FEMA Community Wind Shelters
Background and Research

August 2002

What is a Wind Shelter?

A wind shelter is an interior room or other space within a building, or even an 
entire separate structure, that is designed and constructed to protect its 
occupants from high winds, usually those associated with tornadoes or hurricanes. 
Wind shelters are intended to provide protection against both wind forces and the 
impact of windborne debris.

Wind shelters typically fall into two categories-in-home shelters and community 
shelters. An in-home shelter is usually a small, specially designed ("hardened") 
room,  such as such as a bathroom or closet, or other space within a house that is 
intended to provide a place of refuge only for the people who live in the house. 
In contrast, a community shelter is intended to provide protection for a large 
number of people, anywhere from 12 to as many as several hundred.

Community shelters are usually built within or near large public, institutional, 
or commercial buildings such as schools, hospitals, and nursing homes. A community 
shelter can also be built in a neighborhood to provide protection for residents 
whose homes lack shelters. Although community shelters are designed to accommodate 
large numbers of people, they are not recovery shelters. In other words, they are 
not intended to provide housing for people whose homes have been damaged or 
destroyed during disasters.

Community and in-home shelters are alike in that they are intended to provide 
protection only during a short-term, high-wind event-an event that lasts no more 
than 36 hours, such as a tornado or hurricane. In other ways, however, the two 
types of shelters are quite different. This brochure focuses on community 
shelters. For more information about in-home shelters, refer to the separate FEMA 
brochure In-Home Wind Shelters and to FEMA publication 320, Taking Shelter From 
the Storm: Building a Safe Room Inside Your House.
Types of Community Shelters
A community shelter can be constructed as a separate building (stand-alone 
shelter) or as a room or area within a larger building (internal shelter). An 
example of a stand-alone shelter would be a building constructed in a central 
location within a single-family home neighborhood or manufactured home park. An 
internal shelter could be a specially constructed hallway, cafeteria, restroom, or 
multi-purpose room in a school, hospital, airport, or other large building.

In general, internal shelters are preferable because they offer several advantages 
over stand-alone shelters. The occupants of a building equipped with an internal 
shelter do not need to leave the building and will not have to risk exposure to 
high winds, windborne debris, lightning, or other storm conditions. Another 
advantage is that building occupants will be able to reach an internal shelter 
more quickly and easily. As a result, people threatened by a high-wind event are 
more likely to protect themselves adequately when a shelter is available within 
their building. In some situations, however, the construction of a stand-alone 
shelter may be the only practical choice. For example, incorporating an internal 
shelter into an existing building (retrofitting) may be impractical when extensive 
modifications to the structure or layout of the building would be necessary.

Both stand-alone and internal shelters can be single-use or multi-use structures. 
Single-use shelters are used as shelter space only. The advantages of single-use 
shelters include the following:
* simplified design that may be readily approved by a local building official or 
fire marshal
* simplified electrical and mechanical systems, because they are not required to 
provide normal daily accommodations for people
* no space lost to furnishings, stored materials, and other contents not related 
to the shelter function

Multi-use shelters are designed to serve other purposes in addition to providing 
shelter space. Examples of multi-use shelters are meeting rooms, exercise rooms, 
cafeterias, gymnasiums, libraries, restrooms, and hallways. The advantages of 
single-use shelters include the following:
* immediate return on investment for owners/operators
* efficient use of building space
* lower additional cost for a shelter, because the room is also used for another 
purpose
Where are Community Wind Shelters Needed?
In areas subject to extreme-wind events, building owners, school and hospital 
administrators, neighborhood associations, and other individuals and organizations 
with responsibilities for public safety should consider building a community 
shelter. As noted in the following sections, wind hazards, such as those 
associated with tornadoes and hurricanes, vary throughout the United States. The 
decision to build a wind shelter will be based largely on the magnitude of the 
wind hazard in a given area and on the level of risk considered acceptable.

FEMA publication 361, Design and Construction Guidance for Community Shelters, 
contains tornado and hurricane statistics, wind speed and wind hazard data, a 
shelter benefit-cost model on CD-ROM, evaluation checklists for potential shelter 
areas in existing buildings, and other information that will help the reader 
assess risks in a specific area, determine the need for a shelter, and decide 
where and how a shelter should be built.
Tornadoes - Understanding the Hazards
A tornado is a violently rotating column of air that extends from a thunderstorm 
cloud to the ground. On average, more than 1,200 tornadoes have been reported 
nationwide each year since 1995. Since 1950, tornadoes have caused an average of 
89 deaths and 1,521 injuries annually, as well as devastating personal and 
property losses. As shown by the map, tornadoes occur primarily in the central and 
eastern portions of the United States.

