US2385500A - Fire extinguishing composition and the manufacture thereof - Google Patents

Description

Patented Sept. 25, 1945 UNITED STTE'S FIRE EXTINGUISHING COMPOSITION AND THE MANUFACTURE THEREOF George Arthur Fasoldl, Mount Healthy, and Earold W. Greider, Wyoming, Ohio, asslgnors to The Philip Carey Manulacturing Company, a

corporation of Ohio No Drawing. Application March 12, 1942,

Serial No. 434,350

in Claims. (01. 2sz-2 This invention relates to fire extinguishing compositions and relates especially to'fire extinguishing compositions of the type composed of subdivided solid material which can be distributed carbon tetrachloride, and the like, are unsuitable.

Fires of this character result from the burning of pure magnesium metal and of magnesium alloys containing a high percentage of magnesium, e. g., about ninety per cent. or more, and from the burning of aluminum and sodium.

Fires resulting from the combustioniof metallic magnesium can be extinguished very quickly using the fire extinguishing composition of this invention due to the shutting off of oxygen from the burning metal.

If the fire occurs on a support which is combustible, for example, a fioor made of wood, the

fire extinguishing composition of the present invention is very eilective in preventing the intense heat of burning magnesium from striking through to and burning the combustible support.

This is because the fire extinguishing composi-,

tion of the present invention-not only is very effective in smothering the fire, but also is very eiiective in providing a heat insulating mat which protects adjacent materials from the heat of the burning material.

It is also an advantageous feature of the fire extinguishing composition of the present invention that it tends to remain in position even when subjected to the intense temperature of burning metallic magnesium.

It is a further advantage of the fire extinguishing composition of the present invention that, when exposed to fiame, it does not have objectionable characteristics, such as gassing, violent disintegration tendency, or the like, andis inexpensive.

While this invention is especially suitable for extin uishing fires which are caused by burning magnesium or magnesium alloys, the fire extinguishing composition of the present invention is also useful in extinguishing any type of fire that can be covered with a protective blanket of finely-divided material. However, fires which are difllcult to extinguish with water, such as fires due to burning oil and gasoline in machine shops,

burning sulphur, burning metals, including magnesium, aluminum and sodium, and the like, are types of fire for which the fire extinguishing composition of the present invention is especially suited.

-It is another purpose of this invention to provide a fire extinguishing composition which is not adversely affected by exposure to varying atmospheric conditions, namely, which is not affected by such things as oxidation, mild heat, subatmospheric temperatures, moisture, etc. Moreover,- while in storage or during shipment the material is not susceptible to injury, but can be 'packed in inexpensive containers such as paper or cloth bags without special precautions.

It is a feature of this invention that the fire extinguishing composition occurs in granular form and that a thermoplastic bitumen which is solid at ordinary atmospheric temperatures, but which is meltable at flame temperature, is combined with a, finely-divided solid material which is substantially unmeltable and which is preferably also' heat-resistant at approximately 1200 F., i. e'., within the range of flame temperatures.

' By heat-resistant it is meant that when '7 grams of the finely-divided solid materialin the form of a conical pile is subjected to a temperature of approximately 1200 F. on a metal hot plate for a period of five minutes, the material or some substantial residue thereof will remain in solid or semi-solid form.- By unmeltable it is meant that, when 7 grams of the finely-divided solid material in the form of a conical pile is subjected to a temperature of approximately 1200 F. on a hot plate for a period of five minutes, it is not reduced to a liquid state. A material such as sand or asbestos is both unmeltable and heatresistant, while a material such as wood or ani- 'mal fiber which carbonizes and burns without melting is unmeltable but is not heat-resistant. The bitumen by itself, being meltable at flame temperatures, is capable of being reduced to a liquid condition at 1200 F., but, by incorporating with the bituminous material a substance which is unmeltable and heat-resistant at 1200 F., a composition is afforded which, when reduced to granular form, has remarkable effectiveness in extinguishing fires. While the bitumen in the granules tends to soft'enand melt at the surfaces of the granules when the composition is exposed to'fire, this has the efiect of sealing the fire from access of air. The unmeltable and heat-resistant material in' the granular composition serves to stabilize the bitumen, however, so that the granules tend to gemair in place and the granuing a 325-mesh testing sieve. When the word bitumen isused herein, reflar-material affords a continuous protective sealing blanket of substantial thickness and resistance to displacement about the burning material. Even when the finely-divided solid material is merely unmeltable without being heat-resistant, as defined above, some advantage according to this invention is afforded due to the fact that the A normally solid bitumen is first heated until it is in a heat-liquefied condition and finely-divided solid material is then uniformly incorporated therein so as to be covered by the bitumen. The mass of bitumen and filler is then cooled until it is sufficiently hard to be subjected to a comminuting action as by crushing or grinding in a suitable mill of which many types are known. The hardened mass is then crushed or ground until it is reduced to a granular condition and preferably any fines, e. g., passing a 100=mesh screen are screened out. The resulting granular product is then ready for use.

