On Wednesday, the two workers were in a staging area where casks are stored and moved prior to incineration, Mahall said. Early signs are that the mustard agent got on the worker's clothes in liquid form, subsequently triggering detectors in the airlock.

"It sounds like we're dealing with some sort of liquid splash that came from somewhere, and we've got to find it before we move forward," Mahallsaid.

The workers were wearing less intensive protective clothing, including gas masks, gloves, boots and cotton coveralls. Their clothing was removed, and they were decontaminated. Until the source of the agent is discovered, workers will wear the highest level of protection throughout the incineration facility, Mahall said.

The depot will investigate the source of the gas in the airlock and run blood tests to determine whether the worker was exposed. Depot officials said there was no danger to the public or the environment.

Umatilla began incinerating mustard gas last June. It stopped in October after Oregon environmental regulators proposed a $111,000 penalty for the contractor incinerating mustard gas at the depot, citing eight instances of excess carbon monoxide releases and hazardous waste violations.

Incineration resumed in January after the depot lowered its processing rates and made other changes to satisfy Oregon's Department of Environmental Quality.

In January, the depot reported that it had surpassed 6 million work hours-- nearly 3 1/2 years -- without a lost-time accident.

Under an international treaty, the United States has until 2012 to destroy all its chemical weapon stockpiles. The site's roughly 1,200 workers have already destroyed about 41 percent of the Umatilla depot's 3,700tons of chemical agents, including sarin and VX gasses.
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