FEMA

Risk Management Series

Safe Rooms and 

Shelters

Protecting People Against Terrorist Attacks

FEMA 453 / May 2006

Risk Management Series

Safe Rooms and Shelters 

protecting People Against Terrorist Attacks

FEMA 453 / May 2006
Any opinions, findings, conclusions, or recommendations 

expressed in this publication do not necessarily reflect the views of 

FEMA. Additionally, neither FEMA or any of its employees makes 

any warrantee, 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 

OVERVIEW

T his manual is intended to provide guidance for engineers, architects, building officials, and property owners to design shelters and safe rooms in buildings. It presents 

information about the design and construction of shelters in the 

work place, home, or community building that will provide protection in response to manmade hazards. Because the security needs 

and types of construction vary greatly, users may select the methods 

and measures that best meet their individual situations. The use of 

experts to apply the methodologies contained in this document is 

encouraged.

The information contained herein will assist in the planning and 

design of shelters that may be constructed outside or within dwellings or public buildings. These safe rooms will protect occupants 

from a variety of hazards, including debris impact, accidental or 

intentional explosive detonation, and the accidental or intentional release of a toxic substance into the air. Safe rooms may also 

be designed to protect individuals from assaults and attempted 

kidnapping, which requires design features to resist forced entry 

and ballistic impact. This covers a range of protective options, 

from low-cost expedient protection (what is commonly referred 

to as sheltering-in-place) to safe rooms ventilated and pressurized 

with air purified by ultra-high-efficiency filters. These safe rooms 

protect against toxic gases, vapors, and aerosols (finely divided 

solid or liquid particles). The contents of this manual supplement 

the information provided in FEMA 361, Design and Construction 

Guidance for Community Shelters and FEMA 320, Taking Shelter From 

the Storm: Building a Safe Room Inside Your House. In conjunction 

with FEMA 361 and FEMA 320, this publication can be used for 

the protection of shelters against natural disasters. Although this 

publication specifically does not address nuclear explosions and 

shelters that protect against radiological fallout, that information 

may be found in FEMA TR-87, Standards for Fallout Shelters.
ii foreword and acknowledgments

This guidance focuses on safe rooms as standby systems, ones 

that do not provide protection on a continuous basis. To employ 

a standby system requires warning based on knowledge that a 

hazardous condition exists or is imminent. Protection is initiated as a result of warnings from civil authorities about a release 

of hazardous materials, visible or audible indications of a release 

(e.g., explosion or fire), the odor of a chemical agent, or observed 

symptoms of exposure in people. Although there are automatic 

detectors for chemical agents, such detectors are expensive and 

limited in the number of agents that can be reliably detected. Furthermore, at this point in time, these detectors take too long to 

identify the agent to be useful in making decisions in response to 

an attack. Similarly, an explosive vehicle or suicide bomber attack 

rarely provides advance warning; therefore, the shelter is most 

likely to be used after the fact to protect occupants until it is safe 

to evacuate the building.

Two different types of shelters may be considered for emergency 

use, standalone shelters and internal shelters. A standalone shelter 

is a separate building (i.e., not within or attached to any other 

building) that is designed and constructed to withstand the range 

of natural and manmade hazards. An internal shelter is a specially designed and constructed room or area within or attached 

to a larger building that is structurally independent of the larger 

building and is able to withstand the range of natural and manmade hazards. Both standalone and internal shelters are intended 

to provide emergency refuge for occupants of commercial office 

buildings, school buildings, hospitals, apartment buildings, and 

private homes from the hazards resulting from a wide variety of 

extreme events. 

The shelters may be used during natural disasters following the 

warning that an explosive device may be activated, the discovery of 

an explosive device, or until safe evacuation is established 

following the detonation of an explosive device or the release of 

a toxic substance via an intentional aerosol attack or an industrial 

accident. Standalone community shelters may be constructed in 

neighborhoods where existing homes lack shelters. Community 
foreword and acknowledgments iii

shelters may be intended for use by the occupants of buildings 

they are constructed within or near, or they may be intended for 

use by the residents of surrounding or nearby neighborhoods or 

designated areas. 

BACKGROUND

The attack against the Alfred P. Murrah 

Federal Office Building in Oklahoma 

City and the anthrax attacks in October 2001 made it clear that chemical, 

biological, radiological, and explosive 

(CBRE) attacks are a credible threat 

to our society. Such attacks can cause a large number of fatalities 

or injuries in high-occupancy buildings (e.g., school buildings, 

hospitals and other critical care facilities, nursing homes, day-care 

centers, sports venues, theaters, and commercial buildings) and 

residential neighborhoods. 

Protection against the effects of accidental or intentional explosive detonations and accidental or intentional releases of toxic 

substances into the air or water represent a class of manmade 

hazards that need to be addressed along with the protection that 

may already be provided against the effects of natural hazards such 

as hurricanes and tornadoes. Although there are a wide range of 

scenarios that may create these manmade hazards, to date they are 

extremely rare events. However, although scarce, these events warrant consideration for passive protective measures. These passive 

protective measures may be in the form of a safe room in which 

occupants of a building may be sheltered until it is safe to evacuate. 

The effectiveness of the safe room for protecting occupants from 

manmade threats is dependent on the amount of warning prior to 

the event and its construction. For example, in Israel, a building 

occupant may expect a 3-minute warning prior to a Scud missile 

attack; therefore, the shelter must be accessible to all building 

occupants within this time period. Note that such advance 

warning rarely accompanies the explosive vehicle or suicide 

bomber event; in this case, the function of the safe room is to 

For additional information on CBR and 

explosives, see FEMA 426 and other Risk 

Management Series publications.
iv foreword and acknowledgments

protect occupants until law enforcement agencies determine it is 

safe to evacuate. 

Protection against explosive threats depends to a great extent on 

the size of the explosive, the distance of the detonation relative 

to the shelter, and the type of construction housing the shelter. 

Although there may be opportunities to design a new facility to 

protect against a specified attack scenario, this may be of limited 

feasibility for the retrofit of an existing building. The appropriate 

combination of charge weight and standoff distance as well as 

the intervening structure between the origin of threat and the 

protected space is very site-specific; therefore, it is impractical to 

define a design level threat in these terms. Rather than identify 

a shelter to resist a specified explosive threat, this document will 

provide guidance that will address different types of building 

construction and the reasonable measures that may be taken to 

provide a secure shelter and a debris mitigating enclosure for 

a shelter. This approach does not attempt to address a specific 

threat because there are too many possible scenarios to generalize 

a threat-specific approach; however, it does allow the user to determine the feasible options that may be evaluated on a case by 

case basis to determine a response to any postulated threat. For 

protection against assault and attempted kidnapping, a level of 

forced entry and ballistic resistance may be specified. Several different organizations (e.g., the American Society for Testing and 

Materials (ASTM), H.P. White, Underwriters Laboratories (UL), 

the Department of Justice (DOJ), etc.) define performance levels 

associated with forced entry and ballistic resistance that relate to 

the different sequence of tests that are required to demonstrate 

effectiveness of a given construction product. This document will 

not distinguish between the different types of testing regimes.

Protection against airborne hazardous materials may require active measures. Buildings are designed to exchange air with the 

outdoors in normal operation; therefore, airborne hazardous 

materials can infiltrate buildings readily when released outdoors, 

driven by pressures generated by wind, buoyancy, and fans. Buildings also tend to retain contaminants; that is, it takes longer for 

the toxic materials to be purged from a building than to enter it.
foreword and acknowledgments v

The safe room may also shelter occupants from tornadoes and 

hurricanes, which are the most destructive forces of nature. Since 

1995, over 1,200 tornadoes have been reported nationwide each 

year. Approximately five hurricanes strike the United States mainland every 3 years and two of these storms will cause extensive 

damage. Protection from the effects of these natural occurrences 

may be provided by well designed and amply supplied safe rooms. 

The well designed safe room protects occupants from the extremely rare, but potentially catastrophic effects of a manmade 

threat as well as the statistically more common, but potentially less 

severe effects of a natural disaster.

SCOPE AND ORGANIZATION OF THE MANUAL

This document will discuss the design of shelters to protect against 

CBRE attacks. Fallout shelters that are designed to protect against 

the effects of a nuclear weapon attack are not addressed in this 

publication. The risks of death or injury from CBRE attacks are 

not evenly distributed throughout the United States. This manual 

will guide the reader through the process of designing a shelter to 

protect against CBRE attacks. The intent of this manual is not to 

mandate the construction of shelters for CBRE events, but rather 

to provide design guidance for persons who wish to design and 

build such shelters.

The design and planning necessary for extremely high-capacity 

shelters that may be required for large, public use venues such as 

stadiums or amphitheaters are beyond the scope of this design 

manual. An owner or operator of such a venue may be guided 

by concepts presented in this document, but detailed guidance 

concerning extremely high-capacity shelters is not provided. 

The design of such shelters requires attention to issues such as 

egress and life safety for a number of people that are orders of 

magnitude greater than those proposed for a shelter designed in 

accordance with the guidance provided herein. 

The intent of this manual is not to override or replace current 

codes and standards, but rather to provide important guidance 
vi foreword and acknowledgments

of best practices (based on current technologies and scientific research) where none has been available. No known building, fire, 

life safety code, or engineering standard has previously attempted 

to provide detailed information, guidance, and recommendations 

concerning the design of CBRE shelters for protection of the general public. Therefore, the information provided herein is the best 

available at the time this manual was published. Designing and 

constructing a shelter according to the criteria in this manual does 

not mean that the shelter will be capable of withstanding every 

possible event. The design professional who ultimately designs a 

shelter should state the limiting assumptions and shelter design 

parameters on the project documents.

This manual includes the following chapters and appendices:

m Chapter 1 presents design considerations, potential threats, 

the levels of protection, shelter types, siting, occupancy 

duration, and human factors criteria for shelters (e.g., 

square footage per shelter occupant, proper ventilation, 

distance/travel time and accessibility, special needs, lighting, 

emergency power, route marking and wayfinding, signage, 

evacuation considerations, and key operations zones).

m Chapter 2 discusses the structural design criteria for blast and 

impact resistance, as well as shelters and model building types. 

Structural systems and building envelope elements for shelters 

are analyzed and protective design measures for the defined 

building types are provided. 

m Chapter 3 describes how to add chemical, biological, and 

radiological (CBR) protection capability to a shelter or a safe 

room. It also discusses air filtration, safe room criteria, design 

requirements, operations and maintenance, commissioning, 

and training required to operate a shelter. 

m Chapter 4 discusses emergency management considerations, 

Federal CBRE response teams, emergency response and 
foreword and acknowledgments vii

mass care, community shelter operations plans, descriptions 

of the responsibilities of the shelter team members, 

shelter equipment and supplies, maintenance plans, and 

commercial building shelter operation plans. Key equipment 

considerations and training are also discussed.

m Appendix A presents the references used in the preparation 

of this document.

m Appendix B contains a list of acronyms and abbreviations that 

appear in this document. 

ACKNOWLEDGMENTS

Principal Authors:

Robert Smilowitz, Weidlinger Associates Inc.

William Blewett, Battelle Memorial Institute

Pax Williams, Battelle Memorial Institute

Michael Chipley, PBS&J

Contributors:

Milagros Kennett, FEMA, Project Officer, Risk Management 

Series Publications

Eric Letvin, URS, Project Manager

Deb Daly, Greenhorne & O’Mara, Inc.

Julie Liptak, Greenhorne & O’Mara, Inc.

Wanda Rizer, Consultant
viii foreword and acknowledgments

Project Advisory Panel:

Ronald Barker, DHS, Office of Infrastructure Protection

Wade Belcher, General Service Administration

Curt Betts, U.S. Army Corps of Engineers

Robert Chapman, NIST

Ken Christenson, U.S. Army Corps of Engineers

Roger Cundiff, DOS

Michael Gressel, CDC, NIOSH

Marcelle Habibion, Department of Veterans Affairs

Richard Heiden, U.S. Army Corps of Engineers

Nancy McNabb, NFPA

Kenneth Mead, CDC, NIOSH

Arturo Mendez, NYPD/DHS Liaison

Rudy Perkey, NAVFAC

Joseph Ruocco, SOM

Robert Solomon, NFPA

John Sullivan, PCA
table of contents

table of contents ix

FOREWORD AND Acknowledgments

Overview............................................................................................... i

Background........................................................................................ iii

Scope and Organization of the Manual.............................................v

Acknowledgments..............................................................................vii

Chapter 1– DESIGN CONSIDERATIONS

1.1 Overview..................................................................................1-1

1.2 Potential Threats.....................................................................1-4

1.2.1 Explosive Threats.......................................................1-5

1.2.2 CBR Attacks............................................................. 1-11

1.2.2.1 Chemical Agents......................................... 1-11

1.2.2.2 Biological Warfare Agents......................... 1-12

1.2.2.3 Radiological Attacks................................... 1-13

1.3 Levels of Protection ............................................................ 1-15

1.3.1 Blast Levels of Protection....................................... 1-15

1.3.2 CBR Levels of Protection........................................ 1-17

1.4 Shelter Types........................................................................ 1-19

1.4.1 Standalone Shelters................................................ 1-19

1.4.2 Internal Shelters...................................................... 1-19

1.4.3 Shelter Categories................................................... 1-20

1.5 Siting..................................................................................... 1-23

1.6 Occupancy Duration, Toxic-free Area (TFA)

Floor Space, and Ventilation Requirements...................... 1-31

1.7 Human Factors Criteria....................................................... 1-33

1.7.1 Square Footage/Occupancy Requirements ......... 1-33
x table of contents

1.7.1.1 Tornado or Short-term Shelter

Square Footage Recommendations.......... 1-34

1.7.1.2 Hurricane or Long-term Shelter

Square Footage Recommendations......... 1-35

1.7.2 Distance/Travel Time and Accessibility ............... 1-35

1.7.3 Americans with Disabilities Act (ADA).................. 1-37

1.7.4 Special Needs........................................................... 1-38

1.8 Other Design Considerations.............................................. 1-39

1.8.1 Lighting.................................................................... 1-39

1.8.2 Emergency Power.................................................... 1-39

1.8.3 Route Marking and Wayfinding ............................ 1-40

1.8.4 Signage..................................................................... 1-42

1.8.4.1 Community and Parking Signage............. 1-42

1.8.4.2 Signage at Schools and Places

of Work........................................................ 1-42

1.9 Evacuation Considerations.................................................. 1-44

1.10 Key Operations Zones.......................................................... 1-51

1.10.1 Containment Zones................................................ 1-51

1.10.2 Staging Areas and Designated Entry and

Exit Access Control Points...................................... 1-55

CHAPTER 2 – STRUCTURAL DESIGN CRITERIA

2.1 Overview..................................................................................2-1

2.2 Explosive Threat Parameters.................................................2-1

2.2.1 Blast Effects in Low-rise Buildings............................2-5

2.2.2 Blast Effects in High-rise Buildings:

The Urban Situation..................................................2-8

2.3 Hardened Construction.........................................................2-9
table of contents xi

2.3.1 Structural System........................................................2-9

2.3.2 Loads and Connections.......................................... 2-12

2.3.3 Building Envelope................................................... 2-16

2.3.4 Forced Entry and Ballistic Resistance.................... 2-17

2.4 New Construction................................................................ 2-19

2.4.1 Structure.................................................................. 2-20

2.4.2 Façade and Internal Partitions............................... 2-26

2.5 Existing Construction: Retrofitting Considerations.......... 2-29

2.5.1 Structure.................................................................. 2-30

2.5.2 Façade and Internal Partitions............................... 2-31

2.5.2.1 Anti-shatter Façade..................................... 2-32

2.5.2.2 Façade Debris Catch Systems..................... 2-35

2.5.2.3 Internal Partitions...................................... 2-39

2.5.2.4 Structural Upgrades................................... 2-44

2.5.3 Checklist for Retrofitting Issues............................. 2-45

2.6 Shelters and Model Building Types.................................... 2-46

2.6.1 W1, W1a, and W2 Wood Light Frames

and Wood Commercial Buildings.......................... 2-46

2.6.2 S1, S2, and S3 Steel Moment Frames,

Steel Braced Frames, and Steel Light Frames....... 2-50

2.6.3 S4 and S5 Steel Frames with Concrete

Shearwalls and Infill Masonry Walls ..................... 2-54

2.6.4 C1, C2, and C3 Concrete Moment Frames,

Concrete and Infill Masonry Shearwalls –

Type 1 Bearing Walls and Type 2 Gravity

Frames...................................................................... 2-57

2.6.5 PC1 and PC2 Tilt-up Concrete Shearwalls and

Precast Concrete Frames and Shearwalls.............. 2-62
xii table of contents

2.6.6 RM1 and RM2 Reinforced Masonry Walls

with Flexible Diaphragms or Stiff Diaphragms

and Unreinforced Masonry (URM)

Load-bearing Walls.................................................. 2-65

2.6.7 Conclusions............................................................. 2-69

2.7 Case Study: Blast-Resistant Safe Room............................... 2-69

CHAPTER 3 – CBR THREAT PROTECTION

3.1 Overview .................................................................................3-1

3.2 How Air Filtration Affects Protection ...................................3-5

3.3 Safe Room Criteria .................................................................3-7

3.4 Design and Installation of a Toxic-agent Safe Room ...........3-9

3.4.1 Class 3 Safe Room .................................................. 3-10

3.4.1.1 Tightening the Room................................ 3-10

3.4.1.2 Preparing for Rapidly Sealing

the Room.................................................... 3-11

3.4.1.3 Preparing for Deactivation of Fans........... 3-14

3.4.1.4 Accommodating Air Conditioning

and Heating................................................ 3-14

3.4.1.5 Safety Equipment....................................... 3-16

3.4.2 Class 2 Safe Room................................................... 3-16

3.4.2.1 Filter Unit Requirements for the

Unventilated Class 2 Safe Room................ 3-16

3.4.2.2 Installation and Operation........................ 3-17

3.4.3 Class 1 Safe Room .................................................. 3-18

3.4.3.1 Selecting a Filter Unit for a Class 1

Safe Room................................................... 3-18

3.4.3.2 Sizing the Filter Unit for

Pressurization............................................. 3-20
table of contents xiii

3.4.3.3 Other Considerations for Design of a

Class 1 Safe Room...................................... 3-21

3.5 Operations and Maintenance ............................................ 3-23

3.5.1 Operating a Safe Room in a Home ...................... 3-24

3.5.2 Operating a Safe Room in an Office Building....... 3-25

3.5.3 Operating Procedures for a Class 1

Safe Room................................................................ 3-26

3.6 Maintaining the CBR Shelter ............................................. 3-27

3.6.1 Maintenance for a Class 3 Safe Room .................. 3-27

3.6.2 Maintenance for a Class 2 Safe Room................... 3-27

3.6.3 Maintenance for a Class 1 Safe Room .................. 3-28

3.7 Commissioning a Class 1 CBR Safe Room ........................ 3-31

3.7.1 Measurements......................................................... 3-32

3.7.2 Configuration ......................................................... 3-32

3.7.3 Functionality ........................................................... 3-33

3.8 Upgrading a CBR Safe Room ............................................. 3-34

3.9 Training on the Use of a Safe Room ................................... 3-34

3.10 Case Study: Class 1 Safe Room ........................................... 3-35

CHAPTER 4 – Emergency management considerations

4.1 Overview..................................................................................4-1

4.2 National Emergency Response Framework..........................4-1

4.3 Federal CBRE Response Teams.............................................4-9

4.4 Emergency Response........................................................... 4-11

4.4.1 General Considerations.......................................... 4-11

4.4.2 Evacuation Considerations..................................... 4-12

4.4.3 Mass Care................................................................. 4-16
xiv table of contents

4.5 Community Shelter Operations Plan................................. 4-19

4.5.1 Site Coordinator ..................................................... 4-21

4.5.2 Assistant Site Coordinator ..................................... 4-22

4.5.3 Equipment Manager .............................................. 4-22

4.5.4 Signage Manager .................................................... 4-23

4.5.5 Notification Manager ............................................. 4-24

4.5.6 Field Manager ......................................................... 4-24

4.5.7 Assistant Managers ................................................. 4-25

4.5.8 Emergency Provisions, Equipment,

and Supplies ........................................................... 4-25

4.5.8.1 Food and Water.......................................... 4-25

4.5.8.2 Sanitation Management............................. 4-25

4.5.8.3 Emergency Supplies................................... 4-28

4.5.8.4 Communications Equipment.................... 4-28

4.5.8.5 Masks and Escape Hoods........................... 4-29

4.5.8.6 Portable HVAC Units................................. 4-29

4.5.8.7 Emergency Equipment Credenza

and Wall Units Storage.............................. 4-30

4.6 Shelter Maintenance Plan................................................... 4-30

4.7 Commercial Building Shelter Operations Plan................. 4-30

4.7.1 Emergency Assignments......................................... 4-31

4.7.2 Emergency Call List................................................ 4-33

4.7.3 Event Safety Procedures......................................... 4-34

4.8 General Considerations....................................................... 4-34

4.9 Training and Information................................................... 4-36
table of contents xv

APPENDIces

Appendix A References

Appendix B Abbreviations and Acronyms

tables

Chapter 1

Table 1-1 Safe Evacuation Distances from Explosive

Threats........................................................................1-7

Table 1-2 Safe Evacuation Distances from LPG Threats..........1-8

Table 1-3 Correlation of ISC Levels of Protection and

Incident Pressure to Damage and Injury.............. 1-16

Table 1-4 ISC CBR Levels of Protection................................. 1-18

Table 1-5 Commercial Shelter Categories............................. 1-21

Table 1-6 Evacuation Versus Shelter-in-place Options

Matrix ...................................................................... 1-45

Chapter 2

Table 2-1 UL 752 Ratings of Bullet-resisting Materials......... 2-18

Chapter 3

Table 3-1 Comparison of the Three General Classes

of Toxic-agent Safe Rooms........................................3-3

Table 3-2 Leakage per Square Foot for 0.1 iwg

(estimated makeup airflow rate per square

foot (floor area) to achieve an overpressure

of 0.1 iwg)................................................................ 3-21

Chapter 4

Table 4-1 Shelter Equipment and Supplies........................... 4-26
xvi table of contents

figures

Chapter 1

Figure 1-1 Terrorism by event 1980 through 2001 ................ 1-10

Figure 1-2 Sample anthrax letter............................................. 1-13

Figure 1-3 Radioactive materials smuggling............................ 1-14

Figure 1-4 Example of shelter marking on building,

floor plan, and exterior exits to rally

points....................................................................... 1-25

Figure 1-5 Examples of internal shelter locations in

a residential slab on grade foundation................. 1-28

Figure 1-6 Examples of internal shelter locations in

a residential basement............................................ 1-28

Figure 1-7 Examples of internal shelter locations in a

commercial building.............................................. 1-29

Figure 1-8 Examples of internal shelter locations in

a retail/commercial multi-story building

using parking garage, conference rooms,

data centers, stairwells, and elevator core

areas......................................................................... 1-29

Figure 1-9 Examples of internal shelter locations in

a school/church facility ......................................... 1-30

Figure 1-10 National Weather Service forecast and

warnings................................................................... 1-36

Figure 1-11 Photoluminescent signs, stair treads, and

route marking......................................................... 1-41

Figure 1-12 Shelter signage........................................................ 1-43

Figure 1-13 Operations Zones, Casualty Collection

Point (CCP), and Safe Refuge Area (SRA) .......... 1-52

Figure 1-14 NRP-CIS Ladder Pipe Decontamination

System (LDS).......................................................... 1-53
table of contents xvii

Figure 1-15 NRP-CIS Emergency Decontamination Corridor

System (EDCS)........................................................ 1-54

Figure 1-16 Patient staging area and remains recovery............ 1-55

Figure 1-17 Example of Pentagon staging and recovery

operations................................................................ 1-56

Figure 1-18 Contamination Control Area (CCA)..................... 1-57

Figure 1-19 Site and evidence collection on the site................ 1-58

Figure 1-20 Rescue team coordination prior to entering

a site......................................................................... 1-59

Chapter 2

Figure 2-1 Airblast pressure time history....................................2-3

Figure 2-2 Range to effects chart................................................2-4

Figure 2-3 Blast damage...............................................................2-5

Figure 2-4 Alfred P. Murrah Federal Office Building................2-6

Figure 2-5 Khobar Towers............................................................2-7

Figure 2-6 Ductile detailing of reinforced concrete

structures................................................................. 2-11

Figure 2-7 Effects of uplift and load reversals......................... 2-13

Figure 2-8 Flat slab failure mechanisms.................................. 2-14

Figure 2-9 Blast damaged façade............................................. 2-16

Figure 2-10 Layers of defense..................................................... 2-19

Figure 2-11 Multi-span slab splice locations.............................. 2-21

Figure 2-12 Typical frame detail at interior column................. 2-23

Figure 2-13 Protective façade design......................................... 2-27

Figure 2-14 Mechanically attached anti-shatter film................. 2-34

Figure 2-15 Blast curtain system................................................. 2-37
xviii table of contents

Figure 2-16 Spray-on elastomer coating.................................... 2-40

Figure 2-17 Geotextile debris catch system............................... 2-40

Figure 2-18 Stiffened wall panels............................................... 2-42

Figure 2-19 Metal stud blast wall................................................ 2-43

Figure 2-20 Steel jacket retrofit detail........................................ 2-44

Figure 2-21 W1 wood light frame < 3,000 square feet.............. 2-47

Figure 2-22 W1a wood light frame > 3,000 square feet............ 2-48

Figure 2-23 W2 wood commercial buildings............................. 2-49

Figure 2-24 S1 steel moment frames.......................................... 2-51

Figure 2-25 S2 steel braced frames............................................. 2-52

Figure 2-26 S3 steel light frames................................................ 2-53

Figure 2-27 S4 steel frames with concrete shearwalls............... 2-55

Figure 2-28 S5 steel frames with infill masonry walls................ 2-56

Figure 2-29 C1 concrete moment frames.................................. 2-58

Figure 2-30 C2 concrete shearwalls – type 1 bearing walls........ 2-59

Figure 2 -31 C2 concrete shearwalls – type 2 gravity

frames...................................................................... 2-60

Figure 2-32 C3 concrete frames with infill masonry

shearwalls................................................................. 2-61

Figure 2-33 PC1 tilt-up concrete shearwalls.............................. 2-63

Figure 2-34 PC2 precast concrete frames and shearwalls........ 2-64

Figure 2-35 RM1 reinforced masonry walls with flexible

diaphragms.............................................................. 2-66

Figure 2-36 RM2 reinforced masonry walls with stiff

diaphragms.............................................................. 2-67

Figure 2-37 URM load-bearing walls.......................................... 2-68

Figure 2-38 Schematic of tie forces in a frame structure......... 2-72
table of contents xix

Chapter 3

Figure 3-1 Hinged covers facilitate the rapid sealing

of supply, return, or exhaust ducts in a safe

room........................................................................ 3-13

Figure 3-2 Automatic dampers are used to isolate the

safe room from the ducts or vents used in

normal HVAC system operation............................ 3-22

Figure 3-3 A tabletop recirculation filter unit with

a substantial adsorber is a simple means

of providing higher levels of CBR protection

to unventilated safe rooms..................................... 3-28

Figure 3-4 A canister-type filter unit is often used for

Class 1 Safe Rooms to maximize storage life

of the filters............................................................. 3-31

Figure 3-5 A blower door test on the selected safe room

aids in estimating the size of air-filtration unit

required and in identifying air leakage paths....... 3-37

Figure 3-6 Blower-door test results on the stairwell

selected for a safe room...........................................3-38

Figure 3-7 A military radial-flow CBR filter set was

selected for safe room filtration............................. 3-40

Figure 3-8 A 4,000-cfm filter unit using radial flow

filters was selected for the stairwell safe

room........................................................................ 3-40

Figure 3-9 The Class 1 Safe Room control panel

has a system start/stop switch, status

indicators for dampers, and a pressure

gauge........................................................................ 3-41
xx table of contents

Chapter 4

Figure 4-1 Preparedness versus scale of event............................4-3

Figure 4-2 Flowchart of initial National-level incident

management actions..................................................4-6

Figure 4-3 NRP-CIS Mass Casualty Incident Response..............4-7

Figure 4-4 Emergency Management Group and

Emergency Operations Group .................................4-9

Figure 4-5 High-rise buildings and emergency response....... 4-16
design considerations 1

design considerations 1-

ARC 4496, Standards for Hurricane Evacuation 

Shelter Selection, FEMA 320, Taking Shelter From 

the Storm: Building a Safe Room Inside Your House

and FEMA 361, Design and Construction Guidance 

for Community Shelters

Sources: ARC and FEMA

1.1 OVERVIEW

The attack against the Alfred P. Murrah Federal Office 

Building in Oklahoma City and the anthrax attacks in 

October 2001 made it clear that chemical, biological, radiological, and explosive (CBRE) attacks are a credible threat to 

our society. Such attacks can cause a 

large number of fatalities or injuries in 

high-occupancy buildings (e.g., school 

buildings, hospitals and other critical 

care facilities, nursing homes, day-care 

centers, sports venues, theaters, and 

commercial buildings) and residential 

neighborhoods.

This chapter discusses the potential 

manmade threats to which a shelter may 

be exposed and the level of protection 

(LOP) that may be assumed by building 

owners when deciding to build a shelter 

to support the preparedness objectives 

established in the National Preparedness 

Goal. This guidance complements other 

shelter publications such as the American Red Cross (ARC) 4496, Standards 

for Hurricane Evacuation Shelter Selection; 

FEMA 320, Taking Shelter From the Storm: 

Building a Safe Room Inside Your House; 

and FEMA 361, Design and Construction 

Guidance for Community Shelters.

This manual presents information about 

the design and construction of shelters 

in the work place, home, or community 

building that will provide protection 
1- design considerations 

in response to the manmade CBRE threats as defined in the 

National Response Plan (NRP) and the National Planning Scenarios. As published in the National Preparedness Guidance (April 

2005), the Federal interagency community developed 15 planning scenarios (the National Planning Scenarios or Scenarios) 

for use in national, Federal, state, and local homeland security 

preparedness activities. The National Planning Scenarios are 

planning tools and are representative of the range of potential 

terrorist attacks and natural disasters and the related impacts that 

face our nation. The scenarios establish the range of response requirements to facilitate preparedness planning.

The National Planning Scenarios describe the potential scope 

and magnitude of plausible major events that require coordination among various jurisdictions and levels of government and 

communities.

Scenario 1: Nuclear Detonation – 10-Kiloton Improvised Nuclear 

Device

Scenario 2: Biological Attack – Aerosol Anthrax

Scenario 3: Biological Disease Outbreak – Pandemic Influenza

Scenario 4: Biological Attack – Plague

Scenario 5: Chemical Attack – Blister Agent

Scenario 6: Chemical Attack – Toxic Industrial Chemicals

Scenario 7: Chemical Attack – Nerve Agent

Scenario 8: Chemical Attack – Chlorine Tank Explosion

Scenario 9: Natural Disaster – Major Earthquake

Scenario 10: Natural Disaster – Major Hurricane

Scenario 11: Radiological Attack – Radiological Dispersal Devices

Scenario 12: Explosives Attack – Bombing Using Improvised 

Explosive Device

Scenario 13: Biological Attack – Food Contamination
design considerations 1-

Scenario 14: Biological Attack – Foreign Animal Disease (Foot and 

Mouth Disease)

Scenario 15: Cyber Attack

Manmade threats include threats of terrorism, technological 

accidents, assassinations, kidnappings, hijackings, and cyber attacks (computer-based), and the use of CBRE weapons. High-risk 

targets include military and civilian government facilities, international airports, large cities, and high-profile landmarks. Terrorists 

might also target large public gatherings, water and food supplies, utilities, and corporate centers. Further, they are capable of 

spreading fear by sending explosives or chemical and biological 

agents through the mail.

This chapter also considers shelter design concepts that relate to 

the type of shelter being designed and where it may be located. 

It discusses how shelter use (either single or multiple) may affect 

the type of shelter selected and the location of that shelter on a 

particular site. The chapter describes key operations zones in and 

around a shelter that need to be taken into consideration as a 

means to provide safe ingress and egress and medical assistance 

to victims of a manmade event (terrorist attack or technological 

accident). The decision to enter a shelter is made by the senior 

management staff based on notification of a credible threat or as 

a result of an actual disaster. The National Incident Management 

System (NIMS) and the Catastrophic Incident Supplement (CIS) 

to the NRP established the procedures to respond to and recover 

from a CBRE event. Section 4.2 discusses the plan’s alerting and 

notification, and response and recovery processes. The objective 

of this chapter is to provide a broad vision on how a shelter should 

be designed to protect against catastrophic events.

The decision to design and construct a shelter can be based on a 

single factor or on a collection of factors. Single factors are often 

related to the potential for loss of life or injury (e.g., a hospital 

that cannot move patients housed in an intensive care unit 

decides to build a shelter, or shelters, within the hospital; a school 
1- design considerations 

decides not to chance fate and constructs a shelter). A collection 

of factors could include the type of hazard event, probability of 

event occurrence, severity of the event, probable single and aggregate annual event deaths, shelter costs, and results of computer 

models that evaluate the benefits and costs of the shelter project.

1.2 POTENTIAL THREATS

Rather than identify a specific threat, this document provides 

general guidance that will address different types of building 

construction and the reasonable mitigative measures to provide 

a secure shelter. However, it is important for building owners and 

design professionals to understand the potential threats to which 

buildings may be exposed. This section provides an overview of 

manmade threats.

The term “threat” is typically used to describe the design criteria 

for manmade disasters (technological accident) or terrorism. 

Identifying the threats for manmade threats can be a difficult 

task. Because they are different from other natural hazards such 

as earthquakes, floods, and hurricanes, manmade threats are difficult to predict. Many years of historical and quantitative data, and 

probabilities associated with the cycle, duration, and magnitude of 

natural hazards exist. The fact that data for manmade threats are 

scarce and that the magnitude and recurrence of terrorist attacks 

are almost unpredictable makes the determination of a particular 

threat for any specific site or building difficult and largely subjective. Such asymmetrical threats do not exclusively target buildings 

and may employ diversionary tactics to actually direct occupants to 

a primary attack instrument.

With any manmade threat, it is important to determine who has 

the intent to cause harm. The aggressors seek publicity for their 

cause, monetary gain (in some instances), or political gain through 

their actions. These actions can include injuring or killing people; 

destroying or damaging facilities, property, equipment, or resources; or stealing equipment, material, or information. 
design considerations 1-

Aggressor tactics run the gamut: moving vehicle bombs; stationary vehicle bombs; bombs delivered by persons (suicide 

bombers); exterior attacks (thrown objects like rocks, Molotov 

cocktails, hand grenades, or hand-placed bombs); stand-off 

weapons attacks (rocket propelled grenades, light antitank 

weapons, etc.); ballistic attacks (small arms and high power 

rifles); covert entries (gaining entry by false credentials or circumventing security with or without weapons); mail bombs 

(delivered to individuals); supply bombs (larger bombs processed 

through shipping departments); airborne contamination (CBR 

agents used to contaminate the air supply of a building); and 

waterborne contamination (CBR agents injected into the water 

supply). This section focuses on explosive threats, chemical 

agents, biological warfare agents, and radiological attacks. 

1.2.1 Explosive Threats

The explosive threat is particularly insidious, because all of the ingredients required to assemble an improvised explosive device are 

readily available at a variety of farm and hardware stores. The intensity of the explosive detonation is limited by the expertise of the 

person assembling the device and the means of delivery. Although 

the weight of the explosive depends on the means of transportation and delivery, the origin of the threat depends primarily on 

the access available to the perpetrator. Operational security procedures will define the areas within or around a building at which 

a device may be located, undetected by the building facilities staff. 

These security procedures include screening of vehicles, inspection 

of delivered parcels, and vetting hand carried bags. The extent to 

which this inspection is carried out will determine the size of an explosive device that may evade detection. Despite the most vigilant 

attempts, however, it is unrealistic to expect complete success in 

preventing a small threat from evading detection. Nevertheless, it 

is unlikely that a large threat may be brought into a building. As a 

result, a parcel sized device may be introduced into publicly accessible lobbies, garages, loading docks, cafeterias, or retail spaces and 

it must be assumed that a smaller explosive device may be brought 

anywhere into the building.
1- design considerations 

Although operational security measures can drastically limit 

the size of the explosive device that could be introduced onto 

a building site, there is no means of limiting the size of the explosive that could be contained within a vehicle traveling on the 

surrounding streets or roadways. 

Explosives weigh approximately 100 pounds per cubic foot and, as 

a result, the maximum credible threat corresponds to the weight 

of explosives that can be packaged in a variety of containers or 

vehicles. The Department of Defense (DoD) developed a chart to 

help indicate the weight of explosives and deflagrating materials 

that may reasonably fit within a variety of containers and vehicles 

(see Table 1-1). The table also indicates the safe evacuation distances for occupants of conventional unreinforced buildings, 

based on their ability to withstand severe damage or resist collapse. Similarly, Table 1-1 indicates the safe evacuation distance 

for pedestrians exposed to explosive effects based on the greater 

of fragment throw distance or glass breakage/falling glass hazard 

distance. Because a pipe bomb, suicide belt/vest, backpack, and 

briefcase/suitcase bomb are specifically designed to throw fragments, protection from these devices may require greater safe 

evacuation distances than an equal weight of explosives transported in a vehicle. Table 1-2 shows safe evacuation distances for 

liquefied petroleum gas (LPG) threats.
design considerations 1-

Table 1-1: Safe Evacuation Distances from Explosive Threats

Threat Description

Explosives 

Mass* (TNT 

equivalent)

Building 

Evacuation 

Distance**

Outdoor 

Evacuation 

Distance***

High Explosives (TNT Equivalent)

Pipe Bomb 5 lbs

2.3 kg

70 ft

21 m

850 ft

259 m

Suicide Belt 10 lbs

4.5 kg

90 ft

27 m

1,080 ft

330 m

Suicide Vest 20 lbs

9 kg

110 ft

34 m

1,360 ft

415 m

Briefcase/

Suitcase Bomb

50 lbs

23 kg

150 ft

46 m

1,850 ft

564 m

Compact 

Sedan

500 lbs

227 kg

320 ft

98 m

1,500 ft

457 m

Sedan 1,000 lbs

454 kg

400 ft

122 m

1,750 ft

534 m

Passenger/

Cargo Van

4,000 lbs

1,814 kg

640 ft

195 m

2,750 ft

838 m

Small Moving 

Van/ Delivery 

Truck

10,000 lbs

4,536 kg

860 ft

263 m

3,750 ft

1,143 m

Moving Van/

Water Truck

30,000 lbs

13,608 kg

1,240 ft

375 m

6,500 ft

1,982 m

Semi-trailer 60,000 lbs

27,216 kg

1,570 ft

475 m

7,000 ft

2,134 m

* Based on the maximum amount of material that could reasonably fit into a container or vehicle. Variations are possible.

** Governed by the ability of an unreinforced building to withstand severe damage or collapse.

*** Governed by the greater of fragment throw distance or glass breakage/falling glass hazard distance. These distances can be reduced for 

personnel wearing ballistic protection. Note that the pipe bombs, suicide belts/vests, and briefcase/suitcase bombs are assumed to have a 

fragmentation characteristic that requires greater stand-off distances than an equal amount of explosives in a vehicle.
1- design considerations 

The Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) 

report on Incidents, Casualties and Property Damage for all states for 

2002 lists 553 actual bombing incidents, 32 of which were premature explosions, injuring 80 people, killing 13, and causing over $5 

million in damages. Nearly half of the events were against buildings and nearly a quarter were against vehicles.

Table 1-2: Safe Evacuation Distances from LPG Threats

Threat Description LPG Mass/Volume Fireball 

Diameter*

Safe 

Distance**

Liquefied Petroleum Gas (LPG - Butane or Propane)

Small LPG

Tank

20 lbs/5 gal

9 kg/19 l

40 ft

12 m

160 ft

48 m

Large LPG

Tank

100 lbs/25 gal

45 kg/95 l

69 ft

21 m

276 ft

84 m

Commercial/

Residential 

LPG Tank

2,000 lbs/500 gal

907 kg/1,893 l

184 ft

56 m

736 ft

224 m

Small LPG

Truck

8,000 lbs/2,000 gal

3,630 kg/7,570 l

292 ft

89 m

1,168 ft

356 m

Semi-tanker 

LPG

40,000 lbs/10,000 

gal

18,144 kg/37,850 l

499 ft

152 m

1,996 ft

608 m

* Assuming efficient mixing of the flammable gas with ambient air.

