GB1189297A - Fire Detecting Apparatus - Google Patents

Abstract

1,189,297. Fire detection. NATIONAL RESEARCH DEVELOPMENT CORP. Jan. 12, 1968 [Nov. 24, 1966], No. 52659/66. Heading G1A. In fire detection apparatus, a beam of electromagnetic radiation is directed through the space to be protected towards a detector, the movement of hot gases due to the fire causing refraction of the beam either toward or away from the detector. If the beam is normally (i.e. in the absence of fire) incident on the detector, movement of the beam away from detector, due to refraction, is sensed, to actuate an audible or visible alarm and/or fire control means. Alternatively, in the absence of fire the beam may not be incident on the detector, but refraction of the beam causes illumination of the latter and alarm or control actuation. The source of radiation, which may be a laser, may be located in line with the detector, e.g. a photo-cell, positioned on the opposite side of the space to be protected. A number of such systems can be used to protect a large space. A more economical arrangement utilizes a number of mirrors reflecting the laser beam along a zig-zag path towards the detector. In an arrangement in which the light of the beam is not normally, in the absence of fire, incident on the detector, the beam is of annular cross-section and surrounds the detector. The arrangement in which the detector is normally illuminated provides fail-safe operation. Movement of the hot gases may cause wavering of the beam.