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Publication numberUS2799781 A
Publication typeGrant
Publication dateJul 16, 1957
Filing dateJun 25, 1953
Priority dateJun 25, 1953
Also published asDE964307C
Publication numberUS 2799781 A, US 2799781A, US-A-2799781, US2799781 A, US2799781A
InventorsBradford T Joyce, Albert F Krueger
Original AssigneeElectronics Corp America
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Explosion detection and suppression
US 2799781 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

y 1957, B. 'r. JOYCE I ETAL' 2,79 ,7

EXPLOSION DETECTION AND SUPPRESSION Filed June 25, 1953 0.0. POWER SUPPLY +I5O VOLTS l6 EXPLOSION SUPPRESSOR PHOTOCONDUCTIVE {5 PHOTOCELL 42 EXPLOSION DIFFERENTIATING SUPPRESSOR CIRCUIT \35 FIG. 2

EXPLOSION SUPPRESSOR 2 FUEL & TANK g 49 p v, INVENTORS B.T..JOYCE 1 A..F.KRUEGER ATTORNEY United States Patent EXPLOSION DETECTION AND SUPPRESSION Bradford T. Joyce, Brookline, and Albert F. Krueger, Needham, Mass., assignors to Electronics Corporation of America, a corporation of Massachusetts Application June 25, 1953, Serial No. 364,142

3 Claims. (Cl. 250-214) This invention relates to apparatus to detect an incipient explosion and to suppress it before it has reached a dangerous energylcvel. More particularly, it relates to the detection and suppression of explosions occuring in mixtures of air with combustible vapors or gases, sprays, mists, dusts or the like, and with the prevention or extinction of fires resulting from such explosions.

As compared with the explosion of a substance which carries its own oxygen, an explosion of a mixture such as that of air and gasoline has the characteristic that the rate of development of presure is relatively slow; thus, for example, an explosion of a mixture of air and parafl'in spray may take 0.5 second to develop maximum pressure. a

Thus an explosion of a mixture of a combustible vapor with air begins with a relatively slow build-up of energy, with correspondingly slow rises of pressure, heat and radiation. This rise may be spread over several hundredths of a second before a critical energy level is reached and a dangerous explosive pressure is developed.

An explosion detector and suppressor system has been proposed in which the detector comprises a pressureresponsive diaphragm which detects the rise in pressure occuring in an incipient explosion. This detector is connected in an electric circuit including a contact adapted to be closed by the detector to release an explosion or fire suppressing substance. The detector is made to respond to a small pressure rise when the rate of pressure rise is in excess of 50 lbs. per sq. in. per second, and is capable of closing the contact within .02 second of the initiation of the pressure rise. The suppressor is capable of distributing the explosion or fire suppressing substance within .05 second of the initiation of the pressure rise. The suppressor comprises a frangible container for the explosion or fire suppressing substance. A rapidly-acting detonator, which acts in response to the closing of the detector contact, is arranged to burst the container and thus scatter the explosion or fire suppressing substance which it contains. This system is described in detail in British Patent No. 643,188, published September 15, 1950.

The principal object of this invention is to provide an explosion detector which, together with a suppressor of the kind described above, combines to make an improved explosion detector and suppressor system which is faster acting and more sensitive than prior-art devices.

The explosion detector of this invention is essentially a device which is sensitive to the rise of electromagnetic radiation which occurs in an incipient explosion. This electromagnetic radiation is a flash of light detectable by a photocell, the world light being used here in its wider sense which includes light visible and invisible to the human eye. The most suitable type of photocell for this application is a lead sulfide photoconductive cell such as those shown in U. S. Patents 2,448,516 and 2,636,100. It comprises a photocell, the output of which is connectedto an electronic valve through a diflerentiating network. This valve is normally nonconductive, and conductswhen the photocell detects a rise of radiation of thetype found in incipient explosions. Conduction of the valve actuates the explosion suppressor.

Other and incidental objects of the present invention' will be apparent to those skilled in the art from a reading of this specification and an inspection of the accompanying drawing,- in which: Figure 1 shows an embodiment of the present invention; Figure 2 shows another embodiment of the present invention; and Figure 3 shows schematically av fuel tank equipped with the explosion detector and suppressor of the present invention.

