US 3840075 A
Carbon microspheres are used as an extinguishant for metal fires.
Description (OCR text may contain errors)
1 United States Patent 1191 Schmitt Oct. 8, 1974 EXTINGUISHANT FOR METAL FIRES 2,385,500 9/1945 Fasold 252/2 3,090,749 5 1963 W k 252 2  Inventor: Charles Schmm Oak Rldge, 3,475,332 10/1969 M12311 al 252/2 Tenn- 3,544,459 12/1970 111m 252/2  Assignee: The United States of America as represented by the United States Atomic Energy Commission, Primary -L y K1118 Washington, DC Attorney, Agent, or Firm-John A. Horan; David S. Zachry; John B. Hardaway  Filed: May 3, 1973  App]. N0.: 356,865
52 us. (:1. 169/43, 252/2  ABSTRACT  Int. Cl. A62c 3/00  Field of Search 252/2; 169/1 R, 2 R Carbon mlcfospheres are used as an extmgulshant for metal fires. . References Cited UNITED STATES PATENTS 4 Claims, No Drawings 2,346,627 4/1944 Thrune 252/2 BACKGROUND OF THE INVENTION This invention was made in the course of, or under, a contract with the United States Atomic Energy Commission. It relates generally to a method for extinguishing metal fires.
Pyrophoric metals present a hazard in many industrial areas. Basically, the pyrophoric metals include the alkali and alkaline earth metals. However, many of the rare earth and actinide metals are also pyrophoric. In nuclear processing facilities, sodium, potassium, 'uranium, thorium, and zirconium are the metals which present the principal hazards.
Many solid extinquishants are commercially available for extinguishing metal fires. However, not all extinguishants are suitable for all metal fires and others have detrimental side effects. Silica is satisfactory for extinguishing some fires. However, when silica is placed on a burning sodium potassium mixture, it actually reacts with the burning metal to produce a larger fire. Graphite flour and flakes have proven to be an effective means of extinguishing a metal fire. However, the present graphite extinguishants produce great clouds of black dust when projected at a fire. If projected within an enclosure, such as an ordinary room, the air becomes contaminated with finely divided graphite to the extent that sight and respiration are impossible without special equipment. Sodium chloride has also been used to effectively extinguish metal fires. However, sodium chloride is extremely corrosive. Any equipment in the vicinity of the fire is subject to corrosion by the sodium chloride. Phosphate extinguishants have also been used in the prior art. However, these extinguishants also have a dusting problem as well as causing additional smoke to be emitted from the fire.
In using the above extinguishants it is conventional to use a cannister filled with the extinguishant and supplied with a source of pressurized gas such as N or C The cannisters normally communicate with a hose and nozzle fitting. In use the pressurized gas forces the extinguishant out of the cannister through the hose and nozzle fitting to create a continuous projection of extinguishant. When a solid, such as those described above, is used as the extinguishant, clogging of the hose and nozzle assembly is a frequent problem. Thisproblem is particularly acute when the extinguishant is a hygroscopic material. If moisture exists within or leaks into the cannister, the hygroscopic material becomes sticky so as to effectively prevent any spraying from the cannister at all.
Another problem with some solid extinguishants is that they have a specific gravity which is greater than that of some molten pyrophoric metals. In such cases, the extinguishant is ineffective because the extinguishant merely sinks through the molten metal so as not to separate the metal from the surrounding-air.
SUMMARY OF THE INVENTION It is thus an object of this invention to provide a new extinguishant for metal fires.
It is a further object of this invention to provide a solid extinguishant which can be projected like a liquid and which doesnot dust when projected at a fire.
It is a still further object of this invention to provide an essentially inert extinguishant for metal fires which will not increase the amount of smoke given off from the fire.
These and other objects are accomplished by using carbon microspheres as an extinguishant for metal fires.
DETAILED DESCRIPTION According to this invention it has been found that carbon or graphite microspheres can be used as an extinguishant for metal fires with none of the disadvantages that adhere in the prior art use of graphite flour or flakes. Carbon microspheres can be projected from a conventional powder extinguisher cannister with flow and projection qualities that approximate those of a liquid. Since the microspheres have liquid-like flow properties, there is generally no problem with clogging or sticking within the extinguisher cannister.
