Shelter from the Storm? FPL Debris Launcher

Throughout the United States, hundreds of tornadoes and several hurricanes affect people’s livelihoods each year. Nearly every state east of the Rocky Mountains faces the possibility of devastating tornadoes, with the Midwest being particularly at risk. Living along the gulf and east coasts offers little respite, as powerful hurricanes are apt to cause similar, and potentially more widespread, damage. The following maps show this sobering possibility. Check out those wind speeds!

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Map from FEMA P-320 showing the number of tornadoes in the United States from 1950–2006. (Click to enlarge in Flickr.)

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Design wind zones from FEMA P-320 based on ASCE 7-05 criteria. The zones mirror the locations of high intensity storms, with the addition of higher design requirements along the coasts due to hurricanes. (Click to enlarge in Flickr.)

These natural disasters not only cause structural damage to property, they also cause numerous injuries, and regret­tably, far too many deaths of people caught in their path. When the envelope of a structure is punctured by de­bris, pressure changes from the wind can cause the structure to rapidly fail. In many areas, buildings were not built with resistance to debris in mind. However, with the extensive media coverage of recent disasters such as the devastating tornadoes in Joplin, Missouri, and Moore, Oklahoma, as well as Hurricanes Katrina and Sandy, greater numbers of home and small business owners are seeking to increase their probability of surviving a storm by voluntarily installing a “safe room” to shelter in.

A safe room is defined by the Federal Emergency Manage­ment Agency (FEMA) as “a space where you, your family, or friends and employees can survive a tornado or hurricane with little to no injury.” Guidelines for safe room design are detailed in FEMA P-361, Design and Construction Guid­ance of Community Shelters, and FEMA P-320, Taking Shel­ter from the Storm: Building a Safe Room Inside Your Home.

Safe room design must meet two main criteria. The first is that the room’s structural components must be able to withstand the basic wind load of the tornado or hurricane. The second design criterion is that the safe room must have resistance to flying debris, a particular danger of tornadoes and hurricanes.

As part of their ongoing efforts to improve safe room design, James Bridwell, Robert Ross, Zhiyong Cai, and David Kretschmann conducted performance tests on a series of materials and wall designs that might be used in the construction of safe rooms. Next week we will delve into this unique research described by Bridwell and others in the publication, USDA Forest Products Laboratory’s Debris Launcher.