FEMA 320- Taking Shelter From the Storm

Section I: 
Understanding the 
Hazard


Almost every state in the United States has been affected by extreme windstorms such 
as tornadoes and hurricanes. Virtually every state has been affected by a 
"considerable" tornado (see the terms in Table I.1). All Atlantic and Gulf of Mexico 
coastal areas in the United States - including coastal areas of Puerto Rico and the U.S. 
Virgin Islands - and coastal areas of Hawaii have been affected by hurricanes. Even in 
states not normally considered to be susceptible to extreme windstorms, there are areas 
that experience dangerous high winds. These areas are typically near mountain ranges, 
and include the PaciÞc Northwest coast.


What Is a Tornado?

Tornadoes are categorized by the Fujita scale (see Table I.1). They typically occur in 
the spring and summer months, but can occur at any time in any part of the country. 
Tornadoes are sometimes spawned by hurricanes. 



Category / Typical Damage

F0 Light: Chimneys are damaged, tree branches are broken, shallow-rooted trees are 
toppled.


F1 Moderate: Roof surfaces are peeled off, windows are broken, some tree trunks are 
snapped, unanchored mobile homes are overturned, attached garages may be 
destroyed.

F2 Considerable: Roof structures are damaged, mobile homes are destroyed, debris 
becomes airborne (missiles are generated), large trees are snapped or uprooted.

F3 Severe: Roofs and some walls are torn from structures, some small buildings are 
destroyed, non-reinforced masonry buildings are destroyed, most trees in forest are 
uprooted.

F4 Devastating: Well-constructed houses are destroyed, some structures are lifted from 
foundations and blown some distance, cars are blown some distance, large debris 
becomes airborne.

F5 Incredible: Strong frame houses are lifted from foundations, reinforced concrete 
structures are damaged, automobile-sized missiles become airborne, trees are 
completely debarked.

Not all parts of each state are at equal risk from tornadoes. For example, while Texas 
has the highest number of recorded tornadoes, the state's least tornado-prone 
area-along the Gulf Coast-has been hit by fewer tornadoes than northeastern 
Arkansas. Comparing the numbers of tornadoes recorded in different areas within a 
state can give you a better understanding of the potential tornado activity in those areas. 

Figure I.1 shows the summary of recorded F3, F4, and F5 tornadoes per 3,700 square 
miles in the United States and its possessions and territories.



What Is a Hurricane?

Hurricanes are categorized by the SafÞr-Simpson scale (see Table I.2).

Category / Typical Damage

C1 Minimal: Damage is done primarily to shrubbery and trees, unanchored mobile 
homes are damaged, some signs are damaged, no real damage is done to structures.

C2  Moderate: Some trees are toppled, some roof coverings are damaged, major 
damage is done to mobile homes.

C3  Extensive: Large trees are toppled, some structural damage is done to roofs, 
mobile homes are destroyed, structural damage is done to small homes and utility 
buildings.

C4  Extreme: Extensive damage is done to roofs, windows, and doors; roof systems on 
small buildings completely fail; some curtain walls fail.

C5  Catastrophic: Roof damage is considerable and widespread, window and door 
damage is severe, there are extensive glass failures, some complete buildings fail.


In the United States, 158 hurricanes were recorded to have made landfall between 
1900 and 1996. Hurricanes have made landfall in Florida more than in any other state. 
The second most hurricane-affected state is Texas, but every state on the Gulf Coast 
and bordering the Atlantic Ocean, as well as U.S. island possessions and territories, are 
susceptible to damage caused by hurricanes.
In recent years, the U.S. territories of American Samoa and Guam have been seriously 
affected by numerous tropical cyclones.



Do You Need a Shelter?

On the basis of 40 years of tornado history and more than 100 years of hurricane 
history, the United States has been divided into four zones that geographically reßect 
the number and strength of extreme windstorms. Figure I.2 shows these four zones. 
Zone IV has experienced the most and the strongest tornado activity. Zone III has 
experienced signiÞcant tornado activity and includes coastal areas that are susceptible 
to hurricanes. 

To learn more about the wind history for the area where you live, check with your local 
building ofÞcial, meteorologist, emergency management ofÞcial, or television weather 
reporter.

Your house is probably built in accordance with local building codes that consider the 
effects of minimum, "code-approved" design winds in your area. Building codes 
require that buildings be able to withstand a "design" wind event. A tornado or extreme 
hurricane can cause winds much greater than those on which local code requirements 
are based. Having a house built to "code" does not mean that your house can withstand 
wind from any event, no matter how extreme. The shelter designs in this booklet 
provide a place to seek safe shelter during these extreme wind events.
The worksheet on pages 7 and 8 will help you determine your level of risk from these 
extreme events and will assist you in your consideration of a shelter. If you decide that 
you need a shelter, Section II will help you and your builder/contractor plan your 
shelter.



