Building a Safe Room: Do You Need a Shelter?
FEMA 320, Second
edition - 7.7 MB
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 reflect 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 significant 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 official, meteorologist, emergency management official, 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 Flooded 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 find themselves trapped by Floodwaters.
If you do not know whether your house is in a storm surge area or other area
subject to Flooding, check the community service section of your local phone
book for storm surge evacuation information or ask your local emergency
management or Floodplain management official.
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.