, and a 73-bed behavioral health 

facility. The Pavillion is located north of downtown Pensacola, approximately 3 miles west of Escambia Bay and 7 miles north of Pensacola Bay. 

West Florida was struck by Hurricane Ivan in 2004. The estimated peak 

gust wind speed at this site was 105 to 115 mph. The design wind speed 

in the 2005 edition of ASCE 7 for this location is 135 mph. 

The West Florida Hospital (J on Figure 4-13) and several of the other 

buildings on the campus experienced a variety of damages during the 

storm. The roof membrane was punctured in several places by windborne 

missiles and by damaged rooftop equipment (see Figures 4-14 to 4-16). 

Exterior insulation finish system (EIFS) blew off the hospital and caused 

significant glass breakage in the MOB (Figure 4-17) and the walkway connecting the hospital to the MOB. Some of the lower-level windows may 

have been broken by wind-blown aggregate ballast from the roof over the 

dialysis unit and urgent care facility. In addition, some window frames 

6 The 105 to 1115 mph speeds were estimated for Exposure C.

Figure 4-13:

Site plan
4-18 MAKING HOSPITALS SAFE FROM HIGH WIND

were reportedly blown out. These failures were likely caused by the development of high internal pressure after windows on windward surfaces 

were broken by missiles, combined with suction pressure on the exterior surface of windows on the leeward side of the building. Glass damage 

to the MOB, and subsequent wind and water damage to the interior, resulted in closure of several offices. 

In addition to the window breakage, EIFS blew off the elevator enclosure, 

the stair tower, and the spandrels. The single-ply roof membrane was damaged and the Lightning Protection System (LPS) on the MOB was also 

displaced. 

The hospital originally had exposed concrete walls. However, in a subsequent refurbishing, the walls were faced with EIFS. Steel hat channels 

were installed over the concrete, followed by gypsum board, insulation, 

and synthetic stucco. In areas where the EIFS blew off, the gypsum board 

typically pulled over the screw heads and blew away (Figure 4-23). The 

screws and hat channels were moderately corroded. Although the corrosion could have eventually caused loss of the EIFS, it did not play a role in 

this failure.

With loss of the EIFS wall covering, wind-driven rain destroyed the elevator control equipment (see Figure 4-22). Water damage to the elevator 

control equipment resulted in failure of the MOB stair tower elevator. 

As a result, several people were trapped in the MOB stair tower elevator 

shown in Figure 4-18 during the hurricane. Fortunately, the MOB had 

another bank of elevators in the core of the building that was not damaged, so vertical transportation was still possible, although handicapped 

by the loss of the stair tower elevator. At the MOB stair tower, some of the 

gypsum board on the interior side of the studs collapsed into the stairway, 

thus trapping a maintenance worker who had gone to the mechanical 

penthouse during the hurricane. 

Glass shards from the MOB punctured the ballasted single-ply membrane over the regional dialysis unit and urgent care facility (item L on 

Figure 4-13). Although the roof membrane had been punctured in numerous areas (Figure 4-20), the concrete deck (concrete topping over 

metal decking) over the dialysis unit and urgent care facility acted as 

an secondary line of protection against water leakage and was effective 

in minimizing water infiltration into the facility, thereby minimizing interrupted use of these facilities. By quickly performing emergency roof 

repairs and cleaning up the interior, the dialysis unit was non-operational 

for only 1 day. 

At the cancer treatment facility (H on Figure 4-13), asphalt shingles were 

blown from the roof hips and some eave edge metal lifted. Additionally, 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-19

sewage backed up at this facility because of power loss to a lift station. 

Sewage backup was cleaned up quickly and the facility was non-operational for only 1 day.

At the imaging center (F on Figure 4-13), there were some broken windows and a fan cowling blew away. Some large parking lot light fixtures 

also collapsed because the bottoms of the tubes were severely corroded 

(Figure 4-21).

Communications outside of the hospital were lost about an hour after the 

arrival of high winds because of damage to the communications antenna; 

the LPS was also displaced (Figure 4-15). A canopy at the loading dock 

was blown away, which caused difficulties in materials handling.

Because of rapid emergency response by construction and clean-up crews, 

the hospital and other facilities on campus remained functional. However, 

the damage was very costly and created many hardships for hospital staff. 

Figure 4-14:

Numerous repairs 

where the modified 

bitumen roof 

membrane was 

punctured by missiles. 

Water from the 

punctured membrane 

entered the surgical 

suite. 

Figure 4-14:

Numerous repairs 

where the modified 

bitumen roof 

membrane was 

punctured by missiles. 

Water from the 

punctured membrane 

entered the surgical 

suite. 
4-20 MAKING HOSPITALS SAFE FROM HIGH WIND

Figure 4-15:

Damaged rooftop 

equipment (red 

arrows), collapsed 

antenna (circled), and 

displaced LPS (yellow 

arrows)

Figure 4-16:

Damaged rooftop 

equipment. Although 

some of this damage 

may have been 

caused by wind 

pressure, some of 

it was caused by 

missiles. Note the 

open ducts (red 

arrows).

Figure 4-17:

Broken windows in 

the MOB. Wood 

studs and gypsum 

board had been 

temporarily installed 

after the hurricane to 

prevent patients from 

inadvertently falling 

out of the MOB. 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-21

Figure 4-18:

Broken windows in the connecting walkway 

between the hospital (right) and MOB (left) (red 

arrow). Also note the broken windows and loss of 

EIFS (including the gypsum board on both sides of 

the studs) at the elevator enclosure (blue arrow).

Figure 4-19:

EIFS debris blown off the hospital building (Item J on Figure 4-13) in the background (red square) broke 

numerous windows in the MOB (item G on figure 4-13) in the foreground. 
4-22 MAKING HOSPITALS SAFE FROM HIGH WIND

Figure 4-20:

Looking down at the 

one-story roof to the 

right of the MOB 

in Figure 4-19. The 

small dark areas 

are locations where 

emergency patches 

had been placed to 

repair punctures from 

falling glass shards. 

(Note: At the time 

the photo was taken, 

the ballast had been 

repositioned into rows 

in preparation for 

removal)

Figure 4-21:

Collapsed light fixtures caused by severe 

corrosion (see inset). The cancer treatment 

facility is beyond to the left.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-23

Figure 4-23:

Close-up of the 

damaged EIFS at the 

hospital. In this area 

most of the insulation 

and gypsum board 

was blown from the 

steel furring channels.

Figure 4-22: The only remaining portion of the 

exterior wall surrounding the elevator penthouse 

on the MOB was the steel studs. 
4-24 MAKING HOSPITALS SAFE FROM HIGH WIND

4.2.2 EVALUATING HOSPITALS FOR RISK FROM 

HIGH WINDS

This section describes the process of hazard risk assessment. Although 

no formal methodology for risk assessment has been adopted, prior 

experience provides a sufficient knowledge base upon which a set of 

guidelines can be structured into a recommended procedure for risk 

assessment of hospitals. The procedures presented below establish 

guidelines for evaluating the risk to new and existing buildings from 

windstorms other than tornadoes. These evaluations will allow development of a vulnerability assessment that can be used along with the site’s 

wind regime to assess the risk to hospitals.

In the case of tornadoes, neither the IBC nor ASCE 7 requires buildings (including hospitals) to be designed to resist tornado forces, nor 

are occupant shelters required in buildings located in tornado-prone 

regions. Constructing tornado-resistant hospitals is extremely expensive 

because of the extremely high pressures and missile impact loads that 

tornadoes can generate. Therefore, when consideration is voluntarily 

given to tornado design, the emphasis is typically on occupant protection, which is achieved by “hardening” portions of a hospital for use as 

safe havens. FEMA 361 includes a comprehensive risk assessment procedure that designers can use to assist building owners in determining 

whether a tornado shelter should be included as part of a new hospital. 

See Section 4.5 for recommendations pertaining to hospitals in tornado-prone regions.

4.2.2.1 New Buildings

When designing new hospitals, a two-step procedure is recommended for 

evaluating the risk from windstorms (other than tornadoes).

Step 1: Determine the basic wind speed from ASCE 7. As the basic wind 

speed increases beyond 90 mph, the risk of damage increases. Design, 

construction, and maintenance enhancements are recommended to compensate for the increased risk of damage (see Section 4.3).

Step 2: For hospitals in hurricane-prone regions, refer to the design, construction, and maintenance enhancements recommended in Sections 

4.3.1.5, 4.3.2.1, 4.3.3.2, 4.3.3.4, 4.3.3.6, 4.3.3.8, 4.3.4.2, 4.3.4.4, 4.3.5, and 

4.3.6. 

For hospitals in remote areas outside of hurricane-prone regions, it is 

recommended that robust design measures be considered to minimize 

the potential for disruption resulting from wind damage. Because of their 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-25

remote location, disruption of hospitals could severely affect patients. 

Some of the recommendations in the sections pertaining to hurricaneprone regions may therefore be prudent.

4.2.2.2 Existing Buildings

The resistance of existing buildings is a function of their original design 

and construction, various additions or modifications, and the condition 

of building components (which may have weakened due to deterioration or fatigue). For existing buildings, a two-step procedure is also 

recommended.

Step 1: Calculate the wind loads on the building using the current edition 

of ASCE 7, and compare these loads with the loads for which the building 

was originally designed. The original design loads may be noted on the 

contract drawings. If not, determine what building code or standard was 

used to develop the original design loads, and calculate the loads using 

that code or standard. If the original design loads are significantly lower 

than current loads, upgrading the load resistance of the building envelope and/or structure should be considered. An alternative to comparing 

current loads with original design loads is to evaluate the resistance of the 

existing facility as a function of the current loads to determine what elements are highly overstressed.

Step 2: Perform a field investigation to evaluate the primary building envelope elements, rooftop equipment, and structural system elements, to 

determine if the facility was generally constructed as indicated on the 

original contract drawings. As part of the investigation, the primary elements should be checked for deterioration. Load path continuity should 

also be checked.

If the results of either step indicate the need for remedial work, see Section 4.4.
4-26 MAKING HOSPITALS SAFE FROM HIGH WIND

4.3 REQUIREMENTS AND BEST 

PRACTICES IN HIGH-WIND REGIONS 

4.3.1 General Hospital Design

Considerations

T he performance of hospitals in past wind storms indicates that 

the most frequent and the most significant factor in the disruption of the operations of these facilities has been the failure 

of nonstructural building components. While acknowledging the importance of the structural systems, Chapter 4 emphasizes the building 

envelope components and the nonstructural systems. According to National Institute of Building Sciences (NIBS), the building envelope 

includes the below-grade basement walls and foundation and floor slab 

(although these are generally considered part of the building’s structural 

system). The envelope includes everything that separates the interior of a 

building from the outdoor environment, including the connection of all 

the nonstructural elements to the building structure. The nonstructural 

systems include all mechanical, electrical, electronic, communications, 

and lightning protection systems. Historically, damage to roof coverings 

and rooftop equipment has been the leading cause of building performance problems during windstorms. Special consideration should be 

given to the problem of water infiltration through failed building envelope components, which can cause severe disruptions in the functioning 

of hospitals. 

The key to enhanced wind performance is paying sufficient attention to 

all phases of the construction process (including site selection, design, 

and construction) and to post-occupancy maintenance and repair. 

Hospital Design Considerations In Hurricane-Prone Regions

Following the general design and construction recommendations, this 

manual presents recommendations specific to hospitals located in hurricane-prone regions. These recommendations are additional to the 

ones presented for hospitals located outside of hurricane-prone regions, 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-27

and in many cases supersede those recommendations. Hospitals located 

in hurricane-prone regions require special design and construction attention because of the unique characteristics of this type of windstorm. 

Hurricanes can bring very high winds that last for many hours, which 

can lead to material fatigue failures. The variability of wind direction increases the probability that the wind will approach the building at the 

most critical angle. Hurricanes also generate a large amount of windborne debris, which can damage various building components and cause 

injury and death. 

Hospitals in hurricane-prone regions require special attention because 

they normally have vulnerable occupants (patients) at the time of a hurricane, and afterwards, many injured people seek medical care. Significant 

damage to a hospital can put patients at risk and jeopardize delivery of 

care to those seeking treatment. In order to ensure continuity of service 

during and after hurricanes, the design, construction, and maintenance 

of hospitals should be very robust to provide sufficient resiliency to withstand the effects of hurricanes.

Full or partial evacuation of a hospital prior to, during, or after a hurricane is time consuming, expensive, and for some patients, potentially life 

threatening. Water infiltration that could damage electrical equipment 

or medical supplies, or inhibit the use of critical areas (such as operating 

rooms and nursing floors) needs to be prevented. The emergency and 

standby power systems need to remain operational and be adequately 

sized to power all needed circuits, including the HVAC system. Provisions 

are needed for water and sewer service in the event of loss of municipal 

services, and antenna towers need to be strong enough to resist the wind. 

Because of advanced warning of impending land fall, with the exception of Hurricane Katrina 

(Louisiana and Mississippi, 2005), the death toll from hurricanes in the U.S. has been extremely 

low for the last several decades. However, large numbers of people are often injured and seek 

care at hospitals. Blunt-force trauma injuries caused by wind-borne debris, falling trees, collapsed 

ceilings, or partial building collapse occur during hurricanes. But most of the hurricane-related 

injuries typically occur in the days afterward. These injuries are typically due to chainsaw 

accidents, stepping on nails, lacerations incurred while removing debris, vehicle accidents at 

intersections that no longer have functional traffic lights, people falling off roofs as they attempt to 

make emergency repairs, and carbon monoxide poisoning or electrical shock from improper use 

of emergency generators. Therefore, at a time when many hospitals in an area may be functionally 

impaired or no longer capable of providing service due to building damage (Figures 4-1 and 4-8), 

hospital staffs are faced with a higher than normal number of people seeking treatment. Before 

arrival of a hurricane, hospitals also often receive an influx of women in their third trimester of 

pregnancy, so that they will already be at the hospital in case they go into labor during the storm 

or shortly thereafter, when getting to the hospital could be hazardous or impossible.

Because of advanced warning of impending land fall, with the exception of Hurricane Katrina 

(Louisiana and Mississippi, 2005), the death toll from hurricanes in the U.S. has been extremely 

low for the last several decades. However, large numbers of people are often injured and seek 

care at hospitals. Blunt-force trauma injuries caused by wind-borne debris, falling trees, collapsed 

ceilings, or partial building collapse occur during hurricanes. But most of the hurricane-related 

injuries typically occur in the days afterward. These injuries are typically due to chainsaw 

accidents, stepping on nails, lacerations incurred while removing debris, vehicle accidents at 

intersections that no longer have functional traffic lights, people falling off roofs as they attempt to 

make emergency repairs, and carbon monoxide poisoning or electrical shock from improper use 

of emergency generators. Therefore, at a time when many hospitals in an area may be functionally 

impaired or no longer capable of providing service due to building damage (Figures 4-1 and 4-8), 

hospital staffs are faced with a higher than normal number of people seeking treatment. Before 

arrival of a hurricane, hospitals also often receive an influx of women in their third trimester of 

pregnancy, so that they will already be at the hospital in case they go into labor during the storm 

or shortly thereafter, when getting to the hospital could be hazardous or impossible.
4-28 MAKING HOSPITALS SAFE FROM HIGH WIND

4.3.1.1 Site 

When selecting land for a hospital, sites located in Exposure D (see ASCE 

7 for exposure definitions) should be avoided if possible. Selecting a 

site in Exposure C or preferably in Exposure B would decrease the wind 

loads. Also, where possible, avoid selecting sites located on an escarpment 

or the upper half of a hill, where the abrupt change in the topography 

would result in increased wind loads.

Trees with trunks larger than 6 inches in diameter, poles (e.g., light 

fixture poles, flagpoles, and power poles), or towers (e.g., electrical transmission and large communication towers) should not be placed near the 

building. Falling trees, poles, and towers can severely damage a hospital 

and injure the occupants (see Figure 4-24). Large trees can crash through 

pre-engineered metal buildings and wood frame construction. Falling 

trees can also rupture roof membranes and break windows.

Street signage should be designed to resist the design wind loads so that 

toppled signs do not block access roads or become wind-blown debris. 

AASHTO LTS-4-M (amended by LTS-4-12 2001 and 2003, respectively) 

provides guidance for determining wind loads on highway signs. 

Providing at least two means of site egress is prudent for all hospitals, but 

is particularly important for hospitals in hurricane-prone regions. If one 

route becomes blocked by trees or other debris, or by floodwaters, the 

other access route may still be available.

7 When selecting a site on an escarpment or the upper half of a hill is necessary, the ASCE 7 design procedure 

accounts for wind speed-up associated with this abrupt change in topography.

Figure 4-24:

The roof membrane on 

this hospital’s materials 

management facility 

was ruptured by falling 

trees. Hurricane Ivan 

(Florida, 2004)

Figure 4-24:

The roof membrane on 

this hospital’s materials 

management facility 

was ruptured by falling 

trees. Hurricane Ivan 

(Florida, 2004)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-29

4.3.1.2 Building Design 

Good wind performance depends on good design (including details and 

specifications), materials, installation, maintenance, and repair. A significant shortcoming in any of these five elements could jeopardize the 

performance of a hospital against wind. Design, however, is the key element to achieving good performance of a building against wind damage. 

Design inadequacies frequently cannot be compensated for with other elements. Good design, however, can compensate for other inadequacies to 

some extent. The following steps should be included in the design process for hospitals.

Step 1: Calculate Loads 

Calculate loads on the MWFRS, the building envelope, and rooftop equipment in accordance 

with ASCE 7 or the local building code, whichever procedure results in the highest loads. In 

calculating wind loads, design professionals 

should consider the following items.

Importance factor: The effect of using a 1.15 importance factor versus 1 is that the design loads 

for the MWFRS and C&C are increased by 15 

percent. The importance factor for hospitals is 

required to be 1.15. However, some buildings on 

a hospital campus, such as medical office buildings that are integrally connected to the hospital 

and various types of non-emergency treatment facilities (such as storage, cancer treatment, physical therapy, and dialysis), 

are not specifically required by ASCE 7 to be designed with a 1.15 factor. 

This manual recommends a value of 1.15 for all facilities on a hospital 

campus.

Wind directionality factor: The ASCE 7 wind load 

calculation procedure incorporates a wind directionality factor (kd). The directionality factor 

accounts for the reduced probability of maximum winds coming from any given direction. By 

applying the prescribed value of 0.85, the loads 

are reduced by 15 percent. Because hurricane 

winds can come from any direction, and because 

of the historically poor performance of building 

envelopes and rooftop equipment, this manual 

recommends a more conservative approach for 

In the past, design professionals seldom 

performed load calculations on the 

building envelope (i.e., roof and wall 

coverings, doors, windows, and skylights) 

and rooftop equipment. These building 

components are the ones that have failed 

the most during past wind events. In 

large part they failed because of the 

lack of proper load determination and 

inappropriate design of these elements. 

It is imperative that design professionals 

determine the loads for the building 

envelope and rooftop equipment, and 

design them to accommodate such loads.

In the past, design professionals seldom 

performed load calculations on the 

building envelope (i.e., roof and wall 

coverings, doors, windows, and skylights) 

and rooftop equipment. These building 

components are the ones that have failed 

the most during past wind events. In 

large part they failed because of the 

lack of proper load determination and 

inappropriate design of these elements. 

It is imperative that design professionals 

determine the loads for the building 

envelope and rooftop equipment, and 

design them to accommodate such loads.

Uplift loads on roof assemblies can also be 

determined from FM Global (FMG) Data 

Sheets. If the hospital is FMG insured, and 

the FMG-derived loads are higher than 

those derived from ASCE 7 or the building 

code, the FMG loads should govern. 

However, if the ASCE 7 or code-derived 

loads are higher than those from FMG, 

the ASCE 7 or code-derived loads should 

govern (whichever procedure results in the 

highest loads).

Uplift loads on roof assemblies can also be 

determined from FM Global (FMG) Data 

Sheets. If the hospital is FMG insured, and 

the FMG-derived loads are higher than 

those derived from ASCE 7 or the building 

code, the FMG loads should govern. 

However, if the ASCE 7 or code-derived 

loads are higher than those from FMG, 

the ASCE 7 or code-derived loads should 

govern (whichever procedure results in the 

highest loads).
4-30 MAKING HOSPITALS SAFE FROM HIGH WIND

hospitals in hurricane-prone regions. A directionality factor of 1.0 is recommended for the building envelope and rooftop equipment (a load 

increase over what is required by ASCE 7). For the MWFRS, a directionality factor of 0.85 is recommended (hence, no change for MWFRS).

Step 2: Determine Load Resistance

When using allowable stress design, after loads have been determined, it 

is necessary to determine a reasonable safety factor in order to select the 

minimum required load resistance. For building envelope systems, a minimum safety factor of 2 is recommended. For anchoring exterior-mounted 

mechanical, electrical, and communications equipment (such as satellite dishes), a minimum safety factor of 3 is recommended. When using 

strength design, load combinations and load factors specified in ASCE 7 

are used.

ASCE 7 provides criteria for combining wind 

loads with other types of loads (such as dead 

and flood loads) using allowable stress design.

For structural members and cladding elements 

where strength design can be used, load resistance can be determined by calculations. For 

other elements where allowable stress design 

is used (such as most types of roof coverings), 

load resistance is primarily obtained from 

system testing.

The load resistance criteria need to be provided in contract documents. For structural 

elements, the designer of record typically accounts for load resistance by indicating the 

material, size, spacing, and connection of the 

elements. For nonstructural elements, such 

as roof coverings or windows, the load and 

safety factor can be specified. In this case, 

the specifications should require the contractor’s submittals to demonstrate that the system 

will meet the load resistance criteria. This performance specification approach is necessary if, at the time of the design, it is unknown who will 

manufacture the system.

Regardless of which approach is used, it is important that the designer of 

record ensure that it can be demonstrated, via calculations or tests, that 

the structure, building envelope, and nonstructural systems (exteriorWhen using allowable stress design, a 

safety factor is applied to account for 

reasonable variations in material strengths, 

construction workmanship, and conditions 

when the actual wind speed somewhat 

exceeds the design wind speed. For 

design purposes, the ultimate resistance 

an assembly achieves in testing is reduced 

by the safety factor. For example, if a 

roof assembly resisted an uplift pressure 

of 100 pounds per square foot (psf), after 

applying a safety factor of 2, the assembly 

would be suitable where the design load 

was 50 psf or less. Conversely, if the 

design load is known, multiplying it by the 

safety factor equals the minimum required 

test pressure (e.g., 50 psf design load 

multiplied by a safety factor of 2 equals a 

minimum required test pressure of 100 psf). 

When using allowable stress design, a 

safety factor is applied to account for 

reasonable variations in material strengths, 

construction workmanship, and conditions 

when the actual wind speed somewhat 

exceeds the design wind speed. For 

design purposes, the ultimate resistance 

an assembly achieves in testing is reduced 

by the safety factor. For example, if a 

roof assembly resisted an uplift pressure 

of 100 pounds per square foot (psf), after 

applying a safety factor of 2, the assembly 

would be suitable where the design load 

was 50 psf or less. Conversely, if the 

design load is known, multiplying it by the 

safety factor equals the minimum required 

test pressure (e.g., 50 psf design load 

multiplied by a safety factor of 2 equals a 

minimum required test pressure of 100 psf). 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-31

mounted mechanical, electrical, and communications equipment) have 

sufficient strength to resist design wind loads.

Step 3: Detailed Design

It is vital to design, detail, and specify the structural system, building 

envelope, and exterior-mounted mechanical, electrical, and communications equipment to meet the factored design 

loads (based on appropriate analytical or test 

methods). It is also vital to respond to the risk assessment criteria discussed in Section 4.2.2, as 

appropriate.

As part of the detailed design effort, load path 

continuity should be clearly indicated in the contract documents via illustration of connection 

details. Load paths need to accommodate design uplift, racking, and overturning loads. Load 

path continuity obviously applies to MWFRS elements, but it also applies to building envelope 

elements. Figure 4-25 shows a load path discontinuity between a piece of HVAC equipment and 

its equipment stand. The equipment on this new building blew away because it was resting on vibration isolators that provided lateral resistance, 

but no uplift resistance (also see Figure 4-92).

Figure 4-26 illustrates the load path concept. Members are sized to accommodate the design loads. Connections are designed to transfer uplift 

loads applied to the roof, and the positive and negative loads applied to 

Connections are a key aspect of load 

path continuity between various structural 

and nonstructural building elements. In a 

window, for example, the glass must be 

strong enough to resist the wind pressure 

and must be adequately anchored to the 

window frame, the frame adequately 

anchored to the wall, the wall to the 

foundation, and the foundation to the 

ground. As loads increase, greater 

load capacity must be developed in the 

connections.

Connections are a key aspect of load 

path continuity between various structural 

and nonstructural building elements. In a 

window, for example, the glass must be 

strong enough to resist the wind pressure 

and must be adequately anchored to the 

window frame, the frame adequately 

anchored to the wall, the wall to the 

foundation, and the foundation to the 

ground. As loads increase, greater 

load capacity must be developed in the 

connections.

Figure 4-25:

Temporary coverings 

placed over two large 

openings in the roof 

that were left after the 

ductwork blew away. 

Hurricane Katrina 

(Mississippi, 2005)

Figure 4-25:

Temporary coverings 

placed over two large 

openings in the roof 

that were left after the 

ductwork blew away. 

Hurricane Katrina 

(Mississippi, 2005)
4-32 MAKING HOSPITALS SAFE FROM HIGH WIND

the exterior bearing walls, down to the foundation and into the ground. 

The roof covering (and wall covering, if there is one) is also part of the 

load path. To avoid blow-off, the nonstructural elements must also be adequately attached to the structure.

As part of the detailed design process, special consideration should be 

given to the durability of materials and water infiltration.

Durability: Because some locales have very aggressive atmospheric corrosion (such as areas near oceans), special attention needs to be given to 

the specification of adequate protection for ferrous metals, or to specify 

Figure 4-26:

Illustration of load path 

continuity
MAKING HOSPITALS SAFE FROM HIGH WIND 4-33

alternative metals such as stainless steel. FEMA Technical Bulletin, Corrosion Protection for Metal Connectors in Coastal Areas (FIA-TB-8, 1996), 

contains information on corrosion protection. Attention also needs to be 

given to dry rot avoidance, for example, by specifying preservative-treated 

wood or developing details that avoid excessive moisture accumulation. 

Appendix J of the Coastal Construction Manual, (FEMA 55, 2000) presents 

information on wood durability. 

Durable materials are particularly important for 

components that are inaccessible and cannot 

be inspected regularly (such as fasteners used 

to attach roof insulation). Special attention also 

needs to be given to details. For example, details 

that do not allow water to stand at connections 

or sills are preferred. Without special attention 

to material selection and details, the demands on maintenance and repair will be increased, along with the likelihood of failure of components 

during high winds.

Water infiltration (rain): Although prevention of building collapse and 

major building damage is the primary goal of wind-resistant design, 

consideration should also be given to minimizing water damage and subsequent development of mold from the penetration of wind-driven rain. 

To the extent possible, non-load-bearing walls and door and window 

frames should be designed in accordance with rain-screen principles. 

With this approach, it is assumed that some water will penetrate past the 

face of the building envelope. The water is intercepted in an air-pressure 

equalized cavity that provides drainage from the cavity to the outer surface of the building. See Sections 4.3.3.1 and 4.3.3.5, and Figure 4-45 for 

further discussion and an example. 

Further information on the rain-screen 

principle can be found in the National 

Institute of Building Sciences’ Building 

Envelope Design Guide (www.wbdg.org/

design/envelope.php).

Further information on the rain-screen 

principle can be found in the National 

Institute of Building Sciences’ Building 

Envelope Design Guide (www.wbdg.org/

design/envelope.php).

