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code watch
Take
Cover!
New storm shelter standard wil lhelp provide protection from violent winds.
by David Bowman, P.E.
After the 2004 hurricane season, one
of the most devastating in U.S. history, few people would question that
strong winds can have an enormous impact on people’s lives, property
and communities. For newer properties in Florida, stronger building codes
proved their value by reducing damages and lives lost.
When it comes to protecting the safety of people in mobile home parks and
older subdivisions, schools, hospitals and municipal facilities, storm shelters
also can play a critical role in saving lives. As people in the Midwest
have known for generations, when a tornado hits, storm shelters often mean
the difference between life and death.
To keep people safe from future storms, the International Code Council (ICC)
and the National Storm Shelter Association (NSSA) are partnering to develop
a new consensus standard for storm shelters. The new standard will include
requirements for the design and construction of shelters to protect people
from the violent winds of hurricanes and tornadoes.
THE ISSUES
To fully address the breadth of the standard, the ICC/NSSA Consensus Committee
on Storm Shelters is tackling two vastly different design problems. The
committee must assess the components that storm shelters need to withstand
hurricanes and those that shelters need to protect from tornadoes. If this
task is not challenge enough, the committee also needs to consider storm
shelter size—everything from small safe rooms in residences to large
community shelters.
There are several key factors to consider and incorporate into the new storm
shelter standard. Some are obvious, such as defining wind loads to be used
and the size and velocity of flying debris. Other concerns may not be as
apparent, such as appropriate fire safety and ventilation. Issues include:
• Wind loads. The committee will
base required wind loads for storm shelters on wind speed contour maps developed
specifically for the new standard. The wind load design requirements will
be severe.
Contour maps for wind speed were determined based on a 10,000 -year mean
return period. One map shows 200 mph wind speeds on the coast of Florida
and the Carolinas, and wind speeds higher than 200 mph in some locations.
(These are wind speeds associated with a Category 5 hurricane.)
Such high wind speeds produce flying debris and can turn construction materials
into deadly missiles. For the new standard, flying debris associated with
200 mph wind speeds will be specified as a two-by-four moving at 70 mph.
• Flooding. Of course, wind is
not the only danger associated with a hurricane. Hurricanes often produce
water surge that can be even more damaging to a community. The new standard
designates that storm shelters must be located outside the storm surge area
predicted for a Category 5 hurricane.
• Essential features. Storm shelters
for hurricanes will be required to house people for at least 24 hours. Therefore,
the new standard must stipulate minimum requirements for ventilation, sanitation,
potable water supply, lighting and other essential needs. In the case of
large community hurricane shelters, the following will be required:
• Mechanical ventilation (15 cfm per person), which will be
connected to the back-up power supply.
• Generator to supply back-up power.
• At least one toilet for every 50 occupants. (Can be portable.)
• Potable water at the rate of one gallon per occupant.
• Fire Safety. Hurricane shelters
need to be protected from fire. The new standard will require that all shelters
be equipped with fire extinguishers. In addition, where shelters are part
of a larger facility, such as a safe room in a school, the shelter space
or safe room will be required to have a two-hour fire barrier to separate
it from the remainder of the building.
One of the unique hazards in these kinds of facilities is unattended parts
of the building may contain equipment or materials that could ignite under
certain circumstances. The fire-rated barriers would provide the occupants
of the shelter some protection from such a fire.
• Accessibility. To ensure that
people with disabilities would be able to gain shelter, the entrances and
exits to storm shelters will be required to be accessible. The occupant
load requirements would also need to address space considerations for wheelchairs.
FOR MORE INFO
The development of the new ICC/NSSA storm shelter standard is well under
way. A first draft of the standard is expected in late 2005. For more information,
visit www.iccsafe.org, highlight Codes & Standards, select Standard
Development, and choose Storm Shelters.
The meeting minutes and agendas are posted regularly. The ICC/NSSA Consensus
Committee on Storm Shelters will meet next in conjunction with the ICC Symposium
on Hurricanes February 11 to 13, in Orlando, Fla.
David Bowman, P.E., is Manager of Codes at the
International Code Council.
The International Code Council, is a membership association dedicated to
building safety and fire prevention. It develops the codes used to construct
residential and commercial buildings, including homes and schools.
The National Storm Shelter Association (NSSA) is a non-profit organization
dedicated to developing performance standards, product certification, and
education programs for the design, construction, and performance of storm
shelters. |
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