Hundreds of Joplin homeowners, many of whom survived the 2011 tornado, have made purchasing or building a storm shelter a priority.

But how do homeowners know their shelters will stand up to the kind of storm that rolled down on Joplin that Sunday afternoon — a storm that was strong enough to suck asphalt out of parking lots, shoot lumber through curbs and toss cars onto the roofs of buildings?

The fact is, states don’t regulate the storm shelter industry, said Karen Olsen, a member of the board of directors of the National Storm Shelter Association. Neither does the federal government.

Even if they did, many shelters are custom built on site by contractors as homes go up, and those can’t be taken to a lab and tested.

“There is no oversight in terms of what will keep you and your family safe, so it’s important that people take time to research and educate themselves on what they’re getting,” said Olsen, who also is president and owner of Missouri Storm Shelters, a 10-year-old company based in Nixa. They sell above-ground and in-ground concrete and steel shelters nationwide. They also have a Joplin office.

“It’s very important for people to know about testing, to know the difference in products,” Olsen added.

A 150 mph two-by-four

In order to become certified by the National Storm Shelter Association, a company must put its shelters through testing at the Institute for Disaster Research and the Wind Engineering Research Center at Texas Tech University in Lubbock. In one test, a pneumatic cannon fires a 15-pound two-by-four at the shelter at 150 miles per hour.

Engineers also calculate — based on the size and shape of the shelter — how each would hold together in the winds produced by an EF-5 tornado.

Olsen’s company took its storm shelters to Texas for tests.

So did Neosho-based Twister Safe, owned by Enos Davis, who also has been selling his steel shelters in the Joplin area.

But builders who do on-site, custom shelter construction at a business, home or in the community have no means of doing such missile or wind tests because the rooms can’t be transported, noted John Snider, an engineering manager for Anderson Engineering in Joplin.

Those builders must instead rely on reports from Texas Tech that outline how specific building materials perform in laboratory conditions that simulate tornadoes, Snider said. Those results are contained in FEMA publications and reports by Texas Tech — reports with such titles as “Construction Materials Threshold Testing Report,” and “Debris Impact Testing Report.”

A FEMA review of safe rooms concluded that for on-site builders, concrete is one of the most preferred construction materials. Criteria for an 8-foot-by-8-foot custom-built safe room is wall thickness of six inches minimum, with No. 4 rebar every 12 inches.

Russel Gehrke is building his shelters on site for Joplin families as part of a project named EF Joplin. Snider is helping Gerhke ensure that the shelters meet specs outlined by FEMA and Texas Tech.

Three of the materials used in Gehrke’s safe rooms — concrete, rebar and steel — have been tested.

But Gehrke’s shelters also include T-shaped blocks built of a solid plastic composite for which a patent is pending. The thick plastic blocks are stacked and bound together with a rebar frame. The frame is backed by plywood. Concrete up to 10 inches thick then is poured over the rebar and between the plastic and the plywood.

A steel door and roof are bolted on.

The plastic blocks form the building’s exterior veneer.

“They are the shelter’s ‘bulletproof vest’,” said Gehrke.

Because the blocks are a new product, they have not yet been tested at Texas Tech.

But with a state technical assistance grant he received last year for the shelters, Gehrke hired Anderson Engineering of Joplin to inspect the shelters he already has built and to complete third-party verification of the shelter’s reliability and his use of FEMA-approved building materials and plans.

“Basically he’s following everything, he’s just using his own manufactured blocks,” said Snider.

He also confirmed that the materials Gehrke uses conform to and exceed FEMA guidelines for on-site shelter construction.

“Russ is using the standard set of plans from FEMA, and as long as you follow them they are approved for any shelter,” Snider said. “He’s using the right reinforcing steel, the right concrete, and all of those materials have been tested.”

Although not required, Snider said Anderson also conducted a breaking point test for the composite blocks Gehrke is using in his shelters.

For those tests, Anderson loaded cylinders of the composite block material into a concrete breaking machine. A hydraulic piston on one end squeezed the block, applying pressure that determines when the material breaks apart.

“We were amazed, because his material actually bends at a point when concrete usually breaks,” Snider said. That point usually is about 1,800 pounds per square inch.

“Amazingly, it had strength that was similar to concrete blocks. It was very close,” Snider said.

Gehrke wants to do his own missile test next, he said, and to that end is building a permanent feature on acreage owned by Cycle Connection, south of Joplin. It will enable users to feed in two-by-fours and shoot them as projectiles at a wall using his design and materials.

“He wants to do it right. When he does that, we’ll verify to make sure it’s the right two-by-four, the right length, the right weight, and there will be some kind of time-lapse photography or something to trigger and record a start and stopping point so we can calculate the velocity,” Snider said.