US2858895A - Methods and compositions for controlling fires - Google Patents

Description

States met METHODSAND COMPOfiITIONS FOR CONTROLLINGLES George A. Connelblaos Angeles, Califqassignor to United States. Borax 8av Chemical- Corporation, Los' Angeles, Calif.,:a;corporation of N evada.-.

No Drawing. Application ll iareh 29, 1%? Serial'No. 649,291"

Thisinvention hasto do with methods andcomposi-v tions for controlling. fires;

Whereaswthe invention .;is useful for. many different.

types offirecontrol, it isespeciallyefiective as an aid in checking or.preventing the/spread of fires.

An importantpurpose' of the present invention is to providemeansandmethods for. treating solid fuel in the path of a fire to reduce its flammability and thereby to cluding light brush, leaves. and grass, as welLas heavybranches...and :tree. trunks; and, also .includes other solid combustible materials; such. asuare'. commonly involved in.structurakfires...

In controlling. .fir'es .in;many types of. fuel, particularly in thepresenceof. strong. winds, .it is often.difiicult or impossible to attack the fire directly where it,-is.burning,

intensely. i. That isespecially. true of fires in .forests and inthick brush and scrubsgrowths, such as abound. in.-

the-southwestern'part. ofytheUnited:States. :Under such conditionsitishighly desirable tolimit thespreadrof the fire. Thatis sometimes; attempted by clearing away the fuel; from an.area.in. the path ofthe fired However, to

beefiective, such-clearing mustbefairly complete within astrip'of appreciable width. Once at fire hasstartedrit isusually. difiicult. or impossible. to. prepare such; a cleared strip: rapidly. enough to. be effective.

Previously-available.methods for..treating fuel to reduce its flammability have; been relatively ineffective: for the presenttpurposefl' For example, spraying.- the fuelqwithwater, inadvance.,of-..a firelmayfbe beneficial for a shorttime, ,butrthe waterutends to-hevaporate rapidly, particularly;asithe.fire approaches; That is especially true under conditions 10f: high wind and/om low humidity=,;; which often accompany dangerousfires;

a large scale. lations frequently-requires aisuccessionofdistinct steps,

sometimes;-separatedbydefinite time: intervals, -for-example .tQ. permit- .-.drying.a And" many. such previously.

knowmtreatmenta compositions. are efiectiveonly if the treated.- .materiaL. is deeply penetrated by. the, chemical;

tion. are toaprovidma relatively economical.composition.r which is,.effective toreducefiammabilityof a. .widevariety:

ofsolid 'f'ue'ls', including those typicallyrinvolved in structural'fires as well as all types of vegetation; WhiChiS:

Qfi'ective when applied primarily to surface areas of the Patented. Nov. 4,1958

fuel; and which becomes effective immediately upon application andremains fullyefiective thereafter at least for a period of hours or days.

In'accordance with one aspect of the invention, fuel in the path of a fire iscoated with anadherent layer consisting esssentially of solid calcium-containing borate.

The borate layer may also contain any suitable-type of binder and may, if desired, include-other fire-retardant ingredients. Relatively minor proportions of further additives, such as willbetypically described, may also;be'

included. I have discovered that such a layerof calciumcontaining borate can be formed on surfaces ofsolid fuel of substantially any type'by applying tothe-fuel a suspension ofsolid finely dividedborate particles in an aqueous medium.

It is preferred to include in that suspension a suitable stabilizing agent to render the suspensionstable vduring storage and transportation. Preferred stabilizing agents.

are those which render thesuspension thixotropic; and

which also act'asa binder for the borate particles after applicationof the suspension to'the fuel.

An important advantage of the present invention is thatthe concentration of active fire-retarding agent in the treating composition is not limited, as in many previously available fire-retardantcompositions, by considerations of solubility. Hence the low solubility in water of, calcium-containingborates does not prevent their. elfective application to the fuel by the methods of the invention. That'is accomplished by applying, the boratein the form of an aqueous suspension, rather than as a solu-.

tion.

The compositions of the invention may be employed in a wide variety of ways. for application to fuel in the-path of a fire tocheck its spreading. Since-suchapplication may be made rapidly and becomesefiective immediately, the invention. is particularly valuable: for checking the spread of existing plied to fuel in the path of a fire either closely in advanceof the fire or while the fuel is already actively burning. That type of application, which may often'be made advantageously from aircraft, is particularly well adapted for controlling forest fires in which the upper branches of trees are burning. Such fires are commonly known as crownfires and are particularly difficult to control with previously available methods.

