Why storm shelters are the only tornado-proof buildings
No storm shelter? 'Wind clips' built into your home can give some additional protection from dangerous winds.
Wed, May 22, 2013 at 09:56 AM
How do you protect yourself from a tornado that reaches 2 miles wide with wind gusts above 200 miles per hour?
When the winds blow that hard, there's little you can do to save your house. But when it comes to protecting yourself and your family, the safest bet is to buy a storm shelter, according to engineering professor Larry Tanner of Texas Tech University's Wind Science and Engineering Research Center.
These structures are usually installed inside or nearby a home and made of reinforced concrete, or even of plywood and steel.
Some scientists are looking into structures built of carbon fiber, or underground "subscrapers," that could easily survive extreme weather disasters. But these constructs are still in the experimental stage and are used mostly at military bases and other high-security facilities.
The typical Midwestern family home depends on simpler architectural standbys. Since the 1980s, building codes in the American Midwest require that a house be able to withstand wind gusts up to 90 miles an hour. A standard stick frame house with wooden trusses and support rafters should be able to survive up to 100 miles per hour, if made properly. [Video: Storms that Spawned Deadly Oklahoma Tornadoes Seen from Space]
For additional strength, you can reinforce the joints and connections in your house with metal clips, called "wind clips" or "hurricane clips." These might raise your house's durability another 5 or 10 miles per hour.
But what's that to a tornado like the monstrosity that ripped through Moore, Okla., leveling whole city blocks and killing what's believed to be at least 24 people?
The use of wind clips would likely have narrowed the swath of destruction that the tornado cut into Oklahoma City's suburbs, but they wouldn't have saved the houses directly in the tornado's path, Tanner said.
The clips do nothing to address a house's key structural weakness: doors and windows. Contrary to popular belief, opening your window during a tornado or hurricane is not a good idea. The myth is that if a house's entrances are all sealed, the difference in barometric pressure within and outside of the house could damage it. But it's not the change in barometric pressure you have to worry about — it's wind pressure. If wind starts to blow into your house — either because you’ve opened a window or door or because a piece of debris smashed it open — the combined pressure from both sides can cause the walls to blow out and the roof to blow off.
The basement is relatively safer than the rest of the house, but the wind forces that blew off the roof could also blow off the first floor — in other words, the basement's ceiling — exposing anyone taking shelter down there to flying debris, Tanner said.
"TV news meteorologists say that the only [safe] place is below ground [in a tornado] … that is false, truly false," said Tanner.
The safest place to be in a tornado is in an above-ground storm shelter, said Tanner. These structures are usually made of reinforced concrete, but sometimes are made of plywood and steel. [See also: Futuristic Materials Could Build Tornado-Proof Homes]
At Texas Tech University and the National Storm Shelter Association, Tanner helps test and rate storm shelters. A full list of NSSA-approved engineering firms can be found on the organization's website.
The testing process involves using a wind cannon to blast 2-by-4-inch wooden planks at the shelters at up to 100 miles per hour.
The Federal Emergency Management Agency (FEMA) offers small subsidies for these shelters, which can be installed in a backyard or patio or even inside the residence as a sort of safe room.
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