** Determined by U.S. firefighting practices wherein safe distances are approximately four times the flame height. Note that an LPG tank filled 

with high explosives would require a significantly greater stand-off distance than if it were filled with LPG.
design considerations 1-

Only two domestic terrorist bombings involved the use of large 

quantities of High Energy explosive materials. (For more information on High Energy explosives, see FEMA 426, Reference Manual 

to Mitigate Potential Terrorist Attacks Against Buildings, Chapter 4.) 

Although these events represent the largest explosions that have 

occurred to date, they do not accurately represent the actual 

domestic explosive threat. The 1995 explosion that collapsed 

portions of the Murrah Federal Office Building in Oklahoma 

City contained 4,800 pounds of ammonium nitrate and fuel oil 

(ANFO) and the 1993 explosion within the parking garage beneath the World Trade Center complex contained 1,200 pounds 

of urea nitrate.

Every year, approximately 1,000 intentional explosive detonations 

are reported by the Federal Bureau of Investigation (FBI) Bomb 

Data Center. As implied by the FBI statistics, the majority of the 

domestic events contain significantly smaller weights of Low Energy explosives. (For more information on Low Energy explosives, 

see FEMA 426, Chapter 4.) Figure 1-1 illustrates the breakdown of 

domestic terrorist events from 1980 to 2001. The vast majority of 

the 294 terrorist incidents, 55 suspected terrorist incidents, or 133 

prevented terrorist incidents, involved explosives and 75 percent 

of these events occurred in the 1980s. The explosive that was used 

in the 1996 pipe bomb attack at the Olympics in Atlanta, Georgia, 

consisted of smokeless powder and was preceded by a warning 

that was called in 23 minutes before the detonation.
1-10 design considerations 

Although the majority of these explosions targeted residential 

properties and vehicles, 63 took place in educational facilities, 

causing a total of $68,500 in property damage. By contrast, other 

than the attack against the Murrah Federal Office Building, no 

explosive devices were detonated at a Federal government owned 

facility, and only nine were detonated at local/state government 

facilities. Nearly 80 percent of the people known to be involved in 

bombing incidents were “young offenders,” and less than 1⁄2 percent of the perpetrators were identified as members of terrorist 

groups. Vandalism was the motivation in 53 percent of the known 

intentional and accidental bombing incidents, and the timing of 

the attacks was fairly uniformly distributed throughout the day. 

Figure 1-1 Terrorism by event 1980 through 2001

Source: FBI Terrorism 2000/2001 Publication #308
design considerations 1-11

Nevertheless, the protective design of structures focuses on the effects of High Energy explosives and relates the different mixtures 

to an equivalent weight of trinitrotoluene (TNT).

1.2.2 CBR Attacks

Like explosive threats, CBR threats may be delivered externally 

or internally to the building. External ground-based threats may 

be released at a stand-off distance from the building or may be 

delivered directly through an air intake or other opening. Interior threats may be delivered to accessible areas such as the lobby, 

mailroom, or loading dock, or they may be released into a secure 

area such as a primary egress route. There may not be an official 

or obvious warning prior to a CBR event. Although official warnings should always be heeded, the best defense may be to be alert 

to signs of a release.

There are three potential methods of attacks in terms of CBR:

m A large exterior release originating some distance away from 

the building (includes delivery by aircraft)

m A small localized exterior release at an air intake or other 

opening in the exterior envelope of the building

m A small interior release in a publicly accessible area, a major 

egress route, or other vulnerable area (e.g., elevator lobby, 

mail room, delivery, receiving and shipping, etc.)

Chapter 4 provides additional guidance on emergency management considerations that may have an impact on siting or design 

of a shelter.

1.2.2.1	Chemical Agents. Toxic chemical agents can present airborne hazards when dispersed as gases, vapors, or solid or liquid 

aerosols. Generally, chemical agents produce immediate effects, 

unlike biological or radiological agents. In most cases, toxic 

chemical agents can be detected by the senses, although a few are 
1-12 design considerations 

odorless. Their effects occur mainly through inhalation, although 

they can also cause injury to the eyes and skin. 

1.2.2.2	 Biological Warfare Agents. Biological warfare agents are organisms or toxins that can kill or incapacitate people and livestock, 

and destroy crops. The three basic groups of biological agents that 

would likely be used as weapons are bacteria, viruses, and toxins. 

m Bacteria. Bacteria are small free-living organisms that 

reproduce by simple division and are easy to grow. The diseases 

they produce often respond to treatment with antibiotics.

m Viruses. Viruses are organisms that require living cells in 

which to reproduce and are intimately dependent upon the 

body they infect. The diseases they produce generally do not 

respond to antibiotics; however, antiviral drugs are sometimes 

effective. 

m Toxins. Toxins are poisonous substances found in, and 

extracted from, living plants, animals, or microorganisms; 

some toxins can be produced or altered by chemical means. 

Some toxins can be treated with specific antitoxins and 

selected drugs. 

Most biological agents are difficult to grow and maintain. Many 

break down quickly when exposed to sunlight and other environmental factors, while others such as anthrax spores are very long 

lived. They can be dispersed by spraying them in the air or by 

infected animals that carry the disease, as well through food and 

water contamination:

m Aerosols. Biological agents are dispersed into the air, forming 

a fine mist that may drift for miles. Inhaling the agent may 

cause disease in people or animals. 

m Animals. Some diseases are spread by insects and animals, 

such as fleas, flies, mosquitoes, and mice. Deliberately 

spreading diseases through livestock is also referred to as 

agroterrorism.
design considerations 1-13

m Food and water contamination. Some pathogenic organisms 

and toxins may persist in food and water supplies. Most 

microbes can be killed, and toxins deactivated, by cooking 

food and boiling water.

Person-to-person spread of a few infectious agents is also possible. 

Humans have been the source of infection for smallpox, plague, 

and the Lassa viruses.

Anthrax spores formulated as a white 

powder were mailed to individuals in the 

Federal Government and media in the fall 

of 2001. Postal sorting machines and the 

opening of letters dispersed the spores 

as aerosols. Several deaths resulted. The 

effect was to disrupt mail service and 

to cause a widespread fear of handling 

delivered mail among the public.

Figure 1-2 Sample anthrax letter

Source: FBI Terrorism 2000/2001 Publication #308

1.2.2.3	Radiological Attacks. Shelters described in this manual do 

not address the severe and various effects generated by nuclear 

events, including blinding light, intense heat (thermal radiation), 

initial nuclear radiation, blast, fires started by the heat pulse, 

and secondary fires caused by the destruction. Protection against 

these severe effects of a nuclear explosion is not considered in 

this manual.

Terrorist use of a radiological dispersion device (RDD), often 

called ”dirty nuke” or “dirty bomb,” is considered far more likely 

than use of a nuclear device. These radiological weapons are a 

combination of conventional explosives and radioactive material 

designed to scatter dangerous and sublethal amounts of radioactive material over a general area. Such radiological weapons 
1-14 design considerations 

appeal to terrorists because they require very little technical 

knowledge to build and deploy compared to that of a nuclear 

device. Also, these radioactive materials, used widely in medicine, 

agriculture, industry, and research, are much more readily available and easy to obtain compared to weapons grade uranium or 

plutonium. Figure 1-3 shows the number of incidents of radioactive materials smuggling from 1993 to 2003. 

Figure 1-3 Radioactive materials smuggling

SOURCE: international Atomic Energy Agency

There is no way of knowing how much warning time there would 

be before an attack by a terrorist using a radiological weapon. A 

surprise attack remains a possibility.
design considerations 1-15

1.3 Levels Of Protection 

Currently, there are only two Federal standards that have been 

promulgated for Federal facilities that define LOPs for manmade 

threats: the Interagency Security Committee (ISC) Design Criteria

and the DoD Minimum Antiterrorism Standards, UFC 4-010-01. 

Both standards address blast primarily through the use of standoff distance and ensuring walls and glazing blast pressures are 

strengthened to withstand the blast shock wave. Both standards 

address CBR agents primarily through the use of filtration, emergency shutdown of mechanical and electrical systems, and mass 

notification to building occupants.

Until the building, mechanical, electrical, and life safety codes are 

promulgated for manmade events, the ISC building standards provide a reasonable approach to selecting a level of protection for a 

shelter for CBR agents.

1.3.1 Blast Levels of Protection

The level of protection in response to blast loading defines the 

extent of damage and debris that may be sustained in response to 

the resulting blast pressures and impulses. (For more information 

on blast pressure impulses, see FEMA 426, Chapter 4.) The levels 

of protection are generally defined in the terms of performance. 

Fundamental to the discussion of levels of protection is the notion 

of repairable damage. Repair is typically assumed to be within days 

to weeks and the structure requires partial evacuation during repairs. Table 1-3 provides a synopsis of the ISC blast standards.
1-16 design considerations 

Table 1-3: Correlation of ISC Levels of Protection and Incident Pressure to Damage and Injury

Level of 

Protection Potential Structural Damage Potential Glazing Hazards 

Minimum 

and Low 

The facility or protected space will 

sustain a high level of damage 

without progressive collapse. 

Casualties will occur and assets 

will be damaged. Building 

components, including structural 

members, will require replacement, 

or the facility may be completely 

unrepairable, requiring demolition 

and replacement.

For Minimum Protection, there are no 

restrictions on the type of glazing used.

For Low Protection, there is no requirement 

to design windows for specific blast pressure 

loads. However, the use of glazing materials 

and designs that minimize the risks is 

encouraged.

Glazing cracks and window system fails catastrophically. Fragments enter space, impacting 

a vertical witness panel at a distance of no 

more than 3 m (10 ft) from the window at a 

height greater than 0.6 m (2 ft) above the floor.

Medium 

Moderate damage, repairable. 

The facility or protected space 

will sustain a significant degree 

of damage, but the structure will 

be reusable. Some casualties may 

occur and assets may be damaged. 

Building elements other than major 

structural members may require 

replacement.

For Medium and High Protection, design 

up to the specified load as directed by the 

risk assessment. Window systems design 

(glazing, frames, anchorage to supporting 

walls, etc.) on the exterior façade should be 

balanced to mitigate the hazardous effects of 

flying glazing following an explosive event. 

The walls, anchorage, and window framing 

should fully develop the capacity of the 

glazing material selected.

Glazing cracks. Fragments enter space and 

land on the floor and impact a vertical witness 

panel at a distance of no more than 3 m (10 

ft) from the window at a height greater than 

0.6 m (2 ft) above the floor.

High

Minor damage, repairable. The 

facility or protected space may 

globally sustain minor damage with 

local significant damage possible. 

Occupants may incur some injury, 

and assets receive minor damage.

For Medium and High Protection, design 

up to the specified load as directed by the 

risk assessment. Window systems design 

(glazing, frames, anchorage to supporting 

walls, etc.) on the exterior façade should be 

balanced to mitigate the hazardous effects of 

flying glazing following an explosive event. 

The walls, anchorage, and window framing 

should fully develop the capacity of the 

glazing material selected.

Glazing cracks. Fragments enter space and 

land on the floor no farther than 3 m (10 ft) 

from the window.
design considerations 1-17

1.3.2 CBR Levels of Protection

Protection against airborne chemical, biological, and radiological 

(CBR) agents or contaminants is typically achieved by using particulate and adsorption filters, and personal protective equipment 

(PPE). Many different types of filters are available for CBR releases. Filter efficiency (e.g., how well the filter captures the toxic 

material) varies based on the filter type (e.g., activated or impregnated charcoal) and the specific toxic material. No single filter 

can protect against all CBR materials; therefore, it is important to 

verify which CBR materials a filter protects against.

There are three levels of protection that range from filtration with 

pressurization (Class 1), filtration with little or no pressurization 

(Class 2), and passive protection (Class 3). Class 1 protection is for 

a large-scale release over an extended period of time and would 

apply to mission essential government and commercial buildings 

that must remain operational 24 hours a day/7 days a week. Class 

2 protection is for a terrorist attack or technological accident with 

little or no warning and is characterized as a short duration small 

scale release. Class 3 is typically applicable to an industrial accident that results in a short duration release. These three levels of 

protection are discussed in greater detail in Chapter 3. Table 1-4 

provides a synopsis of the ISC CBR protection standards. 

The CBR levels of protection included in this section are consistent with the Department of 

Homeland Security (DHS) Working Group on Radiological Dispersal Device Preparedness and 

the Health Physics Society’s (HPS’s) Scientific and Public Issues Committee reports:

“Sheltering is 10-80% effective in reducing dose depending upon the duration of exposure, 

building design and ventilation. If there is a passing plume of radioactivity, sheltering may be 

preferable to evacuation. When sheltering, ventilation should be turned off to reduce influx of 

outside air. Sheltering may not be appropriate if doses are projected to be very high or long in 

duration.”

“Sheltering is likely to be more protective than evacuation in responding to a radiological 

terrorist event. Therefore, the HPS recommends that sheltering be the preferred protective action. 

The Protective Action Guidance (PAG) for sheltering is the same as the existing evacuation PAG, 

i.e., 10 mSv (1 rem), with the minimum level for initiation being the same as the existing PAG, 

i.e., 1 mSv (100 mrem).”
1-18 design considerations 

Table 1-4: ISC CBR Levels of Protection

Level of 

Protection

For Biological/

Radiological 

Contaminants

For 

Chemical/

Radiological 

Additional Considerations Class

Low 

Use minimum 

efficiency reporting 

value (MERV) 13 

filter or functional 

equivalent.

None None 3

Medium 

Use high-efficiency 

particulate air (HEPA) 

filter or functional 

equivalent.

Use gas 

absorber for 

outside air.

Design for future detection 

technology

Stairway pressurization 

system should maintain 

positive pressure in stairways 

for occupant refuge, safe 

evacuation, and access 

by firefighters. The entry 

of smoke and hazardous 

gases into stairways must be 

minimized.

Locate utility systems at least 

15 m (50 ft) from loading 

docks, front entrances, and 

parking areas. 

2

High 

Use HEPA filter or 

functional equivalent.

Use gas 

absorber for 

outside air 

and return 

air.

Design for future detection 

technology

Stairway pressurization 

system should maintain 

positive pressure in stairways 

for occupant refuge, safe 

evacuation, and access 

by firefighters. The entry 

of smoke and hazardous 

gases into stairways must be 

minimized.

Locate utility systems at least 

15 m (50 ft) from loading 

docks, front entrances, and 

parking areas.

1, 2
design considerations 1-19

1.4 SHELTER TYPES

A CBRE shelter can be designed as a standalone or internal 

shelter to be used solely as a shelter or to have multiple purposes, 

uses, or occupancies. This section provides a series of definitions 

that can be useful when deciding to build a new shelter or upgrade an existing shelter.

1.4.1 Standalone Shelters

A standalone shelter is considered a separate building (i.e., not 

within or attached to any other building) that is designed and constructed to withstand the range of natural and manmade hazards. 

This type of shelter has the following characteristics:

m It may be sited away from potential debris hazards.

m It will be structurally and mechanically separate from any 

building and therefore not vulnerable to being weakened 

if part of an adjacent structure collapses or if a CBRE event 

occurs in the adjacent building.

m It does not need to be integrated into an existing building 

design.

A shelter for CBRE protection may be as simple as an interior 

residential room to the traditional public shelter able to support 

several hundred people. The number of persons taking refuge in 

a shelter will typically be more than 12 and could be up to several 

hundred or more. 

1.4.2 Internal Shelters

An internal shelter is a specially designed and constructed room 

or area within or attached to a larger building that is designed and 

constructed to be structurally independent of the larger building 

and to withstand the range of natural and manmade hazards. It 

shows the following characteristics:
1-20 design considerations 

m It is partially shielded by the surrounding building and may 

not experience the full force of the blast. (Note that any 

protection provided by the surrounding building should not 

be considered in the shelter design.)

m It is designed to be within a new building and may be located 

in an area of the building that the building occupants can 

reach quickly, easily, and without having to go outside, such as 

a data center, conference room, gymnasium, or cafeteria.

m It may reduce the shelter cost because it is typically part of a 

planned renovation or building project.

1.4.3 Shelter Categories

A standalone or internal shelter may serve as a shelter only, or it 

may have multiple uses (e.g., a multi-use shelter at a school could 

also function as a classroom, lunchroom, or laboratory; a multiuse shelter intended to serve a manufactured housing community 

or single-family-home subdivision could also function as a community center). The decision to design and construct a single-use 

or a multi-use shelter will likely be made by the prospective client 

or the owner of the shelter. To help the designer respond to nonengineering and non-architectural needs of shelter owners, this 

section discusses different shelter categories and usages. Table 1-5 

provides a summary of the commercial shelter categories.
design considerations 1-21

Table 1-5: Commercial Shelter Categories

Shelter 

Considerations In-Ground Single-Use Multi-Use Community

Level of Protection

Blast – Medium

CBR – Class 3

Blast – Low

CBR – Class 3

All All

Expected Capacity 1-100 1-10 1-100 100-1,000

Location

Basement or 

sub-basement 

area without 

windows and 

semi-hardened 

walls and 

ceiling

Interior space 

without 

windows and 

semi-hardened 

walls and 

ceiling

Conference 

Room

Data Center

Bathroom

Stairwell

Elevator Core

School

Church

Mall

Government 

Building

Special 

Considerations

Difficult to site/

build in high 

water table and 

rocky areas 

Annual or 

semi-annual 

inspection and 

rotation of 

supplies

May need 

multiple areas in 

large buildings 

and commercial 

office space; 

plan and 

exercises 

to prevent 

overcrowding

Plan for 

multi-lingual, 

elderly, nonambulatory, and 

special needs 

populations

• Life Safety 

NFPA 101 

and 5000 

guidance

• ADA

compliance

NFP = National Fire Protection Association

ADA = Americans with Disabilities Act

m In-ground shelters. The in-ground shelters referred to in 

this manual are built below ground inside a building and 

therefore can be entered directly from within the building. 

Other types of in-ground shelters are available that are 

designed to be installed outside a building and entering one 

of these exterior in-ground shelters would require leaving the 

building. 
1-22 design considerations 

m	 Single-use shelters. Single-use shelters are used only in 

the event of a hazard event. One advantage of single-use 

shelters is a potentially simplified design that may be readily 

accepted by the authority having local jurisdiction. These 

shelters typically have simplified electrical and mechanical 

systems because they are not required to provide normal daily 

accommodations for people. Single-use shelters are always 

ready for occupants and will not be cluttered with furnishings 

and storage items, which is a concern with multi-use shelters. 

Simplified, single-use shelters may have a lower total cost of 

construction than multi-use shelters. 

The cost of building a single-use shelter is much higher than 

the additional cost of including shelter protection in a multiuse room. Existing maintenance plans will usually consider 

multi-use rooms, but single-use shelters can be expected to 

require an additional annual maintenance cost.

m Multi-use shelters. The ability to use a shelter for more than 

one purpose often makes a multi-use standalone or internal 

shelter appealing to a shelter owner or operator. Multi-use 

shelters also allow immediate return on investment for owners/

operators; the shelter space is used for daily business when 

the shelter is not being used during a hazard event. Hospitals, 

assisted living facilities, and special needs centers would benefit 

from multi-use internal shelters, such as hardened intensive 

care units or surgical suites. Internal multi-use shelters in these 

types of facilities allow optimization of space while providing 

near-absolute protection with easy access for non-ambulatory 

persons. In new buildings being designed and constructed, 

recent FEMA-sponsored projects have indicated that the 

construction cost of hardening a small area or room in a 

building is 10 to 25 percent higher than the construction cost 

for a non-hardened version of the same area or room.

m Community shelters at neighborhoods and or public

facilities. Community shelters are intended to provide 

protection for the residents of neighborhoods and are 
design considerations 1-23

typically located at schools and other similar institutions; they 

are identified, categorized, and labeled by the American Red 

Cross (see ARC 4496). 

1.5 SITING

One of the most important elements in designing a shelter is its 

location or siting. In inspecting areas of existing buildings that are 

used as shelter areas, research has found that owners may overlook the safest area of a building, while the safety of a hallway or 

other shelter areas may be overestimated. Evaluating shelter areas 

in an existing building or determining the best areas for new ones 

is invaluable for saving lives when a disaster strikes.

The location of a shelter on a building site is an important part 

of the design process for shelters. The shelter location on the site 

and capacity should consider how many occupants work in the 

building, as well as how many non-occupants may take refuge in 

the nearest shelter available. At the site and building level, the 

shelter location analysis should include evaluation of potential 

CBRE effects. 

When deciding to build a shelter, a preliminary evaluation may 

be performed by a design professional or by a potential shelter 

owner, property owner, emergency manager, building maintenance person, or other interested party provided he or she has a 

basic knowledge of building sciences and can understand building 

design plans and specifications. Although the threat of damage

from CBRE events may be the predominant focus of the evaluation, additional threats may exist from tornado, hurricane, flood,

and seismic events; therefore, the evaluation should assess the

threat at the site. Prior to the design and construction of a shelter, 

a design professional should perform a more thorough assessment 

in order to confirm or, as necessary, modify the findings of a preliminary assessment. 

An entire building or a section of a building may be designated as 

a potential shelter area. To perform an assessment of an existing 
1-24 design considerations 

structure or a new structure to be used as a shelter, the building 

owner or designers may use the Building Vulnerability Assessment 

Checklist included in FEMA 426, Reference Manual to Mitigate Potential Terrorist Attacks Against Buildings; FEMA 452, A How-To Guide 

to Mitigate Potential Terrorist Attacks Against Buildings for the assessment of CBRE events; and FEMA 433, Using HAZUS-MH for Risk 

Assessment for the assessment of major natural hazards. 

If an existing building is selected for use as a shelter, the Building 

Vulnerability Assessment Checklist will help the user identify 

major vulnerabilities and/or the best shelter areas within the 

building to place the shelter. The checklist consists of questions 

pertaining to structural, nonstructural, and mechanical characteristics of the area being considered. The questions are designed to 

identify structural, nonstructural, and mechanical vulnerabilities 

to CBRE hazards based on typical failure mechanisms. Structural, 

nonstructural, and mechanical deficiencies may be remedied with 

retrofit designs; however, depending on the type and degree of deficiency, the evaluation may indicate that the existing structure is 

unsuitable for use as a shelter area. A detailed analysis should consider if a portion of a particular building can be used as shelter or 

whether that portion is structurally independent of the rest of the 

building. It should also determine if the location is easily accessible, contains the required square footage, and has good ingress 

and egress elements.

The shelter should be located such that all persons designated to 

take refuge may reach the shelter with minimal travel time. Shelters located at one end of a building or one end of a community, 

office complex, or school may be difficult for some users at a site 

to reach in a timely fashion. Routes to the shelter should be easily 

accessible and well marked. Exit routes from the shelter should 

be in a direction away from the threat. Hazard signs should be located following Crime Prevention Through Environmental Design 

(CPTED) principles of natural access control, natural surveillance, 

and territoriality and illustrated in Figure 1-4.
design considerations 1-25

m	 Natural access control (controls access). Guides people 

entering and leaving a space through the placement of 

entrances, exits, fences, landscaping, and lighting. Access 

control can decrease opportunities for terrorist activity by 

denying access to potential targets and creating a perception 

of risk for would-be terrorists.

m Natural surveillance (increases visibility). The placement 

of physical features, activities, and people in a way that 

maximizes visibility. A potential criminal is less likely to 

attempt an act of terrorism if he or she is at risk of being 

observed. At the same time, we are likely to feel safer when we 

can see and be seen.

Figure 1-4 

Example of shelter marking 

on building, floor plan, 

and exterior exits to rally 

points
1-26 design considerations 

m Territoriality (promotes a sense of ownership). The use of 

physical attributes that express ownership such as fences, 

signage, landscaping, lighting, pavement designs, etc. Defined 

property lines and clear distinctions between private and 

public spaces are examples of the application of territoriality. 

Territoriality can be seen in gateways into a community or 

neighborhood.

Shelters should also be located outside areas known to be floodprone, including areas within the 100-year floodplain. Shelters in 

flood-prone areas will be susceptible to damage from hydrostatic 

and hydrodynamic forces associated with rising flood waters. 

Damage may also be caused by debris floating in the water. Most 

importantly, flooding of occupied shelters may well result in injuries or deaths. Furthermore, shelters located in flood-prone areas, 

but properly elevated above the 100-year flood elevation, could 

become isolated if access routes were flooded. As a result, shelter 

occupants could be injured and no emergency services would be 

available.

Where possible, the shelter should be located away from large 

objects and multi-story buildings. Light towers, antennas, satellite dishes, and roof-mounted mechanical equipment may be 

toppled or become airborne during blast, hurricane, tornado, or 

earthquake events. Multi-story buildings adjacent to a shelter may 

be damaged or may fail structurally due to natural or manmade 

hazards. When these types of objects or structures fail, they may 

damage the shelter by collapsing onto it or impacting it. The 

impact forces associated with these objects are well outside the 

design parameters of any building code. 

There are several possible locations in a building or a house 

for a shelter. Perhaps the most convenient and safest is below 

ground level, in a basement. If the building or house does not 

have a basement, an in-ground shelter can be installed beneath 

a concrete slab-on-grade foundation or a concrete garage floor 

(typically would be used as a single-use shelter). Basement 
design considerations 1-27

shelters and in-ground shelters provide the greatest degree of 

protection against missiles and falling debris.

Another alternative shelter location is an interior room on the 

first floor of a building or house. Closets, bathrooms, and small 

storage rooms offer the advantage of having a function other 

than providing occasional storm protection. Typically, these 

rooms have only one door and no windows, which make them 

well-suited for conversion to a shelter. Bathrooms have the added 

advantage of a water supply and toilet.

Regardless of where in a building or house a shelter is built, the 

walls and ceiling of the shelter must be built so that they will 

protect the occupants from missiles and falling debris, and so 

that they will remain standing if the building or house is severely 

damaged by extreme winds. If sections of the building or house 

walls are used as shelter walls, those sections must be separated 

from the structure of the building or house. This is true regardless of whether interior or exterior walls of the building or house 

are used as shelter walls.

Typical floor plans of possible locations for shelters in a home are 

highlighted in yellow in Figures 1-5 and 1-6. These are not floor 

plans developed specifically for houses with shelters, but they show 

how shelters can be added without changes to the layout of rooms.
1-28 design considerations 

Figure 1-5 Examples of internal shelter locations in a residential slab on grade foundation

Source: FEMA 320

Figure 1-6 Examples of internal shelter locations in a residential basement

Source: FEMA 320
design considerations 1-29

Figures 1-7 through 1-9 show examples of internal shelter locations in a commercial basement, concourse, and underground 

parking garage; a retail/commercial multi-story building using a 

parking garage, conference rooms, data centers, stairwells, and elevator core areas; and a school/church facility, respectively.

Figure 1-7 Examples of internal shelter locations in a commercial building

Figure 1-8 Examples of internal shelter locations in a retail/commercial multi-story building using 

parking garage, conference rooms, data centers, stairwells, and elevator core areas
1-30 design considerations 

Currently, standalone shelters are relatively rare and most 

remaining shelters are remnants of the Cold War era that were designed for nuclear weapons protection as “fallout shelters.” These 

shelters were called “dedicated shelters” to make a clear differentiation from dual use shelters (normal facilities in the community 

that had enhanced radiation protection). Dedicated shelters were 

built with very high levels of protection and did not have peace 

time functional compromises. Siting of standalone shelters for 

nuclear protection has typically been underground, as tunnels, 

caves, or buried structures. The mass of the geological materials 

absorbed the blast energy and provided radiation shielding.

Many of the siting and design principles developed by the Office 

of Civil Defense in FEMA TR-29, Architect & Engineer Activities in 

Shelter Development; FEMA RR-7, Civil Defense Shelters A State of the Art 

Assessment 1986; and FEMA TR-87, Standards for Fallout Shelters are 

still applicable.

Figure 1-9 

Examples of internal shelter 

locations in a school/church 

facility 

-

-

-
design considerations 1-31

For a standalone shelter, many sites will be constrained or site limited for underground, and an aboveground structure may be the 

only feasible alternative. For these sites, the siting considerations 

include:

m Outside the floodplain

m Separation distance between buildings and structures to 

prevent progressive collapse or impact from collapsing 

elements

m Separation from major transportation features (road, rail)

m Access to redundant power and communications capabilities

1.6 occupancy duration, Toxicfree Area (TFA) Floor space, and 

ventilation Requirements

Occupancy duration (also known as button-up 

time) is the length of time that people will be 

in the shelter with the doors closed and in the 

protected environment. This period of time 

is determined by the building owner or local 

authorities and can range from several hours 

to several days. For off-site industrial accidents, 

the occupancy duration is usually less than 24 hours; occupancy 

durations longer than 24 hours are generally restricted to wartime. Occupancy duration stops when the doors to the shelter 

are opened. It influences the floor area requirements and the 

amount of consumable and waste storage. Generally, occupancy 

duration will not significantly affect the performance of the collective protection system.

a. Less Than 24 Hours. An occupancy duration of less than 24 hours 

does not require sleeping areas. The occupant load will generally 

be a net 1.86 m2/person (20 square feet/person), depending upon 

the classification of occupancy. The classification of occupancy, 

as stated in NFPA 101, may require a higher or lower occupant 

CBR Collective Protection Shelter Basics

m Occupancy Duration

m Toxic-free Area (TFA) Floor Space

m Ventilation Requirements
1-32 design considerations 

loading depending upon the building classification. The occupant 

loading will be coordinated with the authority having jurisdiction.

b. More Than 24 Hours. An occupancy duration greater than 24 

hours requires sleeping areas. The minimum floor area, with the 

use of single size beds, is approximately 5.6 m2/person (60 square 

feet/person). With the use of bunked beds, the minimum floor 

area is approximately 2.8 m2/person (30 square feet/person).

The total required TFA floor space is determined from the occupancy duration, the number of people sheltered, and the 

required floor area per person. Generally, large open areas such 

as common areas, multi-purpose areas, gymnasiums, etc., provide 

the most efficient floor area for protecting a large number of personnel. The TFA envelope should include bathroom facilities and, 

if possible, kitchen facilities.

Although the planned response to CBR events may be to temporarily deactivate the ventilation systems, both single- and 

multi-use shelters must include ventilation systems capable of 

providing the minimum number of air changes required by the 

building code for the shelter’s occupancy classification. This will 

provide a flushing capability once the CBR hazard has passed and 

facilitate use of the shelter for non-CBR events. For single-use 

shelters, 15 cubic feet per person per minute is the minimum air 

exchange recommended; this recommendation is based on guidance outlined in the International Mechanical Code (IMC). For 

multi-use shelters, the design of mechanical ventilation systems is 

recommended to accommodate the air exchange requirements 

for the occupancy classification of the normal use of the shelter 

area. Although the ventilation system may be overwhelmed in a 

rare event when the area is used as a shelter, air exchange will 

still take place. The designer should still confirm with the local 

building official that the ventilation system may be designed for 

the normal-use occupancy. In the event the community where the 

shelter is to be located has not adopted a model building and/or 

mechanical code, the requirements of the most recent edition of 

the International Building Code (IBC) are recommended.
design considerations 1-33

1.7 HUMAN FACTORS CRITERIA

Human factors criteria for the natural and manmade hazard shelters build on existing guidance provided in this chapter and in 

FEMA 320 and 361. Although existing documents do not address 

all the human factors involved in the design of CBRE shelters, 

they provide the basis for the criteria summarized in this chapter. 

These criteria are detailed in the following sections.

1.7.1 Square Footage/Occupancy Requirements 

The duration of occupancy of a shelter will vary, depending on 

the intended event for which the shelter has been designed. Occupancy duration is an important factor that influences many 

aspects of the design process. 

The recommended minimums are 5 square feet per person for 

tornado shelters and 10 square feet per person for hurricane 

shelters. The shelter designer should be aware of the occupancy 

requirements of the building code governing the construction of 

the shelter. The occupancy loads in the building codes have historically been developed for life safety considerations. Most building 

codes will require the maximum occupancy of the shelter area 

to be clearly posted. Multi-use occupancy classifications are provided in the IBC; NFPA 101, Life Safety Code; NFPA 5000, Building 

Construction and Safety Code; and state and local building codes. 

Conflicts may arise between the code-specified occupancy classifications for normal use and the occupancy needed for sheltering. 

For example, according to the IBC and NFPA 101 and 5000, the 

occupancy classification for educational use is 20 square feet per 

person; however, the recommendation for a tornado shelter is 5 

square feet per person. Without proper signage and posted occupancy requirements, using an area in a school as a shelter can 

create a potential conflict regarding the allowed number of persons in the shelter. If both the normal maximum occupancy and 

the shelter maximum occupancy are posted, and the shelter occupancy is not based on a minimum less than the recommended 

5 square feet per person, the shelter design should be acceptable 

to the building official. The IBC, NFPA 101 and 5000, and the 
1-34 design considerations 

model building codes all have provisions that allow occupancies 

as concentrated as 5 square feet per person. The American Society of Heating, Refrigeration, and Air-Conditioning Engineers 

(ASHRAE) recommends that a minimum head room of 6.5 feet 

and a minimum of 65 cubic feet of net volume be provided per 

shelter occupant. Net volume shall be determined using the net 

area calculated for the space.

ASHRAE Ventilation Standard 62-1981, Ventilation for Smoking-Permitted Areas defines minimum outdoor air supply rates for various 

types of occupancy. These rates have been arrived at through a 

consensus of experts working in the field. A minimum rate of 5 

cfm per person for sedentary activity and normal diet holds the 

carbon dioxide (CO2) level in a space at 0.25 percent under steady 

state conditions. Although normal healthy people tolerate 0.5 

percent CO2 without undesirable symptoms and nuclear submarines sometimes operate with 1 percent CO2

 in the atmosphere, 

a level of 0.25 percent provides a safety factor for increased 

activity, unusual occupancy load, or reduced ventilation. The 

ASHRAE Handbook 1982 Applications Environmental Control for 

Survival states that carbon dioxide concentration should not exceed 3 percent by volume and preferably should be maintained 

below 0.5 percent. For a sedentary man, 3 cfm per person of 

fresh air would maintain a CO2 concentration of 0.5 percent.

1.7.1.1	Tornado or Short-term Shelter Square Footage Recommendations. Historical data indicate that tornado shelters will 

typically have a maximum occupancy time of 2 hours. Because the 

occupancy time is so short, many items that are needed for the 

comfort of occupants for longer durations (in hurricane shelters) 

are not recommended for a tornado shelter. FEMA 361, Section 

8.2 recommends a minimum of 5 square feet per person for tornado shelters. However, other circumstances and human factors 

may require the shelter to accommodate persons who require 

more than 5 square feet. Square footage recommendations for 

persons with special needs are presented below; these recommendations are the same as those provided in the FEMA 1999 National 

Performance Criteria for Tornado Shelters:
design considerations 1-35

m 5 square feet per person adults standing 

m 6 square feet per person adults seated 

m 5 square feet per person children (under the age of 10) 

m 10 square feet per person wheelchair users 

m 30 square feet per person bedridden persons 

1.7.1.2 Hurricane or Long-term Shelter Square Footage Recommendations. Historical data indicate that hurricane shelters will 

typically have a maximum occupancy time of 36 hours. For this 

reason, the occupants of a hurricane shelter need more space and 

comforts than the occupants of a tornado shelter. FEMA 361, Section 8.2 recommends a minimum of 10 square feet per person for 

hurricane shelters (for a hurricane event only; an event expected 

to last less than 36 hours). The American Red Cross 4496 publication recommends the following minimum floor areas (Note: the 

ARC square footage criteria are based on long-term use of the 

shelter [i.e., use of the shelter both as a refuge area during the 

event and as a recovery center after the event]): 

m 20 square feet per person for a short-term stay (i.e., a few days) 

m 40 square feet per person for a long-term stay (i.e., days to 

weeks) 

Again, the designer should be aware that there can be conflicts 

between the occupancy rating for the intended normal use of 

the shelter and the occupancy required for sheltering. This occupancy conflict can directly affect exit (egress) requirements for 

the shelter. 

1.7.2 Distance/Travel Time and Accessibility 

The shelter designer should consider the time required for all occupants of a building or facility to reach the shelter. The National 

Weather Service (NWS) has made great strides in predicting tornadoes and hurricanes and providing warnings that allow time to 

seek shelter; it has now expanded the service to include all hazards. 
1-36 design considerations 

As part of the NIMS, for tornadoes, the time span is often short 

between the NWS warning and the onset of the tornado. Figure 

1-10 shows a sample NWS current watches, warnings, statements, 

and advisories summary. This manual recommends that a tornado 

shelter be designed and located in such a way that the following access criteria are met: all potential users of the shelter should be able 

to reach it within 5 minutes, and the shelter doors should be secured 

within 10 minutes. For hurricane shelters, these restrictions do not 

apply, because warnings are issued much earlier, allowing more 

time for preparation. A CBRE event may have warning such as the 

Irish Republican Army gave to London police and residents, or no 

warning as happened with the events of 9/11, and anthrax and sarin 

releases in October 2001 and the Tokyo subway, respectively.

Figure 1-10 

National Weather Service 

forecast and warnings

Source: NWS

Travel time may be especially important when shelter users have 

disabilities that impair their mobility. Those with special needs 

may require assistance from others to reach the shelter; wheelchair users may require a particular route that accommodates the 

wheelchair. The designer must consider these factors in order to 
design considerations 1-37

provide the shortest possible access time and most accessible route 

for all potential shelter occupants. 

Access is an important element of shelter design. If obstructions 

exist along the travel route, or if the shelter is cluttered with nonessential equipment and storage items, access to the shelter will 

be impeded. It is essential that the path remain unencumbered 

to allow orderly access to the shelter. Hindering access in any way 

can lead to chaos and panic. For example, at a community shelter 

built to serve a residential neighborhood, parking at the shelter 

site may complicate access to the shelter; at a non-residential 

shelter, such as at a manufacturing plant, mechanical equipment 

can impede access. 

Unstable or poorly secured building elements could potentially 

block access if a collapse occurs that creates debris piles along 

the access route or at entrances. A likely scenario is an overhead 

canopy or large overhang that lacks the capacity to withstand 

blast effects collapses over the entranceway. The inclusion of 

these elements should be seriously considered when designing access points in shelters.

1.7.3 Americans with Disabilities Act (ADA)

The needs of persons with disabilities requiring shelter space 

should be considered. The appropriate access for persons with 

disabilities must be provided in accordance with all Federal, state, 

and local ADA requirements and ordinances. If the minimum 

requirements dictate only one ADA-compliant access point for 

the shelter, the design professional should consider providing 

a second ADA-compliant access point for use in the event that 

the primary access point is blocked or inoperable. Additional 

guidance for compliance with the ADA can be found in many privately produced publications. 

The design professional can ensure that the operations plan 

developed for the shelter adheres to requirements of the ADA 

by assisting the owner/operator of the shelter in the development of the plan. All shelters should be managed with an 
1-38 design considerations 

operations and maintenance plan. Developing a sound operations plan is extremely important if compliance with ADA at the 

shelter site requires the use of lifts, elevators, ramps, or other 

considerations for shelters that are not directly accessible to 

non-ambulatory persons.

1.7.4 Special Needs

The use of the shelter also needs to be considered in the design.

Occupancy classifications, life safety code, and ADA requirements 

may dictate the design of such elements as door opening sizes 

and number of doors, but use of the shelter by hospitals, nursing 

homes, assisted living facilities, and other special needs groups 

may affect access requirements to the shelter. For example, basic 

requirements are outlined in the IBC and NFPA 101 and 5000 

regarding the provision of uninterruptible power supplies for 

life support equipment (e.g., oxygen) for patients in hospitals 

and other health care facilities. NFPA 99, Standard for Healthcare 

Facilities, specifies details on subjects such as the type, class, and 

duration of power supplies necessary for critical life support 

equipment. In addition, it also details the design, arrangement, 

and configuration of medical gas piping systems, alarms, and networks. 

In addition, strict requirements concerning issues such as egress, 

emergency lighting, and detection-alarm-communication systems 

are presented in Chapter 10 of the IBC and in NFPA 101, 2006 

Edition, Chapters 18 and 19, for health care occupancies. The 

egress requirements for travel distances, door widths, and locking 

devices on doors for health care occupancies are more restrictive 

than those for an assembly occupancy classification in non-health 

care facilities based on the model building codes for non-health 

care facilities. Additional requirements also exist for health care 

facilities that address automatic fire doors, maximum allowable 

room sizes, and maximum allowable distances to egress points. 

The combination of all these requirements could lead to the construction of multiple small shelters in a health care facility rather 

than one large shelter. 
design considerations 1-39

1.8 Other Design considerations

Emergency lighting and power, as well as a backup power source, 

need to be included in the design of multi-use shelters. Route 

marking and wayfinding, and signage also should be included.

1.8.1 Lighting 

For the regular (i.e., non-shelter) use of multi-use shelters, 

lighting, including emergency lighting for assembly occupancies, 

is required by all model building codes. Emergency lighting is 

recommended for community shelters. A backup power source 

for lighting is essential during a disaster because the main power 

source is often disrupted. A battery-powered system is 

recommended as the backup source because it can be located, 

and fully protected, within the shelter. Flashlights stored in cabinets are useful as secondary lighting provisions, but should not be 

used as the primary backup lighting system. 

