Design and Construction Guidance for Community Safe Rooms
FEMA 361, Second Edition/August 2008

CHAPTER 2  PROTECTION OBJECTIVES

As noted in Chapter 1, FEMA has developed prescriptive designs for 
residential 
and small community safe rooms (for 16 or fewer occupants) designed to 
near-
absolute protection for the occupants of a home or small business during 
extreme-wind events. The May 1999 MAT investigation of the tornadoes in 
Oklahoma 
and Kansas made it clear that an extreme-wind event can cause a large loss 
of 
life or a large number of injuries in high-occupancy buildings (e.g., 
schools, 
hospitals and other critical care facilities, nursing homes, day care 
centers, 
and commercial buildings). Extreme-wind events can also cause a large loss 
of 
life or a large number of injuries in residential neighborhoods where 
people do 
not have access to either in-residence or community safe rooms. Based on 
the 
concepts for the residential safe rooms, the first edition of FEMA 361 was 
developed to provide design professionals with guidance on the design of 
community safe rooms that can accommodate large groups of people for 
protection 
from extreme-wind events for larger, at-risk populations. 

This publication provides guidance addressing the design and engineering 
issues 
for design and construction of stand-alone community safe room 
buildings, 
constructing safe rooms within or as a part of a new building, and adding 
a safe 
room to an existing building. Guidance is also provided by identifying 
wall and 
roof sections capable of withstanding impacts from windborne debris 
(missiles). 
Although arguably not required for life-safety protection from extreme-
wind 
events, the criteria on reconciling non-structural design criteria with 
the 
model building, fire, and life-safety codes are also included, along with 
a 
discussion of emergency considerations such as evacuation and operations 
plans. 

This publication provides guidelines for the design and construction of 
safe 
rooms with the objective of near-absolute protection. This level of life-
safety 
protection, and the criteria upon which it is based, distinguish this 
manual 
from other design standards and model codes, including the ICC-500. To 
better 
understand these differences, Table 2-1, presented later in this chapter, 
gives 
a detailed review of basic criteria and provisions of all major design 
standards, codes, and guidelines related to safe room and shelter design 
and 
construction.

The design and planning necessary for high-capacity safe rooms that may be 
required for use in large, public venues such as stadiums or amphitheaters 
are 
beyond the scope of this manual. An owner or operator of such a venue may 
be 
guided by concepts presented in this publication, but detailed guidance 
concerning extremely high-capacity safe rooms is not provided. The design 
of 
such safe rooms requires attention to behavioral and other non-engineering 
issues that affect the life safety of a large number of people. Egress 
timing 
for thousands of people in a stadium, how to manage a large group of 
individuals 
in a safe room or shelter, and security within a shelter or safe room are 
examples of behavioral and other non-engineering issues that should be 
addressed 
when protecting a large group of people. However, these issues are also 
beyond 
the scope of this publication. 

[Begin text box]
WARNING 
A safe room designed according to the guidance presented in this manual 
provides 
near-absolute protection from death and injury, even though the building 
itself 
may be damaged during a design event. (A design event is determined by 
design 
wind speeds for tornadoes and hurricanes from the maps in Figures 3-1 and 
3-2, 
respectively, of Chapter 3.)
[End text box]

2.1	What is a Safe Room?

A safe room is typically an interior room, a space within a building, or 
an 
entirely separate building, designed and constructed to provide life-
safety 
protection for its occupants from tornadoes or hurricanes. Safe rooms 
constructed to the criteria in this publication will provide protection 
against 
both wind forces and the impact of windborne debris. The level of occupant 
protection provided by a space specifically designed as a safe room is 
intended 
to be much greater than the protection provided by buildings that comply 
with 
the minimum requirements of most model building codes. Model building 
codes 
usually are developed not for life-safety protection, but rather for 
property 
loss protection. The model building codes currently do not provide design 
and 
construction criteria for life safety for sheltering nor do they provide 
design 
criteria for tornadoes, but this will change in 2009. In 2008, the ICC 
will 
release for adoption the ICC-500 Storm Shelter Standard. This document 
will 
provide the basis for the design and construction of shelters that was 
produced 
through the consensus standard process. The ICC-500 will be incorporated 
by 
reference into the 2009 IBC and IRC codes to regulate the design and 
construction of buildings, or portions thereof, that have been designed as 
safe 
rooms to provide life-safety protection from extreme-wind events. The 
purpose 
and scope of the ICC-500 are presented below: 

ICC-500, Section 101.1 Purpose. The purpose of this standard is to 
establish 
minimum requirements to safeguard the public health, safety, and general 
welfare 
relative to the design, construction, and installation of storm shelters 
constructed for protection from high winds associated with tornadoes and 
hurricanes.  This standard is intended for adoption by government agencies 
and 
organizations for use in conjunction with model codes to achieve 
uniformity in 
the technical design and construction of storm shelters.

ICC-500, Section 101.2 Scope. This standard applies to design, 
construction, 
installation, and inspection of storm shelters constructed as separate 
detached 
buildings or constructed as safe rooms within buildings for the purpose of 
providing safe refuge from storms that produce high winds, such as 
tornadoes and 
hurricanes.  Shelters designed and constructed to this standard shall be 
designated to be hurricane shelters, tornado shelters, or combined 
hurricane and 
tornado shelters.

[Begin text box]
NOTE 
Neither FEMA 361 nor the ICC-500 mandates the design and construction of 
residential or community safe rooms or shelters within a jurisdiction. 
Rather, 
these documents provide criteria or requirements for regulating and 
enforcing 
the proper design and construction of safe rooms and shelters.
[End text box]

These statements are very similar to the purpose and scope identified in 
FEMA 
361, but important differences between the two documents do exist. From a 
technical standpoint, the ICC-500 has successfully standardized and 
codified a 
good deal of the original design guidance provided in the first edition of 
FEMA 
361. However, some of the criteria originally proposed in FEMA 361 were 
modified 
during the consensus process that produced the ICC-500. FEMA acknowledged 
the 
rationale behind some of the changes and has accepted the new criteria. 
This 
second edition of FEMA 361 incorporates these changes by referring to 
sections 
of the ICC-500 for the design and construction requirements of a community 
safe 
room.

FEMA continually reviews its safe room design criteria and has interpreted 
the 
available research differently from the consensus standard committee. In 
FEMAs 
view, many wind design, windborne debris hazards, flood hazards, and 
operational 
issues should be addressed from a more conservative standpoint than the 
one 
agreed upon in the consensus standard process. From a procedural 
standpoint, 
FEMAs criteria have been, and will remain, guidance; they are not code or 
standard enforceable in a jurisdiction unless they have been adopted to 
act as a 
standard for extreme-wind protection. The same applies to the ICC-500 from 
its 
release in late 2008 until the release of the 2009 Editions of the IBC and 
IRC. 
Upon the release of the 2009 codes, the ICC-500 will not only be a stand-
alone 
consensus standard document, it will be a part of the building code 
(incorporated by reference) as a readily enforceable design standard. This 
will 
be the case for any jurisdiction that adopts the 2009 IBC and IRC and that 
does 
not eliminate or delete the reference language in the code that invokes 
the use 
of the ICC-500 to govern how shelters should be constructed. 

FEMA safe rooms may be classified into two categories: residential and 
community 
(non-residential) safe rooms. 

- A residential safe room is intended to provide protection for a small 
number 
of people (16 or less). There are two general types of residential safe 
rooms: 
in-residence safe rooms and safe rooms located adjacent to, or near, a 
residence. An in-residence safe room is a small, specially designed 
(hardened) 
room, such as a bathroom or closet, which is intended to provide a place 
of 
refuge for the people who live in the home. An external residential safe 
room is 
similar in function and design, but it is a separate structure installed 
outside 
the home, either above or below ground. The residential safe room criteria 
presented by FEMA are for the combined tornado and hurricane hazards and 
are 
capable of proving life-safety protection as defined in Section 3.5 of 
this 
publication. 
- A community safe room is intended to provide protection for a large 
number of 
people, anywhere from approximately 16 to as many as several hundred 
individuals. These safe rooms include not only public but also private 
safe 
rooms for business and other types of organizations. Tornado and hurricane 
community safe rooms are buildings or portions thereof that have been 
designed 
and constructed to the criteria set forth in Sections 3.3 and 3.4, 
respectively.

The term hardened refers to specialized design and construction applied 
to a 
room or building to allow it to resist wind pressures and windborne debris 
impacts during an extreme-wind event and are capable of providing life-
safety 
protection as defined in Sections 3.3, 3.4, and 3.5 of this publication. 
2.1.1	Structural and Building Envelope Characteristics of Safe Rooms

The primary difference in a buildings structural system designed for use 
as a 
safe room, rather than for conventional use, is the magnitude of the wind 
forces 
that it is designed to withstand. Conventional (normal) buildings are 
designed 
to withstand forces associated with a certain wind speed (termed design 
[basic] 
wind speed) based on historic wind speeds and probabilistic wind events 
documented for different areas of the country and presented in design 
standards 
such as the American Society of Civil Engineers (ASCE) 7-05, Minimum 
Design 
Loads for Buildings and Other Structures. The highest design wind speed 
used in 
conventional construction is near the coastal areas of the Atlantic and 
Gulf 
coasts and is in the range of 140 to 150 mph for a 3-second gust. By 
contrast, 
the design wind speed recommended by FEMA for safe rooms in these same 
areas is 
in the range of 200 to 225 mph for a 3-second gust and is intended to 
build safe 
rooms that can provide near-absolute protection for occupants.

For envelope or cladding systems, the governing design criterion is 
windborne 
debris, commonly referred to as missiles, which causes many of the 
injuries and 
much of the damage from tornadoes and hurricanes. Windows and the glazing 
in 
exterior doors of conventional buildings are not required to resist 
windborne 
debris, except when the buildings are located within windborne debris 
regions. 
Buildings located in windborne debris regions must have impact-resistant 
glazing 
systems or protection systems to protect the glazing. These systems can be 
laminated glass, polycarbonate glazing, or shutters. The ASCE 7-05 missile 
criteria were developed to minimize property damage and improve building 
performance; they were not developed to protect occupants and notably do 
not 
require walls and roof surfaces to be debris impact-resistant. To provide 
occupant protection for a life-safety level of protection, the criteria 
used in 
designing safe rooms include substantially greater resistance to 
penetration 
from windborne debris. Sections 3.3.2, 3.4.2, and 3.5.2 present the debris 
impact-resistance performance criteria for the tornado, hurricane, and 
residential safe rooms, respectively.

