How to Sense Impending Doom

New technologies such as wireless sensors help monitor bridges, but experts who can analyze the results are in short supply

Here's a scary thought: That man you spotted scrutinizing a bridge through binoculars may be a transportation inspector. Even now, in the wake of the Minneapolis disaster, this critical task relies on fallible human eyes.

There are better ways to do it. Companies such as Material Technologies and Physical Acoustics are commercializing wireless sensors an inspector can slap on a bridge to diagnose cracks and stresses long before they become dangerous.

With these artificial eyes and ears, inspectors can see cracks beneath paint or rust and listen to the groans of an ailing bridge, much as a physician puts a stethoscope to a patient's chest. Coaster-sized sensors can monitor vibration, temperature, and corrosion, and relay data to the appropriate Transportation Dept.

Los Angeles-based Material Technologies places sensors between metal sections of a bridge. The company then drives a heavy truck over that area while a computer monitors the emitted signals, watching for that one crack out of many thousands that could cause havoc. "In 10 minutes we get a readout that's equivalent to an electrocardiogram for your heart," says CEO Bob Bernstein. A system like this can test a typical 100-foot bridge for as little $8,000. Installing sensors on just a fraction of bridges classified by authorities as "deficient" could save hundreds of thousands of dollars—and avert a catastrophe.

Sensors from a number of startups are now used on bridges in over 20 states. Physical Acoustics, based in Princeton, N.J., offers a sound-based approach. For fees starting at about $35,000, it will install a sensor to listen to creaks from fissures or the popping of steel-cable fibers, sounds that could be heard months before any flaws are visible to the man with the binoculars.

Experts who can analyze such data are still in short supply. But their ranks are bound to grow, if only because traditional inspection techniques are so inadequate. In a 2001 study by the Federal Highway Administration, visual inspections correctly identified fatigue cracks only 4% of the time.

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