US2912054A - Protection of storage tanks for explosive liquids - Google Patents

Description

Nov. 10, 1959 A. MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE LIQUIDS Filed Oct. 21, 1957 4 Sheets-Sheet 1 ATTQRNEYS Nov. 10, 1959 A. MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE; LIQUIDS Filed Oct. 21, 1957 4 Sheets-Sheet 2 BY I NV ENTOR ATTQRNEW Nov. 10, 1959 Filed Oct. 21, 1957 VA. MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE LIQUIDS 4 Sheets-Sheet 3 J2 'a -2o l l ,/2/ --22 -22 I 22 I 2/\ 2la 2/ l L. 5; My 3/ HLJ/ Q FIG. 4. |-r

Nov. 10, 1959 A MATHISEN 2,912,054

PROTECTION OF STORAGE TANKS FOR EXPLOSIVE LIQUIDS Filed Oct. 21, 1957 4 Sheets-Sheet 4 United ates atentO PROTECTION OF STORAGE TANKS FOR EXPLOSIVE LIQUIDS Anders Mathisen, Alverstoke, England, assignor of onehalf to Graviner Manufacturing Company Limited, and one-half to Wilkinson Sword Limited, both of London, England, both British companies Application October 21, 1957, Serial N0. 691,452

Claims priority, application Great Britain October 22, 1956 2 Claims. (Cl. 169-4) This invention relates to fire and explosion protection systems.

The invention is particularly applicable to the proter tion of vessels in which hydrocarbon liquid fuels such as petroleum and other aviation fuels are stored.

Fires and explosions in static petroleum storage tanks are not infrequent. They may also occur in tankers used for transporting liquid hydrocarbon fuels by road and in fuel bowsers used to carry fuel to aircraft for refuelling. With the latter, apart from normal peaceful hazards, it may be desirable to provide protection against fires or explosions resulting from enemy action.

One of the problems in protecting fuel storage tanks against fires and explosion is that the level of liquid in a tank will vary from time to time in dependence upon the amount of liquid withdrawn from the tank. Thus, the means used for distributing fire or explosion suppressant must function satisfactorily quite independently of the level of the liquid. Heretofore, this problem has been tackled, as far as fire protection is concerned, in many ways. The most usual solution has been to provide a source of fire extinguishing material which can float upon the liquid and thus rise and fall with the level of the liquid in the tank.

The present invention has for its object to provide a novel solution to this problem, which is effective in suppressing explosions in storage tanks, whilst such explosions are still at the incipient stage, and may also be effective in extinguishing fires in the tanks.

The present invention achieves this by providing one or more elongated columns containing explosion suppressant material which is or are mounted vertically to extend at least between the maximum and minimum levels for liquid in the tank, each column containing at least one electrically ignitable explosive charge ignition of which can be effected by explosion detection means upon the onset of an incipient explosion in the tank.

Each column may consist of a plurality of individually operable portions or containers positioned end-torend. In such cases, it may be arranged that only those portions or containers which are above the surface of the liquid are operated in the event of an explosion. This may be achieved by providing liquid-level operated switches mounted at appropriate levels in the tank and arranging to render non-operable those parts of a column which are submerged or partly submerged.

The invention will be better understood from a consideration of the following description of two systems for the protection of fuel storage vessels, the first designed for the protection of static fuel tanks and the second designed for the protection of bowsers or tankers, each system being described as an example only of possible systems in accordance with the invention.

The systems are illustrated in the accompanying diagrammatic drawings, in which:

Figure 1 is a sectional side elevation of a static fuel tank protected in accordance with the first system, and

Figure 2 is a sectional plan view of the tank of Figure 1, whilst Figures 3A and 3B show alternative electric circuits for the inter-connection of the components of the first system;

Figure 4 is a sectional side elevation of a mobile fuel bowser or tanker protected in accordance with the second system, whilst Figure 5 is a sectional view taken along the line VV in Figure 4, and

Figure 6 is a detail sectional view of an alternative form of suppressant distributor.

Referring now to Figures 1 and 2 these show a static fuel tank 10 provided with two incipient-explosion detection means 11 situated on the inside of the roof above the maximum fuel level. The detection means 11 may take the form of pressure-rate-of-rise detectors of the kind described in United States Patent No. 2,693,240 and illustrated in Figures 1 and 2 or 10 and 11, or the modified constructions shown in Figures 1 to 3 of United States Patent No. 2,768,261. On the other hand, where conditions are such that a greater rise in pressure is permissible before suppression occurs, it may be possible to use a simple pressure switch. Alternatively, in order to detect the illumination radiated by a potential ignition source or the incipient explosion flame itself the detection means 11 may be of photoelectric form as described in the specification of United States patent application Serial No. 421,302, filed April 6, 1954, now Patent No. 2,869,647, dated January 20, 1959.