Coastal environments are conducive to metal corrosion, especially in buildings within 3,000 feet 

of the ocean. Most jurisdictions require metal building hardware to be hot-dipped galvanized or 

stainless steel. Some local codes require protective coatings that are thicker than typical “off-theshelf” products. For example, a G90 zinc coating (0.75 mil on each face) may be required. Other 

recommendations include the following:

m Use hot-dipped galvanized or stainless steel hardware. Reinforcing steel should be fully protected 

from corrosion by the surrounding material (masonry, mortar, grout, or concrete). Use galvanized 

or epoxy-coated reinforcing steel in situations where the potential for corrosion is high.

m Avoid joining dissimilar metals, especially those with high galvanic potential.

m Avoid using certain wood preservatives in direct contact with galvanized metal. Verify that 

wood treatment is suitable for use with galvanized metal, or use stainless steel.

m Metal-plate-connected trusses should not be exposed to the elements. Truss joints near vent 

openings are more susceptible to corrosion and may require increased corrosion protection.

Note: Although more resistant than other metals, stainless steel is still subject to corrosion. 
4-34 MAKING HOSPITALS SAFE FROM HIGH WIND

In conjunction with the rain-screen principle, it is desirable to avoid using 

sealant as the first or only line of defense against water infiltration. When 

sealant joints are exposed, obtaining long-lasting watertight performance is 

difficult because of the complexities of sealant joint design and installation 

(see Figure 4-45, which shows the sealant protected by a removable stop).

Step 4: Peer Review

If the design team’s wind expertise and experience is limited, wind 

design input and/or peer review should be sought from a qualified individual. The design input or peer review could be arranged for the entire 

building, or for specific components, such as the roof or glazing systems, 

that are critical and beyond the design team’s expertise. 

Regardless of the design team’s expertise and experience, peer review 

should be considered when a hospital:

m Is located in an area where the basic wind speed is greater than 90 

mph (peak gust).

m Will incorporate a tornado shelter.

4.3.1.3 Construction Contract Administration

After a suitable design is complete, the design team should endeavor to 

ensure that the design intent is achieved during construction. The key elements of construction contract administration are submittal reviews and 

field observations, as discussed below.

Submittal reviews: The specifications need to stipulate the submittal requirements. This includes specifying what systems require submittals (e.g., 

windows) and test data (where appropriate). Each submittal should demonstrate the development of a load path through the system and into its 

supporting element. For example, a window submittal should show that 

the glazing has sufficient strength, its attachment to the frame is adequate, and the attachment of the frame to the wall is adequate.

During submittal review, it is important for the designer of record to 

be diligent in ensuring that all required documents are submitted and 

that they include the necessary information. The submittal information 

needs to be thoroughly checked to ensure its validity. For example, if an 

approved method used to demonstrate compliance with the design load 

has been altered or incorrectly applied, the test data should be rejected, 

unless the contractor can demonstrate the test method was suitable. 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-35

Similarly, if a new test method has been developed by a manufacturer or 

the contractor, the contractor should demonstrate its suitability.

Field observations: It is recommended that the design team analyze the 

design to determine which elements are critical to ensuring high-wind 

performance. The analysis should include the structural system and exterior-mounted electrical equipment, but it should focus on the building 

envelope and exterior-mounted mechanical and communications equipment. After determining the list of critical elements to be observed, 

observation frequency and the need for special inspections by an inspection firm should be determined. Observation frequency and the need for 

special inspections will depend on the magnitude of the results of the risk 

assessment described in Section 4.2.2, complexity of the facility, and the 

competency of the general contractor, subcontractors, and suppliers.

4.3.1.4 Post-Occupancy Inspections, Periodic 

Maintenance, Repair, and Replacement

The design team should advise the building owner of the importance 

of periodic inspections, maintenance, and timely repair. It is important 

for the building owner to understand that a facility’s wind resistance 

will degrade over time due to exposure to weather unless it is regularly 

maintained and repaired. The goal should be to repair or replace items 

before they fail in a storm. This approach is less expensive than waiting 

for failure and then repairing the failed components and consequential 

damage. 

The building envelope and exterior-mounted equipment should be inspected once a year by persons knowledgeable of the systems/materials 

they are inspecting. Items that require maintenance, repair, or replacement should be documented and scheduled for work. For example, the 

deterioration of glazing is often overlooked. After several years of exposure, scratches and chips can become extensive enough to weaken the 

glazing. Also, if an engineered film was surface-applied to glazing for 

wind-borne debris protection, the film should be periodically inspected 

and replaced before it is no longer effective.

A special inspection is recommended following unusually high winds 

(such as a thunderstorm with wind speeds of 70 mph peak gust or 

greater). The purpose of the inspection is to assess whether the storm 

caused damage that needs to be repaired to maintain building strength 

and integrity. In addition to inspecting for obvious signs of damage, the 

inspector should determine if cracks or other openings have developed 

that may allow water infiltration, which could lead to corrosion or dry rot 

of concealed components.
4-36 MAKING HOSPITALS SAFE FROM HIGH WIND

4.3.1.5 Site and General Design Considerations in 

Hurricane-Prone Regions

Via ASCE 7, the 2006 edition of the IBC has only one special wind-related provision pertaining to hospitals in hurricane-prone regions. It 

pertains to glazing protection within wind-borne debris regions (as defined in ASCE 7). This single additional requirement does not provide 

adequate protection for occupants of a hospital during a hurricane, nor 

does it ensure a hospital will remain functional during and after a hurricane. A hospital may comply with IBC but still remain vulnerable to 

water and missile penetration through the roof or walls. To provide occupant protection, the exterior walls and the roof must be designed and 

constructed to resist wind-borne debris as discussed in Sections 4.3.2.1, 

4.3.3.2, 4.3.3.4, 4.3.3.6, and 4.3.3.8. The following recommendations are 

made regarding siting:

m Locate poles, towers, and trees with trunks larger than 6 inches in 

diameter away from primary site access roads so that they do not block 

access to, or hit, the facility if toppled.

m Determine if existing buildings within 1,500 feet of the new facility 

have aggregate surfaced roofs. If roofs with aggregate surfacing are 

present, it is recommended that the aggregate be removed to prevent 

it from striking the new facility. Aggregate removal may necessitate 

reroofing or other remedial work in order to maintain the roof’s fire 

or wind resistance.

m In cases where multiple buildings are occupied during a storm, it 

is recommended that enclosed walkways be designed to connect 

the buildings. The enclosed walkways (above- or below-grade) 

are particularly important for protecting people moving between 

buildings during a hurricane (e.g., to retrieve equipment or supplies) 

or for situations when it is necessary to evacuate occupants from one 

building to another during a hurricane (see Figure 4-27).
MAKING HOSPITALS SAFE FROM HIGH WIND 4-37

4.3.2 Structural Systems 

Based on post-storm damage evaluations, with the exception of strong and 

violent tornado events, the structural systems (i.e., MWFRS and structural 

components such as roof decking) of hospitals have typically performed 

quite well during design wind events. There have, however, been notable 

exceptions; in these cases, the most common problem has been blow-off 

of the roof deck, but instances of collapse have also been documented 

(Figure 4-34). The structural problems have primarily been caused by lack 

of an adequate load path, with connection failure being a common occurrence. Problems have also been caused by workmanship errors (commonly 

associated with steel decks attached by puddle welds), and limited uplift resistance of deck connections in roof perimeters and corners (due to lack 

of code-required enhancement in older editions of the model codes).

With the exception of strong and violent tornado events, structural systems designed and constructed in accordance with the IBC should typically 

offer adequate wind resistance, provided attention was given to load path 

continuity and to the durability of building materials (with respect to 

corrosion and termites). However, the greatest reliability is offered by cast-inplace concrete. There are no known reports of any cast-in-place concrete 

buildings experiencing a significant structural problem during wind events, 

including the strongest hurricanes (Category 5) and tornadoes (F5). 

The following design parameters are recommended for structural systems:

m If a pre-engineered metal building is being contemplated, special steps 

should be taken to ensure the structure has more redundancy than 

Figure 4-27:

Open walkways 

do not provide 

protection from 

wind-borne debris. 

(Hurricane Katrina, 

Mississippi)
4-38 MAKING HOSPITALS SAFE FROM HIGH WIND

is typically the case with pre-engineered buildings. Steps should be 

taken to ensure the structure is not vulnerable to progressive collapse 

in the event a primary bent (steel moment frame) is compromised or 

bracing components fail.

m Exterior load-bearing walls of masonry or precast concrete should 

be designed to have sufficient strength to resist external and internal 

loading when analyzed as C&C. CMU walls should have vertical and 

horizontal reinforcing and grout to resist wind loads. The connections 

of precast concrete wall panels should be designed to have sufficient 

strength to resist wind loads.

m For roof decks, concrete, steel, plywood, or oriented strand board 

(OSB) is recommended. 

m For steel roof decks, it is recommended that a screw attachment be 

specified, rather than puddle welds or powder-driven pins. Screws are 

more reliable and much less susceptible to workmanship problems. 

Figure 4-28 shows decking that was attached with puddle welds. At 

most of the welds, there was only superficial bonding of the metal 

deck to the joist, as illustrated by this example. Only a small portion of 

the deck near the center of the weld area (as delineated by the circle) 

was well fused to the joist. Figures 4-29 and 4-30 show problems with 

acoustical decking attached with powder-driven pins. The pin shown 

on the left of Figure 4-30 is properly seated. However, the pin at the 

right did not penetrate far enough into the steel joist below. 

8 The structural system of pre -engineered metal buildings is composed of rigid steel frames, secondary members 

(including roof purlins and wall girts made of Z- or C-shaped members) and bracing.

Figure 4-28:

View looking down at 

the top of a steel joist 

after the metal decking 

blew away. Only a 

small portion of the 

deck was well fused to 

the joist (circled area). 

Tornado (Oklahoma, 

1999)

Figure 4-28:

View looking down at 

the top of a steel joist 

after the metal decking 

blew away. Only a 

small portion of the 

deck was well fused to 

the joist (circled area). 

Tornado (Oklahoma, 

1999)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-39

m For attaching wood-sheathed roof decks, screws, ring-shank, or screwshank nails are recommended in the corner regions of the roof. 

Where the basic wind speed is greater than 90 mph, these types of 

fasteners are also recommended for the perimeter regions of the roof.

m For precast concrete decks it is recommended that the deck 

connections be designed to resist the design uplift loads because the 

deck dead load itself is often insufficient to resist the uplift. The deck 

in Figure 4-31 had bolts to provide uplift resistance; however, anchor 

plates and nuts had not been installed. Without the anchor plates, the 

dead load of the deck was insufficient to resist the wind uplift load.

Figure 4-31:

Portions of this waffled 

precast concrete roof 

deck were blown off. 

Typhoon Paka (Guam, 

1997)

Figure 4-31:

Portions of this waffled 

precast concrete roof 

deck were blown off. 

Typhoon Paka (Guam, 

1997)

Figure 4-29:

Looking down at a sidelap of a deck attached 

with powder-driven pins. The washer at the top 

pin blew through the deck.

Figure 4-30:

View looking along a sidelap of a deck attached 

with powder-driven pins. The right pin does not 

provide adequate uplift and shear resistance.
4-40 MAKING HOSPITALS SAFE FROM HIGH WIND

m For precast Tee decks, it is recommended that the reinforcing be 

designed to accommodate the uplift loads in addition to the gravity 

loads. Otherwise, large uplift forces can cause member failure due to 

the Tee’s own pre-stress forces after the uplift load exceeds the dead 

load of the Tee. This type of failure occurred at one of the roof panels 

shown in Figure 4-32, where a panel lifted because of the combined 

effects of wind uplift and pre-tension. Also, because the connections 

between the roof and wall panels provided very little uplift load 

resistance, several other roof and wall panels collapsed.

m For buildings that have mechanically attached single-ply or modified 

bitumen membranes, designers should refer to the decking 

recommendations presented in the Wind Design Guide for Mechanically 

Attached Flexible Membrane Roofs, B1049 (National Research Council of 

Canada, 2005).

m If an FMG-rated roof assembly is specified, the roof deck also needs to 

comply with the FMG criteria.

Figure 4-32:

Twin-Tee roof panel 

lifted as a result of 

the combined effects 

of wind uplift and 

pre-tension. Tornado 

(Missouri, May 2003)

Figure 4-32:

Twin-Tee roof panel 

lifted as a result of 

the combined effects 

of wind uplift and 

pre-tension. Tornado 

(Missouri, May 2003)

ASCE 7-05 provides pressure coefficients for open canopies of various 

slopes (referred to as “free roofs” in ASCE 7). The free roof figures for 

MWFRS in ASCE 7-05 (Figures 6-18A to 6-18D) include two load cases, 

Case A and Case B. While there is no discussion describing the two load 

cases, they pertain to fluctuating loads and are intended to represent 

upper and lower limits of instantaneous wind pressures. Loads for both 

cases must be calculated to determine the critical loads. Figures 6-18A 

to 6-18C are for a wind direction normal to the ridge. For wind direction 

parallel to the ridge, use Figure 6-18D in ASCE 7-05.

ASCE 7-05 provides pressure coefficients for open canopies of various 

slopes (referred to as “free roofs” in ASCE 7). The free roof figures for 

MWFRS in ASCE 7-05 (Figures 6-18A to 6-18D) include two load cases, 

Case A and Case B. While there is no discussion describing the two load 

cases, they pertain to fluctuating loads and are intended to represent 

upper and lower limits of instantaneous wind pressures. Loads for both 

cases must be calculated to determine the critical loads. Figures 6-18A 

to 6-18C are for a wind direction normal to the ridge. For wind direction 

parallel to the ridge, use Figure 6-18D in ASCE 7-05.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-41

m Walkway and entrance canopies are often damaged during high winds 

(see Figure 4-33). Wind-borne debris from damaged canopies can 

damage nearby buildings and injure people, hence these elements 

should also receive design and construction attention. 

4.3.2.1 Structural Systems in Hurricane-Prone Regions

Because of the exceptionally good wind performance and wind-borne debris resistance that reinforced cast-in-place concrete structures offer, a 

reinforced concrete roof deck and reinforced concrete or reinforced and 

fully grouted CMU exterior walls are recommended as follows:

Roof deck: A minimum 4-inch-thick, cast-in-place reinforced concrete 

deck is the preferred deck. Other recommended decks are minimum 

4-inch-thick structural concrete topping over steel 

decking, and precast concrete with an additional 

minimum 4-inch structural concrete topping.

If these recommendations are not followed 

for hospitals located in areas where the basic wind speed is 100 mph or 

greater, it is recommended that the roof assembly be able to resist complete penetration of the deck by the “D” missile specified in ASTM E 1996 

(2005) (see text box in Section 4.3.3.2). 

Exterior load-bearing walls: A minimum 6-inch-thick, cast-in-place concrete 

wall reinforced with #4 rebars at 12 inches on center each way is the preferred wall. Other recommended walls are a minimum 8-inch-thick fully 

grouted CMU reinforced vertically with #4 rebars at 16 inches on center, 

and precast concrete that is a minimum 6-inches-thick and reinforced 

equivalent to the recommendations for cast-in-place walls.

Figure 4-33: 

The destroyed 

walkway canopy in 

front of this building 

became wind-borne 

debris. Hurricane Ivan 

(Florida, 2004) 

Figure 4-33: 

The destroyed 

walkway canopy in 

front of this building 

became wind-borne 

debris. Hurricane Ivan 

(Florida, 2004) 

If precast concrete is used for the roof or wall 

structure, the connections should be carefully 

designed, detailed, and constructed.
4-42 MAKING HOSPITALS SAFE FROM HIGH WIND

4.3.3 BUILDING ENVELOPE 

The following section highlights the design considerations for building 

envelope components that have historically sustained the greatest and 

most frequent damage in high winds.

The design considerations for building envelope components of hospitals 

in hurricane-prone regions include a number of additional recommendations. The principal concern that must be addressed is the additional 

risk from wind-borne debris and water leakage. Design considerations specific to hurricane-prone regions are discussed in Sections 4.3.3.2, 4.3.3.4, 

4.3.3.6, and 4.3.3.8.

4.3.3.1 Exterior Doors

This section addresses primary and secondary egress doors, sectional 

(garage) doors, and rolling doors. Although blow-off of personnel doors 

is uncommon, it can cause serious problems 

(see Figure 4-34). Blown-off doors allow 

entrance of rain, and tumbling doors can 

damage buildings and cause injuries. 

Blown off sectional and rolling doors are quite 

common. These failures are typically caused by 

the use of door and track assemblies that have 

insufficient wind resistance, or by inadequate attachment of the tracks or 

nailers to the wall (see Figure 4-35). 

For further general information on doors, 

see “Fenestration Systems” in the National 

Institute of Building Sciences’ Building 

Envelope Design Guide (www.wbdg.org/

design/envelope.php).

For further general information on doors, 

see “Fenestration Systems” in the National 

Institute of Building Sciences’ Building 

Envelope Design Guide (www.wbdg.org/

design/envelope.php).

Figure 4-34:

Door on a hospital 

penthouse blown 

off its hinges during 

Hurricane Katrina 

(Mississippi, 2005)

Figure 4-34:

Door on a hospital 

penthouse blown 

off its hinges during 

Hurricane Katrina 

(Mississippi, 2005)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-43

Loads and Resistance

The IBC requires that the door assembly (i.e., 

door, hardware, frame, and frame attachment 

to the wall) be of sufficient strength to resist the 

positive and negative design wind pressure. Design professionals should require that doors 

comply with wind load testing in accordance 

with ASTM E 1233. Design professionals should 

also specify the attachment of the door frame to the wall (e.g., type, size, 

spacing, and edge distance of frame fasteners). For sectional and rolling 

doors attached to wood nailers, design professionals should also specify 

the attachment of the nailer to the wall.

Water Infiltration

Heavy rain that accompanies high winds (e.g., thunderstorms, tropical 

storms, and hurricanes) can cause significant wind-driven water infiltration problems. The magnitude of the problem increases with the wind 

speed. Leakage can occur between the door and 

its frame, the frame and the wall, and between 

the threshold and the door. When wind speeds 

approach 120 mph, some leakage should be anticipated because of the very high wind pressures 

and numerous opportunities for leakage path 

development. 

For design guidance on attachment of 

door frames, see Technical Data Sheet 

#161, Connecting Garage Door Jambs to 

Building Framing, published by the Door & 

Access Systems Manufacturers Association, 

2003 (available at www.dasma.com).

For design guidance on attachment of 

door frames, see Technical Data Sheet 

#161, Connecting Garage Door Jambs to 

Building Framing, published by the Door & 

Access Systems Manufacturers Association, 

2003 (available at www.dasma.com).

Where corrosion is problematic, anodized 

aluminum or galvanized doors and frames, 

and stainless steel frame anchors and 

hardware are recommended. 

Figure 4-35:

This new rolling 

door failed because 

the CMU spalled 

at the door frame’s 

expansion bolts, which 

were too close to 

the end of the CMU. 

Hurricane Charley 

(Florida, 2004)
4-44 MAKING HOSPITALS SAFE FROM HIGH WIND

The following recommendations should be considered to minimize infiltration around exterior doors. 

Vestibule: Adding a vestibule allows both the inner and outer doors to be 

equipped with weatherstripping. The vestibule can be designed with 

water-resistant finishes (e.g., concrete or tile) and the floor can be 

equipped with a drain. In addition, installing exterior threshold trench 

drains can be helpful (openings must be small enough to avoid trapping 

high-heeled shoes). Note that trench drains do not eliminate the 

problem, since water can still penetrate at door edges.

Door swing: Out-swinging doors have weatherstripping on the interior side of the door, 

where it is less susceptible to degradation, 

which is an advantage when compared to 

in-swinging doors. Some interlocking weatherstripping assemblies are available for 

out-swinging doors.

The successful integration of the door frame 

and the wall is a special challenge when designing doors. See Section 4.3.3.3 for discussion of this juncture. 

ASTM E 2112 provides information pertaining to the installation of doors, 

including the use of sill pan flashings with end dams and rear legs (see 

Figure 4-36). It is recommended that designers use ASTM E 2112 as a design resource.

Weatherstripping

A variety of pre-manufactured weatherstripping components is available, 

including drips, door shoes and bottoms, thresholds, and jamb/head 

weatherstripping. 

For primary swinging entry/exit doors, 

exit door hardware is recommended 

to minimize the possibility of the doors 

being pulled open by wind suction. Exit 

hardware with top and bottom rods is 

more secure than exit hardware that 

latches at the jamb.

For primary swinging entry/exit doors, 

exit door hardware is recommended 

to minimize the possibility of the doors 

being pulled open by wind suction. Exit 

hardware with top and bottom rods is 

more secure than exit hardware that 

latches at the jamb.

Figure 4-36:

Door sill pan flashing 

with end dams, rear 

leg, and turned-down 

front leg

Figure 4-36:

Door sill pan flashing 

with end dams, rear 

leg, and turned-down 

front leg
MAKING HOSPITALS SAFE FROM HIGH WIND 4-45

Door shoes and bottoms: These are intended to 

minimize the gap between the door and the 

threshold. Figure 4-38 illustrates a door shoe 

that incorporates a drip. Figure 4-39 illustrates 

an automatic door bottom. Door bottoms can 

be surface-mounted or mortised. For high-traffic 

doors, periodic replacement of the neoprene 

components will be necessary.

Thresholds: These are available to suit a variety 

of conditions. Thresholds with high (e.g., 1-

inch) vertical offsets offer enhanced resistance 

to wind-driven water infiltration. However, the offset is limited where the 

thresholds are required to comply with the Americans with Disabilities Act 

(ADA), or at high-traffic doors. At other doors, high offsets are preferred. 

Thresholds can be interlocked with the door (see Figure 4-40), or thresholds can have a stop and seal (see Figure 4-41). In some instances, the 

threshold is set directly on the floor. Where this is appropriate, setting the 

threshold in butyl sealant is recommended to avoid water infiltration between the threshold and the floor. In other instances, the threshold is set 

on a pan flashing (as previously discussed in this section). If the threshold 

has weep holes, specify that the weep holes not be obstructed during construction (see Figure 4-40).

Drips: These are intended to shed water away from the opening between 

the frame and the door head, and the opening between the door bottom 

and the threshold (see Figures 4-37 and 4-38). Alternatively, a door sweep 

can be specified (see Figure 4-38). For high-traffic doors, periodic replacement of the neoprene components will be necessary.

Figure 4-37:

Drip at door head and drip with hook at head

Figure 4-38:

Door shoe with drip and vinyl seal (left). 

Neoprene door bottom sweep (right)

Figure 4-39:

Automatic door 

bottom
4-46 MAKING HOSPITALS SAFE FROM HIGH WIND

Adjustable jamb/head weatherstripping: This 

type of weatherstripping is recommended because the wide sponge neoprene offers good 

contact with the door (see Figure 4-42). The 

adjustment feature also helps to ensure good 

contact, provided the proper adjustment is 

maintained.

Meeting stile: At the meeting stile of pairs 

of doors, an overlapping astragal weatherstripping offers greater protection than 

weatherstripping that does not overlap. 

4.3.3.2 Exterior Doors in Hurricane-Prone Regions

Although the ASCE-7 wind-borne debris provisions only apply to glazing 

within a portion of hurricane-prone regions, it is recommended that 

all hospitals located where the basic wind speed is 100 mph or greater 

comply with the following recommendations:

m To minimize the potential for missiles penetrating exterior doors and 

striking people inside the facility, it is recommended that doors (with 

and without glazing) be designed to resist the “E” missile load specified in ASTM E 1996. The doors should be tested in accordance with 

ASTM E 1886 (2005). The test assembly should include the door, door 

frame, and hardware. 

Figure 4-40: Interlocking threshold with drain pan Figure 4-41: Threshold with stop and seal

Figure 4-42:

Adjustable jamb/head 

weatherstripping
MAKING HOSPITALS SAFE FROM HIGH WIND 4-47

4.3.3.3 Windows and Skylights

This section addresses general design considerations for exterior windows and skylights. For 

additional information on windows and skylights 

located in hurricane-prone regions, see Section 

4.3.3.4, and for those in tornado-prone regions, 

see Section 4.5.

Loads and Resistance

The IBC requires that windows, curtain walls, and skylight assemblies (i.e., 

the glazing, frame, and frame attachment to the wall or roof) have sufficient strength to resist the positive and negative design wind pressure 

(see Figure 4-43). Design professionals should specify that these assemblies comply with wind load testing in accordance with ASTM E 1233. It 

is important to specify an adequate load path and to check its continuity 

during submittal review.

Where water infiltration protection is particularly demanding and 

important, it is recommended that onsite water infiltration testing in accordance with ASTM E 1105 be specified.

For further general information on 

windows, see the National Institute of 

Building Sciences’ Building Envelope 

Design Guide (www.wbdg.org/design/

envelope.php).

For further general information on 

windows, see the National Institute of 

Building Sciences’ Building Envelope 

Design Guide (www.wbdg.org/design/

envelope.php).

ASTM E 1996 specifies five missile categories, A through E. The missiles are of various weights 

and fired at various velocities during testing. Building type (critical or non-critical) and basic wind 

speed determine the missiles required for testing. Of the five missiles, the E missile has the greatest 

momentum. Missile E is required for critical facilities located where the basic wind speed is greater 

than or equal to 130 mph. Missile D is permitted where the basic wind speed is less than130 mph. 

FEMA 361 also specifies a missile for shelters. The shelter missile has much greater momentum 

than the D and E missiles, as shown below:

Missile Missile Weight Impact Speed Momentum

ASTM E 1996—D 9 pound 2x4 lumber 50 feet per second 

(34 mph) 14 lbf -s*

ASTM E 1996—E 9 pound 2x4 lumber 80 feet per second

(55 mph) 22 lbf -s*

FEMA 361 (Shelter Missile) 15 pound 2x4 lumber 147 feet per second 

(100 mph) 68 lbf -s*

*lbf -s = pounds force per second
4-48 MAKING HOSPITALS SAFE FROM HIGH WIND

Water Infiltration 

Heavy rain accompanied by high winds can cause wind-driven water infiltration problems. The magnitude of the problem increases with the wind 

speed. Leakage can occur at the glazing/frame interface, the frame itself, 

or between the frame and wall. When the basic wind speed is greater than 

120 mph, because of the very high design wind pressures and numerous 

opportunities for leakage path development, some leakage should be anticipated when the design wind speed conditions are approached.

The successful integration of windows and curtain walls into exterior walls 

is a challenge in protecting against water infiltration. To the extent possible when detailing the interface between the wall and the window or 

curtain wall units, designers should rely on sealants as the secondary line 

of defense against water infiltration, rather than making the sealant the 

primary protection. If a sealant joint is the first line of defense, a second 

line of defense should be designed to intercept and drain water that 

drives past the sealant joint.

When designing joints between walls and windows and curtain wall units, consider the shape 

of the sealant joint (i.e., a square joint is typically preferred) and the type of sealant to be 

specified. The sealant joint should be designed 

to enable the sealant to bond on only two 

opposing surfaces (i.e., a backer rod or bondbreaker tape should be specified). Butyl is 

recommended as a sealant for concealed joints, 

and polyurethane for exposed joints. During 

The maximum test pressure used in the 

current ASTM test standard for evaluating 

resistance of window units to wind-driven 

rain is well below design wind pressures. 

Therefore, units that demonstrate adequate 

wind-driven rain resistance during testing 

may experience leakage during actual 

wind events.

The maximum test pressure used in the 

current ASTM test standard for evaluating 

resistance of window units to wind-driven 

rain is well below design wind pressures. 

Therefore, units that demonstrate adequate 

wind-driven rain resistance during testing 

may experience leakage during actual 

wind events.