DEFINITION
In this guide, the term missiles 
refers to debris and other objects picked up by the wind and moved with enough force 
to damage and even penetrate windows, doors, walls, and other parts of a building. In 
general, the stronger the wind, the larger and heavier the missiles it can carry and the 
greater the risk of severe damage. But even small stones, branches, and other lighter 
missiles can easily break glass doors and windows.



WARNING

A shelter designed to protect you and your family from a hurricane should not be built 
in an area expected to be ßooded during a hurricane. Residents of these hazardous 
coastal areas should abide by the warnings of their local emergency services personnel 
and evacuate to safer ground. The protection from wind provided by safe rooms and 
shelters is quickly negated when stranded homeowners Þnd themselves trapped by 
ßoodwaters. 
If you do not know whether your house is in a storm surge area or other area subject to 
ßooding, check the community service section of your local phone book for storm 
surge evacuation information or ask your local emergency management or ßoodplain 
management ofÞcial.


DEFINITION
In this guide, the term storm surge refers to the rise in the level of the ocean that results 
from the effects of wind and the drop in atmospheric pressure associated with 
hurricanes and other storms.




Homeowner's Worksheet: Assessing Your Risk

To complete the worksheet on the back of this page, refer to the tornado and wind zone 
maps on pages 3 and 6 (Figures I.1 and I.2). Using the map on page 3, note how many 
tornadoes were recorded per 3,700 square miles for the area where you live. Find the 
row on the worksheet that matches that number. Next, look at the map on page 6 and 
note the wind zone (I, II, III, or IV) in which you live. Find the matching column on the 
worksheet. Finally, Þnd the box inside the worksheet that lines up with both the number 
of tornadoes per 3,700 square miles in your area and your wind zone. The color of that 
box tells you the level of your risk from extreme winds and helps you decide whether to 
build a shelter.

For example, if you live in Jackson, Mississippi, you would see that Jackson is in an 
area shaded medium orange on the map on page 3. So according to the map key, the 
number of tornadoes per 3,700 square miles in the Jackson area is 11 - 15.




On the map on page 6, Jackson appears within the red-shaded area. The map key 
tells you that Jackson is in Wind Zone IV.
The box where the 11-15  row and the Zone IV column meet is shaded dark blue, 
which shows that you live in an area of high risk. A shelter is the preferred method of 
wind protection in high-risk areas. Note that some areas of low or 
moderate risk, shown as pale 
blue or medium blue in the 
worksheet, are within the region of 
the United States that is subject to 
hurricanes (see Figure I.2). If you 
live in this hurricane-susceptible 
region, your risk is considered 
high, even if the worksheet 
indicates only a moderate or 
low risk




Emergency Planning and Emergency Supply Kit

Whether or not you decide that you need a shelter in your house, you can take two 
important steps to protect yourself and your family during a hurricane or tornado: 
prepare an emergency plan and put an emergency supply kit together. If you decide to 
build a shelter, your emergency plan should include notifying local emergency 
managers and family members or others outside the immediate area that you have a 
shelter. This will allow emergency personnel to quickly free you if the exit from your 
shelter becomes blocked by debris. You should also prepare an emergency supply kit 
and either keep it in your shelter or be ready to bring it with you if you need to evacuate 
your house. Some of the items that the emergency supply kit should include are:

¥ an adequate supply of water for each person in your household

¥ non-perishable foods that do not have to be prepared or cooked 
(if these include canned goods, remember to bring a can opener)

¥ a Þrst-aid kit, including necessary prescription medicines

¥ tools and supplies:

- ßashlight (do not bring candles or anything that lights with a ßame)
- battery-operated radio  
- cellular phone or CB radio
- extra batteries   
- wrench (to turn off household gas and water)
- clothing and bedding
¥ special items:
- for babies- formula, diapers, bottles, powdered milk
- for adults- contact lenses and supplies, extra glasses

You can get more information about emergency planning from American Red Cross 
(ARC) and FEMA publications, which you can obtain free of charge by calling FEMA 
at 1-800-480-2520, or by writing to FEMA, P.O. Box 2012, Jessup, MD 20794-2012. 

These publications include the following:

Emergency Preparedness Checklist, FEMA L-154 (ARC 4471)

Food and Water in an Emergency, FEMA L-164 (ARC 5055)

Your Family Disaster Supplies Kit, FEMA L-189 (ARC 4463)

Preparing for Emergencies, A Checklist for People with Mobility Problems, FEMA L-
154 (ARC 4497)


These publications are also available on the World Wide Web at the FEMA web site -  
http://www.fema.gov - and at the American Red Cross web site - 
http://www.redcross.org


The Department of Homeland Security (DHS), has developed the READY.gov web 
site. You can Þnd emergency planning and preparation guidance for all types of 
potential hazards. To obtain a copy of Preparing Makes Sense. Get Ready Now, go to 
http://www.Ready.gov