Fire and explosion detection

A fire and explosion detection system for discriminating between radiation produced by a source of fire or explosion to be detected and radiation produced by a source of fire or explosion not to be detected, comprising

• first radiation detecting means responsive to the intensity of radiation in two relatively broad bands which are separated by a narrow band at which that detecting means is not responsive,
• second radiation detecting means responsive to the intensity of radiation in the said narrow band,
• means responsive to at least one of the detecting means for producing a first signal when at least one of the parameters comprising the intensity of the radiation received by one of the detecting means and the rate of rise of the radiation received by one of the detecting means exceeds a predetermined value,
• means responsive to the two detecting means to measure the ratio of the intensities of the radiation respectively received by them and to produce a second signal when the ratio indicates that the source of the radiation is a fire or explosion source to which the system is not to respond, and
• output means connected to receive the first and second signals and operative to produce a fire or explosion indicating output only when the first signal exists in the absence of the second signal.

A fire and explosion detection system for discriminating between radiation produced by a source of fire or explosion to be detected and radiation produced by a source of fire or explosion not to be detected, comprising

• a first radiation detector responsive to the intensity of radiation in a narrow wavelength band centered substantially at 4.4 microns,
• a second radiation detector responsive to the intensity of radiation in a broad wavelength band centered substantially at 4.4 microns,
• a threshold unit connected to receive the output of one of the detectors and operative to produce a threshold signal in response to the intensity of radiation received by that detector exceeding a predetermined threshold,
• a rate of rise unit connected to receive the output of one of the detectors and operative to produce a rate of rise signal in response to the rate of rise of the intensity of radiation received by that detector exceeding a predetermined value,
• a ratio unit connected to receive the output of both detectors and operative to produce an inhibit signal in response to the intensity of radiation received by the first radiation detector being less than that received by the second radiation detector, and
• a coincidence gate connected to receive the threshold signal and the rate of rise signal and responsive to the inhibit signal to produce a fire or explosion indicating output only when the threshold signal and the rate of rise signal exist together in the absence of the inhibit signal.

A method of discriminating between radiation produced by a source of fire or explosion to be detected and radiation produced by a source of fire or explosion not to be detected, comprising the steps of detecting the intensity of radiation in two different wavelength bands to produce respective electrical outputs,

• one said band being relatively broad and the other being relatively narrow and the said broad band including the said narrow band,
• producing a first signal when at least one of the two parameters comprising the intensity of the radiation received in at least one of the wavelength bands and the rate of rise of the intensity of the radiation received in at least one of the wavelength bands exceeds a predetermined value,
• measuring the ratio of the intensities of the radiation respectively received in the two wavelength bands to produce a second signal when the ratio indicates that the source of the radiation is a fire or explosion source to which the system is not to respond, and
• receiving the first and second signals and enabling the production of a fire or explosion indicating output only when the first signal exists in the absence of the second signal.