(193a) Fire and Explosion in An Explosives Conditioning Bunker

An explosion occurred in a munitions bunker that conditioned an explosive at an elevated temperature completely destroying the bunker and damaging nearby bunkers. The explosive was used in the production of missile fuel. Early on, investigators believed that the explosion occurred either due to contamination in the explosives or a fire in the bunker initiated by the heating system. Further investigation determined that the failure of the bunker's heating system initiated a fire that caused the explosives in the bunker to detonate. Information gathered during the investigation revealed that an improperly installed damper partially obstructed the flow of heated air to the bunker. The air heating system was not equipped with over-temperature protection, allowing extremely hot air to enter near the combustible plywood ceiling of the bunker. A 1/4-scale model of the explosives bunker was constructed to evaluate the thermal air stratification process that occurs inside the bunker when the airflow is deficient. Test results indicated that during low flow rate conditions, hot air entering the bunker stratifies, allowing the wood ceiling to be heated sufficiently to ignite before a thermostat at an elevation of approximately four feet would turn off the heater. Burn damage to combustible materials and witness statements also confirm that a fire occurred in the bunker before the explosives detonated. The construction of the incident and adjacent bunkers prevented a chain reaction of explosions in adjacent bunkers.

This incident highlights the fact that careful design and installation is necessary for even relatively standard systems such as HVAC units when handling reactive materials. In this presentation the importance of proper safety interlocks in heating system controls will be discussed. The role of standards in preventing and mitigating incidents of this nature will also be discussed.