A reliable lighting system will help calm shelter occupants during 

a disaster. Failing to provide proper illumination in a shelter may 

make it difficult for shelter owners/operators to minimize the 

agitation and stress of the shelter occupants during the event. If 

the backup power supply for the lighting system is not contained 

within the shelter, it should be protected with a structure designed 

to the same criteria as the shelter itself. Natural lighting provided 

by windows and doors is often a local design requirement, but is 

not required by the IBC for assembly occupancies. The 2003 edition of the IBC and the 2006 edition of NFPA 5000 has additional 

guidance on egress, lighting, and markings. 

1.8.2 Emergency Power 

Shelters will have different emergency (backup) power needs 

based upon the length of time that people will stay in the shelters 

(i.e., shorter duration for tornadoes and longer duration for hurricanes). In addition to the essential requirements that must be 

provided in the design of the shelter, comfort and convenience 

should be addressed. 
1-40 design considerations 

For tornado shelters, the most critical use of emergency power is 

for lighting. Emergency power may also be required in order to 

meet the ventilation requirements described in Chapter 3 and 

Section 1.7.1. The user of the shelter should set this requirement 

for special needs facilities, but most tornado shelters would not 

require additional emergency power. 

For hurricane shelters, emergency power may be required for 

both lighting and ventilation. This is particularly important for 

shelters in hospitals and other special needs facilities. Therefore, 

a backup generator is recommended. Any generator relied on for 

emergency power should be protected with an enclosure designed 

to the same criteria as the shelter.

As illustrated in the previous sections, the manmade hazards 

shelter design criteria require an adjustment to the traditional 

design process for natural hazard shelters. The shelter location, 

operation, and life-cycle costs are now significantly coupled to the 

community, first responders, and government plans and procedures for mass casualty response and recovery; Federal and local 

laws for criminal investigation; and the unique site and building 

design parameters and level of protection that is desired.

1.8.3 Route Marking and Wayfinding 

Route marking or wayfinding in an emergency situation such as 

total darkness has historically relied on fire exit lighting. A new 

technology that is being adopted by many cities is photoluminescent exit path marking. These photoluminescent self-adhesive 

signs and tapes are very visible during the day and will glow for up 

to 8 hours after the light source is removed. These signs have durable, permanent, and renewable fluorescence. Figure 1-11 shows 

sample signs.
design considerations 1-41

Figure 1-11 Photoluminescent signs, stair treads, and route marking
1-42 design considerations 

1.8.4 Signage

The signs should be illuminated, luminescent, and obvious. Key 

elements of signage include the following.

1.8.4.1	Community and Parking Signage. It is very important that 

shelter occupants can reach the shelter quickly and without chaos. 

Parking is often a problem at community shelters; therefore, a 

Community Shelter Operations Plan should instruct occupants to 

proceed to a shelter on foot if time permits. Main pathways should 

be determined and laid out for the community. Pathways should 

be marked to direct users to the shelter. Finally, the exterior of the 

shelter should have a sign that clearly identifies the building as a 

shelter. 

1.8.4.2	Signage at Schools and Places of Work. Signage for shelters at schools and places of work should be clearly posted and 

should direct occupants through the building or from building 

to building. If the shelter is in a government-funded or publicfunded facility, a placard should be placed on the outside of the 

building designating it an emergency shelter (see Figure 1-12). It 

is recommended that signage be posted on the outside of all other 

Reference Standard 6-1

Photoluminescent exit path markings as required by Local Law 26 of 2004, New York City Building 

Code § 27-383(b)

This standard is intended to provide minimum requirements for photoluminescent exit path markings 

that will aid in evacuation from buildings in the event of failure of both the power and back-up 

power to the lighting and illuminated exit signs. Photoluminescent material is charged by exposure 

to light and will emit luminance after the activating light source is unavailable. The markings 

covered by this standard are not designed to provide enough light to illuminate a dark egress 

path, but rather will provide luminescent signs and outlines of the egress path, stairs, handrails, 

and obstacles, so that occupants can discern these egress path elements in dark conditions. The 

markings are generally required to be located at a low location in case of smoke and to be readily 

seen, such as in a crowd situation. They are in addition to, and not as a substitute for, any other 

signage required under the Building Code, such as electrically illuminated exit signs with electrical 

back-up power required under § 27-383(a).
design considerations 1-43

types of shelters as well. It is important to note, however, that once 

a public building has been identified as a shelter, people who live 

or work in the area around the shelter will expect the shelter to 

be open during an event. Shelter owners should be aware of this 

and make it clear that the times when a shelter will be open may 

be limited. For example, a shelter in an elementary school or commercial building may not be accessible at night.

Figure 1-12 Shelter signage
1-44 design considerations 

1.9 EVACUATION CONSIDERATIONS

When designing a shelter, evacuation is one of the most important aspects to save lives. During the attack of the World Trade 

Center, good and well-marked egress was critical for thousands of 

people to evacuate the buildings. The same concept is applicable 

to shelters. Good ingress and egress, along with robustness and redundancy of the structural system, is critical for a sound design. 

The matter of high-rise evacuation has become vital since September 11, 2001, as a result of the fatalities of almost 3,000 

building occupants and emergency personnel. Life safety is provided to building 

occupants by either giving them the opportunity to evacuate to a safer place or be 

protected in place. 

The National Institute of Standards and 

Technology (NIST) Final Report of the National Construction Safety Team on the Collapses 

of the World Trade Center Towers conducted 

analysis of the life safety systems and emergency response to validate and expand the 

state of the practice for high-rise buildings. 

The NIST study was focused on the collapse 

mechanisms and life safety systems performance. 

As a result of the collapse of the World Trade Center towers, 

NIST identified three major scenarios that are not considered adequately in current design practice:

m Frequent but low severity events (for design of sprinkler 

system)

m Moderate but less frequent events (for design of 

compartmentation)

m A maximum credible fire (for design of passive fire protection 

on the structure)

Every building should have an emergency 

evacuation and shelter-in-place plan that 

is coordinated with the local community 

emergency manager. Building stakeholders 

and tenants should develop the plan with 

the objective to save lives and property, and 

to recover and restore the business should 

an event occur. The NFPA 1600 Standard 

on Disaster/Emergency Management and 

Business Continuity Programs publication 

provides a framework and recommendations 

for developing a plan. The building owner, 

property manager, and tenants should work 

with the local community to develop an 

evacuation versus shelter-in-place options 

matrix as shown in Table 1-6. 
design considerations 1-45

Table 1-6: Evacuation Versus Shelter-in-place Options Matrix 

Attack Agent Timeframe and Protection 

Objective Occupant/Personnel Action

Chemical – Exterior Release Immediate - shelter in safe 

room, minimize duration and 

concentration exposure

Use portable air filtration, wait 

for first responder extraction

Chemical – Interior Release Immediate - don PPE and 

evacuate, minimize duration 

and concentration exposure

Move perpendicular to plume 

direction, seek decontamination 

and medical treatment

Biological – Exterior Release Immediate - shelter in safe 

room, do not touch agents, use 

time to advantage to identify 

safe evacuation route

Use portable air filtration, wait 

for first responder extraction, 

seek decontamination and 

medical treatment

Biological – Interior Release Immediate - don PPE and 

evacuate, minimize duration 

and concentration exposure

Seek decontamination and 

medical treatment

Radiological/Nuclear 

– Exterior Release

Immediate - shelter in safe 

room, minimize duration and 

concentration exposure

Use portable air filtration, wait 

for first responder extraction

Radiological/Nuclear 

– Interior Release

Immediate - don PPE and 

evacuate, minimize duration 

and concentration exposure

Seek decontamination and 

medical treatment

Explosive Blast - Exterior Immediate - shelter in safe room Use portable air filtration, wait 

for first responder extraction

Explosive Blast - Interior Immediate - don PPE and 

evacuate

Seek medical treatment
1-46 design considerations 

Three methods are followed for the evacuation of buildings. One 

method consists of evacuating all occupants simultaneously. 

Alternatively, occupants may be evacuated in phases, where the 

floor levels closest to the event are evacuated first and then other 

floor levels are evacuated on an as needed basis. Phased evacuation is instituted to permit people on the floor levels closest to the 

threatening hazard to enter the stairway unobstructed by queues 

formed by people from all other floors also being in the stairway. 

Those who are below the emergency usually are encouraged to 

stay in place until the endangered people from above are already 

below this floor level.

The concept of occupant relocation to other floors is usually the 

best course of action for many types of building emergencies. This 

method normally involves movement of occupants, from the fire 

floor, the floor above, and floor below to a lower level until the 

danger passes.

Evacuation involves providing people with the means to exit the 

building. The egress system involves the following considerations:

Capacity. A sufficient number of exits of adequate width to accommodate the building population need to be provided to allow 

occupants to evacuate safely.

Access. Occupants need to be able to access an exit from wherever 

the fire is, and in sufficient time prior to the onset of untenable 

conditions. Alternative exits should be remotely located so that all 

exits are not simultaneously blocked by a single incident.

Exit Design. Exits need to be separated from all other portions of 

the building in order to provide a protected way of travel to the 

exit discharge. This involves designing to preclude fire and smoke 

from entering the exit and will usually involve structural stability.

In general, the means of egress system is designed so that occupants travel from the office space along access paths such as 

corridors or aisles until they reach the exit or a safer place. An 
design considerations 1-47

exit is commonly defined as a protected path of travel to the exit 

discharge (NFPA 101, 2006). The stairways in a high-rise building 

commonly meet the definition of an exit. In general, the exit is 

intended to provide a continuous, unobstructed path to the exterior or to another area that is considered safe. Most codes require 

that exits discharge directly to the outside. Some codes, such as 

NFPA 101, permit up to half of the exits to discharge within the 

building, given that certain provisions are met.

There is no universally accepted standard on emergency evacuation. Design considerations for high-rise buildings relative to 

these two options involve several aspects, including design of 

means of egress, the structure, and active fire protection systems 

(e.g., detection and alarm, suppression, and smoke management). Many local jurisdictions, through their fire department 

public education programs, have developed comprehensive and 

successful evacuation planning models but, unless they are locally 

adopted, there is no legal mandate to exercise the plans. Seattle, 

Phoenix, Houston, and Portland, Oregon, are among the cities 

that have developed comprehensive programs.

The NIST life safety, egress, and emergency response findings 

provide valuable lessons learned for future shelter evacuation 

design. Currently, building fire protection is based on a four-level 

hierarchical strategy comprising alarm and detection, suppression 

(sprinklers and firefighting), compartmentation, and passive protection of the structure. 

m Manual stations and detectors are typically used to activate 

fire alarms and notify building occupants and emergency 

services.

m Sprinklers are designed to control small and medium fires 

and to prevent fire spread beyond the typical water supply 

design area of about 1,500 square feet.

m Compartmentation mitigates the horizontal spread of more 

severe but less frequent fires and typically requires fire-rated 
1-48 design considerations 

partitions for areas of about 12,000 square feet. Active 

firefighting measures also cover up to about 5,000 square feet 

to 7,500 square feet.

m Passive protection of the structure seeks to ensure that a 

maximum credible fire scenario, with sprinklers compromised 

or overwhelmed and no active firefighting, results in burnout, 

not overall building collapse. The intent of building codes 

is also for the building to withstand local structural collapse 

until occupants can escape and the fire service can complete 

search and rescue operations.

NIST recommends that building evacuation should be improved 

to include system designs that facilitate safe and rapid egress, 

methods for ensuring clear and timely emergency communications to occupants, better occupant preparedness for evacuation 

during emergencies, and incorporation of appropriate egress 

technologies. When designing good evacuation systems and routes 

of ingress and egress, designers should take into account the following considerations: 

m As stated above, improved building evacuation, including 

system designs that facilitate safe and rapid egress, methods 

for ensuring clear and timely emergency communications 

to occupants, better occupant preparedness for evacuation 

during emergencies, and incorporation of appropriate egress 

technologies. Primary and secondary evacuation routes and 

exits should be designated and clearly marked and well lit. 

Signs should be posted.

m Improved emergency response, including better access to the 

buildings and better operations, emergency communications, 

and command and control in large-scale emergencies.

m Emergency lighting should be installed in case a power outage 

occurs during an evacuation.
design considerations 1-49

Recommendation 18. NIST recommends that egress systems should be designed: (1) to 

maximize remoteness of egress components (i.e., stairs, elevators, exits) without negatively 

impacting the average travel distance; (2) to maintain their functional integrity and survivability 

under foreseeable building-specific or large-scale emergencies; and (3) with consistent layouts, 

standard signage, and guidance so that systems become intuitive and obvious to building 

occupants during evacuations.

Recommendation 16. NIST recommends that public agencies, non-profit organizations 

concerned with building and fire safety, and building owners and managers should develop and 

carry out public education campaigns, jointly and on a nationwide scale, to improve building 

occupants’ preparedness for evacuation in case of building emergencies. 16

Recommendation 17. NIST recommends that tall buildings should be designed to 

accommodate timely full building evacuation of occupants due to building-specific or large-scale 

emergencies such as widespread power outages, major earthquakes, tornadoes, hurricanes 

without sufficient advanced warning, fires, accidental explosions, and terrorist attacks. Building 

size, population, function, and iconic status should be taken into account in designing the egress 

system. Stairwell and exit capacity should be adequate to accommodate counterflow due to 

emergency access by responders.

17

18

Recommendation 19. NIST recommends that building owners, managers, and emergency 

responders develop a joint plan and take steps to ensure that accurate emergency information 

is communicated in a timely manner to enhance the situational awareness of building occupants 

and emergency responders affected by an event. This should be accomplished through better 

coordination of information among different emergency responder groups, efficient sharing of 

that information among building occupants and emergency responders, more robust design of 

emergency public address systems, improved emergency responder communication systems, and 

use of the Emergency Broadcast System (now known as the Integrated Public Alert and Warning 

System) and Community Emergency Alert Networks.

19

Recommendation 21. NIST recommends the installation of fire-protected and structurally 

hardened elevators to improve emergency response activities in tall buildings by providing timely 

emergency access to responders and allowing evacuation of mobility-impaired building occupants. 

Such elevators should be installed for exclusive use by emergency responders during emergencies. In 

tall buildings, consideration also should be given to installing such elevators for use by all occupants.

21
1-50 design considerations 

m Evacuation routes and emergency exits should be:

m wide enough to accommodate the number of evacuating 

personnel.

m clear and unobstructed at all times.

m unlikely to expose evacuating personnel to additional 

hazards.

m Evacuation routes should be evaluated by a professional.

It is also important to designate assembly areas 

and a means of obtaining an accurate account of 

personnel after a site evacuation. Designate areas 

where personnel should gather after evacuating 

(see Section 1.10). A head count should be taken 

after the evacuation. The names and last known 

locations of personnel not accounted for should 

be determined and given to the Emergency Operations Coordinator (EOC). (Confusion in the 

assembly areas can lead to unnecessary and dangerous search and rescue operations.) A method 

for accounting for non-employees (e.g., suppliers 

and customers) should also be established.

In addition, procedures should be established for further evacuation in case the incident expands. This may consist of sending 

employees home by normal means or providing them with transportation to an off-site location.

1.10 Key Operations Zones

Key operations zones refer to the shelter site surrounding areas 

and entry and exit control points that need to be taken into consideration when designing a shelter. 

For catastrophic incidents depicted in the planning scenarios 

related to the National Response Plan - Catastrophic Incident 

Supplement (NRP-CIS), decontamination involves several 

The 2006 editions of NFPA 101, 

Life Safety Code and NFPA 5000, 

Building Construction and Safety 

Code addressed the issue of counterflow between first responders and 

descending occupants. The new 

provisions mandate a minimum stair 

width of 56 inches (1,420 mm) when 

a stair is designed to handle an 

aggregate or accumulated of 2,000 

or more occupants. Previous criteria 

required 44 inches (1,120 mm) 

minimum.
design considerations 1-51

related and sequential activities. Chief among these are (1) 

immediate (or gross) decontamination of persons exposed 

to toxic/hazardous substances; (2) continual decontamination of first responders so that they can perform their essential 

functions; (3) decontamination of animals in service to first 

responders; (4) continual decontamination of response 

equipment and vehicles; (5) secondary, or definitive, decontamination of victims at medical treatment facilities to enable 

medical treatment and protect the facility environment; (6) decontamination of facilities (public infrastructure, business and 

residential structures); and (7) environmental (outdoor) decontamination supporting recovery and remediation.

1.10.1 Containment Zones

There are three zones of containment after an event:

m Hot Zone (the area where the agent or contamination is in 

high concentration and high exposure, typically an ellipse or 

cone extending downwind from the release)

m Warm Zone (the area where the agent or contamination is in 

low concentration or minimal exposure, typically a half circle 

in the above wind direction)

m Cold Zone (those areas outside of the Hot and Warm zones 

that have not been exposed to the agent or contamination)

The three zones and staging areas are shown in Figure 1-13.
1-52 design considerations 

Figure 1-13 

Operations Zones, Casualty 

Collection Point (CCP), and 

Safe Refuge Area (SRA) 
design considerations 1-53

Ladder Pipe Decontamination System (LDS)

Advantages

m Rapid setup time

m Provides large capacity high volume low 

pressure shower

m Rapid hands-free mass decontamination

Disadvantages

m No privacy

m Increased chance of hypothermia from 

exposure to elements

Composed of:

m Ladder pipe/truck

m 2 engines

m Hand-held hose lines

Setup:

m Engines placed approximately 20 feet apart

m 2 1/2-inch fog nozzles set at wide fog pattern 

attached to pump discharges

m Truck with fog nozzle placed on ladder pipe to 

provide downward fog pattern

Firefighters (FFs) can be positioned at either 

or both ends of the shower area to apply 

additional decontamination wash

Shelter occupants should not leave the shelter until rescue personnel arrive to escort occupants to the Cold Zone. The building 

occupants must go through several staging areas to ensure that 

any CBR contamination is not spread across a larger geographical 

area. There are two processes currently used to evacuate an area; 

the Ladder Pipe Decontamination System (LDS, see Figure 1-14) 

and the Emergency Decontamination Corridor System (EDCS, see 

Figure 1-15).

Figure 1-14 NRP-CIS Ladder Pipe Decontamination System (LDS)

Source: NRP-CIS
1-54 design considerations 

Figure 1-15

NRP-CIS Emergency Decontamination Corridor System (EDCS)

Source: NRP-CIS

Emergency Decontamination Corridor 

System (EDCS)

Advantages

m Privacy for victims

m Separate male/female corridors

m Shower area can be heated using 

portable heaters

Disadvantages

m Slower setup time than LDS

m Casualty processing slower

m Requires more manpower to set up

Composed of:

m 2 engines

m Salvage covers

Setup:

m 2 engines placed approximately 

20 feet apart

m 3 ladders placed and secured to 

top of engines

m 4th ladder centered atop the other 

three ladders and secured

m 2 nozzles secured to the 4th 

ladder hanging down into the 

shower area

m Salvage covers draped over 

ladders to create corridors
design considerations 1-55

1.10.2 Staging Areas and Designated Entry and 

Exit Access Control Points

To control the potential spread of a CBRE agent and ensure 

the safety of the victims and first responders, the Incident Commander (IC) will establish several staging areas and designated 

entry and exit access control points for the three zones.

m Patient Staging Area (PSA). The PSA is located in the Cold 

Zone and is the transfer point for victims that have been 

stabilized for transport to higher care medical facilities or for 

fatalities to be transported to morgue facilities (see Figures 

1-16 and 1-17). The PSA area must be large enough to 

accommodate helicopter operations and a large number of 

ambulances.

Figure 1-16 Patient staging area and remains recovery

Source: Arlington County After-Action Report
1-56 design considerations 

m Contamination Control Area (CCA). The CCA (see Figure 

1-18) is located on the boundary of the Cold Zone and 

Warm Zone and used by the rescue and decontamination 

personnel to enter and exit the Warm Zone. There are 

several processing stations, a resupply and refurbishment 

area, and a contaminated waste storage area. Mass casualty 

decontamination occurs in the Warm Zone. 

Figure 1-17 Example of Pentagon staging and recovery operations

Source: Arlington County After-Action Report
design considerations 1-57

m Safe Refuge Area (SRA). The SRA is located in the Warm 

Zone and used to assemble survivors and witnesses that are 

not injured and will require minimal medical attention and 

decontamination. Law enforcement and FBI agents can 

conduct interviews and gather evidence at the SRA. 

Evidence collection can occur in any of the three zones as shown 

in Figure 1-19.

Figure 1-18 

Contamination Control Area 

(CCA)
1-58 design considerations 

Figure 1-19 

Site and evidence 

collection on the site

Source: Arlington County 

After-Action Report

Designated entry/exit access control points will be between each 

of the zones. The entry/exit access control point between the Hot 

and Warm Zones is used by the first responders in PPE to enter/

exit the Hot Zone and extract victims and casualties (both contaminated and uncontaminated) to the Warm Zone. The patient 

entry/exit access control point between the Warm and Cold Zones 

is used as a one-way exit out to move decontaminated uninjured 

personnel and medically stabilized casualties. The first responders 

entry/exit between the Cold and Warm Zones is used by the first 

responders, rapid visualization and structural evaluation team, 

and debris operations personnel to enter and exit the site, and includes equipment shown in Figure 1-20.
design considerations 1-59

Between the Hot Zone entry access control point and the patient 

exit control point, there will be a casualty collection point. The 

CCP (Figure 1-13) is located in the Warm Zone and will typically 

have three processing stations:

m Station 1 – Litter decontamination and non-ambulatory 

delayed treatment patients

m Station 2 – Litter decontamination and immediate treatment 

patients

m Station 3 – Ambulatory decontamination, minimal treatment 

patients, and ambulatory delayed treatment patients

Figure 1-20 Rescue team coordination prior to entering a site

Source: Arlington County After-Action Report

Structural design criteria 2

Structural design criteria 2-

2.1 OVERVIEW

T his chapter discusses explosive threat parameters and 

measures needed to protect shelters from blast effects. 

Structural systems and building envelope elements for 

new and existing shelters are analyzed; shelters and FEMA model 

building types are discussed; and protective design measures for 

the defined building types are provided, as are design guidance 

and retrofit issues. The purpose of this chapter is to offer comprehensive information on how to improve the resistance of shelters 

when exposed to blast events.

2.2 Explosive Threat Parameters

A detonation involves supersonic combustion of an explosive material and the formation of a shock wave. The three parameters 

that primarily determine the characteristics and intensity of blast 

loading are the weight of explosives, the type of the explosives, 

and the distance from the point of detonation to the protected 

building. These three parameters will primarily determine the 

characteristics and intensity of the blast loading. The distance of 

the protected building from the point of explosive detonation 

is commonly referred to as the stand-off distance. The critical 

locations for detonation are taken to be at the closest point that 

a vehicle can approach, assuming that all security measures are 

in place. Typically, this would be a vehicle parked along the curb 

directly outside the facility, or at the vehicle access control gate 

where inspection takes place. Similarly, a critical location may be 

the closest point that a hand carried device can be deposited.

There is also no way to effectively know the size of the explosive 

threat. Different types of explosive materials are classified as High 

Energy and Low Energy and these different classifications greatly 

influence the damage potential of the detonation. High Energy 

explosives, which efficiently convert the material’s chemical 
2- Structural design criteria

energy into blast pressure, represent less than 1 percent of all explosive detonations reported by the FBI Bomb Data Center. The 

vast majority of incidents involve Low Energy devices in which a 

significant portion of the explosive material is consumed by deflagration, which is a process of subsonic combustion that usually 

propagates through thermal conductivity and is typically less destructive than a detonation. In these cases, a large portion of the 

material’s chemical energy is dissipated as thermal energy, which 

may cause fires or thermal radiation damage.

For a specific type and weight of explosive material, the intensity of blast loading will depend on the distance and orientation 

of the blast waves relative to the protected space. A shock wave 

is characterized by a nearly instantaneous rise in pressure that 

decays exponentially within a matter of milliseconds, which is followed by a longer term but lower intensity negative phase. The 

initial magnitude of pressure is termed the peak pressure and the 

area under a graph of pressure plotted as a function of time, also 

known as the airblast pressure time history, is termed the impulse 

(see Figure 2-1). Therefore, the impulse associated with the shock 

wave considers both the pressure intensity and the pulse duration. 

As the front of the shock-wave propagates away from the source 

of the detonation at supersonic speed, it expands into increasingly larger volumes of air; the peak incident pressure at the shock 

front decreases and the duration of the pressure pulse increases. 

The magnitude of the peak pressures and impulses are reduced 

with distance from the source and the resulting patterns of blast 

loads appear to be concentric rings of diminishing intensity. This 

effect is analogous to the circular ripples that are created when 

an object is dropped in a pool of water. The shock front first impinges on the leading surfaces of a building located within its path 

and is reflected and diffracted, creating focus and shadow zones 

on the building envelope. These patterns of blast load intensity 

are complicated as the waves engulf the entire building. The pressures that load the roof, sides, and rear of the building are termed 

incident pressures, while the pressures that load the building 

envelope directly opposite the explosion are termed reflected 

pressures. Both the intensity of peak pressure and the impulse 
Structural design criteria 2-

Figure 2-1

Airblast pressure time 

history

affect the hazard potential of the blast loading. A detailed analysis 

is required to determine the magnitude of pressure and impulse 

that may load each surface relative to the origin of the detonation.

The thresholds of different types of injuries associated with 

damage to wall fragments and/or glazing are depicted in Figure 

2-2. This range to effects chart shows a generic interaction between 

the weight of the explosive threat and its distance to an occupied 

building. These generic charts, for conventional construction, 

provide information to law enforcement and public safety officials 

that allow them to establish safe evacuation distances should an explosive device be suspected or detected. However, these distances 

are so site-specific that the generic charts provide little more than 

general guidance in the absence of more reliable site-specific information. Based on the information provided in the chart, the 
2- Structural design criteria

onset of significant glass debris hazards is associated with stand-off 

distances on the order of hundreds of feet from a vehicle-borne 

explosive detonation while the onset of column failure is associated 

with stand-off distances on the order of tens of feet. 

Figure 2-2 Range to effects chart

Source: Defense Threat Reduction Agency
Structural design criteria 2-

2.2.1 Blast Effects in Low-rise Buildings

Many shelters can be part of low-rise buildings. Although small 

weights of explosives are not likely to produce significant blast 

loads on the roof, low-rise buildings may be vulnerable to blast 

loadings resulting from large weights of explosives at large standoff distances that may sweep over the top of the building. The 

blast pressures that may be applied to these roofs are likely to far 

exceed the conventional design loads and, unless the roof is a concrete deck or concrete slab structure, it may fail. There is little that 

can be done to increase the roof’s resistance to blast loading that 

doesn’t require extensive renovation of the building structure. 

Figure 2-3 shows the ever expanding blast wave as it radiates from 

the point of detonation and causes, in sequence of events, the 

building envelope to fail, the internal uplift on the floor slabs, and 

eventually the engulfment of the entire building.

Figure 2-3

Blast damage

SOURCE: Naval Facilities

Engineering Service Center, 

User’s Guide on Protection 

Against Terrorist Vehicle 

Bombs, May 1998
2- Structural design criteria

In addition to the blast pressures that may be directly applied to 

the exterior columns and spandrel beams, the forces collected by 

the building envelope will be transferred through the slabs to the 

structural frame or shear walls that transfer lateral loads to the foundations. The extent of damage will be greatest in close proximity to 

the detonation; however, depending on the intensity of the blast, 

large inelastic deformations will extend throughout the building and 

cause widespread cracking to structural and nonstructural partitions. 

In addition to the hazard of impact by building envelope debris 

propelled into the building or roof damage that may rain down, 

the occupants may also be vulnerable to much heavier debris resulting from structural damage. Progressive collapse occurs when 

an initiating localized failure causes adjoining members to be overloaded and fail, resulting in a cascading sequence of damage that 

is disproportionate to the originating extent 

of localized failure. The initiating localized 

failure may result from a sufficiently sized 

parcel bomb that is in contact with a critical 

structural element or from a vehicle sized 

bomb that is located a short distance from the 

building (see Figure 2-4). However, a large 

explosive device at a large stand-off distance is 

not likely to selectively fail a single structural 

member; any damage that results from this 

scenario is more likely to be widespread and 

the ensuing collapse cannot be considered 

progressive. Although progressive collapse is 

not typically an issue for buildings three stories 

or shorter, transfer girders and non-ductile, 

non-redundant construction may produce 

structural systems that are not tolerant of 

localized damage conditions. The columns 

that support transfer girders and the transfer 

girders themselves may be critical to the stability of a large area of floor space. 

Figure 2-4

Alfred P. Murrah Federal 

Office Building

SOURCE: U.s. air force
Structural design criteria 2-

As an example, panelized construction that is 

sufficiently tied together can resist the localized 

damage or large structural deformations that 

may result from an explosive detonation. 

Although the explosive detonation opposite 

the Khobar Towers destroyed the exterior façade, the panelized structure was sufficiently 

tied together to permit relatively large deformations without loss of structural stability 

(see Figure 2-5). This highlights the benefits 

of ductile and redundant detailing for all 

types of construction.

To mitigate the effects of in-structure shock that may result 

from the infilling of blast pressures through damaged enclosures, nonstructural overhead items should be located below the 

raised floors or tied to the ceiling slabs with seismic restraints. 

Nonstructural building components, such as piping, ducts, 

lighting units, and conduits must be sufficiently tied back to the 

building to prevent failure of the services and the hazard of falling 

debris.

The contents of this manual supplement the information provided in FEMA 361, Design and Construction Guidance for Community 

Shelters and FEMA 320, Taking Shelter From the Storm: Building a Safe 

Room Inside Your House. Although this publication does not specifically address nuclear explosions and shelters that protect against 

radiological fallout, this information may be found in FEMA 

TR-87, Standards for Fallout Shelters. The contents of FEMA 452, A 

How-To Guide to Mitigate Potential Terrorist Attacks Against Buildings

will help the reader identify critical assets and functions within 

buildings, determine the threats to these assets, and assess the vulnerabilities associated with those threats.

Figure 2-5

Khobar Towers

SOURCE: U.s. air force
2- Structural design criteria

2.2.2 Blast Effects in High-rise Buildings: 

The Urban Situation

High-rise buildings must resist significant gravity and lateral load 

effects; although the choice of framing system and specific structural details will determine the overall performance, the lower 

floors, which are in closest proximity to a vehicle-borne threat, are 

inherently robust and more likely to be resistant to blast loading 

than smaller buildings. However, tall buildings are likely to be 

located in dense urban environments that tend to trap the blast 

energy within the canyon like streets as the blast waves reflect off 

of neighboring structures. Furthermore, tall buildings are likely 

to contain underground parking and loading docks that can introduce significant internal explosive threats. While these internal 

threats may be prevented through rigorous access control procedures, there are few conditions in which vehicular traffic can 

be restricted on city streets. Anti-ram streetscape elements are required to maintain a guaranteed stand-off distance from the face of 

the building. 

In addition to the hazard of structural collapse, the façade is a 

much more fragile component. While the lower floor façade is 

likely to fail in response to a sizable vehicle threat at a sidewalk’s 

distance from the building, the peak pressures and impulses at 

higher elevations diminish due to the increased stand-off distance 

and the associated shallow angle of incidence (measured with respect to the vertical height of the building). Although reflections 

off of neighboring structures are likely to affect the intensity of 

blast loads, the façade loads at the upper floors will be considerably lower than the loads at the lower floors and the extent of 

façade debris will reflect this. A detailed building-specific analysis 

of the structure and the façade is required to identify the inherent 

strengths and vulnerabilities. This study will indicate the safest 

place to locate the shelter. 
Structural design criteria 2-

2.3 Hardened ConstrUCTION

2.3.1 Structural System

A shelter will only be effective if the building in which it is located 

remains standing. It is unreasonable to design a shelter within a 

building with the expectation that the surrounding structure may 

collapse. Although the shelter must be able to resist debris impact, 

it is not reasonable for it to withstand the weight of the building 

crashing down upon it. Therefore, the effectiveness of the shelter 

will depend on the ability of the building to sustain damage, but 

remain standing. The ability of a building to withstand an explosive event and remain standing depends on the characteristics of 

the structure. Some of these characteristics include:

m Mass. Lightweight construction may be unsuitable for providing resistance to blast loading. Inertial resistance may be required in addition to the strength and ductility of the system. 

m Shear capacity. Shear is a brittle mode of failure and primary 

members and/or their connections should therefore be 

designed to prevent shear failure prior to the development of 

the flexural capacity. 

m Capacity for resisting load reversals. In response to sizable 

blast loads, structural elements may undergo multiple cycles 

of large deformation. Similarly, some structural elements may 

be subjected to uplift pressures, which oppose conventional 

gravity load design. The effects of rebound and uplift 

therefore require blast-resistant members to be designed for 

significant load reversals. Depending on the cable profile, 

pre-tensioned or post-tensioned construction may provide 

limited capacity for abnormal loading patterns and load 

reversals. Draped tendon systems designed for gravity loads 

may be problematic; however, the higher quality fabrication 

and material properties typical for precast construction 

may provide enhanced performance of precast elements 

designed and detailed to resist uplift and rebound effects 

resulting from blast loading. Seated connection systems for 
2-10 Structural design criteria

steel and precast concrete systems must also be designed and 

detailed to accommodate uplift forces and rebound resulting 

from blast loads. The use of headed studs is recommended 

for affixing concrete fill over steel deck to beams for uplift 

resistance. 

m Redundancy. Multiple alternative load paths in the verticalload-carrying system allow gravity loads to redistribute in the 

event of failure of structural elements. 

m Ties. An integrated system of ties in perpendicular directions 

along the principal lines of structural framing can serve to 

redistribute loads during catastrophic events.

m Ductility. Structural members and their connections may 

have to maintain their strength while undergoing large 

deformations in response to blast loading. The ability of 

a member to develop inelastic deformations allows it to 

dissipate considerable amounts of blast energy. The ratio of 

a member’s maximum inelastic deformation to a member’s 

elastic limit is a measure of its ductility. Special detailing 

is required to enable buildings to develop large inelastic 

deformations (see Figure 2-6). 

Historically, cast-in-place reinforced concrete was the preferred 

material for explosion-mitigating construction. This is the material used for military bunkers, and the military has performed 

extensive research and testing of its performance. Among its benefits, reinforced concrete has significant mass, which improves 

its inertial resistance; it can be readily proportioned for ductile 

behavior and may be detailed to achieve continuity between 

members. Finally, concrete columns are less susceptible to global 

buckling in the event of the loss of a floor system. However, steel 

may be similarly detailed to take advantage of its inherent ductility 

and connections may be designed to provide continuity between 

members. Similarly, panelized precast concrete systems can be detailed to permit significant deformations in response to explosive 

loading, as demonstrated by the performance of Khobar Towers.
Structural design criteria 2-11

Figure 2-6

Ductile detailing of 

reinforced concrete 

structures

Protective design further requires the system to accept localized 

failure without precipitating a collapse of a greater extent of the 

structure. By allowing the building to bridge over failed components, building robustness is greatly improved and the unintended 

consequences of extreme events may be mitigated. However, it 

may not be possible for existing construction to be retrofitted to 

limit the extent of collapse to one floor on either side of a failed 

column. If the members are retrofitted to develop catenary behavior, the adjoining bays must be upgraded to resist the large 

lateral forces associated with this mode of response. This may 

require more extensive retrofit than is either feasible or desirable. 

In such a situation, it may be desirable to isolate the collapsed region rather than risk propagating the collapse to adjoining bays. 

The retrofit of existing buildings to protect against a potential 
2-12 Structural design criteria

progressive collapse resulting from extreme loading may therefore 

best be achieved through the localized hardening of vulnerable 

columns. These columns need only be upgraded to a level of 

resistance that balances the capacities of all adjacent structural 

elements. At greater blast intensities, the resulting damage would 

be extensive and create global collapse rather than progressive 

collapse. Attempts to upgrade the building to conform to the 

alternate path approach would be invasive and potentially counterproductive.

2.3.2 Loads and Connections

Because the shelter will likely suffer significant damage in response to extreme loading conditions, the shelter must be able 

to withstand both the direct loading associated with the natural 

or manmade hazard and the debris associated with the damaged 

building within which it is housed. 

Structural systems that provide a continuous load path that 

supports all vertical and lateral loads acting on a building are 

preferred. A continuous load path ties all structural components 

together and the fasteners used in the connections must be capable of developing the full capacity of the members. In order to 

provide comprehensive protection, the capacity of each component must be balanced with the capacity of all other components 

and the connection details that tie them together. Because all 

applied loads must eventually be transferred to the foundations, 

the load path must be continuous from the uppermost structural 

component to the ground. 

After the appropriate loads are calculated for the shelter, they 

should be applied to the exterior wall and roof surfaces of the 

shelter to determine the design forces for the structural and 

nonstructural elements. The continuous load path carries the 

loads acting on a building’s exterior façade and roof through the 

floor diaphragms to the gravity load-bearing system and lateral 

load-bearing system. The individual components of the façade and 

roof must be able to develop these extraordinary forces, though 
Structural design criteria 2-13

deformed, and transfer them to the underlying beams, trusses, 

girders, shear walls, and columns that provide the global structural 

resistance. These structural systems must also be able to develop 

uplift forces and load reversals that may accompany these extreme 

loading conditions. Uplift forces and load reversals are typically 

applied contrary to the conventional design loads and, therefore, 

details must be developed that account for these contrary patterns 

of deformation (see Figure 2-7). Seismic detailing that addresses 

ductile behavior despite multiple cycles of load reversals are generally well suited for all of these extreme loading conditions and 

building-specific details must consider each threat condition. Some 

construction materials, however, are better suited to developing a 

load path that can withstand loads from multiple directions and 

events. Cast-in-place reinforced concrete and steel moment frame 

construction is more commonly detailed to provide load paths 

than in "progressive collapse" designs utilizing panelized or masonry load-bearing construction. Nevertheless, appropriate details 

must be developed for nearly all structural systems.

Figure 2-7

Effects of uplift and load 

reversals
2-14 Structural design criteria

Figure 2-8 

Flat slab failure mechanisms

Floor slabs are typically designed to resist downward gravity 

loading and have limited capacity to resist uplift pressures or the 

upward deformations experienced during load reversals that may 

precipitate a flexural or punching shear failure (see Figure 2-8). 

Therefore, floor slabs that may be subjected to significant uplift 
Structural design criteria 2-15

pressures, such that they overcome the gravity loads and subject 

the slabs to reversals in curvature, require additional reinforcement. If the slab does not contain this tension reinforcement, it 

must be supplemented with a lightweight carbon fiber application that may be bonded to the surface at the critical locations. 

Carbon fiber reinforcing mats bonded to the top surface of slabs 

would strengthen the floors for upward loading and reduce the 

likelihood of slab collapse from blast infill uplift pressures as well 

as internal explosions in mailrooms or other susceptible regions. 

This lightweight high tensile strength material supplements the 

limited capacity of the concrete to resist these unnatural loading 

conditions. An alternative approach would be to notch grooves 

in the top of concrete slabs and epoxy carbon fiber rods into 

grooves; although this approach may offer a greater capacity, it is 

much more invasive.

Similarly, adequate connections must be provided between the 

roof sheathing and roof structure to prevent uplift forces from 

lifting the roof off of its supports. Reinforcing steel, bolts, steel 

studs, welds, screws, and nails are used to connect the roof 

decking to the supporting structure. The detailing of these connections depends on the magnitude of the uplift or catenary 

forces that may be developed. The attachment of precast planks to 

the supporting structure will require special attention to the connection details. However, as with all other forms of construction, 

ductile and redundant detailing will produce superior performance in response to extreme loading. 

Wall systems are typically connected to foundations using anchor 

bolts, reinforcing steel and imbedded plate systems properly 

welded together, and nailed mechanical fasteners for wood construction. Although these connections benefit from the weight of 

the structure bearing against the foundations and the lateral restraint provided by keyed details, the connections must be capable 

of developing the design forces in both the connectors and the 

materials into which the connectors are anchored. 
2-16 Structural design criteria

2.3.3 Building Envelope

Façade components that must transfer the collected loads to the 

structural system must be designed and detailed to absorb significant amounts of energy associated with the extreme loading 

through controlled deformation. The duration of the extreme 

loading significantly influences the criteria governing the design 

of the building envelope systems. Significant inelastic deformations may be permitted for extraordinary events that impart the 

extreme loading over very short periods of time (e.g., explosive detonations). The building envelope system need only be 

designed to resist the direct shock wave, rebound, and any reflections off of neighboring buildings, all of which will occur within a 

matter of milliseconds (see Figure 2-9). 