Referring to Figure 1, there is shown an explosion suppressor 3 comprising a relatively stiff backing plate 5 which includes a housing 7 for a detonator 9. The wall of the housing 7 is reduced in thickness at the working 'end of the detonator 9. A frangible cup 11, made of phenolic-impregnated fabric, is securely attached to the backing plate: 5 and forms a sealed cavity 13 in which The explosion detector comprises a photocell 15 which p,

is shown'as being of the photoconductive type. One terminal 16 of the photocell 15 is connected to a D. C. power supply 17, and the other terminal 18 of photocell 15 is connected to ground through a resistor 19. The potential at terminal 16 is positive, and its magnitude may be of the order of volts. Terminal 18 is connected through a differentiating circuit 21 and resistor 23 to the control grid 25 of an electronic valve 27 which is shown as an electron tube of the thyratron type. Differentiating circuit 21 comprises a capacitor 29 and a resistor 31, one terminal of which is connected to the junction of capacitor 29 and resistor 23, and the other terminal of which is connected to a source of biasing potential. This source of biasing potential is shown as a potentiometer 33 connected between a source of biasing potential 35 and ground. The anode 36 of valve 27 is connected to power supply 17 through resistor 37, and to ground through capacitor 39. The cathode 41 of valve 27 is connected to ground through the detonator 9 which includes a low electrical resistance.

The operation of the explosion detector of Figure 1 is as follows: the photocell 15 and resistor 19 form a potential divider connected between terminal 16 and ground. The potential at terminal 18 thus varies with the resistance of photocell 15 and, consequently, with the amount of radiant energy impinging upon photocell 15. A negative biasing voltage from potential source 35 is applied through resistors 31 and 23 to the control grid 25 of thyratron 27 which is thus normally held in a nonconductive state. Terminal 18 is coupled to the control grid 25 of thyratron 2'7 through differentiating circuit 21. The time constant of differentiating circuit 21 should be chosen so that it will pass a positive pulse of sufiicient magnitude to overcome the bias on thyratron 27 and fire it only when the rate of change of potential at terminal 18 corresponds to that which would be caused by an incipient explosion. A time constant of 10 milliseconds has been found satisfactory for the detection and suppression of explosions in a mixture of fuel with air. When the bias on thyratron 27 is overcome and it fires, capacitor 39, which was previously charged through resistor 37, discharges through thyratron 27 to ground, and this discharge fires detonator 9 The firing of detonator 9 bursts the cup 11, and the explosion or fire suppressing fluid which it contains is scattered, thus suppressing the explosion.

The explosion detector of Figure 2 differs from that of Figure 1 in that the anode of thyratron 27 is connected,

Patented July 16, 1957 3 through the high-voltage winding 42 of a transformer 43, to an alternating current power supply of the type customarily found in aircraft, The low-voltage winding 47 of transformer 43 is connected: to the detonator 9. The. advantage of this embodiment is that itavoids the use of the large electrolytic capacitor 39 of Figure 1. As in Figure 1, thyratron 2,7, is kept in a nonconductive state until the radiant energy from an incipient explosion impinges upon photocell 15. Thyratron 27 then conducts, and the'current through, winding 47 of transformer 43 fires the detonator 9', thus operating the'suppressor 3.

The photoconductive cell is preferably of the activated' lead sulfide type, 'which has good. sensitivity in the infrared portion of the frequency spectrum. The explosion or fire suppressing fluid may be methyl bromide, carbon tetrachloride or any other extinguishant. Water has been used successfully in. some tests; it acts mainly by.- cooling. Gasoline has also been used successfully; it can suppress an explosion by creating too rich a. mixture of fuel with air.

Figure 3 illustrates an aircraft fuel tank 49 equipped with an explosion detector shown schematically at 51 and with an explosion suppressor 3. The source of ignition of an explosion is shown at 53, and the flame front of the explosion is shown at 55'. The radiant energy from the incipient explosion travels with the speed of light and impinges upon the detector 51. Detector 51 actuates the suppressor 3 which scatters the explosion or fire sup pressing fluid as shown schematically by the broken lines of Figure 3.