The maximum size of the particles of finelydivided material in a fire extinguishing composition according to this invention is determined by the size of the granules in the composition, namely, the particles of finely-divided solid material may approach the size of the granules, although preferably the finely-divided solid material is normally considerably finer than the bituminous granules and is incorporated in the granules and acts as a reinforcing filler for the bitumen. Ordinarily, the finely-divided solid material passes a l4-mesh testing sieve. On the other extreme, the finely-divided solid material may be of any fineness of subdivision, e. g., passerence is made to asphalt, pitch, tar, etc., per se and without admixture therewith of a substantial quantity of finely-divided solid material. When the expression bituminous material" is used, reference is made to bitumen per se or bitumen containing therein some non-bituminous material such as the finely-divided solid materials referred to above.

The bitumen that is used in the fire extinguishing composition of the present invention may be any type of bitumen that is solid at ordinary atmospheric temperatures. The bitumens which are preferred are asphaltic bitumens or natural bitumens. Asphaltic bitumens such as air blown (oxidized) "cracking coil tar residue from the high temperature pressure cracking process of petroleum refining are especially suitable. While bitumens such as coal tar pitch and the like may be used, coal tar pitch is not as satisfactory as asphaltic bitumen, due to the fact that coal tar pitch contains a higher percentage of volatile matter which tends to smoke when the mate= rial is applied to a fire and tends to be excessively brittle, the brittleness resulting in the formation of dust during handling and shipment of the material.

Heretofore it has been proposed to use powdered bitumen per se or mixed with a pulverulent material such as slate flour for extinguishing burning magnesium fires. Such a composition is,

however, subject to the great disadvantage that the powdered bitumen tends to form combustible or explosive mixtures with air and therefore the composition is diflicult and unsafe to apply to fires. Such a composition is also less effective as a fire extinguisher than the composition of the present invention, due to the fact that the bitumen has to first melt down to a quite fiuid state before it becomes effective and then tends to smoke or even burst vigorously into flame. Moreover, if and when the fire is. extinguished and the mass cooled, the bitumen hardens down to a continuous and very hard cementitious mass that is very dimcult to dispose of. It is likewise a disadvantage of a mixture of this character that it is dimcult to maintain uniform. The

powdered bitumen and powdered mineral upon standpoint of its dustiness and dirtiness when handled and used and in cleaning up the residue after the fire.

In fire extinguishing compositions according to the present invention, it is regarded as desirable that the bitumen have a softening point of at least about 125 F., so that it will be solid at ordinary atmospheric temperature. Preferably, the softening point of the bitumen is above175 F. A bitumen having relatively high soften ng Point may be used; but, if the softening point is too high, it is difficult to mix the finely-divided solid material therewith and the resulting mass may be undesirably brittle. Therefore, in making up the composition, it is desirable that the softening' point of the bitumen not be above about 325 F., and it is preferable that the softening point of the bitumen be below about 300 F.

In order to afford a better understanding of the practice of this invention, there will be detions of asphalt and finely-divided asbestos which may be referred to as asbestos dust. The asphalt used may be air blown refined cracking coil tar having a softening point (ring and ball method of the American Society for Testing Materials designation D36-26, published in A. S. T. M. Standards, Vol.11, 1942, pages 488-490 inclusive) of about 260 F. Typical of the asbestos dust used is fine Chrysotile asbestos of which about eighty-five per cent. by weight passes a tfi-mesh standard testing sieve, about sixty-five Per cent. passes a 100-mesh testing sieve, about fifty per cent. passes a ZOO-mesh testing sieve, and about thirty-five per cent. passes a 325-mesh vantageous.

ingthe asphalt to about 450 F. until it is in a heat-liquefied condition. The asbestos dust is then mixed therewith to form a doughlike mass. The mass is then extruded using any suitable typeof extrusion machine and cooled to ordinary temperature. The use of an extrusion machine in the manufacture of the fire extinguishing composition of this invention is especially ad- At ordinary temperature, the mass is hard and tough andcan be easily ground to a granular condition. The mass is ground until the granules pass a one-eighth inch testing sieve and the material is screened so as to utiline only those granules which are retained on a GB-mesh testing screen. The resulting material is suitable for use according to this invention.