Carbon microspheres have a mass such that when sprayed through the air, no dusting occurs. The use of the extinguishant of this invention thus makes it possible to extinguish a fire within an enclosure without creating clouds of noxious dust. By concentrating the extinguishant only on the fire, clean up problems after the fire are greatly reduced since the surrounding area is not covered with extinguishant. Carbon microspheres are essentially inert so that no additional smoke is created when the microspheres contact the burning metal. Once the fire is extinguished, the metal may be easily recovered since no actual reaction occurs between the microspheres and the metal to produce undesirable contaminants. A simple mechanical separation process may be used to separate the microspheres from the previously burning metal.
Carbon microspheres used in the process of this invention extinguish metal fires by first covering the metal surface and thus separating the metal from an oxygen source, and secondly by conducting heat away from the burning metal. Since carbon is of very low density, it will naturally float on the surface of most metals. On metals of lower density, such as lithium, individual microspheresare not heavy enough to break the surface tension so that they are retained on the surface of the metal.
Microspheres for use in the process of this invention have the following characteristics. The microspheres may be within a size range of 50 to'250 microns in radius, but preferably within the range of about to microns. While it is preferred that the microspheres for use in this invention be as nearly spherical as possible, it has been found that microspheres or microspheroids having a major to minor axis ratio of up to about 1.5 are useful in the process of this invention. The microspheres preferably have a bulk density within the range of 1.2 g/cc to 1.9 g/cc and a real particle density or toluene displacement density of 1.3 g/cc to 2.0 g/cc. The internal particle porosity of the microparticles may range from 0.5 to 10.0 percent for use in the process of this invention. Although not a critical characteristic, it has been found that the microparticle compressive strength should be in the range of from 10 to 60 ounces per particle, depending upon particle diameter, so that the particle has sufficient strength to-withstand velocity impact forces during projection andnot be subject to excessive fracturing. Microspheres for use in the invention preferablyhave .an organic content of less than about A higher organic content can cause water adsorption and sticking of the particles.
Microspheres for use with this invention can be prepared by coking a resin such as a cation exchange resin at a temperature of about 850 C in an atmosphere of 5 nitrogen. However, such microspheres are presently commercially available with a very high degree of sphericity. At present, the cheapest source of a suitable microsphere for use in the process of this invention is fluidized petroleum coke. Fluidized petroleum coke having an average major to minor axis ratio of about 1.25 does not possess the sphericity of coked resin beads; however, the petroleum coke is suitable for use in the process of this invention.
A conventional powder cannister is suitable for use in this invention. A cartridge-type extinguisher as illustrated in Fire Protection Handbook, 13th Edition (1969), G. H. Tyron, Editor, pages 18-36, is the preferred extinguisher. It has also been found desirable to modify this type of extinguisher by providing a gate valve between the CO cartridge and the chamber so that the pressure buildup may be relieved in the event of blockage.
As a test of this process of this invention, five pounds of coked resin microspheres formed by heating styrene divinylbenzene resin beads in flowing nitrogen over a gradual heating period of 48 hours were packed into the extinguisher cannister described above. The carbon microspheres were 50 to 100 mesh in size. The cannister was supplied with a C0 pressure of about 20 psig.
About one pound of magnesium shavings were ignited inside an open metal container. The microspheres were blown from the cannister at a distance of 25 feet from the fire. The fire was extinguished within less than a minute. About three pounds of microspheres were used. Similar successful tests were carried out with lithium and sodium fires.
While this invention has been described in terms of carbon or graphite microspheres, several modifications are readily apparent to those of ordinary skill in the art. Such modifications may include impregnation of the microspheres with a neutron poison for use on uranium fires where a danger of criticality may exist.
What is claimed is:
1. A method for extinguishing a metal fire comprising placing on said fire an extinguishant consisting essentially of microspheroids of carbon, said microspheroids having a major to minor axis ratio of less than 1.5 and being in size substantially within the range of 50 to 250 microns in radius.
2. The method according to claim 1 wherein said microspheroids have an organic content of less than 10 percent.
3. The method according to claim 1 wherein said microspheroids have a bulk density within the range of 1.2 to 1.9 grams per cubic centimeter.
4. The method according to claim 1 wherein said microspheroids are projected onto said fire using a pressurized gas as a means of projection.