Workers at Umatilla Chemical Depot on Sunday incinerated the last sarin-armed projectile stored at the Army site, leaving Oregon almost free of the deadly nerve poison.

Sarin was one of three chemical war agents stored at the depot near Hermiston, along with another nerve agent, VX, and mustard gas.

But sarin is much more apt to turn into vapor than the oily VX and mustard gas, so the sarin weapons were more dangerous and destroyed first.

Processing all the sarin removes more than 90 percent of the risk to the public, depot spokesman Bruce Henrickson said.

"Risk still remains," Henrickson said, but mostly for workers inside the plant. "The VX, a few drops of that on you will kill you in a couple minutes."

After a changeover period that should last about four months, he said, workers should start destroying the site's 62,000-plus VX weapons, which hold nearly 365 tons of that nerve agent.

Workers incinerated the last sarin shell, a 155-millimeter artillery projectile, at 7:56 a.m. Sunday. Sarin drained from that shell was burned Sunday evening, Henrickson said.

In all, workers have destroyed more than 155,000 munitions and 1,000 tons of sarin since the incinerator debuted on Sept. 8, 2004.

The work isn't known to have caused any serious injuries. But it did fall well behind schedule because of several human errors and more than a dozen cases of munitions catching fire in the reinforced processing rooms.

The Army has said it could take until 2017 to finish all the work at the depot, though Henrickson said depot officials hope to finish destroying all the chemical weapons between 2010 and 2012. That could be disrupted by a recent legal ruling that requires the state Department of Environmental Quality to reassess whether incineration is the best way to destroy the chemicals there.

Small amounts of sarin remain in carbon filters and in vials used to calibrate chemical sensors, said Rich Duval, administrator of DEQ's Chemical Demilitarization Program. The carbon will be the last thing burned at the plant.

The vials hold sarin levels "low enough that the CDC says we can drink these things . . . Not that I'm going to try it," Duval said.

The destruction of the last sarin follows some unhappy news that hit the facility in recent weeks. The DEQ fined the incinerator's operator, Washington Group International, almost $285,000 last month for "repeated violations at the facility involving improper operation and monitoring of incineration equipment."

Duval said the fine was unusually large and the penalty strongly worded to send a message. "I believe they got the message," he said.

The depot is also coping with the sudden death of a 39-year-old guard who collapsed and died Friday afternoon. The man was not in the processing area, and there's no sign now that a chemical agent influenced his death, Henrickson said. The depot is awaiting an autopsy for the cause of death.