A tornado watch is issued to alert people to the possibility of tornado 
development in an area. A tornado warning is issued when a tornado has actually 
been sighted or is indicated by radar.

Tornadoes are rated by the National Weather Service according to the Fujita Damage 
Scale. Fujita ratings vary from F0, for light damage, to F5, for total 
destruction.

The Fujita Damage Scale

Fujita Damage Rating

Damage Description

F0 Light
Some damage can be seen to poorly maintained roofs. Unsecured lightweight objects, 
such as trash cans, are displaced.

F1 Moderate
Minor damage to roofs occurs, and windows are broken. Larger and heavier objects 
become displaced. Minor damage to trees and landscaping can be observed.

F2 Considerable
Roofs are damaged. Manufactured homes on nonpermanent foundations can be shifted 
off their foundations. Trees and landscaping either snap or are blown over. 
Medium-sized debris becomes airborne, damaging other structures.

F3 Severe
Roofs and some walls, especially unreinforced masonry, are torn from structures. 
Small ancillary buildings are often destroyed. Manufactured homes on nonpermanent 
foundations can be overturned. Some trees are uprooted.

F4 Devastating
Well constructed homes, as well as manufactured homes, are destroyed. Some 
structures are lifted off their foundations. Automobile-sized debris is displaced 
and often tumbles. Trees are often uprooted and blown over.

F5 Incredible
Strong frame houses and engineered buildings are lifted from their foundations or 
are significantly damaged or destroyed. Automobile-sized debris is moved large 
distances. Trees are uprooted and splintered.

All tornadoes produce high winds and carry windborne debris that can pose a danger 
to lives and property. Violent tornadoes (those rated F4 and F5) are capable of 
tremendous destruction with wind speeds of up to 250 mph near ground level. 
Violent tornadoes can rip buildings from their foundations, and the debris carried 
by their winds can easily break windows and even penetrate the walls or roof of a 
building.

Tornado damage paths over 50 miles long and over 1 mile wide have been reported. A 
good example of the destructiveness of tornadoes is the damage caused by the 67 
tornadoes that struck Oklahoma and Kansas on May 3, 1999, which included many F4 
and F5 tornadoes. This tornado outbreak resulted in 49 deaths and leveled entire 
neighborhoods.

Additional information about the Oklahoma and Kansas tornadoes is available in the 
FEMA Building Performance Assessment Team report Midwest Tornadoes of May 3, 1999, 
FEMA 342.

Hurricanes - Understanding the Hazards

A hurricane is a type of tropical cyclone (the general term for all weather 
systems that circulate counterclockwise in the Northern Hemisphere over tropical 
waters) originating in the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. 
Around the core of a hurricane, winds can grow with great velocity. As the storm 
moves ashore, it can push ocean waters inland while spawning tornadoes and 
producing torrential rains and floods.

On average, 10 tropical storms (6 of which become hurricanes) develop each year in 
the Atlantic Ocean. Approximately five hurricanes strike the United States 
mainland every 3 years; two of those storms will be major hurricanes-Category 3 or 
greater on the Saffir-Simpson Hurricane Scale.

The Saffir-Simpson Scale

Saffir-Simpson Damage Rating

Wind Speeds and Damage Description

C-1 Minimal

Wind speeds 74 to 95 mph. Damage is done primarily to shrubbery and trees. 
unanchored manufactured homes are damaged. Some signs are damaged. No real damage 
is done to structures.

C-2 Moderate
Wind speeds 96 to 110 mph. Some trees are toppled. Some roof coverings are 
damaged. Major damage is done to manufactured homes.

C-3 Extensive
Wind speeds 111 to 130 mph. Some structural damage is done to roofs. Manufactured 
homes are destroyed. Structural damage is done to small homes and utility 
buildings.

C-4 Extreme
Wind speeds 131 to 155 mph. Extensive damage is done to roofs, windows, and doors. 
Roof systems on small buildings fail completely. Some curtain walls fail.

C-5 Catastrophic
Speeds 156 mph and higher. Roof damage is considerable and widespread. Window and 
door damage is severe. There are extensive glass failures. Some entire buildings 
fail.

When a hurricane threatens, weather services issue hurricane watches and warnings. 
A hurricane watch is issued when a hurricane is possible within 36 hours. A 
hurricane warning is issued when a hurricane is expected within 24 hours. An 
evacuation notice may be issued in conjunction with a hurricane warning.

