GM Wants 2,500 Trucks Idled Pending Probe : Safety: The auto maker’s advisory on the gas-powered vehicles comes in the wake of two tank explosions.

General Motors Corp. has advised the owners of 2,500 natural-gas-powered trucks, most of them sold to utility and municipal fleets in California and Texas, to take them off the road until the cause of two recent tank explosions can be determined.

The affected trucks are 1992 and 1993 GMC Sierra and Chevrolet three-quarter-ton pickups. The vehicles were fitted at the factory to run on compressed natural gas stored in three underbody aluminum tanks wrapped in fiberglass.

Southern California Gas Co., which uses 160 of the trucks, inspected its fleet for tank cracks after the first explosion Jan. 18, then took the trucks out of use shortly after the second incident Feb. 1.

GM mailed notices to other users in West Hollywood, Irvine, Long Beach and Thousand Oaks and in Santa Barbara and Ventura counties. It also notified customers at UCLA, Northrop Corp. and Rand Corp.

Though GM is not expected to announce the results of its investigation into the incident until next week, early indications are that some sort of acid--possibly from batteries being carried in the trucks--caused the fiberglass wrapping to fail.

“We have requested these owners take them out of service so there isn’t any potential for any other accidents,” a GM spokeswoman said.

The first rupture occurred as a tank was being filled at a Pacific Gas & Electric Co. fueling site in San Francisco. One worker was hospitalized with lacerations. The other, similar incident occurred in Minneapolis. In neither case did the gas ignite.

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The accidents come as cleaner-burning natural gas vehicles are entering the marketplace to help communities around the country reduce air pollution. Skeptics had predicted there would be difficulties handling the fuel in transportation.

“Anytime you’re dealing with . . . fuels, you’re talking about something that’s not totally benign,” said Mark B. Glick, chief executive of Global Environmental Industries Inc., an Austin, Tex.-based natural gas technology firm.

“But the relative factor of safety with natural gas vehicles is exponentially greater than with gasoline vehicles--there’s no doubt about that,” said Glick, who is working with a task force to increase use of alternative fuels in government and private fleets.

Glick noted that more than 30,000 natural gas vehicles are in operation and that finding a solution to the tank problem would probably be easy.

Ford Motor Co., which is building natural gas demonstration vehicles, uses a different tank supplier and has reported no comparable incidents.