Figure 4-43:

Two complete 

windows, including 

frames, blew out as a 

result of an inadequate 

number of fasteners. 

Typhoon Paka (Guam, 

1997)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-49

installation, cleanliness of the sealant substrate 

is important (particularly if polyurethane or silicone sealants are specified), as is the tooling 

of the sealant. ASTM E 2112 provides guidance on the design of sealant joints, as well as 

other information pertaining to the installation of windows, including the use of sill pan 

flashings with end dams and rear legs (see 

Figure 4-44). Windows that do not have nailing 

flanges should typically be installed over a pan 

flashing. It is recommended that designers use 

ASTM E 2112 as a design resource. 

Sealant joints can be protected with a removable stop, as illustrated in Figure 4-45. The 

stop protects the sealant from direct exposure 

to the weather and reduces the possibility of 

wind-driven rain penetration. 

4.3.3.4 Windows and Skylights in Hurricane-Prone 

Regions 

Exterior glazing that is not impact-resistant (such as laminated glass 

or polycarbonate) or protected by shutters is extremely susceptible to 

breaking if struck by wind-borne debris. Even small, low-momentum missiles can easily break glazing that is not protected (see Figures 4-46 and 

4-47). At the hospital shown in Figure 4-46, approximately 400 windows 

were broken. Most of the breakage was caused by wind-blown aggregate 

from the hospital’s aggregate ballasted single-ply membrane roofs, and 

Figure 4-45:

Protecting sealant 

retards weathering 

and reduces the 

exposure to winddriven rain.

Figure 4-45:

Protecting sealant 

retards weathering 

and reduces the 

exposure to winddriven rain.

Figure 4-44:

View of a typical window sill pan flashing with 

end dams and rear legs 

Source: ASTM E 2112
4-50 MAKING HOSPITALS SAFE FROM HIGH WIND

aggregate from built-up roofs. At the hospital shown in Figure 4-47, several 

of the skylight’s tempered glass outer panes were broken by wind-blown aggregate from the hospital’s aggregate ballasted single-ply membrane. The 

inner laminated glass panes were not broken. Note that some of the copings were also blown off (blue arrow)—some of the glazing may have been 

damaged by wind-blown copings. At the grey hospital on the other side of 

the street, much of the roof membrane was blown away (yellow arrow).

With broken windows, a substantial amount of water can be blown into 

a building, and the internal air pressure can be greatly increased, which 

may damage the interior partitions and ceilings. 

9 Glass spandrel panels are opaque glass. They are placed in curtain walls to conceal the area between the 

ceiling and the floor above.

Figure 4-46:

Plywood panels (black 

continuous bands) 

installed after the 

glass spandrel panels 

were broken by roof 

aggregate.9 Hurricane 

Katrina (Mississippi, 

2005) 

Figure 4-46:

Plywood panels (black 

continuous bands) 

installed after the 

glass spandrel panels 

were broken by roof 

aggregate.9 Hurricane 

Katrina (Mississippi, 

2005) 

Figure 4-47:

The outer glass 

panes of the skylight 

were broken by roof 

aggregate (red arrow). 

Hurricane Hugo (South 

Carolina, 1989)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-51

In order to minimize interior damage, the IBC, through ASCE 7, 

prescribes that exterior glazing in wind-borne debris regions be impact-resistant, or be protected with an impact-resistant covering (shutters). For 

Category III and IV buildings in areas with a basic wind speed of 130 mph 

or greater, the glazing is required to resist a larger momentum test missile than would Category II buildings and Category III and IV buildings in 

areas with wind speeds of less than 130 mph.

ASCE 7 refers to ASTM E 1996 for missile loads and to ASTM E 1886 for 

the test method to be used to demonstrate compliance with the E 1996 

load criteria. In addition to testing impact resistance, the window unit is 

subjected to pressure cycling after test missile impact to evaluate whether 

the window can still resist wind loads. If wind-borne debris glazing protection is provided by shutters, the glazing is still required by ASCE 7 to meet 

the positive and negative design air pressures.

Although the ASCE 7 wind-borne debris provisions only apply to glazing 

within a portion of hurricane-prone regions, it is recommended that 

all hospitals located where the basic wind speed is 100 mph or greater 

comply with the following recommendations:

m To minimize the potential for missiles penetrating exterior glazing and 

injuring people, it is recommended that exterior glazing up to 60 feet 

above grade be designed to resist the test Missile E load specified in 

ASTM E 1996 (see text box in Section 4.3.3.2). In addition, if roofs with 

aggregate surfacing are present within 1,500 feet of the facility, glazing 

above 60 feet should be designed to resist the test Missile A load specified 

in ASTM E 1996. The height of the protected glazing should extend a 

minimum of 30 feet above the aggregate surfaced roof per ASCE 7. 

Because large missiles are generally flying at lower elevations, glazing 

that is more than 60 feet above grade and meets the test Missile A load 

should be sufficient. However, if the facility is within a few hundred 

feet of another building that may create debris, such as EIFS, tiles, or 

rooftop equipment, it is recommended that the test Missile E load be 

specified instead of the Missile A for the upper-level glazing.

m For those facilities where glazing resistant to bomb blasts is desired, 

the windows and glazed doors can be 

designed to accommodate wind pressure, 

missile loads, and blast pressure. However, 

the window and door units need to be tested 

for missile loads and cyclic air pressure, 

as well as for blast. A unit that meets blast 

criteria will not necessarily meet the E 1996 

and E 1886 criteria, and vice versa. 

For further information on designing 

glazing to resist blast, see the “Blast Safety” 

resource pages of the National Institute 

of Building Sciences’ Building Envelope 

Design Guide (www.wbdg.org/design/

envelope.php).

For further information on designing 

glazing to resist blast, see the “Blast Safety” 

resource pages of the National Institute 

of Building Sciences’ Building Envelope 

Design Guide (www.wbdg.org/design/

envelope.php).
4-52 MAKING HOSPITALS SAFE FROM HIGH WIND

With the advent of building codes requiring glazing protection in windborne debris regions, a variety of shutter designs have entered the market. 

Shutters typically have a lower initial cost than laminated glass. However, 

unless the shutter is permanently anchored to the building (e.g., an accordion shutter), storage space will be needed. Also, when a hurricane 

is forecast, costs will be incurred each time shutters are installed and removed. The cost and difficulty of shutter deployment and demobilization 

on upper-level glazing may be avoided by using motorized shutters, although laminated glass may be a more economical solution. For further 

information on shutters, see Section 4.4.2.2.

4.3.3.5 Non-Load-Bearing Walls, Wall Coverings, and 

Soffits

This section addresses exterior non-loadbearing walls, exterior wall coverings, and 

soffits, as well as the underside of elevated 

floors, and provides guidance for interior nonload-bearing masonry walls. See Section 4.4.3.6 

for additional information pertaining to hospitals located in hurricane-prone regions, and 

Section 4.5 for additional information pertaining to hospitals located in 

tornado-prone regions. 

For further general information on nonload-bearing walls and wall coverings, see 

the National Institute of Building Sciences’ 

Building Envelope Design Guide (www.

wbdg.org/design/envelope.php).

For further general information on nonload-bearing walls and wall coverings, see 

the National Institute of Building Sciences’ 

Building Envelope Design Guide (www.

wbdg.org/design/envelope.php).

Figure 4-48:

The wall covering blew 

off the penthouse at 

this hospital complex, 

allowing rainwater to 

destroy the elevator 

controls. Hurricane 

Ivan (Florida, 2004)

Figure 4-48:

The wall covering blew 

off the penthouse at 

this hospital complex, 

allowing rainwater to 

destroy the elevator 

controls. Hurricane 

Ivan (Florida, 2004)

To ensure the continuity of elevator service, elevator penthouse walls must possess adequate wind 

and water resistance. If the walls blow away or water leaks through the wall system, the elevator 

controls and/or motors can be destroyed. Loss of elevators may critically affect facility operations 

(see Figures 4-22 and 4-48). The restoration of elevator service can take weeks, even with 

expedited work.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-53

Loads and Resistance 

The IBC requires that soffits, exterior non-load-bearing walls, and wall 

coverings have sufficient strength to resist the positive and negative design 

wind pressures.

Soffits: Depending on the wind direction, soffits can experience either 

positive or negative pressure. Besides the cost of repairing the damaged 

soffits, wind-borne soffit debris can cause property damage and injuries (see Figures 4-49 and 

4-50). Failed soffits may also provide a convenient path for wind-driven rain to enter the 

building. Storm-damage research has shown 

that water blown into attic spaces after the loss 

of soffits can cause significant damage and the 

collapse of ceilings. Even in instances where 

soffits remain in place, water can penetrate 

through soffit vents and cause damage. At this 

time, there are no known specific test standards 

or design guidelines to help design wind- and 

water-resistant soffits and soffit vents.

Where corrosion is a problem, stainless 

steel fasteners are recommended for wall 

and soffit systems. For other components 

(e.g., furring, blocking, struts, and hangers), 

nonferrous components (such as wood), 

stainless steel, or steel with a minimum of 

G-90 hot-dipped galvanized coating are 

recommended. Additionally, access panels 

are recommended so components within 

soffit cavities can be periodically inspected 

for corrosion or dry rot.

Where corrosion is a problem, stainless 

steel fasteners are recommended for wall 

and soffit systems. For other components 

(e.g., furring, blocking, struts, and hangers), 

nonferrous components (such as wood), 

stainless steel, or steel with a minimum of 

G-90 hot-dipped galvanized coating are 

recommended. Additionally, access panels 

are recommended so components within 

soffit cavities can be periodically inspected 

for corrosion or dry rot.

Figure 4-49:

This suspended 

metal soffit was not 

designed for upwardacting wind pressure. 

Typhoon Paka (Guam, 

1997)

Figure 4-49:

This suspended 

metal soffit was not 

designed for upwardacting wind pressure. 

Typhoon Paka (Guam, 

1997)
4-54 MAKING HOSPITALS SAFE FROM HIGH WIND

Exterior non-load-bearing masonry walls: Particular care should be given 

to the design and construction of exterior non-load-bearing masonry 

walls. Although these walls are not intended to carry gravity loads, 

they should be designed to resist the external and internal loading 

for components and cladding in order to avoid collapse. When these 

types of walls collapse, they represent a severe risk to life because of 

their great weight. 

Interior non-load-bearing masonry walls: Special consideration should 

also be given to interior non-load-bearing masonry walls. Although 

these walls are not required by building codes to be designed to resist 

wind loads, if the exterior glazing is broken, or the exterior doors are 

blown away, the interior walls could be subjected to significant load 

as the building rapidly becomes fully pressurized. To avoid casualties, 

it is recommended that interior non-load-bearing masonry walls adjacent to occupied areas be designed to accommodate loads exerted by 

a design wind event, using the partially enclosed pressure coefficient 

(see Figure 4-51). By doing so, wall collapse may be prevented if the 

building envelope is breached. This recommendation is applicable 

to hospitals located in areas with a basic wind speed greater than 

120 mph, and to hospitals in tornado-prone regions that do not have 

shelter space designed in accordance with FEMA 361.

Figure 4-50:

Hospital canopy 

damage. Hurricane 

Katrina (Louisiana, 

2005) 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-55

Wall Coverings

There are a variety of exterior wall coverings. Brick veneer, exterior insulation finish systems (EIFS), stucco, metal wall panels, and aluminum and 

vinyl siding have often exhibited poor wind performance. Veneers (such 

as ceramic tile and stucco) over concrete, stone veneer, and cement-fiber 

panels and siding have also blown off. Wood siding and panels rarely blow 

off. Although tilt-up precast walls have failed during wind storms, precast 

wall panels attached to steel or concrete framed buildings typically offer 

excellent wind performance.

Brick veneer:10 Brick veneer is frequently blown off walls during high 

winds. When brick veneer fails, wind-driven water can enter and damage 

buildings, and building occupants can be vulnerable to injury from windborne debris (particularly if the walls are sheathed with plastic foam 

insulation or wood fiberboard in lieu of wood panels). Pedestrians in the 

vicinity of damaged walls can also be vulnerable to injury from falling 

bricks (see Figure 4-52). Common failure modes include tie (anchor) fastener pull-out (see Figure 4-53), failure of masons to embed ties into the 

mortar, poor bonding between ties and mortar, a mortar of poor quality, 

and tie corrosion.

10The brick veneer discussion is from Attachment of Brick Veneer in High-Wind Regions—Hurricane Katrina 

Recovery Advisory (FEMA, December 2005).

Figure 4-51:

The red arrows show the original location of a CMU 

wall that nearly collapsed following a rolling door 

failure. Hurricane Charley (Florida, 2004)
4-56 MAKING HOSPITALS SAFE FROM HIGH WIND

Ties are often installed before brick laying begins. When this is done, ties 

are often improperly placed above or below the mortar joints. When misaligned, the ties must be angled up or down to be embedded into the 

mortar joints (Figure 4-54). Misalignment not only reduces the embedment depth, but also reduces the effectiveness of the ties, because wind 

forces do not act in parallel direction to the ties.

Corrugated ties typically used in residential veneer construction provide 

little resistance to compressive loads induced by positive and negative 

pressure. The use of compression struts would likely be beneficial, but 

off-the-shelf devices do not currently exist. Two-piece adjustable ties 

(Figure 4-55) provide significantly greater compressive strength than corrugated ties.

Figure 4-52:

The brick veneer 

failure on this building 

was attributed to tie 

corrosion. Hurricane 

Ivan (Florida, 2004)

Figure 4-53:

This tie remained 

embedded in the 

mortar joint while the 

smooth-shank nail 

pulled from the stud.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-57

The following Brick Industry Association (BIA) technical notes provide 

guidance on brick veneer: Technical Notes 28: Anchored Brick Veneer, Wood 

Frame Construction (2002); Technical Notes 28B: Brick Veneer/Steel Stud Walls 

(2005); and Technical Notes 44B: Wall Ties (2003) (available online at 

www.bia.org). These technical notes provide attachment recommendations; however, they are not specific for high-wind regions. To enhance 

wind performance of brick veneer, the following are recommended:

m Calculate wind loads and determine tie spacing in accordance with 

the latest edition of the Building Code Requirements for Masonry 

Structures, ACI 530/ASCE 5/TMS 402 (ACI 530, 2005). A stud 

spacing of 16 inches on center is recommended so that ties can be 

anchored at this spacing.

m Ring-shank nails are recommended in lieu of smooth-shank nails for 

wood studs. A minimum embedment of 2 inches is suggested.

m For use with wood studs, two-piece adjustable ties are recommended. 

However, where corrugated steel ties are used, they should be 22-gauge 

Figure 4-55:

Examples of two-piece 

adjustable ties

Figure 4-54:

Misalignment of 

the tie reduces the 

embedment and 

promotes veneer 

failure.
4-58 MAKING HOSPITALS SAFE FROM HIGH WIND

minimum, 7/8-inch wide by 6-inch long, and comply with ASTM A 

1008, with a zinc coating complying with ASTM A 153 Class B2. For 

ties used with steel studs, see BIA Technical Notes 28B—Brick Veneer/Steel 

Stud Walls. Stainless steel ties should be used for both wood and steel 

studs in areas within 3,000 feet of the coast.

m Install ties as the brick is laid so that the ties are properly aligned with 

the mortar joints.

m Locate ties within 8 inches of door and window openings, and within 

12 inches of the top of veneer sections.

m Although corrugated ties are not recommended, if they are used, 

bend the ties at a 90-degree angle at the nail head to minimize tie 

flexing when the ties cycle between tension and compression loads 

(Figure 4-56).

m Embed ties in joints so that the mortar completely encapsulates the ties. 

Embed a minimum of 11⁄2 inches into the bed joint, with a minimum 

mortar cover of 5/8-inch to the outside face of the wall (Figure 4-57). 

Figure 4-56:

Bend ties at nail heads

Figure 4-57:

Tie embedment 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-59

To avoid water leaking into the building, it is important that weep holes 

be adequately spaced and not be blocked during brick installation, and 

that through-wall flashings be properly designed and installed. When the 

base of the brick veneer occurs near grade, the grade should be designed 

so that it occurs several inches below the weeps so that drainage from the 

weeps is not impeded. Also, landscaping should be kept clear of weeps so 

that vegetation growth does not cause blockage of weeps. At the hospital 

shown in Figure 4-58, water leaked into the building along the base of 

many of the brick veneer walls. When high winds accompany heavy rain, a 

substantial amount of water can be blown into the wall cavity. 

EIFS: Figure 4-59 shows typical EIFS assemblies. Figure 4-48 and several 

figures in Section 4.2.1.3 show EIFS blow-off. In these cases, the molded 

expanded polystyrene (MEPS) was attached to gypsum board, which in 

turn was attached to metal studs or hat channels. The gypsum board detached from the studs/hat channels, which is a common EIFS failure 

mode. When the gypsum board on the exterior side of the studs is blown 

away, it is common for gypsum board on the interior side to also be blown 

off. The opening allows the building to become fully pressurized and allows the entrance of wind-driven rain. Other common types of failure 

include wall framing failure, separation of the MEPS from its substrate, 

and separation of the synthetic stucco from the MEPS. 

Figure 4-58:

Water leaked inside along the base of the 

brick veneer walls (red arrow). Hurricane 

Katrina (Louisiana, 2005) 
4-60 MAKING HOSPITALS SAFE FROM HIGH WIND

At the hospital shown in Figure 4-60, the EIFS was applied over a concrete 

wall. The MEPS debonded from the concrete. In general, a concrete substrate prevents wind and water from entering a building, but if the EIFS 

debonds from the concrete, EIFS debris can break unprotected glazing. 

Glazing damage can be very devastating, as shown and discussed in Section 4.2.1.3.

Figure 4-59:

Typical EIFS 

assemblies
MAKING HOSPITALS SAFE FROM HIGH WIND 4-61

Reliable wind performance of EIFS is very demanding on the designer 

and installer, as well as the maintenance of EIFS and associated sealant 

joints in order to minimize the reduction of EIFS’ wind resistance due to 

water infiltration. It is strongly recommended that EIFS be designed with 

a drainage system that allows for the dissipation of water leaks. For further 

information on EIFS performance during high winds and design guidance, see FEMA 489 and 549.

Another issue associated with EIFS is the potential for judgment errors. 

EIFS applied over studs is sometimes mistaken for a concrete wall, which 

may lead people to seek shelter behind it. However, instead of being protected by several inches of concrete, only two layers of gypsum board (i.e., 

one layer on each side of the studs) and a layer of MEPS separate the occupants from the impact of wind-borne debris that can easily penetrate 

such a wall and cause injury.

Stucco over studs: Wind performance of traditional stucco walls is similar 

to the performance of EIFS, as shown in Figure 4-61. In several areas the 

metal stud system failed; in other areas the gypsum sheathing blew off the 

studs; and in other areas, the metal lath blew off the gypsum sheathing. 

The failure shown in Figure 4-61 illustrates the importance of designing 

and constructing wall framing (including attachment of stud tracks to the 

building and attachment of the studs to the tracks) to resist the design 

wind loads.

Figure 4-60:

EIFS blown off a castin-place concrete wall. 

Note the damaged 

rooftop ductwork. 

Hurricane Ivan 

(Florida, 2004)
4-62 MAKING HOSPITALS SAFE FROM HIGH WIND

Metal wall panels: Wind performance of metal wall panels is highly variable. Performance depends on the strength of the specified panel (which 

is a function of material and thickness, panel profile, panel width, and 

whether the panel is a composite) and the adequacy of the attachment 

(which can be by either concealed clips or exposed fasteners). Excessive spacing between clips/fasteners is the most common problem. 

Clip/fastener spacing should be specified, along with the specific type 

and size of fastener. Figure 4-62 illustrates metal wall panel problems. At 

this building, the metal panels were attached with concealed fasteners. 

The panels unlatched at the standing seams. In addition to generating 

wind-borne debris, loss of panels allowed wind-driven rain to enter the 

building. Water entry was facilitated by lack of a moisture barrier and 

solid sheathing behind the metal panels (as discussed below).

To minimize water infiltration at metal wall panel joints, it is recommended that sealant tape be specified at sidelaps when the basic wind 

speed is in excess of 90 mph. However, endlaps should be left unsealed so 

that moisture behind the panels can be wicked away. Endlaps should be a 

minimum of 3 inches (4 inches where the basic wind speed is greater than 

120 mph) to avoid wind-driven rain infiltration. At the base of the wall, a 

3-inch (4-inch) flashing should also be detailed, or the panels should be 

detailed to overlap with the slab or other components by a minimum of 3 

inches (4 inches).

Figure 4-61:

The stucco wall 

failure was caused 

by inadequate 

attachment between 

the stud tracks and the 

building’s structure. 

Hurricane Ivan 

(Florida, 2004)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-63

Vinyl siding: Vinyl siding blow-off is typically 

caused by nails spaced too far apart and/or the 

use of vinyl siding that has inadequate wind resistance. Vinyl siding is available with enhanced 

wind resistance features, such as an enhanced 

nailing hem, greater interlocking area, and 

greater thickness. 

Secondary line of protection: Almost all wall coverings permit the passage of some water past 

the exterior surface of the covering, particularly 

when the rain is wind-driven. For this reason, 

most wall coverings should be considered watershedding, rather than waterproofing coverings. To avoid moisture-related 

problems, it is recommended that a secondary line of protection with a 

moisture barrier (such as housewrap or asphalt-saturated felt) and flashings around door and window openings be provided. Designers should 

specify that horizontal laps of the moisture barrier be installed so that 

water is allowed to drain from the wall (i.e., the top sheet should lap over 

the bottom sheet so that water running down the sheets remains on their 

outer surface). The bottom of the moisture barrier needs to be designed 

to allow drainage. Had the metal wall panels shown in Figure 4-62 been 

applied over a moisture barrier and sheathing, the amount of water entering the building would have likely been eliminated or greatly reduced. 

In areas that experience frequent wind-driven rain, incorporating a rain 

screen design, by installing vertical furring strips between the moisture 

barrier and siding materials, will facilitate drainage of water from the 

The Vinyl Siding Institute (VSI) sponsors 

a Certified Installer Program that 

recognizes individuals with at least 1 

year of experience who can demonstrate 

proper vinyl siding application. If vinyl 

siding is specified, design professionals 

should consider specifying that the siding 

contractor be a VSI-certified installer. For 

further information on this program, see 

www.vinylsiding.org.

The Vinyl Siding Institute (VSI) sponsors 

a Certified Installer Program that 

recognizes individuals with at least 1 

year of experience who can demonstrate 

proper vinyl siding application. If vinyl 

siding is specified, design professionals 

should consider specifying that the siding 

contractor be a VSI-certified installer. For 

further information on this program, see 

www.vinylsiding.org.

Figure 4-62:

The loss of metal wall 

panels allowed a 

substantial amount of 

wind-driven rain to 

penetrate this building. 

Hurricane Ivan 

(Florida, 2004) 
4-64 MAKING HOSPITALS SAFE FROM HIGH WIND

space between the moisture barrier and backside of the siding. In areas 

that frequently experience strong winds, enhanced flashing is recommended. Enhancements include use of flashings that have extra-long 

flanges, and the use of sealant and tapes. Flashing design should recognize that wind-driven water could be pushed up vertically. The height 

to which water can be pushed increases with wind speed. Water can also 

migrate vertically and horizontally by capillary action between layers of 

materials (e.g., between a flashing flange and housewrap). Use of a rain 

screen design, in conjunction with enhanced flashing design, is recommended in areas that frequently experience wind-driven rain or strong 

winds. It is recommended that designers attempt to determine what type 

of flashing details have successfully been used in the area where the facility will be constructed.

Underside of Elevated Floors

If sheathing is applied to the underside of joists or trusses elevated on 

piles (e.g., to protect insulation installed between the joists/trusses), its attachment should be specified in order to avoid blow-off. Stainless steel or 

hot-dip galvanized nails or screws are recommended. Since ASCE 7 does 

not provide guidance for load determination, professional judgment in 

specifying attachment is needed.

4.3.3.6 Non-Load-Bearing Walls, Wall Coverings, and 

Soffits in Hurricane-Prone Regions 

In order to achieve enhanced missile resistance of non-load-bearing exterior walls, the wall types discussed in Section 4.3.2.1 (i.e., reinforced 

concrete, or reinforced and fully grouted CMU) are recommended. 

To minimize long-term problems with exterior wall coverings and soffits, it 

is recommended that they be avoided to the maximum extent possible. Exposed or painted reinforced concrete or CMU offers greater reliability (i.e., 

they have no coverings that can blow off and become wind-borne debris). 

For all hospitals located where the basic wind speed is 100 mph or greater 

that are not constructed using reinforced concrete or reinforced and fully 

grouted CMU (as is recommended in this manual), it is recommended 

that the wall system selected be sufficient to resist complete penetration of 

the wall by the “E” missile specified in ASTM E 1996. 

For interior non-load-bearing masonry walls in hospitals located where 

the basic wind speed is greater than 120 mph, see the recommendations 

given in Section 4.3.3.5.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-65

4.3.3.7 Roof Systems

Because roof covering damage has historically 

been the most frequent and the costliest type of 

wind damage, special attention needs to be given 

to roof system design. See Section 4.3.3.8 for 

additional information pertaining to hospitals located in hurricane-prone regions, and Section 4.5 for hospitals located in 

tornado-prone regions.

Code Requirements 

The IBC requires the load resistance of the roof assembly to be evaluated 

by one of the test methods listed in IBC’s Chapter 15. Design professionals 

are cautioned that designs that deviate from the tested assembly (either 

with material substitutions or change in thickness or arrangement) may adversely affect the wind performance of the assembly. The IBC does not 

specify a minimum safety factor. However, for the roof system, a safety 

factor of 2 is recommended. To apply the safety factor, divide the test load 

by 2 to determine the allowable design load. Conversely, multiply the design load by 2 to determine the minimum required test resistance.

For structural metal panel systems, the IBC requires test methods UL 580 or ASTM E 1592. It 

is recommended that design professionals specify 

use of E 1592, because it gives a better representation of the system’s uplift performance 

capability. 

Load Resistance 

Specifying the load resistance is commonly done by specifying a Factory 

Mutual Research (FMR) rating, such as FM 1-75. The first number (1) 

indicates that the roof assembly passed the FMR tests for a Class 1 fire 

rating. The second number (75) indicates the uplift resistance in pounds 

per square foot (psf) that the assembly achieved during testing. With a 

safety factor of two this assembly would be suitable for a maximum design 

uplift load of 37.5 psf.

The highest uplift load occurs at the roof corners because of building 

aerodynamics as discussed in Section 4.1.3. The perimeter has a somewhat 

lower load, while the field of the roof has the lowest load. FMG Property 

Loss Prevention Data Sheets are formatted so that a roof assembly can be 

selected for the field of the roof. For the perimeter and corner areas, FMG 

Data Sheet 1-29 provides three options: 1) use the FMG Approval Guide

listing if it includes a perimeter and corner fastening method; 2) use a 

For further general information on roof 

systems, see the National Institute of 

Building Sciences’ Building Envelope 

Design Guide (www.wbdg.org/design/

envelope.php).

For further general information on roof 

systems, see the National Institute of 

Building Sciences’ Building Envelope 

Design Guide (www.wbdg.org/design/

envelope.php).

The roof of the elevator penthouse must 

possess adequate wind and water 

resistance to ensure continuity of elevator 

service. It is recommended that a 

secondary roof membrane, as discussed 

in Section 4.3.3.8, be specified over the 

elevator penthouse roof deck. 

