US 3687329 A
To reduce the fire risk when flammable liquids are stored in bulk, the surface of the liquid is completely occupied by closely packed hollow buoyant spheres formed of moulded plastics. Preferably a sufficient number of said spheres is provided to form a blanket on the surface of the liquid consisting of several layers, for example four layers. Depending on the nature of the liquid and on the storage conditions within the container no special additional precautions may be necessary but in some cases means may be included for supplying an inert gas to a point above the liquid level, or means may be provided for supplying a fire-fighting foam on to the blanket formed by the hollow spheres so that the foam is caused to spread over the surface of the stored liquid. The hollow spheres may contain within them fire-extinguishing media and the spheres may be arranged for ready fracture or bursting under fire conditions. Further the plastics material from which the spheres are made may include fire-retarding media.
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Description (OCR text may contain errors)
United States Patent Baum  LIQUID STORAGE SYSTEM  Inventor: Hans Eduard Baum, London, En-
gland  Assignee: Allplas A.G.
 Filed: May 1, 1970 [211 App]. No.: 33,593
30 Foreign Application Priority Data May 8, 1969 Great Britain ..23,549/69 Jan. 22, 1970 Great Britain ..3,228/70  US. Cl. ..220/26 R, 169/4, 220/88 R  Int. Cl. ..B65d 87/18 ' Field of Search ..220/26 R, 88 R; 169/4  References Cited UNITED STATES PATENTS 1,142,520 6/1915 I-Iolmes ..169/4 1,671,650 5/1928 Newman et'al ..169/4 1,712,321 5/1929 Afonin ..220/26 R 2,798,633 7/1957 Cornell et al. ..220/26 R 3,120,273 2/1964 Kaufman et a1. 169/4 3,346,138 10/1967 Tubbs ..220/26 R 3,401,818 9/1968 Hagen ..220/26 R FOREIGN PATENTS OR APPLICATIONS 1,192,877 4/1959 France ..220/26 R .1 Aug. 29, 1972 1,218,358 6/1966 Germany ..220/26 R 257,538 9/1926 Great Britain ..l69/4 401,005 1 H1933 Great Britain 169/4 470,193 8/1937 Great Britain 169/4 Primary Examiner-George E. Lowrance Assistant Examiner.lames R. Garrett Attorney-Watson, Cole,'Grindle & Watson [5 7 ABSTRACT To reduce the fire risk when flammable liquids are stored in bulk, the surface of the liquid is completely occupied by closely packed hollow buoyant spheres formed of moulded plastics. Preferably a sufficient number of said spheres is provided to form a blanket on the surface of the liquid consisting of several layers, for example four layers. Depending on the nature of the liquid and on the storage conditions within the container no special additional precautions may be necessary but in some cases means may be included for supplying an inert gas to a point above the liquid level, or means may be provided for supplying a firefighting foam on to the blanket formed by the hollow spheres so that the foam is caused to spread over the surface of the stored liquid. The hollow spheres may contain within them fire-extinguishing media and the spheres may be arranged for ready fracture or bursting under fire conditions. Further the plastics material from which the spheres are made may include fire-retarding media.
2 Claims, 3 Drawing Figures P'A'TENTEDwszs m2 Inventor A llorney LIQUID STORAGE SYSTEM The present invention relates to the storage of flammable liquids and to the provision of means intended to reduce the fire risk when storing such liquids or to extinguish or assist extinguishing of the fire in the event of ignition. The present invention includes liquid storage systems incorporating means to reduce the fire risk and to containers incorporating such means, and in some cases further means for admitting fire suppressing or retarding media. It should be understood that references herein to flammable liquids are intended to refer to liquids which emit combustible gases or vapours at normal temperatures or at elevated temperatures.
Such flammable liquids include a wide range of substances including petroleum distillates, lower alcohols such as methanol and ethanol, volatile essential oils such as turpentine, ether, benzene, and liquified hydrocarbons such as methane and butane.
Flammable liquids are often stored in bulk in containers which may be of large capacity and thus such containers represent a substantial fire risk and are often associated with built-in fire-fighting equipment which may involve the provision of means for supplying foam or inert gas to the surface of liquid in the container in the event of fire. It is not however always easy to reduce the fire risk to a tolerable figure as fire-fighting by means of a foam requires that a complete layer or carpet of the foam shall be distributed over the exposed surface of the liquid as rapidly as possible to quench the fire and reduce the risk of the fire spreading. Where storage containers are of large area it is not always easy to ensure that the foam is caused to spread rapidly and uniformly over the surface of the liquid, as is necessary to ensure rapid extinguishing of the fire.
The emission of noxious gases from liquid treatment vats used for carrying out various industrial processes may be reduced by providing the surface of the liquid with one or more layers of closely packed buoyant bodies. The present invention is directed to the problems of the bulk storage of flammable liquids and to the reduction of the fire risks arising from such storage and consists in the fact that the surface of the stored liquid is completely occupied by closely packed buoyant bodies arranged so that the emission of flammable vapour from the surface of the liquid is insufficient to sustain combustion.
