L-125 Rocket Propellant Critical Diametre Issues

February 2006
Frédéric Peugeot (Warhead Technology)

The hazard classification of propellants and large rocket motors incorporating these propellants is an important safety consideration.

Following 1998 revised edition of the US Department of Defense (DOD) Ammunition and Explosives Hazard Classification Procedures Joint Technical Bulletin (TB 700-2) and proposals for alternative shock tests to the tests called out in the UN recommendations on the transport of Dangerous Goods, a lot of effort has been made (at least in the United States) to propose further alternative shock tests. Included in these alternative tests are the unconfined critical diameter test and gap testing at either 150% of the unconfined critical diameter (minimum 5 inches) or motor diameter in motor like confinement.

Following this last years emerging need to determine the critical diameter of high-energy solid propellant, the objective of this report is to review the key factors influencing the critical diameter of rocket propellants. Influencing parameters such as composition, binder, additives, casing/confinement, bore/perforation, L/D ratio are discussed. To conclude, a review of critical diameter testing methods and modelling is proposed.