The roof deck, walls, and doors in conventional construction systems are 
not 
required by the model building codes to resist windborne debris. [Footnote 
1] 
However, if the space defined as a safe room is to provide adequate life-
safety 
occupant protection, the roof deck and walls that define the protected 
area and 
the doors leading into it all must resist windborne debris impacts. 
Additional 
information regarding criteria for the different levels of windborne 
debris 
resistance is provided in Sections 3.3.2, 3.4.2, and 3.5.2. 

[Begin footnote 1]
The last several editions of the Florida Building Code (FBC) have a 
requirement 
for protecting the walls, roofs, doors, and non-opening portions of 
certain 
buildings. Critical and essential facilities designed in special regions 
as High 
Velocity Hurricane Zones (HVHZs) are required by Chapter 16 of the FBC to 
provide debris impact-resistance per the windborne debris requirements of 
the 
American Society for Testing and Materials (ASTM) E 1996.
[End footnote 1]

[Begin text box]
DEFINITION
ASCE 7-05 defines hurricane prone regions and windborne debris regions as 
follows:

Hurricane Prone Regions: Areas vulnerable to hurricanes; in the United 
States 
and its territories defined as:
1. The U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind 
speed 
is greater than 90 mi/h, and
2. Hawaii, Puerto Rico, Guam, Virgin Islands, and American Samoa.

Windborne Debris Regions: Areas within hurricane prone regions located:
1. Within 1 mile of the coastal mean high water line where the basic wind 
speed 
is equal to or greater than 110 mi/h and in Hawaii, or
2. In areas where the basic wind speed is equal to or greater than 120 
mi/h.

* ASCE 7-05 uses mi/h, which equates to mph.
[End text box]

2.1.2	Design Criteria for Different Types of Safe Rooms and Shelters

Safe rooms, shelters, and refuge areas all provide different levels of 
protection depending on the design criteria used. The level of protection 
provided by a safe room or shelter is a function of the design wind speed 
(and 
resulting wind pressures) and of the windborne debris load criteria used 
in 
designing the facility.

The required design strength of the safe room, shelter, or refuge area, is 
dictated by wind pressure criteria given by different guides, codes, and 
standards. FEMA recommends design wind speeds for safe rooms that range 
from 130 
to 250 mph for tornado hazards and from 160 to 255 mph for hurricane 
hazards. 

By contrast, the 2006 IRC and the 2006 IBC, which establish the minimum 
requirements for residential and other building construction, define a 
design 
wind speed as 90 mph in the Midwest (where a corresponding safe room 
design wind 
speed is 250 mph). Table 2-1 compares shelter design criteria and levels 
of 
protection with different guidance manuals, codes, regulations, standards, 
and 
shelter programs. The last row is provided to address the issue of 
selection of 
the area within existing buildings to be used as a refuge of last resort. 
Several publications related to identifying refuge areas from hurricane 
and 
other storm events exist. A good example is FEMA 431, Tornado Protection: 
Selecting Refuge Areas in Buildings. This publication, as well as others, 
does 
not set minimum criteria for improving buildings to resist wind loads and 
debris. Rather, FEMA 431 provides information about how buildings are 
damaged by 
wind and windborne debris so individuals who do not have access to a safe 
room 
or shelter, but are exposed to extreme-wind hazards, may identify the best 
available spaces within a building or structure in which to take refuge. 
This 
guidance in the publication is based on lessons learned and field 
observations 
of buildings and structures that have experienced extreme-wind events. 
However, 
individuals seeking protection in refuges or areas of last resort should 
understand that these portions of buildings have not been designed to 
resist 
extreme-wind loads or debris impacts and may not protect the individuals 
inside 
from being killed or injured during an extreme-wind event.

[Begin table 2-1]
Table 2-1. Wind Safe Room and Shelter Design Codes, Standards, and 
Guidance 
Comparison 

Title or Name of Document Note 1: FEMA Safe Room Publications:
FEMA 320, Taking Shelter From the Storm: Building a Safe Room For Your 
Home or 
Small Business (2008). FEMA 361, Design and Construction Guidance for 
Community 
Safe Rooms (2008)

Code, Regulation, Standard, or Publication: FEMA guidance document, not a 
code 
or standard. Best Practice for extreme-wind safe rooms.

Wind Hazard: Tornado and Hurricane

Wind Map: FEMA 320: Hazard map, maximum wind hazard speed of 250 mph used 
for 
design. FEMA 361, Tornado: Map with four wind speed zones for design (wind 
MRI2 
is 10,000100,000 years). This map is often referred to as the FEMA 361 
map. 
FEMA 361, Hurricane: Uses ICC-500 hurricane map.

Wind Design Coefficient Considerations Notes 3, 4: FEMA 320: Use 250 mph 
and 
calculate pressures using ASCE 7-05 methods and use I=1.0, K subscript 
d=1.0, 
Exposure C, no topographic effects, GC subscript pi=+/-0.55 (this will 
account 
for atmospheric pressure change [APC]).FEMA 361, Tornado: Use FEMA 361 
wind 
speed map with four zones. Calculate pressures using ASCE 7-05 methods and 
use 
I=1.0, K subscript d=1.0, Exposure C, no topographic effects, GC subscript 
pi=+/-0.55 (this will account for APC).FEMA 361, Hurricane: Use ICC-500 
process, 
but also must use Exposure C and design building using GC subscript pi=+/-
0.55.

Debris Impact Criteria Note 5: FEMA 320: Test all safe rooms with the 
representative missile: a 15-lb 2x4 at 100 mph (horizontal) and 67 mph 
(vertical). FEMA 361: Test safe rooms with representative missile (missile 
speed 
dependent on site design wind speed).Tornado: 15-lb 2x4 at 80100 mph 
(horizontal) and 2/3 of this speed (vertical). Hurricane: 9-lb 2x4 at 80-
128 mph 
(horizontal) and 16-26 mph (vertical).

Remarks: FEMA 320: Intent is to provide near-absolute protection with 
prescriptive designs that meet the highest hazard design criteria for both 
tornadoes and hurricanes. FEMA 361: Intent is to provide near-absolute 
protection through appropriate design and construction guidance. Design 
criteria for features such as debris impact-resistance, flood hazard-
resistance, 
and operational criteria are more conservative than criteria in the ICC-
500. 
Safe room operations guidance is provided. Occupancy issues addressed. 
Wall 
section details provided. Building evaluation checklist provided. 
Notes: (1) Does not require the design and construction of safe rooms, but 
provides criteria for doing so. (2) FEMA does not provide safe room 
certification or product approvals.


Title or Name of Document Note 1: International Code Council/National 
Storm 
Shelter Association (ICC/NSSA) Standard for the Design and Construction of 
Storm 
Shelters (ICC-500, August 2008) 

Code, Regulation, Standard, or Publication: Consensus standard for shelter 
design and construction, tentatively available for adoption in 2008. To be 
incorporated by reference into the 2009 IBC and IRC.

Wind Hazard: Tornado and Hurricane

Wind Map: Tornado: Uses FEMA 361 map. Hurricane: Uses revised ASCE 7-05 
map with 
contours at 10,000-year MRI2 with minimum shelter design wind speed of 160 
mph, 
maximum approximately 255 mph.

Wind Design Coefficient Considerations Notes 3, 4: Tornado: Use FEMA 361 
wind 
speed map. Calculate pressures using ASCE 7-05 methods and use I=1.0, K 
subscript d=1.0, Exposure as appropriate, no topographic effects, GC 
subscript 
pi=+/-0.55 or +/-0.18+APC.Hurricane: Use revised ASCE 7-05 map and methods 
and 
use I=1.0, special definitions for enclosure classification, all other 
items as 
per ASCE 7-05, no APC consideration required.

Debris Impact Criteria Note 5: Test safe rooms with representative missile 
(missile speed dependent on site design wind speed): Tornado: 15-lb 2x4 at 
80
100 mph (horizontal) and 2/3 of this speed (vertical). Hurricane: 9-lb 2x4 
at 
64102 mph (horizontal) and 16-26 mph (vertical)

Remarks: Intent is to provide a standard for the design and construction 
of 
extreme-wind shelters. Will not use term near-absolute protection. 
Occupancy, 
ventilation, and use issues are also addressed. 
Notes: (1) The standard does not require the design and construction of 
shelters, but provides criteria for doing so. (2) The ICC-500 does not 
provide 
shelter or shelter component certifications, but rather defines the 
procedure by 
which testing must be performed to be certified and define what type of 
laboratory certification is required.


Title or Name of Document Note 1: Florida State Emergency Shelter Program 
(SESP) 
 Florida Interpretation of the American Red Cross (ARC) 4496 Guidance. 
Note: 
shelters in this category will range from Enhanced Hurricane Protection 
Area 
(EHPA) recommended design levels, shown in this row, to the code 
requirement 
levels (next row), to the ARC 4496 requirements (see below).

Code, Regulation, Standard, or Publication: Guidance in the FBC 
recommending 
above-code requirements for EHPAs. See also Appendix G of the SESP report 
for 
the detailed design guidance.

Wind Hazard: Tornado and Hurricane

Wind Map: Florida Building Code (FBC) map +40 mph recommended, based on 
ASCE 7-
05 (maps basically equivalent); MRI is 50100 years in coastal areas and 
adjusted with importance factor.

Wind Design Coefficient Considerations Notes 3, 4: Recommends that 
designer add 
40 mph to basic wind speed from map, Exposure C, I=1.15, K subscript 
d=0.85, GC 
subscript pi as required by design (typically +/-0.18), but recommends +/-
0.55 
for tornado shelter uses.

Debris Impact Criteria Note 5: In windborne debris region (120 mph+): 
Small  
pea gravel; Large  9-lb 2x4 at 34 mph (horizontal), up to 60 feet above 
grade, 
but recommends 15-lb 2x4 at 50 mph (horizontal).

Remarks: The building, or a portion of a building, is defined as an 
essential 
facility and as a shelter. Designer is required to submit a signed/sealed 
statement to building department and state offices stating the structure 
has 
been designed as a shelter (EHPA plus added recommended criteria).