The roof of the elevator penthouse must 

possess adequate wind and water 

resistance to ensure continuity of elevator 

service. It is recommended that a 

secondary roof membrane, as discussed 

in Section 4.3.3.8, be specified over the 

elevator penthouse roof deck. 
4-66 MAKING HOSPITALS SAFE FROM HIGH WIND

roof system with the appropriate FMG Approval rating in the field, perimeter, and corner, in accordance with Table 1 in FMG Data Sheet 1-29; 

or 3) use prescriptive recommendations given in FMG Data Sheet 1-29. 

When perimeter and corner uplift resistance values are based on a prescriptive method rather than testing, the field assembly is adjusted to 

meet the higher loads in the perimeter and corners by increasing the 

number of fasteners or decreasing the spacing of adhesive ribbons by 

a required amount. However, this assumes that the failure is the result 

of the fastener pulling out from the deck, or that the failure is in the 

vicinity of the fastener plate, which may not be the case. Also, the increased number of fasteners required by FMG 

may not be sufficient to comply with the perimeter and corner loads derived from the 

building code. Therefore, if FMG resistance 

data are specified, it is prudent for the design 

professional to specify the resistance for each 

zone of the roof separately. Using the example 

cited above, if the field of the roof is specified as 1-75, the perimeter would be specified 

as 1-130 and the corner would be specified as 

1-190. 

If the roof system is fully adhered, it is not 

possible to increase the uplift resistance in the 

perimeter and corners. Therefore, for fully 

adhered systems, the uplift resistance requirement should be based on the corner load 

rather than the field load.

Roof System Performance 

Storm-damage research has shown that sprayed polyurethane foam (SPF) 

and liquid-applied roof systems are very reliable high-wind performers. 

If the substrate to which the SPF or liquid-applied membrane is applied 

does not lift, it is highly unlikely that these systems will blow off. Both systems are also more resistant to leakage after missile impact damage than 

most other systems. Built-up roofs (BURs) and modified bitumen systems have also demonstrated good wind performance provided the edge 

flashing/coping does not fail (which happens frequently). The exception 

is aggregate surfacing, which is prone to blow-off (see Figures 4-10 and 

4-81). Modified bitumen applied to a concrete deck has demonstrated excellent resistance to progressive peeling after blow-off of the metal edge 

flashing. Metal panel performance is highly variable. Some systems are 

very wind-resistant, while others are quite vulnerable. 

FM Global (FMG) is the name of the 

Factory Mutual Insurance Company and its 

affiliates. One of FMG’s affiliates, Factory 

Mutual Research (FMR) provides testing 

services, produces documents that can be 

used by designers and contractors, and 

develops test standards for construction 

products and systems. FMR evaluates 

roofing materials and systems for resistance 

to fire, wind, hail, water, foot traffic and 

corrosion. Roof assemblies and components 

are evaluated to establish acceptable levels 

of performance. Some documents and 

activities are under the auspices of FMG 

and others are under FMR.

FM Global (FMG) is the name of the 

Factory Mutual Insurance Company and its 

affiliates. One of FMG’s affiliates, Factory 

Mutual Research (FMR) provides testing 

services, produces documents that can be 

used by designers and contractors, and 

develops test standards for construction 

products and systems. FMR evaluates 

roofing materials and systems for resistance 

to fire, wind, hail, water, foot traffic and 

corrosion. Roof assemblies and components 

are evaluated to establish acceptable levels 

of performance. Some documents and 

activities are under the auspices of FMG 

and others are under FMR.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-67

Of the single-ply attachment methods, the paver-ballasted and fully adhered methods are the least problematic. Systems with aggregate ballast 

are prone to blow-off, unless care is taken in specifying the size of aggregate and the parapet height (see Figures 4-5, 4-46, and 4-47). The 

performance of protected membrane roofs (PMRs) with a factory-applied cementitious coating over insulation boards is highly variable. When 

these boards are installed over a loose-laid membrane, it is critical that an 

air retarder be incorporated to prevent the membrane from ballooning 

and disengaging the boards. ANSI/SPRI RP-4 (which is referenced in 

the IBC) provides wind guidance for ballasted systems using aggregate, 

pavers, and cementitious-coated boards. 

The National Research Council of Canada, Institute for Research in Construction’s Wind Design Guide for Mechanically Attached Flexible Membrane 

Roofs (B1049, 2005) provides recommendations related to mechanically 

attached single-ply and modified bituminous systems. B1049 is a comprehensive wind design guide that includes discussion on air retarders. Air 

retarders can be effective in reducing membrane flutter, in addition to 

being beneficial for use in ballasted single-ply systems. When a mechanically attached system is specified, careful coordination with the structural 

engineer in selecting deck type and thickness is important. 

If a steel deck is selected, it is critical to specify that the membrane fasteners be attached in rows perpendicular to the steel flanges to avoid 

overstressing the attachment of the deck to the deck support structure. 

At the building shown in Figure 4-63, the fastener rows of the mechanically attached single-ply membrane ran parallel to the top flange of the 

steel deck. The deck fasteners were overstressed and a portion of the 

deck blew off and the membrane progressively tore. At another building, 

shown in Figure 4-64, the membrane fastener rows also ran parallel to the 

top flange of the steel deck. When membrane fasteners run parallel to the 

flange, the flange with membrane fasteners essentially carries the entire 

uplift load because of the deck’s inability to transfer any significant load 

to adjacent flanges. Hence, at the joists shown in Figure 4-64, the deck fasteners on either side of the flange with the membrane fasteners are the 

only connections to the joist that are carrying substantial uplift load.
4-68 MAKING HOSPITALS SAFE FROM HIGH WIND

For metal panel roof systems, the following are recommended:

m When clip or panel fasteners are attached to nailers, detail the 

connection of the nailer to the nailer support (including the detail of 

where nailers are spliced over a support). 

m When clip or panel fasteners are loaded in withdrawal (tension), 

screws are recommended in lieu of nails. 

m For concealed clips over a solid substrate, it is recommended that 

chalk lines be specified so that the clips are correctly spaced.

Figure 4-63:

The orientation of the 

membrane fastener 

rows led to blow-off 

of the steel deck. 

Hurricane Marilyn 

(U.S. Virgin Islands, 

1995)

Figure 4-64:

View of the 

underside of a steel 

deck showing the 

mechanically attached 

single-ply membrane 

fastener rows running 

parallel to, instead of 

across, the top flange 

of the deck. 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-69

m When the basic wind speed is 110 mph or greater, it is recommended 

that two clips be used along the eaves, ridges, and hips.

m For copper panel roofs in areas with a basic wind speed greater than 

90 mph, it is recommended that Type 316 stainless steel clips and 

stainless steel screws be used in lieu of copper clips.

m Close spacing of fasteners is recommended at hip and ridge flashings 

(e.g., spacing in the range of 3 to 6 inches on center, commensurate 

with the design wind loads.)

Edge Flashings and Copings

Roof membrane blow-off is almost always a result of lifting and peeling 

of the metal edge flashing or coping, which serves to clamp down the 

membrane at the roof edge. Therefore, it is important for the design professional to carefully consider the design of metal edge flashings, copings, 

and the nailers to which they are attached. The metal edge flashing on 

the modified bitumen membrane roof shown in Figure 4-65 was installed 

underneath the membrane, rather than on top of it, and then stripped 

in. In this location, the edge flashing was unable to clamp the membrane 

down. At one area, the membrane was not sealed to the flashing. An ink 

pen was inserted into the opening prior to photographing to demonstrate 

how wind could catch the opening and lift and peel the membrane. 

ANSI/SPRI ES-1, Wind Design Standard for Edge Systems Used in Low Slope 

Roofing Systems (2003) provides general design guidance including a 

methodology for determining the outward-acting load on the vertical 

flange of the flashing/coping (ASCE 7 does not provide this guidance). 

Figure 4-65:

The ink pen shows an 

opening that the wind 

can catch, and cause 

lifting and peeling of 

the membrane. 
4-70 MAKING HOSPITALS SAFE FROM HIGH WIND

ANSI/SPRI ES-1 is referenced in the IBC. ANSI/SPRI ES-1 also includes 

test methods for assessing flashing/coping resistance. This manual recommends a minimum safety factor of 3 for edge flashings, copings, and 

nailers for hospitals. For FMG-insured facilities, FMR-approved flashing 

should be used and FM Data Sheet 1-49 should also be consulted. 

The traditional edge flashing/coping attachment method relies on concealed cleats that can deform under wind load and lead to disengagement 

of the flashing/coping (see Figure 4-66) and subsequent lifting and 

peeling of the roof membrane. When a vertical flange disengages and lifts 

up, the edge flashing and membrane are very susceptible to failure. Normally, when a flange lifts the failure continues to propagate and the metal 

edge flashing and roof membrane blows off.

Storm-damage research has revealed that, in lieu of cleat attachment, the 

use of exposed fasteners to attach the vertical flanges of copings and edge 

flashings has been found to be a very effective and reliable attachment 

method. The coping shown in Figure 4-67 was attached with 1

/4-inch diameter stainless steel concrete spikes at 12 inches on center. When the 

fastener is placed in wood, #12 stainless steel screws with stainless steel 

washers are recommended. The fasteners should be more closely spaced 

in the corner areas (the spacing will depend upon the design wind loads). 

ANSI/SPRI ES-1 provides guidance on fastener spacing and thickness of 

the coping and edge flashing.

Figure 4-66:

The metal edge 

flashing on this 

hospital disengaged 

from the continuous 

cleat and the vertical 

flange lifted. Hurricane 

Hugo (South Carolina, 

1989)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-71

Gutters 

Storm-damage research has shown that gutters are seldom constructed to 

resist wind loads (see Figure 4-68). When a gutter lifts, it typically causes 

the edge flashing that laps into the gutter to lift as well. Frequently, this 

results in a progressive lifting and peeling of the roof membrane. The 

membrane blow-off shown in Figure 4-69 was initiated by gutter uplift. 

The gutter was similar to that shown in Figure 4-68. The membrane blowoff caused significant interior water damage.

Figure 4-68:

This gutter, supported 

by a type of bracket 

that provides no 

significant uplift 

resistance, failed 

when wind lifted it, 

together with the metal 

edge flashing that 

lapped into the gutter. 

Hurricane Francis 

(Florida, 2004)

Figure 4-67:

Both vertical faces 

of the coping were 

attached with exposed 

fasteners instead of 

concealed cleats. 

Typhoon Paka (Guam, 

1997)
4-72 MAKING HOSPITALS SAFE FROM HIGH WIND

Special design attention needs to be given to attaching gutters to prevent uplift, particularly for those in excess of 6 inches in width. Currently, 

there are no standards pertaining to gutter wind resistance. It is recommended that the designer calculate the uplift load on gutters using the 

overhang coefficient from ASCE 7. There are two approaches to resist 

gutter uplift.

m Gravity-support brackets can be designed to resist uplift loads. In 

these cases, in addition to being attached at its top, the bracket should 

also be attached at its low end to the wall. The gutter also needs to 

be designed so it is attached securely to the bracket in a way that 

will effectively transfer the gutter uplift load to the bracket. Bracket 

spacing will depend on the gravity and uplift load, the bracket’s 

strength, and the strength of connections between the gutter/bracket 

and the bracket/wall. With this option, the bracket’s top will typically 

be attached to a wood nailer, and that fastener will be designed to 

carry the gravity load. The bracket’s lower connection will resist the 

rotational force induced by gutter uplift. Because brackets are usually 

spaced close together to carry the gravity load, developing adequate 

connection strength at the lower fastener is generally not difficult. 

m The other option is to use gravity-support brackets only to resist gravity 

loads, and use separate sheet-metal straps at 45-degree angles to the 

wall to resist uplift loads. Strap spacing will depend on the gutter uplift 

load and strength of the connections between the gutter/strap and the 

strap/wall. Note that FMG Data Sheet 1-49 recommends placing straps 

10 feet apart. However, at that spacing with wide gutters, fastener loads 

induced by uplift are quite high. When straps are spaced at 10 feet, it 

can be difficult to achieve sufficiently strong uplift connections.

Figure 4-69:

The original modified 

bitumen membrane 

was blown away 

after the gutter lifted 

in the area shown 

by the red arrow (the 

black membrane is 

a temporary roof). 

Hurricane Francis 

(Florida, 2004)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-73

When designing a bracket’s lower connection to a wall or a strap’s 

connection to a wall, designers should determine appropriate screw 

pull-out values. With this option, a minimum of two screws at each end 

of a strap is recommended. At a wall, screws should be placed side by 

side, rather than vertically aligned, so the strap load is carried equally 

by the two fasteners. When fasteners are vertically aligned, most of the 

load is carried by the top fastener.

Since the uplift load in the corners is much higher than the load between 

the corners, enhanced attachment is needed in corner areas regardless 

of the option chosen. ASCE 7 provides guidance about determining a 

corner area’s length.

Parapet Base Flashings 

Information on loads for parapet base flashings was first introduced in 

the 2002 edition of ASCE 7. The loads on base flashings are greater than 

the loads on the roof covering if the parapet’s exterior side is air-permeable. When base flashing is fully adhered, it has sufficient wind resistance 

in most cases. However, when base flashing is mechanically fastened, typical fastening patterns may be inadequate, depending on design wind 

conditions (see Figure 4-70). Therefore, it is imperative that the base 

flashing loads be calculated, and attachments designed to accommodate 

these loads. It is also important for designers to specify the attachment 

spacing in parapet corner regions to differentiate them from the regions 

between corners.

Figure 4-70:

If mechanically 

attached base 

flashings have an 

insufficient number of 

fasteners, the base 

flashing can be blown 

away. Hurricane 

Andrew (Florida, 

1992) 
4-74 MAKING HOSPITALS SAFE FROM HIGH WIND

When the roof membrane is specified to be adhered, it is recommended 

that fully adhered base flashings be specified in lieu of mechanically attached base flashings. Otherwise, if the base flashing is mechanically 

attached, ballooning of the base flashing during high winds can lead to 

lifting and progressive peeling of the roof membrane.

Steep-Slope Roof Coverings 

For a discussion of wind performance of asphalt shingle and tile roof 

coverings, see FEMA 488 (2005), 489 (2005), and 549 (2006). For recommendations pertaining to asphalt shingles and tiles, see Fact Sheets 19, 20, 

and 21 in FEMA 499 (2005).

4.3.3.8 Roof Systems in Hurricane-Prone Regions

The following types of roof systems are recommended for hospitals in 

hurricane-prone regions, because they are more likely to avoid water infiltration if the roof is hit by wind-borne debris, and also because these 

systems are less likely to become sources of wind-borne debris:

m In tropical climates where insulation is not needed above the roof 

deck, specify either liquid-applied membrane over cast-in-place 

concrete deck, or modified bitumen membrane torched directly to 

primed cast-in-place concrete deck.

m Install a secondary membrane over a concrete deck (if another type 

of deck is specified, a cover board may be needed over the deck). Seal 

the secondary membrane at perimeters and penetrations. Specify 

rigid insulation over the secondary membrane. Where the basic wind 

speed is up to 110 mph, a minimum 2-inch thick layer of insulation 

is recommended. Where the speed is between 110 and 130 mph, a 

total minimum thickness of 3 inches is recommended (installed in two 

layers). Where the speed is greater than 130 mph, a total minimum 

thickness of 4 inches is recommended (installed in two layers). A 

layer of 5

/8 -inch thick glass mat gypsum roof board is recommended 

over the insulation, followed by a modified bitumen membrane. 

A modified bitumen membrane is recommended for the primary 

membrane because of its somewhat enhanced resistance to puncture 

by small missiles compared with other types of roof membranes.

m When fully adhering boards to concrete decks, it is recommended 

that a planar flatness of a maximum of 1

/4-inch variation over a 10 foot 

length (when measured by a straightedge) be specified. Prior to 

installation of the roof insulation, it is recommended that the planar 

flatness be checked with a straightedge. If the deck is outside of the 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-75

1

/4-inch variation, it is recommended that the 

high spots be ground or the low spots be 

suitably filled.

m The purpose of the insulation and gypsum 

roof board is to absorb missile energy. If the 

primary membrane is punctured or blown 

off during a storm, the secondary membrane 

should provide watertight protection unless 

the roof is hit with missiles of very high 

momentum that penetrate the insulation 

and secondary membrane. Figure 4-72 

illustrates the merit of specifying a secondary 

membrane. The copper roof blew off the 

hospital’s intensive care unit (ICU). Patients 

and staff were frightened by the loud noise 

generated by the metal panels as they banged 

around during the hurricane. Fortunately 

there was a very robust underlayment (a 

built-up membrane) that remained in place. 

Since only minor leakage occurred, the ICU 

continued to function. 

When fully adhering insulation boards, 

it is recommended that the boards be 

no larger than 4 feet by 4 feet. It is also 

recommended that the board thickness 

not exceed 2 inches ( 11/2 inches is 

preferable). Use of small thin boards 

makes it easier for the contractor to 

conform the boards to the substrate. At 

the hospital shown in Figure 4-71, 4 

foot by 8 foot insulation boards were 

set in hot asphalt over a concrete deck. 

A few of the boards detached from the 

deck. The boards may have initiated the 

membrane blow off, or the membrane 

blow off may have been initiated by 

lifting and peeling of the metal edge 

flashing, in which case, loss of the 

insulation boards was a secondary failure. 

Figure 4-71:

The blown off 

insulation (red arrow) 

may have initiated 

blow off of the roof 

membrane. Hurricane 

Ivan (Florida, 2004)
4-76 MAKING HOSPITALS SAFE FROM HIGH WIND

m For an SPF roof system over a concrete deck, where the basic wind 

speed is less than 130 mph, it is recommended that the foam be a 

minimum of 3 inches thick to avoid missile penetration through 

the entire layer of foam. Where the speed is greater than 130 

mph, a 4-inch minimum thickness is recommended. It is also 

recommended that the SPF be coated, rather than protected with 

an aggregate surfacing.

m For a PMR, it is recommended that pavers weighing a minimum of 22 

psf be specified. In addition, base flashings should be protected with 

metal (such as shown in Figure 4-79) to provide debris protection. 

Parapets with a 3-foot minimum height (or higher if so indicated by 

ANSI/SPRI RP-4, 2002) are recommended at roof edges. This manual 

recommends that PMRs not be used for hospitals in hurricane-prone 

regions where the basic wind speed exceeds 130 mph. 

m For structural metal roofs, it is recommended that a roof deck be 

specified, rather than attaching the panels directly to purlins as is 

commonly done with pre-engineered metal buildings. If panels blow 

off buildings without roof decking, wind-borne debris and rain are 

free to enter the building. 

Structural standing seam metal roof panels with concealed clips 

and mechanically seamed ribs spaced at 12 inches on center are 

recommended. If the panels are installed over a concrete deck, a 

modified bitumen secondary membrane is recommended if the 

deck has a slope less than 1

/2:12. If the panels are installed over a steel 

Figure 4-72:

The secondary 

membrane prevented 

leakage into the ICU 

after the copper roof 

blew off. Hurricane 

Andrew (Florida, 

1992) 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-77

deck or wood sheathing, a modified bitumen secondary membrane 

(over a suitable cover board when over steel decking) is recommend, 

followed by rigid insulation and metal panels. Where the basic wind 

speed is up to 110 mph, a minimum 2-inch-thick layer of insulation 

is recommended. Where the speed is between 110 and 130 mph, 

a total minimum thickness of 3 inches is recommended. Where 

the speed is greater than 130 mph, a total minimum thickness of 4 

inches is recommended. Although some clips are designed to bear 

on insulation, it is recommended that the panels be attached to wood 

nailers attached to the deck, because nailers provide a more stable 

foundation for the clips. 

If the metal panels are blown off or punctured during a hurricane, 

the secondary membrane should provide watertight protection unless 

the roof is hit with missiles of very high momentum. At the roof 

shown in Figure 4-73, the structural standing seam panel clips bore 

on rigid insulation over a steel deck. Had a secondary membrane 

been installed over the steel deck, the membrane would have likely 

prevented significant interior water damage and facility disruption.

m Based on field performance of architectural metal panels in 

hurricane-prone regions, exposed fastener panels are recommended 

in lieu of architectural panels with concealed clips. For panel 

fasteners, stainless steel screws are recommended. A secondary 

membrane protected with insulation is recommended, as discussed 

above for structural standing seam systems. 

Figure 4-73:

Significant interior 

water damage and 

facility interruption 

occurred after the 

standing seam roof 

blew off. Hurricane 

Marilyn (U.S. Virgin 

Islands, 1995)
4-78 MAKING HOSPITALS SAFE FROM HIGH WIND

In order to avoid the possibility of roofing components blowing off and 

striking people arriving at a hospital during a storm, the following roof 

systems are not recommended: aggregate surfacings, either on BUR, 

single-plies or SPF; lightweight concrete pavers; cementitious-coated insulation boards; slate; and tile (see Figure 4-74). Even when slates and tiles 

are properly attached to resist wind loads, their brittleness makes them 

vulnerable to breakage as a result of wind-borne debris impact. The tile 

and slate fragments can be blown off the roof, and fragments can damage 

other parts of the roof, causing a cascading failure. 

Mechanically attached and air-pressure equalized single-ply membrane 

systems are susceptible to massive progressive failure after missile impact, 

and are therefore not recommended for hospitals in hurricane-prone 

regions. At the building shown in Figure 4-75, a missile struck the fully 

adhered low-sloped roof and slid into the steep-sloped reinforced mechanically attached single-ply membrane in the vicinity of the red arrow. 

A large area of the mechanically attached membrane was blown away as 

a result of progressive membrane tearing. Fully adhered single-ply membranes are very vulnerable to missile puncture and are not recommended 

unless they are ballasted with pavers. At the hospital shown in Figure 4-76, 

several missiles, including exhaust fans and copings struck the roof. 

Figure 4-74:

Brittle roof coverings, 

like slate and tile, can 

be broken by missiles, 

and tile debris can 

break other tiles. 

Hurricane Charley 

(Florida, 2004)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-79

Edge flashings and copings: If cleats are used for attachment, it is recommended that a “peel-stop” bar be placed over the roof membrane near 

the edge flashing/coping, as illustrated in Figure 4-77. The purpose of 

the bar is to provide secondary protection against membrane lifting and 

peeling in the event that edge flashing/coping fails. A robust bar specifically made for bar-over mechanically attached single-ply systems is 

recommended. The bar needs to be very well anchored to the parapet 

or the deck. Depending on design wind loads, spacing between 4 and 12 

inches on center is recommended. A gap of a few inches should be left between each bar to allow for water flow across the membrane. After the bar 

is attached, it is stripped over with a stripping ply.

Figure 4-75:

Mechanically attached 

single-ply membrane 

progressively tore 

after being cut by 

wind-borne debris. 

Hurricane Andrew 

(Florida, 1992)

Figure 4-76:

This fully adhered 

single-ply roof 

membrane was 

struck by a variety of 

missiles. Hurricane 

Marilyn (U.S. Virgin 

Islands, 1995) 
4-80 MAKING HOSPITALS SAFE FROM HIGH WIND

Walkway pads: Roof walkway pads are frequently blown off during hurricanes (Figures 4-78 and 4-82). Pad blow-off does not usually damage 

the roof membrane. However, wind-borne pad debris can damage other 

building components and injure people. Currently there is no test standard to evaluate uplift resistance of walkway pads. Walkway pads are 

therefore not recommended in hurricane-prone regions.

Figure 4-78:

Several rubber 

walkway pads were 

blown off the single-ply 

membrane roof on this 

hospital. Hurricane 

Katrina (Mississippi, 

2005)

Figure 4-77:

A continuous peel-stop bar over the membrane may prevent a catastrophic progressive failure if the edge 

flashing or coping is blown off. (Modified from FEMA 55, 2000)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-81

Parapets: For low-sloped roofs, minimum 3-foot high parapets are recommended. With parapets of this height or greater, the uplift load in the 

corner region is substantially reduced (ASCE 7 permits treating the corner 

zone as a perimeter zone). Also, a high parapet (as shown in Figures 4- 96) 

may intercept wind-borne debris and keep it from blowing off the roof 

and damaging other building components or injuring people. To protect base flashings from wind-borne debris damage and subsequent water 

leakage, it is recommended that metal panels on furring strips be installed 

over the base flashing (Figure 4-79). Exposed stainless steel screws are recommended for attaching the panels to the furring strips, because using 

exposed fasteners is more reliable than using concealed fasteners or clips 

(as were used for the failed panels shown in Figure 4-62). 

4.3.3.9 The Case of DeSoto Memorial Hospital, 

Arcadia, Florida

The case of DeSoto Memorial Hospital illustrates damage caused by aggregate-surfaced roofs. The 82-bed hospital is located just off Florida 

Highway 17 in Arcadia, approximately 30 miles east of Florida’s gulf coast. 

The hospital was constructed in 1964, though the current emergency 

room (ER), ICU, and third floor patient rooms were added in 1984. A 

separate pre-engineered storage building was constructed in 1979.

The facility was struck by Hurricane Charley in 2004, with an estimated 

peak gust wind speed between 125 to 140 mph.11 Since the design wind 

speed in the 2005 edition of ASCE 7 for this location is 110 mph, the esti11The 125 to 140 mph speeds were estimated for Exposure C.

Figure 4-79:

Base flashing 

protected by metal 

panels attached with 

exposed screws. 

Hurricane Katrina 

(Mississippi, 2005)
4-82 MAKING HOSPITALS SAFE FROM HIGH WIND

mated speeds at this site were above current design conditions. Also, even 

with the 1.15 importance factor, the actual wind pressures were above the 

design pressures.

The hospital sustained damage to windows, rooftop equipment, and a 

freestanding storage building on the campus. Thirty-three windows were 

broken, including patient room windows and windows at three of the 

eight ICU rooms (Figures 4-80 and 4-81). Windows were also broken in 

many vehicles in the parking lot. The majority of the glass breakage was 

caused by aggregate blown from the hospital built-up roofs. Some of the 

glass breakage may have been due to blown-off gutters and walkway pads 

from the hospital’s roof (Figure 4-82) or other missiles such as tree limbs; 

blown off gutters can be high-momentum missiles that can travel a substantial distance (see Figure 4-81). 

As a result of the window breakage the entire ICU was evacuated during 

the hurricane and closed for about 2 weeks before repairs were completed and the unit reoccupied. Some patients were moved to lower 

floors; the elevator could not be used so the patients were either carried 

down or slid down the stairs on mattresses. Fortunately, no one was injured during the evacuation.

A portion of the roof covering was blown off and the satellite dish was 

nearly blown off too. The LPS was displaced in a few areas (see Figure 

4-83). As a result of the damage to the roof covering and to rooftop equipment, water leaked into the building in several areas, which caused the 

closing of the operating room (OR), sterile processing, portions of the 

lab, and numerous offices. The OR was temporarily relocated to the Caesarian section (C-section) room. It was about a month before the OR was 

repaired and reoccupied. 

The metal storage building that contained the hospital’s supplies, maintenance shop, environmental services, and shipping and receiving 

collapsed, and its loss was significant for the hospital operations. Almost 

all of the tools and stock materials for repairs were lost (Figure 4-84). 

Tents were set up after the hurricane to provide storage. Because of subsequent storms in the next several weeks (including two hurricanes), the 

stored items had to be moved in and out of the tents on several occasions. 

Municipal power and water were lost during the hurricane. The hospital ran on its generators for about 5 days before power was restored. 

Municipal water service was out for about 2 weeks, but fortunately the 

hospital had a secondary well for potable water, so water service was not 

interrupted. 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-83

Access to the hospital was not hampered by fallen trees or by flooding. 

However, some staff and emergency medical service (EMS) personnel 

were unable to get to the hospital quickly after the storm because of 

downed trees or floodwaters in their neighborhoods. Landline telephone 

service was not lost, but paging and cell phone services were. The homes 

of many staff members were no longer habitable after the storm, so tents 

were set up on the hospital campus to house staff and volunteers that 

came to provide assistance. This in turn required additional security services and shower and laundry facilities.