In the present specification and claimsthe phrase in the path of a fire includes potential-as well as existing fires, and includes not only portions of the fire path well in advance of any existing fire, but also portions that are already burning.

A particular advantage of the'calcium-containing borate coatings of the invention for the present purpose is that they are very light in color, typically white or substantially white. That fact, provides a distinctive ap pearance of treated areas, showing clearly whichareas have been treated and which have not. It also facilitates observation of the degreeof coverage that has been attained, permitting maximum economy of material without sacrifice of effectiveness. That is especially important in combatting firesinremote locations, where economy of material isv often critical.

One illustrative calcium-containing borate that may be They are particularly useful:-

employed in the invention is the sodium-calcium borate that corresponds essentially to the formula Sodium-calcium borate of that type is available, for example, as a naturally occurring mineral known as ulexite. Ulexite is mined especially in Kern County, California, and is also imported from Chile. Ulexite is known both in massive form and in a filimentary form known as cottonball.

Another illustrative calcium-containing borate is the calcium borate that corresponds essentially to the formula Ca B O -H O. Calcium borate of that type is available as the naturally occurring mineral known as colemanite, which is mined, for example, in Inyo County, California.

A further example of calcium-containing borate, which is particularly convenient and effective for the present purpose, is a type of natural ore that is essentially a mixture of colemanite and ulexite and contains also an appreciable proportion of insoluble gangue material. Natural ore of that type is mined, for example, at Shoshone in Inyo County, California. For convenience of description, that type of ore will be referred to herein as Shoshone ore,-but without implying any limitation as to actual origin. A typical variety of such Shoshone ore contains substantially 58% ulexite, 23% colernanite and the remainder insoluble gangue. The borate components of such ore may thus be characterized as so dium oxide, calcium oxide and boron trioxide in an overall relative ratio approximating 1:328, respectively, by weight. The insoluble gangue of Shoshone ore is useful in aiding formation of an aqueous suspension of the ore and in stabilizing the resulting suspension, but, from the standpoint of the direct fire retarding action of the resulting coating on the fuel, the gangue is not an essential component of the composition.

'It is desirable that the calcium-containing borate be finer than about 50 mesh. Superior results are obtained when it is ground to such a relatively fine mesh size, for example, that about 80% of the material will pass a No. 200 U. S. Standard screen. When coarser material is used it is preferred to exclude any particles larger than about 50 mesh, both to avoid risk of clogging the spray nozzle and because larger particles reduce the strength and adherence of the resulting coating on the fuel.

In accordance with the invention, calcium-containing borates such as those illustratively described can be applied to surfaces of fuel as an aqueous suspension and is then immediately appreciably more effective than a corresponding weight of water for checking a fire. Moreover, upon evaporation of the liquid water, such an aqueous suspension will form a solid, hard and remarkably durable coating. That coating layer has been found to greatly reduce flammability of the fuel. That result is particularly striking when the fuel is exposed briefly to a very hot fire, as typically occurs, for example, in wild brush and forest fires.

Such reduction in flammability of fuel is obtainable with suspensions of calcium-containing borate over a wide range of borate concentrations. In general, effective results may be obtained with compositions comprising from about 2 lbs. to as much as lbs. or more of ca1cium-containing borate per gallon of water. For any particular application, the most effective concentration of calciumcontaining borate in the aqueous suspension depends upon such factors as the nature of the fuel to be treated, the detailed manner of application and the amount and type of stabilizing agent, if any, that is included in the composition. Under most practical conditions the preferred compositions contain from about 3 to about 8 pounds of calcium-containing'borate per gallon of water. It is often convenient, however, to make up a stock suspension containing a relatively large concentration of solid ingredients, for example, from 8 to 20 pounds per gallon of water, and to dilute that stock solution with water to increase its fluidity before actual use.

Any convenient mixing procedure may be employed in preparing the aqueous suspension of borate. Measured quantities of Water and of dry granular ingredients may be added to a mixing tank provided with any suitable automatic agitating means. Such means may comprise, forexample, a paddle-type agitator or a centrifugal pump with a by-pass connection from the pump outlet back to the bottom of the tank. The resulting mixture is stirred until a uniform suspension is obtained. It is preferred to include a suitable agent to render the suspension stable, so that, once mixing is completed, agitation may be stopped, at least until just before the suspension is to be used.