Title or Name of Document Note 1: Florida Building Code EHPAs  code 
requirements for public shelters (FBC Section 423.25)
Code, Regulation, Standard, or Publication: Statewide code requirements 
for 
EHPAs

Wind Hazard: Hurricane 

Wind Map: FBC map, based on ASCE 7-05 (maps basically equivalent); MRI is 
50100 
years in coastal areas and adjusted with importance factor.

Wind Design Coefficient Considerations Notes 3, 4: Use basic wind speed at 
site 
as identified on FBC wind speed map, use exposure at site, use I=1.15, K 
subscript d=0.85, GC subscript pi as required by design (typically +/-
0.18).

Debris Impact Criteria Note 5: In windborne debris region: Small  pea 
gravel; 
Large  9-lb 2x4 at 34 mph (horizontal), up to 60 feet above grade

Remarks: The building or a portion of a building is defined as an 
essential 
facility and as an EHPA. Designer is required to submit a signed/sealed 
statement to building department and state offices stating the structure 
has 
been designed as an EHPA.


Title or Name of Document Note 1: FBC 2000 and later International 
Building Code 
(IBC)/International Residential Code (IRC 2000) and later/ASCE 7-98 and 
later.
Code, Regulation, Standard, or Publication: Building code and design 
standards 
for regular (non-shelter) buildings. Some additional guidance is provided 
in the 
commentary.

Wind Hazard: Hurricane

Wind Map: ASCE has its own wind speed map based on historical and 
probabilistic 
data; MRI is 50100 years in coastal areas and adjusted with importance 
factor.

Wind Design Coefficient Considerations Notes 3, 4: Method is the basis of 
most 
wind pressure calculation methods. All items in design process are site-
specific. Use I=1.15 for critical and essential facilities.

Debris Impact Criteria Note 5: In windborne debris region: Small  pea 
gravel; 
Large  9-lb 2x4 at 34 mph (horizontal), up to 60 feet above grade.
Note: FBC, IBC, and ASCE 7-05 require the 9-lb 2x4 (large) missile to be 
tested 
at 55 mph for critical and essential facilities.

Remarks: Code requires increased design parameters only for buildings 
designated 
as critical or essential facilities. For improved performance of 
residential 
buildings (but not life-safety protection), design criteria and 
prescriptive 
solutions can be found in ICC-6, Standard for Residential Construction in 
High 
Wind Regions (Fall 2008)


Title or Name of Document Note 1: American Red Cross (ARC 4496) Standards 
for 
Hurricane Evacuation Shelter Selection
Code, Regulation, Standard, or Publication: Guidance for identifying 
buildings 
to use as hurricane evacuation shelters

Wind Hazard: Hurricane

Wind Map: None

Wind Design Coefficient Considerations Notes 3, 4: None

Debris Impact Criteria Note 5: None

Remarks: Provides guidance on how to select buildings and areas of a 
building 
for use as a wind shelter or refuge area during wind events. Does not 
provide or 
require a technical assessment of the proposed shelter facility.


Title or Name of Document Note 1: Pre-2000 Building Codes
Code, Regulation, Standard, or Publication: Building code and design 
standards 
for regular (non-shelter) buildings

Wind Hazard: Hurricane

Wind Map: Each of the older codes used their own published wind contour 
maps.

Wind Design Coefficient Considerations Notes 3, 4: Typically these older 
codes 
provided a hurricane regional factor for design wind speeds, but little 
attention was paid to components and cladding.

Debris Impact Criteria Note 5: Not required for all buildings. Where 
required, 
the Standard Building Code (SBC) note 6 developed and recommended debris 
impact 
standards for use in hurricane-prone regions.

Remarks: These codes specified limited hazard-resistant requirements. Some 
guidance was provided with SSTD 10 from SBCCI for the design and 
construction of 
buildings in extreme-wind and hurricane-prone regions. Buildings 
constructed to 
these early codes were not required to have structural systems capable of 
resisting wind loads.


Title or Name of Document Note 1: Refuge Areas of Last Resort
Code, Regulation, Standard, or Publication: Guidance from FEMA and others 
for 
selecting best-available refuge areas

Wind Hazard: Tornado and Hurricane

Wind Map: None

Wind Design Coefficient Considerations Notes 3, 4: None

Debris Impact Criteria Note 5: None

Remarks: Best available refuge areas should be identified in all buildings 
without shelters. FEMA 431, Tornado Protection: Selecting Refuge Areas in 
Buildings, provides guidance to help identify the best available refuge 
areas in 
existing buildings. Because best available refuge areas are not 
specifically 
designed as shelters, their occupants may be injured or killed during a 
tornado 
or hurricane.

Notes:
1. The wind shelter guidance and requirements shown here are presented 
from 
highest to least amount of protection provided. 

2. Mean recurrence intervals (MRIs) for wind speeds maps are identified by 
the 
code or standard that developed the map. Typically, the MRI for non-
shelter 
construction in non-hurricane-prone areas is 50 years and in hurricane-
prone 
regions, approximately 100 years. 

3. ASCE 7-05 Minimum Design Loads for Buildings and Other Structures 
(2005) is 
the load determination standard referenced by the model building codes. 
The wind 
design procedures used for any shelter type in this table use one of the 
wind 
design methods as specified in ASCE 7-05, but with changes to certain 
design 
coefficients that are identified by the different codes, standards, or 
guidance 
summarized in this table.

4. From ASCE 7-05 method: I = importance factor; K subscript d = wind 
directionality factor; GC subscript pi = internal pressure coefficient.

5. Roof deck, walls, doors, openings, and opening protectives must all be 
tested 
to show resistance to the design missile for the FEMA, ICC, and FL EHPA 
criteria.

6. From the Southern Building Code Congress International, Inc. (SBCCI).
[End table]

Table 2-2 presents comparative data for three locations using these design 
criteria for the different safe room and shelter documents. N/A (not 
applicable) is used to indicate that no guidance is provided for 
sheltering or 
basic construction., Not required indicates that there are no 
requirements. 

[Begin table 2-2]
Table 2-2. Wind Safe Room and Shelter Design Values Comparison

SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: FEMA 361

Data - note 1: Design wind speed
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 200 mph 
(tornado) 225 mph (hurricane)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 200 
mph 
(tornado) 160 mph (hurricane)
Example Location #3: Greenburg, Kansas Tornado Hazards: 250 mph (tornado)

Data - note 1: Pressure on windward wall - note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 107 psf 
(tornado) 136 psf (hurricane)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 107 
psf 
(tornado) 69 psf (hurricane)
Example Location #3: Greenburg, Kansas Tornado Hazards: 167 psf (tornado)

Data - note 1: Pressure on roof section  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 257 psf 
(tornado, suction) 325 psf (hurricane, suction)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 257 
psf 
(tornado, suction) 202 psf (hurricane, suction)
Example Location #3: Greenburg, Kansas Tornado Hazards: 401 psf (tornado, 
suction)

Data note 1: Test missile momentum at impact  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 62 lb 
subscript f-s (tornado) 46 lb subscript f-s (hurricane)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 62 lb 
subscript f-s (tornado) 33 lb subscript f-s (hurricane)
Example Location #3: Greenburg, Kansas Tornado Hazards: 68 lb subscript f-
s 
(tornado) 

SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: ICC-500 (note3)

Data - note 1: Design wind speed
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 200 mph 
(tornado) 225 mph (hurricane)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 200 
mph 
(tornado) 160 mph (hurricane)
Example Location #3: Greenburg, Kansas Tornado Hazards: 250 mph (tornado)

Data - note 1: Pressure on windward wall- note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 107 psf 
(tornado) 136 psf (hurricane)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 107 
psf 
(tornado) 69 psf (hurricane)
Example Location #3: Greenburg, Kansas Tornado Hazards: 167 psf (tornado)

Data - note 1: Pressure on roof section2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 257 psf 
(tornado, suction) 325 psf (hurricane, suction)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 257 
psf 
(tornado, suction) 202 psf (hurricane, suction)
Example Location #3: Greenburg, Kansas Tornado Hazards: 401 psf (tornado, 
suction)

Data - note 1: Test missile momentum at impact  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 62 lb 
subscript f-s (tornado) 36 lb subscript f-s (hurricane)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 62 lb 
subscript f-s (tornado) 26 lb subscript f-s (hurricane)
Example Location #3: Greenburg, Kansas Tornado Hazards: 68 lb subscript f-
s 
(tornado) 


SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: FBC EHPA/SESP Recommend 
Criteria 
(using basic wind speed + 40 mph)

Data - note 1: FBC EHPA/SESP Recommend Criteria (using basic wind speed + 
40 
mph)
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Design 
wind 
speed 186 mph
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 130 
mph
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A

Data - note 1: Pressure on windward wall  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 91 psf
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 44 
psf
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A


Data - note 1: Pressure on roof section  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 217 psf 
(suction)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 106 
psf 
(suction)
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A

Data - note 1: Test missile momentum at impact- note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 34 lb 
subscript f-s
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 14 lb 
subscript f-s
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A

SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: FBC EHPA (Required per FBC 
Section 
423.25)
Data - note 1: Design wind speed
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 146 mph
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: N/A
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A

Data - note 1: Pressure on windward wall  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 39 psf
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: N/A
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A

Data - note 1: Pressure on roof section  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 117 psf 
(suction)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: N/A
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A

Data - note 1: Test missile momentum at impact - note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 14 lb 
subscript f-s
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: N/A
Example Location #3: Greenburg, Kansas Tornado Hazards: N/A

SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: ASCE 7-05/IBC 2006 (ASTM E 
1996)

Data - note 1: Design wind speed
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 150 mph
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 105 
mph
Example Location #3: Greenburg, Kansas Tornado Hazards: 90 mph

Data - note 1: Pressure on windward wall- note2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 41 psf
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 18 
psf
Example Location #3: Greenburg, Kansas Tornado Hazards: 15 psf

Data - note 1: Pressure on roof section  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 124 psf 
(suction)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 52 
psf 
(suction)
Example Location #3: Greenburg, Kansas Tornado Hazards: 44 psf (suction)

Data - note 1: Test missile momentum at impact note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 14 lb 
subscript f-s
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: Not 
required
Example Location #3: Greenburg, Kansas Tornado Hazards: Not required

SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: ARC 4496

Data - note 1: Design wind speed
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Not 
specified
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: Not 
specified
Example Location #3: Greenburg, Kansas Tornado Hazards: Not specified

Data - note 1: Pressure on windward wall  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Not 
specified
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: Not 
specified
Example Location #3: Greenburg, Kansas Tornado Hazards: Not specified