Resistance to blast is often compared to 

resistance to natural hazards with the 

expectation that the protection against 

one will provide protection against the 

other. Therefore, as a first step, one 

should consider any inherent resistance 

derived from a building’s design to resist 

environmental loading. Extreme wind 

loading resulting from tornadoes may 

similarly be of short enough duration to 

permit a large deformation of the façade 

in response to the peak loading. Certainly, the debris impact criteria will be 

similar to that for blast loading. However, 

hurricane winds may persist for extended 

periods of time and the performance criteria for façade components in response 

to these sustained pressures permit 

smaller deformations and less damage to 

the system. Breach of the façade components would permit pressures to fill the 

building and loads to be applied to nonstructural components. 

Anchorages and connections must be capable of holding the 

Figure 2-9 

Blast damaged façade
Structural design criteria 2-17

façade materials intact and attached to the building. Brittle modes 

of failure must be avoided to allow ductile deformations to occur.

2.3.4 Forced Entry and Ballistic Resistance

Ballistic-resistant design involves both the blocking of sightlines to 

conceal the occupants and the use of ballistic-resistant materials 

to minimize the effectiveness of the weapon. To reduce exposure, the safe room should be located as far as possible into the 

interior of the facility and walls should be arranged to eliminate 

sightlines through doorways. In order to provide the required 

level of resistance, the walls must be constructed using the appropriate thickness of ballistic-resistant materials, such as reinforced 

concrete, masonry, mild steel plate, or composite materials. The 

required thickness of these materials depends on the level of 

ballistic resistance; however, resistance to a high level of ballistic 

threat may be achieved using 6.5 inches of reinforced concrete, 

8 inches of grouted concrete masonry unit (CMU) or brick, 1 

inch mild steel plate, or 3⁄4 inch armor steel plate. A 1⁄2-inch thick 

layer of bullet-resistant fiberglass may provide resistance up to a 

medium level of ballistic threat. Bullet-resistant doors are required 

for a high level of protection; however, hollow steel or steel clad 

doors with pressed steel frames may be used with an appropriate 

concealed entryway. Ballistic-resistant window assemblies contain 

multiple layers of laminated glass or polycarbonate materials and 

steel frames. Because these assemblies tend to be both heavy and 

expensive, their number and size should be minimized. Roof 

structures should contain materials similar to the ballistic-resistant 

wall assemblies. Ratings of bullet-resisting materials are presented 

in Table 2-1.
2-18 Structural design criteria

Forced entry resistance is measured in the time it takes for an aggressor to penetrate the enclosure using a variety of hand tools 

and weapons. The required delay time is based on the probability 

of detecting the aggressors and the probability of a response force 

arriving within a specified amount of time. The different layers 

of defense create a succeeding number of security layers that are 

more difficult to penetrate, provide additional warning and response time, and allow building occupants to move into defensive 

positions or designated safe haven protection (see Figure 2-10). 

The rated delay time for each component comprising a defense 

layer (walls, doors, windows, roofs, floors, ceilings, and utility 

openings) must be known in order to determine the effective 

delay time for the safe room. Conventional construction offers 

little resistance to most forced entry threat severity levels and the 

rating of different forced entry-resistant materials is based on standardized testing under laboratory conditions.

Table 2-1: UL 752 Ratings of Bullet-resisting Materials

Rating Ammunition Grain Minimum Velocity (fps)

Level 1 9 mm full metal copper jacket with lead core 124 1,185

Level 2 .357 Magnum jacketed lead soft point 158 1,250

Level 3 .44 Magnum lead semi-wadcutter gas checked 240 1,350

Level 4 .30 caliber rifle lead core soft point 180 2,540

Level 5 7.62 mm rifle lead core full metal copper jacket, 

military ball 150 2,750

Level 6 9 mm full metal copper jacket with lead core 124 1,400

Level 7 5.56 mm rifle full metal copper jacket with lead 

core

55 3,080

Level 8 7.62 mm rifle lead core full metal copper jacket, 

military ball 150 2,750

UL = Underwriters Laboratories
Structural design criteria 2-19

Figure 2-10 

Layers of defense

2.4 New Construction

The design of new buildings to contain shelters provides greater 

opportunities than the retrofit of existing buildings. Whether 

the entire building or just the shelter is to be resistant to the 

explosive terrorist threat may have a significant impact on the 

architectural and structural design of the building. Furthermore, 

unless the building is required to satisfy an established security 

design criteria, the weight of explosive that the building is to be 

designed to resist must be established by a site-specific threat and 

risk assessment. Even so, given the evolving nature of the terrorist 

threat, it is impossible to predict all the extreme conditions to 

which the building may be exposed over its life. Therefore, even 

if the building is not to be designed to resist any specific explosive threat, the American Society of Civil Engineers Minimum 

Design Loads for Buildings and Other Structures (ASCE-7) requires 

the building to be designed to sustain local damage without the 

building as a whole “being damaged to an extent disproportionate 

to the original local damage.” The building can therefore be designed to prevent the progression of collapse in the unlikely event 

a primary member loses its load carrying capacity. This minimum 

design feature, achieved through the indirect prescriptive method 

or direct alternate path approach, will improve the structural 
2-20 Structural design criteria

integrity and provide an additional measure of safety to occupants. Incorporating continuity, redundancy, and ductility into 

the design will allow a damaged building to bridge over a failed 

element and redistribute loads through flexure or catenary action. This will limit the extent of debris that might otherwise rain 

down upon the hardened shelter. Where specific threats are defined, the vulnerable structural components may be hardened to 

withstand the intensity of explosive loading. The local hardening 

of vulnerable components in addition to the indirect prescriptive 

detailing of the structural system to bridge over damaged components will provide the most protection to the building.

2.4.1 Structure

Both steel frame and reinforced concrete buildings may be designed and detailed to resist the effects of an exterior vehicle 

explosive threat and an interior satchel explosion. Although steel 

construction may be more efficient for many types of loading, 

both conventional and unconventional, cast-in-place reinforced 

concrete construction provide an inherent continuity and mass 

that makes it desirable for blast-resistant buildings. 

Reinforced concrete is a composite material in which the concrete 

provides the primary resistance to compression and shear and 

the steel reinforcement provides the resistance to tension and 

confines the concrete core. In addition to ductile detailing, which 

allows the reinforced concrete members to sustain large deformations and uncharacteristic reversals of curvature, the structural 

elements are typically stockier and more massive than their steel 

frame counterparts. The additional inertial resistance as well as 

the continuity of cast-in-place construction facilitates designs that 

are capable of sustaining the high intensity and short duration 

effects of close-in explosions. Furthermore, reinforced concrete 

buildings tend to crack and dissipate large amounts of energy 

through internal damping. This limits the extent of rebound 

forces and deformations.
Structural design criteria 2-21

Blast-resistant detailing requires continuous top and bottom reinforcement with tension lap splices staggered over the spans, 

confinement of the plastic hinge regions by means of closely 

spaced ties, and the prevention of shear failure prior to developing the flexural capacity (see Figure 2-11). One- or two-way 

slabs supported on beams provide the best resistance to near contact satchel threats, which may produce localized breach, but allow 

the structure to redistribute the gravity loads. Concrete columns 

must be confined with closely spaced spiral ties, steel jackets, or 

composite wraps. This confinement increases the shear resistance, 

improves the ductility, and protects against the shattering effects 

resulting from a near contact explosion. Cast-in-place exterior 

walls or precast panels are best able to withstand a sizable stand-off 

vehicular explosive threat and may be easily detailed to interact 

with the reinforced concrete frame as part of the lateral load-resisting system. 

Figure 2-11 Multi-span slab splice locations
2-22 Structural design criteria

Steelwork is generally better suited to resist relatively low intensity, 

but long duration effects of large stand-off explosions. Steel is 

an inherently ductile material that is capable of sustaining large 

deformations; however, the very efficient thin-flanged sections 

make the conventional frame construction vulnerable to localized 

damage. Complex stress combinations and concentrations may 

occur that cause localized distress and prevent the section from 

developing its ultimate strength. Steel buildings may experience 

significant rebound and must therefore be designed to support 

significant reversals of loading. Concrete filled tube sections or 

concrete encased flanged sections may be used to protect the thinflanged sections and supplement the inertial resistance. Concrete 

encasement should extend a minimum of 4 inches beyond the 

width and depth of the steel flanges and reinforcing bars may be 

detailed to tie into the concrete slabs.

To allow the concrete encasement to be tied into the floor slabs, 

the typical metal pan with concrete deck construction will require 

special detailing. Metal deck construction provides a spall shield 

to the underside of the slabs, which provides additional protection 

to a near contact satchel situated on a floor. However, the internal 

explosive threat will also load the ceiling slabs from beneath and 

the beams must contain an ample amount of studs, which far exceeds the requirements for conventional gravity design, to transfer 

the slab reactions to the steel supports without pulling out. If the 

slabs are adequately connected to the steel-framing members, 

these beams will be subjected to abnormal reversals of curvature. 

These reversals will subject the mid-span bottom flanges to transient compressive stress and may induce a localized buckling. 

Because the blast loads are transient, the dominant gravity loads 

will eventually restore the mid-span bottom flange to tension; 

however, unless it is adequately braced, the transient buckling will 

produce localized damage.

The concrete encasement of the steel beams will provide torsional 

resistance to the cross-section and minimize the need for intermediate bracing. If the depth of the composite section is to be 

minimized by embedding the steel section into the thickness of 
Structural design criteria 2-23

the slab, the slab reinforcement must either be welded to the webs 

or run through holes drilled into the webs in order to maintain 

continuity. All welding of reinforcing steel must be in accordance 

with seismic detailing to prevent brittle failures. Steel columns 

require full moment splices and the relatively thin flange sections 

require concrete encasement to prevent localized damage. To 

take full advantage of the steel capacity and dissipate the greatest 

amount of energy through ductile inelastic deformation, the beam 

to column connections must be capable of developing the plastic 

flexural capacity of the members. Connection details, similar to 

those used in seismic regions, will be required to develop the 

corresponding flexural and shear capacity (see Figure 2-12). Connecting exterior cast-in-place reinforced concrete walls to the steel 

frame will require details that transfer both the direct blast loads 

in bearing and the subsequent rebound effects in tension. Precast 

panels are simply supported at the ends and, unless they span over 

multiple floors, they lack the continuity of monolithic cast-in-place 

wall construction. Cold joints in the cast-in-place construction require special detailing and the connection details for the precast 

panels must be able to resist both the direct blast loads in bearing 

and the subsequent rebound effects in tension. 

Figure 2-12 

Typical frame detail at 

interior column
2-24 Structural design criteria

Regardless of the materials, framed buildings perform best when 

column spacing is limited and the use of transfer girders is limited. Bearing wall systems that rely on interior cross-walls will 

benefit from periodically spaced longitudinal walls that enhance 

stability and control the lateral progression of damage. Bearing 

wall systems that rely on exterior walls will benefit from periodically spaced perpendicular walls or substantial pilasters that limit 

the extent of wall that is likely to be affected.

Free-standing columns do not have much surface area; therefore, air-blast loads on columns are limited by clear-time effects 

in which relief waves from the free edges attenuate the reflected 

intensity of the blast loads. Where the exterior façade inhibits 

clear-time effects prior to façade failure, the columns will receive 

the full intensity of the reflected blast pressures. Large stand-off 

explosive threats may produce large inelastic flexural deformations that could initiate P- induced instabilities. Short stand-off 

explosive threats may cause shear, base plate, or column splice 

failures. Near contact threats may cause brisance, which is the 

shattering of reinforced concrete sections. Confinement of reinforced concrete members by means of spiral reinforcement, steel 

jackets, or carbon fiber wraps may improve their resistance. Encasement of steel sections will inhibit local flange and web plate 

deformations that could precipitate a section failure. Exterior 

column splices should be located as high above grade level as 

practical and match the capacity of the column section.

Load-bearing walls do not benefit from clear-time effects as columns do and therefore collect the full intensity of the reflected 

blast pressure pulse. Nevertheless, reinforced concrete loadbearing walls are particularly effective if adequately reinforced. 

Fully grouted masonry walls, on the other hand, are more brittle 

and seismic levels of reinforcement greatly increase the ductility 

and performance of masonry walls. Continuous reinforced bond 

beams, with a minimum of one #4 bar or equivalent, are required 

in the wall at the top and bottom of each floor and roof level. Interior horizontal ties are required in the floors perpendicular to 

the wall. The ties are equivalent to a #4 bent bar at a maximum 
Structural design criteria 2-25

spacing of 16 inches that extends into the slab and the wall the 

greater of the development length of the bar or 30 inches. Vertical 

ties are required from floor to floor at columns, piers, and walls. 

The ties should be equivalent to a #4 bar at a maximum spacing 

of 16 inches coinciding with the horizontal ties. The ties should 

be continuous through the floor and extend into the wall above 

and below the floor the greater of the development length of the 

bar or 30 inches. Partition walls surrounding critical systems or isolating areas of internal threat, such as lobbies, loading docks, and 

mailrooms, require fully grouted reinforced masonry construction. It is particularly difficult to extend the reinforcement to the 

full height of the partition wall and develop the reaction forces. 

Reinforced bond beams are required as for load-bearing walls. 

Flat roof systems are exposed to the incident blast pressures that 

diffuse over the top of the building, causing complex patterns 

of shadowing and focusing on the surface. Subsequent negative 

phase effects may subject the pre-weakened roof systems to low 

intensity, but long duration suction pressures; therefore, lightweight roof systems may be susceptible to uplift effects. Two-way 

beam slab systems are preferred for reinforced concrete construction and metal deck with reinforced concrete fill is preferred for 

steel frame construction. Both of these roof systems provide the 

required mass, strength, and continuity to resist all phases of blast 

loading. The performance of conventional precast concrete plank 

systems depends to a great extent on the connection details, and 

these connections need to be detailed to provide continuity. Flat 

slab and flat plate construction requires continuous bottom reinforcement in both directions to improve the integrity and special 

details at the columns to prevent a punching shear failure. Posttensioned slab systems are particularly problematic because the 

cable profile is typically designed to resist the predominant patterns of gravity load and the system is inherently weak in response 

to load reversals. 
2-26 Structural design criteria

2.4.2 Façade and Internal Partitions

The building’s façade is its first real defense against the effects of a 

bomb and is typically the weakest component that will be subjected 

to blast pressures. Debris mitigating façade systems may be designed 

to provide a reasonable level of protection to a low or moderate 

intensity threat; however, façade materials may be locally overwhelmed in response to a low intensity short stand-off detonation 

or globally overwhelmed in response to a large intensity long standoff detonation. As a result, it is unreasonable to design a façade 

to resist the actual pressures resulting from the design level threat 

everywhere over the surface of the building. In fact, successful performance of the blast-resistant façade may be defined as throwing 

debris with less than high hazard velocities. This is particularly true 

for the glazed fenestration. The peak pressures and impulses that 

are used to select the laminated glazing makeup are typically established such that no more than 10 percent of the glazed fenestration 

will produce debris that is propelled with high hazard velocities 

into the occupied space in response to any single detonation of the 

design level threat. The definitions of high hazard velocities were 

adapted from the United Kingdom hazard guides and correspond 

to debris that is propelled 10 feet from the plane of the glazing and 

strikes a witness panel higher than 2 feet above the floor. Similarly, 

a medium level of hazard corresponds to debris that strikes the 

witness panel no higher than 2 feet above the floor. A low level of 

hazard corresponds to debris that strikes the floor no farther than 

10 feet from the plane of the glazing and a very low level of hazard 

corresponds to debris that strikes the floor no farther than 3.3 feet 

from the plane of the glazing. Glass hazard response software was 

developed for the U.S. Army Corps of Engineers, the General Services Administration, and the Department of State to determine 

the performance of a wide variety of glazing systems in response to 

blast loading. These simplified single-degree-of-freedom dynamic 

analyses account for the strength of the glass prior to cracking 

and the post-damage capacity of the laminated interlayers. While 

many of these glass hazard response software remain restricted, the 

American Society for Testing and Materials (ASTM) 2248 relates 

the design of glass to resist blast loading to an equivalent 3-second 

equivalent wind load. 
Structural design criteria 2-27

In order for the glazing to realize its theoretical capacity, it must 

be retained by the mullions with an adequately sized bite, by 

means of a structural silicone adhesive, or a combination of the 

two. Furthermore, in order for the mechanical bite and silicone 

adhesive to be effective, the mullion deformations over the length 

of the lite must be limited (see Figure 2-13). Unfortunately, the 

maximum extent of deformation that the mullion may sustain 

prior to dislodging the glass is poorly defined. A conservative limit 

of 2 degrees is often assumed for typical protective glazing systems; 

however, advanced analytics may justify a significantly greater mullion deformation limit. Mullions must therefore be able to accept 

the reaction forces from the edges of the glazed elements and 

remain intact and attached to the building. Analyses of mullion 

deformations and anchorage details are required to demonstrate 

the safe performance of the glazed fenestration. 

Window of protected spaces 

may be bullet-resistant Strong attachment 

to secure mullion

Insulated glazing with 

laminated inner lite 

Window adhered to the 

frame with structural silicone 

sealant to keep fractured 

window in frame 

Strengthened mullion system must 

be stronger than glass to hold 

fractured window in place 

Figure 2-13 Protective façade design
2-28 Structural design criteria

Curtainwall systems are inherently lightweight and flexible 

façade systems; however, well designed curtainwall systems 

demonstrated, through explosive testing, considerable 

resilience in response to blast loading. Furthermore, the glazed 

components are subjected to less intense loads as their flexible 

supports deform in response to the blast pressures. A multidegree-of-freedom model of the façade will determine the 

accurate interaction of the individual mullions and the phasing 

of the interconnecting forces. Because all response calculations 

must be dynamic and inelastic, the accurate representation of the 

phasing of these forces may significantly affect the performance. 

Curtainwall anchors are attached directly to the floor slabs where 

the large lateral loads may be transferred directly through the 

diaphragms into the lateral load-resisting systems.

Façade systems may contain combinations of glazing, metal 

panels, precast concrete, or stone panels. Metal panels provide 

little inertial resistance, but are capable of developing large inelastic deformations. The fasteners that attach these panels to the 

mullions or metal studs must be designed to transfer the large 

membrane forces. Stone panels provide significant inertial resistance, but are relatively brittle and have little strength beyond 

their modulus of rupture. Stud wall systems that restrain these 

façade panels may deform within acceptable levels and develop 

a membrane stiffening capacity, and strain energy methods may 

be used to calculate their response. However, the anchorage of 

the studs to the floor and ceiling slabs are likely to limit the forces 

they can develop.

Precast panels may easily be designed to provide inelastic deformation in response to the design level threats. However, the design of 

their anchorage to hold them to the building during both the direct loading and subsequent rebound phase require more robust 

details. Because the primary load carrying elements may buckle in 

response to the large collected forces, precast panels are attached 

directly to the floor slabs where the forces may be transferred 

through the diaphragms to the lateral load-resisting elements. 

Where mullions are attached within punched out openings in 
Structural design criteria 2-29

precast panels, the spacing of the anchorages will determine the 

span of the mullions and the force each anchorage is required 

to resist. Embedded anchors within the precast panels will be required to accept these anchorage forces.

Fully grouted and reinforced CMU façades may be designed to 

accept the large lateral loads produced by blast events; however, 

it is often difficult to detail them to transfer the reaction forces to 

the floor slabs. A continuous exterior CMU wall that bears against 

the floor slabs may avoid many of the construction and connection difficulties, but this is not typical construction practice. Brick 

or stone veneer does not appreciably increase the strength of the 

CMU wall, but the added mass increases its inertial resistance.

2.5 Existing Construction: Retrofitting 

Considerations

Although retrofitting existing buildings to include a shelter can 

be expensive and disruptive to users, it may be the only available 

option. When retrofitting existing space within a building is considered, data centers, interior conference rooms, stairwells, and 

other areas that can be structurally and mechanically isolated provide the best options. Designers should be aware that an area of a 

building currently used for refuge may not necessarily be the best 

candidate for retrofitting when the goal is to provide comprehensive protection.

An existing area that has been retrofitted to serve as a shelter is 

unlikely to provide the same degree of protection as a shelter 

designed as new construction. When existing space is retrofitted 

for shelter use, issues have arisen that have challenged both 

designers and shelter operators. For example, glass and unreinforced masonry façades are particularly vulnerable to blast 

loading. Substantial stand-off distances are required for the unprotected structure and these distances may be significantly reduced 

through the use of debris mitigating retrofit systems. Furthermore, because blast loads diminish with distance and incidence 

of blast wave to the loaded surface, the larger threats at larger 
2-30 Structural design criteria

stand-off distances are likely to damage a larger percentage of façade elements than the more localized effects of smaller threats at 

shorter stand-off distances. Safe rooms that may be located within 

a building should therefore be located in windowless spaces or 

spaces in which the window glazing was upgraded with a fragment 

retention film (FRF). 

2.5.1 Structure

The building’s lateral load-resisting system, the structural frame 

or shear walls that resist wind and seismic loads, will be required 

to receive the blast loads that are applied to the exterior façade 

and transfer them to the building’s foundation. This load path 

is typically through the floor slabs that act as diaphragms and 

interconnect the different lateral load-resisting elements. The 

lateral load-resisting system for a building depends to a great 

extent on the type of construction and region. In many cases, lowrise buildings do not receive substantial wind and seismic forces 

and, therefore, do not require substantial lateral load-resisting 

systems. Because blast loads diminish with distance, a package 

sized explosive threat is likely to locally overwhelm the façade, 

thereby limiting the force that may be transferred to the lateral 

load-resisting system. However, the intensity of the blast loads that 

may be applied to the building could exceed the design limits for 

most conventional construction. As a result, the building is likely 

to be subjected to large inelastic deformations that may produce 

severe cracks to the structural and nonstructural partitions. There 

is little that can be done to upgrade the existing structure to make 

it more ductile in response to a blast loading that doesn’t require 

extensive renovation of the building; therefore, safe rooms should 

be located close to the interior shear walls or reinforced masonry 

walls in order to provide maximum structural support in response 

to these uncharacteristically large lateral loads.

Unless the structure is designed to resist an extreme loading, 

such as a hurricane or an earthquake, it is not likely to sustain 

extensive structural damage without precipitating a progressive 

collapse. The effects of a satchel-sized explosive in close contact 
Structural design criteria 2-31

to a column or a vehicle-borne explosive device at a sidewalk’s distance from the façade may initiate a failure of a primary structure 

that may propagate as the supported loads attempt to redistribute 

to an adjoining structure. Transfer girders that create long span 

structures and support large tributary areas are particularly susceptible to localized damage conditions. As a result, safe rooms 

should not be located on a structure that is either supported by or 

underneath a structure that is supported by transfer girders unless 

the building is evaluated by a licensed professional engineer. The 

connection details for multi-story precast structures should also be 

evaluated before the building is used to house a safe room. 

Nonstructural building components, such as piping, ducts, 

lighting units, and conduits that are located within safe rooms 

must be sufficiently tied back to a solid structure to prevent failure 

of the services and the hazard of falling debris. To mitigate the 

effects of in-structure shock that may result from the infilling of 

blast pressures through damaged windows, the nonstructural 

systems should be located below the raised floors or tied to the 

ceiling slabs with seismic restraints.

2.5.2 Façade and Internal Partitions

Safe rooms in existing buildings should be selected to provide 

the space required to accommodate the building population and 

should be centrally located to allow quick access from any location 

within the building, enclosed with fragment mitigating partitions 

or façade, and within robust structural systems that will resist collapse. These large spaces are best located at the lower floors, away 

from a lightweight roof and exterior glazing elements. If such a 

space does not exist within the existing building, the available 

spaces may be upgraded to achieve as many of these attributes 

as possible. This will involve the treatment of the exterior façade 

with fragment mitigating films, blast curtains, debris catch systems, 

spray-on applications of elasto-polymers to unreinforced masonry 

walls, and hardening of select columns and slabs with composite 

fiber wraps, steel jackets, or concrete encasements.
2-32 Structural design criteria

2.5.2.1 Anti-shatter Façade. The conversion of existing construction to provide blast-resistant protection requires upgrades to the 

most fragile or brittle elements enclosing the safe room. Failure of 

the glazed portion of the façade represents the greatest hazard to 

the occupants. Therefore, the exterior glazed elements of the façade and, in particular, the glazed elements of the designated safe 

rooms, should be protected with an FRF, also commonly known 

as anti-shatter film (ASF), “shatter-resistant window film” (SRWF), 

or “security film.” These materials consist of a laminate that will 

improve post-damage performance of existing windows. Applied 

to the interior face of glass, ASF holds the fragments of broken 

glass together in one sheet, thus reducing the projectile hazard of 

flying glass fragments. 

Most ASFs are made from polyester-based materials and coated 

with adhesives. ASFs are available as clear, with minimal effects to 

the optical characteristics of the glass, and tinted, which provides 

a variety of aesthetic and optical enhancements and can increase 

the effectiveness of existing heating/cooling systems. Most films 

are designed with solar inhibitors to screen out ultraviolet (UV) 

rays and are available treated with an abrasion-resistant coating 

that can prolong the life of tempered glass.1 However, over time, 

the UV absorption damages the film and degrades its effectiveness.

According to published reports, testing has shown that a 7-mil 

thick film, or specially manufactured 4-mil thick film, is the minimum thickness that is required to provide hazard mitigation from 

blast. Therefore, a 4-mil thick ASF should be utilized only if it has 

demonstrated, through explosive testing, that it is capable of providing the desired hazard level response. 

The application of security film must, at a minimum, cover the 

clear area of the window. The clear area is defined as the portion 

of the glass unobstructed by the frame. This minimum application, termed daylight installation, is commonly used for retrofitting 

windows. By this method, the film is applied to the exposed glass 

1 Abrasions on the faces of tempered glass reduce the glass strength.
Structural design criteria 2-33

without any means of attachment or capture within the frame. 

Application of the film to the edge of the glass panel, thereby extending the film to cover the glass within the bite, is called an edge 

to edge installation and is often used in dry glazing installations. 

Other methods of retrofit application may improve the film performance, thereby reducing the hazards; however, these are typically 

more expensive to install, especially in a retrofit situation.

Although a film may be effective in keeping glass fragments together, it may not be particularly effective in retaining the glass in 

the frame. ASF is most effective when it is used with a blast tested 

anchorage system. Such a system prevents the failed glass from exiting the frame (see Figure 2-14). 

The wet glazed installation, a system where the film is positively 

attached to the frame, offers more protection than the daylight 

installation. This system of attaching the film to the frame reduces 

glass fragmentation entering the building. The wet glazing system 

utilizes a high strength liquid sealant, such as silicone, to attach 

the glazing system to the frame. This method is more costly than 

the daylight installation. 

Securing the film to the frame with a mechanically connected 

anchorage system further reduces the likelihood of the glazing 

system exiting the frame. Mechanical attachment includes anchoring methods that employ screws and/or batten strips that 

anchor the film to the frame along two or four sides. The mechanical attachment method can be less aesthetically pleasing when 

compared to wet glazing because additional framework is necessary and is more expensive than the wet glazed installation.

Window framing systems and their anchorage must be capable 

of transferring the blast loads to the surrounding walls. Unless 

the frames and anchorages are competent, the effectiveness 

of the attached films will be limited. Similarly, the walls must 

be able to withstand the blast loads that are directly applied to 

them and accept the blast loads that are transferred by the windows. The strength of these walls may limit the effectiveness of 

the glazing upgrades.
2-34 Structural design criteria

If a major rehabilitation of the façade is required to improve the 

mechanical characteristics of the building envelope, a laminated 

glazing replacement is recommended. Laminated glass consists 

of two or more pieces of glass permanently bonded together by 

a tough plastic interlayer made of polyvinyl butyral (PVB) resin. 

Once sealed together, the glass “sandwich” behaves as a single 

unit. Annealed, heat strengthened, tempered glass, or 

Figure 2-14

Mechanically attached 

anti-shatter film
Structural design criteria 2-35

polycarbonate glazing can be mixed and matched between layers 

of laminated glass in order to design the most effective lite for a 

given application. When fractured, fragments of laminated glass 

tend to adhere to the PVB interlayer rather than falling free and 

potentially causing injury.

Laminated glass can be expected to last as long as ordinary glass, 

provided it is not broken or damaged in any way. It is very important that laminated glass is correctly installed to ensure long life. 

Regardless of the degree of protection required from the window, 

laminated glass needs to be installed with adequate sealant to prevent water from coming in contact with the edges of the glass. A 

structural sealant will adhere the glazing to the frame and allow the 

PVB interlayer to develop its full membrane capacity. Similar to attached film upgrades, the window frames and anchorages must be 

capable of transferring the blast loads to the surrounding walls.

2.5.2.2 Façade Debris Catch Systems. Blast curtains are made 

from a variety of materials, including a warp knit fabric or a polyethylene fiber. The fiber can be woven into a panel as thin as 0.029 

inch that weighs less than 1.5 ounces per square foot. This fact 

dispels the myth that blast curtains are heavy sheets of lead that 

completely obstruct a window opening and eliminate all natural 

light from the interior of a protected building. The blast curtains 

are affixed to the interior frame of a window opening and essentially catch the glass fragments produced by a blast wave. The 

debris is then deposited on the floor at the base of the window. 

Therefore, the use of these curtains does not eliminate the possibility of glass fragments penetrating the interior of the occupied 

space, but instead limits the travel distance of the airborne debris. 

Overall, the hazard level to occupants is significantly reduced by 

the implementation of the blast curtains. However, a person sitting 

directly adjacent to a window outfitted with a blast curtain may still 

be injured by shards of glass in the event of an explosion.

The main components of any blast curtain system are the curtain 

itself, the attachment mechanism by which the curtain is affixed 

to the window frame, and either a trough or other retaining 
2-36 Structural design criteria

mechanism at the base of the window to hold the excess curtain 

material. The blast curtain with curtain rod attachment and sill 

trough differ largely from one manufacturer to the next. The 

curtain fabric, material properties, method of attachment, and 

manner in which they operate all vary, thereby providing many 

options within the overall classification of blast curtains. This fact 

makes blast curtains applicable in many situations.

Blast curtains differ from standard curtains in that they do not 

open and close in the typical manner. Although blast curtains are 

intended to remain in a closed position at all times, they may be 

pulled away from the window to allow for cleaning and blind or 

shade operation. However, the curtains can be rendered ineffective if installed such that easy access would provide opportunity 

for occupants to defeat their operation. The color and openness 

factor of the fabric contributes to the amount of light that is transmitted through the curtains and the see-through visibility of the 

curtains. Although the color and weave of these curtains may be 

varied to suit the aesthetics of the interior décor, the appearance 

of the windows is altered by the presence of the curtains.

The curtains may either be anchored at the top and bottom of 

the window frame or anchored at the top only and outfitted with 

a weighted hem. The curtain needs to be extra long, with the surplus either wound around a dynamic tension retainer or stored in 

a reservoir housing. When an explosion occurs, the curtain feeds 

out of the receptacle to absorb the force of the flying glass fragments. The effectiveness of the blast curtains relies on their use 

and no protection is provided when these curtains are pulled away 

from the glazing (see Figure 2-15). 
Structural design criteria 2-37

Figure 2-15

Blast curtain system

Rigid catch bar systems were designed and tested as a means of 

increasing the effectiveness of filmed and laminated window upgrades. Anti-shatter film and laminated glazing are designed to 

hold the glass shards together as the window is damaged; however, 

unless the window frames and attachments are upgraded as well to 

withstand the capacity of the glazing, this retrofit will not prevent 

the entire sheet from flying free of the window frames. The rigid 

catch bars intercept the filmed or laminated glass and disrupt their 

flight; however, they are limited in their effectiveness, tending to 

break the dislodged façade materials into smaller projectiles. 

Rigid catch systems collect huge forces upon impact and require 

considerable anchorage into a very substantial structure to prevent failure. If either the attachments or the supporting structure 

are incapable of restraining the forces, the catch system will be 

dislodged and become part of the debris. Alternatively, the debris 
2-38 Structural design criteria

may be sliced by the rigid impact and the effectiveness of the catch 

bar will be severely reduced. Finally, the effectiveness of debris 

catch systems are limited where double pane, insulated glazing 

units (IGUs) are used. Since anti-shatter film or laminated glass is 

typically applied to only the inner surface of an IGU, debris from 

the damaged outer lite could be blown past the catch bar into the 

protected space.

Flexible catch bars can be designed to absorb a significant amount 

of the energy upon impact, thereby keeping the debris intact 

and impeding their flight. These systems may be designed to 

effectively repel the debris and inhibit their flight into the occupied spaces; they also may be designed to repel the debris from 

the failed glazing as well as the walls in which the windows are 

mounted. The design of the debris restraint system must be strong 

enough to withstand the momentum transferred upon impact 

and the connections must be capable of transferring the forces 

to the supporting slabs and spandrel beams. However, under no 

circumstances can the design of the restraint system add significant amounts of mass to the structure that may be dislodged and 

present an even greater risk to the occupants of the building.

Cables are extensively used to absorb significant amounts of 

energy upon impact and their flexibility makes them easily adaptable to many situations. The diameter of the cable, the spacing 

of the strands, and the means of attachment are all critical in 

designing an effective catch system. These catch cable concepts 

have been used by protective design window manufacturers as 

restraints for laminated lites. The use of cable systems has long 

been recognized as an effective means of stopping massive objects 

moving at high velocity. An analytical simulation or a physical test 

is required to confirm the adequacy of the cable catch system to 

restrain the debris resulting from an explosive event.

High performance energy absorbing cable catcher systems retain glass and frame fragments and limit the force transmitted 

to the supporting structure. These commercially available retrofit products consist of a series of 1⁄4-inch diameter 
Structural design criteria 2-39

stainless steel cables connected with a shock-absorbing device 

to an aluminum box section, which is attached to the jambs, 

the underside of the header, and topside of the sill. The energy 

absorbing characteristics allow the catch systems to be attached 

to relatively weakly constructed walls without the need for additional costly structural reinforcement. To reduce the possibility 

of slicing the laminated glass, the cable may either be sheathed 

in a tube or an aluminum strip may be affixed to the glass directly behind the cable.

2.5.2.3 Internal Partitions. Unreinforced masonry walls provide 

limited protection against airblast due to explosions. When subjected to overload from air blast, brittle unreinforced CMU walls 

will fail and the debris will be propelled into the interior of the 

structure, possibly causing severe injury or death to the occupants. 

This wall type has been prohibited for new construction where 

protection against explosive threats is required. Existing unreinforced CMU walls may be retrofitted with a sprayed-on polymer 

coating to improve their air blast resistance. This innovative retrofit technique takes advantage of the toughness and resiliency 

of modern polymer materials to effectively deform and dissipate 

the blast energy while containing the shattered wall fragments. 

Although the sprayed walls may shatter in a blast event, the elastomer material remains intact and contains the debris.

The blast mitigation retrofit for unreinforced CMU walls consists 

of an interior and optional exterior layer of polyurea applied to 

exterior walls and ceilings (see Figure 2-16). The polyurea provides a ductile and resilient membrane that catches and retains 

secondary fragmentation from the existing concrete block as it 

breaks apart in response to an air blast wave. These fragments, if 

allowed to enter the occupied space, are capable of producing serious injury or death to occupants of the structure.
2-40 Structural design criteria

In lieu of the elastomer, an aramid (Geotextile) debris catching 

system may be attached to the structure by means of plates bolted 

through the floor and ceiling slabs (see Figure 2-17). Similar to 

the elastomer retrofit, the aramid layer does not strengthen the 

wall; instead, it restrains the debris that would otherwise be propelled into the occupied spaces. 

Figure 2-17

Geotextile debris catch 

system

Figure 2-16

Spray-on elastomer coating
Structural design criteria 2-41

Alternatively, an unreinforced masonry wall may be upgraded 

with an application of shotcrete sprayed onto the wall with a 

welded wire fabric. This method supplements the tensile capacity 

of the existing wall and limits the extent of debris that might be 

propelled into the protected space. Steel sections may also be installed up against existing walls to reduce the span and provide an 

alternate load transfer to the floor diaphragms. Load-bearing masonry walls require additional redundancy to prevent the initiation 

of a catastrophic progression of collapse. Therefore, the fragment 

protection that may be provided by a spray-on elasto-polymer, a 

fabric spall shield, or a metal panel must be supplemented with 

structural supports that can sustain the gravity loads in the event 

of excessive wall deformation. The design of stiffened steel-plate 

wall systems to withstand the effects of explosive loading is one 

way of achieving such redundancy and fragment protection. 

These load-bearing wall retrofits require a more stringent design, 

capable of resisting lateral loads and the transfer of axial forces. 

Stiffened wall panels, consisting of steel plates to catch the debris 

and welded tube sections spaced some 3 feet on center to supplement the gravity load carrying capacity of the bearing walls, must 

be connected to the existing floor and ceiling slabs by means of 

base plates and anchor bolt connectors (see Figure 2-18). 

A steel stud wall construction technique may also be used for 

new buildings or the retrofit of existing structures requiring blast 

resistance. Commercially available 18-gauge steel studs may be attached web to web (back to back) and 16-gauge sheet metal may 

be installed outboard of the steel studs behind the cladding (see 

Figure 2-19). While the wall absorbs a considerable amount of 

the blast energy through deformation, its connection to the surrounding structure must develop the large tensile reaction forces. 

In order to prevent a premature failure, these connections should 

be able to develop the ultimate capacity of the stud in tension. 

Ballistic testing of various building cladding materials requires a 

nominal 4-inch thickness of stone, brick, masonry, or concrete. 

Forced entry protection requires a 1⁄4-inch thick layer of A36 steel 

plate that is behind the building’s veneer and welded or screwed 

to the steel stud framing in lieu of the 16-gauge sheet metal. 
2-42 Structural design criteria

Figure 2-18 

Stiffened wall panels
Structural design criteria 2-43

Internal installations require an interstitial sheathing of 1⁄2-inch 

A36 steel plate. Regardless whether a 1⁄4-inch steel plate or a 16-

gauge sheet metal is used, the interior face of the stud should be 

finished with a steel-backed composite gypsum board product.

Figure 2-19 Metal stud blast wall
2-44 Structural design criteria

2.5.2.4 Structural Upgrades. Conventionally designed columns 

may be vulnerable to the effects of explosives, particularly when 

placed in contact with their surface. Stand-off elements, in the 

form of partitions and enclosures, may be designed to guarantee 

a minimum stand-off distance; however, this alone may not be 

sufficient. Additional resistance may be provided to reinforced 

concrete structures by means of a steel jacket or a carbon fiber 

wrap that effectively confines the concrete core, thereby increasing the confined strength and shear capacity of the column, 

and holds the rubble together to permit it to continue carrying 

the axial loads (see Figure 2-20). The capacity of steel flanged 

columns may be increased with a reinforced concrete encasement 

that adds mass to the steel section and protects the relatively thin 

flange sections. The details for these retrofits must be designed to 

resist the specific weight of explosives and stand-off distance.

Figure 2-20 

Steel jacket retrofit detail

1" Clear space 

around columns

filled with 5,000 psi

non-shrink grout

Chip corners 1"

and grind 

smooth 

1" Radius 

bent plate Sand blast concrete 

Concrete 

surfaces prior to

jacketing 

3/8" Steel jacket 
Structural design criteria 2-45

2.5.3 Checklist for Retrofitting Issues

A Building Vulnerability Assessment Checklist was developed for 

FEMA 426 and FEMA 452 to help identify structural conditions 

that may suffer in response to blast loading. Each building in 

consideration needs to be evaluated by a professional engineer, 

experienced in the protective design of structures, to determine 

the ability to withstand blast loading. 

In addition, the following questions will help address key retrofitting issues. Issues related to the retrofitting of existing refuge 

areas (e.g., hallways/corridors, bathrooms, workrooms, laboratory 

areas, kitchens, and mechanical rooms) that should be considered 

include the following:

m The roof system. Is the roof system over the proposed 

refuge area structurally independent of the remainder of 

the building? If not, is it capable of resisting the expected 

blast, wind, and debris loads? Are there openings in the roof 

system for mechanical equipment or lighting that cannot be 

protected during a blast or high-wind event? It may not be 

reasonable to retrofit the rest of the proposed shelter area if 

the roof system is part of a building that was not designed for 

high-wind load requirements.

m The wall system. Can the wall systems be accessed so that 

they can be retrofitted for resistance to blast and high-wind 

pressures and missile impact? It may not be reasonable to 

retrofit a proposed shelter area to protect openings if the 

wall systems (load-bearing or non-load-bearing) cannot 

withstand blast and wind pressures or cannot be retrofitted in 

a reasonable manner to withstand blast or wind pressures and 

missile impacts.

m Openings. Are the windows and doors vulnerable to blast and 

wind pressures and debris impact? Are doors constructed of 

impact-resistant materials (e.g., steel doors) and secured with 

six points of connection (typically three hinges and three 
2-46 Structural design criteria

latching mechanisms)? Are door frames constructed of at least 

16-gauge metal and adequately secured to the walls to prevent 

the complete failure of the door/frame assemblies? Does the 

building rely on shutter systems for resistance to the effects of 

hurricanes? There is often only minimal warning time before 

a CBRE or tornado event; therefore, a shelter design that 

relies on manually installed shutters is impractical. Automated 

shutter systems may be considered, but they would require a 

protected backup power system to ensure that the shutters are 

closed before an event. 