It has the advantages both for use in extinguishing fires and for shipment, handling and storage that have been mentioned hereinabove.

The fire extinguishing composition of the foregoing example also has been satisfactorily prepared, using about fifty-five per cent. of the asbestos dust above referred to, together with twenty-five per cent. of air blown refined cracking coil tar having a softening point of about 260 F. and forty per cent. of asphalt having a softening point of 230 F., namely, air-blown heatand vacuum-refined pipe still bottoms produced as a residuum from the distillation of petroleum.

The following are additional examples of fireextinguishing compositions according to this invention:

Per cent Asphalt (air blown cracking coil tar having a softening point of about 200 F.) 27

No. 16asbestos fiber (Q. A. P. A. 7'! grade)--- 30 Sand passing a 20-mesh sieve and retained on a 150-mesh sieve 43 (Q. A. P. A. above is an abbreviation of Quebec Asbestos Producers Association, the reference being to the asbestos fiber classification system adopted by the Committee on Uniform Classification and Grading of Asbestos Mines Products of the asbestos producers of Quebec, Canada.)

Per cent Asphalt (air blown cracking coil tar having a softening point of about 200 F.) 40 Organic fiber (rag) 10 No. 16 asbestos fiber (Q. A. P. A. 7T grade)--- 25 Sand passing a 20-mesh sieve and retained on The No. 16 asbestos fiber referred to above is a fine asbestos that is somewhat coarser than the asbestos dust above mentioned, but is very much shorter than the asbestos classified as fiber by the Quebec Asbestos Producers Association and has approximately the following sieve analysis byweight:

limited to those materials which are mentioned in the foregoing examples. The finely-divided solid materials which are ordinarily used in the practice of this invention are inorganic fillers, many of them being mineral fillers. Examples of such materials which may be used in finely-divided form are serpentine rock,'hydrated Portland cement, precipitated calcium carbonate, limestone, chalk, dolomitic rock, slate, other sedimentary rocks, brick and other ceramic materials, slag, fly ash, household ash, ash concrete, pumice, clays, dead burned calcium sulphate, marble, sandstone, granite and other igneous rocks, micas, mica schist, quartz, non-alkali metal oxides, etc. Ground asbestos-cement scrap, e. g., from asbestos cement shingles containing about 20 per cent. by weight of asbestos fiber and 80 per cent. of hydrated Portland cement, is also suitable. Some of the filler materials mentioned above, such as the clays, hydrated Portland cement, asbestoscement, and certain varieties of asbestos such as Chrysotile asbestos, contain water of constitution that is liberatable when the filler material is sub- Jected to elevated temperatures such as, for example, 1200 F. Thus Chrysotile asbestos contains upwards of 13 per cent. water or constitution, while materials such as hydrated Portland cement contains about 15 to 20 per cent. water of constitution. Materials such as chalk, precipitated calcium carbonate, dolomitic rock, etc., are

1 decomposed when subjected to temperatures such as 1200 F. so as to liberate carbon dioxide which mayconstitute per cent. by weight or even more of the finely-divided solid material. Material such as dead burned calcium sulphate is decomposed when subjected to such temperatures so as to give oil sulphur dioxide. Such materials are referred to generally herein as finely-divided solid materials containing matter that is volatilizable at 1200 F. The employment of filler materials of this character is preferable according to this invention. When bituminous granules contain finely-divided filler material encased in the bitumen and are subjected to flame temperature, the filler, if it contains volatilizable matter. will be decomposedwith production of gaseous material that acts to expand the granules. This Per cent Passing a 48-mesh sieve 65 Passing a 100-mesh sieve 45 Passing a 200-mesh sieve 30 Passin a 325-me'sh sieve 15 While short asbestos fiber that is customarily regarded as waste material may beused in the manufacture of fire extinguishing compositions according to present invention, it is not necessary to use such finely-divided asbestos, inasmuch as longer fibers may also be used. The longer fibers are, however, broken up during the grinding operation, and for this reason it is ordinarily advantageous commercially not to use the long fiber asbestos which is much in demand for use in reinforcing heat insulations, in the manufacture of asbestos paper, etc., and to use the short dustlike material which is ordinarily regarded as waste.