Data - note 1: Pressure on roof section  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards:
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards:
Example Location #3: Greenburg, Kansas Tornado Hazards:

Data - note 1: Test missile momentum at impact  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Not 
specified
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: Not 
specified
Example Location #3: Greenburg, Kansas Tornado Hazards: Not specified

SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: Pre-2000 Building Codes

Data - note 1: Design wind speed
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: 140 mph 
and 
less
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 90 
mph and 
less
Example Location #3: Greenburg, Kansas Tornado Hazards: 90 mph and less

Data - note 1: Pressure on windward wall  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: < 40 
psf 
(varies)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: < 15 
psf 
(varies)
Example Location #3: Greenburg, Kansas Tornado Hazards: < 15 psf (varies)

Data - note 1: Pressure on roof section  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: < 120 
psf 
(varies)
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: < 45 
psf 
(varies)
Example Location #3: Greenburg, Kansas Tornado Hazards: < 45 psf (varies)

Data - note 1: Test missile momentum at impact  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Not 
required 
by all codes
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: Not 
required
Example Location #3: Greenburg, Kansas Tornado Hazards: Not required
SHELTER DESIGN STANDARD, CODE, OR DOCUMENT: Refuge Areas of Last Resort

Data - note 1: Design wind speed
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Unknown
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 
Unknown
Example Location #3: Greenburg, Kansas Tornado Hazards: Unknown

Data - note 1: Pressure on windward wall  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Unknown
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 
Unknown
Example Location #3: Greenburg, Kansas Tornado Hazards: Unknown

Data - note 1: Pressure on roof section  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Unknown
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: 
Unknown
Example Location #3: Greenburg, Kansas Tornado Hazards: Unknown

Data - note 1: Test missile momentum at impact  note 2
Example Location #1: Miami, Florida Tornado and Hurricane Hazards: Not 
required
Example Location #2: Galveston, Texas Tornado and Hurricane Hazards: Not 
required
Example Location #3: Greenburg, Kansas Tornado Hazards: Not required

Notes:
1. Wind pressures were calculated based on a 40-foot x 40-foot building, 
with a 
10-foot eave height and a 10-degree roof pitch.

2. psf  pounds per square foot; lb subscript f-s  pounds (force) 
seconds.

3. ICC-500 Hurricane design criteria used the most restrictive case that 
may be 
appropriate, which results in the use of GC subscript pi=+/-0.55 and 
Exposure 
Category C at the site.
[End table]

2.1.3	Occupant Safety

This publication presents guidance for the design of engineered safe rooms 
that 
will protect large numbers of people during an extreme-wind event. Safe 
rooms 
designed by a professional according to the criteria outlined in this 
publication (including the safe room design wind speed selected in Chapter 
3) 
are intended to minimize the probability of death and injury during an 
extreme-
wind event by providing their occupants with near-absolute protection. 

The risk of death or injury from tornadoes or hurricanes is not evenly 
distributed throughout the United States. This publication guides the 
reader 
through the process of identifying the risk of extreme winds in a 
particular 
location and mitigating that risk. The intent is not to mandate the 
construction 
requirements for safe rooms for extreme-wind events, but rather to provide 
design guidance for persons who wish to design and build such facilities. 
Levels 
of risk, and tools for determining the levels of risk, are presented in 
this 
chapter.

The intent of this publication is not to override or replace current codes 
and 
standards, but rather to continue to provide important guidance where none 
has 
been available before. Until the development of the ICC-500 Storm Shelter 
Standard, no building, fire, or life-safety code or engineering standard 
had 
provided detailed design criteria for the design of tornado or other 
extreme-
wind shelters. FEMA 361 remains unique in that its goal is not just to 
help 
provide a safe space for individuals to take shelter from extreme-wind 
events, 
but it also presents guidance on how to achieve near-absolute protection. 
The 
information provided in this document is the best available at the time of 
publication. This information will support the design of a safe room that 
provides near-absolute protection during an event with a specified design 
wind 
speed that has been determined to define the wind threat for a given 
geographic 
area. Designing and constructing a safe room according to the criteria in 
this 
publication does not mean that the shelter will be capable of withstanding 
every 
possible extreme-wind event. The design professional who ultimately 
designs a 
safe room should state what the design parameters are and describe them in 
detail in the project documents as required by Sections 3.8 and 3.9. 
Examples of 
actual safe rooms that have been designed to the criteria presented in 
this 
publication are contained in Appendices C and D.

2.2	Safe Room Design Process 

The decision to design and construct a safe room 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., officials at a hospital that cannot move 
patients housed in an intensive care unit, officials at a school that 
takes care 
of a large number of small children, etc.). Other factors that are 
considered in 
the risk assessment process should include the type of hazard event, 
probability 
of event occurrence and severity, vulnerability of buildings in the 
community, 
size of the population at risk, and probable single and aggregate annual 
event 
casualties.

The flowchart in Figure 2-1 presents the decision-making process that 
should 
take place when the construction of a community safe room is being 
considered. 
The major steps of this process are discussed in Sections 2.2.1 through 
2.2.5.

[Begin figure]
Figure 2-1. Process for risk and needs assessments for safe rooms (flow 
chart)
There are 2 paths: one for new construction, the other for existing 
buildings.

Path 1: Determine which extreme-wind hazards are threats for the 
community. 
Then determine the extent to which the building stock is vulnerable to 
extreme-
wind damage. Then determine the type, size, and location of the population 
at 
risk that needs protection. Then identify the type of safe room required.
If it is new construction when no adequate space is available, or a 
portion of a 
new building to be used as a safe room, then design and project 
development 
including cost estimates needs to be done. Consider funding alternative, 
or 
determine cost-effectiveness by performing standard benefit-cost analysis 
of 
(BCA) with FEMA-approved assessment tools. Benefit-cost ration (BCE) 
greater 
than 1: May be eligible for federal funding assistance. Comply 
with 
all Federal grant eligibility requirements. Obtain community buy-in and 
initiate 
construction. Notify population to be protected that safe room is ready for 
use.

Path 2: Determine which extreme-wind hazards are threats for the 
community. 
Then determine the extent to which the building stock is vulnerable to 
extreme-
wind damage. Then determine the type, size, and location of the population 
at 
risk that needs protection. Then identify the type of safe room required. 
If it 
is an existing building or a portion of it can be adapted for safe room, 
then a 
detailed vulnerability assessment of the existing building and portions 
considered for safe areas need to be prepared. Then the design and project 
development, including cost estimates needs to be prepared. Then determine 
the 
cost-effectiveness by performing standard benefit-cost analysis of (BCA) 
with 
FEMA-approved assessment tolls. If the BCR is less than 1 there are 2 
paths. You 
can proceed with the design and construction without federal assistance. 
Obtain 
community buy-in and initiate construction and notify population to be 
protected 
that safe room is ready for use. Or if the BCR is less than one it may not 
be 
eligible for federal funding. If federal funding is required, revisit the 
initial design program.

[End figure]

2.2.1	The Threat From Extreme-Wind Events

The assessment of the level of threat from extreme winds is a first step 
in 
quantifying the risk to which a community is exposed. The exposure to 
extreme-
wind hazards differs greatly in various parts of the country. Although the 
level 
of exposure to wind hazards is not easy to quantify accurately, areas 
exposed to 
stronger or more frequent tornadoes or hurricanes have been identified and 
mapped. 

The assessment of the level of threat, or the exposure to wind hazards, is 
determined on the basis of probability of occurrence of a hazard event of 
specific magnitude at a specific location. The probabilities of occurrence 
are 
statistical estimates drawn from historical records of previous hazard 
events 
that describe not only the time and place, but also the details related to 
the 
intensity, size, duration, general circumstances, and effects of the 
event. Much 
of this information has been compiled into a number of risk assessment 
tools 
such as wind speed maps and frequency maps and tables. 

Frequency or Probability of Occurrence Maps

Researchers have complied data that illustrate the frequency of extreme-
wind 
events. These frequency maps show the number of extreme-wind hazard 
events, such 
as tornadoes, that occurred in various parts of the country. Although 
tornadoes 
were recorded as far back as 1700s, the systematic gathering of data 
related to 
tornado events did not start until the early 1950s. Therefore, the 
historical 
records used for statistical analysis of frequencies span only slightly 
more 
than 50 years. Figure 2-2 shows the areas of the United States with the 
greatest 
incidence of strong tornadoes, those that were designated as EF3, EF4, or 
EF5. 
The historical information on past windstorms is used to calculate their 
statistical frequency or the probability of occurrence of a wind event of 
certain magnitude. The probability of occurrence therefore describes a 
wind 
event of specific intensity irrespective of the place of occurrence. This 
wind 
event characteristic is known as the mean recurrence interval (MRI). The 
mean 
recurrence interval represents the frequency with which large or small 
hazard 
events take place. For example, most buildings are designed and 
constructed to 
resist wind pressures resulting from a wind event with a 50-year MRI or 2 
percent annual probability of exceedence. 

[Begin figure]
Figure 2-2. Tornado occurrence map. This map shows the tornado activity in 
the 
United States bases on NOAA, Storm Prediction Center Statistics. Summary 
of 
recorded EF3, EF$, and EF% tornadoes per 2,470 square miles (1950-2006).
[End figure]
Most wind speed maps in use today reflect a specific MRI that was adopted 
as a 
risk indicator for that design standard. ASCE 7-05 wind maps, for example, 
use a 
50-year MRI to determine the basic wind speeds for non-hurricane-prone 
areas. 
Some occupancies categorized by ASCE 7-05 as Category III and IV buildings 
are 
required to be designed for 100-year wind events, which necessarily 
involves 
higher wind speeds. This adjustment in the MRI is accomplished through the 
use 
of an importance factor (I) in the wind load calculations. The FEMA 361 
map for 
tornado hazards, which is identical to the ICC-500 tornado map, uses 
10,000 to 
100,000 MRI wind events to determine the wind speed zones for tornado safe 
rooms. The low probability of occurrence or the mean recurrence interval 
of 
10,000 to 100,000 years is used in order to make sure that safe rooms are 
protected even against the rarest of wind storms with extreme-wind speeds 
of 250 
mph (3-second gust).

