PORTLAND, Ore. — A review seeking the reason for fires in nerve-gas rockets being cut up for incineration in Oregon and Arkansas found no definite root cause, Department of Energy researchers said in a report.

The report, by Sandia National Laboratories, said wear on blades used to cut the rockets or contamination may have been a factor.

Fires broke out at the U.S. Army’s Umatilla Weapons Depot near Hermiston on April 7, April 23 and May 18 as M55 rockets containing the sarin GB nerve agent were being cut up for incineration.

The Pine Bluff Arsenal in Arkansas had similar fires May 11 and May 22.

Incineration was halted at Umatilla but resumed on June 9 after a review by the Oregon Department of Environmental Quality concluded it was safe to continue. Processing and incineration also has resumed in Arkansas.

Umatilla depot spokesman Mary Binder said the three fires that burned there involved propellant manufactured in October of 1962, and that rockets being burned now have propellants of different batches.

She said nine rocket motors with propellants from three batches have been shipped to the Picatinny Arsenal, the Army weapons research and development facility in New Jersey, but that results are not back.

In each case the fire started as blades cutting up the weapons into eight pieces sliced into the propellant section.

The New Mexico-based Sandia report said wear and pitting on one blade was visible, although it had been used in the destruction of fewer than 1,000 rockets, far fewer than the 2,500-rocket expectation.

It also said variations in the stability of the propellant because of contamination or manufacturing variations may have played a role.

Wear and pitting of the blades could have facilitated the retention of contaminants, the report said.

It said the blades are inspected after every 800 rockets.

The fires in reinforced unmanned rooms caused no injuries and little damage. Binder said the rooms are designed to withstand such fires, and that others may occur.

Crews at Umatilla have added more spray nozzles to cool the rocket-chopping blade and extinguish flames.

The depot contains about 12 percent of the nation’s supply of chemical rockets, bombs, mines and artillery shells and began the burning late last year to comply with treaty obligations.

The M55 rockets contain about 10 pounds of sarin each. A half a milligram is considered fatal, and the chemical is 500 times more poisonous than cyanide.

So far the depot has destroyed about 18,000 of the 91,000 sarin GB rockets stored there.

This story was published Thursday, June 23, 2005.