A particular problem arises in the case of the storage of lower alcohols such as methanol which may be stored by towns gas supply authorities to provide a means for rapidly boosting production to meet a sudden heavy demand beyond the capacity of the normal source of towns gas, which, except in areas supplied by natural gas, is generally produced by reforming type equipment from a petroleum distillate feed stock. Normal protein-containing types of fire-fighting foam are however rapidly degraded in contact with such alcohols and it is therefore difficult to provide proper fire-pro tection without using special and relatively expensive types of foam-producing materials which are not degraded by the methanol.
The present invention may however be applied in the bulk storage of a wide range of flammable liquids and may be applied in various ways according to the local conditions, to the nature of the liquid to be stored and to associated fire-fighting or fire-retarding equipment that may be utilised under some conditions. In many cases it may be sufficient to provide enough buoyant bodies to form a covering or blanket on the surface of the liquid, such covering or blanket consisting of at least one layer of such bodies. In many cases several layers may be desirable to give adequate protection and typically at least four layers may be used if no special or external fire-fighting equipment or other means are provided for retarding or suppressing combustion in the space above the liquid.
Depending especially on the degree of venting of the part of the container lying above the liquid level, it may be preferred for safety reasons and when storing certain liquids, to provide for the use of foams, inert gases or other fire suppressant media, and in these cases the use of closely packed buoyant bodies on the liquid surface provides a collocation of impermeable zones which ensure the formation of a natant layer of fire suppressant medium, especially foam, supplied to the space above the liquid surface. This arrangement may be applied to the storage of a wide range of liquids and may be defined as a bulk storage system in which the surface of the stored liquid is completely occupied by closely packed buoyant bodies, and means are provided to supply a fire suppressant medium above the liquid surface in the event of fire conditions to form a natant layer of said medium above said surface.
The present invention further comprises as an independent feature buoyant hollow bodies adapted and intended to form a blanket on the surface of a bulk storage liquid, comprising hollow shells of a thermoplastic synthetic resin and containing within them a fire-retarding or fire-extinguishing product. Such hollow shells are preferably formed of a polyacetal thermoplastic resin by blow moulding procedures and contain a compound such as bromochlorodifluoromethane as a fire-retarding or fire-extinguishing medium, and the shells are preferably designed so that they fracture or burst in the event of fire to effect distribution of the tire-retarding or fire-extinguishing media.
Certain features of the invention are illustrated by way of example on the accompanying drawings in which:
FIG. 1 is a view illustrating a storage tank for flammable liquids having a number of layers of buoyant bodies on the surface of the liquid, and
FIGS. 2 and 3 are views illustrating suitable hollow buoyant bodies in accordance with another feature of the invention.
As shown on the drawing, a liquid storage container of any suitable type is indicated at 4 and is of conventional construction, being for example formed of steel, either supported above the ground surface or at least partly buried in the ground. The container is provided with a cover 5 and with pipes 6 and 7 for admitting liquid to the container and for withdrawing liquid as and when required. The surface of the liquid is provided with at least one layer of buoyant bodies or spheres, as indicated at 8, which form a blanket on the surface. One layer of such buoyant bodies may be used especially if they are hollow bodies containing a fire-retarding or fire-extinguishing medium which is released in the event of fire conditions, as explained below. If however buoyant bodies are used for the primary purpose of forming a protective blanket on the surface of the liquid, two or more layers will normally be preferable and four layers will be sufficient in many cases. The provision of a blanket consisting of two or more layers is sufficient in many cases to reduce the fire risk to an acceptable level and depending on the particular liquid being stored, the surrounding temperature and the degree of venting above the liquid level, no further provision to reduce the fire risk need be made. In other cases the cover 5 may be provided with venting means 9 and/or with admission valves 10 for admitting an inert gas to the space above the stored liquid.
In many cases it may be desirable to provide for the admission of fire-fighting foam to the upper part of the container 4. For this purpose a ring-shaped pipe 1 1 may receive a foam supply from a rising pipe 12 to which foam is supplied for a foam generator. In some cases it may be supplied by a pump 13 controlled by a pump control unit 14. The pump control unit 14 is controlled by a flame detector 16 fitted to the centre of the cover 5 and coupled to the unit 14 through a lead 17. The ring pipe 1 I feeds a number of distributed delivery nozzles 15, conveniently of swan neck form, through which the foam is delivered through an outlet into the container in a direction towards the inner wall so that it flows down the wall or rebounds from the wall until it reaches the layers of buoyant bodies 8 where it spreads uniformly over the surface of the blanket with little mixing of the foam with the liquid, to promote rapid fire extinction. The buoyant bodies provide a network which even if it is partially fused by the action of a fire nevertheless assists in maintaining a coherent layer of fire-fighting foam.