For the hurricane hazard, NOAA and other meteorological groups have more 
readily 
available tracking maps to illustrate the occurrence of hurricanes. 
Furthermore, 
the ASCE 7-05 basic wind speed map was developed from a combination of 
historical and probabilistic storm events (which include hurricanes, but 
not 
tornadoes). As a result, for the hurricane-prone regions the mapped speeds 
reflect the hurricane influence and hazard and should be considered to be 
100-
year MRI basic wind speeds. [Footnote 2] The FEMA 361 map uses the ICC-500 
Shelter Design Wind Speeds for Hurricanes Map (ICC-500, Figure 304.2.2), 
which 
has been developed using the same modeling approach and inputs as the ASCE 
7-05 
basic wind speed map. However, it has been developed for an ultimate wind 
event 
of 10,000 MRI (based on both historical and probabilistic storm data). As 
a 
result, appropriate maximum hazard wind speeds associated with the 
hurricane 
event alone (tornadoes are not included in this model) are 225 mph for the 
mainland U.S. and 255 mph for certain U.S. island territories (3-second 
gust). 

[Begin footnote 2]
For a complete discussion on the MRI use for hurricane and non-hurricane 
wind 
speeds depicted in the ASCE 7-05 Basic Wind Speed Map, see the commentary 
for 
Chapter 6 of ASCE 7-05.
[End footnote]
Wind Speed Maps

Safe rooms are designed to protect the occupants from windstorms such as 
tornadoes, hurricanes, or thunderstorms. The prevailing wind hazard along 
the 
Gulf of Mexico and Atlantic coasts and in the Caribbean and some Pacific 
Islands 
is a hurricane, although some regions of the Pacific and Alaska refer to 
the 
extra-tropical cyclones as typhoons. Interior areas in the United States 
are 
mainly threatened by tornadoes or thunderstorms.

The wind speed maps in Figures 3-1 and 3-2 consider tornado and hurricane 
hazards separately and present safe room design wind speed maps for each 
hazard. 
For the tornado hazard, this map is primarily based on historical data. 
Since 
1997, almost 1,300 tornadoes, on average, have been reported nationwide 
each 
year. Most tornadoes are short-lived, average less than 500 feet wide, and 
traverse less than 2,000 feet. Some large tornadoes have been known to 
cause 
damage along paths that are 1-mile wide and many miles long; however, 
tornadoes 
such as these occur only a few times each year. The land area directly 
impacted 
by all tornadoes in a year is relatively small. At present, it is not 
possible 
to directly measure wind speeds in a tornado because of its short life. 
Thus, 
the data available for tornadoes, intensity, and area of damage are 
relatively 
sparse and require special consideration in the probability assessment of 
wind 
speeds.

For hurricane wind speeds along the Gulf of Mexico and Atlantic coasts, 
ASCE 7-
05 uses the Monte Carlo numerical simulation procedure to establish design 
wind 
speeds. The numerical simulation procedure provides reasonable wind speeds 
for 
an annual probability of exceedance of 0.02 (50-year MRI). For wind speeds 
with 
an extremely low probability of occurrence, the current numerical 
procedure, 
according to some critics, gives unusual answers (e.g., wind speed 
estimates in 
Maine are higher than those in Florida). The ICC-500 Review Committee, 
which 
prepared the new map for the hurricane hazard, considered these issues in 
its 
work with the ASCE modelers who developed a set of maps that the committee 
believed appropriately represented the hurricane wind hazards along the 
coastal 
U.S.

The measure (or units) used to identify tornadic and hurricane safe room 
design 
wind speeds are unified to one averaging time: a 3-second gust wind speed. 
The 
resulting 3-second gust speeds are consistent with the reference wind 
speeds 
used in ASCE 7-05. Consequently, they can be used in the wind pressure 
calculation formulas from ASCE 7-05 to determine wind loads as discussed 
in 
Chapters 3 and 6. Further, unless otherwise noted, all wind speeds 
presented in 
this publication are 3-second gust wind speeds, for Exposure C, over land, 
at 33 
feet (height) above the ground. 

The safe room design wind speeds shown in Figures 3-1 and 3-2 are valid 
for most 
regions of the country. However, the Special Wind Regions (e.g., 
mountainous 
terrain, river gorges, ocean promontories) shown on the ASCE 7-05 basic 
wind 
speed map are susceptible to local effects that may cause substantially 
higher 
wind speeds at safe room sites. Mountainous areas often experience 
localized 
winds of considerable magnitude. For instance, mountain-induced windstorms 
in 
the lee of the Colorado Front Range (generally the eastern side of the 
range) 
have been documented at speeds approaching 120 mph. In Boulder, Colorado, 
straight-line winds in excess of 60 mph are observed about once a year. 
The 
frequency and maximum intensity of such extreme-wind events at higher 
elevations 
within Special Wind Regions are likely to be more frequent and even 
stronger. 
When the desired shelter location is within one of these regions, or there 
is 
reason to believe that the wind speeds on the map do not reflect the local 
wind 
climate, the design professional should seek expert advice from a wind 
engineer 
or meteorologist.

Based on this information as well as a communitys own historical records, 
it is 
possible to determine to what extent the area is susceptible to extreme-
wind 
hazards. The information within this section was provided to help better 
understand the risk associated with the jurisdiction in which a safe room 
may be 
designed or constructed. 

2.2.2	Vulnerability Assessment

When a community is exposed to extreme-wind hazards, the level of threat 
is 
determined using the historical information described in the previous 
section. 
This represents a first step in determining the actual risks to the 
community 
from extreme-wind events. Community safe rooms are built to provide safe 
areas 
for a local, at-risk population that may be exposed to extreme-wind 
hazards. 
Life safety depends on the ability of people to reach a hardened, safe 
location 
in a timely manner and remain inside unharmed during the wind storm. Since 
not 
all buildings and structures can be considered a safe room in a wind 
storm, it 
is necessary to evaluate the building stock in the community in order to 
identify their potential vulnerability to wind damage that could cause 
casualties. This is a critical step for all high-occupancy buildings or 
buildings that house highly vulnerable populations. (See Appendix B for a 
checklist to assist in the performance of the assessments discussed 
below.)

1. Vulnerability of buildings 
An inventory of vulnerable buildings based on architectural/engineering 
(A/E) 
review of building-specific factors such as structural integrity, age, 
condition, building materials, design, quality of construction, etc., 
should be 
conducted. It is recommended that a building vulnerability assessment be 
performed in two stages. The first stage should comprise a general survey 
of the 
building stock in the community to identify the buildings that could 
potentially 
pose the greatest risk of serious damage or collapse in an extreme-wind 
event. 
The buildings that would need to be identified in advance comprise older 
manufactured housing units, old wood-frame and unreinforced masonry (URM) 
buildings, and especially any potentially hazardous high-occupancy 
structures 
that might require a more detailed inspection. The second stage would need 
to be 
performed by a well-qualified and experienced professional. It is 
recommended 
that the second stage should identify all high-occupancy buildings that 
are 
prone to wind damage and rank them according to the level of potentially 
harmful 
wind effects. This stage is an especially important component of the risk 
analysis that will assist communities in prioritizing their safe room 
needs. It 
is also recommended that the second stage of the vulnerability assessment 
identify the interior areas of high-occupancy buildings that may serve as 
the 
safest refuge areas in the event of an extreme-wind event. These areas 
should 
not be confused with safe rooms or other types of wind shelters because 
they 
would not be able to offer the near-absolute level of life-safety 
protection. 
The occupants of buildings, however, should be aware of the best places in 
the 
building in which to seek refuge in an emergency. 

2. Identify buildings or structures that could be used as safe rooms 
During the second stage of the vulnerability assessment, special attention 
should be made to identify stand-alone buildings, portions of existing 
buildings, or the interior areas of high-occupancy buildings that could be 
used 
as safe rooms after the structural hardening and other recommended 
improvements 
are completed. The main criteria for selection of structures as potential 
safe 
rooms are related to their suitability for a retrofit according to the 
design 
and construction recommendations described in Chapter 3. Other criteria 
that 
outline how the space should be used and how the occupants should be 
provided 
for are no less important and should also be considered. The accessibility 
of 
such places should be evaluated along with their size or their everyday 
functions with respect to their availability for safe room usage in an 
emergency.

3. Potential losses as a result of identified weaknesses of buildings
Physical vulnerability of the built environment to wind damage represents 
only 
one component of the vulnerability assessment. It must be combined with 
the 
level of exposure of building occupants to potential wind damage in order 
to 
calculate the potential losses in the event of an extreme-wind event. 
Potential 
losses should therefore be estimated on the basis of identified weaknesses 
in 
the buildings and their occupancy type (see Section 2.2.3). Occupancy 
types such 
as hospitals, long-term care centers (nursing homes), or elementary 
schools and 
day care centers are likely to suffer greater losses than other types of 
occupancies with the same level of a buildings physical vulnerability to 
wind 
damage.

4. Identify areas with high concentration of vulnerable structures 
The above-mentioned first stage of the vulnerability assessment of the 
communitys building inventory serves another important purpose. By 
identifying 
the areas of high concentrations of vulnerable structures and occupancies 
based 
on area-specific factors such as the presence of manufactured housing 
parks, old 
residential neighborhoods, blighted areas, topography, and others, local 
communities can easily map and plan their safe room needs. This can be an 
invaluable tool in selecting the most appropriate and most effective sites 
for 
new and retrofitted safe rooms.

2.2.3	Population at Risk 

Community safe rooms have a single purpose - to protect the life safety of 
the 
population at risk during the storm event. The population at risk is 
understood 
to encompass only those people who are unable to evacuate ahead of the 
storm for 
any reason. The community safe rooms are different from other types of 
shelters 
in that they are designed to safeguard people only during a relatively 
short 
period of time when the extreme winds are the strongest and able to cause 
the 
greatest damage. FEMA considers this period to be a minimum of 
approximately 2 
hours for tornadoes and a minimum of approximately 24 hours for 
hurricanes. 

Since the warning times for approaching hurricanes are considerably longer 
than 
for tornadoes, the at-risk population for hurricane safe rooms might 
include 
those who must remain in the area (like emergency response personnel) and 
those 
who are unable to evacuate on time either because of their frailty, lack 
of 
transport, a suitable place to go, or other reasons. In the case of 
approaching 
tornadoes, the definition of special population that cannot evacuate on 
time is 
extended to include practically all the people in buildings deemed 
vulnerable to 
damage and failure from extreme-wind events. 