For distributing the fire or explosion suppressant material elongated frangible suppressant containers 12 are provided. These containers are of the general form described and illustrated in United States Patent No. 2,787,330, and a number of such containers 12 are mounted end-to-end in a plurality of columns which are positioned vertically to extend between the base and roof of the tank 10. As is explained in United States Patent No. 2,787,330 when the explosive charge in a container 12 is ignited, the suppressant material therein is distributed radially outwards in all directions. Thus, by arranging the vertical columns of containers 12 at suitable spacings it can be ensured that the whole volume of the tank above the liquid is filled with suppressant material with suificient rapidity and in a sufiicient concentration to effect I suppression of an explosion before it has passed the incipient stage, or extinguish a fire if the vapour-air mixture is not of explosive concentration.

It will be understood that the detection means 11 are electrically connected via a source of electrical power 13 suitably positioned outside the tank, to the igniters of the explosive charges in the containers 12, so that when the detection means 11 are operated by the occurrence of a fire or explosion they complete a firing circuit for the igniters. A suitable power supply apparatus 13 for use with detection means of the kind in which a pair of electrical contacts are closed, is described and illustrated in United States Patent No. 2,782,402.

With such an arrangement it may be undesirable to explode those containers which are located below the fuel level, in view of the risk of the resultant hydraulic shock damaging the walls of the tank 10. In such a case, in accordance with the invention, level switches 14 of known form are provided in order to cut out those suppressant containers 12 which are submerged, and possibly those containers which are partly submerged. These level switches 14 have a float 14a supported by a pivotable arm 14b. When the level of the fuel rises above a particular switch the float 14a rises and pivots the arm 14b which is arranged to close a pair of electrical contacts in a sealed housing 14c. The closing of these contacts short-circuits the igniters of the explosive charges of the submerged or partially submerged containers. In this way, all containers beneath the liquid are rendered non-operative and only those located above the fuel are operated in the event of a fire or explosion. Instead of being float operated, the disconnecting switches may have the form of a bellows or diaphragm which is moved to close the contacts when it is submerged.

Figure 3A shows a circuit diagram which makes it clear how the explosive charge of a container 12 is only supplied with current from the power source 13 in the event of closure of one or both of the detector contacts 11, if the contacts of the level switch 14 at the corresponding level are also open because the fuel is below that level.

Alternatively, the circuit of Figure 3B may be employed in which case the level switches 14 are arranged to open the pair of contacts of a switch when the float rises, the contacts thereby open-circuiting the corresponding igniters of the explosive charges.

The second system shown in Figures 4 to 6 is 'designe for the protection of mobile fuel bowsers or tankers. In this case, two incipient explosion detectors 20 are mounted on opposite ends of the tank 21. Where pressure-rate-ofrise detectors of the kind referred to in connection with Figures 1 and 2 are used, the contacts of these are connected in series so that both must be operated in order to effect distribution of suppressant. In this way, movement of the fuel to one end of the container, due to its inertia when stopping or starting, will not cause inadvertent operation because only one or the other of the detectors is likely to respond to such fuel movements.

Due tothe fact that the depth of such a tank is usually much less than that of a static tank, the suppressors 22 may'in this case be'of sufiicient length for only one to be used in each of the three compartments defined by the two apertured bafiles 21a which are provided to limit movement of the fuel in the tank. The construction of the suppressors 22 may be similar tothat described in United States patent specification No. 2,787,330, but an alternative construction illustrated in Figure 6' will now be described. In this construction the suppressor consists of a glass envelope 22a, and the explosive charge 23 is of known cord form and is supported in a glass tube 24 extending along the axis of the envelope 22a. Firing of the charge 23 is initiated by an electrically-fireddetonatorlS the leads 25a of which are connected to the terminals of aterminal box 26. The envelope 22a is held against a mounting plate 27 by a clamp 28 secured to the mounting plate 26 by three bolts 29 (only one of which can be seen in this figure). The plate 27 is in turn secured across an aperture in the upper surface of the tank 21 by bolts 30. Supports 31 are provided for the lower end of each sup-v pressor 22.

The suppressors 22 are electrically connected to the detectors 20 to a power supply 32.

What I claim is: r 1. In combination, a plurality of elongated frangible liquid containers fitted in a closed storage tank for exploliquid operated electric switches which is located at a level corresponding to that of the container in which the respective igniting means is mounted.

2. In combination, at least one column of frangible elongated liquid containers mounted vertically in a closed storage tank for explosive liquids, said column consisting of a number of individual containers joined end-to-end and each containing an explosion suppressant material and an explosive charge, said explosive charge having electrical igniting means whereby upon ignition of said explosive charge the container is burst and the material therein is dispersed explosion detection means responsive to an explosion whilst it is still in the incipient state, said detection means having circuit closure means which is closed upon response of said detection means to an incipient explosion, a source of electric current, and a number of liquid-level electric switches each mounted at a different level in said tank, said level switches being equal in number to the number of individual containers and each having contacts which are opened when the liquid in the tank is at a predetermined level relative to the switch, and electrical conductors for coupling each igniting means in a separate circuit with said circuit closure means and said current source and with that one of said level switches Whose contacts will be opened when the container in which that igniting means is mounted is at least partly submerged in the liquid stored in the tank.

' References Cited in the file of this patent UNITED STATES PATENTS

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