PORTLAND -- Army attorneys argued Tuesday that more than four dozen construction workers who became ill while working at the Umatilla Chemical Depot have failed to prove that chemical weapons were the cause.

But attorneys for the workers said the Army has refused to take responsibility for the accident or to provide any other reasonable explanation for the symptoms the workers suffered on Sept. 15, 1999.

Tuesday was the final day of the second phase of the trial between the workers and the Army. The case now goes to U.S. District Court Judge Dennis Hubel for a ruling.

The workers are suing the Army for negligence, claiming they were exposed to the chemical agents stored at the depot, which is about 35 miles south of Kennewick.

They were building the incinerator plant that will be used to destroy the 3,717 tons of sarin, VX and blister agent stored at the depot.

In February, four months after the first phase of the trial concluded, Hubel ruled the Army was negligent in not providing immediate medical care for the workers.

Several of the workers have been unable to work since the accident and are receiving disability. Some have been diagnosed with reduced lung capacity, chemical sensitivity and post-traumatic stress disorder.

In this phase of the trial, plaintiffs' attorneys James McCandlish and Keith Dozier tried to prove the workers were exposed to a leak of sarin gas that day, and that the Army's negligence added to the workers' injuries.

McCandlish said the Army too quickly ruled out chemical agent as a possible cause of the accident, referring to an Army news release sent out just hours after the accident that stated chemical agents were not involved.

He said that release was sent out before any monitoring was done to check for chemical agents.

McCandlish added that the Army's failure to decontaminate the workers aggravated their conditions.

"Dr. (Drew) Brodkin said the clothing should have been removed, which would have eliminated 85 to 90 percent of the contamination, and it should have been performed in the field," McCandlish said.

But Henry Miller, a Department of Justice attorney representing the Army, said McCandlish had failed to prove his case.

"They bear the burden of coming forth with credible evidence to prove it was chemical agent and that the Army's alleged lack of medical response added to the injuries," Miller said.

Miller said Brodkin, an occupational and environmental health sciences professor at the University of Washington, erred when he testified that emergency medical technicians at the site didn't have the training to determine if chemical agent had caused the accident.

Miller said Matt Greenup, one of the injured workers, was immediately put on oxygen and EMTs kept looking at his eyes. "They were trained and were looking for the signs," he said.

Not one worker was documented as having miosis, a constriction of the pupils that is common in sarin exposure, Miller said.

Also, Miller said testimony by Dr. Leslie Hutchinson, an occupational and environmental medicine specialist who helped investigate the accident in the week afterward, indicated he did not find any signs of chemical agent either.

Although four separate investigations have been conducted of the accident by various state and federal agencies, none has pinpointed a cause for the accident.

But that's not the Army's problem, Miller said. "We don't have to come up with a cause," he said during his closing argument. "That's up to the plaintiff."

He also said the plaintiffs have not produced any evidence their illnesses are related to the incident.

McCandlish, however, said the Army has failed to accept Hubel's earlier ruling that it was negligent in medical response. "They refuse to take responsibility," he said.

It could take months for Hubel to rule on the case. If he rules in favor of the workers, a third phase likely will be added to the trial to determine damages.