At least 24 people are dead after a powerful tornado tore through Moore, Okla., Monday. “Numerous neighborhoods were completely leveled,” Sgt. Gary Knight of the Oklahoma City Police Department told the New York Times. According to Moore resident Ricky Stover, the twister even tore open his locked cellar door. Is anywhere safe in such a powerful tornado?
Yes. While there are several recorded instances of powerful storms ripping open the doors to storm cellars and other shelters, no such instance has been documented with a shelter tested and approved by the National Wind Institute (NWI) at Texas Tech University. While other storm shelters may be old or poorly designed in the first place, the shelters approved by the NWI are designed to withstand winds up to 250 mph, which includes nearly all recorded tornadoes (including Monday’s) and most tornadoes rated as EF5s on the Enhanced Fujita scale. In the case of the EF5 tornado that touched down in Joplin, Mo., in 2011, the deadliest twister in decades, all 11 aboveground shelters in the area protected their occupants. In 1999, only one year after FEMA published its modern standards for in-residence shelters, an above-ground shelter survived the record-breaking F5 tornado around Oklahoma City, which also passed through Moore.
To test shelter designs, the NWI shoots them with 15-foot-long wooden 2-by-4s propelled at 100 miles per hour, approximating the force of debris in a tornado with 250 mph winds. Of course, larger and heavier objects, such as tin roofs and barns, could be found in such a tornado, but the heavier something is, the slower it travels, so it’s unlikely that they would hit with any more force than these 15-pound wooden missiles. Additionally, planks torn from houses are the predominant objects found in the debris fields of large tornadoes, making them the ideal objects for testing.
Though NWI also tests and approves some designs for stand-alone storm cellars, FEMA and the NWI suggest that shelters be installed as safe rooms inside of family residences. This is primarily because many people are killed or injured by flying debris while they’re en route to their outdoor shelters, especially if they have little warning or leave it to the last minute to make their way to the cellar. These in-residence safe rooms can be installed in homes for about $2,500, with $2,000 of that cost—at least in theory—being reimbursed by FEMA, whose guidelines for building a safe room are available online. Even if you already have a basement (though many Oklahoma houses do not have basements, because of soil conditions and other factors), many kinds of basements do not provide sufficient protection, and so the NWI suggests that you still build a safe room, possibly within the basement. Though many photos appear to show whole neighborhoods flattened by the storm, the NWI’s Larry Tanner suggests that if you don’t see any aboveground shelters standing, they were probably never there at all.
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Explainer thanks Larry Tanner of the National Wind Institute at Texas Tech University.
Read more of Slate’s coverage of the Oklahoma tornado.