Photograph by Scott Olson, Getty Images

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Dean Dye looks over a storm shelter in a home destroyed by the May 20 tornado in Moore, Oklahoma.

Photograph by Scott Olson, Getty Images

Taking Cover: A Guide to Tornado Shelters

For homes in Tornado Alley, engineers are designing shelters to weather a storm.

Oklahoma's tornado safety guide recommends going into an enclosed basement or underground shelter if a tornado is imminent.

But many suburban homes built in so-called Tornado Alley don't have basements due to rocky soil conditions and high water tables, which often make building basements impossible. An interior room or closet—often recommended for those without basements—may not be effective when extreme winds or debris strike.

On Wednesday, the mayor of Moore, Oklahoma (map)—the hardest-hit town in this week's storm—announced that he was planning to propose an ordinance that would modify building codes and require all new homes built in the town to have either a reinforced storm shelter or safe room installed. The Federal Emergency Management Agency (FEMA) also encourages homeowners in tornado-prone regions to build safe rooms.

A storm shelter is a structure designed to protect people from tornado-strength winds and flying debris. There are several types.

Underground shelter: It's an updated version of what you might remember from the movie The Wizard of Oz. Underground storm shelters, made from reinforced steel or concrete, are prebuilt structures that are installed underground in a yard or underneath a garage. They're slightly different from a basement: Both the walls and ceilings are made from reinforced material. Underground storm shelters are resistant to extreme winds and debris, but might not be accessible during a storm (it might be dangerous to leave the house and go outside).

Part of the house: Depending on the water table in your neighborhood, it might not be possible to build an underground shelter where you live. An alternative is a structure that is placed inside a home while it's under construction. New homes can be outfitted with something that looks like a fortified bank safe. The structure is often made using reinforced concrete or wood and steel—and can double as a closet or storage room. It should be self-contained and anchored to a home's foundation to resist overturning or lifting up during windy conditions.

Prebuilt shelter: Homeowners can also purchase a prebuilt structure to install inside an existing home. (The best place is on the home's first floor.) Prebuilt shelters come in a range of styles: welded steel box, steel skeleton with steel panels, or a prefabricated unit that is then bolted together. They should also be anchored to a home's foundation.

FEMA estimates that the cost for a steel-reinforced 8-by-8-foot room is between $6,600 and $8,700. The agency has some rebate programs to offset these costs for homeowners.

Many local municipalities in Oklahoma have applied for federal rebate money to offset the costs of building shelters. In 2012, Oklahoma launched a program called SoonerSafe, which can give homeowners up to 75 percent of the cost of building a safe room—as much as $2,000. The money comes from the federal government and is dependent on unused FEMA funds. Last year, 16,000 people applied for the funds and 500 were awarded grants through a lottery.

Testing Storm Shelters

If you do build a home storm shelter, it's important to make sure the product has been tested and approved for use during tornadoes. Though FEMA issues guidelines for storm structures, the agency does not approve storm structures or the material used to construct them. Instead, most of the testing in the United States is conducted at the National Wind Institute at Texas Tech University in Lubbock.

There, researchers test shelter components and reinforced doors by hitting them with 15-pound two-by-fours through a "modified potato gun." The device mimics flying debris traveling at 100 miles per hour (160 kilometers per hour). In a different room, a tornado vortex simulation mimics wind speeds of up to 250 miles per hour (402 kilometers per hour). (Related: "How Does a Tornado Work?") "We enjoy blowing things up here," says Larry Tanner, a structural engineer and research associate at Texas Tech.

Tanner and team test aboveground shelters as well as doors created for belowground shelters. He suggests that homeowners put storm shelters in a hall closet or laundry room on the first floor of their homes. He also recommends installing a shelter in homes with partially aboveground basements, which are common in Texas and Oklahoma.

"Now you might say, 'Why would I need a shelter in my basement?'" he says. "If your basement is a walk-out basement [part of the basement is not underground], at least one wall is exposed. Also, you don't know what the strength of basement walls is—they may or may not be reinforced. And the ceilings too—when a house blows away, it will frequently take the basement ceiling along with it."

Tanner says it's better to build a safe room in a closet or interior area rather than designing a completely tornado-proof home.

"It's not cost-effective and it will be rather ugly," he says. "It's a glorified bomb shelter, and you would still have windows and doors and garage doors, and they would be extremely vulnerable."

On the other hand, a storm shelter can be made to look fairly normal, he says.

"I've been in numerous safe rooms in people's homes and you don't even know it's a safe room," he says. "You might notice the door is rather heavy and it has three locks on it, but other than that it looks like any other room."

Both FEMA and Texas Tech recommend outfitting a safe room with a flashlight, a first-aid kit, an emergency radio, batteries, basic tools, blankets, some water, and dry food. Homeowners in some locations, like Oklahoma City, can also register their storm shelter with first responders, who will then know to check the structures after a tornado.

Tanner—who is planning to install a storm shelter in his own home—says it's extremely important to have a plan for shelter in the event of a tornado warning.

"I've been doing this for 15 years and I've been through several," he says. "I think everybody needs to take notice that it's a true peril."