The Army's chemical weapons incinerator 20 miles south of Tooele automatically shut down early Tuesday when workers mistakenly fed a bomb containing too much nerve agent into a waste metal furnace.

On Wednesday the $600 million facility was ready to go back to work burning the nerve and blister weapons stockpiled at Deseret Chemical Depot. But it remained inactive, awaiting approval by state officials to start up again.The metal parts furnace is designed to function at 1,600 degrees and the afterburner's nominal temperature is 2,000 degrees. The furnace is fueled by natural gas but nerve agent itself burns hotter than natural gas. Because the bomb contained more nerve agent than expected, the error caused temperatures in the afterburner to rise to about 2,200 degrees, triggering the shutdown.

Meanwhile, says Jon Pettebone, spokesman for the incinerator, all of the nerve agent in the furnace was burned harmlessly. Sensitive monitors on the smokestack showed there was no release to the environment, and workers inside the plant were not in danger, he said.

Workers were in the process of burning a 750-pound bomb, a type called an MC-1. As stored, the bomb has 220 pounds of GB nerve agent, 15 pounds of explosives and 520 pounds of steel. The first step in its destruction is to remove the explosives.

Next a hole is punched in the bomb and all but four pounds of agent is drained, to be destroyed in the plant's two liquid incinerators. Two methods check whether the proper amount of agent is removed: the probe that drains it has a device like a dipstick that tells how much is left, and the bomb is weighed.

The final step is that the bomb casing and the residual four pounds of agent are sent to the metal parts furnace to be burned, resulting in harmless slag.

"Apparently the probe was installed misaligned" in this incident, Pettebone said. The drain probe indicated that the proper amount of agent was drawn out when it wasn't. Meanwhile, the weight check showed that too much agent remained in the bomb.

Pettebone said workers then put the probe back in, got the same report, and concluded that the bomb was correctly drained.

"They went ahead and processed the bomb," he said. "Well, there was more agent in there than there was supposed to be. At that point all the safety features of the furnace took over."

When the temperature in the afterburner shot up, sensors detected the rise and shut off the natural gas and air flow. Still, the heat remained above the 1,200 degrees necessary to destroy all the nerve agent.

Other than the initial errors that triggered the incident, he said, "everything worked like it was supposed to."

The production line had been stopped so the bomb involved could undergo routine sampling. When that was finished and demilitarization resumed shortly before 3:30 a.m., the probe was aligned wrong.

How did it become misaligned? "That's still under investigation right now," said Mike Rowe, general manager for contractor EG&G Defense Materials Inc. Also, he said he preferred not to say how much nerve agent was left in the bomb until the investigation is finished.