During a routine mixing operation, a 1:1 mixture of titanium and pentaerythritol tetranitrate (PETN) powders accidentally ignited. This prompted an investigation into the cause of the accident. Friction, impact, thermal, and electrostatic stimuli, as well as incompatibility between the powders, were evaluated for their potential to serve as the ignition mechanism. Although a definitive determination of the mechanism was not made, the operation that is believed to have imparted the requisite energy to cause ignition has been identified. The results of these studies, as well as recommended changes to the mixing operations, are described. 16 refs., 2 figs.