Abstract

There is disclosed a fire and explosion detection system and method comprising at least one first channel including a photocell and accompanying electronics for converting incident radiant energy of a first narrow band of wavelengths into a first electric signal; and, at least one type of second channel means including a photocell and accompanying electronics for producing a second electrical signal proportional to incident radiant energy of a second narrow band of wavelengths corresponding to background, black body emissions. The signal outputs of these two channels are further processed by a ratio detection circuit which produces yet another output electrical signal when the ratio of the two input signals exceeds a predetermined number. The output of this ratio detection circuit is further processed by a so called flicker frequency detection circuit which counts pulses indicative of the flicker frequency of the fire and gives a first warning if that flicker frequency exceeds a predetermined number. Additional circuit means process the output of the ratio detection circuit to determine if that signal exceeds a predetermine magnitude to indicate the presence of an explosion or flash fire. An overload protection circuit is included to inhibit the alarm function of the invention in the situation where the detector is first exposed to sunlight, incandescent light, etc. having characteristic emissions in the band widths of the two photocells. Representative wavelengths for the two channels are described. In particular, the black body emission channel is set at 3.8 microns while the other channel is set at 4.3 microns.