The aqueous suspension may be distributed over the fuel surface in any convenient manner. Application by spraying is particularly rapid, effective and economical when the fuel to be treated is reasonably accessible. It is preferred to utilize a type of nozzle that produces a fine spray, one such nozzle being known as a Bean spray gun. A pump pressure of about 100 to 200 pounds per square inch is preferred, but effective coverage can usually be obtained with much lower pressures such as are typically available with fully portable equipment. When suitable power pumps are available, a nozzle opening of about inch has been found effective and will typically deliver from 4 to 8 gallons of suspension per minute.

The compositions of the invention are also particularly well suited for aerial distribution. For example, an aircraft of the type employed for spraying crops may be fitted with tanks having a valve-controlled outlet of large I diameter, typically 6 to 24 inches, for rapid dumping of a found in the lower hills of Southern California may be' effectively treated in most instances by applying to the vegetation on each square feet of ground surface 5 from about 10 to about 20 pounds of calcium-containing borate in the form of an aqueous suspension per 100 square 7 By such application strips of treated fuel of suitable width may be prepared, extending feet of ground surface.

across the path of the fire. The most advantageous width for such strips varies with such factors as the detailed nature of the fuel, the slope of the ground and the amount and direction of the wind. It has been found, in general, that a fire can be effectively checked by so treating a strip of about the same width that would be required if the ground were completely cleared of vegetation. Thus a strip 4 to 6 feet Wide is usually suflicient to check a fire on level ground in absence of wind, whereas a strip 6 to 8 feet wide or more may be preferable under less favorable conditions. Backfiring has been successfully carried out from a strip 2 to 4 feet wide treated as described by crews moving through grass and light brush at a fast walk.

When trees or clumps of tall brush occur inside a fire line of the described type, it is desirable to treat the surface fuels at the base of the trees and also the lower part of each crown. For example, scrub oak treated in that manner typically does not ignite and crown out, whereas untreated trees of the same type burn readily, producing a serious source of spot fires.

Suspensions of calcium-containing borate can be rendered stable for an indefinite period by providing asuitable stabilizing agent. A preferred type of stabilizing agent comprises a finely divided inorganic solid which is chemically inert with respect to the borate and which renders the solutionthixotropie'; Clays-.of'ithe montmorile for the present purpose. Illustrative.of;such* days are hectorite and Wyoming bentonite. Such clays may be combined with calcium-containing borate, suchaszul'exite, colemanite, or a mixture. of thensame, innaratiotofclay to borate. of from about 1:20 to 'about.1:4to' give-the borate suspension. a -useful degree oftstability. Effective stabilitymay also be. produced,- for example, with a-ttype of clay that is commonly available-under .thetradename Aquagel. A further example of a useful stabilizing agent is .the insoluble gangue portion-ofthe natural ore already referredI-to as C ore;. Thatgangue comprises primarily a shale that tends to break down on'wetting into a fine clay. Becauseof thatiaction.of:the insoluble component, finely divided-C oremay besuspended directly in water without other additive to produce a suspension that is remarkably stable and effective overawide range of concentrations.

Stabilizing agents of the type just described have the particular advantage that,:upon drying of the composition after applicationto thefuel, they act-as-a-bindert-which tends to improve the uniformityand durability of the coating-that is produced. By thus improving the'physicalnatureof the coating layer, stabilizingagents of the-de scribed type contribute *appreciablyto therpractical eifeca tiveness of the treatingcompositionsr That indirect ac.- tion, however, is to be clearly distinguished. from the direct fire retarding action of thesolid calcium-containing borate, which preferably comprises the major portion of the coating layer.

Further additives may advantageously-beincluded in the compositions of the invention. .For example, it is sometimes desirable to provide a minor proportion of a wetting. agent to promote uniform-wetting ofthe'fuelsurface by the aqueous borate suspension. .Such enhancement ofthe wettingqualities of the composition tends toproduce a.

more uniform and continuous coatingof the fuel, It may 7 also be extremely helpful in obtaining effective penetration of the suspension to portionsv of the fuel thatare. partially hidden or enclosed, for example penetration. mm thick brush or. into a thick coveringoflitter onthe ground. Useful wetting .agents. for such purposes include,.. for. example, aryl alkyl sulfonates, which. are available. under such trade names as Oronite D-40 and Petro P."