Identifying the population at risk is required not only for risk 
assessment 
(determining potential losses as a result of possible building damage), 
but also 
for effective mitigation, by determining the location and optimal 
size/capacity 
of a community safe room. The intent of the guidance in this section on 
the at-
risk population is to start the thought process necessary to determine the 
size 
of the safe room that may be needed. The design criteria in this document 
have 
been defined using a minimum floor area per occupant approach, in order to 
ensure that adequate hardened space is provided for the safe room 
population, 
irrespective of who comprises that population. However, state and local 
agencies 
responsible for emergency management and developing and executing 
evacuation 
plans should be consulted when identifying a population in need of 
protection. 
FEMA safe room guidance should also be reviewed for detailed 
recommendations for 
determining the population at risk. 

2.2.4	Risk Analysis 

Risk analysis is the final step in the risk assessment process in which 
all 
components are brought together to estimate the risk and help prioritize 
the 
mitigation activities. In the case of the safe room risk assessment 
process, 
risk analysis should be performed for each proposed safe room project to 
make 
sure that the safe room will serve those most at risk. The potential 
losses 
determined on the basis of the vulnerability of a building and its 
occupants to 
damage and resultant death and injury from an extreme- wind event of a 
certain 
magnitude are compared with the probability of occurrence of such an event 
at 
that location. Table 2-3 below proposes a basic matrix for categorizing or 
quantifying the risk into three general risk levels: low (L), moderate 
(M), and 
high (H). Once a moderate level of risk can be identified, a safe room 
should be 
considered for the community. Communities are, however, encouraged to 
devise 
their own methods and risk levels that are best suited to local 
conditions.
[Begin Table]

Table 2-3.	Risk Analysis Matrix
Probability of Occurrence of an Extreme-Wind Event

Potential Losses: Minor
Low: L
Moderate: L 
High: L 
Very High: M

Potential Losses: Moderate	
Low: L	
Moderate: M	
High: M	
Very High: H


Potential Losses: Severe	
Low: M	
Moderate: M	
High: H	
Very High: H

Potential Losses: Catastrophic	
Low: M	
Moderate: H	
High: H	
Very High: H
[End table]
2.2.5	Types of Safe Rooms

In inspecting areas of existing buildings that are used as safe room 
areas, FEMA 
has found that owners may overlook the safest area of a building. In 
addition, 
the safety of a hallway or other potential safe room area may be 
overestimated. 
Evaluating safe room areas in an existing building helps the owner:

- Determine whether the safest part of the building is being used as a 
safe room
- Identify possible ways to make existing areas safer
- Decide whether to design and build a safe room according to the guidance 
in 
this publication

[Begin text box]
CROSS-REFERENCE 
For improved flood hazard assessment checklists and criteria, see FEMA 
543. For 
improved seismic hazard assessment checklists and criteria, see ASCE  
31-03.
[End text box]

A preliminary evaluation may be performed by a design professional or by a 
potential safe room owner, property owner, emergency manager, building 
maintenance person, or other interested party. This person must have a 
basic 
knowledge of building sciences and be able to read and understand building 
design plans and specifications.

The wind hazard evaluation checklists in Appendix B will help the user 
assess a 
buildings susceptibility to damage from extreme-wind events such as 
tornadoes 
and severe hurricanes. Although the threat of damage from extreme-wind 
events is 
the predominant focus of the evaluation, additional threats may exist from 
flood 
and seismic events. Therefore, flood and seismic hazard evaluations should 
be 
performed in conjunction with the wind hazard evaluation to assess the 
multi-
hazard threats at the site. Checklists for flood and seismic hazard 
evaluations 
are also provided in Appendix B. However, the checklists are designed to 
support 
only a generalized evaluation (the wind hazard section includes detailed 
screening processes for the building structure).

The wind, flood, and seismic hazard evaluation checklists in Appendix B 
may be 
used for the preliminary assessment. Prior to the design and construction 
of a 
safe room, a design professional should perform a more thorough assessment 
in 
order to confirm or, as necessary, modify the findings of a preliminary 
assessment. The checklists in Appendix B can provide a starting point for 
the 
more thorough assessment.

An entire building or a section of a building may be designated a 
potential safe 
room area. If an existing building is selected for use as a community safe 
room, 
the hazard evaluation checklists will help the user identify potential 
safe room 
areas within the building and evaluate their vulnerability to natural 
hazards. 
The intent of the checklist evaluation process is to guide the user 
through the 
selection of the best safe room areas within the building and focus the 
evaluation on the critical sections of the building. For example, an 
evaluator 
who inspects a portion of a building being considered for use as a safe 
room 
should determine whether that portion is structurally independent of the 
rest of 
the building, easily accessible, and of sufficient size. 

[Begin text box]
CROSS-REFERENCE 
Guidance concerning the siting of safe rooms is presented in Chapter 5 of 
this 
publication.
[End text box]


The checklists consist of questions pertaining to structural and non-
structural 
characteristics of the area being considered. The questions are designed 
to 
identify structural and non-structural vulnerabilities to wind hazards 
based on 
typical failure modes. Structural or non-structural deficiencies may be 
remedied 
with retrofit designs (structural and non-structural mitigation); however, 
depending on the type and degree of deficiency, the evaluation may 
indicate that 
the existing structure is unsuitable for use as a safe room area. The 
checklists 
are not a substitute for a detailed engineering analysis, but they can 
assist 
the decision-makers involved with hazard mitigation and emergency 
management to 
determine whether a building or section of a building has the potential to 
serve 
as a safe room. 

The checklists are also used to comparatively rank multiple facilities 
within a 
given geographic region that are considered potential safe room sites. A 
scoring 
system is included to enable the user to compare performance 
characteristics at 
various potential safe room sites and to highlight vulnerabilities. For 
each 
question on the checklist, deficiencies and vulnerabilities are assessed 
penalty 
points. Therefore, a high score reflects higher hazard vulnerability and a 
low 
score reflects lower hazard vulnerability, but only relative to the other 
buildings considered in the scoring system. There is a minimum possible 
score 
for the checklists, but this minimum score will vary, depending on the 
design 
wind speed selected from Figures 3-1 and 3-2. Therefore, although a low 
score is 
desired, there is no passing score or minimum acceptable score for 
protection. Again, these checklists help a user determine which area of a 
building is likely to perform best during an extreme-wind event and which 
areas 
require engineering and retrofit design if they are to provide protection 
from a 
tornado, a hurricane, or both.

2.3	Safe Room Costs

Costs for the design, construction, and maintenance of community safe 
rooms will 
vary by location and construction type. This section presents information 
related to safe room costs and the relative impact of different aspects of 
the 
design and construction on the cost of a safe room. 

2.3.1	Design Parameters Affecting Safe Room Costs

As part of the risk assessment plan discussed earlier in this chapter, 
budgetary 
cost estimates (estimates that will be  30 percent accurate) should be 
prepared 
by the design professional for each proposed safe room alternative. Key 
design 
parameters that drive the cost of community safe rooms are:

- Safe room use. Single or dual-use of the safe room (multi-purpose space 
within 
a building) will affect the cost of many building components, finishes, 
furnishings, and other occupancy-driven design parameters.

- Simplicity of design. The simpler the safe room construction system 
(short 
walls, short roof spans, and minimal interior finishes), the lower the 
cost. 
Safe rooms with large, open spaces that require more elaborate 
construction 
systems will undoubtedly cost more than an ordinary building. The choices 
made 
during the initial planning and design stage will have a direct impact on 
cost.

- Safe room design wind speed. The safe room design wind speed will affect 
the 
strength criteria, which both the structural system and exterior 
components and 
cladding of the safe room need to satisfy in order to resist the design 
wind 
loads

- Safe room debris impact-resistance criteria. These design criteria 
arguably 
have the most significant influence over cost. Common building materials 
are 
readily available to harden wall and roof systems to be debris impact-
resistant. 
However, opening protection systems and devices for doors, windows, vents, 
and 
other elements that may protrude through the safe room are much less 
common. 
Costs for these systems range from $50 (basic code compliance for building 
protection) to $400 per square foot of opening (for life-safety protection 
that 
meets FEMA 361 safe room criteria). Thus, the more openings desired by the 
safe 
room owner/operator/designer, the greater the cost of the safe room. The 
decision to include more windows or openings in a safe room, because it 
has uses 
other than sheltering, will have a significant impact on the safe room 
cost.

- Exterior walls and roof materials. The materials selected by designers 
may be 
readily available common building materials or newer technologies that may 
improve the safe room performance, but at a premium cost. 

- Location of the safe room  impact on foundation type. The foundation of 
a 
safe room may be a simple, slab-on-grade with minimal footings and a 
relatively 
low cost. A basement safe room will cost more to excavate, but these 
increased 
costs are offset by higher levels of debris impact protection afforded by 
the 
surrounding soils in addition to debris impact-resistant walls. A safe 
room 
needed to protect at risk population located in an area subject to 
flooding may 
require elevated foundations that are more expensive than other options, 
but are 
inevitable for this type of a safe room.

- Location of the safe room  other hazards. A safe room constructed in an 
open 
field may not be exposed to any additional hazards such as falling objects 
and 
building debris. However, safe rooms located on the lower floors of small 
buildings that have not been designed to resist high winds, or those 
located 
near trees or large power, telephone, light, or cellular towers and poles, 
are 
usually exposed to falling debris hazards. The safe rooms that cannot 
avoid 
these additional risks can be designed to resist them, but often at a 
premium 
cost. Additionally, the location of a safe room with respect to local 
seismic 
risk must also be considered. When constructing safe rooms in areas 
subject to 
seismic activity, these loads may govern some aspects of the design, 
resulting 
in an increase to the cost of the safe room.

2.3.2	Recent Safe Room Cost Data 

Community shelters and safe rooms have been designed long before the first 
edition of FEMA 361 was released in July 2000. However, since that time 
there 
have been hundreds of extreme-wind hazard community safe rooms designed 
and 
constructed across the country. Since 2000, over 500 community safe rooms 
have 
been constructed around the country with some federal funding being 
provided 
through FEMA grant programs. For the update to this publication, FEMA 
reviewed a 
more recent series of cost estimates from 2005 to 2008 (including the 2008 
Pre-
Disaster Mitigation [PDM] Grant Program cycle, which included 36 safe room 
grant 
applications from 12 states). Table 2-4 presents cost metrics that have 
been 
developed to assist groups planning to design and construct safe rooms. 
These 
data were compiled from extreme-wind-hazard safe room projects.

