HERMISTON -- Oregon state officials ordered the Umatilla Chemical Depot incinerator to shut down destruction of chemical weapon rockets after a third incident in which a sarin-filled rocket caught fire Wednesday morning.

The first fire could be seen as an unusual occurrence and the second still could have been an anomaly, "but now with the third one, it begins to look like a pattern," said Dennis Murphey, administrator of the Oregon Department of Environmental Quality's chemical demilitarization program.

The move means the massive incineration facility will need state approval before resuming rocket destruction, Murphey said.

As with the other fires, Wednesday's accident happened in one of two containment rooms, which are designed to withstand explosions, said depot spokeswoman Mary Binder.

No sarin vapor escaped from the room, and the fire was extinguished after a few seconds, she said.

After the first two incidents, the incinerator, which is 35 miles south of the Tri-Cities, also stopped processing rockets. But those stops were made voluntarily by Washington Group International, which runs the plant, Murphey said.

Investigations of the two prior fires failed to identify the cause.

Wednesday's order gives DEQ, which oversees the depot's permits, a greater role in the investigation this time, Murphey said, adding that he did not know when rocket destruction might restart.

The fire happened at about 11:30 a.m., said Adam Russell, spokesman for Washington Group International. As in the two prior incidents on April 7 and 25, a fire started in the M55 GB sarin rockets' motor section as a shearing machine was making the fifth of eight cuts chopping up the rocket.

The depot also had another fire in mid-November, but investigators determined it was caused by a failure in the system that cools the shearing machine blades.

The stop order only affects rocket destruction, Murphey said. Russell said the incinerator still was processing liquid chemical agent drained from rockets and spent decontamination solution.

Binder credited modifications made to the containment room's fire control system for Wednesday's fire lasting only seconds. The previous two fires lasted several minutes.

Also, only one rocket was in the room during the fire, Binder said. In the last two cases, a second rocket was in the room at another station. Since the April 25 fire, the facility has been processing rockets one at a time as an additional precaution, Binder said.

Murphey said the Army has been investigating whether the fires could be caused by aging propellant in the rocket motors. Because the fires may be related to aging of the weapons, he said he hopes rocket processing can be restarted soon.

Umatilla is not the only site to have experienced a rocket fire. The incinerator at Anniston, Ala., had a similar fire Nov. 13, 2003. The investigation never determined the cause.

And on May 11, the incinerator at Pine Bluffs Arsenal in Arkansas also had a rocket fire. The Army's Chemical Materials Agency did not tell the public about that incident until Monday.

After the Umatilla depot's first fire April 7, official notice wasn't sent out for a week -- after the media learned of the incident through unofficial sources. There also was a delay of several days in announcing an incident last week at Umatilla in which sarin vapor escaped into a corridor -- potentially exposing two unprotected workers.

However, after the second rocket fire April 25, the Army quickly notified the media, and there was little delay Wednesday, when the Army issued a notice by early afternoon.

Emergency managers in Umatilla and Morrow counties said they were quickly notified of Wednesday's fire. Getting the information promptly was important, they said.

"If we don't know what is going on, we can't make a decision," said Meg Capps, Umatilla County emergency manager.

Oregon Chemical Stockpile Emergency Preparedness Program Director Chris Brown said he expected the fires will be discussed during tonight's Oregon Chemical Demilitarization Citizens Advisory Commission meeting. Binder said depot managers will tell the panel what they are doing about the fires.

The meeting, which is open to the public, will be at 7 p.m. at Good Shepherd Community Health Care Center, 610 N.W. 11th St., Hermiston.