2.6 SHELTERS AND MODEL BUILDING TYPES

This section will provide basic FEMA model building types to 

describe protective design and structural systems for shelters in 

the most effective manner. This section is based on FEMA 310, 

Handbook for the Seismic Evaluation of Buildings, which is dedicated 

to instructing the design professional on how to determine if a 

building is adequately designed and constructed to resist particular 

types of forces. Graphics included in this section were prepared for 

FEMA 454, Designing for Earthquakes: A Manual for Architects.

2.6.1 W1, W1a, and W2 Wood Light Frames 

and Wood Commercial Buildings

Small wood light frame buildings (<3,000 square feet) are single 

or multiple family dwellings of one or more stories in height (see 

Figure 2-21). Building loads are light and the framing spans are 

short. Floor and roof framing consists of closely spaced wood joists 

or rafters on wood studs. The first floor framing is supported directly on the foundation, or is raised up on cripple studs and post 

and beam supports. The foundation consists of spread footings 

constructed of concrete, concrete masonry block, or brick masonry in older construction. Chimneys, when present, consist of 

solid brick masonry, masonry veneer, or wood frame with internal 

metal flues. Lateral forces are resisted by wood frame diaphragms 

and shear walls. Floor and roof diaphragms consist of straight or 

diagonal wood sheathing, tongue and groove planks, or plywood. 
Structural design criteria 2-47

Shearwalls consist of straight or diagonal wood sheathing, plank 

siding, plywood, stucco, gypsum board, particle board, or fiberboard. Interior partitions are sheathed with plaster or gypsum 

board.

Large wood light frame buildings (> 3,000 square feet) are 

multi-story, multi-unit residences similar in construction to W1 

buildings, but with open front garages at the first story (see Figure 

2-22). The first story consists of wood floor framing on wood stud 

walls and steel pipe columns, or a concrete slab on concrete or 

concrete masonry block walls.

Wood commercial or industrial buildings with a floor area of 5,000 

square feet or more carry heavier loads than light frame construction (see Figure 2-23). In these buildings, the framing spans are 

long and there are few, if any, interior walls. The floor and roof 

framing consists of wood or steel trusses, glulam or steel beams, 

and wood posts or steel columns. Lateral forces are resisted by 

wood diaphragms and exterior stud walls sheathed with plywood, 

Figure 2-21

W1 wood light frame 

< 3,000 square feet
2-48 Structural design criteria

stucco, plaster, straight or diagonal wood sheathing, or braced 

with rod bracing. Large openings for storefronts and garages, 

when present, are framed by post-and-beam framing. Lateral force 

resistance around openings is provided by steel rigid frames or diagonal bracing. 

Figure 2-22 

W1a wood light frame 

> 3,000 square feet
Structural design criteria 2-49

Figure 2-23

W2 wood commercial 

buildings

Light wood frame structures do not possess significant resistance 

to blast loads although larger wood commercial buildings will be 

better able to accept these lateral loads than light frame wood 

construction. These buildings are likely to suffer heavy damage 

in response to 50 pounds of TNT at a stand-off distance of 20 to 

50 feet. A shelter would best be located in a basement where the 

protection to blast loading would be provided by the surrounding 

soil. Large explosive detonations in close proximity to the 

building will not only destroy the superstructure, but the effects of 

ground shock are likely to fail the foundation walls as well; therefore, protected spaces should be located interior to the building. 

Locating the shelter on the ground floor, for slab on grade structures, provides the maximum number of floors between occupants 

and possible roof debris. Debris catch systems may be installed 

beneath roof rafters of single-story buildings; however, the effectiveness of the debris catch system will be limited if the zone of 

roof damage is extensive.
2-50 Structural design criteria

Metal stud blast walls built within the existing building may be 

used to supplement the enclosure; however, in order for these 

walls to develop their resistance to lateral loads, they must be anchored to an existing structure. Windows enclosing the selected 

shelter must either be laminated or treated with an anti-shatter 

film. Either the laminated glass or the anti-shatter film should 

be anchored to the surrounding wall with a system that can develop but not overwhelm the capacity of the wall. A conservative 

estimate of the ultimate capacity of an existing wall may be determined, in the absence of actual design information, by scaling the 

code specified wind pressures with the appropriate factor of safety. 

2.6.2 S1, S2, and S3 Steel Moment Frames, 

Steel Braced Frames, and Steel Light 

Frames 

Steel moment frame and braced frame buildings with cast-inplace concrete slabs or metal deck with concrete fill supported 

on steel beams, open web joists, or steel trusses are well suited 

for a hardened shelter construction. Lateral forces in steel 

moment frame buildings are resisted by means of rigid or semirigid beam-column connections (see Figure 2-24). When all 

connections are moment-resisting connections, the entire frame 

participates in lateral force resistance. When only selected 

connections are moment-resisting connections, resistance is provided along discrete frame lines. Columns are oriented so that 

each principal direction of the building has columns resisting 

forces in strong axis bending. Diaphragms consist of concrete or 

metal deck with concrete fill and are stiff relative to the frames. 

Walls may consist of metal panel curtainwalls, glazing, brick 

masonry, or precast concrete panels. When the interior of the 

structure is finished, frames are concealed by ceilings, partition 

walls, and architectural column furring. Foundations consist of 

concrete spread footings or deep pile foundations.

Lateral forces in steel braced frame buildings are resisted by 

tension and compression forces in diagonal steel members (see 

Figure 2-25). When diagonal brace connections are concentric to 
Structural design criteria 2-51

beam column joints, all member stresses are primarily axial. When 

diagonal brace connections are eccentric to the joints, members 

are subjected to bending and axial stresses. Diaphragms consist of 

concrete or metal deck with concrete fill and are stiff relative to 

the frames. Walls may consist of metal panel curtainwalls, glazing, 

brick masonry, or precast concrete panels. When the interior of 

the structure is finished, frames are concealed by ceilings, partition walls, and architectural furring. Foundations consist of 

concrete spread footings or deep pile foundations.

Figure 2-24

S1steel moment frames
2-52 Structural design criteria

Light frame steel structures are pre-engineered and prefabricated 

with transverse rigid steel frames (see Figure 2-26). They are onestory in height and the roof and walls consist of lightweight metal, 

fiberglass, or cementitious panels. The frames are designed for 

maximum efficiency and the beams and columns consist of tapered, built-up sections with thin plates. The frames are built in 

segments and assembled in the field with bolted or welded joints. 

Lateral forces in the transverse direction are resisted by the rigid 

frames. Lateral forces in the longitudinal direction are resisted by 

wall panel shear elements or rod bracing. Diaphragm forces are 

resisted by untopped metal deck, roof panel shear elements, or a 

system of tension-only rod bracing.

Figure 2-25

S2 steel braced frames
Structural design criteria 2-53

Steel moment frame structures provide excellent ductility and 

redundancy in response to blast loading. Steel braced frames may 

similarly be designed to resist high intensity blast loads; however, 

they are less effective in resisting the progression of collapse following the loss of a primary load-bearing element. As a result, 

first floor steel columns of existing buildings may be concrete 

encased and first floor splices may be reinforced to increase their 

resistance to local failure that could precipitate a progression of 

collapse. The exterior façade represents the most fragile element 

and is likely to be severely damaged in response to an exterior 

detonation. Debris may be minimized by means of reinforced 

masonry, sufficiently detailed precast panels, or laminated glass 

façade. Nevertheless, a shelter within steel frame buildings would 

best be located within interior space or a building core. Hardened 

interior partitions may easily be constructed and anchored to existing floor slabs, and lightweight metal gauge walls may be used 

to retrofit existing buildings. Metal deck roofs with rigid insulation supported by bar joist structural elements possess minimal 

Figure 2-26

S3 steel light frames
2-54 Structural design criteria

resistance to blast pressures. The additional mass, stiffness, and 

strength of metal deck roofs with concrete fill make them much 

better able to resist the effects of direct blast loading and the subsequent rebound. Therefore, lightweight roofs of light frame steel 

structures are likely to be severely damaged in response to any 

sizable blast loading and a shelter should either be located in the 

basement or as interior to the building (as far from the exterior 

façade) as possible.

2.6.3 S4 and S5 Steel Frames with Concrete 

Shearwalls and Infill Masonry Walls 

Steel frame buildings with concrete or infill masonry shear walls 

with cast-in-place concrete slabs or metal deck with concrete fill 

supported on steel beams, open web joists, or steel trusses are 

well suited for a hardened shelter construction. When lateral 

forces are resisted by cast-in-place concrete shear walls, the walls 

carry their own weight. In older construction, the steel frame is 

designed for vertical loads only. In modern dual systems, the steel 

moment frames are designed to work together with the concrete 

shear walls in proportion to their relative rigidity (see Figure 

2-27). In the case of a dual system, the walls should be evaluated 

under this building type and the frames should be evaluated 

under S1 steel moment frames. Diaphragms consist of concrete 

or metal deck with or without concrete fill. The steel frame may 

provide a secondary lateral-force-resisting system, depending on 

the stiffness of the frame and the moment capacity of the beamcolumn connections.
Structural design criteria 2-55

Steel frames with infill masonry walls is an older type of building 

construction (see Figure 2-28). The walls consist of infill panels 

constructed of solid clay brick, concrete block, or hollow clay tile 

masonry. Infill walls may completely encase the frame members, 

and present a smooth masonry exterior with no indication of the 

frame. The lateral resistance of this type of construction depends 

on the interaction between the frame and infill panels. The combined behavior is more like a shear wall structure than a frame 

structure. Solidly infilled masonry panels form diagonal compression struts between the intersections of the frame members. If the 

walls are offset from the frame and do not fully engage the frame 

Figure 2-27

S4 steel frames with 

concrete shearwalls
2-56 Structural design criteria

members, the diagonal compression struts will not develop. The 

strength of the infill panel is limited by the shear capacity of the 

masonry bed joint or the compression capacity of the strut. The 

post-cracking strength is determined by an analysis of a moment 

frame that is partially restrained by the cracked infill. The diaphragms consist of concrete floors and are stiff relative to the walls.

Figure 2-28 

S5 steel frames with infill 

masonry walls

Steel frame structures with either concrete shear walls or infill 

masonry walls are not moment connected; therefore, the frame is 

more vulnerable to collapse resulting from the loss of a column. 

As a point of reference, steel moment frame buildings with lightly 

reinforced CMU infill walls are likely to suffer heavy damage in 
Structural design criteria 2-57

response to 500 pounds of TNT at a stand-off distance of 50 feet 

or less. The first floor steel columns of existing buildings may 

be concrete encased and first floor splices may be reinforced to 

increase their resistance to local failure that could precipitate a 

progression of collapse. The exterior façade is likely to be damaged in response to an exterior detonation and debris may be 

minimized by means of reinforced masonry, sufficiently detailed 

precast panels, or laminated glass façade. Nevertheless, a shelter 

within these buildings would best be located within interior space 

or a building core, preferably enclosed on one or more sides by 

the shear walls. Existing masonry infill walls may be retrofitted 

to supplement existing reinforcement by either grouting cables 

within holes cored within the walls or with a spray-on application 

of a shotcrete and welded wire fabric or a polyurea debris catch 

membrane. Alternatively, hardened interior partitions may easily 

be constructed and anchored to existing floor slabs, and lightweight metal stud walls may be used to retrofit existing buildings. 

2.6.4 C1, C2, and C3 Concrete Moment 

Frames, Concrete and Infill Masonry 

Shearwalls – Type 1 Bearing Walls and 

Type 2 Gravity Frames

These buildings consist of a frame assembly of cast-in-place 

concrete beams and columns. Floor and roof framing consists 

of cast-in-place concrete slabs, concrete beams, one-way joists, 

two-way waffle joists, or flat slabs. Lateral forces are resisted by 

concrete moment frames that develop their stiffness through 

monolithic beam-column connections (see Figure 2-29). In 

older construction, or in regions of low seismicity, the moment 

frames may consist of the column strips of two-way flat slab systems. Modern frames in regions of high seismicity have joint 

reinforcing, closely spaced ties, and special detailing to provide 

ductile performance. This detailing is not present in older construction. Foundations consist of concrete spread footings or 

deep pile foundations.
2-58 Structural design criteria

Concrete and infill masonry shearwall building systems have 

floor and roof framing that consists of cast-in-place concrete 

slabs, concrete beams, one-way joists, two-way waffle joists, or flat 

slabs. Floors are supported on concrete columns or bearing walls. 

Lateral forces are resisted by cast-in-place concrete shear walls 

or infill panels constructed of solid clay brick, concrete block, 

or hollow clay tile masonry (see Figures 2-30, 2-31, and 2-32). In 

older construction, cast-in-place shear walls are lightly reinforced, 

but often extend throughout the building. In more recent construction, shear walls occur in isolated locations and are more 

heavily reinforced with boundary elements and closely spaced ties 

Figure 2-29 

C1 concrete moment 

frames
Structural design criteria 2-59

to provide ductile performance. The diaphragms consist of concrete slabs and are stiff relative to the walls. Foundations consist 

of concrete spread footings or deep pile foundations. The seismic 

performance of infill panel construction depends on the interaction between the frame and infill panels. The combined behavior 

is more like a shear wall structure than a frame structure. If the 

infilled masonry panels are in line with the frame, they form diagonal compression struts between the intersections of the frame 

members; otherwise, the diagonal compression struts will not 

develop. The strength of the infill panel is limited by the shear 

capacity of the masonry bed joint or the compression capacity of 

the strut. The post-cracking strength is determined by an analysis 

of a moment frame that is partially restrained by the cracked infill. 

The shear strength of the concrete columns, after cracking of the 

infill, may limit the semiductile behavior of the system. 

Figure 2-30 

C2 concrete shearwalls 

– type 1 bearing walls
2-60 Structural design criteria

Figure 2-31

C2 concrete shearwalls 

– type 2 gravity frames
Structural design criteria 2-61

Unless sited in a seismic zone, concrete frame structures are not 

typically designed and detailed to develop large inelastic deformations and withstand significant load reversals. As a point of 

reference, a building with 8-inch thick reinforced concrete loadbearing exterior walls and interior columns is likely to suffer heavy 

damage in response to 500 pounds of TNT at a distance of 70 feet 

or less. The exterior façade is likely to be damaged in response to 

an exterior detonation and debris may be minimized by means of 

reinforced masonry, sufficiently detailed precast panels, or laminated glass façade. Nevertheless, a shelter within concrete frame 

and shearwall buildings would best be located within interior 

space or a building core, preferably enclosed on one or more sides 

Figure 2-32 

C3 concrete frames with 

infill masonry shearwalls
2-62 Structural design criteria

by the shear walls. Existing masonry infill walls may be retrofitted 

to supplement existing reinforcement by either grouting cables 

within holes cored within the walls or with a spray-on application of 

a shotcrete and welded wire fabric or a polyurea debris catch membrane. Alternatively, hardened interior partitions may easily be 

constructed and anchored to existing floor slabs, and lightweight 

metal stud walls may be used to retrofit existing buildings. 

2.6.5 PC1 and PC2 Tilt-up Concrete Shearwalls 

and Precast Concrete Frames and 

Shearwalls

Tilt-up concrete buildings are one or more stories in height and 

have precast concrete perimeter wall panels that are cast on site 

and tilted into place (see Figure 2-33). Floor and roof framing 

consists of wood joists, glulam beams, steel beams, open web 

joists, or precast plank sections. Framing is supported on interior 

steel or concrete columns and perimeter concrete bearing walls. 

The floors consist of wood sheathing, concrete over form deck, 

or composite concrete slabs. Roofs are typically untopped metal 

deck, but may contain lightweight concrete fill. Lateral forces are 

resisted by the precast concrete perimeter wall panels. Wall panels 

may be solid, or have large window and door openings that cause 

the panels to behave more as frames than as shear walls. In older 

construction, wood framing is attached to the walls with wood ledgers. Foundations typically consist of concrete spread footings or 

deep pile foundations.
Structural design criteria 2-63

Precast concrete frames and shearwalls consist of precast concrete 

planks, tees, or double-tees supported on precast concrete girders 

and precast columns (see Figure 2-34). Lateral forces are resisted 

by precast or cast-in-place concrete shear walls. Diaphragms 

consist of precast elements interconnected with welded inserts, 

cast-in-place closure strips, or reinforced concrete topping slabs.

Figure 2-33

PC1 tilt-up concrete 

shearwalls
2-64 Structural design criteria

Precast construction benefits from higher quality wall and frame 

components than cast-in-place structures; however, it lacks the 

continuity of construction present in these systems. The resistance blast loading depends, to a great extent, on the mechanical 

connections between the components. Designers must consider 

the blast loading effects when designing and detailing these connections. A shelter would best be located in a basement where 

the protection to blast loading would be provided by the surrounding soil. Large explosive detonations in close proximity 

to the building will not only destroy the superstructure, but the 

effects of ground shock are likely to fail the foundation walls as 

well; therefore, protected spaces should be located interior to the 

Figure 2-34

PC2 precast concrete 

frames and shearwalls
Structural design criteria 2-65

building. Locating the shelter in the basement, for slab on grade 

buildings, provides the maximum number of floors between occupants and possible roof debris. Debris catch systems may be 

installed beneath roof rafters of single-story buildings; however, 

the effectiveness of the debris catch system will be limited if the 

zone of roof damage is extensive.

Metal stud blast walls built within the existing building may be 

used to supplement the enclosure; however, in order for these 

walls to develop their resistance to lateral loads, they must be anchored to an existing structure. Windows enclosing the selected 

shelter must either be laminated or treated with an anti-shatter 

film. Either the laminated glass or the anti-shatter film should 

be anchored to the surrounding wall with a system that can develop, but not overwhelm the capacity of the wall. A conservative 

estimate of the ultimate capacity of an existing wall may be determined, in the absence of actual design information, by scaling the 

code specified wind pressures with the appropriate factor of safety. 

2.6.6 RM1 and RM2 Reinforced Masonry 

Walls with Flexible Diaphragms or Stiff 

Diaphragms and Unreinforced Masonry 

(URM) Load-bearing Walls

These buildings have bearing walls that consist of reinforced brick 

or concrete block masonry. Wood floor and roof framing consists of wood joists, glulam beams, and wood posts or small steel 

columns. Steel floor and roof framing consists of steel beams or 

open web joists, steel girders, and steel columns. Lateral forces are 

resisted by the reinforced brick or concrete block masonry shear 

walls. Diaphragms consist of straight or diagonal wood sheathing, 

plywood, or untopped metal deck, and are flexible relative to the 

walls (see Figure 2-35). Foundations consist of brick or concrete 

spread footings.
2-66 Structural design criteria

Buildings with reinforced masonry walls and stiff diaphragms are 

similar to RM1 buildings, except the diaphragms consist of metal 

deck with concrete fill, precast concrete planks, tees, or doubletees, with or without a cast-in-place concrete topping slab, and 

are stiff relative to the walls (see Figure 2-36). The floor and roof 

framing is supported on interior steel or concrete frames or interior reinforced masonry walls.

Figure 2-35

RM1 reinforced masonry 

walls with flexible 

diaphragms
Structural design criteria 2-67

Unreinforced load-bearing masonry buildings often contain 

perimeter bearing walls and interior bearing walls made of clay 

brick masonry (see Figure 2-37). In older construction, floor and 

roof framing consists of straight or diagonal lumber sheathing 

supported by wood joists, on posts and timbers. In more recent construction, floors consist of structural panel or plywood 

sheathing rather than lumber sheathing. The diaphragms are 

flexible relative to the walls. When they exist, ties between the 

walls and diaphragms consist of bent steel plates or government 

anchors embedded in the mortar joints and attached to framing. 

Foundations consist of brick or concrete spread footings. As a 

variation, some URM buildings have stiff diaphragms relative to 

the unreinforced masonry walls and interior framing. In older construction or large, multi-story buildings, diaphragms may consist of 

Figure 2-36

RM2 reinforced masonry 

walls with stiff diaphragms
2-68 Structural design criteria

cast-in-place concrete. In regions of low seismicity, more recent 

construction consists of metal deck and concrete fill supported 

on steel framing.

Figure 2-37

URM load-bearing walls 

Unless sited in a seismic zone, reinforced masonry structures 

are not typically detailed to develop significant inelastic deformations and withstand significant load reversals. Unreinforced 

masonry structures are extremely brittle. As a point of reference, 

a reinforced masonry building with 8-inch thick reinforced CMU 

exterior walls is likely to suffer heavy damage in response to 500 

pounds of TNT at a distance of 150 feet or less. An unreinforced 

masonry building with reinforced CMU pilasters will suffer heavy 
Structural design criteria 2-69

damage in response to 500 pounds of TNT at a distance of 250 

feet or less. At these loads, the structure supported by the loadbearing masonry wall is likely to suffer localized collapse. Grout 

and additional reinforcement may be inserted within the cores of 

existing masonry walls; however, a stiffened steel panel provides 

the most effective way to restrain the debris and assume the gravity 

loads following the loss of load carrying capacity within the wall. 

A shelter within these buildings would best be located within interior space or a building core, preferably enclosed on one or more 

sides by the shear walls. 

2.6.7 Conclusions

Despite the various types of construction, the following protective 

measures may be used to establish a hardened space that will limit 

the extent of debris resulting from an explosive event. A shelter is 

best located within interior space or a building core at the lowest 

levels of a building or on the ground floor for a slab on grade 

structure. A debris catch system should be installed beneath the 

roof rafters of a single-story building. The exterior façade should 

be either reinforced masonry or precast panels and windows 

should either be laminated or treated with an anti-shatter film 

that is anchored to the surrounding walls. First floor steel columns 

may be concrete encased and first floor splices may be reinforced. 

Existing masonry infill walls may be retrofitted by either grouting 

cables within holes cored within the walls or with a spray-on application of a shotcrete and welded wire fabric or a polyurea debris 

catch membrane. Hardened interior partitions, such as metal 

stud blast walls, may be used to enclose the shelter and these walls 

should be anchored to an existing structure. A stiffened steel 

panel may be constructed interior to existing load-bearing masonry walls. 

2.7 CASE STUDY: BLAST-RESISTANT SAFE

ROOM

Consider the example of a safe room established in the stairwell of 

a multi-story office building: it may be assumed the original 
2-70 Structural design criteria

construction did not provide for reinforced masonry or reinforced concrete enclosures. To achieve the greatest stand-off 

distance and isolate the safe room from a vehicle-borne explosive 

threat, the stairwell should be interior to the structure. This will 

provide the maximum level of protection from an undefined 

explosive threat. Although it is common to place emergency 

stairs within the building core, one can only reasonably expect a 

reinforced concrete or reinforced masonry stair enclosure for a 

shearwall lateral resisting structural system. Due to the large difference in weight and constructability, a stud wall with gypsum 

board stair enclosure will be routinely used in lieu of reinforced 

masonry or concrete for framed construction. The stair enclosures may therefore be designed or upgraded to include 16-gauge 

sheet metal supported by 18-gauge steel studs that are attached 

web to web (back to back). These walls must be adequately anchored to the existing floor slabs to develop the plastic capacity of 

the studs acting both in flexure and in tension. Alternatively, fully 

grouted reinforced masonry stairwell enclosures, #4 bars in each 

cell, may be specified. The masonry walls must be adequately anchored to the existing floor slabs to develop the ultimate lateral 

resistance of the wall in order to transfer the reaction loads into 

the lateral resisting system of the building. Doors to the stairway 

enclosures are to be hollow steel or steel clad, such as 14-gauge 

steel doors with 20-gauge ribs, with pressed steel frames; double 

doors should utilize a center stile. Doors should open away from 

the safe room and be securely anchored to the wall construction, 

locally reinforced around the door. 

Any windows within the stairwell enclosures are to contain 

laminated glass, utilizing 0.060 PVB, that is adhered within the 

mullions with a 1⁄2-inch bead of structural silicone. The mullions are to be anchored into the surrounding walls to develop 

the full capacity of the glazing materials. Alternatively, a 7-mil 

anti-shatter film may be applied to existing windows and mechanically attached to the surrounding mullions to develop the 

full capacity of the film. A wet glazed attachment of the film may 

alternatively be applied; however, this provides a less reliable 

bond to the existing mullions.
Structural design criteria 2-71

Floor slabs within an interior stairwell will be isolated from the 

most direct effects of an exterior explosive event and will not be 

subjected to significant uplift pressures resulting from an exterior 

explosive event. Nevertheless, for new construction, floor slabs 

should be designed to withstand a net upward load of magnitude 

equal to the dead load plus half the live load for the floor system. 

For new construction, the structural frames are to be sufficiently 

tied as to provide alternate load paths to surrounding columns or 

beams in the event of localized damage. These tie forces should, 

at a minimum, conform to the DoD Unified Facilities Criteria 

(UFC) 4-023-03, Design of Buildings to Prevent Progressive Collapse. 

For reinforced concrete structures, seismic hooks and seismic 

development lengths, as specified in Chapter 21 of the American 

Concrete Institute (ACI) 318-05, should be used to anchor and 

develop steel reinforcement. Internal tie reinforcement should 

be distributed in two perpendicular directions and be continuous 

from one edge of the floor or roof to the far edge of the floor or 

roof, using lap splices, welds, or mechanical splices. In order to 

redistribute the forces that may develop, the internal ties must 

be anchored to the peripheral ties at each end (see Figure 2-38). 

Steel structures must be similarly tied, and each column must 

be effectively held in position by means of horizontal ties in two 

orthogonal directions at each principal floor level supported by 

that column.
2-72 Structural design criteria

Figure 2-38 Schematic of tie forces in a frame structure

Internal ties (dotted lines)

Horizontal tie to column 

Vertical tie

Peripheral ties 

(dashed lines)
CBR THreat protection 3

CBR Threat protection 3-

3.1 OVERVIEW 

T his chapter describes how to add CBR protection capability 

to a shelter or safe room. 

A CBR safe room protects its occupants from contaminated 

air outside it by providing clean, breathable air in two ways: (1) 

by trapping air inside the room and minimizing the air exchange 

(an unventilated safe room) and (2) by passing contaminated air 

through a filter to purify it as it is supplied to the room (a ventilated safe room).

Unventilated safe rooms that are tightly sealed cannot be occupied for long periods without the risk of high carbon dioxide 

levels. This constraint does not apply to ventilated safe rooms, 

which can be designed to provide filtered and conditioned fresh 

air at any desired rate. Ventilated safe rooms can therefore be 

used on a routine basis, although most are designed as standby systems, not for continuous, routine use.

Obtaining protection from an unventilated safe room can be as 

simple as selecting a relatively tight room, entering it, and closing 

the door. This procedure is commonly referred to as expedient 

sheltering-in-place. In this simple form, a safe room protects its 

occupants by retaining a volume of clean air and minimizing the 

infiltration of contaminated outdoor air. In practice, however, a 

safe room is not perfectly tight. The natural forces of wind and 

buoyancy act on small, distributed leakage paths to exchange air 

between the inside and outside. 

As contaminated air infiltrates a safe room, the level of protection 

to the occupants diminishes with time. With infiltration in a sustained exposure, the concentration of toxic vapor, gas, or aerosol 

in the safe room may actually exceed the concentration outdoors 

because the sealed safe room tends to retain the airborne 
3- CBR Threat protection

contaminants when they infiltrate. Once contaminants have 

entered, they are released slowly after the outdoor hazard has 

passed. To minimize the hazard of this retention, an unventilated 

safe room requires two actions to achieve protection: 

m The first is to tighten the safe room, to reduce the indooroutdoor air exchange rate, before the hazardous plume 

arrives. This is done by closing doors and windows and turning 

off fans, air conditioners, and combustion heaters. 

m The second is to aerate, to increase the indoor-outdoor air 

exchange rate as soon as the plume has passed. This is done 

by opening doors and windows and turning on all fans and/or 

exiting the building into clean outdoor air. 

The protection a safe room provides can be increased substantially by adding high-efficiency air filtration. Filtration is employed 

in two different ways to remove contaminants from the air as it 

enters the safe room or to remove contaminants as air is circulated within the room. 

The two ways of incorporating filtration, or 

not incorporating it at all, yield three general 

configurations or classes of safe rooms, designated Classes 1, 2, and 3. Table 3-1 shows 

these three classes and summarizes their advantages and limitations. A common element 

of all three is a tight enclosure. The three 

classes differ in whether/how air filtration is 

applied, resulting in differences in cost, level 

of protection, and duration of protection. 

m Class 1. In a Class 1 Safe Room, air is drawn from outside 

the room, filtered, and discharged inside the room at a rate 

sufficient to produce an internal pressure. The safe room is 

thus ventilated with filtered air, eliminating the constraints 

related to carbon dioxide accumulation. The internal pressure 

produced with filtered air prevents infiltration of outside air 

through leakage paths. 

When planning to use sheltering as a 

protective action from a CBR release, it is 

important to consider when the sheltering 

process should end. Sheltering provides 

protection by reducing the airflow from 

the outside that could contain potentially 

contaminated air. However, some leakage 

into the shelter may occur and air inside 

the shelter may reach unacceptable levels 

of contamination. It is important to leave the 

shelter when the threat outside has passed.
CBR Threat protection 3-

m Class 2. This class also includes air filtration, but with little 

or no internal pressure. Without positive pressure, the safe 

room does not prevent the infiltration of contaminated air. 

A Class 2 Safe Room may be ventilated or unventilated. In an 

unventilated Class 2 Safe Room, air is drawn from inside the 

safe room, filtered, and discharged inside it. In a ventilated 

Class 2 Safe Room, air is drawn from outside but at a flow rate 

too small to create a measurable differential pressure. 

m Class 3. This class has no air-filtering capability and is 

unventilated. It is a basic safe room that derives protection only 

by retained clean air within its tight enclosure. Use of the Class 

3 Safe Room is commonly referred to as sheltering-in-place. 

The Class 1 Safe Room provides the highest level of protection for 

most chemicals, but the lowest level of protection for those chemicals that are not filterable. It is also the most expensive option. Its 

disadvantage is that it does not protect against a limited number 

of toxic gases that cannot be filtered by conventional gas filters/

adsorbers. 

Although the Class 2 Safe Room employs air filters, it does not 

prevent the infiltration of outdoor air driven by natural forces 

Table 3-1: Comparison of the Three General Classes of Toxic-agent Safe Rooms

Class Protection Cost Advantages and Limitations

1. Ventilated and 

pressurized with 

filtered air

high high

Protection has no time limits, but it provides no 

protection against some toxic chemicals of high 

vapor pressure.

2. Filtration with 

little or no 

pressurization

medium medium

Unventilated Class 2 is protective against all gases, 

but protection diminishes with duration of exposure 

(and against non-filterable gases). 

3. Unventilated, no 

filtration low low

Protective against all agents, but protection 

diminishes with time of exposure. Carbon dioxide 

buildup may limit time in the shelter.
3- CBR Threat protection

of wind and buoyancy. It therefore provides a lower level of 

protection than a Class 1. If exposed to an unfilterable gas, the 

unventilated Class 2 Safe Room retains a level of protection 

provided by the sealed enclosure. The unventilated Class 2 Safe 

Room would thus not have a complete loss of protection as could 

occur with the gas penetrating the filter of a Class 1 or Class 2 

ventilated Safe Room. 

The Class 3 Safe Room, with no air filtration, is the simplest 

and lowest in cost. It can be prepared with permanent sealing 

measures or with the quick application of expedient sealing techniques such as applying duct tape over the gap at the bottom of 

the door or over the bathroom exhaust fan grille. The disadvantage is that there is no intentional ventilation; therefore, this class 

of safe room cannot conform to ventilation requirements of other 

types of emergency shelters. 

Most safe rooms are designed as standby systems; that is, certain 

actions must be taken to make them protective when a hazardous 

condition occurs or is expected. They do not provide protection 

on a continuous basis. Merely tightening a room or weatherizing a 

building does not increase the protection to the occupants. Making 

the safe room protective requires turning off fans, air conditioners, 

and combustion heaters as well as closing doors and windows. It 

may also involve closing off supply, return, or exhaust ducts or 

temporarily sealing them with duct tape. In a residence, taking 

these actions is relatively simple and can be done quickly. In an office building, doing so usually requires more time and planning, 

as there may be several switches for air-handling units and exhaust 

fans, which may be at diverse locations around the building. 

Unventilated safe rooms have been widely used in shelteringin-place to protect against accidental releases of industrial 

chemicals. Local authorities make the decision on whether to 

shelter-in-place or evacuate based on conditions, the likely duration of the hazard, and the time needed to evacuate. Although 

sheltering-in-place (i.e., use of an unventilated safe room) is applicable for relatively short durations, experience shows that it 
CBR Threat protection 3-

may be necessary for people to occupy safe rooms for longer periods as a precautionary measure. 

The potential for safe room stays of longer duration make it important to consider human factors in designing and planning 

safe rooms. Human factors considerations include ventilation, 

environmental control, drinking water, toilets, lighting, and communications. 

3.2 HOW AIR FILTRATION AFFECTS 

PROTECTION

The addition of air filtering improves the protection a safe room 

provides, although there are limitations as to what gases can be 

filtered. Ventilation with filtered air also removes the time constraints associated with unventilated shelters. 

To protect against the many gases, vapors, and aerosols that could 

be released in an accident or terrorist act requires three different 

filtering processes. Mechanical filtration is most commonly used 

for aerosols; physical adsorption, for chemical agents of low vapor 

pressure; and chemisorption, for chemical agents of high vapor 

pressure. These three processes can be provided by a combination of two types of filters: the HEPA filter to remove aerosols 

and a high-efficiency gas adsorber with impregnated carbon to 

remove vapors and gases. A filter system for a safe room must 

contain at least one HEPA and one gas adsorber in series, with 

the HEPA normally placed first in the flow stream. 

HEPA adequately removes all toxic aerosols, including sub-micron size biological agents. A gas adsorber works for most, but not 

all gases/vapors. Several of the common industrial gases, such as 

ammonia, are not removed by the best broad-spectrum impregnated carbon available. 

To protect against highly toxic chemicals, a Class 1 system 

requires ultra high-efficiency filtration, at least 99.999 percent removal in a single pass. HEPA filters, which are defined as having 
3- CBR Threat protection

at least 99.97 percent efficiency against the most penetrating 

particle size (about 0.3 micron), have efficiencies greater than 

99.999 percent against aerosols of 1- to 10-micron size, the most 

likely size range for biological-agent aerosols. 

With a filtration system drawing outside air, the level of protection the safe room provides is a function of the filter efficiency. 

With an unventilated Class 2 system, the level of protection is not 

affected as greatly by changes in filter efficiency. For example, 

increasing filter efficiency from 99 percent to 99.999 percent in 

an unventilated Class 2 system improves the protection factor by 

about 1 percent. The same change in a Class 1 system yields a protection factor 1,000 times higher. 

All filters have limited service life. In operation, a gas adsorber 

loads as molecules fill the micropores of the carbon, and a HEPA 

filter loads with dust and other particles to increase the resistance 

to flow. The adsorber loses capacity for gases over time when exposed to the atmosphere, even if air is not flowing through it. The 

shelf life of an adsorber ranges from 5 to 10 years when the filters 

are hermetically sealed in a container. The service life of the adsorber varies with the operating environment and is generally less 

than 5 years. For this reason, filters intended for use in safe rooms 

in the home or office are typically designed to remain sealed in a 

metal canister until they are needed in an emergency. This hermetic sealing can ensure the filters retain full filtering capacity for 

10 years or more, although most manufacturers do not warranty 

them for more than 10 years. 

Commercial filter units that are designed for indoor air quality can 

be used in an unventilated Class 2 Safe Room. There are many different models available from several manufacturers; however, the 

filtering performance varies over a wide range. These filter units 

can be ceiling-mounted, duct-mounted, or free-standing floor or 

table units having both HEPA filters and adsorbers (usually an activated carbon and zeolite mix). The HEPA filter element provides 

protection against a biological agent and other solid aerosols such 

as tear gas, while the adsorber protects against gases and vapors. 
CBR Threat protection 3-

3.3 SAFE ROOM CRITERIA

This section presents criteria for selecting or designing a safe 

room for protection against airborne toxic materials. Although 

the protective envelope can be defined as the whole building, a 

room within the building (i.e., a safe room) can provide a higher 

level of protection if it is tighter than the building as a whole and/

or the location of the room is less subject to wind or buoyancy 

forces that induce infiltration. 

Any type of room can be used as a safe room if it meets the criteria 

listed below. In office buildings, safe rooms have been established 

in conference rooms, offices, stairwells, and other large common 

areas. In dwellings, safe rooms have been established in bedrooms, 

basements, and bathrooms. The criteria are as follows: 

m Accessibility. The safe room must be rapidly accessible to all 

people who are to be sheltered. It should be located so that 

it can be reached in minimum time with minimum outdoor 

travel. There are no specific requirements for the time to 

reach a safe room; however, moving to the safe room from 

the most distant point in the building should take less than 

2 minutes. For maximum accessibility, the ideal safe room is 

one in which one spends a substantial portion of time during 

a normal day. The safe room should be accessible to persons 

with mobility, cognitive, or other disabilities. Appropriate use 

of stirs or ramps when shelters are located above or below 

grade must account for such occupants.

m Size. The size criterion for the toxic-agent safe room is the 

same as tornado shelters. Per FEMA 361, the room should 

provide 5 square feet per standing adult, 6 square feet per 

seated adult, and 10 square feet per wheelchair user for 

occupancy of up to 2 hours. 

m Tightness. There is no specific criterion for air tightness. 

With doors closed, the safe room must have a low rate of air 

exchange between it and the outdoors or the adjacent indoor 
3- CBR Threat protection

spaces. Rooms with few or no windows are preferable if the 

windows are of a type and condition that do not seal tightly 

(e.g., older sliders). The room must not have lay-in ceilings 

(suspended tile ceilings) unless there is a hard ceiling above. 

The room should have a minimum number of doors, and 

the doors should not have louvers unless they can be sealed 

quickly. The door undercut must be small enough to allow 

sealing with a door-sweep weather strip or expediently with 

duct tape. 

m HVAC system. The safe room must be isolated or capable of 

being isolated quickly from the HVAC system of the building. 

If the selected room is served by supply and return ducts, 

modifications or preparations must include a means of 

temporarily closing the ducts to the safe room. In the simplest 

form, this involves placing duct tape or contact paper over the 

supply, return, and exhaust grilles and turning off fans and airhandling units. If there is a window-type or through-the-wall 

air conditioner in the selected room, plastic sheeting and tape 

must be available to place over the inside of the window and/

or air conditioner, which must be turned off when sheltering 

in the safe room. 

m Ventilation. For Class 1 Safe Rooms, 15 cfm per person 

is the desired ventilation rate; however, the minimum 

ventilation rate is 5 cfm per person if that rate is adequate for 

pressurization. Class 3 and unventilated Class 2 Safe Rooms are 

suitable only for short-duration use, not only because the low 

ventilation rate when occupied can cause carbon dioxide levels 

to rise, but also because protection diminishes as the time of 

exposure to the hazard increases. 

m Location. For unventilated shelters (Class 3 and some Class 2), 

there are three considerations for location within a building. 

First, relative to the prevailing wind, the safe room should be 

on the leeward side of a building. Second, if there is a toxicmaterials storage or processing plant in the community, the 

safe room should be on the side opposite the plant. Third, an 
CBR Threat protection 3-

interior room is preferable to a room with exterior walls, if it 

meets criteria for size, tightness, and accessibility. For a low-rise 

building, there is no substantial advantage in a room on the 

higher floors, and a location should not be selected based on 

height above ground level if it increases the time required to 

reach the shelter in an emergency. 

m Water and toilets. Drinking water and a toilet(s) should be 

available to occupants of a safe room. This may involve the use 

of canned/bottled water and portable toilets. Toilet fixture 

allowance is presented in FEMA 361. 

m Communications. For sheltering situations initiated by local 

authorities, the safe room must contain a radio with which 

to receive emergency instructions for the termination of 

sheltering. A telephone or cell phone can be used to receive 

emergency instructions and to communicate with emergency 

management agencies. Electrical power and lighting are also 

required. 