The hospital did not have a contingency plan to cope with the damages, and therefore, did not have pre-arranged contracts with contractors 

to perform inspections and emergency repairs. Fortunately, there were 

no problems finding contractors quickly after the storm, although the 

building materials needed for repairs were in short supply. 

Figure 4-80:

The second floor 

beyond the canopy 

houses the ICU. 

Several windows 

along the two ICU 

walls that are visible 

were broken. 
4-84 MAKING HOSPITALS SAFE FROM HIGH WIND

Figure 4-81:

A view of the ICU 

from the third floor 

roof. The gutters (red 

arrow) are from the 

back side of the third 

floor roof.

Figure 4-82:

View of the back 

side of the third 

floor roof where the 

gutter and an asphalt 

plank walkway pad 

were blown away. 

The loose aggregate 

surfacing was also 

blown away.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-85

4.3.4 NONSTRUCTURAL SYSTEMS AND 

EQUIPMENT

Nonstructural systems and equipment include all components that are 

not part of the structural system or building envelope. Exterior-mounted 

mechanical equipment (e.g., exhaust fans, HVAC units, relief air hoods, 

rooftop ductwork, and boiler stacks), electrical equipment (e.g., light 

fixtures and lightning protection systems), and communications equipment (e.g., antennae and satellite dishes) are often damaged during high 

winds. Damaged equipment can impair the operation of the facility, the 

equipment can detach and become wind-borne missiles, and water can 

Figure 4-83:

This satellite dish 

was held down only 

with CMU. Note the 

displaced LPS at the 

corner (circled). 

Figure 4-84:

This pre-engineered 

storage building 

contained the 

hospital supplies 

and maintenance 

shop. 
4-86 MAKING HOSPITALS SAFE FROM HIGH WIND

enter the facility where equipment was displaced (see Figure 4-85). The 

most common problems typically relate to inadequate equipment anchorage, inadequate strength of the equipment itself, and corrosion.

Exterior-mounted equipment is especially vulnerable to hurricane-induced damage, and special attention should be paid to positioning and 

mounting of these components in hurricane-prone regions. Specific information pertaining to hospitals located in hurricane-prone regions is 

presented for each of the nonstructural component sections below.

4.3.4.1 Exterior-Mounted Mechanical Equipment

This section discusses loads and attachment methods, as well as the problems of corrosion and water infiltration.

Loads and Attachment Methods12

Information on loads on rooftop equipment was first introduced in the 

2002 edition of ASCE 7. For guidance on load calculations, see “Calculating Wind Loads and Anchorage Requirements for Rooftop Equipment” 

(ASHRAE, 2006). A minimum safety factor of 3 is recommended for hospitals. Loads and resistance should also be calculated for heavy pieces 

of equipment since the dead load of the equipment is often inadequate 

12 Discussion is based on: Attachment of Rooftop Equipment in High-Wind Regions - Hurricane Katrina Recovery 

Advisory (May 2006, revised July 2006)

Figure 4-85:

This gooseneck was 

attached with only 

two small screws. A 

substantial amount 

of water was able 

to enter the building 

during Hurricane 

Francis. (Florida, 

2004)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-87

to resist the design wind load. The 30' x 10' x 8' 

18,000-pound HVAC unit shown in Figure 4-86 

was attached to its curb with 16 straps (one screw 

per strap). Although the wind speeds were estimated to be only 85 to 95 miles per hour (peak 

gust), the HVAC unit blew off the medical office 

building. The inset at Figure 4-86 shows the curb 

upon which the unit was attached. A substantial 

amount of water entered the building at the curb 

openings before the temporary tarp was placed.

To anchor fans, small HVAC units, and relief air hoods, the minimum 

attachment schedule provided in Table 4-1 is recommended. The attachment of the curb to the roof deck also needs to be designed and 

constructed to resist the design loads. The cast-in-place concrete curb 

shown in Figure 4-87 was cold-cast over a concrete roof deck. Dowels were 

not installed between the deck and the curb, hence a weak connection 

occurred.

Figure 4-86:

Although this 18,000-

pound HVAC unit was 

attached to its curb 

with 16 straps, it blew 

off during Hurricane 

Ivan. (Florida, 2004)

Mechanical penetrations through the elevator 

penthouse roof and walls must possess 

adequate wind and water resistance to 

ensure continuity of elevator service (see 

Section 4.3.3.5). In addition to paying 

special attention to equipment attachment, 

air intakes and exhausts should be designed 

and constructed to prevent wind-driven water 

from entering the penthouse.
4-88 MAKING HOSPITALS SAFE FROM HIGH WIND

Fan cowling attachment: Fans are frequently blown off their curbs because they are poorly attached. When fans are well attached, the cowlings 

frequently blow off (see Figure 4-88). Blown off cowlings can tear roof 

membranes and break glazing. Unless the fan manufacturer specifically 

engineered the cowling attachment to resist the design wind load, cable 

tie-downs (see Figure 4-89) are recommended to avoid cowling blow-off. 

For fan cowlings less than 4 feet in diameter, 1

/2 -inch diameter stainless 

steel cables are recommended. For larger cowlings, use 3

/16-inch diameter cables. When the basic wind speed is 120 mph or less, specify two 

cables. Where the basic wind speed is greater 

than 120 mph, specify four cables. To minimize leakage potential at the anchor point, it 

is recommended that the cables be adequately 

anchored to the equipment curb (rather than 

anchored to the roof deck). The attachment 

of the curb itself also needs to be designed and 

specified. 

To avoid corrosion-induced failure (Figure 

4-21), it is recommended that exteriormounted mechanical, electrical, and 

communications equipment be made of 

nonferrous metals, stainless steel, or steel 

with minimum G-90 hot-dip galvanized 

coating for the equipment body, stands, 

anchors, and fasteners. When equipment 

with enhanced corrosion protection is not 

available, the designer should advise the 

building owner that periodic equipment 

maintenance and inspection is particularly 

important to avoid advanced corrosion 

and subsequent equipment damage during 

a windstorm.

Figure 4-87:

The gooseneck on 

this hospital remained 

attached to the curb, 

but the curb detached 

from the deck. 

Typhoon Paka (Guam, 

1997)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-89

Table 4-1: Number of #12 Screws for Base Case Attachment of Rooftop Equipment

Case No Curb Size and Equipment Type Equipment Attachment

Fastener Factor 

for Each Side of 

Curb or Flange

1 12” x 12” Curb with Gooseneck 

Relief Air Hood Hood Screwed to Curb 1.6

2 12” x 12” Gooseneck Relief Air 

Hood with Flange 

Flange Screwed to 22 Gauge 

Steel Roof Deck 2.8

3 12” x 12” Gooseneck Relief Air 

Hood with Flange

Flange Screwed to 15/32” OSB 

Roof Deck 2.9

4 24” x 24” Curb with Gooseneck 

Relief Air Hood Hood Screwed to Curb 4.6

5 24” x 24” Gooseneck Relief Air 

Hood with Flange

Flange Screwed to 22 Gauge 

Steel Roof Deck 8.1

6 24” x 24” Gooseneck Relief Air 

Hood with Flange

Flange Screwed to 15/32” OSB 

Roof Deck 8.2

7 24” x 24” Curb with Exhaust Fan Fan Screwed to Curb 2.5

8 36” x 36” Curb with Exhaust Fan Fan Screwed to Curb 3.3

9 5’-9” x 3’- 8” Curb with 2’- 8” 

high HVAC Unit HVAC Unit Screwed to Curb 4.5*

10 5’-9 ”x 3’- 8” Curb with 2’- 8” 

high Relief Air Hood Hood Screwed to Curb 35.6*

Notes to Table 4-1: 

1. The loads are based on ASCE 7-05. The resistance includes equipment weight.

2. The Base Case for the tabulated numbers of #12 screws (or 1⁄4 pan-head screws for flange-attachment) is a 90-mph basic wind 

speed, 1.15 importance factor, 30’ building height, Exposure C, using a safety factor of 3. 

3. For other basic wind speeds, multiply the tabulated number of #12 screws by to determine the required number 

of #12 screws (or 1⁄4 pan-head screws) required for the desired basic wind speed, VD (mph). 

4. For other roof heights up to 200’, multiply the tabulated number of #12 screws by (1.00 + 0.003 [h - 30]) to determine the 

required number of #12 screws or 1⁄4 pan-head screws for buildings between 30’ and 200’.

Example A: 24” x 24” exhaust fan screwed to curb (table row 7), Base Case conditions (see Note 1): 2.5 screws per side; 

therefore, round up and specify 3 screws per side.

Example B: 24” x 24” exhaust fan screwed to curb (table row 7), Base Case conditions, except 120 mph: 1202 x 1 ÷ 902 = 

1.78 x 2.5 screws per side = 4.44 screws per side; therefore, round down and specify 4 screws per side.

Example C: 24” x 24” exhaust fan screwed to curb (table row 7), Base Case conditions, except 150’ roof height: 1.00 + 0.003 

(150’ - 30’) = 1.00 + 0.36 = 1.36 x 2.5 screws per side = 3.4 screws per side; therefore, round down and specify 3 screws 

per side.

* This factor only applies to the long sides. At the short sides, use the fastener spacing used at the long sides.

V2

D

90 ( 2)
4-90 MAKING HOSPITALS SAFE FROM HIGH WIND

Ductwork: To avoid wind and wind-borne debris damage to rooftop ductwork, it is recommended that ductwork not be installed on the roof (see 

Figures 4-16, 4-60, and 4-124). If ductwork is installed on the roof, it is recommended that the ducts’ gauge and the method of attachment be able 

to resist the design wind loads. 

Condenser attachment: In lieu of placing rooftop-mounted condensers on 

wood sleepers resting on the roof (see Figure 4-90), it is recommended 

that condensers be anchored to equipment stands. The attachment of the 

stand to the roof deck also needs to be designed to resist the design loads. 

In addition to anchoring the base of the condenser to the stand, two 

Figure 4-88:

Cowlings blew off 

two of the three fans. 

Note also the loose 

lightning protection 

system conductors and 

missing walkway pad 

(red arrow). Hurricane 

Charley (Florida, 

2004) 

Figure 4-89:

Cables were attached 

to prevent the cowling 

from blowing off. 

Typhoon Paka (Guam, 

1997)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-91

metal straps with two side-by-side #12 screws or bolts with proper end and 

edge distances at each strap end are recommended when the basic wind 

speed is greater than 90 mph (see Figure 4-91).

Figure 4-90:

Sleeper-mounted 

condensers displaced 

by high winds. 

Hurricane Katrina 

(Mississippi, 2005) 

Figure 4-91:

This condenser 

had supplemental 

attachment straps (see 

red arrows). Typhoon 

Paka (Guam, 1997)
4-92 MAKING HOSPITALS SAFE FROM HIGH WIND

Vibration isolators: If vibration isolators are used to mount equipment, 

only those able to resist design uplift loads should be specified and installed, or an alternative means to accommodate uplift resistance should 

be provided (see Figure 4-92). 

Figure 4-92:

Failure of vibration 

isolators that provided 

lateral resistance but 

no uplift resistance 

caused equipment 

damage. A damaged 

vibration isolator is 

shown in the inset. 

Hurricane Katrina 

(Mississippi, 2005)

Three publications pertaining to seismic restraint of equipment provide general information on 

fasteners and edge distances: 

m Installing Seismic Restraints for Mechanical Equipment (FEMA 412, 2002) 

m Installing Seismic Restraints for Electrical Equipment (FEMA 413, 2004)

m Installing Seismic Restraints for Duct and Pipe (FEMA 414, 2004) 

Boiler and exhaust stack attachment: To avoid wind damage to boiler and 

exhaust stacks, wind loads on stacks should be calculated and guy-wires 

should be designed and constructed to resist the loads. Toppled stacks, as 

shown at the hospital in Figure 4-93, can allow water to enter the building 

at the stack penetration, damage the roof membrane, and become 

wind-borne debris. The designer should advise the building owner that 

guy-wires should be inspected annually to ensure they are taut.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-93

Access panel attachment: Equipment access panels frequently blow off. To 

minimize this, job-site modifications, such as attaching hasps and locking 

devices like carabiners, are recommended. The modification details need 

to be customized. Detailed design may be needed after the equipment has 

been delivered to the job site. Modification details should be approved by 

the equipment manufacturer.

Equipment screens: Screens around rooftop equipment are frequently 

blown away (see Figure 4-94). Screens should be designed to resist the 

wind load derived from ASCE 7. Since the effect of screens on equipment 

wind loads is unknown, the equipment attachment behind the screens 

should be designed to resist the design load. 

Figure 4-94:

Equipment screen 

panels, such as these 

blown away at a 

hospital, can break 

glazing, puncture roof 

membranes, and cause 

injury. Hurricane Ivan 

(Florida, 2004)

Figure 4-93:

Three of the five stacks 

that did not have guywires were blown 

down. Hurricane 

Marilyn (U.S. Virgin 

Islands, 1995) 
4-94 MAKING HOSPITALS SAFE FROM HIGH WIND

Water Infiltration

During high winds, wind-driven rain can be driven through air intakes 

and exhausts unless special measures are taken. Louvers should be designed and constructed to prevent leakage between the louver and wall. 

The louver itself should be designed to avoid water being driven past 

the louver. However, it is difficult to prevent infiltration during very high 

winds. Designing sumps with drains that will intercept water driving past 

louvers or air intakes should be considered. ASHRAE 62.1 (2004) provides some information on rain and snow intrusion. The Standard 62.1 

User’s Manual provides additional information, including examples and illustrations of various designs.

4.3.4.2 Nonstructural Systems and Mechanical 

Equipment in Hurricane-Prone Regions

Elevators: Where interruption of elevator service would significantly disrupt facility operations, it is recommended that elevators be placed in 

separate locations within the building and be served by separate elevator 

penthouses. This is recommended, irrespective of the elevator penthouse 

enhancements recommended in Sections 4.3.3.5, 4.3.3.7, and 4.3.4.1, 

because of the greater likelihood that at least one of the elevators will remain operational and therefore allow the facility to function as intended, 

as discussed in Section 4.2.1.3.

Mechanical Penthouses: By placing equipment in mechanical penthouses 

rather than leaving them exposed on the roof, equipment can be shielded 

from high-wind loads and wind-borne debris. Although screens (such 

as shown in Figure 4-94) could be designed and constructed to protect 

equipment from horizontally-flying debris, they are not effective in protecting equipment from missiles that have an angular trajectory. It is 

therefore recommended that mechanical equipment be placed inside 

mechanical penthouses. The penthouse itself should be designed and 

constructed in accordance with the recommendations given in Sections 

4.3.2.1, 4.3.3.6, and 4.3.3.8.

4.3.4.3 Exterior-Mounted Electrical and 

Communications Equipment

Damage to exterior-mounted electrical equipment is infrequent, mostly 

because of its small size (e.g., disconnect switches). Exceptions include communication towers, surveillance cameras, electrical service masts, satellite 

dishes, and lightning protection systems. The damage is typically caused by 

inadequate mounting as a result of failure to perform wind load calculations 

and anchorage design. Damage is also sometimes caused by corrosion (see 

Figure 4-21 and text box in Section 4.3.4.1 regarding corrosion).
MAKING HOSPITALS SAFE FROM HIGH WIND 4-95

Communication towers and poles: ANSI/C2 provides guidance for determining wind loads on power distribution and transmission poles and 

towers. AASHTO LTS-4-M (amended by LTS-4-12 2001 and 2003, respectively) provides guidance for determining wind loads on light fixture 

poles (standards).

Both ASCE 7 and ANSI/TIA-222-G contain wind load provisions for 

communication towers (structures). The IBC allows the use of either approach. The ASCE wind load provisions are generally consistent with 

those contained in ANSI/TIA-222-G. ASCE 7, however, contains provisions for dynamically sensitive towers that are not present in the 

ANSI/TIA standard. ANSI/TIA classifies towers according to their use 

(Class I, Class II, and Class III). This manual recommends that towers (including antennae) that are mounted on, located near, or serve hospitals 

be designed as Class III structures.

Collapse of both large and small communication towers at hospitals is 

quite common during high-wind events (see Figures 4-15 and 4-95). 

These failures often result in complete loss of communication capabilities. In addition to the disruption of communications, collapsed towers 

can puncture roof membranes and allow water leakage into the hospital, 

unless the roof system incorporated a secondary membrane (as discussed 

in Section 4.3.3.8). At the tower shown in Figure 4-95, the anchor bolts 

were pulled out of the deck, which resulted in a progressive peeling of the 

fully adhered single-ply roof membrane. Tower collapse can also injure or 

kill people. 

Figure 4-95:

The collapse of the 

antenna tower caused 

progressive peeling of 

the roof membrane. 

Also note that the 

exhaust fan blew off 

the curb, but the high 

parapet kept it from 

blowing off the roof. 

Hurricane Andrew 

(Florida, 1992) 
4-96 MAKING HOSPITALS SAFE FROM HIGH WIND

See Sections 4.3.1.1 and 4.3.1.5 regarding site considerations for light fixture poles, power poles, and electrical and communications towers.

Electrical service masts: Service mast failure is typically caused by collapse 

of overhead power lines, which can be avoided by using underground 

service. Where overhead service is provided, it is recommended that the 

service mast not penetrate the roof. Otherwise, a downed service line 

could pull on the mast and rupture the roof membrane. 

Satellite dishes: For the satellite dish shown in Figure 4-96, the dish mast 

was anchored to a large metal pan that rested on the roof membrane. 

CMU was placed on the pan to provide overturning resistance. This anchorage method should only be used where calculations demonstrate that 

it provides sufficient resistance. In this case the wind approached the satellite dish in such a way that it experienced very little wind pressure. In 

hurricane-prone regions, use of this anchorage method is not recommended (see Figures 4-83 and 4-97). 

Figure 4-96:

Common anchoring 

method for satellite 

dish. Hurricane Ivan 

(Florida, 2004)

Figure 4-97:

A satellite dish 

anchored similarly to 

that shown in Figure 

4-96 was blown off 

this five-story building. 

Hurricane Charley 

(Florida, 2004) 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-97

Lightning protection systems: For attachment of building lightning protection systems higher than 100 feet above grade, and for buildings located 

where the basic wind speed is in excess of 90 mph, see the following section on attaching LPS in hurricane-prone regions.

4.3.4.4 Lightning Protection Systems (LPS) in 

Hurricane-Prone Regions

Lightning protection systems frequently become disconnected from rooftops during hurricanes. Displaced LPS components can puncture and 

tear roof coverings, thus allowing water to leak into buildings (see Figures 

4-98 and 4-99). Prolonged and repeated slashing of the roof membrane 

by loose conductors (“cables”) and puncturing by air terminals (“lightning rods”) can result in lifting and peeling of the membrane. Also, when 

displaced, the LPS is no longer capable of providing lightning protection 

in the vicinity of the displaced conductors and air terminals. 

Figure 4-98: An air 

terminal debonded 

from the hospital’s 

roof. Displaced air 

terminals can puncture 

tough membranes, 

such as this modified 

bitumen membrane. 

Hurricane Ivan 

(Florida, 2004)

Figure 4-99: View of an 

end of a conductor 

at a hospital that 

became disconnected. 

Hurricane Katrina 

(Mississippi, 2005) 
4-98 MAKING HOSPITALS SAFE FROM HIGH WIND

Lightning protection standards such as NFPA 780 and UL 96A provide 

inadequate guidance for attaching LPS to rooftops in hurricane-prone 

regions, as are those recommendations typically provided by LPS and 

roofing material manufacturers. LPS conductors are typically attached to 

the roof at 3-foot intervals. The conductors are flexible, and when they are 

exposed to high winds, the conductors exert dynamic loads on the conductor connectors (“clips”). Guidance for calculating the dynamic loads 

does not exist. LPS conductor connectors typically have prongs to anchor 

the conductor. When the connector is well-attached to the roof surface, 

during high winds the conductor frequently bends back the malleable 

connector prongs (see Figure 4-100). Conductor connectors have also 

debonded from roof surfaces during high winds. Based on observations 

after Hurricane Katrina and other hurricanes, it is apparent that pronged 

conductor connectors typically have not provided reliable attachment.

To enhance the wind performance of LPS, the following are 

recommended13:

Parapet attachment: When the parapet is 12-inches high or greater, it is 

recommended that the air terminal base plates and conductor connectors 

be mechanically attached with #12 screws that have minimum 11⁄4-inch 

embedment into the inside face of the parapet nailer and are properly 

sealed for watertight protection. Instead of conductor connectors that 

have prongs, it is recommended that mechanically attached looped connectors be installed (see Figure 4-101). 

13Discussion is based on Rooftop Attachment of Lightning Protection Systems in High-Wind Regions—Hurricane 

Katrina Recovery Advisory (May 2006, Revised July 2006).

Figure 4-100:

The conductor 

deformed the prongs 

under wind pressure, 

and pulled away 

from the connector. 

Hurricane Katrina 

(Mississippi, 2005)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-99

Attachment to built-up, modified bitumen, and single-ply membranes: For builtup and modified bitumen membranes, attach the air terminal base plates 

with asphalt roof cement. For single-ply membranes, attach the air terminal base plates with pourable sealer (of the type recommended by the 

membrane manufacturer). 

In lieu of attaching conductors with conductor connectors, it is recommended that conductors be attached with strips of membrane installed by 

the roofing contractor. For built-up and modified bitumen membranes, 

use strips of modified bitumen cap sheet, approximately 9 inches wide at 

a minimum. If strips are torch-applied, avoid overheating the conductors. 

For single-ply membranes, use self-adhering flashing strips, approximately 

9 inches wide at a minimum. Start the strips approximately 3 inches from 

either side of the air terminal base plates. Use strips that are approximately 3 feet long, separated by a gap of approximately 3 inches (see 

Figure 4-102).

Figure 4-102: Plan showing conductor attachment 

Figure 4-101:

This conductor was 

attached to the 

coping with a looped 

connector. Hurricane 

Katrina (Mississippi, 

2005)
4-100 MAKING HOSPITALS SAFE FROM HIGH WIND

As an option to securing the conductors with stripping plies, conductor 

connectors that do not rely on prongs could be used (such as the one 

shown in Figure 4-103). However, the magnitude of the dynamic loads induced by the conductor is unknown, and there 

is a lack of data on the resistance provided 

by adhesively-attached connectors. For this 

reason, attachment with stripping plies is the 

preferred option, because the plies shield the 

conductor from the wind. If adhesive-applied 

conductor connectors are used, it is recommended that they be spaced more closely than 

the 3-foot spacing required by NFPA 780 and 

UL 96A. Depending on wind loads, a spacing 

of 6 to 12 inches on center may be needed in 

the corner regions of the roof, with a spacing 

of 12 to 18 inches on center at roof perimeters 

(see ASCE 7 for the size of corner regions).

Mechanically attached single-ply membranes: It is 

recommended that conductors be placed parallel to, and within 8 inches of, membrane 

fastener rows. Where the conductor falls between or is perpendicular to membrane 

fastener rows, install an additional row of membrane fasteners where the conductor will be 

located, and install a membrane cover-strip over the membrane fasteners. 

Place the conductor over the cover-strip and secure the conductor as recommended above.

By following the above recommendations, additional rows of membrane 

fasteners (beyond those needed to attach the membrane) may be needed 

to accommodate the layout of the conductors. The additional membrane 

fasteners and cover-strip should be coordinated with, and installed by, the 

roofing contractor.

Standing seam metal roofs: It is recommended that pre-manufactured, 

mechanically attached clips that are commonly 

used to attach various items to roof panels be 

used. After anchoring the clips to the panel 

ribs, the air terminal base plates and conductor connectors are anchored to the panel 

clips. In lieu of conductor connectors that 

have prongs, it is recommended that mechanically attached looped connectors be installed 

(see Figure 4-101). 

It is recommended that the building 

designer advise the building owner to 

have the LPS inspected each spring, to 

verify that connectors are still attached to 

the roof surface, that they still engage the 

conductors, and that the splice connectors 

are still secure. Inspections are also 

recommended after high-wind events.

Figure 4-103:

Adhesively attached conductor connector 

that does not use prongs
MAKING HOSPITALS SAFE FROM HIGH WIND 4-101

Conductor splice connectors: In lieu of pronged splice connectors (see 

Figure 4-104), bolted splice connectors are recommended because they 

provide a more reliable connection (see Figure 4-105). It is recommended 

that strips of flashing membrane (as recommended above) be placed 

approximately 3 inches from either side of the splice connector to minimize conductor movement and to avoid the possibility of the conductors 

becoming disconnected. To allow for observation during maintenance inspections, do not cover the connectors.

Figure 4-104:

If conductors detach 

from the roof, they 

are likely to pull out 

from pronged splice 

connectors. Hurricane 

Charley (Florida, 

2004) 

Figure 4-105:

Bolted splice 

connectors are 

recommended to 

prevent free ends of 

connectors from being 

whipped around 

by wind. Hurricane 

Katrina (Mississippi, 

2005)
4-102 MAKING HOSPITALS SAFE FROM HIGH WIND

4.3.4.5 The Case of Martin Memorial Medical Center, 

Stuart, Florida

The case of Martin Memorial Hospital illustrates the importance of elevator penthouse envelopes. Martin Memorial Medical Center is a 244-bed 

facility located on the south bank of the St. Lucie River in Stuart, Florida. 

The original hospital building, opened in 1939, is still in use but not 

for patient care. Currently the main hospital building is the six-story 

North Tower constructed in the early 1970s. MOBs and a cancer treatment facility are also located on the hospital campus. In 2004 the facility 

was struck by Hurricane Frances, and about 3 weeks later by Hurricane 

Jeanne. The estimated peak gust wind speed at this site during Hurricane 

Frances was 100 mph.14 The design wind speed in the 2005 edition of 

ASCE 7 for this location is 140 mph.

The hospital sustained damage to the elevator penthouse, roof covering, 

and roof-mounted equipment. Many of the metal panels on the elevator 

penthouse of the North Tower that were blown off during Hurricane 

Frances (Figure 4-106) tore the roof membrane on the tower roof as well 

as on lower roofs. Mechanical equipment was damaged on the tower roof 

(Figure 4-107) and on lower roofs. The LPS was displaced on the tower 

roof (Figure 4-108) and on lower roofs. Unlike the windows on the first 

floor that were protected with shutters, the upper-level windows were 

not protected. However, none of them were broken, although a significant amount of water leaked through many of these windows. The second 

hurricane (Jeanne) caused additional water infiltration and interrupted 

reconstruction work.

14 The 100 mph speed was estimated for exposure C.

Figure 4-106:

View of the 

reconstruction of the 

damaged walls at the 

elevator penthouse
MAKING HOSPITALS SAFE FROM HIGH WIND 4-103

Loss of the elevator penthouse panels allowed water infiltration into the 

elevator equipment room, which destroyed the control equipment. Water 

also leaked into the nursing floors, which made it necessary to evacuate 

the patients. Because of significant interior water damage and lack of vertical transportation, many patients had to be evacuated by helicopter. 

As dramatically illustrated at this hospital, water infiltration and the lack 

of elevator service can take portions of the hospital offline for several 

weeks. Rather than simply replace the elevator penthouse walls, an engineer was retained to design a more wind-resistant wall covering system. 

The new design for the elevator penthouse wall system was developed 

and new elevator control equipment was installed, bringing the 5th floor 

back online about 4 weeks after the first hurricane struck. The remaining 

floors (2, 3, 4, and 6) were brought back online at a rate of about one 

floor every 2 weeks after the 5th floor was reopened. It cost $3,733,233 to 

repair the North Tower. In addition to this expenditure, the hospital lost a 

significant amount of patient revenue. 

