"There's not a whole lot you can do because of the way they are constructed," says McDonald, who also directs the Institute for Disaster Research. "It's a very lightweight structure with a large, exposed surface area ... that's built with very little margin for error."

Getting Stronger
Mobile home companies are making these buildings stronger, in response to a 1993 regulation. The federal government passed the regulation after seeing how mobile homes were damaged and destroyed by Hurricane Andrew in 1992.

The regulation strengthens building standards for mobile homes, so new models should be able to withstand 30 to 40 percent higher winds. McDonald says earlier homes were built to withstand barely 60 mph.

The standards will improve fastenings within the home, with particular emphasis on exterior corners where wind stresses are particularly severe.

Don't Fly Away!
Tornadoes are strong enough to pick up and entire mobile home. To prevent the home from flying away, many people anchor the homes to the ground by screwing steel rods into the ground.

"But there's a catch-22," he notes. "If the ground is soft enough for the anchor to penetrate, the soil is too soft to prevent it from pulling out. If the ground is stronger, the stake won't go in deeply enough."

McDonald,suggests going a step further and cementing the home down. He notes that, "95 percent of mobile homes are never moved after they are placed." Thus he advocates anchoring mobile homes to concrete foundations, an expensive measure that can be done to existing homes.

Would that make them safe?
The new building standards and anchoring ideas can't change some mobile -home facts. The basic drawbacks of lightweight construction and the lack of a basement remain.

Would McDonald feel comfortable riding out a tornado warning in a new-standard mobile home bolted to a concrete foundation? His answer: "No."

Final Challenge: Tornado Quiz!

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This lesson created by "The Why Files," a NISE project funded by the NSF. Lesson used by permission. Original lesson and graphics copyright NISE. Modifications copyright BPNM.
Photos courtesy James McDonald.