3.4 DESIGN AND INSTALLATION OF A TOXICAGENT SAFE ROOM 

After the room or location for the safe room has been decided 

based on the criteria listed above, the first design decision is to determine the class of safe room. Design details for the three classes 

of safe rooms are presented below. A Class 3 Safe Room is the 

simplest in that it requires only a tight enclosure. It is presented 

first because the requirements of the tight enclosure are common 

to all three classes. The unventilated Class 2 Safe Room, which 

involves the simplest application of a filter unit, is presented next, 

and the Class 1 Safe Room, which involves a more complex application of a filter unit, is presented last. 
3-10 CBR Threat protection

3.4.1 Class 3 Safe Room 

Features of the Class 3 Safe Room can be either permanent or 

expedient. Guidance for preparing the safe room is presented in 

four parts: 

m How to tighten the room before an emergency – to 

permanently seal unintentional openings 

m How to prepare for sealing the room in an emergency – to 

temporarily close intentional openings such as ducts, doors, 

and windows in an emergency 

m How to prepare for rapid deactivation of fans 

m How to accommodate the safe use of air conditioning or 

heating in protective mode 

3.4.1.1 Tightening the Room 

m Ceiling-to-wall juncture. Typically, most leakage occurs through 

the wall-to-ceiling and wall-to-floor junctures, particularly if 

suspended lay-in ceilings are used without a hard ceiling or a 

well-sealed roof-wall juncture above the lay-in ceiling. If the 

selected room has only a lay-in ceiling between the living space 

and attic space, the ceiling should be replaced with one of 

gypsum wallboard or other monolithic ceiling configuration. 

m Floor-to-wall juncture. A baseboard often obscures leakage 

paths at the floor-to-wall juncture, and to seal these leakage 

paths may require sealing behind the baseboards. One 

approach is to temporarily remove the baseboards and apply 

foam sealant in the gap at the floor-to-wall juncture. The 

alternate approach is to use clear or paintable caulk to seal the 

top and bottom of baseboards and quarter rounds. If there are 

electric baseboard heaters, the heaters should be temporarily 

removed to seal the wiring penetrations and the gap at the 

floor-to-wall juncture. 
CBR Threat protection 3-11

m Penetrations. Measures for reducing air leakage through 

penetrations are as follows: 

m Seal penetrations for pipes, conduits, ducts, and cables 

using caulk, foam sealants, or duct seal. 

m Place weather-stripping (including a door sweep) on 

the door(s) of the safe room. If the selected room is a 

bathroom, and there is a supply duct but no exhaust 

duct, the door sweep may be omitted because it would 

reduce the supply flow rate in normal use. In this case, 

duct tape can be used to seal the gap beneath the door 

temporarily in an emergency. If there is carpeting in 

the safe room, a door sweep may be more effective 

than tape. There may be louvers in the door for return 

airflow, but they should not be modified to ensure 

proper ventilation can be maintained in normal 

conditions. Door louvers should be expediently sealed 

as described in Section 3.4.1.2. 

m Windows that are old and/or in poor condition 

can allow substantial leakage; however, newer, 

non-operable windows are not likely to require 

any sealing. Window leakage can be measured 

using a blower door to determine whether window 

replacement or sealing measures are necessary. In 

some cases, the leakage of windows, such as poorly 

maintained sliders, can be reduced only by replacing 

them or by using expedient sealing measures such as 

taping plastic sheeting over them. 

m Expanding foam can be used to seal electrical outlets 

and switches. Also, ready-made outlet sealers can be 

used to seal gaps behind switches and outlets. 

3.4.1.2 Preparing for Rapidly Sealing the Room. The selected safe 

room may have one or all of the following intentional openings, 

which are necessary for normal operation. The openings must be 
3-12 CBR Threat protection

sealed so that the safe room can be used in a toxic-materials emergency unless the HVAC system for the safe room is designed to 

safely operate in the protective mode (as described below). 

m Supply and return ducts 

m Exhaust fan 

m Door louvers 

m Window-type air conditioner or unit ventilator 

m Door undercut 

It is neither practical or advisable to seal these openings beforehand if the room is one that has normal day-to-day use, in which 

case plans and preparations should be made for sealing them 

temporarily during rapid transition to the protective mode. The 

sealing capability can be either permanent or expedient. 

m Permanent capabilities for rapid sealing. There are two 

general approaches to closing the intentional openings in 

transition to the protective mode. The first is to use hinged 

covers mounted within the safe room. The second is to use 

automatic dampers, particularly in ducts for supply, return, 

and exhaust. Hinged covers can be custom-made of sheet 

metal or wood, as shown in Figure 3-1, to be attached above 

or beside the opening for all applications except the door 

periphery. A hinged cover provides the capability to seal vents 

rapidly. In a safe room having several openings to be sealed, 

use of hinged covers allows the sealing to be completed more 

quickly than use of tape and adhesive backed plastic material. 
CBR Threat protection 3-13

m Temporary measures for rapid sealing. For expedient sealing, 

a small kit of materials should be provided in the safe room, 

along with a written checklist of the sealing measures required 

specifically for the safe room. The following is an example of a 

checklist that applies to a bathroom. The sealing supplies are 

contact paper, precut to size, and 2-inch wide painter’s tape. 

Alternately, duct tape and plastic sheeting can be used. 

m Cover the door louvers with adhesive backed film 

(contact paper) 18 inches by 12 inches in size.

m Cover the gap beneath the door with a strip of 2-inchwide tape. 

m Cover the exhaust fan grille with adhesive-backed film 

(18 inches by 18 inches).

m Cover the supply grille with adhesive backed film (12 

inches by 12 inches).

m Pour water into the floor drain and drains of the 

shower and sink to ensure the traps are filled. 

Figure 3-1

Hinged covers facilitate the rapid sealing of supply, return, or exhaust ducts in a safe room.

Source: Battelle
3-14 CBR Threat protection

In a bathroom, drain traps for the sink, tub, shower, or floor are 

usually filled with water, but should be checked to ensure water is 

present to prevent air leakage through the drain pipes. 

A window-type or through-the-wall air conditioner can be sealed 

by turning it off, and placing either contact paper or plastic 

sheeting with duct tape over the air conditioner. 

3.4.1.3 Preparing for Deactivation of Fans. Some safe room systems have been designed with the capability to automatically 

deactivate all fans in the building with a single switch. This singleswitch control can also be designed to close dampers in outside-air 

ducts serving the safe room. The low-cost alternative to automatic 

fan shutoff is to record on a checklist the location of switches for 

all fans in the building, not just those that serve the safe room. 

This includes air-handling units, exhaust fans, supply fans, window 

air conditioners, and combustion heaters. 

This checklist must also include the procedures for the purging 

step of sheltering-in-place (e.g., opening windows and doors, and 

turning on fans and air handlers that were turned off to shelter-inplace after the hazardous condition has passed). 

3.4.1.4 Accommodating Air Conditioning and Heating. Conventional air conditioning and heating systems must not be operated 

in the protective mode because the fans directly or indirectly introduce outside air. This includes the air-handling units and fans 

serving spaces outside the safe room. An exception is combustion 

heaters of hydronic systems that are located in separately ventilated mechanical rooms. 

In extreme weather conditions, however, confining people in a 

sealed room without air conditioning or heating can result in intolerable conditions, causing people to exit the safe room before 

it is safe to do so. 

The mechanical ventilation system often has a higher potential 

for indoor-outdoor air exchange than the leakage paths of the 
CBR Threat protection 3-15

enclosure subjected to wind and buoyancy pressures. Windowtype air conditioners and unit ventilators cannot be used in the 

protective mode, because they introduce outdoor air, even when 

set to the recirculating mode. The dampers for outside air in 

such units seal poorly even when well maintained. 

The following are options for air conditioning and heating systems that can be safely operated in the protective mode: 

m Ductless mini split-type air-conditioner. This type of room air 

conditioner, an alternative to the standard unitary window air 

conditioner, circulates air across the indoor coils without ducts 

and does not introduce outdoor air in either the normal or 

protective mode. The only required penetration through the 

safe room boundary wall is for a conduit for refrigerant tubing, 

suction tubing, condensate drain, and power cable. 

m Electric heater or steam radiator. Similar to the ductless splittype air conditioner, the electric or steam heater does not 

introduce outdoor air and does not require ducts. 

m Fully enclosed air-handling unit. An air-handling unit can be 

operated in a safe room in the protective mode only if the unit 

and its ducts are fully within the safe room (i.e., the unit is 

in an interior mechanical closet and the return ducts are not 

above the ceiling, beneath the floor, or outside the walls). If 

the air-handling unit draws outdoor air through a duct, it must 

also have a damper system for reliably cutting off outside air in 

the protective mode. This may require a set of three dampers: 

two dampers in the outside air duct with a relief damper 

between them that opens (to protected space) when the other 

two close. The air-handling unit must serve the safe room 

exclusively. 

m Makeup air unit. This is a once-through type unit for 

introducing fresh air; it is not applicable to an unventilated 

safe room. The makeup-air unit does not recirculate air 

through ducts; it supplies filtered air through duct coils for 

cooling and heating. 
3-16 CBR Threat protection

3.4.1.5 Safety Equipment. Unventilated safe rooms, whether Class 

2 or Class 3, must have a carbon dioxide detector or monitor in 

the safe room. 

3.4.2 Class 2 Safe Room

The design details of the enclosure presented above apply also to 

the Class 2 Safe Room, ventilated and unventilated. The ventilated 

Class 2 Safe Room is one that supplies filtered air from outside the 

safe room, but has inadequate air flow to pressurize the room. For 

the unventilated Class 2 Safe Room, the improvement in protection over the Class 3 Safe Room is determined by the flow rate 

and the efficiency of the particulate filter for aerosols and the efficiency of the adsorber for gases and vapors. These filter units, 

commonly referred to as indoor air purifiers, indoor air cleaners, 

or indoor air quality units, recirculate air within the safe room. 

There are four configurations: 

m Free-standing table top unit 

m Free-standing floor unit 

m Ceiling-mounted unit 

m Duct-mounted unit (with ducts completely inside the safe 

room) 

3.4.2.1 Filter Unit Requirements for the Unventilated Class 2 Safe 

Room. The protection provided by an unventilated Class 2 Safe 

Room is determined by the clean-air delivery rate of the filter unit 

and the tightness of the enclosure. The clean-air delivery rate is 

a product of the filter removal efficiency (expressed as a decimal 

fraction) and the actual flow rate of the filter unit. If a high-efficiency filter unit is used, the clean-air delivery rate approaches 

the actual flow rate of the unit. If the filter has a single-pass efficiency of 50 percent, for example, the clean-air delivery rate is half 

the actual flow rate. For a given unit, the clean-air delivery rate is 

likely to be higher for aerosols than for gases and vapors because 

efficiencies of adsorbers are typically lower than the efficiencies of 

particulate filters in these units. 
CBR Threat protection 3-17

Many models of these indoor air purifiers are available commercially, but not all of them have performance suitable for use 

in protecting against toxic aerosols, gases, and vapors. The following are criteria for selection of recirculating filter units for 

use in safe rooms: 

m The filter unit must have both an adsorber containing 

activated carbon and a particulate filter.

m The adsorber must have at least 1 pound of activated carbon 

for each 20 cfm of flow rate. For example, a 200-cfm unit 

requires at least 10 pounds of carbon adsorbent. 

m The particulate filter must have an efficiency of at least 99 

percent against 1-micron particles. 

m The unit(s) must provide a total clean-air delivery rate of at 

least 1 cfm per square foot of floor area. 

m The adsorber must have the capability for chemisorption 

(i.e., for removal of gases that are not removed by physical 

adsorption). 

There are also ventilated Class 2 Safe Rooms and essentially these 

are ones for which the filter unit has inadequate capacity to produce a measurable overpressure with the size of the selected safe 

room. In essence, the filter units are over-rated by the filter unit 

manufacturer. Generally, if a filter unit capacity in cfm is less than 

one-fourth the area (in square feet) of the selected safe room, 

depending on the type of construction, it will not produce a 

measurable overpressure. Matching the filter unit capacity to safe 

room size for Class 1 (pressurized) Safe Rooms is addressed in 

Section 3.4.3.2.

3.4.2.2 Installation and Operation. For the unventilated safe 

room, floor/table model filter units and ceiling-mounted models 

should be placed in the center of the room to maximize air 

mixing. There should be no obstruction to the airflow into and 

out of the filter units. 
3-18 CBR Threat protection

Duct-mounted models must conform to the requirements stated 

above for air-handling units. Ducts cannot be outside the envelope 

formed by the walls, ceiling, and floor. 

The adsorbers of these commercial units are generally lacking 

in capability for filtering a broad range of high-vapor-pressure 

agents. Several of the common industrial chemicals (e.g., ammonia) are not removed. 

The filter unit can be used routinely for indoor air quality; a spare 

set of filters should be kept on hand for use in a toxic-materials 

emergency, along with instructions for changing the filters so that 

the change can be made rapidly. 

3.4.3 Class 1 Safe Room 

Designing and installing a ventilated safe room is much more 

complex than an unventilated safe room, particularly with regard 

to the filter unit. Pressurization requires introducing air from outside the protective enclosure; therefore, the removal efficiency of 

the filters is more critical in determining the protection provided. 

The system must employ ultra-high efficiency filters, and it must 

allow no air to bypass the filter as it is forced into the safe room. 

Except for military standards, there are no performance standards 

specifically for ultra-high efficiency adsorbers intended for protection of people from highly toxic chemicals. Performance of HEPA 

filters for aerosols is defined by ASME AG-1, Code on Nuclear Air 

and Gas Treatment, and N509, Nuclear Power Plant Air-Cleaning Units 

and Components. The specifications for filter units available commercially may present information that only partially defines the 

performance of an adsorber.

3.4.3.1 Selecting a Filter Unit for a Class 1 Safe Room. Generally, 

filter units available commercially are not designed to standards 

that ensure protection against highly toxic chemical, biological, 

and radiological materials. Some may provide very little protection, particularly if the manufacturer is not experienced in 
CBR Threat protection 3-19

designing and building ultra-high efficiency filter units. Minimum 

requirements for the Class 1 applications are listed below. In 

purchasing a filter unit, certifications relative to the following requirements should be provided by the vendor: 

m The filter unit must have both a HEPA filter and an ultra-highefficiency gas adsorber in series. 

m The adsorber must contain carbon impregnated ASZM-TEDA 

or the equivalent. Carbon mesh size should be 12x30 or 8x16. 

m The adsorber must have efficiency of at least 99.999 percent 

for physically adsorbed chemical agents and 99.9 percent for 

chemisorbed agents. 

m The adsorber must have a total capacity of 300,000 milligram 

(mg)-minutes per cubic meter for physically adsorbed 

chemical agents. 

m Bypass at the seals between the adsorber and its housing must 

not exceed 0.1 percent. 

m For installation of the filter unit outside the safe room, the fan 

must be upstream of the filters (blow-through configuration). 

For installation inside with a duct from the wall to the filter 

unit, the fan must be downstream of the filters (draw-through 

configuration). 

m If a flexible duct is used outside the shelter to convey air from 

the filter unit to the safe room, it must be made of a material 

resistant to the penetration of toxic chemicals. 

m If chemical manufacturing and storage facilities in the 

community present a special risk for release of toxic materials, 

special sorbents or sorbent layers may be required. In some 

cases, the chemicals produced/stored may not be filterable 

with a broad-spectrum impregnated carbon. For example, 

a nearby ammonia plant requires a special adsorber for 

protection against ammonia. 
3-20 CBR Threat protection

3.4.3.2 Sizing the Filter Unit for Pressurization. If a filter unit is 

undersized (i.e., it provides inadequate flow for pressurization), 

the result is substantially lower protection factors and the system 

becomes a ventilated Class 2 Safe Room. Filter unit(s) must be 

sized to provide makeup air at a flow rate sufficient to produce a 

pressure of at least 0.1 inch water gauge (iwg) in the shelter for 

protected zones of one or two stories. Taller buildings require an 

internal pressure higher than 0.1 iwg to overcome the buoyancy 

pressures that result in extreme weather conditions (i.e., large 

temperature differences between the inside and outside of the 

safe room). 

The airflow rate needed to achieve this pressure in a safe room 

varies with the size and construction of the safe room. Generally, 

commercial filter units designed for home or office safe rooms 

are under-rated with regard to the quantity of air needed for pressurization. For safe rooms of frame construction and standard 

ceiling height, most can be pressurized to 0.1 iwg with airflow in 

the range of 0.5 to 1 cfm per square foot. Table 3-2 provides additional guidance in estimating the size of a filter unit for a safe 

room based on square footage. 

The recommended procedure for ensuring that pressurization 

can be achieved is to perform a blower door test after all permanent sealing measures have been completed. The test should 

be conducted per ASTM E779-03, Standard Test Method for Determining Air Leakage by Fan Pressurization with temporary sealing 

measures in place. 
CBR Threat protection 3-21

Table 3-2: Leakage per Square Foot for 0.1 Iwg (estimated makeup airflow rate per square foot (floor area) to achieve an overpressure of 

0.1 inch water gauge)

Construction Type cfm per square foot of floor area

Very tight: 26-inch thick concrete walls and roof with no 

windows

0.04

Tight: 12-inch thick concrete or block walls and roof with 

tight windows and multiple, sealed penetrations

 0.20

Typical: 12-inch thick concrete or block walls with 

gypsum wall board ceilings or composition roof and 

multiple, sealed penetrations

0.50

Loose: Wood-frame construction without special sealing 

measures 

1.00

3.4.3.3 Other Considerations for Design of a Class 1 Safe Room 

m Heating and cooling the safe room. A safe room does not 

require heating and cooling; however, in extreme weather, 

the conditions in the safe room may become uncomfortable 

due to the lack of ventilation or the introduction of outdoor 

air that is not tempered. In hot weather, this can be worsened 

by the temperature rise that occurs as air passes through the 

filter unit. Because of the relatively high pressure drop across 

the high efficiency filters, the temperature of the air typically 

increases by 5 to 10 degrees Fahrenheit as it passes through 

the filter unit. The use of inefficient fans, such as brush-type 

high-speed fans, should be avoided for this reason, because a 

temperature rise of 15 degrees can result. 

m Control system. An interlocking system should be considered 

for closing automatic dampers (as shown in Figure 3-2), 

turning off air-handling units, exhaust fans, and ventilation 

fans serving the building’s unprotected spaces while the safe 

room is in the protective mode. This increases the level of 

protection the safe room provides against an outdoor release 

of agent. 
3-22 CBR Threat protection

m Heating system safety. If a fuel-fired indirect heater (i.e., 

heat exchanger) is used to heat the safe room, a carbon 

monoxide detector with a visual display and an audible alarm 

should be installed in the safe room. Electric coil and hotwater coil systems do not require a carbon monoxide detector. 

m Pressure gauge. For Class 1 Safe Rooms, the pressure gauge 

is the indicator that the system is operating properly. This 

gauge displays the pressure in the safe room relative to 

outdoors or outside the safe room indoors. If the reference 

pressure is measured indoors, the readings can be subject 

to variations caused by fan pressures unless other building 

heating, ventilation, and air conditioning (HVAC) fans are 

turned off when the safe room is in use. Reading the reference 

pressure outdoors can be subject to positive and negative 

variations caused by air flows over and around the building. If 

the pressure sensor is outdoors, it should be shielded from the 

wind. Indoors is the best location if the building HVAC fans 

are turned off when the safe room is in use. 

Figure 3-2

Automatic dampers are 

used to isolate the safe 

room from the ducts or 

vents used in normal HVAC 

system operation.

Source: chemical stockpile 

emergency preparedness

program
CBR Threat protection 3-23

3.5 OPERATIONS AND MAINTENANCE

For a shelter to be successful, it is critical to have an understanding and dedication to operations and maintenance. 

Depending on the shelter type, specific operations instructions 

and maintenance are needed.

m Instructions and checklists. As a minimum for operating 

procedures, the condensed operating and maintenance 

instructions should be posted in each safe room. The 

operating instructions should explain the steps of placing the 

safe room into operation and may be as simple as a one-page 

typed checklist; instructions that should be included are safe 

room operating procedures, a list of doors to be secured, a 

list of switches for fans to be turned off, stations/channels for 

emergency instructions, emergency phone numbers, and dates 

by which filters should be changed, if applicable. 

m Status indicators. For safe rooms that require multiple 

automatic dampers to isolate the safe room from the HVAC 

ducts in the protective mode, status lights and/or visual 

indicators should be used to show the position of each damper. 

Indicators can also be used to show door position, if there are 

multiple boundary doors in the safe room. Each status light 

should be marked with a reference number corresponding to 

a diagram so an operator can easily determine the location of 

any damper/door and conduct troubleshooting if problems 

occur. The indicator lights should have push-to-test capability 

for the light bulbs of the status lights. 

m Public-address system. For safe rooms in large buildings, 

a public address system is the most efficient means of 

instructing building occupants to proceed to a safe room in 

an emergency. Telephone or audible alarm systems can also 

be used, but they are less efficient than a broadcast voice 

system. Communications systems (telephone, alarm, and mass 

notification systems) should be tied to emergency phone 

systems. Non-verbal warning systems are generally less effective 
3-24 CBR Threat protection

because they require training on the meaning of different 

types of alarm sounds. 

m Auxiliary or Battery Power. Class 3 Safe Rooms do not require 

electrical power to protect their occupants. Class 1 and Class 

2 Safe Rooms require power for the air-filtration units to 

protect at a higher level than Class 3. If power is lost in a Class 

1 or Class 2 Safe Room, it will continue to protect at the level 

of a Class 3 Safe Room as long as the room remains sealed. 

Power failure, therefore, does not lead to protective failure, 

but rather a reduced level of protection and reduced level of 

comfort in some conditions. For this reason, auxiliary power is 

not essential for a CBR safe room. Auxiliary power is provided 

on some CBR safe rooms so that the highest level of protection 

and comfortable conditions can be maintained if a power loss 

is caused by or coincides with the event causing the release of 

toxic agent. 

3.5.1 Operating a Safe Room in a Home 

The essence of operating a Class 3 Safe Room is to close the safe 

room and ensure that building fans, combustion heaters, and air 

conditioners are turned off so that they do not cause an exchange 

of air between the safe room and its surroundings. General procedures for the home safe room are as follows: 

m Close all windows and doors (both interior doors and exterior 

doors of the home). 

m Turn off the central fan, exhaust fans, window air conditioners, 

or combustion heaters in the home. 

m Enter the safe room. If there is no telephone in the safe room, 

take a cell phone or portable phone into the safe room for 

emergency communications.

m Close the safe room door and apply tape to the periphery of 

the door, unless there are weather seals on the door. 
CBR Threat protection 3-25

m Turn on a radio or TV in the safe room and listen for 

emergency information.

m If the safe room has a carbon dioxide detector, monitor it, 

particularly if the time in the sealed safe room exceeds 1 hour.

m When the “all clear” determination is made, open the windows 

and doors, turn on ventilation systems, and go outside until 

the house has been fully aerated. 

The following is a list of supplies for the safe room: 

m Rolls of duct tape for sealing doors and securing plastic over 

vents and windows 

m Pre-cut plastic sheeting to fit over supply and return vents (also 

for windows if they are judged to be less than airtight)

m Battery operated radio with spare batteries 

m Flashlight with spare batteries 

m Drinking water 

m First aid kit 

m Telephone (cell phone) for emergency instructions

3.5.2 Operating a Safe Room in an Office 

Building 

For the office-building safe room, the supplies are generally the 

same as the home safe room listed above. 

Procedures differ in that there are likely to be more exterior 

doors to be closed and multiple locations for the switches that 

control building fans. To ensure that all doors are closed and fans 

are turned off, an emergency plan and checklist should be developed, assigning employees to these tasks at various locations in 

the building. The general procedures for the office building safe 

room are as follows: 
3-26 CBR Threat protection

m A building-wide announcement is made for all building 

occupants to proceed to the designated safe room(s). 

m Assigned monitors secure all exterior doors and windows. 

m Assigned building engineering staff turn off all air handling 

units, ventilation fans, and window air conditioners as 

applicable (or security turns them off if a single switch 

capability has been installed). 

m Safe room doors are secured as soon as possible once all who 

are assigned to the safe room have entered.

m Employees and visitors are accounted for by use of a roster and 

visitor’s sign-in sheets.

m Emergency information is obtained by radio, TV, telephone, or 

cell phone in the safe room. 

m If the safe room has a carbon dioxide detector, monitor it if 

the time in the safe room exceeds 1 hour.

m When the “all clear” determination is made, open the windows 

and doors, turn on ventilation systems, and go outside until 

the building has been fully aerated. 

3.5.3 Operating Procedures for a Class 1 Safe 

Room

Operating procedures for Class 1 (pressurized) Safe Rooms are 

similar to those of Classes 2 and 3. 

The system is turned on immediately upon receipt of a warning. 

Control panels for Class 1 systems typically include pressure 

gauges and status lights for automatic dampers, which provide 

assurance that the system is operating properly and a means of 

troubleshooting if the system does not pressurize. 
CBR Threat protection 3-27

Tape, plastic, and carbon dioxide detectors are not necessary in 

the Class 1 Safe Room. 

3.6 MAINTAINING THE CBR SHELTER 

Depending on the shelter type, the shelter may require more 

maintenance. Shelters that have increasing levels of protection 

from filters will require more frequent checks and will require 

more funding to keep them operational.

3.6.1 Maintenance for a Class 3 Safe Room 

The Class 3 Safe Room has no air filtration equipment and, 

therefore, requires little or no routine maintenance. It has no 

mechanical equipment unless there are dampers for isolating the 

air conditioner (configured for fail-safe operation). Maintenance 

requirements are limited to periodically checking supplies for 

deterioration or loss: duct tape, plastic sheeting, radio spare batteries, flashlight spare batteries, drinking water, and first aid kit. 

3.6.2 Maintenance for a Class 2 Safe Room

The filter unit used in a Class 2 safe room is an indoor air quality 

filter unit (see Figure 3-3) and, as such, it can be used routinely 

to improve the air quality in the spaces in or around the designated safe room. If this is done, a spare filter set, both adsorber 

and HEPA filter, should be stored in a sealed bag in the safe 

room along with instructions and any tools needed for changing 

the filter quickly in an emergency. Other supplies to be checked 

on a regular basis are the same as listed for the Class 3 Safe 

Room above. 
3-28 CBR Threat protection

3.6.3 Maintenance for a Class 1 Safe Room 

Maintenance of the Class 1 Safe Room consists primarily of 

serviceability checks and replacing filters. Serviceability checks 

should be performed about every 2 months by turning the system 

on and checking for the following while it is operating: 

m System pressure. The system pressure is indicated by a gauge 

typically mounted on the control panel, with the correct 

operating range marked on the gauge. If the pressure is 

outside this range while the system operates, troubleshooting 

should be initiated. 

Figure 3-3

A tabletop recirculation 

filter unit with a substantial 

adsorber is a simple 

means of providing higher 

levels of CBR protection to 

unventilated safe rooms.

Source: Battelle
CBR Threat protection 3-29

m Isolation dampers. Correct damper positioning is indicated 

by damper status lights on the control panel. Troubleshooting 

should be initiated if the status lights indicate a damper is not 

properly positioned. 

m Relief damper. If the system contains a pressure-relief damper, 

it should be visually inspected while the system is operating. A 

properly functioning relief damper should be open when the 

safe room is pressurized, and it should close immediately when 

a door is opened into the safe room, releasing pressure. 

m HEPA filter resistance. The differential pressure across the 

HEPA filter is measured by a gauge mounted on the filter 

unit with taps on either side of the HEPA filter. If the pressure 

across the filter is greater than specified (approximately 3 iwg 

or higher), it is an indication that the HEPA filter has become 

loaded with dust and its higher resistance is reducing the flow 

rate of the filter unit. If such is the case, the HEPA filter should 

be changed. 

m Cooling system. If the safe room supply air is cooled and heated, the temperature of the air flowing from the supply register 

should be checked with a thermometer during serviceability 

checks. In warm weather, this should be approximately 55 degrees if the cooling system is operating properly. 

m Door latches. All doors into the safe room should be adjusted 

to latch automatically with the force of the door closer. For safe 

rooms with multiple doors, leakage past unlatched doors can 

cause internal pressure to fall below the specified operating 

range. 

m Weather stripping. The weather stripping on each door on 

the boundary of the safe room should be visually inspected 

to ensure it has not been removed or damaged through 

wear and tear. For wipe seals at the bottom of the door, the 

alignment and height of the seal above the floor should be 

inspected and adjusted as necessary. 
3-30 CBR Threat protection

m Filters. Routine maintenance includes replacing filters. 

If a canister-type filter is used, it is replaced as a unit at its 

expiration date. For other types of filter units, three types of 

filters are replaced: the pre-filter, HEPA filter, and carbon 

adsorber. Ideally, with only intermittent operation, all three 

types of filters should be replaced at the same time, every 3 to 

4 years. This period is defined mainly by the service life of the 

adsorber. 

Each time the CBR filters are replaced, in-place leakage 

testing should be performed, except in the case of canister 

filters (see Figure 3-4), to ensure the critical seals between the 

filters and/or between the mounting frame and the filters are 

established properly (i.e., there is no leakage past the filters’ 

peripheral seals). To test the seals of the HEPA filter, the unit 

is challenged with an aerosol; poly-alpha olefin (PAO) is the 

industry standard. To test the seals of the adsorbers requires 

a chemical that is loosely adsorbed in the filter bed. Halide 

gases are typically used for this purpose. For the adsorber, the 

criterion is that the leak must be less than 0.1 percent of the 

upstream concentration. For the HEPA filter, the criterion 

is 0.03 percent. Procedures for both tests are described in 

American National Standards Institute/American Society of 

Mechanical Engineers (ANSI/ASME) N510, Testing of Nuclear 

Air Treatment Systems.
CBR Threat protection 3-31

Figure 3-4

A canister-type filter unit 

is often used for Class 1

Safe Rooms to maximize 

storage life of the filters.

Source: Battelle

3.7 COMMISSIONING A CLASS 1 

CBR SAFE ROOM 

Commissioning applies to the Class 1 Safe Room. It involves 

testing, checking the configuration, and performing functional 

checks to ensure the safe room has been installed properly, 

protects as intended, and can be operated and maintained by 

its owner. Commissioning addresses not only the safe room 

and its components, but also the operations and maintenance 

instructions. 
3-32 CBR Threat protection

For a Class 1 Safe Room, the principal performance indicator is 

the pressure developed in the safe room by the flow of filtered 

air. Commissioning requires measuring the internal pressure, 

the supply air flow rate, and leakage at the seals of the filters. 

If an air conditioning and/or heating system and dampers are 

part of the system, it also requires verifying their proper function. The following should be addressed in commissioning a 

Class 1 Safe Room: 

3.7.1 Measurements 

m Measure the flow rate of filtered air and compare with design 

flow rate. Airflow rate measurements are usually made by 

certified test-and-balance contractors. A filter unit with integral 

motor-blower and fixed supply-duct length may not require 

airflow measurements after installation. 

m Conduct in-place leakage testing to determine if filters are 

sealed properly to their mounting frames to prevent air 

bypassing the filters. This is necessary if the filter unit has 

replaceable filters. If a canister type filter unit is employed, 

these critical seals are factory tested, and in-place testing for 

bypass is not necessary. 

m Measure the pressure in the safe room with a calibrated gauge 

independent of the installed pressure gauge. 

m Measure the temperature of the supply air and compare it with 

design values for both heating and cooling modes. 

3.7.2 Configuration 

m Visually inspect the seals applied to wall penetrations (pipes, 

cables, conduit) and to doors (weather-stripping and wipe seals). 

m For filter units with replaceable filters, determine that the filter 

unit has been installed with adequate clearance for changing 

the filters. 

m Verify that the pressure-sensing tubes for the pressure gauge 

have been installed properly, reference pressure sensors 
CBR Threat protection 3-33

have been appropriately placed to provide accurate ambient 

pressure readings without the effects of dynamic pressure, and 

that they are shielded to prevent blockage by moisture, insects, 

etc. 

m If there is air conditioning or heating, inspect to determine 

that outside air will not be drawn in through closed dampers 

or other leakage points. 

m Verify that gauge and status lights of the control panel gauges 

are marked with operating ranges. 

m Verify that markings, signs, and condensed operating 

instructions are adequate for the user to operate the system 

properly. 

3.7.3 Functionality 

m Visually inspect all dampers to ensure they move freely and 

assume the correct position for both normal and protective 

modes. 

m For a mechanical pressure gauge, determine that the gauge 

has been zeroed properly. 

m If there is a low-pressure alarm or status indicator, verify it has 

been adjusted to the correct pressure threshold. 

m Verify that status lights accurately indicate position/operation 

of dampers and fans. 

m Verify the push-to-test capability for status lights. 

m Verify that instructions for operating and maintaining the 

system are available at the safe room and provide clear and 

accurate guidance for an untrained operator to activate the 

protective system. 

m Verify the operation of communications equipment for safe 

room occupants. 

m Verify the proper function of the change-HEPA gauge or 

indicator. 
3-34 CBR Threat protection

3.8 UPGRADING A CBR SAFE ROOM 

The simplest and least costly upgrade in protective capability for a 

safe room is to upgrade from Class 3 to unventilated Class 2. This 

involves adding a recirculation filter unit, the simplest of which 

is a free-standing unit. This type of filter unit is available in many 

models, flow rates, filter types, and cost levels; however, not all 

have the same capability. Requirements for the grade of adsorbers 

and particulate filters, as well as flow rate per square foot of safe 

room, are listed in Section 3.4.2.1. 

Upgrading from Class 2 or 3 to Class 1 involves the greatest expense. It can be as simple as purchasing a high-efficiency filter 

unit and installing it to supply filtered air through a special duct. 

Rules of thumb on flow rates required to pressurize the safe room 

are presented in Section 3.4.3.2. An interlocking system should be 

considered for turning off air-handling units, exhaust fans, and 

ventilation fans of the building’s unprotected zones while the safe 

room is in the protective mode. 

3.9 TRAINING ON THE USE OF A SAFE ROOM 

As is the case with fire safety, all people who are to be protected in 

a safe room, whether in a home or commercial building, must be 

familiar with the procedures of using the safe room. Getting into 

it quickly and closing the safe room door(s) is important for all 

types of shelters. Whether sheltering from toxic agents, blast, or 

storms, the protection a safe room provides is compromised when 

it is not fully closed. 

Training the people who work or reside in the building on safe 

room procedures has four main objectives: 

m To familiarize them with the locations of the safe rooms and 

the procedures for using them. 

m To inform them about who the emergency manager/

coordinator of the building is, what his/her responsibilities 

are, and how he/she can be contacted. 
CBR Threat protection 3-35

m To develop an understanding of the range of protective 

responses, including evacuation, and what to do for each of 

the possible protective actions. 

m To develop an employee awareness of the threats and hazards. 

Trained building occupants can serve to detect threats and 

reduce the time to respond by being aware of indications of 

suspicious activities, symptoms of toxic agent exposure, or 

odors from chemical releases. 

Plans should be made to conduct a safe room drill, similar to a fire 

drill, semi-annually. 

3.10 CASE STUDY: CLASS 1 SAFE ROOM 

This case study describes a Class 1 Safe Room, one that is ventilated and pressurized with an ultra-high efficiency filter unit in a 

multi-story office building. 

The concept of operation for this safe room is that, in response 

to a release of toxic chemicals outside the building, security personnel activate the safe room filtration unit and turn off all other 

HVAC fans in the building to place the building in the shelterin-place mode. Employees are instructed via the public-address 

system to proceed immediately to the safe room. They remain in 

the safe room until building security officers, consulting with the 

local emergency management agency, determine that there is no 

longer a hazard. 

A ventilated, pressurized safe room was selected so that a large 

number of people could be protected during a sheltering period 

of 1 to 2 hours without the potential for carbon dioxide buildup.

Task 1. Select the Safe Room Space 

Applying the criteria of adequate space, accessibility, and capability to be rapidly secured, the fire-rated stairwell is the best 

choice in a multi-story office building for a safe room. 
3-36 CBR Threat protection

The safe room must accommodate all occupants and visitors in 

this portion of the building. The stairwell is 11 stories high (140 

feet) with cross-section dimensions of 35 feet by 12 feet. At 5 

square feet per person, it can accommodate 600 people.

The stairwell meets the criterion of accessibility because it spans 

all floors of the building and is accessible to all building occupants 

in an estimated 1 minute or less. It also provides access for people 

with impaired mobility.

As a fire-rated stairwell, it is unventilated. It can therefore be rapidly secured and isolated from the mechanical ventilation system 

and the other spaces of the building. With no mechanical ventilation, it can be secured by simply closing its doors, which are 

normally held closed by door closers for fire-safety purposes. 

Task 2. Determine How Well the Selected Space Can Be Sealed

Airtightness is indicated by the construction of the stairwell, which 

is of cast-in-place concrete with few wall penetrations, none of 

which has apparent sealing requirements beyond caulk or foam 

sealant. Penetrations include sprinkler standpipes and conduit/

cables for wall-mounted lights at each landing, an emergency telephone, and intercom. The doors into the stairwell are fire-rated 

and have an undercut of 1⁄2 to 1 inch. Collectively, the undercut of 

the doors into the stairwell is the largest leakage path to be sealed.

To confirm the airtightness and estimate the airflow capacity of 

the filter unit, a blower-door test, as illustrated in Figure 3-5, was 

performed per ASTM E779-03. Use of the blower door in the depressurization mode can also facilitate finding leaks that may not 

be readily apparent. 
CBR Threat protection 3-37

Task 3. Determine the Level of Safe Room Positive Pressure 

Required

For a safe room of this height, buoyancy pressure is significant, 

and both wind pressure and buoyancy pressure must be considered in determining the safe room operating pressure. As a corner 

stairwell, it has two exterior walls. The pressure requirement is defined as the velocity pressure of a 20-mph wind plus the buoyancy 

pressure that occurs against ground-level doors and other points 

of leakage at winter design conditions. With a height of 140 feet, 

the maximum buoyancy pressure at the lowest level of the stairwell 

is calculated at 0.11 iwg for a 60-degree Fahrenheit indooroutdoor temperature differential. Adding the maximum wind 

pressure of 0.2 iwg for a 20-mph wind yields a design pressure of 

0.3 iwg. At an internal pressure of 0.3 iwg, the force required to 

Figure 3-5

A blower door test on the selected safe room aids 

in estimating the size of air-filtration unit required 

and in identifying air leakage paths.

Source: Battelle
3-38 CBR Threat protection

open the doors into the stairwell is slightly less than 30 pounds at 

the door handle for the (inward opening) doors, the maximum 

door opening force allowed by fire code. 

Ideally, a blower door-test is performed after the permanent sealing 

measures, including door seals, have been added. In performing 

the blower door test before these permanent sealing measures are 

applied, the doors are taped temporarily at the periphery to simulate their being permanently sealed. Results of the blower door test, 

graphed in Figure 3-6, show that, with doors sealed with tape, the 

stairwell could be pressurized to 0.3 iwg with about 3,000 cubic feet 

per minute (cfm). 

Figure 3-6

Blower-door test results on the stairwell selected for a safe room

Source: Battelle
CBR Threat protection 3-39

Task 4. Determine How Much Filtered Air Flow is Required

The total filtered, ventilation air flow required is the larger of: 

(1) the flow rate required for pressurization and (2) the flow rate 

required to supply greater than 5 cfm of outside air per person in 

the safe room. At a maximum safe room occupancy of 600 people, 

the 5 cfm/person ventilation requirement is met with a flow rate 

of 3,000 cfm. Using a filter unit of 4,000 cfm capacity yields a ventilation rate greater than 5 cfm per person. This ventilation flow 

rate is not adequate; however, to deliver the cooling required for 

the heat load of the fully occupied stairwell, two fan-coil units are 

added to the lower levels for additional cooling.

Task 5. Design and Install the System

Design and installation requires a licensed mechanical contractor with experience in the installation of high-efficiency 

filtration systems. 

The safe room requires the following components installed in 

the stairwell and a penthouse mechanical room adjacent to the 

stairwell: 

m Air-filtration unit and supply fan of 4,000-cfm capacity 

m Pre-heat coil cabinet containing pre-filters, heating coils, and 

isolation damper 

m Cooling-coil cabinet containing coils and an isolation damper 

m Spiral ductwork 

m Control panel with pressure gauge and system status lights 

m Remote on/off switch connected via the building automation 

system 

m Pressure relief damper at the lowest level of the stairwell 

m Supply register at the top level of the stairwell 

m Pressure sensor and thermostats installed in the stairwell 

m Weather stripping and wipe seals on doors into the stairwell 
3-40 CBR Threat protection

Air-filtration Unit Type. A filter unit employing an adsorber containing ASZM-TEDA carbon of 12x30 mesh size was selected to 

provide ultra-high efficiency filtration of a broad spectrum of toxic 

chemicals. A military radial-flow filter set, carbon adsorber, and 

HEPA filter, shown in Figure 3-7, were selected. Manufactured to 

a government purchase description, the 4,000-cfm filter unit employs 20 replaceable sets of radial-flow filters. The filter sets were 

purchased from Hunter Manufacturing Company, Solon, OH, 

part number HF-200S. 

