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Shelter From the Storm
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Trend in tornado shelters and doors moves from private homes to public buildings
Tornadoes, hurricanes, typhoons and cyclones add new meaning to the term "gone with the wind," as they continue causing hundreds of millions of dollars in property damage and ending thousands of lives. Now, especially in areas where tornadoes are an ever-present danger, steps are being taken to save lives by building "safe rooms," originally in homes and more recently in schools and other public buildings. Built to withstand extreme wind loads and multiple impacts from flying debris, these shelters or 'Safe Rooms" are often the only thing left standing after the entire building structure around them is destroyed. Although the walls and roof are constructed of reinforced concrete and steel, the entrance doors to the Safe Room also must meet the daily needs of entry and exit, and also withstand potentially devastating storm damage. Major door manufacturers are now introducing products designed specifically to pass the rigorous tests needed to withstand these forces of nature.
 
The Trouble with Tornadoes
 
Wind loading shear in a tornado is a major cause of damage, but more complex combinations of forces are also generated. In addition to severe winds, extremely high positive and negative pressures can create forces strong enough to lift objects which then become wind blown missiles capable of being driven through walls.
 
All severe storms carry the danger of damaging winds, and tornadoes have perhaps the most potential for destruction due to their changing pressures and violent travel. Tornadoes can pick up and carry debris with enough force to penetrate windows, doors, walls and other parts of a building. Entire buildings can collapse in an instant. People require more than a simple shelter to survive.
 
Doing Something About It
 
The desire for personal safety has led some homeowners to add safe rooms in which they could take shelter from an approaching storm. Located either below grade in a basement or in the center of the house, these rooms typically have common features that include heavily reinforced concrete walls and ceilings but no windows. At first, standard metal doors and frames were used, but the need to withstand extreme forces, yet allow people to get out after the storm ended, called for something even stronger.
 
Larry Tanner, PE, R.A., a research associate with the Wind Engineering Research Center of Texas Tech University, says the University began studying wind loading and impact more than 31 years ago and published its first guidelines on above-ground shelters in 1974. Tanner explains that interest really increased after the 1997 tornado that struck Texas. In the area where that storm hit, the rocky soil precluded basement shelters, so the emphasis turned to aboveground survival.
 
The Federal Emergency Management Agency (FEMA) realized that a proactive approach would save lives and possibly reduce disaster claims as well. After sponsoring some additional research at the Texas Tech facility, FEMA released its first edition of Taking Shelter From the Storm: Building a Safe Room Inside Your House (FEMA 320), for residential shelters, which subsequently was updated with a second edition in August, 1999. After FEMA 320 had been out for about six months, an F5 tornado, the most severe category, hit Oklahoma City on May 3, 1999. Within the next year, FEMA 361 was issued by the agency, covering design and construction guidance for community shelters.
 
More People, Bigger Shelters
 
Larry Tanner notes that there is a significant difference in design pressure between a small, fairly tight residential shelter and a larger community-size shelter, since it is almost impossible to seal off the larger area. This leads to greater internal pressurization during a storm, which can increase the possibility of damage. According to Tanner, the pressure test for residential shelter doors is 1.35 pi, as opposed to 1.75 pi for commercial shelters. FEMA allows five sq. ft. per person, and anything with a capacity of above 12 people or 60 sq. ft. is considered a commercial shelter. Most community shelters, however, are much larger, including high school classrooms and even gymnasiums.
 
While no uniform codes have yet been established for resisting the complex combinations of forces found in a tornado, some localities that are under a higher threat of tornado damage have implemented various local codes or guidelines to ensure that key public buildings will provide adequate shelter from severe winds. These local codes or guidelines tend to be based heavily on the extensive tests performed by the Wind Engineering Research Center at Texas Tech University. In Wichita, Kansas, for example, recent educational levies include requirements for storm shelters. Omaha and Lincoln, Nebraska are among a number of cities considering mandating Safe Rooms in any construction of publicly funded buildings. These generally are rooms used for other purposes, such as storage rooms, restrooms or even gymnasiums. However, they are always internal areas that are built with reinforced walls and ceilings but without windows.
 
Doors Hold the Key
 
FEMA 320 emphasizes that one of the most vulnerable parts of a shelter is the door. Door and frame manufacturers are responding with products designed to withstand the extra demands of these applications. Among recent developments is a new door being introduced by Steelcraft, which the company has named the Paladin™ Severe Weather Door System. Working with the Wind Engineering Center, Steelcraft developed the door to meet the requirements of FEMA 361. In a flying debris test, the new door survived three impacts of a 15 lb. missile traveling perpendicular to the surface of the door at 100 mph. Features of the new Paladin door include special lock edge reinforcement and internal stiffeners that resist crushing and bending.
 
Hardware is an integral part of the tests, with the choice most often dictated by the design intent and building code regulations. In the case of public buildings, such factors as occupancy classification and egress path definitions must be considered to meet life safety requirements, including the NFPA 101 Life Safety Code and the NFPA 80 Standard for Fire Doors and Fire Windows.
 
Building code regulations have always addressed the fire and life safety issues with requirements for fire rated doors, frames, exit devices and variations such as alarmed and delayed egress options. The immerging Storm Shelter applications are further complicated by the need to prevent someone from opening the door during the storm while still allowing safe, easy egress in case of fire. In the end, this decision is still governed by fire and life safety codes, which require exit devices.
 
Unless definitive model code provisions are developed, locally mandated door specifications will continue to be a critical part of the success of any tornado shelter. By considering the FEMA 361 guidelines and the manufacturer's test results from a facility such as the Wind Engineering Research Center, it should be possible to ensure that the critical door portion of a shelter will perform as intended.