[Begin table]
Table 2-4. Cost Data From Recent Community Safe Room Projects
General Safe Room and Shelter Data

Description: Safe room average cost per square foot
Cost Metric: $150  $240 per square foot (sf)
Comments: Single use community safe rooms consistently had the lowest 
associated 
(estimated or actual) per square foot cost. Safe rooms in the lower range 
of 
this cost had low walls and short roof spans. Average costs at the higher 
end 
were typically for larger safe rooms (by square footage and occupancy) 
with much 
of the protected areas designed as large, open spaces with long roof 
spans.

Description: Percent increase in building cost to harden a portion of a 
new 
building to resist 250-mph winds from a 140-mph basic wind speed
Cost Metric: 5%  7%
Comments: Percent increase in cost per square foot associated with the 
structural and envelope hardening to meet 250-mph safe room design wind 
speed 
versus 140-mph basic wind speed from the building code. This is a cost 
increase 
per square foot of the safe room area being hardened.

Description: Percent increase in building cost to harden a portion of a 
new 
building to resist 250-mph winds from a 90-mph basic wind speed
Cost Metric: 15%  20%
Comments: Percent increase in cost per square foot associated with the 
structural and envelope hardening to meet 250-mph safe room design wind 
speed 
versus 90-mph basic wind speed from the building code. This is a cost 
increase 
per square foot of the safe room area being hardened.

Description: Percent increase in building cost to harden a portion of a 
new 
building to resist debris impact from a 15-lb 2x4 board missile traveling 
horizontally at 100 mph and impacting vertical surfaces and the same 
missile 
traveling vertically at 67 mph and impacting horizontal surfaces
Cost Metric: 5%  27%
Comments: Percent increase in cost per square foot associated with the 
hardening 
of all portions of the safe room exterior walls, roofs, and opening 
protective 
devices versus providing no debris impact protection at all (debris impact 
resistance only, wind pressure resistance not considered). This is an 
increase 
to the cost per square foot of the safe room area being hardened. The 
percent 
increase for hardening the safe room exterior components to resist debris 
impact 
is highly dependent on a number of factors including, but not limited to: 
size 
of the safe room, materials used, strength in wall and roof systems 
already 
provided by designing to resist wind loads from the safe room design wind 
speed, 
the percentage of openings in the safe room exterior, the number of egress 
points to be protected, and several others. For the purposes of this 
comparison, 
the safe room projects considered had minimal doors and building exteriors 
requiring protection for openings (windows) that ranged from 0% to 10% of 
the 
total building exterior.

Description: Percent increase in building cost to harden a portion of a 
new 
building to resist 250-mph winds and associated debris impacts from a 90-
mph 
basic wind speed
Cost Metric: 20%  32%
Comments: Percent increase in cost per square foot associated with the 
structural and envelope hardening to meet 250-mph safe room design wind 
speed 
versus 100-mph basic wind speed and provide debris impact protection from 
a 15-
lb missile traveling at 90 mph. This is a cost increase per square foot of 
the 
safe room area being hardened.


2008 PDM Grant Application Sample Cost Data (36 safe room projects)

Description: Safe room sizes proposed
Cost Metric: Max = 32,000 sf, Min = 700 sf, Avg = 6,500 sf
Comments: Most projects associated with the submittals for this cycle 
proposed 
an entire building as the safe room (78% of projects). In most instances, 
85% of 
the usable space within the proposed protected area was considered 
available for 
occupants; see Chapter 3 for appropriate occupant loads per square foot of 
available space. 

Description: Range of safe room average cost per square foot for projects 
considered technically feasible and effective for providing protection
Cost Metric: Max = $480/sf, Min = $90/sf, Avg = $188/sf
Comments: These cost figures are as proposed. Their incorporation here is 
for 
informational purposes only. These numbers were separately evaluated on a 
project by project basis for cost-effectiveness. 

Notes:
1. Costs were based on safe room and shelter projects meeting the criteria 
of 
FEMA 361 (July 2000).
2. Safe room sizes for the General Safe Room and Shelter Data sections of 
the 
table varied from 5,000 square feet to 32,000 square feet.
3. Data in this table are from several sources including, but not limited 
to: 
cost estimates prepared by designers/architects/engineers on behalf of 
prospective and actual safe room owners, FEMA analyses, FEMA grant 
applications, 
and state and local emergency management agencies.
[End table]

2.3.3	Other Factors Impacting Cost

The most cost-effective means of constructing a safe room at a site is to 
incorporate the safe room into a new building design in the initial 
planning 
stage. The cost to design and construct hardened safe room areas within 
new 
buildings is much lower than the cost of retrofit (i.e., when the existing 
buildings or portions of existing buildings need to be hardened). For 
example, 
in recent FEMA-funded mitigation projects in many midwestern and 
southeastern 
states, the construction costs (per square foot) for retrofitting safe 
rooms 
have been (at a minimum) approximately 10 to 15 percent higher than 
construction 
costs for safe rooms in new buildings. It is important to remember, 
however, 
that this increase in cost applies only to a small area of the building 
(i.e., 
the area being hardened and not the entire building). 

Also, Table 2-4 shows how the relative cost per square foot for safe rooms 
included as a part of a building project increases when life-safety 
protection 
is provided. For large new building projects, however, the percent 
increase in 
the overall project cost is quite small. For example, many safe rooms 
protecting 
200 to 300 occupants being constructed as part of a new school have added 
only 1 
to 2 percent to the total project cost when the safe room was included in 
the 
design process at the beginning of the project. 

The level of protection afforded by a safe room also impacts the cost of 
the 
safe room; however, that does not always mean that a safe room constructed 
for a 
higher level of protection will cost more than one that has been 
constructed for 
a lower level of protection. Table 2-1 provides a comparison of different 
levels 
of protection offered by FEMA safe rooms and shelters designed and 
constructed 
to other criteria or code requirements. For example, a simplified design 
for a 
single-use, tornado community safe room may cost less than a large, multi-
use 
hurricane community safe room that has multiple uses and a long-span roof 
system. Similarly, constructing a shelter or safe room to comply with ICC-
500 
flood criteria in a V zone may cost upwards of 10 percent more (per square 
foot 
of the entire project cost) than the same safe room constructed to meet 
the FEMA 
361 community safe room flood design criteria that does not permit safe 
room 
construction in V zones. Although a higher level of protection is provided 
by 
the FEMA compliant safe room because it has been removed from the velocity 
zone, 
the elevation of the shelter to the ICC criteria (which allows placement 
in the 
V zone) results in a more expensive solution because of the elevated 
foundation 
required even though the hazard is still present.

Table 2-4 shows relative incremental cost increases for constructing safe 
rooms 
to FEMA 361 criteria in comparison to building code required construction, 
even 
in hurricane-prone regions where the design of buildings is more robust. 
In 
these cases, buildings such as critical or essential facilities 
constructed in 
coastal areas called wind-borne debris regions are required to be 
designed and 
constructed to resist wind speeds up to 145 to 150 mph (3-second gust) and 
also 
have debris impact-resistance for a 9-lb missile traveling at 55 mph. This 
improved level of protection is required for these areas by the building 
code to 
reduce damage to these facilities by known hazards; however, they do not 
provide 
a level of protection that can be considered near-absolute for life-safety 
of 
occupants within the building. Further, Table 2-4 presents data from 
recent 
projects indicating that safe rooms constructed to the FEMA 361 criteria 
for 250 
mph (to resist both wind pressures and debris impacts) where the protected 
areas 
provide near-absolute protection for its occupants have been constructed 
for as 
little as 5 percent more (on a cost per square foot basis) than critical 
and 
essential facilities designed to a 140-mph basic wind speed. 

Intuitively, it may be stated that when two safe rooms are constructed of 
the 
same materials, but one is designed to the level of protection being 
offered by 
a FEMA 361 tornado community safe room while the second is designed to the 
level 
of protection offered by a FEMA 361 hurricane community safe room (where 
the 
safe room design wind speed and the design missile impact is based on a 
smaller 
and slower missile), the cost of the hurricane community safe room may be 
even 
closer to that of the critical facility designed to resist 140 mph (and 
associated debris impacts) per ASCE 7-05. This is based on the assumption 
that 
smaller quantities of the building materials are required and thus the 
safe room 
will cost less. The same may be said when comparing differences in costs 
associated with the level of protection offered by a FEMA 361 safe room 
and an 
ICC-500 shelter (for either hazard or for the combined tornado and 
hurricane 
hazards) constructed of the same materials. But such a comparison needs to 
be 
completed carefully. Factors such as single-use versus multi-use shelters 
or 
safe rooms and optional features that result from the selection of a 
multi-use 
safe room (such as taller walls, more windows, more doors/egress points, 
etc.) 
must be identified when comparing the cost estimates for two protected 
areas 
designed to different criteria. No two safe rooms or shelters were able to 
be 
identified with matching building materials and design assumptions, thus 
specific cost comparisons could not be made at the time this publication 
was 
prepared.

Both the new FEMA 361 hurricane community safe room design criteria 
presented in 
Chapter 3 and the new ICC-500 hurricane community shelter criteria specify 
new 
wind speed ranges and new debris impact-resistance criteria. Because these 
criteria are new, no products other than those that satisfy the existing 
FEMA 
361 life-safety criteria (250 mph and a 15-lb 2x4 board missile traveling 
at 100 
mph) are available in the market for a number of the components. Thus, 
specific 
wall systems, opening protection devices and systems, and glazing or 
glazing 
protection systems that satisfy the new criteria do not yet exist. Since 
no 
products have been developed at this time, no cost comparisons can be 
made. 

Depending upon the features included in the design of a safe room or 
shelter, 
arguments may be made that a combined hazard safe room can likely be 
constructed 
for nearly the same cost as a hurricane-specific hazard safe room 
(depending 
upon size, number of openings, building materials selected, etc.), but it 
is 
difficult to quantify for many of the reasons discussed above. As such, it 
is 
also difficult to state or prove that a hurricane-specific safe room will 
cost 
significantly less to construct than a combined-hazard safe room with 
minimal 
doors and openings. At this time, the percent cost difference between a 
FEMA 361 
hurricane community safe room and a FEMA 361 combined tornado and 
hurricane 
community safe room cannot be specifically provided, but is assumed to be 
less 
than 5 percent. This statement is based on the project data in Table 2-4 
that 
showed cost per square foot increases as small as 5 to 7 percent to 
improve 
building wind resistance from the level of a critical facility constructed 
to 
the building code in a hurricane-prone region with 140-mph design wind 
speed 
criteria and the 250-mph safe room design wind speed criteria presented in 
Chapter 3. It would follow that, to reduce the design parameters to a 
slightly 
lower wind speed (250 to 200 mph) and to reduce the debris impact 
resistance 
requirements for the lighter missile of the FEMA 361 hurricane safe room 
criteria, because the magnitude of the design criteria is not as 
significant as 
to drop back to code-level requirements, the cost impact would also not be 
as 
dramatic.

