US3537873A - Process for rendering vegetation fire retardant - Google Patents

Description

United States Patent 3,537,873 PROCESS FOR RENDERING VEGETATION FIRE RETARDANT Edward R. Degginger, Convent Station, N.J., assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing. Continuation-impart of application Ser. No. 728,822, May 13, 1968. This application June 27, 1968, Ser. No. 740,452

Int. Cl. A01n 1/02; C09d 5/18 US. Cl. 1173 9 Claims ABSTRACT OF THE DISCLOSURE Aqueous solutions containing from 0.5 to 5.0 weight.

percent water-soluble vinyl alcohol polymer, from 0.5 to 5.0 weight percent alkali metal borate, and preferably from 1.0 to 10.0 weight percent C to C polyol and at least 0.5 weight percent urea are effective fire retardants for combating fires, especially forest, brush and range fires.

BACKGROUND OF THE INVENTION This application is a continuation-in-part of my copending application Ser. No. 728,822 filed May 13, 1968, now abandoned.

Forest, brush and grass-range fires cause enormous damage each year, for example, in the decade 1948- 1957, over 100 million acres of forest land were destroyed by fire. Not only is valuable timber destroyed, but frequently houses, business structures, and lives are lost. The threat of such fires is ever present in many areas of the country, particularly during the drier months of the year. Such fires will hereinafter be referred to as forest fires, although it will be understood that the burning vegetation may comprise trees, leaves, or other dead vegetation, shrubs, bushes, grass, farm crops, or any combination thereof. Likewise, buildings having a substantial amount of surrounding vegetation frequently are largely composed of combustible matter and are thereby destroyed when such vegetation catches fire.

The important common denominator of all such outdoor vegetation fires is that, once ignited, the fire spreads from its source through adjacent vegetation or other combustible matter until it is extinguished or burns up all such surrounding combustible matter. Such fires ordinarily spread by successive ignition of unburned vegetation adjacent to the burning area. This vegetation is brought to ignition temperature by heat radiated and convected from the flame front.

Generally, vegetation must be very close to or even enveloped by flame or superheated by gases in a convection column before igniting. This mechanism results in a more or less continuous advancement of such a fire. Fire spread may also be caused by spotting, that is, ignition by turning brands carried outside the fire area by wind and turbulence. Nearby buildings are very frequently ignited by burning brands falling on the roofs thereof.

One of the most common methods of controlling and suppressing a forest fire is by creating a fuel-less barrier. This may be done, for example, by digging a trench through surface vegetation down to mineral soil ahead of an approaching fire of sufficient width to prevent the fire from crossing. However, this may require a trench of considerable width, i.e., approximately the square of the height of the flames. In some instances, it is desirable to burn off an area containing noxious vegetation, e.g., poison ivy, while at the same time insuring that the fire does not spread to the surrounding vegetation. Under these circumstances, digging of a trench may not be practicable.

Since the early 1950s, use has been made of chemicals to prepare a nonfiammable fire-line either in preventing the spread of forest fires or in burn-off operations. An aqueous slurry or solution is sprayed in a line upon surface vegetation to provide a noncombustible line in the same manner as a trench. More commonly, in the case of forest fires, the aqueous slurry is dropped or sprayed in bulk from a low-flying airplane in a line just ahead of the advancing flame front. The fire, on reaching the slurrycoated or solution-sprayed vegetation, either stops completely or is sufficiently reduced in intensity to enable groundcrews to work safely and effectively with conventional firefighting equipment, for example, water hoses.

Such aqueous slurries or solutions are conventionally referred to as fire retardants in contradistinction to fire extinguishing, suppressing or fighting agents in that a fire retardants function is to render fuel at or ahead of the flame front substantially or completely noncombustible rather than to actually extinguish already burning or glowing material by direct application thereto.

Water alone, although exceedingly effective for a brief period at rendering vegetation noncombustible, is not really usable as a fire retardant since it is rapidly lost after application to the vegetation by evaporation, runoff and absorption into the ground. Desirably, the retardant will adhere to the vegetation to which it is applied and be comparatively nonvolatile and resistant to absorption into the soil. These characteristics collectively determine the effectiveness of the retardant. Other characteristics desirable in a fire retardant include ease of aerial application and from tank trucks, low metal corrositivity and abrasivity, minimal toxicity, and cost, ease of mixing and pumping, and good storage stability. Currently used fire retardants, which generally comprise water as a major constituent, plus one or more thickening agents, have deficiencies in one or more of the above-indicated characteristics. For example, many fire-retardant formulations contain pectin or algin, both of which deteriorate in storage. Other retardant formulations contain high concentrations of sodium calcium borate, which is toxic to vegetation. Particularly desirable in a fire retardant is the ability to render vegetation fire resistant for a more or less prolonged period of time. This requires in general not only that the retardant have good adherence to the vegetation, but also that the retardant be resistant to wash-off by rain and evaporative water loss.

SUMMARY OF THE INVENTION It is an object of this invention to provide a new and improved fire-retardant composition. It is a further object to provide a fire-retardant composition which is inexpensive and substantially noncorrosive and nontoxic.

It is a still further object of this invention to provide a process to retard the spread of forest fires.

Further objects and advantages will become apparent from the description of the invention Which follows in greater detail.

It has now been found in accordance with this invention that compositions containing as essential constituents water, water-soluble vinyl alcohol polymer and alkali metal borate are excellent fire retardants. Watersoluble C to C polyols and/or urea may advantageously be added to such compositions to enhance their effectiveness as fire retardants. The proportions and nature of the above-indicated constituents will be more explicitly described hereinafter.