The finely-divided solid materials that may be used according to this invention are by no means expansionof the granules assists in causing the granules to pack together to form an air-tight seal that prevents access of oxygen to the buming material. The formation of the gaseou material in the granules also makes the granules porousand tends to make the mass as a whole of an increased porosity which serves. to greatly increase the heat insulating effectiveness of the composition.

As a substantial part of the finely-divided solid material that is used, it is preferred to use mineral fiber. Use of asbestos fiber has been mentioned above and has been illustrated in connection with the foregoing examples. In addition to or in lieu of asbestos fibers, other mineral fibers may be used, such as glass fiber, mineral wool, e. g., rock wool, and the like, The Chrysotile asbestos fiber, due to the fact that it contains water of constitution, is preferable; but other types of asbe'stiiorm mineral fiber, such as actinolite, Amosite, crocidolite, etc., may be used. The mineral fiber is peculiarly effective in making the bituminous granules tough, so. that they will not crumble in handling, and also areyery effective in increasing the viscosity and stability of the bituminous material. They also have the advantage of being both non-meltable and heatules contain at least about ten per cent. by weight of mineral fiber and preferably at least about twenty per cent. by weight of mineral fiber.

While employment of mineral fiber is preferable, it is not essential that mineral fibers be used. Other fibrous materials are efiective in increasing the toughness of the bituminous granules so that they will not disintegrate with formation of dust to an excessive degree during handling and shipment. Any organic fiber may be used, such as paper fiber and other wood fibers, rag fibers, artificial cellulosic fibers, animal fibers and the like. Such fibers, while combustible and not heat-resistant, are not incompatible with the fire extinguishing composition of the present invention. As has been mentioned above, a small amount of material which is volatilizable is desirable in the bituminous granules of the fire extinguishing composition of this invention, due to the fact that the generation of gas or vapor within the granules in contact with a fire tends to expand them, thus causing the granules in the fire extinguishing covering layer to pack together and to develop pores therein. Thus organic fibers in an amount corresponding to ten per cent or more, or even twenty per cent or more, may advantageously be incorporated in the bituminous granules. Such organic fibers may, for example, be used in conjunction with finely-divided solid mineral or other heat-resistant materials in the bituminous granules.

The fact that organic fibers may be used in the fire extinguishing compositions Of the present invention makes it apparent that finely-divided solid organic materials other than organic fibers may be present in the fire extinguishing compositions embodying this invention. A number of such materials are suitable when occurring in finely-divided condition. Suitable materials which may be mentioned by way of example are rubberized scrap material, linoleum scrap, ground hardened synthetic resins, e. g., of the phenolaldehyde type, coke, and the like. Since such organic materials as well as organic fibers of the character above-mentioned, when subjected to temperatures such as 1200 F., tend to evolve gaseous material and, in fact, may be substantially entirely gasified and consumed, they are to be regarded as finely-divided solid materials comprising matter that is volatllizable at temperatures of 1200 F.

It is preferable that the finely-divided solid material contained in the bituminous granules contain some matter that is volatilizable at 1200 F. and, when such volatilizable matter constitutes about two per cent. by weight of the bituminous granules, it has some effectiveness in this regard. Preferably, the amount of volatilizable material is somewhat greater, namely, five per cent. by weight, or more, of the bituminous granules. Also preferably, the amount of volatilizable matter that is contained in the finelydivided solid material in the bituminous granules is less than twenty per cent. by weight of the bituminous granules. If the amount of volatilizable matter exceeds about thirty per cent. by weight of the bituminous granules, the amount of gaseous material that is driven ofi is somewhat excessive when the fire extinguishing composition .is used for extinguishing materials such as burning magnesium, which burns at very high temperatures. For extinguishing ordinary fires, such as smoldering rags and the like, the amount of matter volatllizable at 1200 F. may be greater than thirty per cent. without detracting seriously from the effectiveness of the fire extinguishirfg composition.

