INSTITUTE, W.Va. (AP) - Union Carbide Corp. announced it is temporarily suspending production of aldicarb oxime, the poison gas involved in a chemical leak that injured 135 people, and acknowledged its computerized safety system never was programmed to track the chemical.

Meanwhile, a non-toxic chemical leaked Tuesday night at Carbide's South Charleston plant five miles away, driving some residents from their homes, Kanawha County Emergency Services p'ramedic Jerry Brown said. No health threat was reported, a Carbide spokesman said.

The tracking system erroneously told workers that Sunday's leak was contained over the Institute plant site. Carbide has blamed the tracking system for a 20-minute reporting delay that allowed a toxic chemical cloud to settle on nearby homes before warning sirens sounded.

"I am sure if we had used the system correctly, it would have worked better," Carbide spokesman Thad Epps said. "We substituted a chemical with close to the same components. We got reasonably good programming."

The production halt was announced as a delegation of top federal officials, including Environmental Protection Agency Administrator Lee Thomas, inspected the plant.

"After looking at the operation, I have a heightened sense of urgency," Thomas said after viewing the three gaskets that failed, sending a toxic cloud of aldicarb oxime over houses nearby.

The company has acknowledged in an internal report that aldicarb oxime is capable of causing cancer, infertility, and "irreversible" nerve damage.

But company officials said Tuesday that residents were exposed only to low levels of the gas during Sunday's leak and disputed reports that the chemical is as toxic as methyl isocyanate, the gas that killed 2,000 people last year at Bhopal , India. The Institute plant also is the only U.S. producer of MIC.

Union Carbide said it was halting the use of aldicarb oxime until officials know how the accident occurred.