Electrical service was interrupted for 36 hours (generators were used 

during that time), though there was no disruption of site access or water, 

Figure 4-107:

Damaged HVAC equipment. Work is underway 

on the elevator penthouse beyond. 

Figure 4-108:

Displaced LPS
4-104 MAKING HOSPITALS SAFE FROM HIGH WIND

sewer, and communications services. The hospital had an existing contingency plan, which was helpful during the response to these hurricanes. 

For instance, the hospital had contractors on site the day after the hurricane struck to perform emergency repairs; some of these contractors were 

under a pre-arranged contract with the hospital. The contingency plan was 

updated and modified based on experiences with these two hurricanes. 

4.3.5 MUNICIPAL UTILITIES IN HURRICANEPRONE REGIONS

Hurricanes typically disrupt municipal electrical service, and often they 

disrupt telephone (both cellular and landline), water, and sewer services. 

These disruptions may last from several days to several weeks. Electrical 

power disruptions can be caused by damage to power generation stations 

and by damaged lines, such as major transmission lines and secondary 

feeders. Water disruptions can be caused by damage to water treatment 

or well facilities, lack of power for pumps or treatment facilities, or by 

broken water lines caused by uprooted trees. Sewer disruptions can be 

caused by damage to treatment facilities, lack of power for treatment facilities or lift stations, or broken sewer lines. Phone disruptions can be 

caused by damage at switching facilities and collapse of towers. Hospitals 

should be designed to prevent the disruption of services arising from prolonged loss of municipal services. 

4.3.5.1 Electrical Power 

It is recommended that buildings on hospital campuses that will be occupied during a hurricane, or will be needed within the first few weeks 

afterwards, be equipped with one or more emergency generators. In addition to providing emergency generators, it is recommended that one 

or more additional standby generators be considered, because continued 

availability of electrical power is vital. The purpose of providing the 

standby generators is to power those circuits that are not powered by the 

emergency generators. With both emergency and standby generators, the 

entire facility will be completely backed up. It is recommended that the 

emergency generator and standby generator systems be electrically connected via manual transfer switches to allow for interconnectivity in the 

event of emergency generator failure. The standby circuits can be disconnected from the standby generators, and the emergency circuits can be 

manually added. The emergency generators should be rated for prime 

power (continuous operation). 

Running generators for extended time periods frequently results in 

equipment failure. Thus, provisions for back-up generation capacity are 

important, because the municipal power system may be out of service for 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-105

many days or even weeks. Therefore, it is recommended that an exterior 

box for single pole cable cam locking connectors be provided, so that a 

portable generator can be connected to the facility. With a cam locking 

box, if one or more of the emergency or standby generators malfunction, 

a portable generator can be brought to the facility and quickly connected. 

Back-up portable generators should be viewed as a third source of power 

(i.e., they should not replace standby generators), because it may take several days to get a back-up portable generator to the site. 

Generators should be placed inside wind-borne debris resistant buildings 

(see recommendations in Sections 4.3.2.1, 4.3.3.2, 4.3.3.6 and 4.3.3.8) so 

that they are not susceptible to damage from debris or tree fall. Locating 

generators outdoors or inside weak enclosures (see Figure 4-138) is not 

recommended. 

It is recommended that wall louvers for generators be capable of resisting 

the test Missile E load specified in ASTM E 1996. Alternatively, wall louvers can be protected with a debris-resistant screen wall so that wind-borne 

debris is unable to penetrate the louvers and damage the generators. If a 

screen wall is used, it should be designed to allow adequate air flow to the 

generator in order to avoid overheating the generator. 

It is recommended that sufficient onsite fuel storage be provided to allow 

all of the facility’s emergency and standby generators to operate at full capacity for a minimum of 96 hours (4 days).15 If at any time it appears that 

refueling won’t occur within 96 hours, provision should be made to shut off 

part or all the standby circuits in order to provide 

longer operation of the emergency circuits. For remote facilities or situations where it is believed that 

refueling may not occur within 96 hours, the onsite fuel storage capacity should be increased as 

deemed appropriate. It is recommended that fuel 

storage tanks, piping, and pumps be placed inside 

wind-borne debris resistant buildings, or underground. If the site is susceptible to flooding, refer 

to Chapter 3 recommendations.

4.3.5.2 Water Service 

It is recommended that hospitals be provided with an independent water 

supply — a well or onsite water storage. If water is needed for cooling 

towers, the independent water supply should be sized to accommodate 

the system. It is recommended that the well or onsite storage be capable 

of providing an adequate water supply for fire sprinklers. Alternatively, it 

15 The 96-hour fuel supply is based in part on the Department of Veterans Affairs criteria.

It is recommended that a minimum of 96 

hours (4 days) of onsite fuel storage be 

provided for boilers. Storage tanks, piping, 

and pumps should be located within windborne debris resistant buildings or be 

placed underground (if site is susceptible 

to flooding, refer to Chapter 3).
4-106 MAKING HOSPITALS SAFE FROM HIGH WIND

is recommended that the building designer should advise the building 

owner to implement a continual fire-watch and provide additional fire 

extinguishers until the municipal water service is restored. It is recommended that the well or onsite water storage be capable of providing a 

minimum of 100 gallons of potable water per day per patient bed for four 

days (the 100 gallons includes water for cooling towers).16

It is recommended that pumps for wells or onsite 

storage be connected to an emergency power circuit, that a valve be provided on the municipal 

service line, and that onsite water treatment capability be provided where appropriate.

4.3.5.3 Sewer Service 

It is recommended that hospitals be provided with an alternative means 

of waste disposal, such as a temporary storage tank that can be pumped 

out by a local contractor. It is also recommended that back-flow preventors be provided.

4.3.6 POST-DESIGN CONSIDERATIONS IN 

HURRICANE-PRONE REGIONS

In addition to adequate design, proper attention must be given to construction, post-occupancy inspections, and maintenance. 

4.3.6.1 Construction Contract Administration 

It is important for owners of hospitals in hurricane-prone regions to obtain the services of a professional contractor who will execute the work 

described in the contract documents in a diligent and technically proficient manner. The frequency of field observations and extent of special 

inspections and testing should be greater than those employed on hospitals that are not in hurricane-prone regions.

4.3.6.2 Periodic Inspections, Maintenance, and Repair 

The recommendations given in Section 4.3.1.4 for post-occupancy and 

post-storm inspections, maintenance, and repair are crucial for hospitals 

in hurricane-prone regions. Failure of a building component that was not 

maintained properly, repaired, or replaced can present a considerable 

risk of injury or death to occupants, and the continued operation of the 

facility can be jeopardized. 

16 This recommendation is based on the Department of Veterans Affairs criteria.

It is recommended that onsite storage 

of medical gases be sized to provide a 

minimum of 96 hours (4 days) of service. 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-107

4.4 REMEDIAL WORK ON EXISTING 

FACILITIES

Many existing hospitals need to strengthen their structural or 

building envelope components. The reasons for this are the 

deterioration that has occurred over time, or inadequate facility strength to resist current design level winds. It is recommended 

that building owners have a vulnerability assessment performed by a 

qualified architectural and engineering team. A vulnerability assessment should be performed for all facilities older than 5 years. An 

assessment is recommended for all facilities located in areas where the 

basic wind speed is greater than 90 mph (even if the facility is younger 

than 5 years—see Figure 4-109). It is particularly important to perform 

vulnerability assessments on hospitals located in hurricane-prone and 

tornado-prone regions.

Components that typically make buildings constructed before the early 

1990s vulnerable to high winds are weak non-load-bearing masonry walls, 

poorly connected precast concrete panels, long-span roof structures with 

limited uplift resistance, inadequately connected roof decks, weak glass 

curtain walls, building envelope, and exteriormounted equipment. Although the technical 

solutions to these problems are not difficult, the 

cost of the remedial work is typically quite high. 

If funds are not available for strengthening or replacement, it is important to minimize the risk of 

injury and death by evacuating areas adjacent to 

weak non-load-bearing walls, weak glass curtain 

walls, and areas below long-span roof structures 

when winds above 60 mph are forecast. 

As a result of building code changes and 

heightened awareness, some of the common 

building vulnerabilities have generally been 

eliminated for facilities constructed in the 

Although it is unlikely, a hospital may 

occupy a building that was originally 

intended for another use. Buildings that 

were not designed for a critical occupancy 

were likely designed with a 1.0 rather 

than a 1.15 importance factor, and hence 

are not as wind-resistant as needed. It 

is particularly important to perform a 

vulnerability assessment if a hospital 

is located in a building not originally 

designed for a critical occupancy, 

especially if the hospital is located in a 

hurricane- or tornado-prone region.
4-108 MAKING HOSPITALS SAFE FROM HIGH WIND

By performing a vulnerability assessment, items that need to be strengthened or replaced can be identified and prioritized. A proactive approach 

in mitigating weaknesses can save significant sums of money and decrease 

disruption or total breakdown in hospital operations after a storm. For 

example, a vulnerability assessment on a hospital such as that shown in 

Figure 4-110 may identify weakness of the roof 

membrane and/or rooftop equipment. Replacing weak components before a hurricane 

is much cheaper than replacing them and repairing consequential damages after a storm, 

and proactive work avoids the loss of use while 

repairs are made.

mid-1990s or later. Components that typically remain vulnerable to 

high winds are the building envelope and exterior-mounted mechanical, electrical, and communications equipment. Many failures can be 

averted by identifying weaknesses and correcting them. 

Figure 4-109:

The roof on this 5-year 

old hospital blew off. 

Water leaked into the 

patient floor below. 

The floor was taken 

out of service for 

more than a month. 

Hurricane Katrina 

(Mississippi, 2005) 

Before beginning remedial work, it is 

necessary to understand all significant 

aspects of the vulnerability of a hospital 

with respect to wind and wind-driven rain. 

If funds are not available to correct all 

identified deficiencies, the work should be 

systematically prioritized so that the items of 

greatest need are first corrected. Mitigation 

efforts can be very ineffective if they do not 

address all items that are likely to fail.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-109

A comprehensive guide for remedial work on existing facilities is beyond 

the scope of this manual. However, the following are examples of mitigation measures that are often applicable. 

4.4.1 STRUCTURAL SYSTEMS

As discussed in Section 4.1.4.1, roof decks on many facilities designed 

prior to the 1982 edition of the SBC and UBC and the 1987 edition of the 

NBC are very susceptible to failure. Poorly attached decks that are not upgraded are susceptible to blow-off, as shown in Figures 4-111 and 4-132. 

Decks constructed of cementitious wood-fiber, gypsum, and lightweight 

insulating concrete over form boards were commonly used on buildings 

built in the 1950s and 1960s. In that era, these types of decks, as well as 

precast concrete decks, typically had very limited uplift resistance due to 

weak connections to the support structure. Steel deck attachment is frequently not adequate because of an inadequate number of welds, or welds 

of poor quality. Older buildings with overhangs are particularly susceptible to blow-off, as shown in Figure 4-112, because older codes provided 

inadequate uplift criteria.

Figure 4-110:

The roof membrane 

and some of the 

rooftop equipment 

blew off. Although 

the deck was cast-inplace concrete, water 

leaked into the patient 

floor below. Hurricane 

Charley (Florida, 

2004)
4-110 MAKING HOSPITALS SAFE FROM HIGH WIND

Figure 4-112:

The cementitious 

wood-fiber deck 

panels detached 

from the joists along 

the overhangs and 

caused the built-up 

membranes to lift 

and peel. Hurricane 

Katrina (Mississippi, 

2005)

Figure 4-111:

The built-up roof blew 

off after one of the 

cementitious woodfiber deck panels 

detached from the 

joists. Hurricane 

Katrina (Mississippi, 

2005) 

A vulnerability assessment of the roof deck should include evaluating the 

existing deck attachment, spot checking the structural integrity of the 

deck (including the underside, if possible), and evaluating the integrity 

of the beams/joists. If the deck attachment is significantly overstressed 

under current design wind conditions or the deck integrity is compromised, the deck should be replaced or strengthened as needed. The 

evaluation should be conducted by an investigator experienced with the 

type of deck used on the building. 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-111

If a low-slope roof is converted to a steep-slope roof, the new support 

structure should be engineered and constructed to resist the wind loads 

and avoid the kind of damage shown in Figure 4-113.

4.4.2 BUILDING ENVELOPE 

The following recommendations apply to building envelope components 

of existing hospitals.

4.4.2.1 Sectional and Rolling Doors

Sectional and rolling doors (e.g., at hospital loading docks and ambulance garages), installed in older buildings before attention was given to 

the wind resistance of these elements, are very susceptible to being blown 

away. Although weak doors can be retrofitted, it is difficult to ensure that 

the door, door tracks, and connections between the door and tracks are 

sufficient. It is therefore recommended that weak doors and tracks be replaced with new assemblies that have been tested to meet the factored 

design wind loads. As part of the replacement work, nailers between the 

tracks and building structure should either be replaced, or their attachment should be strengthened.

If a facility has more than one sectional or rolling door, all doors should 

be replaced, rather than just replacing one of the doors. The building 

shown in Figure 4-114 had six sectional doors. One door had been replaced before a hurricane. It performed very well, but three of the older 

doors were blown away and two of the older doors remained in place but 

had some wind damage.

Figure 4-113:

The steel truss 

superstructure installed 

as part of a steepslope conversion 

blew away because 

of inadequate 

attachment. Hurricane 

Marilyn (U.S. Virgin 

Islands, 1995)
4-112 MAKING HOSPITALS SAFE FROM HIGH WIND

4.4.2.2 Windows and Skylights

Windows in older facilities may possess inadequate resistance to wind 

pressure. Window failures are typically caused by wind-borne debris, however, glazing or window frames may fail as a result of wind pressure (see 

Figure 4-115). Failure can be caused by inadequate resistance of the 

glazing, inadequate anchorage of the glazing to the frame, failure of the 

frame itself, or inadequate attachment of the frame to the wall. For older 

windows that are too weak to resist the current design pressures, window 

assembly replacement is recommended. Some older window assemblies 

have sufficient strength to resist the design pressure, but are inadequate 

to resist wind-driven rain. If the lack of water resistance is due to worn 

glazing gaskets or sealants, replacing the gaskets or sealant may be viable. 

In other situations, replacing the existing assemblies with new, higher-performance assemblies may be necessary.

It is recommended that all non-impact-resistant, exterior glazing located in hurricane-prone regions (with a basic wind speed of 100 mph or 

greater) be replaced with impact-resistant glazing or be protected with 

shutters, as discussed in Section 4.3.3.4. Shutters are typically a more economical approach for existing facilities. There are a variety of shutter 

types, all illustrated by Figures 4-116 to 4-118. Accordion shutters are 

permanently attached to the wall (Figure 4-116). When a hurricane is 

forecast, the shutters are pulled together and latched into place. Panel 

shutters (Figure 4-117) are made of metal or polycarbonate. When a hurricane is forecast, the shutters are taken from storage and inserted into 

metal tracks that are permanently mounted to the wall above and below 

Figure 4-114:

The new door in the 

center performed very 

well, but the older 

doors on either side of 

it were blown away. 

Hurricane Charley 

(Florida, 2004)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-113

the window frame. The panels are locked into the frame with wing nuts 

or clips. Track designs that have permanently mounted studs for the 

nuts have been shown to be more reliable than track designs using studs 

that slide into the track. A disadvantage of panel shutters is the need for 

storage space. Roll-down shutters (Figure 4-118) can be motorized or 

pulled down manually. Figure 4-118 illustrates the benefits of shuttering. 

Two of the unprotected window units experienced glass breakage and the 

third window unit blew in. 

Deploying accordion or panel shutters a few stories above grade is expensive. Although motorized shutters have greater initial cost, their 

operational cost should be lower. Other options for providing missile protection on upper levels include replacing the existing assemblies with 

laminated glass assemblies, or installing permanent impact resistant 

screens. Engineered films are also available for application to the interior 

of the glass. The film needs to be anchored to the frame, and the frame 

needs to be adequately anchored to the wall. The film degrades over time 

and requires replacement (approximately every decade). Use of laminated glass or shutters is recommended in lieu of engineered films.

Figure 4-115:

Wind pressure caused 

the window frames on 

the upper floor to fail 

(red arrow). Hurricane 

Katrina (Mississippi, 

2005)
4-114 MAKING HOSPITALS SAFE FROM HIGH WIND

Figure 4-116:

This building has 

accordion shutters. 

Hurricane Ivan 

(Florida, 2004)

Figure 4-117:

A metal panel shutter. 

Hurricane Georges 

(Puerto Rico, 1998) 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-115

4.4.2.3 Roof Coverings

For roofs with weak metal edge flashing or coping attachment, face-attachment of the edge flashing/coping (as shown in Figure 4-67) is a 

cost-effective approach to greatly improve the wind-resistance of the roof 

system. 

The vulnerability assessment of roofs ballasted with aggregate, pavers, or 

cementitious-coated insulation boards, should determine whether the ballast complies with ASNI/SPRI RP-4. Corrective action is recommended 

for non-compliant roof coverings. It is recommended that roof coverings with aggregate surfacing, lightweight pavers, or cementitious-coated 

insulation boards on buildings located in hurricane-prone regions be replaced to avoid blow-off (Figures 4-5, 4-46, and 4-47). 

When planning the replacement of a roof covering, it is recommended 

that all existing roof covering be removed down to the deck rather than 

simply re-covering the roof. Tearing off the covering provides an opportunity to evaluate the structural integrity of the deck and correct deck 

attachment and other problems. For example, if a roof deck was deteriorated due to roof leakage (see Figure 4-119), the deterioration would 

likely not be identified if the roof was simply re-covered. By tearing off 

Figure 4-118:

The lower window assembly was protected with a 

motorized shutter. Hurricane Ivan (Florida, 2004)
4-116 MAKING HOSPITALS SAFE FROM HIGH WIND

down to the deck, deteriorated decking like that shown in Figure 4-119 

can be found and replaced. In addition, it is recommended that the attachment of the wood nailers at the top of parapets and roof edges be 

evaluated and strengthened where needed, to avoid blow-off and progressive lifting and peeling of the new roof membrane (see Figure 4-126). 

If the roof has a parapet, it is recommended that the inside of the parapet be properly prepared to receive the new base flashing. In many 

instances, it is prudent to re-skin the parapet with sheathing to provide a suitable substrate. Base flashing should not be applied directly 

to brick parapets because they have irregular surfaces that inhibit good 

bonding of the base flashing to the brick (see Figure 4-120). Also, if moisture drives into the wall from the exterior side of the parapet with base 

flashing attached directly to brick, the base flashing can inhibit drying 

of the wall. Therefore, rather than totally sealing the parapet with membrane base flashing, the upper portion of the brick can be protected by 

metal panels (as shown in Figure 4-79), which permit drying of the brick.

If the parapet is constructed of masonry, it is recommended that its wind 

resistance be evaluated and strengthened if found to be inadequate. The 

masonry parapet shown in Figure 4-139 fell onto the roof. Had it fallen in 

the other direction, it would have blocked the entry and would have had 

the potential to cause injury.

Figure 4-119:

The built-up roof was 

blown off after a few 

of the rotted wood 

planks detached from 

the joists. Hurricane 

Katrina (Mississippi, 

2005)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-117

4.4.3 EXTERIOR-MOUNTED EQUIPMENT

Exterior-mounted equipment on existing hospitals should be carefully examined and evaluated.

4.4.3.1 Antenna (Communications Mast)

Antenna collapse is very common. Besides loss of communications, collapsed masts can puncture roof membranes or cause other building 

damage as shown in Figure 4-121. This case also demonstrates the benefits 

of a high parapet. Although the roof still experienced high winds that 

blew off this penthouse door, the parapet prevented the door from 

blowing off the roof (red arrow in Figure 4-121).

In hurricane-prone regions, it is recommended that antennae strength 

be evaluated as part of the vulnerability assessment. Chapter 15 of ANSI/TIA-222-G provides 

guidance on the structural evaluation of existing 

towers. Appendix J of that standard contains 

checklists for maintenance and condition assessments. Additional bracing, guy-wires, or tower 

strengthening or replacement may be needed.

Fastening rooftop equipment to curbs, 

as discussed in Section 4.3.4.1, is a 

cost-effective approach to minimize windinduced problems.

Figure 4-120:

Failed base flashing 

adhered directly to 

the brick parapet. 

Hurricane Katrina 

(Louisiana, 2005) 
4-118 MAKING HOSPITALS SAFE FROM HIGH WIND

4.4.3.2 Lightning Protection Systems

Adhesively attached conductor connectors and pronged splice connectors 

typically have not provided reliable attachment during hurricanes. To provide more reliable attachment for LPS located in hurricane-prone regions 

where the basic wind speed is 100 mph or greater, or on hospitals more 

than 100 feet above grade, it is recommended that attachment modifications based on the guidance given in Section 4.3.4.4 be used. 

4.4.4 The Case of Baptist Hospital, 

Pensacola, Florida

The case of Baptist Hospital illustrates the challenges faced by older facilities. Baptist Hospital is a 492-bed tertiary care hospital located in 

downtown Pensacola on West Moreno St. approximately 2 miles north of 

Pensacola Bay. This hospital campus, which dates back to the 1950s, includes the hospital itself, a psychiatric hospital, and MOBs. 

This facility was also struck by Hurricane Ivan. The estimated wind speed 

and design wind speed at this hospital are the same as the case study presented in Section 4.2.1.3. Figure 4-122 shows the site plan and Figure 

4-123 is a general view from the northwest (looking southeast).

Figure 4-121:

The antenna at this 

hospital collapsed 

and was whipped 

back and forth across 

the roof membrane. 

Hurricane Andrew 

(Florida, 1992) 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-119

Figure 4-122:

Site plan

Figure 4-123:

General view

Damage

Water entered the hospital at damaged rooftop equipment (Figure 4-

124), and at areas where the roof membrane blew off (Figures 4-125 and 

4-126) and where it was punctured. The roof failure shown in Figure 4-

126 was caused by an inadequately attached edge nailer anchored to the 

brick wall. Failure of the nailer caused a progressive lifting and peeling 

of the roof membrane. Gutters and downspouts were blown off and a few 

windows were broken. The elevator penthouse roof was damaged at the 

psychiatric hospital (Figure 4-127) and the MOBs (Figure 4-125).
4-120 MAKING HOSPITALS SAFE FROM HIGH WIND

Figure 4-125:

The roof covering blew 

off – an emergency 

roof covering had 

been installed (yellow 

arrow). Note the 

damaged MOB 

penthouse beyond (red 

arrow).

Figure 4-124:

This hospital had a 

substantial amount 

of rooftop ductwork. 

Ductwork and fan units 

were damaged in 

several locations (see 

inset). Some of the 

windows in this area 

were also broken. 

Note the missing 

downspout (yellow 

arrow). 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-121

Figure 4-126:

The roof covering blew off – an emergency roof 

covering had been installed (blue arrow). The 

failure was caused by the inadequately attached 

nailer (see inset). The leaning mast at the right 

is a ladder (yellow arrow), with an extension for 

communications and an anemometer for the nearby 

heliport. 

Figure 4-127:

An emergency roof 

covering had been 

installed over the 

elevator penthouse 

at the psychiatric 

hospital.
4-122 MAKING HOSPITALS SAFE FROM HIGH WIND

4.5 Best Practices in Tornado- Prone Regions

Strong and violent tornadoes may reach wind speeds substantially greater than those recorded in the strongest hurricanes. The wind pressures that these tornadoes can exert on a building 

are tremendous, and far exceed the minimum pressures derived from 

building codes. 

Strong and violent tornadoes can generate very powerful missiles. Experience shows that large and heavy objects, including vehicles, can be 

hurled into buildings at high speeds. The missile sticking out of the roof 

in the foreground of Figure 4-128 is a double 2-inch by 6-inch wood 

member. The portion sticking out of the roof is 13 feet long. It penetrated 

a ballasted ethylene propylene diene monomer (EPDM) membrane, approximately 3 inches of polyisocyanurate roof insulation, and the steel 

roof deck. The missile lying on the roof just beyond is a 2-inch by 10-inch 

by 16-foot long wood member. 

Figure 4-128:

A violent tornado 

showered the roof with 

missiles. (Oklahoma, 

1999)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-123

Besides the case studies presented in Sections 4.5.1 and 4.5.2, there is 

little documentation regarding tornado-induced damage to hospitals. 

Most of the damage reports on critical facilities pertain to schools because 

schools are the most prevalent type of critical facilities and, therefore, are 

more likely to be struck. A 1978 report prepared for the Veterans Administration17 identified four hospitals that were struck by tornadoes between 

1973 and 1976. Table 4-2 (taken from that report) further illustrates the 

effects tornados can have on hospitals. 

17 A Study of Building Damage Caused by Wind Forces, McDonald, J.R. and Lea, P.A, Institute for Disaster 

Research, Texas Tech University, 1978.

Table 4-2: Examples of Ramifications of Tornado Damage at Four Hospitals

Location and Building 

Characteristics

Tornado 

Characteristics Damage Ramifications of Damage

Mountain View, Missouri (St. 

Francis Hospital). One-story steel 

frame with non-load bearing 

masonry exterior walls.

The tornado 

crossed over 

one end of the 

hospital. 

Metal roof decking was 

blown off, some windows 

were broken, and rooftop 

mechanical equipment was 

displaced.

Patients were moved to 

undamaged areas of the 

hospital.

Omaha, Nebraska (Bishop Bergen 

Mercy Hospital). Five-story 

reinforced concrete frame. 

Maximum wind 

speed estimated 

at 200 mph. 

Proximity to 

hospital not 

documented.

Windows were broken, 

and rooftop mechanical 

equipment was 

damaged and displaced. 

Communications and 

electrical power were lost 

(emergency generators 

provided power). 

A few minor cuts; “double 

walled corridors” provided 

protection for patients and staff. 

Some incoming emergency 

room patients (injured 

elsewhere in the city) were 

rerouted to other hospitals. Loss 

of communications hampered 

the rerouting.

Omaha, Nebraska (Bishop Bergen 

Mercy Hospital – Ambulatory 

Care Unit). One-story load bearing 

CMU walls with steel joists. 

See above. The building was a total 

loss due to wall and roof 

collapse.

Patients were evacuated to 

the first floor of the main 

hospital when the tornado 

watch was issued.

Corsicana, Texas (Navarro County 

Memorial Hospital). Five-story 

reinforced concrete frame with 

masonry non-load bearing walls in 

some areas and glass curtain walls. 

The tornado was 

very weak.

Many windows were 

broken by aggregate from 

the hospital’s built-up roofs. 

Intake duct work in the 

penthouse collapsed.

Two people in the parking lot 

received minor injuries from 

roof aggregate. Electrical 

power was lost for 2 hours 

(emergency generators 

provided power).

Monahans, Texas (Ward Memorial 

Hospital). One-story load bearing 

CMU walls with steel joists. Some 

areas had metal roof deck and 

others had gypsum deck.

The tornado 

passed directly 

over the 

hospital, with 

maximum wind 

speed estimated 

at 150 mph. 

The roof structure was 

blown away on a portion 

of the building (the bond 

beam pulled away from the 

wall). Many windows were 

broken. Rooftop mechanical 

equipment was damaged.
4-124 MAKING HOSPITALS SAFE FROM HIGH WIND

For hospitals located in tornado-prone regions (as defined in the text 

box), the following are recommended:

m Incorporate a shelter within the facility to provide occupant 

protection. For shelter design, FEMA 361 criteria are recommended. 

m For interior non-load-bearing masonry walls, see the 

recommendations given in 4.3.3.5. 

m Brick veneer, aggregate roof surfacing, roof pavers, slate, and tile 

cannot be effectively anchored to prevent them from becoming 

missiles if a strong or violent tornado passes near a building with these 

components. To reduce the potential number of missiles, and hence 

reduce the potential for building damage and injury to people, it is 

recommended that these materials not be specified for hospitals in 

tornado-prone regions. 

m To minimize disruption from nearby weak tornadoes and from strong 

and violent tornados that are on the periphery of a hospital, the 

following are recommended:

1) For the roof deck, exterior walls, and doors, follow the 

recommendations given in Sections 4.3.2.1, 4.3.3.2, and 4.3.3.6. 