When it is said that the finely-divided solid material contains volatilizable matter when subjected to 1200 F., the proportion by weight of matter that is vo'latilized when a layer of the finely-divided solid material approximately oneeighth inch thick is contacted for five minutes with a plate heated to 1200 F. is referred to. Referring to the fire extinguishing composition as a whole, including both the finely-divided solid material and the bitumen, it is preferable that tire composition contain less than forty per cent.

by weight of matter volatilizable at 1200 F.,

namely, the proportion by weight of matter volatilized when a layer of the composition as a whole approximately one-eighth inch thick is contacted for five minutes with a plate maintained at 1200 F.

In addition to finely-divided solid materials above referred to, asphaltites such as gilsonite, grahamite, albertite may be used in finely-divided condition in conjunction with the bitumen. These asphaltites when heated intumesce but do not melt and, therefore, serve to stabilize the bitumen and also expand the bituminous granules containing them. Such materials are both unmeltable and heat-resistant as these terms are used herein.

While organic fibers and other finely-divided solid organic materials may be used, it is preferable that the finely-divided solid material in the bituminous granules'consist in major proportion of inorganic unmeltable heat-resistant material.

It is preferable, in the preparation of a fire extinguishing composition according to this invention, that the finely-divided solid material be non-hygroscopic. Hygroscopic material, if present, tends to cause moisture to be absorbed by the fire extinguishing composition. This is not detrimental when the fire extinguishing composition is used for extinguishing ordinary fires such as burning wood, rags, paper, and the like. However, when the fire extinguishing composition is used for extinguishing burning magnesium, any water that is present in the composition serves to accelerate the combustion and detracts from the effectiveness of the bituminous granules. The effect of a hygroscopic filler can be counteracted by manufacturing the fire extinguishing composition in a dry condition and then packaging it while dry in an airtight container. However, by use of non-hydroscopic filler materials, no such precaution has to be taken and the fire extinguishing composition can be stored even in damp places without danger of absorbing an excessive amount of moisture. A fire extinguishing composition which comprises a substance such as Chrysotile asbestos fiber, hydrated Portland cement, or the like, containing water of constitution, is, however, to be regarded as a dry granular composition, if the composition does not contain any substantial amount of free or hygroscopic water.

'In usual practice, the finely-divided solid material is mixed with the bitumen while the bitumen is in a heated liquefied condition. The bitumen is usually heated about to 250 F. above its softening point. Ordinarily, the mixing temperature is around 350 to 450 F. There are some finely-divided solid materials which are decompose-d at such temperatures, and for this reason it is desirable to use finely-divided solid materials maintain their structural integrity, except for possible loss of water of constitution, or the like,

at such temperatures during a'mixing operation.

. The use of high temperatures during the preparation of the fire extinguishing composition can be avoided, however, by mixing the filler material with powdered high-softening-point bitumen, mixing the materials with a fluxing material that is adapted to combine with the powdered bitumen at relatively low temperatures, e. g., at temperatures not above about 200 F., to produce asphaltic material having a softening point within the range above mentioned and then causing the bitumen components to occur, e. g., by application of pressure, in an amalgamated condition. The resulting material, solid at ordinary temperatures, can then be crushed or ground to a granular condition. In such case, it isnot essential to use a finely-divided solid material that is heat resistant I at 450 F.

80 nous granules may be tough and coherent and in order that there may be suflicient bituminous material present to seal the granules together when the granules are distributed over a fire. However, even greater amounts of finely-divided solid material may be used, even up to eighty per cent. by weight of the bituminous granules, with some degree of effectiveness.

When the proportion of finely-divided solid material is relatively low,; that is, under about fifty per cent. by weight of the bituminous granules, the bituminous granules may be somewhat adhesive and may tend to stick together, particularly if the softening point of the bitumen is below about 200 F. Ordinarily, it is desirable to make the fire extinguishing composition so that the bituminous granules will not tend to stick to- I gether in storage, but will remain in a granular condition for long periods of storing by utilizing a sufflcientamount of finely-divided solid material to counteract any natural a-dhesiveness of the bitumen per se. If, however, the granules have a tendency to sticktogether, this may be counteracted by including with the bituminous granules a dustlike separating material such as powdered talc, slate dust, ground slag, brick dust,- etc. The use of such materials should be kept relatively low, however, and should merely occur as a superficial dust on the bituminous granules. For example, about two per cent. of the fire extinguishing composition may be in the form of the separating dust adherent to the bituminous granules. It is preferable that the amount of such dust occurring on the outside of the bituminous granules constitute less than about ten per cent. of the fire extinguishing composition.

