On the evening of May 3, 1999, tornadoes tore through parts of Oklahoma and Kansas, leveling entire neighborhoods and killing 49 people. On May 10, 1999, the Federal Emergency Management Agency (FEMA) deployed a Building Performance Assessment Team (BPAT) to assess the damage caused by the tornadoes. The BPAT?s investigation made it clear that a severe wind event can cause a large loss of life or a large number of injuries in high-occupancy buildings and in residential neighborhoods where people do not have access to shelters (FEMA 342 Midwest Tornadoes of May 3, 1999).
Studies have been done since the early 1970s to determine design parameters for shelters intended to provide protection from tornadoes. FEMA, in association with Texas Tech University, in 1998 published guidelines for small, in-residence safe rooms in homes (FEMA 320: Taking Shelter from the Storm: Building a Safe Room Inside Your House). Based upon the observations of the damage from the May 3, 1999, tornadoes, FEMA developed guidelines for larger facility and community shelters (FEMA 361: Design and Construction Guidance for Community Shelters). FEMA 361 provides performance guidelines for the design and construction of community shelters, methods to evaluate potential shelters in existing facilities, and benefit/cost analyses (including a CD-ROM with the B/C Model software).
Evaluating Existing Areas to Be Used as Shelters
Observations in the BPAT?s investigations of the May 3, 1999, tornadoes showed extensive damage to areas in facilities that were designated as tornado refuge areas. This included many refuge areas in schools. It was observed that many walls of hallways, which were designated refuge areas, collapsed onto where the children would have been if the tornadoes had occurred during school. It also noted that many areas that were the safest in these facilities were overlooked by the owners as places of refuge. Many items not recognized as potential hazards during tornadoes were shown to cause excessive damage. These items included non-tied down equipment or propane tanks, adjacent light poles and telephone poles, gravel from gravel-ballested roofs, and other small items that became missile-like projectiles.
Based upon these observations, FEMA analyzed the observations and developed checklist criteria for ranking safe refuge areas. The objective of the checklists is twofold:
- To identify structural and non-structural vulnerabilities to tornado events.
- To rank a group of facilities to determine which have the least structural resistance to high wind forces and are in greatest need of retrofitting.
Using this method, several areas of the facility are determined to be possible safe areas. By analyzing each of the potential safe areas, this analysis will help the owner to determine:
- If the safest parts of the facility are being used for the tornado shelter (or locate one if there isn?t already a designated shelter).
- Adequacy of the strength, safety and size of the shelter.
- Possible ways to make the shelter areas safer.
- Whether it is advisable to design and build a new shelter per the guidelines in FEMA 361.
Site Assessment Checklists (From FEMA 361)
The checklists are designed to walk the user through a step-by-step process and should be filled out in sequence. This process is a rapid visual screening and does not involve any destructive testing or detailed engineering calculations. A large portion of the checklists can be filled out using data obtained from design or construction plans. It is important to verify th...