FIRE AND EXPLOSION PROTECTION SYSTEM

A fire or explosion detection system is disclosed for reliably discriminating between a hydrocarbon fire in an armored vehicle and other sources of radiant energy including explosion of an armor-piercing ammunition round without an accompanying hydrocarbon fire. Radiation detectors sensitive to radiation at 4.4 microns and 0.9 microns, respectively, each produce logic outputs if the viewed radiation intensity exceeds a predetermined relatively low threshold and, in the case of the 4.4 micron detector, is rising at least a predetermined rate or, in the case of the 0.9 micron detector, is not falling at more than a predetermined rate. The logic outputs are fed to a coincidence gate which produces a fire- or explosion-indicating output only if all of the outputs are received concurrently for at least a predetermined period of time. A third radiation detector, in combination with the 0.9 micron detector, measures the color temperature of the radiation source being monitored, and inhibits the coincidence gate if the color temperature exceeds a predetermined value. Further discriminating capability is provided in the form of a medium threshold unit operable to produce an inhibit signal for a relatively short period of time if the output of the 0.9 micron detector exceeds a medium-level threshold.