In the western Pacific, hurricanes are called typhoons and affect the Pacific 
Islands, including Hawaii, Guam, and American Samoa. Historically, typhoons have 
been classified by strength as either typhoons (storms with less than 150 mph 
winds) or super typhoons (storms with wind speeds of 150 mph or greater) rather 
than by the Saffir-Simpson Hurricane Scale.

Although the highest wind speeds associated with hurricanes are not as great as 
those of the most severe tornadoes, hurricane winds and the debris they can carry 
are still extremely dangerous. The loss of life and property from hurricane-
generated winds can be staggering. An example of a hurricane that caused severe 
wind damage is Hurricane Andrew, which made landfall in southeastern Florida in 
August 1992, generating strong winds and heavy rain over a vast portion of 
southern Dade County. This Category 4 storm (having a range of sustained wind 
speeds from 131 mph to 155 mph) produced high storm surge, but the most extensive 
damage was caused by wind.

Andrew caused unprecedented economic devastation; damage in the United States was 
in the tens of billions of dollars, making this the most expensive natural 
disaster in U.S. history. In Dade County, the storm forces caused 15 deaths and 
left almost one-quarter million people temporarily homeless. Additional 
information about Hurricane Andrew is available in the FEMA Building Performance 
Assessment Team report Building Performance: Hurricane Andrew in Florida, FIA-22.

Shelter Strength

Clearly, to survive a tornado or hurricane, a building needs an extremely strong 
structure-to resist high-wind forces-and an extremely resistant envelope (the 
"skin" of the building)-to resist the impact of windborne debris. The results of 
research presented in FEMA 361 show that a shelter that can withstand 250-mph 
winds and the impact of a 15-pound 2x4 traveling at 100 mph will provide "near-
absolute protection" for its occupants in virtually any high-wind event.

A shelter that provides near-absolute protection will protect its occupants from 
death and injury. This term does not mean that the shelter itself will be 
undamaged by high winds or debris. Repairs to a shelter's walls, ceilings,  and 
doors may be necessary after a extreme-wind event.

For the goal of near-absolute protection to be met, the entire shelter-including 
its walls, ceilings, and doors-must be designed and constructed to provide the 
required strength and impact resistance. Shelter designs typically call for 
larger, stronger, and a greater number of construction materials such as concrete 
bocks, reinforcing rods, connectors, and door hardware. Openings into the shelter 
area, such as windows, must be eliminated or kept to a minimum. When present, they 
must be protected with shutters or other coverings of adequate strength and impact 
resistance. Shelter design and construction must also consider other potential 
natural hazards at the site, such as flooding and earthquakes.

FEMA 361 contains examples of shelter design plans that include construction 
details and materials lists.

Other Considerations

Although essential to successful performance, strength is not the sole 
consideration in shelter design and construction. Shelters must also:

* be readily accessible
* be sited to minimize hazards
* provide for the comfort of their occupants
* be equipped with emergency supplies
* be operated and maintained according to formal plans

Accessibility

Shelters must be readily accessible to their users, especially those with 
disabilities that affect mobility. Accessibility requirements include the 
following:

* Shelters and the routes to them must be clearly identified by signs.
* Travel time to the shelter must be minimized.

* Walkways, hallways, and other routes to the shelter must be free of 
obstructions.
* Shelter design must meet all Federal, state, and local Americans with 
Disabilities Act (ADA) requirements.

Information about providing for the needs of disabled persons during emergencies 
is provided in FEMA's United States Fire Administration publication Emergency 
Procedures for Employees with Disabilities in Office Occupancies.

Siting

In addition to being located where they are readily accessible, shelters must be 
sited to minimize additional hazards-for example, outside the 500-year floodplain 
and away from large objects that could become windborne debris, such as light 
towers, antennas, and satellite dishes.

Occupant Comfort

The comfort of shelter occupants will depend largely on the amount of space 
provided per occupant and adequate ventilation, lighting, water and food, and 
toilets.

The amount of space required per person depends on the duration of occupancy. For 
this reason, the required space differs between shelters intended for tornado 
protection and those intended for hurricane protection. Historical data indicate 
that a tornado shelter will typically have a maximum occupancy time of 2 hours. By 
contrast, a hurricane shelter will have a maximum occupancy time of 36 hours. The 
recommended minimums for occupant space are 5 square feet per person for tornado 
shelters and 10 square feet per person for hurricane shelters.