Similarly, the cost differences between a FEMA 361 safe room and an ICC-
500 
shelter cannot be quantified at this time. Even though the differences in 
design 
criteria exist, FEMA criteria are mostly equivalent to or slightly more 
restrictive than the ICC-500 requirements. The wind speeds are the same 
and the 
missiles are the same. The small differences in design parameters and 
missile 
impact speeds (for FEMA hurricane safe rooms versus the ICC-500 shelters) 
are 
less in magnitude than the design parameters for essential facilities that 
are 
constructed at protection levels based on 140 mph 3-second gust at costs 
of 5 to 
7 percent less than the costs associated with a FEMA 361 safe room. As 
such, the 
cost differential to construct an ICC-500 shelter should be between these 
two 
costs since the design criteria required for compliance are between the 
FEMA 361 
and the essential facility criteria of the building code.

2.3.4	Additional Factors to Consider When Constructing a Safe Room

A number of factors can influence the decision-making process in addition 
to 
cost considerations. The potential for death or injury may be a sufficient 
reason to build a safe room at a given building site. The benefit-cost 
ratio of 
constructing a safe room discussed in Section 2.4 may be a contributing 
factor 
or a requirement of the safe room design process, depending upon the 
funding 
source. However, additional factors may be involved in the decision-making 
process:

- Do the residents feel safe without a safe room?
- Does a business want to provide the protection for its workers?
- Does a safe room allow for faster business recovery after an extreme-
wind 
event?
- Is the building in question a government-owned building that is required 
to 
have a safe room?
- Do zoning ordinances require it?
- Are there insurance benefits?

2.4	Benefit-Cost Analysis

Benefit-cost analysis (BCA) is a method used to determine the cost-
effectiveness 
of proposed projects. FEMA regulations require mitigation projects funded 
under 
Hazard Mitigation Assistance (HMA) programs to have benefits (avoided 
losses) 
that exceed costs, usually expressed as a benefit-cost ratio (BCR) greater 
than 
1.0.

The July 2000 Edition of FEMA 361, Design and Construction Guidance for 
Community Shelters, included BCA software for tornado and hurricane 
shelters, 
which will be referred to below as the existing shelter BCA software. 
This 
software focused exclusively on the reduction of injuries and deaths 
(life-
safety benefits) from shelters as the basis for benefits. Beginning in 
2007, in 
parallel with revisions to FEMA 361, FEMA undertook to redesign all BCA 
software 
associated with their mitigation grant programs for flood, earthquake, 
hurricane, and tornado hazards. As the new Tornado Safe Room BCA and 
Hurricane 
Safe Room BCA software are finalized, they will be used in place of the 
existing 
shelter BCA software. The new Tornado Safe Room BCA software will be 
included in 
release 4.0 of the new Benefit-Cost Analysis software, with an anticipated 
release date of fall 2008. The Hurricane Safe Room BCA software requires 
more 
extensive revisions and is planned to be included in release 5.0 of the 
Benefit-
Cost Analysis software, with an anticipated release in 2009. Copies of the 
existing and new BCA software and information on the final releases of the 
new 
software can be found at the FEMA BCA website, 
http://www.fema.gov/government/grant/bca.shtm.

2.4.1	Existing Shelter BCA Software

The existing shelter BCA software was designed based on the presumed need 
to 
provide community safe rooms that were either retrofits of existing 
structures, 
such as schools, or retrofits of designs for new structures ( e.g., adding 
a 
hardened hallway to the design of a new town hall). Figure 2-3 is a 
flowchart of 
the existing benefit-cost model. The project costs to be inputted should 
be 
based on the costs of building construction and any additional maintenance 
costs 
incurred by the project. Benefits, or avoided damages, are based on the 
reduction of casualties (injuries and deaths) resulting from the 
construction of 
the proposed shelter. The four main factors used to calculate these 
benefits 
are:

- Losses associated with injury or death
- Safe room occupancy
- Probability of injury and death due to tornado or hurricane winds
- Probability of tornado or hurricane wind events

[Begin figure]
Figure 2-3. Flowchart for the existing benefit-cost model

Three boxes across the top reading from left to right:
Project information. Building information. Mitigation project information.
These 3 boxes all lead to 2 additional boxes. Box 1: Tornado hazard data. 
Box 2 
Hurricane hazard.
These two boxes lead to Wind speed mapping and benefits, which then leads 
to 
benefit-cost ration computation
[End figure]

Original default loss values are based on values from the 1990s used by 
the 
Federal Aviation Administration (FAA) for insurance purposes. These 
defaults 
include a single injury level estimated to cost $12,500 per person and a 
death 
is estimated as $2,200,000 per person. Safe room occupancy is based on 
average 
hourly occupancy counts throughout a 24-hour period. The software was 
developed 
with the assumption that these occupants would only include the people who 
would 
have already been in the structure, which eliminates the consideration of 
issues 
such as warning response time and travel time to the safe room. These 
values are 
entered by the user.
The probability of an injury or death is represented by casualty rate 
tables 
giving estimated death and injury percentages for five building types 
(with two 
window covering categories) over nine wind speed ranges. Building types 
represent before-mitigation (pre-safe room) conditions. To represent the 
safe 
room, the before-mitigation death and injury values are reduced by a 
certain 
percentage based on safe room design. These tables were developed by FEMA 
tornado experts and consultants on the basis of professional experience 
and 
judgment.
The probability of a tornado hitting a safe room is based on the NOAA 
Storm 
Prediction Centers Historical Tornado Data Archive from 1950-2006. 
County-based 
tornado statistics were calculated directly from this archive for Fujita 
(F) and 
now Enhanced Fujita (EF) class, time of day, and tornado length and width. 
Because tornado occurrence is infrequent for certain Fujita classes, 
especially 
F3 (and EF3) and greater, the current software used a geographic 
information 
system (GIS)-based approach that has the user select a region of counties 
surrounding the county of the safe room until a significant number of 
tornadoes 
has been reached. Probability of tornado occurrence is then calculated for 
this 
region of counties based on NOAA data and the shelter footprint area. The 
probability of hurricane events is based on the ASCE 7-98 map of 50-year 
MRI 
wind speeds and adjustment equations for other recurrence intervals 
compared 
against maximum anticipated wind speeds from storms.  

The final benefit calculation compares the before- and after-mitigation 
expected 
deaths and injuries. This calculation is performed separately for 
tornadoes and 
hurricanes and then added for the total benefits.

2.4.2	New Tornado Safe Room BCA Software

The use of the existing shelter BCA software for grant programs like PDM 
has 
highlighted a number of issues. The New Tornado Safe Room BCA software 
addresses 
many of these issues and allows users to choose between the following safe 
room 
projects:

- New vs. retrofit safe room
- Stand-alone vs. internal safe room
- Community vs. residential safe room

The benefits (losses avoided) are calculated as a difference between 
losses that 
would occur before the safe room is built and the losses that would occur 
after 
the safe room is fully operational. The losses before mitigation (safe 
room 
construction) are determined on the basis of potential damage to different 
types 
of buildings where potential safe room occupants would be taking shelter 
during 
the storm.

In many cases, a new safe room, especially a stand-alone one, will serve a 
population that would not necessarily be on site. The potential safe room 
occupants would need to travel to the safe room from the surrounding area 
within 
the minimum allowed time period. This approach now requires the new 
methodology 
to take into account warning response times and travel times to the safe 
room. 

The four main factors used to calculate the benefits remain the same:

- Costs associated with injury and death
- Shelter occupancy
- Probability of injury and death due to tornado winds
- Probability of tornado wind events

However, the way that each of these factors is calculated has changed. In 
2007, 
FEMA convened an outside panel of building performance experts (with 
significant 
knowledge in tornado and hurricane building damage assessments) and life-
safety 
experts from consulting firms, research organizations, and academia. This 
expert 
panel evaluated the existing methods for calculating benefits and provided 
guidance on updated methods. The costs associated with casualties are now 
divided between three injury levels (self-treat, treat and release, 
hospitalized) and death, based on updated tables from the FAA (2007 
dollars). 

The occupancy load is counted for three intervals during a 24-hour period: 
day, 
evening, and night. Since the majority of the potential occupants of the 
community safe room will come from the surrounding areas, the new 
methodology 
allows the user to select up to two before-mitigation structure types to 
represent the level of risk to which the potential occupants would be 
exposed in 
conditions without a safe room. These two types can be selected from eight 
pre-
defined structure types provided in the model, based on the categories 
used in 
the development of the Enhanced Fujita Scale. The casualty rates for each 
damage 
state were defined on the basis of damage indicators and degree of damage 
tables 
published in the Enhanced Fujita Scale report (TTU 2006). [Footnote 3]

[Begin footnote 3 - A Recommendation for an Enhanced Fujita Scale (EF-
Scale), 
Revision 2, October 2006, prepared by the Wind Science and Engineering 
Research 
Center, Texas Tech University.End footnote] 

The probability of a tornado striking a safe room is still based on NOAA 
tornado 
historical records, but employs a regional analysis method to eliminate 
the need 
for user-selected regions. Tornado records with recorded paths or start 
points 
were expanded and updated to cover the period from 1950 to 2006. This 
information was used as part of a geospatial analysis method, based on 
tornado 
probability research, to produce tornado occurrence maps for each Enhanced 
Fujita class. Tornado probability is then calculated using published 
average 
national tornado length and width values. When the user selects the county 
where 
the safe room will be located, the pre-calculated tornado probabilities 
are 
accessed from the software database.
The basis for project costs (initial project costs and maintenance) has 
remained 
the same as in the existing model; however, new cost estimation tools have 
been 
developed. As a result of all of these changes and overall changes to the 
BCA 
software platform, the new Tornado Safe Room BCA provides an updated, 
defensible, and more user-friendly tool to calculate life-safety benefits 
for 
tornado safe rooms, for both the community and residential units.