Air-filtration Unit Location. A penthouse mechanical room adjacent to the stairwell is selected as the mounting location for 

the filter unit to provide an elevated and secure location for the 

equipment and its air intake. This is selected to achieve physical 

security of the intake and to make it most-distant from ground 

level releases. The filter unit, with its access panel removed, is 

shown in Figure 3-8. 

Isolation Dampers. Two sets of automatic dampers are installed in 

the system, one upstream and one downstream of the filter unit to 

isolate the filters when not in use. 

Figure 3-8

A 4,000-cfm filter unit 

using radial flow filters was 

selected for the stairwell safe 

room.

Source: Battelle

Figure 3-7

A military radial-flow CBR 

filter set was selected for 

safe room filtration.

Photo courtesy of Hunter

Manufacturing Company
CBR Threat protection 3-41

Figure 3-9

The Class 1 Safe Room control panel has a system 

start/stop switch, status indicators for dampers, 

and a pressure gauge.

Source: Battelle

Pre-heat Coil Module. This module contains pre-filters, pre-heat 

coil, and an outside air damper. Pre-filters selected for the system 

are ASHRAE 25-35 percent pleated. The building in which this 

system is installed has chilled water and hot water service from a 

central plant. 

Cooling-coil Module. Cooling coils and an isolation damper 

are contained in a module mounted on the wall between the 

mechanical room and stairwell. Temperature control of the pressurization air is maintained with an electronic thermostat located 

in the stairwell. 

Control Panel. The control panel as shown in Figure 3-9 has the 

following controls and indicators: 

m Start/stop switch 

m Status lights for the system, supply fan, and two isolation 

dampers

m Pressure gauge indicating the pressure differential between 

the stairwell and the adjoining hallway 
3-42 CBR Threat protection

Relief Damper. In supplying filtered air from the top of the stairwell, the carbon dioxide concentration in the occupied stairwell 

increases with the vertical distance from the source of fresh air, 

because leakage paths are evenly distributed along the vertical 

axis. To ensure carbon dioxide levels remain within safe limits at 

the lowest levels of the stairwell and to facilitate removal of heat 

and humidity generated by the occupants, a relief damper was 

installed at the lowest level to maximize the flow-path length for 

clean air. The relief damper was adjusted to prevent the internal 

pressure from exceeding 0.30 iwg, a pressure above which the 

doors that open into the stairwell could require more than 30 

pounds of force at the door handle to open (depending upon 

door closer force). 

Door Seals. Weather-type seals were installed on doors into the 

stairwell to minimize air leakage around the closed doors. According to blower door test results, leakage around the stairwell 

doors before the addition of weather-stripping and wipe seals was 

substantial (approximately 3,000 cfm at 0.3 iwg). 

Warning System. A public address system was installed in the 

building so that voice messages could be broadcast throughout 

the building to notify people at any location of an emergency. 

Accessibility. The stairwell offers a point of entry accessible to 

wheelchairs, and each landing provides an area adequate for two 

wheelchairs without blocking access to the door. 

Drinking Water. The stairwell has no accommodation for drinking 

water. There were plans to make water available by storing bottled 

water in a compartment on each landing of the stairwell. 

Communications. Each level of the stairwell has an emergency 

telephone and an intercom to provide contact with the security 

operations center. 

Cost. Total cost of the installed system was $190,000, or about $300 

per person sheltered. This does not include the cost of the public 
CBR Threat protection 3-43

address system or the single-switch fan shutdown for the building. 

Cost of the filter unit and initial set of filters was about one-fourth 

the total cost of the system. Costs included: 

m Purchase of filter unit and supply fan, $28,000 

m Purchase of CBR filters, 20 sets, $22,000 

m Detailed design and purchase and installation of other 

components, $140,000: 

m Chilled-water coils, hot water coils, piping, insulation, 

supports 

m Double-wall and single-wall spiral ductwork 

m Two isolation dampers and one relief damper 

m Control panel and remote activation capability 

m Concrete equipment pads 

m Door sweeps and jamb seals on stairwell doors 

m Sealing penetrations through stairwell walls 

m Motor control center and electrical service 

m Test, adjust, and balance 

m In-place leak testing of filter unit 

m Signage for condensed operating instructions 

emergency management considerations 4

Emergency management considerations 4-

4.1 OVERVIEW

T his chapter first outlines how DHS has planned for and 

responds to incidences of natural significance that would 

affect a shelter. These plans, policies, and procedures may 

be mirrored or modified by shelter owners and/or communities. 

Users of this document should check with local emergency management to determine their capabilities and plans for responding 

to an incident. The data presented for the Federal Government's 

approach to emergency management can be used to develop 

shelter operations plans and shelter maintenance plans.

4.2 NATIONAL Emergency Response 

Framework

On December 17, 2003, Homeland Security Presidential Directive (HSPD) 8: National Preparedness was issued. HSPD-8 defines 

preparedness as “the existence of plans, procedures, policies, training, 

and equipment necessary at the Federal, State, and local level to maximize 

the ability to prevent, respond to, and recover from major events. The term 

‘readiness’ is used interchangeably with preparedness.” HSPD-8 refers 

to preparedness for major events as “all-hazards preparedness.” It 

defines major events as “domestic terrorist attacks, major disasters, and 

other emergencies.” 

The Department of Homeland Security developed the National 

Response Plan (NRP) and the Catastrophic Supplement to the 

NRP and is now encouraging state and local government, private 

industry, and non-government organizations to achieve a multihazards capability as defined in the National Preparedness Goal.
4- Emergency management considerations

National Response Plan

In Homeland Security Presidential Directive (HSPD)-5, the President directed the development of 

a new National Response Plan (NRP) to align Federal coordination of structures, capabilities, 

and resources into a unified, all discipline, and all-hazards approach to domestic incident 

management. This approach is unique and far-reaching in that it, for the first time, eliminates 

critical seams and ties together a complete spectrum of incident management activities to include 

the prevention of, preparedness for, response to, and recovery from terrorism, major natural 

disasters, and other major emergencies. The end result is vastly improved coordination among 

Federal, state, local, and tribal organizations to help save lives and protect communities by 

increasing the speed, effectiveness, and efficiency of incident management.

The Homeland Security Digital Library (HSDL, https://www.hsdl.org) should be consulted for the 

following publications. The HSDL is the nation’s premier collection of homeland security policy and 

strategy related documents.

The National Incident Management System

The National Incident Management System (NIMS) integrates existing best practices into a 

consistent, nationwide approach to domestic incident management that is applicable at all 

jurisdictional levels and across functional disciplines in an all-hazards context. https://www.hsdl.

org/homesec/docs/dhs/nps14-030604-02.pdf

National Response Plan (Final) Base Plan and Appendices

The President directed the development of a new National Response Plan (NRP) to align Federal 

coordination structures, capabilities, and resources into a unified, all-discipline, and all-hazards 

approach to domestic incident management. https://www.hsdl.org/homesec/docs/dhs/nps08-

010605-07.pdf

National Preparedness Goal [Final Draft]

The President directed the development of a National Preparedness Goal that reorients how the 

Federal government proposes to strengthen the preparedness of the United States to prevent, 

protect against, respond to, and recover from terrorist attacks, major disasters, and other 

emergencies. https://www.hsdl.org/homesec/docs/dhs/nps03-010306-02.pdf
Emergency management considerations 4-

DHS has identified two emergency levels: routine and catastrophic, as shown in Figure 4-1. The types of emergencies 

that occur on a daily basis, such as car accidents, road spills, 

or house fires, are routine events. Catastrophic events, such as 

tornadoes, terrorist attacks, or floods, tend to cover a larger 

area, impact a greater number of citizens, cost more to recover 

from, and occur less frequently. Emergencies are complicated 

as the extent increases due to the additional layers of coordination and communication that need to occur as the event crosses 

jurisdictional boundaries and overburdens the resources at the 

origin of the event. 

Figure 4-1 Preparedness versus scale of event

Source: DHS National Geospatial Preparedness Needs Assessment
4- Emergency management considerations

The NRP provides the structure and mechanisms for 

the coordination of Federal support to state, local, 

tribal, and incident managers, and for exercising direct Federal authorities and responsibilities. It assists 

in the important security mission of preventing terrorist attacks within the United States, reducing the 

vulnerability to all natural and manmade hazards, and 

minimizing the damage and assisting in the recovery 

from any type of incident that occurs.

The NRP is the core plan for managing domestic incidents and details the Federal coordinating structures 

and processes used during Incidents of National Significance. 

The National Incident Management System (NIMS) establishes standardized incident management processes, 

protocols, and procedures that all responders (Federal, 

state, local, and tribal) will use to coordinate and conduct response actions. With responders using the same 

standardized procedures, they will all share a common 

focus, and will be able to place full emphasis on incident management when a homeland security incident 

occurs, whether a manmade or natural disaster. In 

addition, national preparedness and readiness in 

responding to and recovering from an incident is enhanced because all of the Nation’s emergency teams 

and authorities are using a common language and set 

of procedures. 

Using the NIMS and NRP framework, the shelter plan 

should implement direction and control for managing 

resources, analyzing information, and making decisions. The direction and control system described 

below assumes a facility of sufficient size. Some facilities 

may require a less sophisticated system, although the 

principles described here will still apply.

The National Fire Protection 

Association developed, in 

cooperation and coordination 

with representatives from 

FEMA, the National 

Emergency Management 

Association (NEMA), and the 

International Association of 

Emergency Managers (IAEM), 

the 2004 edition of the NFPA

1600 Standard on Disaster/

Emergency Management and 

Business Continuity Programs. 

This coordinated effort was 

reflected in the expansion 

of the title of the standard 

for disaster and emergency 

management, as well as 

information on business 

continuity programs.

Source: NFPA
Emergency management considerations 4-

At the Federal headquarters level, incident information-sharing, 

operational planning, and deployment of Federal resources 

are coordinated by the Homeland Security Operations Center 

(HSOC), and its component element, the National Response Coordination Center (NRCC).

The national structure for incident management establishes a 

clear progression of coordination and communication from the 

local level to the regional level to the national headquarters level. 

The local incident command structures (namely the Incident 

Command Post (ICP) and Area Command) are responsible for 

directing on-scene emergency management and maintaining command and control of on-scene incident operations. Figure 4-2 is a 

flowchart of initial National-level incident management actions.

A CBRE event can affect a large region and the shelter designer 

should consider how response and recovery teams can access and 

work in the vicinity of an incident as shown in Figure 4-3. 

An Emergency Management Group (EMG) is the team responsible for the direction and control of a shelter plan. It controls all 

incident-related activities. The Incident Commander (IC) oversees 

the technical aspects of the response. The EMG supports the IC by 

allocating resources and by interfacing with the community, the 

media, outside response organizations, and regulatory agencies. 

The EMG is headed by the Emergency Director (ED), who should 

be the facility manager. The ED is in command and control of all 

aspects of the emergency. Other EMG members should be senior 

managers who have the authority to:

m Determine the short- and long-term effects of an 

emergency

m Order the evacuation or shutdown of the facility

m Interface with outside organizations and the media

m Issue press releases
4- Emergency management considerations

From established reporting 

mechanisms, e.g.:

• FBI SIOC

• National Response Center

• NCTC

• Other Federal EOCs

• State EOCs

• Federal agency command 

posts

• ISAOs

A basic premise of the NRP is that incidents are generally handled at the lowest jurisdictional 

level possible. In an Incident of National Significance, the Secretary of Homeland Security, in 

coordination with other Federal departments and agencies, initiates actions to prevent, prepare 

for, respond to, and recover from the incident. These actions are taken in conjunction with state, 

local, tribal, nongovernmental, and private-sector entities.

Figure 4-2 Flowchart of initial National-level incident management actions

Source: DHS National Response Plan
Emergency management considerations 4-

Figure 4-3 NRP-CIS Mass Casualty Incident Response

Source: NRP-CIS
4- Emergency management considerations

An Emergency Operations Center (EOC) should be established 

within the shelter that serves as a centralized management center 

for emergency operations. Here, decisions are made by the EMG 

based upon information provided by the IC and other personnel. 

Regardless of size or process, every facility should designate an 

area where decision-makers can gather during an emergency. 

Each facility must determine its requirements for an EOC based 

upon the functions to be performed and the number of people 

involved. Ideally, the EOC is a dedicated area equipped with communications equipment, reference materials, activity logs, and 

all the tools necessary to respond quickly and appropriately to an 

emergency.

The relationship between the EMG and the Emergency Operations Group (EOG) is shown in Figure 4-4.

An Incident Command System (ICS) provides for coordinated 

response and a clear chain of command and safe operations. The 

IC is responsible for front-line management of the incident, for 

tactical planning and execution, determining whether outside assistance is needed, and relaying requests for internal resources or 

outside assistance through the EOC. The IC can be any employee, 

but a member of management with the authority to make decisions is usually the best choice. The IC must have the capability 

and authority to:

m Assume command

m Assess the situation

m Implement the emergency management plan

m Determine response strategies

m Activate resources

m Order an evacuation

m Oversee all incident response activities

m Declare that the incident is “over”
Emergency management considerations 4-

4.3 Federal CBRE Response Teams

The NIMS standardizes resource and asset typing. The following 

teams are resources that have been typed or are in the process of 

being typed. These teams are good examples of how to type resources, are available for state and Federal response operations, 

and can provide technical design guidance for shelters:

Figure 4-4 Emergency Management Group and Emergency Operations Group 
4-10 Emergency management considerations

m Weapons of Mass Destruction-Civil Support Team (WMDCST): A team that supports civil authorities at a domestic 

CBRE incident site by identifying CBRE agents/substances, 

assessing current and projected consequences, advising on 

response measures, and assisting with appropriate requests 

for state support. The National Guard Bureau fosters the 

development of WMD-CSTs.

m Disaster Medical Assistance Team (DMAT): A group of 

professional and paraprofessional medical personnel 

(supported by a cadre of logistical and administrative staff) 

designed to provide emergency medical care during a 

disaster or other event. The National Disaster Medical System 

(NDMS), through the U.S. Public Health Service (PHS), 

fosters the development of DMATs.

m Disaster Mortuary Operational Response Team (DMORT): 

A team that works under the guidance of local authorities 

by providing technical assistance and personnel to recover, 

identify, and process deceased victims. DMORTs are composed 

of private citizens, each with a particular field of expertise, who 

are activated in the event of a disaster. The NDMS, through 

the PHS, and the National Association for Search and Rescue 

(NASAR) fosters the development of DMORTs.

m National Medical Response Team-Weapons of Mass 

Destruction (NMRT-WMD): A specialized response force 

designed to provide medical care following a nuclear, 

biological, and/or chemical incident. This unit is capable of 

providing mass casualty decontamination, medical triage, and 

primary and secondary medical care to stabilize victims for 

transportation to tertiary care facilities in a hazardous material 

environment. There are four NMRT-WMDs geographically 

dispersed throughout the United States. The NDMS, through 

the PHS, fosters the development of NMRTs.

m Urban Search and Rescue (US&R) Task Force: A highly 

trained team for search-and-rescue operations in damaged 
Emergency management considerations 4-11

or collapsed structures, hazardous materials evaluations, 

and stabilization of damaged structures; it also can provide 

emergency medical care to the injured. US&R is a partnership 

between local fire departments, law enforcement agencies, 

Federal and local governmental agencies, and private 

companies. 

m Incident Management Team (IMT): A team of highly trained, 

experienced individuals who are organized to manage 

large and/or complex incidents. They provide full logistical 

support for receiving and distribution centers. Each IMT 

is hosted and managed by one of the United States Forest 

Service’s Geographic Area Coordination Centers. 

4.4 Emergency Response

Although the NIMS, the NRP, and the National Preparedness Goal 

provide the designer with factors that may impact shelter management on a regional scale, the incident response occurs at the local 

level. The IC must evaluate the situation and make a number of time 

critical decisions. A shelter’s location, orientation, and surrounding 

property adjacent to the site must be evaluated and the locations of 

the entry access control point, decontamination and disposal areas, 

and site cordons established, often with little more than the visual 

inspection of the event area. 

4.4.1 General Considerations

The shelter site and surrounding areas should be selected to allow 

law, fire, and medical vehicles and personnel access for mass decontamination operations in case of an emergency. Runoff from 

decontamination operations must be controlled or contained to 

prevent further site contamination. To help the IC, the Emergency 

Response to Terrorism Job Aid 2.0 should be used. This includes 

both tactical and strategic issues that range from line personnel to 

unit officers. 
4-12 Emergency management considerations

The Job Aid is divided into five primary sections that are tabbed and color coded for 

rapid access to information:

m Introduction (Gray) 

m Operational Considerations (Yellow) 

m Incident-Specific Actions (White) 

m Agency-Related Actions (Blue) 

m Glossary (Tan) 

As the IC begins the direction of the response and recovery teams 

in the field, the mobilization of resources to coordinate the Federal, state, local, and tribal efforts will have begun. 

4.4.2 Evacuation Considerations

Many of the NIST findings (see Section 1.9) and recommendations for emergency response can be applied to all building types 

and shelters:

m Active fire protection systems for many buildings are designed 

to the same performance specifications, regardless of height, 

size, and threat profile.

m Approximately 87 percent of the World Trade Center (WTC) 

occupants, and over 99 percent of those below the floors of 

impact, were able to evacuate successfully.

m At the time of the aircraft impacts, the towers were only 

about one-third occupied. Had they been at the full capacity 

of 25,000 workers and visitors per tower, computer egress 

modeling indicated that a full evacuation would have required 

about 4 hours. Under those circumstances, over 14,000 

occupants might have perished in the building collapses.

m There were 8,900 ± 750 people in WTC 1 at 8:46 a.m. on 

September 11, 2001. Of those, 7,470 (or 84 percent) survived, 

while 1,462 to 1,533 occupants died. At least 107 occupants 

DHS/FEMA and the Office for Domestic 

Preparedness developed the Emergency 

Response to Terrorism Job Aid 2.0 (http://

www.usfa.fema.gov/subjects/terror/

download-jobaid.shtm), which is designed 

to assist the first responder from the fire, 

Emergency Medical Services (EMS), 

hazardous material (HazMat), and law 

enforcement disciplines respond to a CBRE 

event. 
Emergency management considerations 4-13

were killed below the aircraft impact zone. No one who was 

above the 91st floor in WTC 1 after the aircraft impact survived. 

This was due to the fact that the stairwells and elevators were 

destroyed and helicopter rescue was impossible.

m There were 8,540 ± 920 people in WTC 2 at 8:46 a.m. on 

September 11, 2001. Of those, 7,940 (or 93 percent) survived, 

while 630 to 701 occupants were killed. Eleven occupants died 

below the aircraft impact zone. Approximately 75 percent of 

the occupants above the 78th floor at 8:46 a.m. had successfully 

descended below the 78th floor prior to the aircraft impact 

at 9:03 a.m. The use of elevators and self-initiated evacuation 

during this period saved roughly 3,000 lives.

m The delays of about 5 minutes in starting evacuation were largely 

spent trying to obtain additional information, trying to make 

sense of the situation, and generally preparing to evacuate.

m People who started their evacuation on higher floors took 

longer to start leaving and substantially increased their odds 

of encountering smoke, damage, or fire. These encounters, 

along with interruption for any reason, had a significant 

effect on increasing the amount of time that people spent to 

traverse their evacuation stairwell.

m The WTC occupants were inadequately prepared to 

encounter horizontal transfers during the evacuation process 

and were occasionally delayed by the confusion as to whether 

a hallway led to a stairwell as well as confusion about whether 

the transfer hallway doors would open or be locked.

m The WTC occupants were often unprepared for the physical 

challenge of full building evacuation. Numerous occupants 

required one or more rest periods during stairwell descent.

m In WTC 1, the average surviving occupant spent 

approximately 48 seconds per floor in the stairwell, about 

twice that observed in non-emergency evacuation drills. 
4-14 Emergency management considerations

The 48 seconds do not include the time prior to entering 

the stairwell, which was often substantial. Some occupants 

delayed or interrupted their evacuation, either by choice or 

instruction.

m Downward traveling evacuees reported slowing of their travel 

due to ascending emergency responders, but this counterflow 

was not a major factor in determining the length of their 

evacuation time. 

m Approximately 1,000 surviving occupants had a limitation that 

impacted their ability to evacuate, including recent surgery 

or injury, obesity, heart condition, asthma, advanced age, 

and pregnancy. The most frequently reported disabilities 

were recent injuries and chronic illnesses. The number of 

occupants requiring use of a wheelchair was very small.

m Mobility challenged occupants were not universally accounted 

for by existing evacuation procedures, as some were left 

by colleagues (later rescued by strangers); some in WTC 1 

were temporarily removed from the stairwells in order to 

allow more able occupants to evacuate the building, and 

others chose not to identify their mobility challenge to any 

colleagues.

m Most mobility challenged individuals were able to evacuate 

successfully, often with assistance from co-workers or emergency 

responders, and it is not clear how many were among the 118 

from below the impact floors who did not survive. It does not 

appear that mobility challenged individuals were significantly 

over-represented amongst the decedents.

m As many as 40 to 60 mobility challenged occupants and 

their companions were found on the 12th floor of WTC 1 by 

emergency responders. About 20 of these were making their 

way down the stairs shortly before the building collapsed. It is 

not known how many from this group survived.
Emergency management considerations 4-15

m The first emergency responders were colleagues and regular 

building occupants. Acts of individual heroism saved many 

people whom traditional emergency responders would have 

been unable to reach in time.

m Only one elevator in each building was of use to the 

responders. To gain access to the injured and trapped 

occupants, firefighters had to climb the stairs, carrying the 

equipment with them.

m NIST estimated that emergency responder climbing rates 

varied between approximately 1.4 minutes per floor for 

personnel not carrying extra equipment to approximately 2.0 

minutes per floor for personnel wearing protective clothing 

and carrying between 50 and 100 pounds of extra equipment.

m With a few special exceptions, building codes in the 

United States do not permit use of fireprotected elevators 

for routine emergency access by first responders or as a 

secondary method (after stairwells) for emergency evacuation 

of building occupants. The elevator use by emergency 

responders would additionally mitigate counterflow problems 

in stairwells.

m Although the United States conducted research on specially 

protected elevators in the late 1970s, the United Kingdom 

along with several other countries that typically utilize British 

standards have required such “firefighter lifts,” located in 

protected shafts, for a number of years.

m Although it is difficult to maintain this pace for more 

than about the first 20 stories, it would take an emergency 

responder between 11⁄2 to 2 hours to reach, for example, the 

60th floor of a tall building if that pace could be maintained 

(see Figure 4-5).
4-16 Emergency management considerations

m Such a delay, combined with the resulting fatigue and physical 

effects on emergency responders that were reported on 

September 11, 2001, would make firefighting and rescue 

efforts difficult even in tall building emergencies not involving 

a terrorist attack.

4.4.3 Mass Care

The shelter plays a critical role in the mass care and response capability as developed in Appendix 3 of the NRP-CIS:

“Mass Care coordinates Federal assistance in support of Regional, 

State, and local efforts to meet the mass care needs of victims of a 

disaster. This Federal assistance will support the delivery of mass 

care services of shelter, feeding, and emergency first aid to disaster 

victims; the establishment of systems to provide bulk distribution 

Figure 4-5 

High-rise buildings and 

emergency response

Source: NIST WTC report

High-Rise Buildings and Emergency Response

Example: Fire department response to a 60-story high-rise building, 

occupants trapped on the 58th and no operating elevators.

Firefighters carrying equipment and 

wearing PPE ~ 125 minutes

Firefighters carrying no equipment and 

not wearing PPE ~ 90 minutes

Firefighters carrying equipment and 

wearing PPE ~ 70 minutes

Firefighters carrying no equipment and 

not wearing PPE ~ 50 minutes

Firefighters begin to climb – 10 minutes

Fire department arrival – 4 minutes

60th floor

58th floor

30th floor

FIRES

Lobby
Emergency management considerations 4-17

of emergency relief supplies to disaster victims; and the collection 

of information to operate a Disaster Welfare Information (DWI) 

system to report victim status and assist in family reunification. 

Depending on the nature of the event, a catastrophic disaster will 

cause a substantial need for mass sheltering and feeding within, 

near, and beyond the disaster-affected area.”

There are a number of assumptions that are used to define the parameters of which the design, utilization, length of occupancy, and 

shelter capacity should be able to support:

m As a result of the incident, many local emergency personnel 

(paid and volunteer) that normally respond to disasters may 

be dead, injured, involved with family concerns, or otherwise 

unable to reach their assigned posts.

m Depending on the nature of the event, a catastrophic disaster 

will cause a substantial need for mass sheltering and feeding 

within, near, and beyond the disaster-affected area.

m State and local resources will immediately be overwhelmed; 

therefore, Federal assistance will be needed immediately.

m Extensive self-directed population evacuations may also occur 

with families and individuals traveling throughout the United 

States to stay with friends and relatives outside the affected area.

m Populations likely to require mass care services include the 

following:

m Primary victims (with damaged or destroyed homes)

m Secondary and tertiary victims (denied access to 

homes)

m Transients (visitors and travelers within the affected 

area)

m Emergency workers (seeking feeding support, respite 

shelter(s), and lodging)
4-18 Emergency management considerations

m In the initial phase (hours and days) of a catastrophic 

disaster, organized and spontaneous sheltering will occur 

simultaneously within and at the periphery of the affected 

area as people leave the area. Additional congregate 

sheltering may be required for those evacuating to adjacent 

population centers.

m The wide dispersal of disaster victims will complicate Federal 

Government assistance eligibility and delivery processes 

for extended temporary housing, tracking, and need for 

registering the diseased, ill, injured, and exposed.

m More people will initially flee and seek shelter from terrorist 

attacks involving CBRE agents than for natural catastrophic 

disaster events. They will also exhibit a heightened concern 

for the health-related implications related to the disaster 

agent.

m Long-term sheltering, interim housing, and the mass relocation of affected populations may be required for incidents 

with significant residential damage and/or contamination. 

m Substantial numbers of trained mass care specialists and 

managers will be required for an extended period of time to 

augment local responders and to sustain mass care sheltering 

and feeding activities.

m Timely logistical support to shelters and feeding sites will be 

essential and required for a sustained period of time. Food 

supplies from the U.S. Department of Agriculture (USDA) 

positioned at various locations across the country will need to 

be accessed and transported to the affected area in a timely 

manner.

m Public safety, health, and contamination monitoring expertise 

will be needed at shelters following CBRE events. Measures to 

ensure food and water safety will be necessary, and the general 
Emergency management considerations 4-19

public will also need to be reassured concerning food and 

water safety.

m Immediately following major CBRE events, decontamination 

facilities may not be readily available in all locations during 

the early stages of self-directed population evacuations. 

People who are unaware that they are contaminated may 

seek entry to shelters. These facilities may, as a result, become 

contaminated, adversely affecting resident health and general 

public trust.

m Public health and medical care in shelters will be a significant 

challenge as local EMS resources and medical facilities will 

likely be overwhelmed quickly. The deployment of public 

health and medical personnel and equipment to support 

medical needs in shelters will need to be immediate and 

sustained by the Department of Health and Human Services 

(HHS). 

m Shelters will likely experience large numbers of elderly with 

specific medication requirements and other evacuees on 

critical home medical care maintenance regimens. 

m Significant numbers of special needs shelters will likely be 

required as nursing homes and other similar care facilities 

are rendered inoperable and are unable to execute their 

evacuation mutual plans and agreements with other local 

facilities. The American Red Cross will coordinate with HHS 

in these situations.

4.5 COMMUNITY SHELTER OPERATIONS PLAN

Community shelters should have a Shelter Operations Plan. The 

plan should describe the different hazards warnings (CBRE, tornadoes, hurricanes, floods, etc.) and Homeland Security Advisory 

System, and clearly define the actions to be taken for each type 

of event. A Community Shelter Management Team composed of 

members committed to performing various duties should be 
4-20 Emergency management considerations

designated. The following is a list of action items for the Community Shelter Operations Plan: 

m The names and all contact information for the coordinators/

managers detailed in Sections 4.5.1 through 4.5.7 should be 

presented in the beginning of the plan. 

m A hazard event notification, natural or manmade, is issued by 

the DHS. 

m When an event notification is issued, the Community Shelter 

Management Team is on alert.

m When a warning is issued, the Community Shelter 

Management Team is activated and begins performing the 

following tasks: 

m Sending the warning signal to the community, alerting 

them to go to the shelter

m Evacuating the community residents from their 

business or homes and to the shelter

m Taking a head count in the shelter 

m Securing the shelter 

m Monitoring the event from within the shelter 

m After the event is over, when conditions warrant, 

allowing shelter occupants to leave and return to their 

homes 

m After the event is over, cleaning the shelter and 

restocking emergency supplies 

A member of the Community Shelter Management Team can take 

on multiple assignments or roles as long as all assigned tasks can 

be performed effectively by the team member before and during 

an event. 
Emergency management considerations 4-21

The following team members would be responsible for overseeing 

the Community Shelter Operations Plan: 

m Site Coordinator 

m Assistant Site Coordinator 

m Equipment Manager 

m Signage Manager 

m Notification Manager 

m Field Manager 

m Assistant Managers 

As previously stated, full contact information (i.e., home and 

work telephone, cell phone, satellite phone, and pager numbers) should be provided for all team members, as well as their 

designated backups. The responsibilities of each of these team 

members are presented in Sections 4.5.1 through 4.5.7. Suggested 

equipment and supplies for shelters are listed in Section 4.5.8 and 

Table 4-1. 

4.5.1 Site Coordinator 

The Site Coordinator’s responsibilities include the following:

m Organizing and coordinating the Community Shelter 

Operations Plan

m Ensuring that personnel are in place to facilitate the 

Community Shelter Operations Plan

m Ensuring that all aspects of the Community Shelter 

Operations Plan are implemented 

m Developing community education and training programs 

m Setting up first aid teams
4-22 Emergency management considerations

m Coordinating shelter evacuation practice drills and 

determining how many should be conducted in order to be 

ready for a real event 

m Conducting regular community meetings to discuss 

emergency planning 

m Preparing and distributing newsletters to area residents 

m Distributing phone numbers of key personnel to area 

residents

m Ensuring that the Community Shelter Operations Plan is 

periodically reviewed and updated as necessary 

4.5.2 Assistant Site Coordinator 

The Assistant Site Coordinator’s responsibilities include the following: 

m Performing duties of the Site Coordinator when he/she is off 

site or unable to carry out his/her responsibilities 

m Performing duties as assigned by the Site Coordinator 

4.5.3 Equipment Manager 

The Equipment Manager’s responsibilities include the following: 

m Understanding and operating all shelter equipment 

(including communications, lighting, and safety equipment, 

and closures for shelter openings) 

m Maintaining and updating, as necessary, the Shelter 

Maintenance Plan (see Section 4.6) 

m Maintaining equipment or ensuring that equipment is 

maintained year-round, and ensuring that it will work 

properly during an event 
Emergency management considerations 4-23

m Informing the Site Coordinator if equipment is defective or 

needs to be upgraded 

m Purchasing supplies, maintaining storage, keeping inventory, 

and replacing outdated supplies 

m Replenishing supplies to pre-established levels following 

shelter usage 

4.5.4 Signage Manager 

The Signage Manager’s responsibilities include the following: 

m Determining what signage and maps are needed to help 

intended shelter occupants get to the shelter in the fastest and 

safest manner possible

m Preparing or acquiring placards to be posted along routes to 

the shelter throughout the community that direct intended 

occupants to the shelter 

m Ensuring that signage complies with ADA requirements 

(including those for the blind) 

m Providing signage in other languages as appropriate for the 

intended shelter occupants 

m Working with the Equipment Manager to ensure that signage 

is illuminated or luminescent after dark and that all lighting 

will operate if a power outage occurs

m Periodically checking signage for theft, defacement, or 

deterioration and repairing or replacing signs as necessary

m Providing signage that clearly identifies all restrictions that 

apply to those seeking refuge in the shelter (e.g., no pets, 

limits on personal belongings) 
4-24 Emergency management considerations

4.5.5 Notification Manager 

The Notification Manager’s responsibilities include the following:

m Developing a notification warning system that lets intended 

shelter occupants know they should proceed immediately to 

the shelter 

m Implementing the notification system when an event warning 

is issued 

m Ensuring that non-English-speaking shelter occupants 

understand the notification (this may require communication 

in other languages or the use of prerecorded tapes) 

m Ensuring that shelter occupants who are deaf receive 

notification (this may require sign language, installation of 

flashing lights, or handwritten notes)

m Ensuring that shelter occupants with special needs receive 

notification in an acceptable manner 

4.5.6 Field Manager 

The Field Manager’s responsibilities include the following: 

m Ensuring that shelter occupants enter the shelter in an 

orderly fashion 

m Pre-identifying shelter occupants with special needs such as 

those who are disabled or have serious medical problems 

m Arranging assistance for those shelter occupants who need 

help getting to the shelter (all complications should be 

anticipated and managed prior to the event) 

m Administering and overseeing first aid by those trained in it 

m Providing information to shelter occupants during an event 

m Determining when it is safe to leave the shelter after an event 
Emergency management considerations 4-25

4.5.7 Assistant Managers 

Additional persons should be designated to serve as backups to 

the Site Coordinator, Assistant Site Coordinator, Equipment Manager, Signage Manager, Notification Manager, and Field Manager 

when they are off site or unable to carry out their responsibilities. 

4.5.8 Emergency Provisions, Equipment, and 

Supplies 

Shelters designed and constructed to the criteria in this manual 

are intended to provide short-term safe refuge. These shelters 

serve a different function from shelters designed for use as longterm recovery shelters after an event; however, shelter managers 

may elect to provide supplies that increase the comfort level within 

the short-term shelters. Table 4-1 lists suggested equipment and 

supplies for community shelters.

Emergency provisions will vary for different hazard events. In general, emergency provisions will include food and water, sanitation 

management, emergency supplies, and communications equipment. 

The necessary emergency provisions are as follows: 

4.5.8.1 Food and Water. For tornado shelters, because of the short 

duration of occupancy, stored food is not a primary concern; however, water should be provided. For hurricane shelters, providing 

and storing food and water are of primary 

concern. As noted previously, the duration of 

occupancy in a hurricane shelter could be as 

long as 36 hours. Food and water would be required, and storage areas for them need to be 

included in the design of the shelter. 

4.5.8.2 Sanitation Management. A minimum of two toilets 

are recommended for both tornado and hurricane shelters. 

Although the short duration of a tornado might suggest that 

toilets are not an essential requirement for a tornado shelter, 

the shelter owner/operator is advised to provide two toilets or at 

least two self-contained, chemical-type receptacles/toilets (and 

FEMA and ARC publications concerning 

food and water storage in shelters may 

be found at http://www.fema.gov and at 

http://www.redcross.org, respectively. 
4-26 Emergency management considerations

Table 4-1: Shelter Equipment and Supplies

Type Equipment/Supplies

Communications 

Equipment

National Oceanic and Atmospheric Administration (NOAA) weather radios or 

receivers for commercial broadcast if NOAA broadcasts are not available

Ham radios or emergency radios connected to the police or the fire and rescue 

systems

Cellular and/or satellite telephones (may not operate during an event and may 

require a signal amplifier to be able to transmit within the shelter)

Battery-powered radio transmitters or signal emitting devices that can signal 

local emergency personnel

Portable generators with uninterruptible power supply (UPS) systems and vented 

exhaust systems

Portable computers with modem and internet capabilities

Fax/copier/scanner

Public address systems

Standard office supplies (paper, notepads, staplers, tape, whiteboards and 

markers, etc.)

Emergency 

Equipment

A minimum of two copies of the Shelter Operations Plan

Flashlights and batteries, glow sticks

Fire extinguishers

Blankets

Pry-bars (for opening doors that may have been damaged or blocked by debris)

Stretchers and/or backboards

Trash receptacles

Automated External Defibrillator (AED)

First aid kit

Trash can liners and ties

Tool kits

Heaters

Megaphones

Note: many of these items may be stored in wall units or credenzas

a room or private area where they may be used) for shelter occupants. Meeting this criterion will provide separate facilities for 

men and women. 
Emergency management considerations 4-27

First Aid Supplies

Adhesive tape and bandages in assorted sizes

Safety pins in assorted sizes

Latex gloves

Scissors and tweezers

Antiseptic solutions

Antibiotic ointments

Moistened towelettes

Non-prescription drugs (e.g., aspirin and non-aspirin pain relievers, antidiarrhea medications, antacids, syrup of ipecac, laxatives)

Smelling salts for fainting spells

Petroleum jelly

Eye drops

Wooden splints

Thermometers

Towels

Fold up cots

First aid handbooks

Water Adequate quantities for the duration of the expected event(s)

Sanitary Supplies

Toilet paper

Moistened towelettes

Paper towels

Personal hygiene items

Disinfectants

Chlorine bleach

Plastic bags

Portable chemical toilet(s), when regular toilets are not contained in the shelter

Infant and 

Children Supplies

Disposable diapers

Powders and ointments

Moistened towelettes

Pacifiers

Blankets

Table 4-1: Shelter Equipment and Supplies (continued)

Type Equipment/Supplies
4-28 Emergency management considerations

Toilets would be needed by the occupants of hurricane shelters 

because of the long duration of hurricanes. The toilets would 

need to function without power, water supply, and possibly waste 

disposal. Whether equipped with standard or chemical toilets, the 

shelter should have at least one toilet for every 75 occupants, in 

addition to the two minimum recommended toilets. 

4.5.8.3 Emergency Supplies. Shelter space should contain, at a 

minimum, the following safety equipment: 

m Flashlights with continuously charging batteries (one 

flashlight per 10 shelter occupants) and glow sticks

m Fire extinguishers (number required based on occupancy 

type) appropriate for use in a closed environment with human 

occupancy, surface mounted on the shelter wall 

m First aid kits rated for the shelter occupancy 

m NOAA weather radio with continuously charging batteries 

m A radio with continuously charging batteries for receiving 

commercial radio broadcasts 

m A supply of extra batteries to operate radios and flashlights 

m An audible sounding device that continuously charges or 

operates without a power source (e.g., canned air horn) to 

signal rescue workers if shelter egress is blocked 

4.5.8.4 Communications Equipment. A means of communication 

other than a landline telephone is recommended for all 

shelters. Blasts, tornadoes, and hurricanes are likely to cause a 

disruption in telephone service. At least one means of backup 

communication should be stored in or brought to the shelter. 

This could be a ham radio, cellular telephone, satellite telephone, 

citizens band radio, or emergency radio capable of reaching 

police, fire, or other emergency service. If cellular telephones are 

relied upon for communications, the owners/operators of the 

shelter should install a signal amplifier to send/receive cellular 

signals from within the shelter. It should be noted that cellular 
Emergency management considerations 4-29

systems may be completely saturated in the hours immediately 

after an event if regular telephone service has been interrupted. 

The shelter should also contain either a battery-powered radio 

transmitter or a signal-emitting device that can be used to signal 

the location of the shelter to local emergency personnel should 

occupants in the shelter become trapped by debris blocking the 

shelter access door. The shelter owner/operator is also encouraged to inform police, fire, and rescue organizations of the shelter 

location before an event occurs. These recommendations apply to 

both aboveground and belowground shelters. 

4.5.8.5 Masks and Escape Hoods. Escape hoods, portable air 

filtration units, and victim recovery units can provide substantial 

protection and response capability against most agents for a minimal cost and without major changes to the space and structural 

system.

Escape masks or hoods (personal protective equipment) can 

be stored at individual desks and in credenzas or wall units in 

common areas. There are many types of escape masks and hoods 

that will provide protection against gases and vapors created by 

fire, chemical and biological agents, and nuclear particles. They 

can be donned very easily and very fast, generally less than 10 seconds and come in one size fits all. 

4.5.8.6 Portable HVAC Units. There are a number of portable 

filtration units designed for hospital, manufacturing, printing, 

and other industries that can be used in a safe room with little 

building modification. The systems typically use HEPA filters to 

filter the air in a room. Combined HEPA-ultraviolet germicidal irradiation (UVGI) units are now becoming available. These units 

can provide substantial protection against biological and radiological particulates. There are several units with combined HEPA 

and activated granular carbon that can provide protection against 

chemical agents as well. The filtration units can be stored in conference rooms, closets, or in specially designed rooms such as 

information technology (IT) closets. 
4-30 Emergency management considerations

4.5.8.7 Emergency Equipment Credenza and Wall Units Storage. 

Many Federal government buildings are being outfitted with 

either an emergency equipment credenza, or built-in wall 

storage units placed in or near the elevator lobby and other 

public egress areas. These units can store the first aid kits, 

escape hoods and masks, and other emergency preparedness 

and response equipment. 

