PORTLAND -- A federal judge ruled Thursday that the Army was not responsible for injuries suffered by 49 construction workers who believe they were exposed to a chemical weapons leak at the Umatilla Chemical Depot in 1999.

In his 41-page ruling, Judge Dennis Hubel said the workers had failed during a two-week June trial to prove the Army caused or exacerbated their injuries.

In February, after the first phase of the trial concluded, Hubel had issued an opinion that said the Army had been negligent by not providing the workers prompt medical care at the time of the accident. The workers were helping build a massive incinerator that is being used to destroy part of the depot's stockpile of 3,717 tons of chemical weapons.

James McCandlish, the Portland-based attorney representing the depot workers, said he will appeal Thursday's ruling.

"The court earlier ruled the Army had utterly failed in its duty to provide emergency medical treatment to victims of this mass toxic exposure," he said. "However, according to today's disappointing decision, that failure didn't cause the already serious injuries to be worse. We respectfully believe the court is wrong and will appeal the ruling."

The workers simultaneously became ill while working on the project Sept. 15, 1999. Many began having problems breathing and vomited. Some had to be carried out of the building by other workers.

The workers, who believe they were exposed to sarin gas, sued the Army and Raytheon, the Army's contractor. Last year, Raytheon settled out of court with the workers.

The Army has denied that chemical weapons caused the workers' injuries.

"From the very beginning we knew the chemical warfare agents stored at the depot did not cause that incident," said Mary Binder, the Army's depot spokeswoman. "The judge's decision reinforces what we have stated from the beginning."

John Tucker, one of the injured workers, said he was stunned by the news. He was in the courtroom for both phases of the trial, each of which lasted two weeks.

"It's shocking ... devastating," Tucker said. "After sitting through the trial, I can't imagine how he came to this conclusion."

Hubel wrote in his decision that there was no evidence the workers had been exposed to mustard agent and none of the injured workers showed signs of miosis, one of the earliest symptoms of sarin exposure.

"I conclude the plaintiffs were exposed to an unknown respiratory irritant and that it was an inhalation exposure," Hubel wrote.

Although Hubel had earlier ruled the Army was negligent by not providing immediate medical response for the workers, his ruling Thursday stated the negligence had little effect on the workers.

"Exposure to a respiratory irritant calls for evacuation into fresh air, and in some cases, the administration of oxygen," Hubel wrote.

He said all the affected workers were evacuated immediately and "the few individuals who needed additional treatment, in the form of oxygen, received it at the first aid trailer."

"The great majority of the workers transported to the hospital were evaluated and released," Hubel wrote. "There is no indication that had they been taken to the hospital sooner, the outcome would have been different."