America's only chemical weapons incinerator got permission to restart on Friday and promptly resumed its work.

The Army's $1 billion incinerator near Stockton, Tooele County, had been shut down since an incident the night of May 8 and 9, in which a minute amount of GB nerve agent escaped from the plant's stack. The release was so tiny that it posed no risk to area residents, workers or the environment, according to investigating agencies.

"We've given the approval to go ahead and use the two liquid incinerator units and the metal parts furnace," Dennis R. Downs, director of the Utah Division of Solid and Hazardous Waste, said Friday.

Those units were not involved in the May incident, which occurred in the deactivation furnace, he said. The deactivation furnace is to be restarted later, Downs added.

Michael J. Rowe, the plant's general manager, said the state's approval came about 4:30 p.m. Friday. The plant was running shortly afterward.

However, the deactivation furnace should remain out of service for several weeks, Rowe said.

"We're finishing some engineering modifications for the unit, and when those are complete and we get those approved by the state . . . we'll restart that unit."

Modifications to the deactivation furnace include:

Changes to the flue gas system so the furnace does not have such a high gas flow that it can trigger another incident.

Improvements to the feed gates to minimize the possibility of debris causing a jamb.

"There are a host of changes," Rowe added. "Those are the big ones."

The engineering changes plus improvements in controls and training will prevent the recurrence of a similar problem, he believes.

However, Jason Groenewold, director of the anti-incineration group Families Against Incinerator Risk, Salt Lake City, was critical about the restart.

A report by incinerator contractor EG&G Defense Materials Inc. identifies 57 incidents from March through the releases on the night of May 8-9, he said. However, when he looked at reports operators turned in to state officials, "the most that we found would be 25, give or take a couple."

That leaves "a huge gap" in information, Groenewold added.

He said a report by the Army says that on April 30, the plant had a fire in its cyclone enclosure and that plant officials worried filter banks might also catch on fire. The filters are "just loaded with agent," he said.

"If that had caught on fire, you're talking about a serious event that could be catastrophic," Groenewold said.

Rowe disputed Groenewold's account. He said an incident happened on that date in which "we had smoke and overheating in that room," but not a fire. Asked if the filters could have caught on fire, he replied, "Absolutely not."