Beads of nitroglycerin "sweating" from rocket propellant are the most likely cause for a series of fires at Umatilla Chemical Depot's incinerator, the U.S. Army Chemical Materials Agency says.
A months-long investigation into 21 fires at Umatilla and other chemical weapons incinerators found no definite cause. The Army started investigating after fires hit the incinerator near Hermiston last year as rockets were cut up for incineration. No one was hurt, but incineration work at the plant was stopped for weeks.
Scientists tested nine rockets from Umatilla and found nitroglycerin-rich
liquid beads on the surface of each rocket's propellant cylinder. Similar
liquid was found on six of nine rockets tested from a depot in Pine Bluff,
Ark.
The propellant is about 24 percent nitroglycerin, which seems to move over time to the surface, where it is trapped by an "inhibitor" layer and the rocket casing. Scientists don't think any more of the explosive liquid will sweat out over time.
Investigators said the fires probably hit at random, when a metal blade happens to strike an explosive droplet. Before the remaining M55 rockets are destroyed, they predict about 15 more fires, with three or four likely at Umatilla.
Investigators suggested limiting future fires by spraying more water onto the chopping blade that cuts rockets and upgrading systems to detect explosions and quench fires. All three incinerators processing the rockets have already made those changes, the Army said. The full reports are online at www.cma.army.mil.
-- Andy Dworkin