We claim:

1. An explosion detector comprising: a radiation-sensitive circuit including a photoelectric cell, an electron tube having an anode, a cathode and a control electrode, biasing means to maintain said electron tube normally nonconductive, a capacitor connected between the anode of said electron tube and a point of reference potential, means adapted to charge said, capacitor, means to connect to the cathode of said electron tube explosion suppressor means responsive to the discharge of said capacitor through said electron tube, and means including a dilferentiatifig c1rcuit connected between said radiation-sensitive circuit and the control electrode of said electron tube.

2. An explosion detector comprising: a radiationsensitive circuit including a photoelectric cell, an electron tube having an anode, a cathode and a control electrode, biasing means to maintain said electron tube normally nonconductive, a source of alternating current, a transformer having two windings, means to connect a first winding of said transformer between the anode of said electron tube and said source, means to connect the cathode of said electron tube to a point of reference potential, means to connect to a second winding of said transformer explosion suppressor means responsive to the passage of current through said transformer and through said electron tube, and means including a differentiating circuit connected between said radiation-sensitive circuit and. the control electrode of said electron tube.

3.. An explosion detector and suppressor system comprising: a radiation-sensitive circuit including a photoconductive cell, an electronic valve having an input and an output, biasing means to maintain said electronic valve normally nonconduct-ive, detonator-actuated explosion suppressor means responsive to conduction through said valve, means to connect said explosion suppressor means to the output of said valve, and means including a differentiating circuit connected between said radiationsensitive circuit and the input of said valve.

References Cited in the file of this patent UNITED STATES PATENTS 1,453,091 Delbare Apr. 24, 1923 1,708,869 Buddecke Apr. 9, 1929 2,355,664 McMann Aug. 15, 1944 2,492,148 Herbold Dec. 27, 1949 2,570,280 Rotfman Oct. 9, 1951 2,668,289 Conrad et al Feb. 9, 1954

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1453091 *Jan 3, 1921Apr 24, 1923Delbare Hector EMeans for extinguishing fire
US1708869 *Aug 21, 1926Apr 9, 1929Hartmut BuddeckeFire extinguisher
US2355664 *Aug 16, 1940Aug 15, 1944Mcmann Ira HFire control apparatus
US2492148 *May 13, 1947Dec 27, 1949Lafayette M HughesAutomatic navigating instrument for craft guidance
US2570280 *Apr 26, 1951Oct 9, 1951Roffman EugeneAutomatic fire-detecting and extinguishing apparatus
US2668289 *Mar 10, 1951Feb 9, 1954Harry ConradStitch failure detector
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3064552 *Jan 8, 1960Nov 20, 1962American Mach & FoundryBlast actuated closures
US3213179 *Apr 17, 1963Oct 19, 1965Clauson Ralph AOrgan combination action
US3339624 *Jun 17, 1965Sep 5, 1967 Apparatus for cooling molds
US3428130 *Apr 5, 1966Feb 18, 1969Fenwal IncControl and indication system for explosion suppressors
US3515217 *Oct 23, 1967Jun 2, 1970Nat Mine Service CoMethod and apparatus for arresting an explosion in a mine
US3731743 *Oct 20, 1971May 8, 1973Us NavyFire control apparatus air pollution product abatement
US4359097 *Jun 2, 1980Nov 16, 1982Aktiebolaget BoforsSprinkler system
US5122628 *May 25, 1990Jun 16, 1992Fike CorporationSudden pressure rise detector
US6031462 *Nov 3, 1998Feb 29, 2000Fike CorporationRate of rise detector for use with explosion detection suppression equipment
Classifications
U.S. Classification250/214.00R, 169/61, 169/62, 250/215
International ClassificationG08B17/06, G08B17/12, A62C99/00
Cooperative ClassificationG08B17/06, G08B17/12, A62C99/009
European ClassificationG08B17/12, G08B17/06, A62C99/00F