It is important that the fire extinguishing composition of the present invention be in granular form. It is preferable that the composition be such that it will pass an 8- mesh screen and will be retained on a 65-mesh screen. It is also preferable that the granules be graded in size. Thus, it is desirable to have in the composition some granules which are retained on the 14-mesh screen, some which are retained on a 28-mesh 78 screen, and, in addition, some granules which pass a 48-mesh screen. Preferably, at least about thirty per cent. by weight of the compositionis retained on a i l-mesh testing screen and at least about sixty-five per cent. by weight is retained on a 28-mesh testing sieve, while at least about two percent. by weight passes a 48-mesh testing sieve and is retained on a 65-mesh testing sieve. When the particles are graded in this manner, they tend to form an impervious blan-' ket with greater rapidity upon being placed on a mass of burning material thanlf the granules all are of substantially the same size. The particular sizes above-mentioned, while preferred, are not essential, inasmuch as coarser granules, namely, around 4-mesh granules, may be used and some amounts of finer granules, such as those Just retained on a IOO-mesh sieve, may' be included. It is ordinarily desirable that the granules be of irregular shape, inasmuch as granules of irregular shape tend to stay in place, when deposited as a covering layer on a burning mass,

better than granules which are more or less spheroidal in form.

' When the bituminous granules contain a considerable amount of finely-divided solid material, especially fibrous material, they can be prepared so as to be tough and so as not to crumble in handling and shipment, although, as aforesaid, if the amount of bitumen is' reduced excessively the granules become excessively brittle and tend to crumble. On the other hand, if onl a small amount of finely-divided solid material is used in having a softening point about 300 F., the material is quite brittle and tends to form dust during handling and shipment. -The toughness of the granules can! be conveniently tested by placing grams of the granular material in a cylindrical metal container two inches in internal diameter and four feet in length that contains nine smooth round stones about one inch in diameter of the type used in ball mills. The granular material before being placed in the container is screened so as to eliminate substantially all material passing a IOO-mesh screen. The container is theninverted a given number of times, which, for the purpose of test, is one hundred times. If, after the material has been treated in this manner, less than five per cent. of the granular material can be screened through a 100- mesh testing screen, the material is registered as tough," as this term is used herein. It is preferable, but'not essential, that the bituminous granules be tough so that they will not crumble and disintegrate into dust during handling and shipment.

The stability of the bituminous material, namely, its resistance to displacement or fiow at elevated temperature, may be ascertained by determining its viscosity index at 1200 F. While we do not know of anystandard method of determining viscosity index at this temperature, such value can conveniently be determined in the following way. A metal plate is heated to, and maintained at, substantially 1200 F. Seven grams of the fire extinguishing composition in granular form are placed on the plate in the form of a cone. The time required for the bituminous granules to melt and form a liquid mass on the plate is taken as the viscosity index of the material. Preferred bituminous granular fire extinguishing composition, according to this inventlon, does not appear to melt at all, but retains its granular form on the plate with only slight fluxing of the granules together to form a cakelike mass. Other flre extinguishing compositions soiten somewhat. but tend to carbonize gradually without melting and substantial lateral flowing to form a liquid mass on the plate. Such materials are also suitable for use according to this invention. It is desirable that the viscosity index be greater than about fifteen minutes. If the bituminous composition contains more than about fifty per cent. of finely-divided heat resistant solid material, the viscosity index at 1200 F. is normally so high that the fire extinguishing composition does not melt at all. Certain filler materials, such as mineral fiber, are especially effective in increasing the viscosity index at 1200 F. of the bituminous. material, and if such materials are present, bituminous fire extinguishing compositions having a viscosity index in excess of fifteen minutes, may be made even when considerably less than fifty per cent. of finely-divided solid material is present. The use of fire extinguishlng composition having a viscosity index above about fifteen minutes is especially dean-=- able when the composition is used in extinguish ing burning magnesium or magnesium alloys. inasmuch as the fire extinguishing composition does not tend to new of the burning metal. Moreover, when the composition has a high vis cosity index, the b metal can be transferred to a layer of the fire extinguishing composition spread on a support and, notwithstanding the intense heat of the burning metal, the fireextin= guishing composition does not melt so as to permit the metal to settle to the support as would be the case if granular bitumen by itself were used. This is advantageous not only when the lire is on a support such as a wood floor. but it is also advantageous when the fire is on a con crete floor. Concrete floors contain water of com stitution in the hydrated Portland cement, which water of constitution is liberated by the intense heat of burning magnesium metal. The sudden liberation of this water caused by the heat of the burning metal tends to forcefully disrupt the com crete, thereby scattering the burning metal, thus spreading the fire, increasing the hazard to persons attempting to extinguishthe fire, and, oi course, injuring the concrete iloor.