The provision of buoyant bodies or spheres on the surface of the stored liquid naturally provides the advantages which are inherent in the use of such bodies on the exposed surface of a liquid, for example of reducing losses by evaporation and access of air and atmospheric moisture. The reduction in evaporation of a flammable liquid is in some cases an essential factor and in other cases a contributory factor, in reducing the fire risk when storing such liquids.
One advantage of the use of buoyant bodies, spheres or the like, when provision is made for the delivery of fire-fighting foam to a storage tank, is that it is not necessary to provide any complicated means within the storage tank for effecting distribution of a fire-fighting foam over the surface of the stored liquid. Buoyant bodies or spheres on the liquid surface ensure that if foam is pumped to the foam inlets in the container, this foam spreads out on to the buoyant bodies without contact with the stored liquid even if the foam splashes down from a considerable height, as would be the case if the container were nearly empty; thereby aiding rapid extinction of the fire.
The bodies or spheres delay intermingling of the liquid with the foam and prevent or minimise degradation especially of protein-type foam where the stored liquid is an alcohol. The heat from a tire may result in partial fusion of the surfaces of the bodies or spheres to form a more or less coherent network which constitutes a surface capable of supporting the foam and in minimising mixing of the foam and the liquid to be protected.
The buoyant bodies referred to may be made of various materials and of various shapes but preferably consist of hollow bodies formed of a shell of thermoplastic material, such as a polyolefine, and of a regular geometrical shape. Conveniently such bodies may be hollow spherical bodies 8, as shown in FIG. 2, formed by blow moulding from a suitable plastics material. Such spherical bodies may be formed with a peripheral rib or welt 18 which gives added strength and restricts or minimizes free rotation of the spheres when placed on the surface of a liquid to be protected. The surfaces of the bodies may moreover be provided with additional projecting ribs, or the surface may be covered with suitably spaced projecting ribs or with grooves arranged in various desired patterns. Hollow bodies produced by blow moulding will normally be air-filled. They may however be filled with an inert gas such as nitrogen or carbon dioxide.
The present invention further comprises independently of the foregoing features the use of buoyant hollow bodies, such as are shown in FIGS. 2 and 3, consisting of a relatively thin shell of a thermoplastic material comprising within them a liquid, powder or solid substance, for example bromochlorodifluoromethane, as indicated at 19, to serve as a fire-retarding or fire-extinguishing medium which is released at the surface of the stored liquid in the event of a fire. Such hollow shells are produced from a material which is unaffected by the fire-retarding or like medium contained within them, and for this purpose suitable grades of thermoplastic material are chosen such as polyacetal resins. The shells of such buoyant hollow bodies are produced by blow moulding and after production are partially filled under pressure with the fire-retarding or like substance or substances to be inserted into them and are thereafter sealed. Such buoyant hollow bodies containing such substances within them are preferably of a thin-walled construction which permits ready fracture or bursting of the shells under fire conditions to ensure distribution of the fire-retarding or other medium within them into the fire to ensure rapid suppression of the fire. In some cases the hollow bodies may be provided, as shown in FIG. 3, with a weakened zone 20 formed for example by a peripheral internal or external groove to assist fracture at a definite temperature, preferably with a bursting action.
The types of plastics materials which are convenient and economical for the production of such buoyant bodies, including those produced by blow-moulding procedures, are in some cases combustible under certain conditions, although they are not normally regarded as a serious fire risk.
For this reason buoyant bodies according to the invention may also therefore incorporate a fire-retarding compound or mixture in the composition from which they are moulded; for example the composition may include carbonates which release carbon dioxide at an elevated temperature or other known fire retardants such as a mixture of antimony trioxide and chlorinated hydrocarbons, the mixture being present in the moulding composition to the extent say of 20 to 40 percent by weight. A suitable proprietary polypropylene material containing a fire retardant is Vestolen 6206 made by Chemische Werke Hills, of Marl, Cermany.
Further, the moulding composition may contain a compound having substituents which confer fire-retarding properties on the polymer.
What we claim is:
l. A liquid container for flammable liquids, comprising at least one complete layer of buoyant spheres floating on the surface of the liquid the layer of spheres so formed being confined solely by the walls of the container to form a protective blanket on the whole of said surface to reduce emission of flammable vapor from the liquid, and external means for delivering a fire suppressant medium to the upper part of the container to rest on said layer to suppress fire above said surface, said layer minimizing mixing of the fire suppressant medium and the liquid to maintain effectiveness of said medium, said means for delivering a fire suppressant medium to the upper part of the container comprising a ring-shaped delivery pipe disposed circumferentially of the upper portion of the container for feeding foamproducing substances to a plurality of circumferentially distributed delivery nozzles which deliver foamed products toward the inner surface of the wall of the container along which such products flow onto the layer of buoyant spheres and then spread over the liquid surface.
2. A liquid container according to claim 1, wherein the buoyant spheres consist of thermoplastic material formed with an equatorial welt to limit free rotation in the liquid and in which the thermoplastic material is capable of fusing under fire conditions at the points of contact between adjacent spheres to form coherent networks of spheres at the surface of the liquid.