Abstract: Apparatus for predicting the cookoff characteristics of a confined explosive includes a cylindrical housing retained between an instrumentation plate and a witness plate. Small explosive samples contained in sample tubes are inserted within a heat conductive sleeve which is further disposed within the cylindrical housing. Electrical ring heaters are a source of heat the application of which eventually causes the confined explosive to react. Temperature measurements within the housing are obtained utilizing a thermocouple assembly which is inserted through the instrumentation plate and into a groove in the heat conductive sleeve. The degree of damage to the apparatus occasioned by the reaction of the heated explosive predicts the reaction of a full scale ordnance item containing that explosive to exposure to a fire.