scope:

Description of Driving Event:

During the filling of a liquid hydrogen test apparatus mounted in an AJ-2 airplane low-g test facility, an explosion occurred followed by a fire. The cause of the mishap was determined to be a leak due to a loose "AN" fitting on a 1/2 inch vent line that was teed to the fill line of the research package. The ignition source was found to be hydrogen detectors mounted in the airplane near the test rig for safety considerations.

Proof of the ignition source was determined by bench testing the detectors. The test consisted of flowing mixtures of hydrogen and air through them to determine if the flame fronts generated by the catalyst would be stopped by the flame arrestors. At a hydrogen volume ratio of 5 percent, the detectors signaled a warning and the flame fronts were stopped by the screens. When the volume ratio was increased to 15 percent, the arrestors failed to confine the flame.