turn can lead to a risk of autoignition of the propellant. Thus, storage risk increases with storage time. Although stabilizer depletion is known to occur in the case of M28 propellant, previous studies have estimated that the frequency of autoignition of propellant in intact M55 rockets and the overall storage risk are very low (U.S. Army, 2002).
The storage risk may be greater in the case of separated rocket motors than intact M55 rockets. The shipping and firing tube that contains the intact M55 rocket isolates the rocket motor from environmental conditions. During processing at BGCAPP, the shipping and firing tube is cut, and this exposes the separated rocket motor to environmental factors, such as humidity and heat, more than when it is part of an assembled M55 rocket. Humidity can accelerate chemical reactions with the nitrogen oxide gases formed from the degrading nitrate ester. The nitrogen oxide gases accelerate nitrocellulose decomposition and stabilizer depletion; this leads to a self-accelerating cycle. Heat also increases the stabilizer depletion rate in the M28 propellant by increasing the rate of nitrocellulose degradation. The storage of intact M55 rockets in their pallets and in overpacked configurations and their ability to dissipate excess heat from the propellant were studied in 2002. The study found no immediate risk of propellant autoignition in these configurations (U.S. Army, 2002). However, when the rocket motors are separated from the M55 rockets and placed in new packaging, they are in a new configuration, and prior safe-storage assessments may not be directly applicable. Thus, separated rocket motors may have a shorter safe-storage life than assembled M55 rockets.
Finding 4-5. Storage risk may increase more quickly in the case of separated rocket motors than assembled M55 rockets because of the increased environmental exposure of the separated motors. The effects of this environmental exposure on the separated rocket motors have not been characterized.
Recommendation 4-3. The Blue Grass Chemical Agent-Destruction Pilot Plant program staff should dispose of separated rocket motors as soon as possible, using a “first in, first out” protocol to minimize storage time and reduce risk.
U.S. Army. 2002. M55 Rocket Assessment Summary Report, July. Aberdeen Proving Ground, Md.: U.S. Army Program Manager for Chemical Demilitarization.
U.S. Army. 2011. Ammunition and Explosives Safety Standards, Department of the Army Pamphlet 385–64, May 24. Available online at http://armypubs.army.mil/epubs/pdf/p385_64.pdf. Last accessed May 17, 2012.