Hereinabove fire extinguishing compositions of this invention have been described as consisting of bituminous granules, or such granules carrying a light coating of dusting material to prevent them sticking together at ordinary temperatures. This is of great importance in the practice of the present invention, for in such. a composition the bituminous particles are in essentially contigu= ous relation, so that, as soon as the bitumen in the granules is softened by exposure to fire, the granules tend to adhere together and form a, seal which excludes air from the fire. If an excessive amount of non-theroplastic granular or powdered dusting material were distributed about among the bituminous granules, the bituminous granules would not, when softened, produce an effective seal to prevent the air from coming in contact with the burning material.

While this invention has been described in com nection with various examples of the practice thereof, it is to be understood that this has been done for illustrative purposes only, and that the composition and preparation of fire-extinguish ing compositions may be varied within quite wide limits according to our invention. Thus, while this invention has been described in connection with the use of bitumens, other thermoplastic materials, solid at ordinary temperatures but meltable atflametemperature, may be employed in compositions of the character aforesaid, especially those having characteristics similar to the bitumens hereinabove described. Such materials should, however, be similar to normally hard bltumens in that, when subjected to a temperature of about 1200 F., they should not give of! a substantial amount of oxygen-containing volatile matter that promotes the combustion of burning metallic magnesium. Examples of such thermoplastic materials are coumarone-indene resins, resins produced from petroleum, hard par. afiinaceous thermoplastic waxes, and chlorinated diphenyls. Moreover, mixtures of different bitumens or of diflerent thermoplastic materials generally may be employed, as well as mixtures of different finely-divided solid materials. The scope of this invention is to be governed by the language of the following claims.

We claim: l. A fire extinguishing composition in the form of a granular product, said product comprising a multiplicity of essentially contiguous bituminous granules containing bitumen solid at ordinary atmospheric temperatures and containing finelydivided solid material that is unmeltable when subjected for 5 minutes to a temperature of about 1200 F. and that is uniformly incorporated and intimately commingled with the bitumen in said granules as an integral part of said individual bituminous granules.

2. A fire extinguishing composition in the form of a granular product, said product comprising a multiplicity of essentially contiguous bituminous. I granules containing at least about thirty per cent.

by weight of bitumen having a softening point above about F. and containing at least about twenty-five per cent. by weight of finely divided solid material that is unmeltable when subjected 'to a temperature of about 1200 Z6. and that is uniformly incorporated and intimately commingled with the bitumen in said granules as an integral part of the individual bituminous granules, said composition not containing more than forty per cent. by weight of matter volatilizable in 5 minutes exposure at 1200 R, and said composition having a viscosity index at 1200 F. of at least 15 minutes.

3. Anre extinguishing composition according to claim 2, wherein a major proportion of said.

unmeltable finely-divided solid material is inorganic material that is heat resistant when subjected for 5 minutes to a temperature of 12t0 F., and wherein said granules are of the order of size passing an 8 mesh testing sieve with at least about 65% by weight retained on a 28 mesh testing sieve.

4. A fire extinguishing composition in the form of a granular product, said product comprising a multiplicity of essentially contiguous tough bituminous granules containing at least about thirty per cent. by weight of bitumen having a softening point above about 125 F. and not above about 325 F., and containing finely-divided solid material uniformly incorporated and intimately commingled with the bitumen in said granules as an integral part of the individual bituminous granules, said finely-divided solid material compri ing particles that are unmeltable and heat resistant about 1200 F. and that constitute at least about twenty-five per cent. by weight of said bituminous granules, and said finely-divided solid material not containing an amount of matter volatilizable material not containing an amount or matterv in 5 minutes exposure at 1200 F. that is greater than thirty per cent. by weight or said bituminous granules.

5. A fire extinguishing composition in the form or a granular product, according to claim 4,

' wherein said finely-divided solid material contains an amount of matter volatiiizable in 5 minutes exposure at 1200 F, that constitutes at least about two per cent. by weight oi said bituminous granules.