Note that these square footage figures are minimums; larger amounts of space are 
required for special situations. For example, the 5 square feet minimum for 
tornado shelters assumes that the shelter occupants will be standing for the 
duration of the event. Larger amounts of space are required for seated occupants 
and those with special needs, such as wheelchair users. Additional information 
about required shelter space is presented in FEMA 361.

Shelter ventilation systems can be passive or active. Passive systems depend on 
ducts or other openings that allow for the natural flow of air. Active systems 
depend on mechanical fans or blowers. Both types of systems must meet the 
requirements of local codes. Active systems should be provided with emergency 
backup power.

For multi-use shelters, lighting, including emergency lighting, is usually 
required by local codes. Similar lighting is recommended for single-use shelters 
as well. A backup power source is essential for emergency lighting systems. 
Batteries are recommended because they can be placed within the shelter area, 
where they will be protected. Natural lighting for shelter areas is also possible, 
but all windows must be protected with covers that meet the requirements for 
resistance to wind pressures and debris impact.

Adequate supplies of water are essential for both tornado and hurricane shelters. 
Food should be provided in hurricane shelters, but is not a major concern in 
tornado shelters, because of the short duration of use.

A minimum of two toilets are recommended for both tornado and hurricane shelters. 
In hurricane shelters, which will be occupied for longer periods, the toilets must 
be able to function without power, water supply, and possibly waste disposal. 
Chemical toilets are a practical alternative to standard toilets. Shelter 
operators should ensure that the toilets are installed in a separate room or 
screened for privacy.

Emergency Supplies

All shelters should be equipped with emergency supplies, including flashlights, 
fire extinguishers, first-aid kits, radios (including weather radios and extra 
batteries), and a signaling device (such as an air horn).

Operations and Maintenance Plans

Operations and maintenance plans are required for all community shelters. The 
Operations Plan should clearly describe, and define the appropriate actions to be 
taken for, tornado watches and warnings and hurricane watches and warnings. The 
plan should also designate a Community Shelter Management Team and its 
responsibilities. Tasks assigned to the team should include the following:

* sending the warning signal to those who rely on the shelter
* evacuating community residents or building occupants and directing them to the 
shelter
* opening the shelter
* taking a head count at the shelter
* securing the shelter
* monitoring the storm from within the shelter and determining when it is 
safe for the occupants to leave
* cleaning and restocking the shelter
* conducting practice drills

The Maintenance Plan should include the following:
* a checklist of emergency supplies
* a schedule of regular maintenance activities (e.g., supply inventories, 
equipment checks)

New Construction vs. Retrofitting

An additional consideration is whether a shelter will be built as new or retrofit 
construction. Building a shelter as a new building or part of a new building is 
generally more efficient and economical than retrofitting (modifying an existing 
building to meet specific design requirements).

Retrofit shelter construction involves making all changes necessary to strengthen 
an existing room or area of a building so that it will provide the required 
resistance to wind forces and debris impact. This process could involve extensive 
modifications to the foundation, frame, envelope, connections, and other building 
components. It could also involve modifications outside the shelter area as 
necessary to meet access, ventilation, emergency power, and other requirements. In 
addition, an internal shelter created through retrofitting must be structurally 
separate from the surrounding building so that damage to the surrounding building 
would not affect the shelter. Although retrofit shelter construction can be 
disruptive to building occupants, as well as more expensive than new construction, 
it may be the only option in some circumstances. 

Sources of Shelter Information

FEMA has prepared a series of case studies that document the construction of 
community wind shelters. The issues covered include shelter needs, funding 
mechanisms, shelter design and construction, multiple uses for shelter areas, and 
shelter performance in actual events.

Other sources of wind shelter information include the following publications:

Association Standard for the Design, Construction, and Performance of Storm 
Shelters, by the National Storm Shelter Association, Lubbock, TX, 2001.

Design and Construction Guidance for Community Shelters (FEMA 361), by FEMA, 
Washington, DC, July 2000.

Safe Room & Community Shelter Resource CD (FEMA 388-CD), by FEMA, Washington, DC, 
October 2001.

Taking Shelter From the Storm: Building a Safe Room Inside Your House (FEMA 320), 
by FEMA, Washington, DC, August 1999.

Tornado Protection - Selecting Safe Areas in Buildings (FEMA 431), Washington, DC, 
November 2003.

Copies of FEMA publications are available from the FEMA Publications Distribution 
Center at (800)480-2520.