Adherence to the fuel of the film, of solid calcium-containing borate may be further increased by including in the composition a suitable minor proportion of a sticking agent, such asthe animal protein materialfsold as a commercial sticking agent under the trade name Armours Sticker; the long-chain fatty acidpreparation with di ethylene glycol abietate which is available under the trade name DuPont Spreader and Sticker; or the lignin sulfonate which is available under the trade name Orazan. From about 1 to about 10% of such sticking agents may be desirable. The duPont preparation also acts as wetting agent and has the particular advantage of not interfering with normal stability of the suspensions.

The compositions of the present invention are well adapted for application to the fuel in the form of a foam. A suitable foam, consisting of a mass of very small bubbles of the fluid composition, may be produced by adding to the herein described compositions an effective amount of a suitable foaming agent, and applying the composition to the fuel by spraying from a known type of foam-producing nozzle. From about 1 to about 3% of a conventional foaming agent has been found to be effective under most conditions.

Application of the compositions of the invention as a foam tends to promote their adherence to certain types of fuel which have an unusually smooth or waxy surface, such, for example, as the leaf surfaces of Manzanita brush. Moreover,'the foam can be built up on the fuel to a considerable thickness without consumption of an undue amount of material. It has been found particular- 1y effective-under some. conditionslorinclude a 'foamirfgz' agent in: compositions for applicationzby aerial dropi Up-;-. on release from the aircraft the; suspension then becomes;

a light, fluify and expanded material capable ofrcovering a relatively: large area.

The :following: particular: compositions are :described'i as illus trati'onsof the wide :varietyofcompositionsawithinthez: scope of. theminventiont. However; that scope is not in= tended tobe limited-bytparticulars of theillustrative ex amples, but is defined by the appended claims;

Example 1=.An. illustrative "and;- highly effective-compositiomin accordance with th-cipresent iI1V6I1tl0I1'.WaS" prepared by grinding ulexite to a particle size such-that:

substantially 80% passed a 200. mesh" screen-rand. suspending thewfinely divided=ulexite in'water ata concen-.: tration of 4- pounds-ofrulexiterper gallon. of water. :The resulting suspension was effectively. stable for;periods1.of:

the order of onehour, and could be maintained fluid for longer-time periods .-by mild agitation". tions containing from about 3 to about '8 pounds. of ulexite per gallonrofwwaterare: also highly t-satisfactory.

Example 2.Finely divided. ulexiteaof'the typ-eem:

slightly; viscous suspension 1 which was 1 highlyrstable and could .bewstored for several days without; significant settling.

' Example: 3: Colemanite: was ground. to predominantly pass a 200 mesh screen and was suspended. in water in a concentration. of'4 pounds per gallon..of.;water.; .The. resulting-suspension was similar to that. of Examplel Colemanite may also be; employed at concentrations.

from about 3 to 8 pounds per gallon.of.water. .'I'he stability of; such suspension can be. greatlyincreasedby addition of astabilizingv agent of thedescribed' type, for example hectorite, in a ratio'of' about 0.05 to.0.2.pound of agent-.per pound of colemanite;

Example. 4 ;-A particularly economical andiconvenient composition consists essentially of an aqueous'suspem sion of finely ground shoshonesore'; already described;

For example, such ore was ground to. a particlesize predominantly minus 200 mesh and'stirred in water atconcentrations of about 3 to about 8- pounds per gallon of water, the preferred .value. being approximately 4' pounds per'gallon of water.: The resultingisu'spensions' were highly stable and could readily'zbe handled by hydrauliotmethods;

Example 5.Ulexite and colemanite were finely ground and suspended in water in a ratio of approximately 5 pounds of ulexite and 2 pounds of colemanite per gallon of water. Stability of the resulting suspension is adequate for many purposes, but may be greatly increased by adding a stabilizing agent of the type described, for example a Wyoming bentonite, in a ratio of from about 0.05 to about 0.2 pound of the agent per pound of the other solid ingredients.

All of the compositions illustratively described in Examples 1 through 5 give satisfactory surface coverage on many types of fuel. Under certain conditions that action may be further improved by the use of further additives, as has already been described.