2) For exterior glazing, specify laminated glass window 

assemblies that are designed to resist the test Missile E load 

specified in ASTM E 1996, and are tested in accordance with 

ASTM E 1886. Note that missile loads used for designing 

tornado shelters significantly exceed the 

missile loads used for designing glazing 

protection in hurricane-prone regions. Missiles 

from a strong or violent tornado passing near 

the facility could penetrate the laminated 

glazing and result in injury or interior damage. 

Therefore, to increase occupant safety, 

even when laminated glass is specified, the 

facility should also incorporate a shelter as 

recommended above.

In this manual, the term “tornado-prone regions” refers to those areas of the United States where the 

number of recorded F3, F4, and F5 tornadoes per 3,700 square miles is 6 or greater per year (see 

Figure 4-129). However, an owner of a hospital may decide to use other frequency values (e.g., 1 

or greater, 16 or greater, or greater than 25) in defining whether the hospital is in a tornado-prone 

area. In this manual, tornado shelters are recommended for all hospitals in tornado-prone regions.

Where the frequency value is 1 or greater, and the hospital does not have a tornado shelter, the 

best available refuge areas should be identified, as discussed at the end of this Section.

It is recommended that hospitals have 

a National Oceanic and Atmospheric 

Administration (NOAA) weather radio, so 

that they will be aware of tornado watches 

and warnings. It is also recommended that 

hospitals have a plan to distribute notice 

of watches and warnings received via the 

radio to hospital staff.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-125

Existing Hospitals without Tornado Shelters 

Where the number of recorded F3, F4, and F5 tornadoes per 3,700 square 

miles is one or greater (see Figure 4-129), the best available refuge areas 

should be identified if the hospital does not have a tornado shelter. FEMA 

431, Tornado Protection, Selecting Refuge Areas in Buildings provides useful 

information for building owners, architects, and engineers who perform 

evaluations of existing facilities.

To minimize casualties in hospitals, it is very important that the best available refuge areas be identified by a qualified architect or engineer.18

Once identified, those areas need to be clearly marked so that occupants 

can reach the refuge areas without delay. Building occupants should not 

wait for the arrival of a tornado to try to find the best available refuge area 

18It should be understood that the occupants of a “best available refuge area” are still vulnerable to death and 

injury if the refuge area was not specifically designed as a tornado shelter.

Figure 4-129: Frequency of recorded F3, F4, and F5 tornadoes (1950-1998)
4-126 MAKING HOSPITALS SAFE FROM HIGH WIND

in a particular facility; by that time, it will be too late. If refuge areas have 

not been identified beforehand, occupants will take cover wherever they 

can, frequently in very dangerous places. Corridors, as shown in Figure 4-

142, sometimes provide protection, but they can also be death traps. 

Retrofitting a shelter space inside an existing hospital can be very expensive. An economical alternative is an addition that can function as 

a shelter as well as serve another purpose. This approach works well for 

smaller facilities. For very large facilities, constructing two or more shelter 

additions should be considered in order to reduce the time it takes to 

reach the shelter (often there is ample warning time, but sometimes an 

approaching tornado is not noticed until a few minutes before it strikes). 

This is particularly important for hospitals because of the difficulty of accommodating patients with different medical needs. 

4.5.1 The case of Kiowa County Memorial

Hospital, Greensburg, Kansas

The case of Kiowa County Memorial Hospital illustrates damage that is indicative of smaller, older facilities that are struck by strong tornadoes. The 

hospital is a 28-bed, one-story facility. The original hospital comprised 

three separate buildings (two of these are shown in Figure 4-131): a 

patient wing, a kitchen facility, and an equipment building, and was constructed in 1950. Additions were built in 1965 and 1982. A separate, 

ambulance garage was built prior to 1979, and a separate pre-engineered 

metal storage building was added in 2006. The original buildings had 

precast twin-tee roof structures and at the time of the storm, they had aggregate ballasted single-ply membrane roof systems. The additions all had 

different structural systems. The 1965 patient wing addition had a concrete topping slab over metal form deck over steel roof joists. The 1982 

addition, which housed the emergency room, semi-intensive care, operating room, MRI, lab, medical records, and business offices, had a 

plywood roof deck over wood joists. The ambulance garage had a precast 

twin-tee roof structure. 

Except for the storage building, the majority of the exterior walls were 

brick veneer over unreinforced CMU. A finished basement was built 

under portions of the 1965 and 1982 additions (the two basements were 

not interconnected). 

Figure 4-130 shows the site plan.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-127

The hospital was struck by a tornado in 2007. The National Weather Service rated a portion of the track as an EF5 (with an estimated peak gust 

speed in excess of 200 mph). At the hospital site, the damage was indicative of an EF3 (with a speed between 136 and 165 mph). The 2005 edition 

of ASCE 7 lists the design wind speed for this location as 90 mph. Therefore, the speeds at this site were well above current design conditions.

Figure 4-130:

Site Plan

Figure 4-131:

The building housing 

the generator is 

shown by the yellow 

arrow. The kitchen 

facility is shown by 

the blue arrow. The 

red arrow shows the 

collapsed storage 

building. 
4-128 MAKING HOSPITALS SAFE FROM HIGH WIND

One of the precast twin-tees from the original building blew off and flew 

approximately 80 feet (Figures 4-132 and 4-133). Where the tees rested on 

the bearing wall, steel bearing plates were embedded in the tee’s beams, 

and bearing plates were embedded on top of the wall. At the wall in the 

foreground of Figure 4-132, the bearing plates had not been welded together. Hence, at that end of the tee, no uplift resistance was provided 

other than the tee’s dead load. At the opposite bearing wall, the bearing 

plates were welded, but the bolts anchoring the plates to the wall failed in 

tension as the tee lifted. Both of the bearing plates had two small anchor 

bolts (about 3

/8 -inch diameter).

Using the Damage Indicators in the Enhanced Fujita Scale (EF-Scale) for the main portion of the 

hospital, the Degree of Damage (DOD) indicated an expected wind speed during the tornado of 

142 mph (with lower and upper bounds ranging from 119 to 163 mph). Failure analysis of the 

precast twin-tee that blew off the hospital indicated that a speed of approximately 147 mph was 

needed to blow off the tee, and a speed of approximately 193 mph was needed to toss it the 80 

feet that it traveled.

The DOD at the pre-engineered storage building indicated an expected wind speed of 155 mph 

(with lower and upper bounds ranging from 132 to 178 mph). 

Thus, the DOD of the hospital, the DOD of the storage building and the failure analysis of tee blow 

off indicate essentially the same estimated speed (142, 147, and 155 mph). The upper bound values 

of the DODs (163 and 178 mph) are lower than the 193 mph speed that was calculated to have 

tossed the tee. Based on the EF-Scale DODs, the 193 mph speed appears to be high.

Figure 4-132:

View of the end of the 

patient wing where the 

twin-tee blew off. Note 

the missing window. 
MAKING HOSPITALS SAFE FROM HIGH WIND 4-129

The hospital complex was struck with a very large number of missiles. Virtually all of the hospital’s exterior glazing was broken. Figure 4-134 shows a 

damaged door at the kitchen facility. A piece of built-up roof (BUR) membrane struck the right door. Although the doors were out-swinging, the 

missile pushed the door inward. The lower right hinge was broken, and the 

right side of the door frame buckled and pulled from the rough opening. 

The laminated glass in the door was broken, but remained in place.

Figure 4-133:

The missing tee shown 

in Figure 4-132 landed 

about 80 feet away 

(red oval). The red 

arrows show tees that 

were blown from the 

ambulance garage. 

Note the missing 

wood roof structure 

on the 1982 addition 

(yellow arrow). 

Figure 4-134:

The BUR missile (red arrow) struck the right door. 

Missiles also punctured the siding and wood 

sheathing (red oval).
4-130 MAKING HOSPITALS SAFE FROM HIGH WIND

Aggregate from the ballasted single-ply membrane roofs broke several 

windows (Figure 4-135), and pieces of the large aggregate (11

/2 -inches in 

diameter, nominal) were found inside the building. Windows were also 

broken by 2x wood framing (Figure 4-136).

Figure 4-136:

A large missile (2x framing) penetrated this patient room. Note the debris on the bed in the inset (the 

arrow shows the same 2x missile).

Figure 4-135:

All six panes of glass were broken. The craters shown in the right center pane and at the vehicle 

windshield were caused by the large aggregate blown from the ballasted single-ply membranes.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-131

Figure 4-137 illustrates an opening through the entire exterior wall.

The building shown in Figure 4-131 (yellow arrow) and in Figure 4-138 

housed the emergency generator. The sectional door collapsed and allowed wind-borne debris to strike the generator. All window panes in the 

wall adjacent to the sectional door were broken (see inset at Figure 

4‐138). The wall louver adjacent to the window, which served the generator room, escaped damage. 

There was no apparent structural damage to the 1965 addition. However, 

the unreinforced brick/CMU parapet shown in Figure 4-139 fell onto 

the roof, rather than in the other direction, where it would have blocked 

the entry and possibly could have caused injuries. Virtually all of the exterior windows were broken (see Figures 4-135 and 4-136). The roof insulation 

and aggregate-ballasted single-ply roof membrane were blown off. The wood 

roof structure blew off the majority of the 1982 addition (Figures 4-133 

and 4-140), and virtually all of the exterior windows were broken. 

The precast twin-tees on the ambulance garage blew off and landed against 

the wall of the 1982 addition (Figures 4-133 and inset at 4-141). The garage 

door and virtually all of the exterior unreinforced brick/CMU bearing 

walls collapsed (Figure 4-141). Where the tees rested on the bearing wall, 

steel bearing plates were embedded in the tee’s beams. However, bearing 

plates had not been embedded on top of the support walls. Rather, where 

Figure 4-137:

A missile impact created an opening in the brick 

veneer and unreinforced CMU.
4-132 MAKING HOSPITALS SAFE FROM HIGH WIND

the tee’s beams rested on the wall, a piece of roof membrane had been installed between the beams and the wall. Hence, at the ends of the tees, no 

uplift resistance was provided other than the tee’s dead load. 

Figure 4-138:

The sectional door (red 

arrow) at the generator 

building was blown 

in and windows were 

broken by debris. 

Figure 4-139:

Collapsed 

unreinforced masonry 

parapet. Note the 

broken windows. 

There were 20 patients and 10 staff in the facility when the tornado struck 

around 9:45 p.m. Fortunately, the staff was aware of the tornado warning 

that was issued by the National Weather Service. Patients and staff took 

refuge in the basement of the 1965 addition per the hospital’s tornado 

plan. Because of the extensive structural and non-structural damage, it 

was necessary to completely evacuate the hospital after the storm. Evac-
MAKING HOSPITALS SAFE FROM HIGH WIND 4-133

uation was completed by around 2:45 a.m. (about 5 hours after the 

tornado). None of the occupants were injured during the storm or evacuation. The ambulance shown in Figure 4-141 was not usable because of 

missile damage. Even though some portions of the facility could be salvaged, significant demolition and reconstruction will be necessary.

Figure 4-140:

Loss of the wood 

roof structure at the 

1982 addition. 

Figure 4-141:

View of the collapsed 

ambulance garage. 

The twin-tees (red 

arrows) flew to the left, 

as shown in the inset.
4-134 MAKING HOSPITALS SAFE FROM HIGH WIND

The loss of life and avoidance of injuries was attributed to three factors. 

1) A tornado warning was issued by the National Weather Service about 

20 minutes before the tornado struck, and the hospital’s staff was aware 

of the warning. 2) The hospital had a tornado evacuation plan and there 

was sufficient time to execute the plan. 3) Although it is believed that the 

basement was not specifically designed as a tornado shelter, it provided 

a safe area of refuge for patients and staff. For hospitals located in tornado-prone regions, the experience from this tornado demonstrates the 

importance of having a pre-identified, best available refuge area (or preferably a FEMA 361-compliant shelter). Although small interior rooms 

and corridors sometimes provide adequate protection during tornadoes, 

unless specifically designed as a tornado shelter, they often provide inadequate protection, as shown in Figure 4-142.

Figure 4-142:

View of a main 

corridor in the 1982 

addition 

It was determined that with minimal work, the basement under the 1965 addition could be used 

as an interim, best available refuge area for the city. In the weeks and months following the storm, 

several hundred people would be in the city performing demolition, salvaging personal items, and 

conducting reconstruction. Much of this work would occur during the time of year when tornado 

activity is high. Hence, although severely damaged, a portion of the hospital continued to serve 

the community by providing an interim refuge area.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-135

The damage investigation of this facility validates several of the recommendations provided in Section 4.5, summarized below:

m Incorporate a tornado shelter within the facility.

m Don't use aggregate roof surfacing.

m Use roof decks, exterior walls, and doors as recommended in sections 

4.3.2.1, 4.3.3.2, and 4.3.3.6.

m Use laminated glass window assemblies that are designed to resist the 

test Missile E.

4.5.2 The case of Sumter Regional

Hospital, Americus, Georgia

The previous case study reported on a smaller, older hospital that was 

struck by a tornado. The case of Sumter Regional Hospital illustrates the 

performance of a much larger and newer hospital. This hospital is a 143-

bed, four-story facility built in 1953, and expanded in 1975, 1983, and 

1999. The 1999 addition had a cast-in-place concrete roof deck. All of the 

other buildings had steel roof decks. Roof coverings included single-ply 

membranes (exposed and aggregate-ballasted) and aggregate surfaced 

built-up. Exterior walls included brick veneer (over unreinforced CMU 

and over steel studs) and EIFS over steel studs. 

Figure 4-143:

Aerial view of the facility after it was struck by the tornado. The red arrow indicates the general direction 

of the tornado. The blue arrow shows the 1953 building, and the yellow arrow shows the 1999 building. 

The 1975 and 1983 additions are adjacent to and behind the 1953 and 1999 buildings. 

Courtesy of the National Weather Service.

Tornado Direction
4-136 MAKING HOSPITALS SAFE FROM HIGH WIND

The hospital was struck by a tornado in 2007. The National Weather 

Service rated a portion of the track as an EF3 (with an estimated peak 

gust speed between 136 and 165 mph). At the hospital site, the damage 

was indicative of an EF2 (with a speed between 111 and 135 mph). The 

2005 edition of ASCE 7 lists the design wind speed for this location as 

90 mph. Therefore, the speeds at this site were well above current 

design conditions.

As the tornado approached the southwest 

side of the hospital, numerous tree branches 

from trees in front of the hospital were thrown 

against the building. Missiles broke virtually 

all of the glass in the southwest walls (Figures 

4-144 and 4-145), and missiles penetrated the 

EIFS and landed inside the building. Roof 

decking and steel joists were blown off of 

portions of the 1953 building, and the roof 

membrane was blown off of several different areas of the facility. 

The right (curved) portion of the building in Figure 4-144 is the 1999 addition. This portion of the first floor housed waiting and exam rooms. 

Offices were on the second floor, and medical offices were on the third 

floor. Figures 4-144 and 4-146 also show part of the 1953 building. Offices 

were on the first floor, and patient rooms were on the second and third 

floors. 

Using the Damage Indicators in the 

Enhanced Fujita Scale (EF-Scale), the 

Degree of Damage (DOD) at the hospital 

indicated an expected wind speed during 

the tornado of 131 mph (with lower and 

upper bounds ranging from 110 to 152 

mph).

Figure 4-144:

The 1999 addition is 

on the right, and the 

1953 building is to the 

left. Virtually all of the 

glass on these facades 

was broken.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-137

Figure 4-145:

One window frame 

was blown away 

(red circle). The EIFS 

was penetrated by 

many missiles, and 

in some areas, the 

entire wall (except 

the studs) was blown 

away (arrows).

Figure 4-146:

Several of the 

window frames were 

blown away, along 

with some of the 

brick veneer (1999 

addition).

Broken glass showered the rooms along the exterior walls. The breach of 

the building envelope allowed strong winds to enter the rooms and corridors, which led to the collapse of suspended acoustical ceilings and light 

fixtures. Figure 4-147 illustrates the extent of the interior damage.
4-138 MAKING HOSPITALS SAFE FROM HIGH WIND

Figure 4-147:

Glass shards and 

other debris in the 

lobby area housing 

retail shops and 

offices. 

Damage also occurred on other facades, including collapse of a glass curtain wall and a portion of a brick veneer/unreinforced CMU wall (Figure 

4-148). A large unreinforced brick chimney collapsed on a roof, and a 

large rooftop air handling unit (20 x 7 x 9 feet) was shifted several feet. A 

substantial amount of water entered the building at various places where 

the envelope was breached. 

Much of the aggregate ballast (11/2 - inch nominal diameter) was blown 

from the roof, and broke numerous vehicle windows in the parking lot.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-139

Figure 4-148:

Collapsed brick 

veneer/CMU wall at a 

mechanical room. The 

cast-in-place concrete 

wall (arrow) remained, 

but the brick veneer 

was blown away.

There were 54 patients in the facility when the tornado struck around 

9:15 p.m. Staff was not aware of the approaching tornado until just before 

it struck. Most of the patients and newborn infants were moved into hallways as the tornado struck the building. Some remained in their beds 

during the few seconds of the tornado impact. People were injured, but 

none seriously. Because of the extensive damage, it was necessary to completely evacuate the hospital after the storm. Evacuation was completed by 

around 2:00 a.m. (about 5 hours after the tornado).

Within a couple of days, an urgent care facility was temporarily set up in 

a tent. Temporary modular buildings were also 

brought in to provide space for an expanded 

array of healthcare services for the community. 

After approximately 3 months of study, it was decided to demolish the entire hospital complex 

and build a new facility. An interim facility was 

expected to be completed by the fall of 2007. 

As with the previous case study, the damage investigation of this facility validates several of 

the recommendations provided in Section 4.5. 

In particular, this case study validates the recommendations pertaining to use of roof decks, 

exterior walls, and doors, as recommended 

In addition to the impacts on delivery of 

healthcare to the community, the damage 

had potential impacts on the economy. 

The hospital had approximately 700 

employees and was one of the largest 

employers in the county. Had there 

been significant interruptions in meeting 

payroll, or had it been decided to close 

the facility and rely on a hospital that was 

approximately 40 miles away, the loss of 

jobs would likely have been difficult on the 

community.
4-140 MAKING HOSPITALS SAFE FROM HIGH WIND

in sections 4.3.2.1, 4.3.3.2, and 4.3.3.6, and the use of laminated glass 

window assemblies that are designed to resist the test Missile E. In those 

instances where there is little or no warning of an impending tornado 

strike, maintaining building envelope integrity is crucial to providing protection to patients and staff, and in minimizing disruption of services.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-141

4.6 Checklist for Building

Vulnerability of HOSPITALS 

Exposed to High Winds

T he Building Vulnerability Assessment Checklist (Table 4-3) is a tool 

that can help in assessing the vulnerability of various building components during the preliminary design of a new building, or the 

rehabilitation of an existing building. In addition to examining design issues that affect vulnerability to high winds, the checklist also examines 

the potential adverse effects on the functionality of the critical and emergency systems upon which most critical facilities depend. The checklist is 

organized into separate sections, so that each section can be assigned to a 

subject expert for greater accuracy of the examination. The results should 

be integrated into a master vulnerability assessment to guide the design 

process and the choice of appropriate mitigation measures.

Table 4-3: Checklist for Building Vulnerability of Hospitals Exposed to High Winds

Vulnerability Sections Guidance Observations

General

What is the age of the facility, and what 

building code and edition was used for the 

design of the building?

Substantial wind load improvements were 

made to the model building codes in the 

1980s. Many buildings constructed prior to 

these improvements have structural vulnerabilities. Since the 1990s, several additional 

changes have been made, the majority of 

which pertain to the building envelope. 

Older buildings, not designed and constructed in accordance with the practices 

developed since the early 1990s, are generally more susceptible to damage than newer 

buildings.
4-142 MAKING HOSPITALS SAFE FROM HIGH WIND

Vulnerability Sections Guidance Observations

General (continued)

Is the hospital older than 5 years, or is it located 

in a zone with basic wind speed greater than 

90 mph?

In either case, perform a vulnerability 

assessment with life-safety issues as the 

first priority, and property damage and 

interruption of service as the second 

priority.

Site

What is the design wind speed at the site? Are 

there topographic features that will result in 

wind speed-up?

ASCE 7

What is the wind exposure on site? Avoid selecting sites in Exposure D, and 

avoid escarpments and hills

Are there trees or towers on site? Avoid trees and towers near the facility. 

If the site is in a hurricane-prone region, 

avoid trees and towers near primary 

access roads.

Road access Provide two separate means of access.

Is the site in a hurricane-prone region? ASCE 7. If yes, follow hurricane-resistant 

design guidance.

If in a hurricane-prone region, are there 

aggregate surfaced roofs within 1,500 feet of 

the facility?

Remove aggregate from existing roofs. If 

the buildings with aggregate are owned 

by other parties, attempt to negotiate the 

removal of the aggregate (e.g., consider 

offering to pay the reroofing costs).

Architectural 

Will the facility be used as a shelter? If yes, refer to FEMA 361.

Are there interior non-load-bearing walls? Design for wind load.

Are there multiple buildings on site in a 

hurricane-prone region?

Provide enclosed walkways between 

buildings that will be occupied during a 

hurricane.

Are multiple elevators needed for the building? Place elevators in separate locations 

served by separate penthouses.

Table 4-3: Checklist for Building Vulnerability of Hospitals Exposed to High Winds (continued)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-143

Vulnerability Sections Guidance Observations

Structural Systems Section 4.3.2

Is a pre-engineered building being considered? If yes, ensure the structure is not 

vulnerable to progressive collapse. If a 

pre-engineered building exists, evaluate to 

determine if it is vulnerable to progressive 

collapse.

Is precast concrete being considered? If yes, design the connections to resist 

wind loads. If precast concrete elements 

exist, verify that the connections are 

adequate to resist the wind loads.

Are exterior load-bearing walls being 

considered?

If yes, design as MWFRS and C&C. 

Is an FM Global-rated roof assembly specified? If yes, comply with FM Global deck 

criteria.

Is there a covered walkway or canopy? If yes, use “free roof” pressure coefficients 

from ASCE 7.Canopy decks and canopy 

framing members on older buildings often 

have inadequate wind resistance. Windborne debris from canopies can damage 

adjacent buildings and cause injury. 

Is the site in a hurricane-prone region? A reinforced cast-in-place concrete 

structural system, and reinforced concrete 

or fully grouted and reinforced CMU 

walls, are recommended.

Is the site in a tornado-prone region? If yes, provide occupant protection. See 

FEMA 361.

Do portions of the existing facility have longspan roof structures (e.g., a gymnasium)?

Evaluate structural strength, since older 

long-span structures often have limited 

uplift resistance.

Is there adequate uplift resistance of the 

existing roof deck and deck support structure?

The 1979 (and earlier) SBC and UBC, 

and 1984 (and earlier) BOCA/NBC, did 

not prescribe increased wind loads at roof 

perimeters and corners. Decks (except 

cast-in-place concrete) and deck support 

structures designed in accordance with 

these older codes are quite vulnerable.The 

strengthening of the deck attachment and 

deck support structure is recommended for 

older buildings.

Table 4-3: Checklist for Building Vulnerability of Hospitals Exposed to High Winds (continued)
4-144 MAKING HOSPITALS SAFE FROM HIGH WIND

Vulnerability Sections Guidance Observations

Structural Systems Section 4.3.2 (continued)

Are there existing roof overhangs that 

cantilever more than 2 feet?

Overhangs on older buildings often have 

inadequate uplift resistance.

Building Envelope Section 4.3.3

Exterior doors, walls, roof systems, windows, 

and skylights.

Select materials and systems, and detail to 

resist wind and wind-driven rain.

Are soffits considered for the building? Design to resist wind and wind-driven 

water infiltration. If there are existing soffits, evaluate their wind and wind-driven 

rain resistance. If the soffit is the only 

element preventing wind-driven rain from 

being blown into an attic space, consider 

strengthening the soffit.

Are there elevator penthouses on the roof? Design to prevent water infiltration at 

walls, roof, and mechanical penetrations.

Is a low-slope roof considered on a site in a 

hurricane-prone region?

A minimum 3-foot parapet is 

recommended on low-slope roofs.

Is an EOC, healthcare facility, shelter, or other 

particularly important hospital in a hurricaneprone region?

If yes, a very robust building 

envelope, resistant to missile impact, is 

recommended.

Is the site in a tornado-prone region? To minimize generation of wind-borne 

missiles, avoid the use of brick veneer, 

aggregate roof surfacing, roof pavers, 

slate, and tile.

Are there existing sectional or rolling doors? Older doors often lack sufficient wind 

resistance. 

Does the existing building have large windows 

or curtain walls?

If an older building, evaluate their wind 

resistance.

Does the existing building have exterior 

glazing (windows, glazed doors, or skylights)?

If the building is in a hurricane-prone 

region, replace with impact-resistant 

glazing, or protect with shutters.

Does the existing building have operable 

windows?

If an older building, evaluate its winddriven rain resistance.

Are there existing exterior non-load-bearing 

masonry walls?

If the building is in a hurricane- or tornadoprone region, strengthen or replace.

Table 4-3: Checklist for Building Vulnerability of Hospitals Exposed to High Winds (continued)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-145

Vulnerability Sections Guidance Observations

Building Envelope Section 4.3.3 (continued)

Are there existing brick veneer, EIFS, or stucco 

exterior coverings?

If the building is in a hurricane-prone 

region, evaluate attachments. To evaluate 

wind resistance of EIFS, see ASTM E 2359 

(2006).

Are existing exterior walls resistant to windborne debris?

If the building is in a hurricane-prone 

region, consider enhancing debris resistance, particularly if dealing with an 

important hospital.

Are there existing ballasted single-ply roof 

membranes?

Determine if they are in compliance with 

ANSI/SPRI RP-4. If non-compliant, take 

corrective action.

Does the existing roof have aggregate 

surfacing, lightweight pavers, or cementitiouscoated insulation boards?

If the building is in a hurricane- prone 

region, replace the roof covering to avoid 

blow-off.

Does the existing roof have edge flashing or 

coping?

Evaluate the adequacy of the attachment. 

Does the existing roof system incorporate a 

secondary membrane?

If not, and if the building is in a hurricaneprone region, reroof and incorporate a 

secondary membrane into the new system. 

Does the existing building have a brittle roof 

covering, such as slate or tile?

If the building is in a hurricane-prone 

region, consider replacing with a nonbrittle covering, particularly if it is an 

important hospital.

Exterior-Mounted Mechanical Equipment

Is there mechanical equipment mounted 

outside at grade or on the roof?

Anchor the equipment to resist wind loads. 

If there is existing equipment, evaluate the 

adequacy of the attachment, including attachment of cowlings and access panels.

Are there penetrations through the roof? Design intakes and exhausts to avoid 

water leakage.

Is the site in a hurricane-prone region? If yes, place the equipment in a penthouse, 

rather than exposed on the roof.

Exterior-Mounted Electrical and Communications Equipment 

Are there antennae (communication masts) or 

satellite dishes?

If there are existing antennae or satellite 

dishes and the building is located in a 

hurricane-prone region, evaluate wind 

resistance. For antennae evaluation, see 

Chapter 15 of ANSI/TIA-222-G-2005.

