Investigators trying to determine what caused fires at chemical weapons disposal facilities in Oregon and Pine Bluff in April and May are focusing on a chemical in the rockets and have taken steps to prevent similar accidents, officials said this week.

Tests conducted on nine disassembled M55 rocket motor assemblies at the Picatinny Arsenal in New Jersey confirmed that nitroglycerin had seeped through a protective coating into the space between the motor and the steel tube housing, according to a news release for the U.S. Army Chemical Materials Agency.

Nitroglycerin is extremely volatile and likely caused the fires during the rocket disposal process.

The agency is investigating three fires at the Umatilla Chemical Agent Disposal Facility in April and two in May at the Pine Bluff Chemical Agent Disposal Facility at the Pine Bluff Arsenal. The fires occurred during the disposal of M55 rockets. No one was injured in any of the incidents.

The preliminary report issued this week focuses on rocket motor assemblies from the Oregon facility. A final report is expected in mid-August, said Gregory Mahall, an agency spokesman.

Testing on nine rocket motor assemblies from the Pine Bluff facility is expected to start by late this month at the New Jersey arsenal. A preliminary report is expected around mid-September, Mahall said.

Fires during the disposal of rockets are common, Mahall said, but five fires in two months "kind of made us sit up and take notice."

Processing was stopped at both facilities after the fires.

The amount of water used during disposal has been increased to reduce the likelihood of fires, Mahall said.

Last week, the Umatilla facility resumed disposing of M55 rockets, Mahall said, and there have not been any more fires there.

The Pine Bluff facility is expected to resume destroying M55 rockets next week, spokesman Raini Wright said. A small flame and smoke were spotted early Sunday in the explosives containment room of the incinerator. The incident, which is still being investigated, slowed the process of resuming disposal of the rockets, she said. Maintenance was being performed on the area at the time and no disposal was taking place.

"We probably would have started earlier," said Wright, adding that disposal could have resumed earlier this week.

This story was published Saturday, July 23, 2005.