Blocked pipes have been blamed for smoke that filled a small area of an incinerator plant at the Umatilla Chemical Depot in Hermiston Wednesday.
The depot is disposing of deadly VX nerve agent left over from the Cold War. It burned its stockpile of sarin nerve gas, even more deadly, earlier.
Depot spokesman Bruce Henrickson said the smoke was in the furnace room of Incinerator No. 1 after some strainers became plugged, leading to an overheating in the pipe system. He said no chemical agent was released.
Henrickson said negative air pressure is used in toxic areas, which pulls any released agent back into the facility.
He said all three incinerators were shut down until Army officials could complete an analysis but that all plant protective systems worked as intended.
The depot currently is destroying 155mm artillery shells containing the agent and expects to be done destroying all of its VX by early next year.
Then the depot will convert to destroying more than 4 million pounds of mustard gas, a blistering agent.
At one time the depot contained an estimated 12 percent of the nation's stockpile of chemical weapons.
Depots in Indiana, Arkansas, Alabama and Utah also are destroying the chemical weapons under terms of an international treaty.
Incineration began at Umatilla in 2004 and is expected to take several years.