6. A fire extinguishing composition in the form of a granular product, said product comprising a multiplicity of essentially contiguous granules containing a thermoplastic material that is meltable at 1200 F., that does not produce when subjected to such temperature substantial quantities of oxygen-containing volatile matter that promotes the combustion of burning metallic magnesium and that is solid at ordinary atmospheric temperatures, and containing finely-divided solid material that is unmeltable when subjected for 5 minutes to a temperature oi about 1200 F. and that is uniformly incorporated and intimately commingled with said thermoplastic material as an integral part 01' the individual granules.

7. A fire extinguishing composition in the form of a dry granular product, said product comprising. a multiplicity of essentially contiguous tough granules containing a thermoplastic material that has a softening point between about 125 F, and about 325 1". and that does not produce,

when brought into contact with burning mag-' nesium, substantial quantities of oxygen-containing volatile matter that promotes the combustion of burning magnesium, and containing at least,

twenty-five per cent by weight or finely-divided solid material that is unmeltable and heat resistant when subjected for 5 minutes to a temperature of 1200 F. and that is uniformly incorporated and intimately commingled with said thermoplastic material as an integral part of the individual granules, the viscosity index 0! said composition being greater than about 15 minutes, and said finely-divided solid material containing not more than about thirty per cent. by weight of matter volatillzable in minutes exposure at 12001.

8. A fire extinguishing composition in the form of a granular product, said product comprising a multiplicity of essentially contiguous granules containing about thirty per cent. to about seventy-five per cent. by weight of bitumen having a softening point between about 125 F. and about 325 F. and containing about twenty-five per cent. t about seventy per cent. by weight of finely-divided solid material uniformly incor-I porated and intimately commingled with the bitumen in said granules as an integral part of the individual bituminous granules. said finely-divided solid material comprising mineral fiber constituting at least about ten per cent. of said b uminous granules, and said finely-divided solid volatilizable in 5 minutes exposure at 1:200 F.

' part 01' said bituminous granules,

that is greater than about thirty per cent. by weight 01' said bituminous granules.

9. A method oi extinguishing burning mates rial, which comprises applying to the burning material a granular material containing a multiplicity of essentially contiguous granules containing at least about thirty per cent. by weight of bituminous material that is solid at ordinary atmospheric temperature and containing at least about twenty-five per cent. by weight of finelydivided solid material that is unmeltable and heat resistant when subjected for 5 minutes to a temperature oi about 1200 F. and that is unitormly incorporated and intimately commingled with the bitumen in said granules as an integral thereby softening the bitumen in said contiguous granules adjacent the burning material and causing said granules to adhere together to form an air-excluding protective blanket which exclr'les air from said burning material, a bitumen in said granules adjacent said burning material carbonizing and forming with the skeletal body of finely-divided' unmeltable and heat resistant material in said granules a coherent granular heat insulating mass. 10. A method of extinguishing burning material, which comprises applying to the burning material a granular material containing a multiplicity oi essentially contiguous granules containing' at least about thirty per cent. by weight 01' bituminous material having a softening point of about F. to about 325 F. and containing at least about twenty-five per cent. by weight of finely-divided solid material that is unmeltable and heat resistant when subjected for 5 minutes to a temperature of about 1200 F. and that is uniformly incorporated and intimately comminled with the bitumen in said granules as an integral part of said bituminous granules, the said finely-divided solid material containing about two per cent. to about thirty per cent. by weight or the bituminous granules of matter volatilizable upon 5 minutes exposure at 1200 F. and the said composition having a viscosity index of at least about 15 minutes, thereby softening the bitumen in said contiguous granules adjacent the air from said burning material, the bi- CERTIFiCATE 0F CORRECTION. Patent No. 2,585,500.; September 2 191 GEORGE ARFIHUR FASOLD, ET AL- It is hereby certified that error appears in the printed specification of the above numbered patent reqniring correction as follows: Page 5, first column, line 11, for "of air insert --of the air": page 5, second column,

line 52, strike out "registered" and. insert instead --regarded-; page 7,

second column, line 25, clsim 9, for "elbitumen" read --the bitumen--.; and.

that the said Letters Patent should be read with this correction therein that the same may conio m to the record of the case in the Patent Office. I

Signed and sealed this 25th day of December, A. Do 1915.

Leslie Frazer (seal) First Aseietant Commissioner of Patents,