Table 4-3: Checklist for Building Vulnerability of Hospitals Exposed to High Winds (continued)
4-146 MAKING HOSPITALS SAFE FROM HIGH WIND

Vulnerability Sections Guidance Observations

Exterior-Mounted Electrical and Communications Equipment (continued)

Does the building have a lightning protection 

system?

See Sections 4.3.4.4 and 4.4.3.2 for 

lightning protection system attachment. 

For existing lightning protection systems, 

evaluate wind resistance, see Section 

4.4.3.2.

Municipal Utilities

Is the site in a hurricane-prone region? See Section 4.3.5.1 for emergency and 

standby power recommendations.

Is the emergency generator(s) housed in a 

wind- and debris-resistant enclosure?

If not, build an enclosure to provide debris 

protection in a hurricane-prone region.

Is the emergency generator’s wall louver 

protected from wind-borne debris?

If the building is in a hurricane-prone 

region, install louver debris impact 

protection.

Is the site in a hurricane-prone region? If yes, an independent water supply and 

alternative means of sewer service are 

recommended, independent of municipal 

services. 

Table 4-3: Checklist for Building Vulnerability of Hospitals Exposed to High Winds (continued)
MAKING HOSPITALS SAFE FROM HIGH WIND 4-147

4.7 References and Sources of

Additional Information

Note: FEMA publications may be obtained at no cost by calling (800) 

480-2520, faxing a request to (301) 497-6378, or downloading from the library/publications section online at http://www.fema.gov.

American Association of State Highway and Transportation Officials, 

Standard Specifications for Structural Supports for Highway Signs, 

Luminaires and Traffic Signals, LTS-4-M and LTS-4-12, January 2001 and 

October 2003.

American Concrete Institute, ASCE, The Masonry Society, Building Code 

Requirements for Masonry Structures, ACI 530/ASCE 5/TMS 402, 2005.

American Institute of Architects, Buildings at Risk: Wind Design Basics 

for Practicing Architects, 1997. 

American National Standards Institute/SPRI RP-4, Wind Design 

Standard for Ballasted Single-Ply Roofing Systems, 2002.

American National Standards Institute/SPRI ES-1, Wind Design 

Standard for Edge Systems Used in Low Slope Roofing Systems, 2003.

American National Standards Institute/Telecommunications Industry 

Association, Structural Standards for Antenna Supporting Structures and 

Antennas, ANSI/TIA-222-G, August 2005.

American Red Cross, Standards for Hurricane Evacuation Shelter Selection, 

Publication 4496, July 1992, rev. January 2002.

American Society of Civil Engineers, Structural Engineering Institute, 

Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-

05, Reston, VA, 2005.
4-148 MAKING HOSPITALS SAFE FROM HIGH WIND

American Society for Testing and Materials, Standard Test Method for 

Field Determination of Water Penetration of Installed Exterior Windows, 

Skylights, Doors, and Curtain Walls by Uniform or Cyclic Static Air Pressure 

Difference, ASTM E1105, 2000.

American Society for Testing and Materials, Standard Test Method for 

Structural Performance of Sheet Metal Roof and Siding Systems by Uniform 

Static Air Pressure Difference, ASTM E1592, 2000.

American Society for Testing and Materials, Standard Test Method for 

Structural Performance of Exterior Windows, Curtain Walls, and Doors by 

Cyclic Static Air Pressure Differential, ASTM E1233, December 2000.

American Society for Testing and Materials, Standard Practice for 

Installation of Exterior Windows, Doors and Skylights, ASTM E2112, 2001.

American Society for Testing and Materials, Standard Test Method 

for Performance of Exterior Windows, Curtain Walls, Doors, and Impact 

Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure 

Differentials, ASTM E1886, 2005.

American Society for Testing and Materials, Standard Specification for 

Performance of Exterior Windows, Curtain Walls, Doors and Impact Protective 

Systems Impacted by Windborne Debris in Hurricanes, ASTM E1996, 2005.

American Society for Testing and Materials, Standard Specification for 

Zinc Coating (Hot-Dip) on Iron and Steel Hardware, ASTM A153, April 

2005.

American Society for Testing and Materials, Standard Specification for 

Steel, Sheet, Cold-Rolled, Carbon, Structural, High-Strength Low-Alloy, HighStrength Low-Alloy with Improved Formability, Solution Hardened, and Bake 

Hardenable, ASTM A1008/A1008M, 2006.

American Society for Testing and Materials, Test Method for Field Pull 

Testing of an In-Place Exterior Insulation and Finish System Clad Wall 

Assembly, ASTM E 2359, 2006.

American Society for Testing and Materials, Standard Test Method for 

Structural Performance of Exterior Windows, Doors, Skylights, and Curtain 

Walls by Cyclic Air Pressure Differential, ASTM E1233, 2006.

American Society of Heating, Refrigeration and Air-Conditioning 

Engineers, Inc. (ASHRAE), Ventilation for Acceptable Indoor Air Quality, 

Standard 62.1, 2004.
MAKING HOSPITALS SAFE FROM HIGH WIND 4-149

American Society of Heating, Refrigeration and Air-Conditioning 

Engineers, Inc. (ASHRAE), Standard 62.1 User’s Manual, 2006.

Brick Industry Association, Anchored Brick Veneer-Wood Frame 

Construction, Technical Notes 28, Revised August 2002.

Brick Industry Association, Wall Ties for Brick Masonry, Technical Notes 

44B, Revised May 2003.

Brick Industry Association, Brick Veneer/Steel Stud Walls, Technical 

Notes 28B, December 2005.

Door & Access Systems Manufacturers Association, Connecting Garage 

Door Jambs to Building Framing, Technical Data Sheet #161, December 

2003.

FM Global, Loss Prevention Data for Roofing Contractors, Norwood, MA, 

dates vary.

Factory Mutual Research, Approval Guide, Norwood, MA, updated 

quarterly.

FEMA, Building Performance: Hurricane Andrew in Florida, FEMA FIA-22, 

Washington, DC, December 1992.

FEMA, Building Performance: Hurricane Iniki in Hawaii, FEMA FIA-23, 

Washington, DC, January 1993.

FEMA, Corrosion Protection for Metal Connectors in Coastal Areas, FEMA 

Technical Bulletin 8-96, Washington, DC, August 1996. 

FEMA, Typhoon Paka: Observations and Recommendations on Building 

Performance and Electrical Power Distribution System, FEMA-1193-DR-GU, 

Washington, DC, March 1998.

FEMA, Hurricane Georges in Puerto Rico, FEMA 339, Washington, DC, 

March 1999.

FEMA, Oklahoma and Kansas Midwest Tornadoes of May 3, 1999, FEMA 

342, Washington, DC, October 1999.

FEMA, Coastal Construction Manual, Third Edition, FEMA 55, 

Washington, DC, 2000.

FEMA, Design and Construction Guidance for Community Shelters, FEMA 

361, Washington, DC, July 2000.
4-150 MAKING HOSPITALS SAFE FROM HIGH WIND

FEMA, Installing Seismic Restraints for Mechanical Equipment, FEMA 412, 

Washington, DC, December 2002.

FEMA, Tornado Protection, Selecting Safe Areas in Buildings,

FEMA 431, Washington, DC, October 2003.

FEMA, Installing Seismic Restraints for Electrical Equipment,

FEMA 413, Washington, DC, January 2004. 

FEMA, Installing Seismic Restraints for Duct and Pipe, FEMA 414, 

Washington, DC, January 2004.

FEMA, Taking Shelter From the Storm: Building a Safe Room Inside Your 

House, FEMA 320, Washington, DC, March 2004.

FEMA, MAT Report: Hurricane Charley in Florida, FEMA 488, 

Washington, DC, April 2005.

FEMA, MAT Report: Hurricane Ivan in Alabama and Florida, FEMA 489, 

Washington, DC, August 2005.

FEMA, Home Builder’s Guide to Coastal Construction Technical Fact Sheet 

Series, FEMA 499, August 2005.

FEMA, Attachment of Brick Veneer in High-Wind Regions—Hurricane 

Katrina Recovery Advisory, Washington, DC, December 2005. 

FEMA, MAT Report: Hurricane Katrina in the Gulf Coast, FEMA 549, 

Washington, DC, July 2006. 

FEMA, Attachment of Rooftop Equipment in High-Wind Regions—Hurricane 

Katrina Recovery Advisory, Washington, DC, May 2006, rev. July 2006.

FEMA, Rooftop Attachment of Lighting Protection Systems in High-Wind 

Regions—Hurricane Katrina Recovery Advisory, Washington, DC, May 

2006, rev. July 2006. 

Institute of Electrical and Electronics Engineers, Inc., National 

Electrical Safety Code, ANSI/IEE/C2, 2006.

International Code Council, 2006 International Building Code, ICC IBC2006, March 2006.

McDonald, J.R. and Lea, P.A, A Study of Building Damage Caused by 

Wind Forces, Institute for Disaster Research, Texas Tech University, 

1978. 
ACRONYMS A

ACRONYMS A-1

ABFE	 	 Advisory Base Flood Elevation

ACI	 	 American Concrete Institute

ADA	 	 Americans with Disabilities Act

ANSI	 	 American National Standards Institute

ASCE	 	 American Society of Civil Engineers

ASHRAE 	 American Society of Heating, Refrigeration and Air-	 	

	 	 Conditioning Engineers, Inc.

ASTM	 	 American Society for Testing and Materials

BCFH	 	 Boulder Community Foothills Hospital

BFE	 	 Base Flood Elevation

BIA	 	 Brick Industry Association

BOCA	 	 Building Officials and Code Administrators

	 	 International, Inc.

BURs	 	 Built-Up Roofs

C&C	 	 Components and Cladding

CMU	 	 Concrete Masonry Unit

DFE	 	 Design Flood Elevation

EERI 	 	 Earthquake Engineering Research Institute

EIFS	 	 Exterior Insulation Finish Systems

ELF 	 	 Equivalent Lateral Force

EMS 	 	 Emergency Medical Service

EOC	 	 Emergency Operation Center

ER	 	 Emergency Room

FEMA	 	 Federal Emergency Management Agency

FIRMs	 	 Flood Insurance Rate Maps

FISs	 	 Flood Insurance Studies

FMG	 	 Factory Mutual Global
A-2 ACRONYMS

FMR	 	 Factory Mutual Research

GAO	 	 General Accounting Office

HSSA 	 Hospital Seismic Safety Act (California)

HVAC 	 Heating, Ventilating, and Air-Conditioning

IBC	 	 International Building Code

ICBO	 	 International Conference of Building Officials

ICC	 	 International Code Council

ICU	 	 Intensive Care Unit

IEE	 	 Institute of Electrical and Electronics Engineers, Inc.

KCH 	 	 Kona Community Hospital

LACDHS 	 Los Angeles County, Department of Health Services

LPS	 	 Lightning Protection System

M/E/P 		 Mechanical/Electrical/Plumbing

MEPS	 	 Molded Expanded Polystyrene

MMI	 	 Modified Mercalli Intensity

MOB	 	 Medical Office Building

MWFRS		 Main Wind-Force Resisting System

NBC	 	 National Building Code

NEHRP	 	 National Earthquake Hazard Reduction Program

NFIP	 	 National Flood Insurance Program

NFPA	 	 National Fire Protection Association

NIBS 	 	 National Institute of Building Sciences

NOAA 	 	 National Oceanic and Atmospheric Administration

NSC 	 	 Nonstructural Seismic Coordinator

OR 	 	 operating room

OSB 	 	 Oriented Strand Board

OSHPD	 	 Office of Statewide Health Planning and Development (California)

PCI 	 	 Precast/Prestressed Concrete Institute

PGA	 	 Peak Ground Acceleration

PMRs	 	 Protected Membrane Roof
ACRONYMS A-3

REACH	 	 Rapid Evaluation and Assessment Checklist

SBC	 	 Standard Building Code

SBCCI	 	 Southern Building Code Congress International, Inc.

SDC	 	 Seismic Design Category

SPF	 	 Sprayed Polyurethane Foam

TIA	 	 Telecommunications Industry Association

USACE	 	 U.S. Army Corp of Engineers

UBC 	 	 Uniform Building Code

URM	 	 Unreinforced Masonry

USGS	 	 U. S. Geological Survey

VA	 	 U.S. Department of Veterans Affairs

VSI	 	 Vinyl Siding Institute

GLOSSARY OF TERMS B

GLOSSARY OF TERMS B-1

100-year flood. See “base flood.”

A

Astragal. The center member of a double door, which is attached to the fixed or inactive door 

panel.

B

Base flood. The flood having a 1 percent chance of being equaled or exceeded in any given year, 

commonly referred to as the “100-year flood.” The base flood is the national standard used by 

the NFIP and all Federal agencies for the purposes of requiring the purchase of flood insurance 

and regulating new development. 

Base flood elevation (BFE). The height of the base (1 percent or 100-year) flood in relation to a 

specified datum, usually the National Geodetic Vertical Datum of 1929, or the North American 

Vertical Datum of 1988. 

Base isolation. Also called seismic isolation. A design concept that reduces the earthquake motions in the building superstructure by isolating the building from ground motions.

Basic wind speed. A 3-second gust speed at 33 feet above the ground in Exposure C. (Exposure C 

is flat open terrain with scattered obstructions having heights generally less than 30 feet.) Note: 

Since 1995, ASCE 7 has used a 3-second peak gust measuring time. A 3-second peak gust is the 

maximum instantaneous speed with a duration of approximately 3 seconds. A 3-second peak gust 

speed could be associated with a given windstorm (e.g., a particular storm could have a 40-mph 

peak gust speed), or a 3-second peak gust speed could be associated with a design-level event 

(e.g., the basic wind speed prescribed in ASCE 7).

Building configuration. Size, shape, and proportions of the building; size, shape, and location of 

structural elements; and the type, size, and location of nonstructural elements.

Building, enclosed. A building that does not comply with the requirements for open or partially enclosed buildings.

Building, open. A building having each wall at least 80 percent open. This condition is expressed 

by an equation in ASCE 7.

Building, partially enclosed. A building that complies with both of the following conditions:

1. The total area of openings in a wall that receives positive external pressure exceeds the 
B-2 GLOSSARY OF TERMS

sum of the areas of openings in the balance of the building envelope (walls and roof) by 

more than 10 percent.

2. The total area of openings in a wall that receives positive external pressure exceeds 4 

square feet, or 1 percent of the area of that wall, whichever is smaller, and the percentage 

of openings in the balance of the building envelope does not exceed 20 percent.

These conditions are expressed by equations in ASCE 7.

Building, period. The rate at which a building will vibrate as a result of ground motion.

Building, regularly shaped. A building having no unusual geometrical irregularity in spatial form.

Building, simple diaphragm. An enclosed or partially enclosed building in which wind loads are 

transmitted through floor and roof diaphragms to the vertical main wind-force resisting system.

C

Coastal Flooding. The accumulation of water experienced along the Atlantic, Gulf, and Pacific 

coasts, and the Great Lakes due to storm surges, extratropical systems, tsunamis, and sometimes 

wind-driven waves. 

Components and cladding (C&C). Elements of the building envelope that do not qualify as part of 

the main wind-force resisting system.

Coping. The cover piece on top of a wall exposed to the weather, usually made of metal, masonry, 

or stone, and sloped to carry off water.

D

Damping. The rate at which natural vibration decays as a result of the absorption of energy. In 

buildings it is an inherent nature to resonate inefficiently to vibration depending on structural 

connections, kinds of materials, and nonstructural elements used. “Damping” design measures 

can reduce the magnitude of seismic forces. 

Design flood. The greater of the following two flood events: (1) the base flood, affecting those 

areas identified as special flood hazard areas on a community’s Flood Insurance Rate Map 

(FIRM); or (2) the flood corresponding to the area designated as a flood hazard area on a community’s flood hazard map or otherwise legally designated.

Design flood elevation (DFE). The elevation of the design flood, including wave height, relative to 

the datum specified on a community’s flood hazard map.

Downburst. Also known as a microburst. A powerful downdraft associated with a thunderstorm. 

Down-slope wind. A wind blowing down the slope of mountains (frequently occurs in Alaska and 

Colorado).
GLOSSARY OF TERMS B-3

Drift. The term used in seismic design to describe the horizontal deflection of structural members in response to seismic forces.

Dry floodproofing. An adjustment, modification, or addition of a feature, or any combination 

thereof, that eliminates or reduces the potential for flood damage by sealing walls and closing 

openings to keep water from entering a building. 

Ductility. The characteristic of certain materials—steel in particular—to fail only after considerable distortion or deformation has occurred.

E

Escarpment. Also known as a scarp. With respect to topographic effects, a cliff or steep slope generally separating two levels or gently sloping areas. 

Equivalent Lateral Force (ELF) Procedure. A procedure used in building design that allows adjustments of the design force for varying site seismicities, alternative soil types, different structural 

and nonstructural systems and materials, different building heights, and occupancies of varying 

importance. 

Epicenter. The epicenter is the place on the surface of the earth under which an earthquake rupture originates, often given in degrees of latitude and longitude.

Exposure. The characteristics of the ground roughness and surface irregularities in the vicinity of 

a building. ASCE 7 defines three exposure categories—Exposures B, C, and D. 

Extratropical storm. A cyclonic storm that forms outside of the tropical zone. Extratropical storms 

may be large, often 1,500 miles (2,400 kilometers) in diameter, and usually contain a cold front 

that extends toward the equator for hundreds of miles.

F

Fault. A fault is a fracture along which the blocks of earth’s crust on either side have moved relative to one another parallel to the fracture. 

Federal Emergency Management Agency (FEMA). The Federal Emergency Management Agency is the 

Federal agency which administers the National Flood Insurance Program (NFIP).

Flashing. Any piece of material, usually metal or plastic, installed to prevent water from penetrating a structure.

Flood Insurance Rate Map (FIRM). The official map of a community on which FEMA has delineated 

both the special hazard areas, and the risk premium zones applicable to the community.
B-4 GLOSSARY OF TERMS

Flood Insurance Study (FIS). An engineering study performed by FEMA to identify flood hazard 

areas, flood insurance risk zones, and other flood data in a community; used in the development 

of the FIRM.

Floodplain. Any land area, including the watercourse, that is susceptible to partial or complete inundation by water, from any source.

Floodplain management regulations. Zoning ordinances, subdivision regulations, building codes, or 

special-purpose ordinances that set flood-resistant standards for new construction, land use, and 

development.

Flood profile. A graph of computed flood elevations at points located along a riverine waterway. A 

flood profile typically is available for a waterway that has Base Flood Elevations (BFEs) shown on 

the Flood Insurance Rate Map (FIRM). Flood profiles are usually found in the Flood Insurance 

Study (FIS) report.

Floodway. The channel and that portion of the floodplain that is to be reserved to convey the base 

flood, without cumulatively increasing the water surface elevation more than a designated height.

Floodway fringe. The area of the floodplain outside of the floodway, where floodwaters may be 

shallower and slower. 

Freeboard. A factor of safety, usually expressed in feet above a flood level, for purposes of floodplain management. Freeboard also compensates for the many unknown factors that could 

contribute to flood heights greater than the height calculated for a selected size flood and 

floodway conditions, such as wave action, constricting bridge openings, and the hydrological effect 

of urbanization of the watershed. A freeboard of from 1 to 3 feet is often applied to critical facilities.

G

Glazing. Glass or a transparent or translucent plastic sheet used in windows, doors, and skylights.

Glazing, impact-resistant. Glazing that has been shown, by an approved test method, to withstand 

the impact of wind-borne missiles likely to be generated in wind-borne debris regions during design winds.

Ground motion. The movement of the earth’s surface from earthquakes or explosions. Ground 

motion is produced by waves that are generated by sudden slip on a fault or sudden pressure at 

the explosive source, and travel through the earth and along its surface.

H

Hurricane-prone regions. Areas vulnerable to hurricanes; in the United States and its territories defined as:

1. The U.S. Atlantic Ocean and Gulf of Mexico coasts, where the basic wind speed is 

greater than 90 miles per hour.
GLOSSARY OF TERMS B-5

2. Hawaii, Puerto Rico, Guam, U.S. Virgin Islands, and American Samoa.

Human intervention. The presence and active involvement of people necessary to enact or implement floodproofing measures prior to the onset of flooding.

Hydrodynamic load. Loads imposed by water flowing against and around an object or structure, including the impacts of debris and waves.

Hydrostatic load. Load (pressure) imposed on an object or structure by a standing mass of water; 

the deeper the water, the greater the load or pressure against the object or structure.

I

Impact-resistant covering. A covering designed to protect glazing, which has been shown by an 

approved test method to withstand the impact of wind-borne missiles likely to be generated in 

wind-borne debris regions during design winds.

Importance factor, I. A factor that accounts for the degree of hazard to human life and damage to 

property. Importance factors are given in ASCE 7.

L

Landslides. The slipping of soil and rock on sloping ground triggered by earthquake ground 

motion.

Liquefaction. The temporary change of loose granular soils and sand in the presence of water 

from a solid to a liquid state when subjected to ground shaking. 

Lowest floor. The lowest floor of the lowest enclosed area (including basement). An unfinished 

or flood-resistant enclosure, usable solely for parking of vehicles, building access, or storage, in 

an area other than a basement area, is not considered a building’s lowest floor, provided that the 

enclosure is compliant with flood-resistant requirements.

M

Magnitude. The magnitude is a number that characterizes the relative size of an earthquake. 

Magnitude is based on measurement of the maximum motion recorded by a seismograph. 

Best known scales are “Richter magnitude,” and “moment magnitude.” The moment magnitude (Mw) scale, based on the concept of seismic moment, is uniformly applicable to all sizes of 

earthquakes. 

Main wind-force resisting system. An assemblage of structural elements assigned to provide support and stability for the overall structure. The system generally receives wind loading from more 

than one surface.
B-6 GLOSSARY OF TERMS

Mean roof height, (h). The average of the roof eave height and the height to the highest point on the 

roof surface, except that, for roof angles of less than or equal to 10 degrees, the mean roof height 

shall be the roof eave height.

Missiles. Debris that could become propelled into the wind stream. 

Modified Mercalli Intensity (MMI) scale. Intensity scale used to measure the level of earthquake 

damage. 

Moment Frame. Frames in which structural members and joints resist lateral forces by bending. 

There are “ordinary,” “intermediate,” and “special” moment frames. The latter provide the most 

resistance.

N

National Flood Insurance Program (NFIP). A Federal program to identify flood-prone areas nationwide, and make flood insurance available for properties in communities that participate in the 

program. 

NEHRP. The Federal National Earthquake Hazard Reduction Program, enacted in 1977, to 

reduce potential losses from earthquakes by funding research in earthquake prediction and hazards and to guide the implementation of earthquake loss-reduction programs. 

Nor’easter. Nor’easters are non-tropical storms that typically occur in the eastern United States, 

any time between October and April, when moisture and cold air are plentiful. They are known 

for dumping heavy amounts of rain and snow, producing hurricane-force winds, and creating 

high surfs that cause severe beach erosion and coastal flooding. A nor’easter is named for the 

winds that blow in from the northeast and drive the storm along the east coast and the Gulf 

Stream, a band of warm water that lies off the Atlantic Coast. 

O

Openings. Apertures or holes in the building envelope that allow air to flow through the building 

envelope. A door that is intended to be in the closed position during a windstorm would not be 

considered an opening. Glazed openings are also not typically considered openings. However, 

if the building is located in a wind-borne debris region and the glazing is not impact-resistant or 

protected with an impact-resistant covering, the glazing is considered an opening.

P

Passive Energy Dissipation. The reduction of earthquake forces in a building by the introduction 

of devices designed to dissipate the earthquake energy in a controlled manner using friction, hydraulics, or deformation of material specially placed for this purpose.

Peak Ground Acceleration. The largest acceleration that occurs during earthquake-induced ground 

motion.
GLOSSARY OF TERMS B-7

R

Racking. Lateral deflection of a structure resulting from external forces, such as wind or lateral 

ground movement in an earthquake.

Resonance. The increase in vibrations and accelerations to a vibrating building from the transmission of ground motion.

Response spectrum. A characterization of ground motion (representing the suite of spectral ordinates) measuring the extent of shaking different structures will experience based on their 

natural period of vibration. 

Richter magnitude scale. Developed in 1935 by Charles F. Richter of the California Institute of 

Technology. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in 

the distance between the various seismographs and the epicenter of the earthquakes. On the 

Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a 

magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might 

be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number 

increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of 

energy, each whole number step in the magnitude scale corresponds to the release of about 31 

times more energy than the amount associated with the preceding whole number value. 

Ridge. With respect to topographic effects, an elongated crest of a hill characterized by strong 

relief in two directions.

Riverine Flooding. The accumulation of runoff from rainfall or snowmelt, such that the volume 

of flow exceeds the capacity of waterway channels and spreads out over the adjacent land.

S

Seiche. A wave that oscillates in lakes, bays, or gulfs from a few minutes to a few hours as a result 

of seismic or atmospheric disturbances.

Seismic ground motion. The movement of ground surfaces in every direction simultaneously, 

back and forth, side to side, and up and down during an earthquake.

Seismograph. Also known as seismometer, is an instrument used to detect and record earthquakes. Generally, it consists of a mass attached to a fixed base. During an earthquake, the base 

moves and the mass does not. The motion of the base with respect to the mass is commonly 

transformed into an electrical voltage. The electrical voltage is recorded on paper, magnetic 

tape, or another recording medium. This record is proportional to the motion of the seismometer mass relative to the earth, but it can be mathematically converted to a record of the 

absolute motion of the ground. 
B-8 GLOSSARY OF TERMS

Shear. A force that causes parts of a material to slide past one another in opposite directions

Shear wall. Solid wall that resists shear forces, used in buildings constructed in earthquake and 

high-wind zones.

Sheetflow. Rainfall runoff that flows over relatively flat land without concentrating into streams 

or channels.

Spectral Acceleration. The acceleration to be experienced by structures of different periods.

Stiffness. Rigidity, or resistance to deflection or drift. A measure of deflection or of staying in 

alignment within a certain stress.

Stillwater elevation. The elevation that the surface of coastal flood waters would assume in the absence of waves, referenced to a datum.

Straight-line wind. A wind blowing in a straight line with wind speeds ranging from very low to 

very high (the most common wind occurring throughout United States and its territories). 

Substantial damage. Damage of any origin sustained by a structure, whereby the cost of restoring 

the structure to its predamage condition equals or exceeds 50 percent of the market value of 

the structure before the damage occurred (or smaller percentage if established by the authority 

having jurisdiction). Structures that are determined to be substantially damaged are considered 

to be substantial improvements, regardless of the actual repair work performed. 

Substantial improvement. Any reconstruction, rehabilitation, addition, or other improvement of 

a structure, the cost of which equals or exceeds 50 percent of the market value of the structure 

(or smaller percentage if established by the authority having jurisdiction) before the start of the 

improvement. 

T

Torsion. Twisting around an axis. The center of the mass does not coincide with the center of resultant force of the resisting building elements causing rotation or twisting action in plans and 

stress concentrations. Symmetry in general reduces torsion. 

Tsunami. An unusually large sea wave produced by submarine earth movement or a volcanic 

eruption.

W

Wet floodproofing. Permanent or contingent measures and construction techniques, applied to 

a structure or its contents, that prevent or provide resistance to damage from flooding while 

allowing floodwaters to enter the structure. Generally, this includes properly anchoring the 
GLOSSARY OF TERMS B-9

structure, using flood-resistant materials below the BFE, protection of mechanical and utility 

equipment, and the use of openings or breakaway walls. 

Wind-borne debris regions. Areas within hurricane-prone regions located:

1. Within 1 mile of the coastal mean high water line, where the basic wind speed is equal 

to or greater than 110 mph, and in Hawaii.

2. In areas where the basic wind speed is equal to or greater than 120 mph.