An indication of the effectiveness of the compositions of the invention was obtained by assembling a pile of cut dry brush approximately 12 feet in diameter and 6 feet high. The downwind half of the pile was then sprayed with the composition of Example 4 in sufiicient quantity to coat substantially all exposed surfaces of the fuel. Evaporation of the water left the fuel coated with a hard dry solid film consisting essentially of calciumcontaining borate. The untreated half of the brush pile was then set on fire. The untreated brush burned hotly and was substantially consumed in a few minutes. Most Composi-I' of the treated brush remained unburnt. tions illustratively described in the other examples are similarly effective in checking the spread of fires.

I claim:

1. A composition for coating surfaces of fuel in the path of a fire to retard the same, said composition consisting essentially of an aqueous suspension of finely divided solid calcium-containing borate in a concentration between about 3 and about 20 pounds of said borate per gallon of water.

2. A composition as defined in claim 1, and in which the solid calcium-containing borate consists essentially of ulexite.

3. A composition as defined in claim 1, and in which the solid calcium-containing borate consists essentially of calcium borate and sodium-calcium borate in a weight ratio of approximately 2 to 5.

4. A composition as defined in claim 1 and in which the solid calcium-containing borate is predominantly finer than about 50 mesh. 7

5. A composition for coating surfaces of fuel in the path of a fire to retard the same, said composition consisting essentially of an aqueous suspension containing from about 3 to about 20 pounds per gallon of water of solid finely divided solid calcium-containing borate and containing also a finely divided substantially insoluble solid stabilizing agent in a concentration between about & and about A that of said borate, said stabilizing agent rendering the suspension stable and thixotropic.

6. A composition for coating surfaces of fuel in the path of a fire to retard the same, said composition consisting essentially of an aqueous suspension of a finely divided natural ore in a concentration between about 3 and about 20 pounds per gallon of water, said ore consisting essentially of sodium borate, sodium-calcium borate and insoluble gangue.

7. A composition for coating surfaces of fuel in the path of a fire to retard the same, said composition consisting essentially of an aqueous suspension containing between about 3 and about 20 pounds per gallon of water of a finely divided solid borate composition comprising sodium oxide, calcium oxide and boron trioxide in overall relative proportions approximating 1:3:8, respectively, by weight.

8. The method of retardin'g fire in solid fuel that has an exposed surface; said method comprising forming on a major portion of the fuel surface a substantially continuous adherent layer consisting essentially of solid calcium-containing borate.

9. The method of retarding fire in solid fuel that has The composi- Y the class consistingof calcium borate and sodium calcium borate.

10. The method of retarding fire in solid fuel that has an exposed surface; said method comprising forming on a major portion of the fuel surface a substantially continuous adherent layer of a natural ore consisting essentially of calcium borate, sodium-calcium borate and insoluble gangue.

11. The method of retarding fire in solid fuel that has an exposed surface; said method comprising distributing over the fuel surface an aqueous suspension of solid granular calcium-containing borate, the particle size of said borate being predominantly finer than about mesh, and the rate of application of the suspension being suflicient to produce, upon evaporation of water there from, a solid coating over a major portion of the fuel surface.

12. The method of retarding fire in solid fuel that has an exposed surface; said method comprising distributing over the fuel surface an aqueous suspension of granular natural ore consisting essentially of calcium borate, calcium-sodium borate and insoluble gangue, the particle size of the ore being predominantly finer than about 50 mesh, and the rate of application of the suspension being sufficient to produce, upon evaporation of water therefrom, a solid coating over a major portion of the fuel surface.

13. The method of retarding fire in solid fuel that has an exposed surface; said method comprising distributing over the fuel surface an aqueous suspension containing between about 3 and about 10 pounds per gallon of Water of a finely divided solid borate composition comprising sodium oxide, calcium oxide and boron trioxide in overall relative proportions approximating 1:3:8, respectively, by weight, the rate of application of the suspension being suificient to produce, upon evaporation of water therefrom, a solid coating over a major portion of the fuel surface.

14. The method defined in claim 11 and in which the said aqueous suspension is distributed over the fuel surface in the form of a foam.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A COMPOSITION FOR COATING SURFACES OF FUEL IN THE PATH OF A FIRE TO RETARD THE SAME, SAID COMPOSITION CONSISTING ESSENTIALLY OF AN AQUEOUS SUSPENSION OF FINELY DIVIDED SOLID CALCIUM-CONTAINING BORATE IN A CONCENTRATION BETWEEN ABOUT 3 AND ABOUT 20 POUNDS OF SAID BORATE PER GALLON OF WATER.