Patent GB-643188-A (GB)
Title: Improvements relating to means for the suppression of explosions and the prevention or extinction of fires
IPC: A62C99/00
Filed: 1948-02-05
Abstract: 643,188. Preventing fires and explosions. GLENDINNING, W. G., MACLENNAN, A. M., and GRAVINER MANUFACTURING CO., Ltd. Feb. 5,1948, No. 3394. [Class 47 (ii)] Fire or explosion detecting and suppressing apparatus comprises pressure responsive diaphragm means for detecting rise in pressure occurring in incipient fire or explosion, the diaphragm means being selected to be of a high order of sensitivity such as to respond to a small pressure rise when the rate of pressure rise is in excess of 50 lbs. per sq. inch per second and being capable of closing an electric contact within 0.02 second of the initiation of the pressure rise to release fire or explosion suppressing substance. Means for detecting a pressure rise in an aircraft fuel tank 11, Fig. 1, comprises a stack of thin metal sheet capsules 2 of the kind used in barometric apparatus, secured to a flanged stem 7 and mounted within a casing 8 which is secured within a hole formed in the tank wall. A plate 3 secured over the central aperture of the external capsule 2 carries insulated therefrom an electrical contact stud 4 from which a lead 30 extends to a terminal block 23 mounted on the outer portion of the casing 8. A contact screw 27 which passes through an insulating bush 28 is axially adjustable with respect to the contact 4 by means of nuts 29 and is connected to a terminal on the block 23, the arrangement being such that a rapid rise of pressure within the tank causes the stud 4 and the screw 27 to make contact. The space within the capsules communicates with the space within the tank by means of an orifice 21 in the flange of stem 7 whereby relatively slow changes of pressure are equalised. As shown in Fig. 1, the device is adapted to be submerged in the fuel, in which case a vent tube 22 hooded at 22c to prevent ingress of fuel during inverted flying or in a steep dive, projects above the normal fuel level. Explosive means for distributing within the tank combustion suppressing or fire preventing material is shown in Fig. 3 and comprises a casing 31 mounted in a hole in the top wall of the fuel tank and having secured thereto a frangible container portion 32. The casing 31 contains a filling orifice normally closed by a plug 34 provided with an explosive charge 36 having electrical ignition means 37 connected to a terminal block 40. An aircraft fuel tank may contain two pressure responsive units as shown in Fig. 1, one submerged in the fuel to respond to shock waves due to a crash or to the penetration of a bullet and the other secured above fuel level to respond to an explosion of fuel vapour. The pressure sensitive and explosivelyoperated means in the fuel tank are interconnected with known forms of fire extinguishing and preventing and crash equipment. The invention may also be applied to the suppression of explosions in coal mines and modified forms of the appliances shown in Figs. 1 and 3 are used, the explosion detecting devices being placed at possible danger points, the explosive means for scattering the explosion suppression substance across the roadways or galleries being positioned on either side of the detecting device. The explosion or combustion suppression or extinguishing material may comprise methyl bromide or other substances including stone dust. The invention may also be applied to processes such as cotton spinning and flour milling.