4.6 SHELTER MAINTENANCE PLAN

Each shelter should have a maintenance plan that includes the 

following: 

m An inventory checklist of the emergency supplies (see Table 4-1) 

m Information concerning the availability of emergency 

generators to be used to provide power for lighting and 

ventilation 

m A schedule of regular maintenance of the shelter to be 

performed by a designated party 

Such plans will help to ensure that the shelter equipment and 

supplies are fully functional during an event. 

4.7 Commercial Building Shelter 

Operations Plan

A shelter designed to the criteria of this manual may be used by a 

group other than a residential community (e.g., the shelter may 

have been provided by a commercial business for its workers or by 

a school for its students). Guidance for preparing a Commercial 

Building Shelter Operations Plan is presented in this section. 

4.7.1 Emergency Assignments

It is important to have personnel assigned to various tasks and 

responsibilities for emergency situations before they occur. 

An Emergency Committee, consisting of a Site Emergency 
Emergency management considerations 4-31

Coordinator, a Safety Manager, and an Emergency Security 

Coordinator (and backups), should be formed, and additional 

personnel should be assigned to serve on the committee. 

The Site Emergency Coordinator’s responsibilities include the 

following:

m Maintaining a current Shelter Operations Plan

m Overseeing the activation of the Shelter Operations Plan 

m Providing signage 

m Notifying local authorities 

m Implementing emergency procedures 

m As necessary, providing for emergency housing and feeding 

needs of personnel isolated at the site because of an 

emergency situation 

m Maintaining a log of events 

The Safety Manager’s responsibilities include the following: 

m Ensuring that all personnel are thoroughly familiar with 

the Shelter Operations Plan and are conducting training 

programs that include the following, at a minimum: 

m The various warning signals used, what they mean, 

and what responses are required

m What to do in an emergency (e.g., where to report) 

m The identification, location, and use of common 

emergency equipment (e.g., fire extinguishers)

m Shutdown and startup procedures
4-32 Emergency management considerations

m Evacuation and sheltering procedures (e.g., routes, 

locations of safe areas)

m Conducting drills and exercises (at a minimum, twice 

annually) to evaluate the Shelter Operations Plan and 

to test the capability of the emergency procedures

m Ensuring that employees with special needs have been 

consulted about their specific limitations and then 

determining how best to provide them with assistance during 

an emergency 

m Conducting an evaluation after a drill, exercise, or actual 

occurrence of an emergency situation, in order to determine 

the adequacy and effectiveness of the Shelter Operations 

Plan and the appropriateness of the response by the site 

emergency personnel 

The Emergency Security Coordinator’s responsibilities include the 

following: 

m Opening the shelter for occupancy

m Controlling the movement of people and vehicles at the site 

and maintaining access lanes for emergency vehicles and 

personnel 

m “Locking down” the shelter 

m Assisting with the care and handling of injured persons 

m Preventing unauthorized entry into hazardous or secured 

areas 

m Assisting with fire suppression, if necessary 

FEMA’s United States 

Fire Administration 

publication Emergency 

Procedures for 

Employees with 

Disabilities in Office 

Occupancies [http://

www.usfa.fema.

gov/downloads/pdf/

publications/fa-154.

pdf] is an excellent 

source of information 

on this topic
Emergency management considerations 4-33

The Emergency Committee’s responsibilities include the following: 

m Informing employees in their assigned areas when to shut 

down work or equipment and evacuate the area 

m Accounting for all employees in their assigned areas 

m Turning off all equipment

4.7.2 Emergency Call List

A Shelter Operations Plan for a commercial building should 

include a list of all current emergency contact numbers. A copy 

of the list should be kept in the designated shelter area. The following is a suggested list of what agencies/numbers should be 

included: 

m Office emergency management contacts for the building 

m Local fire department—both emergency and non-emergency 

numbers 

m Local police department—both emergency and nonemergency numbers 

m Local ambulance 

m Local emergency utilities (e.g., gas, electric, water, telephone) 

m Emergency contractors (e.g., electrical, mechanical, 

plumbing, fire alarm and sprinkler service, window 

replacement, temporary emergency windows, general 

building repairs) 

m Any regional office services pertinent to the company 

or companies occupying the building (e.g., catastrophe 

preparedness unit, company cars, communications, mail 

center, maintenance, records management, purchasing/

supply, data processing) 

m Local services (e.g., cleaning, grounds maintenance, waste 

disposal, vending machines, snow removal, post office, 

postage equipment, copy machine repair) 
4-34 Emergency management considerations

4.7.3 Event Safety Procedures

The following safety procedures should be followed upon declaration of an event: 

m The person first aware of the event should notify the 

switchboard operator or receptionist, or management 

immediately. 

m If the switchboard operator or receptionist is notified, he or 

she should notify management immediately. 

m Radios or televisions should be tuned to a local news or 

weather station, and the weather conditions should be 

monitored closely. 

m If official instruction is given to proceed to shelters or 

conditions otherwise warrant, management should notify the 

employees to proceed to and assemble in a designated safe 

area(s). A suggested announcement would be “The area has 

been exposed to a CBRE event (type of event). Please proceed 

immediately to the designated safe area and stay away from all 

windows.” 

m Employees should sit on the floor in the designated 

safe area(s) and remain there until the Site Emergency 

Coordinator announces that conditions are safe for returning 

to work or evacuation. 

4.8 GENERAL CONSIDERATIONS

The Shelter Manager and staff should be familiar with how to do the 

following:

m Avoid contact with liquids on the ground, victim’s clothing, or 

other surfaces

m Evaluate signs/symptoms to determine the type of agent 

involved
Emergency management considerations 4-35

m Separate the victims into groups of symptomatic and 

asymptomatic, ambulatory and non-ambulatory

m Prepare occupants for decontamination (patients may 

undergo gross decontamination with the use of fire hose lines 

or individual shower and portable decontamination units)

In the case of fire, an immediate evacuation to a predetermined 

area away from the facility may be necessary. In a hurricane, evacuation could involve the entire community and take place over a 

period of days. To develop an evacuation policy and procedure:

m Determine the conditions under which an evacuation would 

be necessary.

m Establish a clear chain of command. Identify personnel with 

the authority to order an evacuation. Designate “evacuation 

wardens” to assist others in an evacuation and to account for 

personnel.

m Establish specific evacuation procedures and a system for 

accounting for personnel. Consider employees’ transportation 

needs for community wide evacuations.

m Establish procedures for assisting persons with disabilities and 

those who do not speak English.

m Establish post evacuation procedures.

m Designate personnel to continue or shut down critical 

operations while an evacuation is underway. They must be 

capable of recognizing when to abandon the operation and 

evacuate themselves.

m Coordinate plans with the local emergency management 

office.
4-36 Emergency management considerations

4.9 TRAINING AND INFORMATION

Employees should be trained in evacuation, shelter, and other 

safety procedures. Sessions should be conducted at least annually 

or when:

m Employees are hired.

m Evacuation wardens, shelter managers, and others with special 

assignments are designated.

m New equipment, materials, or processes are introduced.

m Procedures are updated or revised.

m Exercises show that employee performance must be 

improved.

In addition:

m Emergency information such as checklists and evacuation 

maps should be provided.

m Evacuation maps should be posted in strategic locations.

m The information needs of customers and others who visit the 

facility should be considered.
References A

references A-

American Concrete Institute. 1999. Building Code Requirements for 

Structural Concrete and Commentary. ACI 318-02, ACI 318-99, and 

ACI 318R-99. Farmington Hills, MI.

American Red Cross. 2002. Standards for Hurricane Evacuation 

Shelter Selection. ARC 4496. January.

American Society of Civil Engineers, Minimum Design Loads for 

Buildings and Other Structures, ASCE 7-98 Public Ballot Copy, 

American Society of Civil Engineers. Reston, VA. 

American Society for Testing and Materials, Standard Practice for 

Specifying an Equivalent 3-Second Duration Design Loading for Blast 

Resistant Glazing Fabricated with Laminated Glass. ASTM 2248. ASTM 

International, 100 Barr Harbor Drive, West Conshohocken, PA.

ANSI/AF&PA NDS-1997. 1997. National Design Specification for Wood 

Construction. August. 

Batts, M.E., Cordes, M.R., Russell, L.R., Shaver, J.R. and Simiu, 

E. 1980. Hurricane Wind Speeds in the United States. NBS Building 

Science Series 124. National Bureau of Standards (NBS), 

Washington, DC. pp. 41.

Blewett, W.K., Reeves, D.W., Arca, V.J., Fatkin, D.P., and Cannon, 

B.D. May 1996. Sheltering in Place: An Evaluation for the Chemical 

Stockpile Emergency Preparedness Program, ERDEC-TR-336, U.S. Army 

Edgewood Research, Development and Engineering Center, Aberdeen Proving Ground, MD.

Blewett, W.K. February 2002. Fail-Safe Application and Design of Air 

Conditioners for NBC Collective Protection Systems, ECBC-TR-223, U.S. 

Army Edgewood Chemical Biological Center, Aberdeen Proving 

Ground, MD.
A- references

Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). 

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Blewett, W.K., and Arca, V.J. June 1999. Experiments in Sheltering in 

Place: How Filtering Affects Protection Against Sarin and Mustard Vapor, 

ECBC-TR-034, U.S. Army Edgewood Chemical Biological Center, 

Aberdeen Proving Ground, MD.

Carter, R. R. May 1998. Wind-Generated Missile Impact on Composite 

Wall Systems. MS Thesis. Department of Civil Engineering, Texas 

Tech University, Lubbock, TX. 

Clemson University Department of Civil Engineering. January 

2000. Enhanced Protection from Severe Wind Storms. Clemson 

University, Clemson, SC.

Coats, D. W., and Murray, R. C. August 1985. Natural Phenomena 

Hazards Modeling Project: Extreme Wind/Tornado Hazard Models 

for Department of Energy Sites. UCRL-53526. Rev. 1. Lawrence 

Livermore National Laboratory, University of California, 

Livermore, CA. 

“Design of Collective Protection Shelters to Resist Chemical, 

Biological, and Radiological Agents.” ETL-1110-3-498, February 

24, 1999. U.S. Army Corps of Engineers, Washington, DC.

Durst, C.S. 1960. “Wind Speeds Over Short Periods of Time,” 

Meteorology Magazine, 89. pp.181-187.

Engelmann, R.J. May 1990. Effectiveness of Sheltering in Buildings and 

Vehicles for Plutonium, DE90-016697, U.S. Department of Energy, 

Washington, DC.

Federal Emergency Management Agency. 1980. Interim Guidelines 

for Building Occupant Protection From Tornadoes and Extreme Winds. 

TR-83A. September. 
references A-

Federal Emergency Management Agency. 1982. Tornado Protection: 

Selecting and Designing Safe Areas in Buildings. TR-83B. October.

FEMA RR-7. 1986. Civil Defense Shelters A State of the Art Assessment.

FEMA TR-87. Standards for Fallout Shelters.

FEMA TR-29. Architect and Engineer Activities in Shelter Development.

Federal Emergency Management Agency. 1988. Rapid Visual 

Screening of Building for Potential Seismic Hazards: A Handbook FEMA 

154 Earthquake Hazards Reduction Series 41. July.

Federal Emergency Management Agency. 1988. Handbook for the 

Seismic Evaluation of Buildings. FEMA 310.

Federal Emergency Management Agency. 1997. NEHRP 

Recommended Provisions for Seismic Regulations for New Buildings. 

FEMA 302A.

Federal Emergency Management Agency. 1999a. Midwest Tornadoes 

of May 3, 1999: Observations, Recommendations, and Technical 

Guidance. FEMA 342. October.

Federal Emergency Management Agency. 1999b. National 

Performance Criteria for Tornado Shelters. May.

Federal Emergency Management Agency. 2000. Design and 

Construction Guidance for Community Shelters. FEMA 361. July.

Federal Emergency Management Agency. 2003. Reference Manual 

to Mitigate Potential Terrorist Attacks Against Buildings. FEMA 426. 

December.

Federal Emergency Management Agency. 2004. Taking Shelter From 

the Storm: Building a Safe Room Inside Your House. FEMA 320. March.
A- references

Federal Emergency Management Agency. 2004. Using HAZUS-MH 

for Risk Assessment. FEMA 433. August.

Federal Emergency Management Agency. 2005. A How-To Guide 

to Mitigate Potential Terrorist Attacks Against Buildings. FEMA 452. 

January.

Federal Emergency Management Agency. Designing for Earthquakes: 

A Manual for Architects. FEMA 454. Undated.

Federal Emergency Management Agency and U.S. Fire 

Administration. Emergency Procedures for Employees with Disabilities in 

Office Occupancies. FEMA 154. Undated. 

Fujita, T.T. 1971. Proposed Characterization of Tornadoes and 

Hurricanes by Area and Intensity. SMRP No. 91. University of 

Chicago, Chicago, IL.

HQ AFCESA/CES, Structural Evaluation of Existing Buildings for 

Seismic and Wind Loads. Engineering Technical Letter (ETL) 97-10.

Kelly, D.L., J.T. Schaefer, R.P. McNulty, C.A. Doswell III, and R.F. 

Abbey, Jr. 1978. “An Augmented Tornado Climatology.” Monthly 

Weather Review, Vol. 106, pp. 1172-1183.

Krayer, W.R. and Marshall, R.D. 1992. Gust Factors Applied to 

Hurricane Winds. Bulletin of the American Meteorology Society, 

Vol. 73, pp. 613-617.

Masonry Standards Joint Committee. 1999. Building Code 

Requirements for Masonry Structures and Specification for Masonry 

Structures. ACI 530-99/ASCE 5-99/TMS 402-99 and ACI 530.1/

ASCE 6-99/TMS 602-99.

Mehta, K.C. 1970. “Windspeed Estimates: Engineering Analyses.” 

Proceedings of the Symposium on Tornadoes: Assessment of Knowledge and 

Implications for Man. 22-24 June 1970, Lubbock, TX. pp. 89-103.
references A-

Mehta, K.C., and Carter, R.R. 1999. “Assessment of Tornado 

Wind Speed From Damage to Jefferson County, Alabama.” Wind 

Engineering into the 21st Century: Proceedings, 10th International 

Conference on Wind Engineering, A. Larsen, G.L. Larose, and F.M. 

Livesey, Eds. Copenhagen, Denmark. June 21-24. pp. 265-271.

Mehta, K.C., Minor, J.E., and McDonald, J.R. 1976. “Wind Speed 

Analysis of April 3-4, 1974 Tornadoes.” Journal of the Structural 

Division, ASCE, 102(ST9). pp. 1709-1724.

Minor, J.E., McDonald, J.R., and Peterson, R.E. 1982. “Analysis 

of Near-Ground Windfields.” Proceedings of the Twelfth Conference 

on Severe Local Storms (San Antonio, Texas, 11-15 January 1982). 

American Meteorological Society, Boston, MA.

National Concrete Masonry Association. 1972. Design of Concrete 

Masonry Warehouse Walls. TEK 37. Herndon, VA.

National Fire Protection Association. 1999. Standard for Healthcare 

Facilities. NFPA 99.

National Fire Protection Association. 2003. Building Construction 

and Safety Code Handbook. NFPA 5000.

National Fire Protection Association. 2004. Disaster/Engineering 

Management and Business Continuity Programs. NFPA 1600.

National Fire Protection Association. 2006. Life Safety Code. NFPA 

101. 

NIST Technical Note 1426. U.S. Department of Commerce 

Technology Administration, National Institute of Standards and 

Technology, Washington, DC. July.

O’Neil, S., and Pinelli, J.P. 1998. Recommendations for the Mitigation 

of Tornado Induced Damages on Masonry Structures. Report No. 

1998-1. Wind & Hurricane Impact Research Laboratory, Florida 

Institute of Technology. December.
A- references

Phan, L.T., and Simiu, E. 1998. The Fujita Tornado Intensity Scale: A 

Critique Based on Observations of the Jarrell Tornado of May 27, 1997.

Pietras, B. K. 1997. “Analysis of Angular Wind Borne Debris 

Impact Loads.” Senior Independent Study Report. Department of 

Civil Engineering, Clemson University, Clemson, SC. May.

Powell, M.D. 1993. Wind Measurement and Archival Under the 

Automated Surface Observing System (ASOS). Bulletin of American 

Meteorological Society, Vol. 74, 615-623.

Powell, M.D., Houston, S.H., and Reinhold, T.A. 1994. 

“Standardizing Wind Measurements for Documentation of 

Surface Wind Fields in Hurricane Andrew.” Proceedings of the 

Symposium: Hurricanes of 1992 (Miami, FL, December 1-3, 1993). 

ASCE, New York. pp. 52-69.

Recommendations to Appendix E, “Planning Guidelines for 

Protective Actions and Responses for the Chemical Stockpile 

Emergency Preparedness Program,” Section E.4, 17 May 96.

Rogers, G.O., Watson, A.P., Sorensen, J.H., Sharp, R.D., and 

Carnes, S.A. 1990. Evaluating Protective Actions for Chemical Agent 

Emergencies, ORNL-6615, Oak Ridge National Laboratory, Oak 

Ridge, TN. April.

Sciaudone, J.C. 1996. Analysis of Wind Borne Debris Impact Loads. 

MS Thesis. Department of Civil Engineering, Clemson University, 

Clemson, SC. August.

Steel Joist Institute. Steel Joist Institute 60-Year Manual 1928-1988. 

Texas Tech University Wind Engineering Research Center. 

1998. Design of Residential Shelters From Extreme Winds. Texas Tech 

University, Lubbock, TX. July.

Twisdale, L.A., and Dunn, W.L. 1981. Tornado Missile Simulation 

and Design Methodology. EPRI NP-2005 (Volumes I and II). 

Technical Report. Electric Power Research Institute, Palo Alto, 

CA. August.
references A-

Twisdale, L.A. 1985. “Analysis of Random Impact Loading Conditions.” Proceedings of the Second Symposium on The Interaction of 

Non-Nuclear Munitions with Structures. Panama City Beach, FL. April 

15-18.

U.S. Department of Energy. 1994. Natural Phenomena Hazards 

Design and Evaluation Criteria for Department of Energy Facilities. DOESTD-1020-94. Washington, DC. April.

General Use Security Documents 

DoD Field Manual No. 3-19.30, Physical Security, 8 January 2001. 

Headquarters, Department of the Army, Washington, DC.

UG-2031-SHR: Protection Against Terrorist Vehicle Bombs, May 1998. 

Naval Facilities Engineering Service Center, Security Engineering 

Division Port Hueneme, CA 93043.

Department of the Air Force, Force Protection Battlelab Vehicle Bomb 

Mitigation Guide, 01 July 1999.

Terrorist Bomb Threat Stand-Off Card. Defense Threat Reduction 

Agency, Washington, DC. 1995.

Project Development and Design Security 

Documents

DoD Army TM 5-853-1/AFMAN 88-56, Vol. 1, 5/94, Security Engineering Project Development. Department of the Army, U.S. Army 

Corps of Engineers, Washington, DC 20314-1000.

Army TM 5-853-2/Air Force AFMAN 32-1071, Vol. 2, Security 

Engineering Concept Design, 5/94. Department of the Army, U.S. 

Army Corps of Engineers, ATM: CEYP-ET, Washington, DC 20314-

1OOU.

DoD Army TM 5-853-3/AFMAN 32-1071, Vol. 3, 5/94, Security Engineering Final Design. U.S. Army Corps of Engineers, Washington, 

DC 20314-1OOU.
A- references

Army TM 5-853-4, Security Engineering Electronic Security Systems,

5/94. U.S. Army Corps of Engineers, Washington, DC 20314-

1OOU.

DoD Army TM 5-855-4/AFMAN 32-1071, Vol. 3, 11/86, Heating, 

Ventilation, and Air Conditioning of Hardened Installations. U.S. Army 

Corps of Engineers, Washington, DC 20314-1OOU.

DoD UFC 4-010-01, Minimum Antiterrorism Standards.

DoD UFC 4-023-03, Design of Buildings to Prevent Progressive Collapse.

DC 20314-1OOU20314-1OOUB.7 Army Corps of Engineers Blast 

Analysis Manual, Part 1 - Level of Protection Assessment Guide, PDCTR-91-6 dated 7/91. U.S. Army Corps of Engineers, Omaha, NE.

TDS 2063-SHR, Blast Shielding Walls, 9/98. U.S. Army Corps of Engineers, Washington, DC 20314-1OOU.

UG-2030-SHR: Security Glazing Applications, 5/98. U.S. Army Corps 

of Engineers, Washington, DC 20314-1OOU.

Threat, Vulnerability, and Risk Assessment

Risk Assessment Method Property Analysis and Ranking Tool (RAMPART) being developed by Sandia National Laboratories for GSA. 

(Currently no copy available)

CNO Antiterrorism/Force Protection Division (N34) Integrated 

Vulnerability Assessment (IVA) Guide.

Vulnerability Assessment Worksheet from U.S. Army Reserve. Headquarters, Department of the Army, Washington, DC.

Port Integrated Vulnerability Assessment (PIVA) For Civilian and Other 

Non-US Military Ports (Rev-00).

TDS 2062-SHR, Estimated Damage to Structures from Terrorist Bombs,

9/98. U.S. Army Corps of Engineers, Washington, DC.
references A-

Military Handbook, Design Guidelines for Security Fencing, Gates, Barriers, and Guard Facilities, MIL-HDBK-1013/10, 5/93. Department 

of Defense, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Progressive 

Collapse Design Guidance, 4/00. Department of Defense, Washington, DC.

TDS-2079-SHR, Planning and Design Considerations for Incorporating 

Blast Mitigation in Mailrooms. Naval Facilities Engineering Service 

Center, Port Hueneme, CA.

Corps of Engineers Guide Specifications for Construction of Fencing,

4/99. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Vehicle Barriers, 3/98. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Blast Resistant 

Doors, 11/97. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Fragment 

Retention Film for Glass, 7/92. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Security Vault 

Door, 12/97. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Forced Entry 

Resistant Components, 4/99. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Bullet-resistant 

Components, 4/00. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Guide Specifications for Construction of Electromagnetic (Em) Shielding, 4/99. U.S. Army Corps of Engineers, 

Washington, DC.
A-10 references

Corps of Engineers Guide Specifications for Construction of Self-acting 

Blast Valves, 7/97. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Technical Letter No. 1110-3-494, Airblast Protection Retrofit for Unreinforced Concrete Masonry Walls, 7/99. U.S. Army 

Corps of Engineers, Washington, DC.

Corps of Engineers Technical Letter No. 1110-3-495, Estimating 

Damage To Structures From Terrorist Bombs, Field Operations Guide,

7/99. U.S. Army Corps of Engineers, Washington, DC.

Corps of Engineers Technical Letter No. 1110-3-498, Design of Collective Protection Shelters to Resist Chemical, Biological, and Radiological 

(CBR) Agents, 2/99. U.S. Army Corps of Engineers, Washington, 

DC.

Emergency Management and Protective Actions

Preparing Makes Sense. Get Ready Now. http://www.ready.gov

General guidance from DHS on steps to take to prepare for and 

respond to intentional or accidental releases of chemical, biological and radiological agents and a nuclear blast. Covers schools 

and daycare, neighborhoods and apartment buildings, and the 

workplace. 

Bioterrorism Preparedness and the Citizen. Centers for Disease Control and 

Prevention. http://www.pamf.org/bioterror/links.html (chemical 

and radiological preparedness guidance)

Current guidance on proper actions to take for chemical and radiological events.

Facts About Shelter in Place – Chemical Emergencies. Centers for Disease Control. http://www.bt.cdc.gov/planning/shelteringfacts.pdf

More detailed guidance on protective actions in event of chemical 

release.
references A-11

Websites on Sheltering in Place. http://www.scchealth.org/docs/

doche/bt/interim.html

Warning, Evacuation and In-Place Protection Handbook, Emergency 

Management Division, Michigan Division of Emergency Management, 1994. http://floridadisaster.org/bpr/

Warning systems, protective action decision-making, case studies 

involving chlorine, bromide, and sulfuric acid. Good source for 

protective actions and shelter considerations in a chemical incident.

Will Duct Tape and Plastic Really Work? Issues Related to Expedient 

Shelter-In-Place. John Sorensen and Barbara Vogt. August 2001. 

CSEPP, FEMA. 

Defines and discusses expedient sheltering and the effectiveness 

of select materials, including duct tape. 

Shelters by Building Occupancy

Sheltering in the Workplace

Sheltering in Place at Your Office – A general guide for preparing a 

shelter in place plan in the workplace. National Institute for Chemical 

Studies. http://www.nicsinfo.org

Provides a sample shelter plan that lists procedures, responsible 

parties, and needed supplies, equipment and rules. 

Fact Sheet on Shelter-in-Place, American Red Cross. 

Provides the basics on shelter-in-place at home and the workplace. 

February 2003

Fire and Explosion Planning Matrix (OSHA, 2004). 

http://www.osha.gov/dep/fire-expmatrix/index.html
A-12 references

Addresses workplace vulnerability to acts of terrorism and identifies of series of terrorism risk factors (see below) that may elevate 

the risk of that facility to terrorism acts. These factors may be 

considered in this project as criteria for higher level of in-place 

shelter. 

In its Worksite Risk Assessment List [http://www.llr.state.sc.us/

workplace/sectone.pdf – 507kb PDF], an employer will be asked 

whether the worksite is characterized by any of the following terrorism risk factors:

m	 uses, handles, stores or transports hazardous materials; 

m	 provides essential services (e.g., sewer treatment, 

electricity, fuels, telephone, etc.); 

m	 has a high volume of pedestrian traffic; 

m	 has limited means of egress, such as a high-rise 

complex or underground operations; 

m	 has a high volume of incoming materials (e.g., mail, 

imports/exports, raw materials); 

m	 is considered a high profile site, such as a water dam, 

military installation, or classified site; or 

m	 is part of the transportation system, such as shipyard, 

bus line, trucking, airline. 

Sheltering in Schools

Fairfax County, VA school preparedness and emergency management – good overall document for school preparedness and 

shelter in place. http://www.fcps.edu/emergencyplan/faq.htm

Comprehensive guidance on protective actions for public schools.

Schools and Terrorism: A Supplement to the National Advisory Committee 

on Children and Terrorism, Recommendations to the Secretary (August 

12, 2003) 
references A-13

Examines the broader issues of integrating school vulnerability 

and safety issues into community preparedness. 

Primer to Design Safe School Projects in Case of Terrorist Attacks. 2003. 

FEMA. December. 

Provides comprehensive guidance to protect students, faculty, staff 

and their school buildings from terrorist attacks. 

Creating a Safe Haven, Dennis Young, http://asumag.com/ar/university_creating_safe_haven/

Guidance on incorporating safe haven principles into school design and construction.

Sheltering in Place – Princeton University 

Guidance on protective actions for a campus setting.

Shelters by Hazard – Natural

Hurricanes

Hurricane Shelters, American Red Cross. Provides basic criteria 

for shelter designation for hurricane shelters. http://www.ih2000.

net/jasperem/Hurricane%20-%20Shelters.pdf

Shelter Implementation Workshop. Florida Division of Emergency 

Management, June 2000. 

Proceedings on workshop that addresses problems, issues, and solutions for implementing statewide plan for hurricane shelters. 

Standards for Hurricane Evacuation Shelter Selection. American Red 

Cross (ARC 4496). January 2002

ARC 4496 is the national standard for hurricane evacuation 

shelter selection criteria. Provides detailed guidance and standards for hurricane shelter selection. 
A-14 references

State of Florida Shelter Plan, Florida Division of Emergency 

Management, 2004. http://floridadisaster.org/bpr/Response/

engineers/documents/2004SESP/Individual%20Elements/2004-

SESP-AppxB.pdf

Public shelter design criteria, based on ARC 4496 and Florida design criteria. State requirements for education facilities. 

http://floridadisaster.org/bpr/Response/engineers/2004sesp.

htm. The website of the Critical Infrastructure and Engineering 

Unit of the Florida Division of Emergency Management. Contains 

links to shelter surveys and plans. 

Tornadoes and High Winds

Taking Shelter From the Storm: Building a Safe Room Inside Your House. 

FEMA 320. http://www.fema.gov/pdf/fima/fema320.pdf.

FEMA 320 provides guidance on shelter design and construction 

of the following types of shelters:

m shelter underneath a house

m shelter in the basement of a new house

m shelter in the interior of a new house

m modification of an existing house to add a shelter in 

one of these areas

FEMA Community Wind Shelters: Background and Research. 2002.

Extreme Event Protection (Hurricanes and Tornadoes). 

http://www.builtsafe.com/steelclad.pdf

Example of one Texas-based product on the market for extreme 

wind event protection.
references A-15

Earthquakes

Federal Emergency Management Agency. 1988. Handbook for the 

Seismic Evaluation of Buildings. FEMA 310. January.

Federal Emergency Management Agency. 1990. Seismic Considerations for Elementary and Secondary Schools. FEMA 149.

Federal Emergency Management Agency. 2003. Existing School 

Buildings: Incremental Seismic Retrofit Opportunities. FEMA 318. December.

Shelters by Hazard – Manmade Hazards/Threats 

Harden Structures and Systems – Apocalypse House (2003). 

Focuses on shelter design for climatic, nuclear, biological, 

chemical and conventional weapons threats, and the guidelines 

established by the Federal Emergency Management Agency 

(FEMA), the U. S. Department of Energy Oak Ridge National 

Laboratory, as well as more rigorous standards set by the Technical 

Directives for Shelters by the Swiss Federal Department of Civil 

Defense. 

Building and Shelter Design: Security and 

Protection Issues 

Building Security Through Design: A Primer for Architects, Design Professionals and Their Clients. AIA. 

Protecting Occupants of High-Rise Buildings. Rae Archibald (Deputy 

Fire Commissioner for NYC), http://www.rand.org/publications/

randreview/issues/rr.08.02/occupants.html

Recommended actions for building owners of high-rise buildings. 

Guidance Publication for Emergency Operations Centers: Project Development and Capabilities Assessment, Florida Division of Emergency 
A-16 references

Management (2003) http://floridadisaster.org/bpr/Response/

engineers/eoc/eocguide.pdf

Provides guidance on a broad range of vulnerability assessment 

and vulnerability reduction measures for the FDEM EOC. Many 

of the recommendations for EOC survivability, sustainability, and 

interoperability can be applied to multi-hazard shelters. 

Security Engineering (Army TM 5-853/Air Force Manual 32-1071)

Design and Analysis of Hardened Structures to Conventional Weapons Effects (TM 5-855-1)

The Homeland Defense Office of the U.S. Army Soldier and Biological Chemical Command (publications, products, and services):

ANSI/ASME N510, Testing of Nuclear Air Treatment Systems, 1989.

ASHRAE, Handbook of Fundamentals, 1997.

ASHRAE 52.1, Gravimetric and Dust-Spot Procedures for Testing AirCleaning Devices Used in General Ventilation for Removing Particulate 

Matter, 1992.

ASHRAE, Handbook Applications Environmental Control for Survival,

1982.

ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality,

1989.

ASHRAE Ventilation Standard 62-1981,1

ASME AG-1, Section FC, Code on Nuclear Air and Gas Treatment,

1996.

ASME N509, Nuclear Power Plant Air-Cleaning Units and Components,

1989.
references A-17

ASME NQA-1, Quality Assurance Requirements for Nuclear Facility Applications, 1994.

ASTM E779-03, Standard Test Method for Determining Air Leakage Rate 

by Fan Pressurization, 1987.

EA-C-1704, Carbon-Activated, Impregnated, Copper-Silver-Zinc-Molybdenum-Triethylenediamine (ASZM-TEDA), U.S. Army Edgewood 

Research, Development and Engineering Center (ERDEC), Aberdeen Proving Grounds, MD. January 1992.

ERDEC-TR-336, Expedient Sheltering In Place: An Evaluation for the 

Chemical Stockpile Emergency Preparedness Program, U.S. Army Edgewood Research, Development and Engineering Center (ERDEC), 

Aberdeen Proving Grounds, MD. June 1996.

FM 3-4, NBC Protection, 29 May 1992.

IEEE Std-344, IEEE Recommended Practice for Seismic Qualification of 

Class 1E Equipment for Nuclear Power Generating Stations, 1987.

MIL-PRF-32016(EA), Performance Specification Cell, Gas Phase, Adsorber, 26 November 1997.

MIL-STD-282, Filter Units, Protective Clothing, Gas-Mask Components 

and Related Products: Performance-Test Method, 28 May 1956.

MS MIL-F-51079D, Filter Medium, Fire-Resistant, High-Efficiency, 17 

February 1988.

NFPA 101, Life Safety Code, 1997.

TM 5-810-1, Mechanical Design Heating, Ventilating, and Air Conditioning, 15 June 1991.

TM 5-855-1, Design and Analysis of Hardened Structures to Conventional Weapons Effects, August 1998.
A-18 references

UL 586, High-Efficiency, Particulate, Air Filter Units, 1996.

ER 1110-345-100, Design Policy for Military Construction. 
ABBREVIATIONS AND ACRONYMS B

Abbreviations and Acronyms B-

A

ACI	 American Concrete Institute

ADA	 Americans with Disabilities Act

AED	 Automated External Defibrillator

AF & PA	 American Forest and Paper Association

AFCESA	 Air Force Civil Engineering Support Agency

AFMAN	 Air Force Manual

AIA	 American Institute of Architects

ANFO	 ammonium nitrate and fuel oil

ANSI	 American National Standards Institute

ARC	 American Red Cross

ASCE	 American Society of Civil Engineers

ASF	 anti-shatter film

ASHRAE	 American Society of Heating, Refrigeration, and 

Air-Conditioning Engineers

ASME	 American Society of Mechanical Engineers

ASOS	 Automated Surface Observing System

ASTM	 American Society for Testing and Materials

ATF	 Bureau of Alcohol, Tobacco, Firearms, and 

Explosives
B- Abbreviations and Acronyms

C

CA	 California

C&C	 components and cladding

CBF	 concentric braced frame

CBR	 chemical, biological, and radiological

CBRE	 chemical, biological, radiological, and explosive

CBRNE	 chemical, biological, radiological, nuclear, and 

explosive

CCA	 Contamination Control Area

CCP	 Casualty Collection Point

cfm	 cubic feet per minute

CIS	 Catastrophic Incident Supplement

cm centimeter

CMU	 concrete masonry unit

CO2 carbon dioxide

CPTED	 Crime Prevention Through Environmental Design

CSEPP	 Chemical Stockpile Emergency Preparedness 

Program

CST	 Civil Support Team

D

DBT	 design basis threat

DC	 District of Columbia

DHS	 Department of Homeland Security

DMAT	 Disaster Medical Assistance Team
Abbreviations and Acronyms B-

DMORT	 Disaster Mortuary Operational Response Team

DoD	 Department of Defense

DOE	 Department of Energy

DOJ	 Department of Justice

DWI	 Disaster Welfare Information

E

EBF	 eccentric braced frame

ECBC	 Edgewood Chemical Biological Center

ED	 Emergency Director

EDCS	 Emergency Decontamination Corridor System

EMG	 Emergency Management Group

EMS	 Emergency Medical Services

EOC	 Emergency Operations Center 

EOC	 Emergency Operator Coordinator

EOD	 Explosive Ordnance Dispersal

EOG	 Emergency Operations Group

EPRI	 Electric Power Research Institute

ERDEC	 Edgewood Research, Development, and 

Engineering Center (U.S. Army)

ERT-JA	 Emergency Response to Terrorism: Job Aid

ESF	 Emergency Support Function

ETL	 Engineering Technical Letter
B- Abbreviations and Acronyms

F

FBI	 Federal Bureau of Investigation

FCO	 Federal Coordinating Officer 

FDEM	 Florida Department of Emergency Management

FEMA	 Federal Emergency Management Agency

FF	 firefighter

FL	 Florida

FMC Federal Mobilization Center

fps	 feet per second

FRC	 Federal Resources Coordinator

FRF	 fragment retention film

ft	 foot, feet

ft2 square foot, feet

G

gal	 gallon, gallons

GSA	 General Services Administration

H

HazMat	 hazardous material

HEGA	 high-efficiency gas adsorber

HEPA	 high-efficiency particulate air

HHS	 Department of Health and Human Services

HPS	 Health Physics Society
Abbreviations and Acronyms B-

HQ	 Headquarters

hr	 hour, hours

HSDL Homeland Security Digital Library

HSOC	 Homeland Security Operations Center

HSPD	 Homeland Security Presidential Directive

HSS	 Hollow Structural Section

HVAC	 heating, ventilation, and air conditioning 

I

IAEA	 International Atomic Energy Agency

IAEM	 International Association of Emergency Managers

IBC	 International Building Code

IC	 Incident Commander

ICP	 Incident Command Post

ICS	 Incident Command System

IEEE Institute of Electrical and Electronics Engineers

IGU	 insulated glazing unit

IIMG	 Interagency Incident Management Group

IL	 Illinois

IMC	 International Mechanical Code

IMT	 Incident Management Team

ISAO	 Information Sharing and Analysis Organization

ISC	 Interagency Security Commitee

IT	 information technology

IVA	 Integrated Vulnerability Assessment

iwg	 inch water gauge
B- Abbreviations and Acronyms

J

JFO	 Joint Field Office

K

kb	 kilobyte

kg	 kilogram

km	 kilometer

l

l	 liter

lb	 pound

lbs pounds

LDS	 Ladder Pipe Decontamination System

LOP	 level of protection

LPG	 liquefied petroleum gas

M

m	 meter

MA	 Massachusetts

MCC	 Movement Coordination Center

MD	 Maryland

MERV	 minimum efficiency reporting value

mg	 milligram 

MI	 Michigan
Abbreviations and Acronyms B-

min minimum

mm millimeter

mph	 miles per hour

N

NASAR	 National Association for Search and Rescue

NBS National Bureau of Standards

NCIS National Institute for Chemical Studies

NCTC National Counterterrorism Center

NDMS	 National Disaster Medical System

NDS	 National Design Specifications

NE Nebraska

NEHRP National Earthquake Hazards Reduction Program

NEMA	 National Emergency Management Association

NFPA	 National Fire Protection Association

NIMS	 National Incident Management System

NIST	 National Institute of Standards and Technology

NMRT	 National Medical Response Team

NMRT-WMD	 National Medical Response Team-Weapons of 

Mass Destruction

NOAA	 National Oceanic and Atmospheric 

Administration

NRCC	 National Response Coordination Center

NRP	 National Response Plan

NWS	 National Weather Service
B- Abbreviations and Acronyms

O

O.C. on center

OG	 outer garments

OH	 Ohio

ORNL	 Oak Ridge National Laboratory

OSHA	 U.S. Occupational Safety and Health 

Administration

P

PA Pennsylvania

PAG	 Protective Action Guidance

PAO	 poly-alpha olefin

PC	 personal computer

PDA	 personal data assistant

PFO	 Principal Federal Official

PHS	 U.S. Public Health Service

PIVA	 Port Integrated Vulnerability Assessment

PPE	 personal protective equipment

PSA	 Patient Staging Area

psi	 pounds per square inch

PVB	 polyvinyl butyral

R

RAMPART	 Risk Assessment Method Property Analysis and 

Ranking Tool
Abbreviations and Acronyms B-

RDD	 radiological dispersal device (“dirty bomb”)

RRCC	 Regional Response Coordination Center

S

SC	 South Carolina

SCWB	 strong-column weak-beam

SFPE	 Society of Fire Protection Engineers

SGP	 Sentry Glass ® Plus

SIOC	 Strategic Information and Operations Center 

(FBI HQ)

sq ft	 square feet

SRA Safe Refuge Area

SRWF	 shatter-resistant window film

STD	 Standard

T

TCL	 Target Capabilities List

TFA	 Toxic-free Area

TM	 Technical Manual

TMS	 The Masonry Society

TN	 Tennessee

TNT	 trinitrotoluene

TR	 Technical Report

TX	 Texas
B-10 Abbreviations and Acronyms

U

UBC	 Building Code

UCRL University of California Radiation Laboratory

UFC	 United Facilities Criteria

UK	 United Kingdom

UL	 Underwriters Laboratories

UPS	 uninterruptible power supply

URM	 unreinforced masonry

U.S.	 United States

US&R	 Urban Search and Rescue

USDA	 U.S. Department of Agriculture

UTL	 Universal Task List

UV	 ultraviolet

UVGI ultraviolet germicidal irradiation

V

VA	 Virginia

W

WA	 Washington

WMD	 Weapons of Mass Destruction

WMD-CST	 Weapons of Mass Destruction-Civil Support Team

WTC	 World Trade Center