What the invention comprises, therefore, is the application of various aqueous solutions, as hereinafter defined, to living or dead vegetation at or ahead of a flame front so as to substantially reduce the combustibility of said vegetation. Aqueous solutions per se containing borate and water-soluble vinyl alcohol polymer are claimed in c-opending, commonly assigned US. application Ser. No. 602,760 filed Dec. 19, 1966.

The aqueous solutions as used in the practice of the instant invention contain (a) from about 0.5 to about 5.0 weight percent of an alkali metal borate and (b) from about 0.5 to about 5.0 Weight percent of a water-soluble vinyl alcohol polymer.

Such solutions possess many desirable properties from the standpoint of fire-retardant applications; they are sticky and adhere readily to smooth and irregular surfaces, e.g., leaves, bark, etc. After deposition on vegetation, such solutions form a comparatively impermeable surface skin that results in significantly reduced loss of water constitutent of the solution by evaporation or drainoff.

I have discovered that the addition of about 1.0 to 10.0 weight percent of a C to C polyol, i.e., a C to C polyhydroxy nonaromatic hydrocarbon, to the aqueous borate, plus vinyl alcohol polymer-containing solution has several beneficial effects. The polyol makes the solution both stickier and more resistant to evaporative water loss. The improved stickness of the polycol-containing solution means that a greater percentage of the solution deposited on the vegetation in advance of the flame front will adhere thereto and not drain off onto the ground. Likewise, polyol-containing dilatant solutions have a lower rate of evaporative water loss when deposited on vegetation than non-polyol-containing solutions. This is because of the hygroscopic nature of these polyols. Obviously, both effects serve to render the solution more effective as a fire retardant since the more water present on the vegetation, the less combustible the vegetation is.

I have found, moreover, that the addition of at least about 0.5 weight percent of urea:

to the aqueous solution of alkali metal borate and vinyl alcohol polymer imparts beneficial effects which complement those obtained by the addition of polyol. That is, the solution is rather surprisingly made less viscous by the addition of urea. This reduction in viscosity makes it easier to apply the urea-containing solution to the vegetation using conventional spraying equipment. It also increases the infusion of fire-retardant solution into porous portions of the vegetation, e.g., leaves, bark, etc. Also, urea has been found to actually increase the fire resistance of the treated vegetation. Also, the duration of the fire resistance of the treated vegetation is substantially increased in that, even after complete evaporation of the aqueous component of the deposited solution, the urea being nonvolatile remains behind on the vegetation and serves to significantly reduce the combustibility thereof. Vegetation treated with aqueous solution containing only borate and vinyl alcohol polymer produces only limited flame retardance over untreated vegetation after evaporation of the water. Polyol, although it reduces the rate of evaporative water loss of the deposited solution, has a very limited retardant effect after the water has finally evaporated. An added benefit when urea is incorporated resides in the fact that the addition of urea imparts fertilizing properties to the solution. At least about 0.5 weight percent of urea must be added to impart the aboveindicated beneficial properties to the fire-retardant solution. The maximum amount of urea that can effectively be added is limited in fact only by the maximum amount of urea which is soluble in the solution at handling temperature. An amount of urea by weight approximately equivalent to the amount of water present in the solution is about the maximum practical limit. The exact solubility limit for the urea in any particular solution is, of course, dependent upon the nature and quantity of the other solution constituents, i.e., borate, vinyl alcohol polymer, and polyol.

For reasons of economy, it may be more practical not to incorporate the maximum soluble amount of urea into the fire-retardant solution. I have found that the benefi- 4 cial properties imparted by the addition of urea as above indicated can generally be most advantageously achieved by the presence of from about 1.0 to 20.0 Weight percent of urea in the fire-retardant solution.

Polyol and urea are compatible and both may be incorporated advantageously into the solution in view of the distinct benefits imparted by each. Ordinarily, therefore, the preferred fire-retardant solution will contain alkali metal borate, vinyl alcohol polymer, and both polyol and urea.

The term alkali metal borate, as used in the instant specification and in the appended claims, embraces not only the alkali metal salts of the common boric acids, i.e., tetraboric acid, H2B407, metaboric acid, HBO and orthoboric acid, H BO but also the other boric acids such as HzBgOq, HZBGOH), H2B12019, H6B409, and H B O With the exception of the metaand ortho-borate salts, such alkali metal borates have the general formula:

wherein M denotes an alkali metal and m can range from 1 to 4. Hydrates of the above-enumerated borate salts are also suitable.

Either a single borate salt or any mixture thereof can be used. Ordinarily no advantage accrues from the use of a mixture of borates. Likewise, although alkali metals other than sodium and potassium are perfectly usable, they are not prefered for economic reasons.

The preferred borate is borax, i.e., sodium tetraborate decahydrate.

The term water-soluble vinyl alcohol polymer as used herein and in the appended claims embraces vinyl alco hol polymers having up to 50% of the hydroxyl groups thereof replaced by methoxy, ethoxy, acetyl, propionyl or butyryl radicals, i.e., partially etherified or esterified polyvinyl alcohol. Said methoxy and ethoxy ether radicals can be unsubstituted or substituted with hydroxyl or carboxyl groups. said acetyl, propionyl and butyryl radicals can likewise be unsubstituted or can be halogenor hydroxyl-substituted. Preferably, no more than about 20% of the polyvinyl alcohol hydroxyl groups will be replaced by any of the aforementioned ether or ester radicals. The term water soluble means that the polymer is soluble to the extent of at least 5.0 weight percent in water at room temperature, although heating the water to a higher temperature may be necessary to initially dissolve the polymer.

The vinyl alcohol polymers utilized in the practice of the instant invention can, therefore, be represented by the structural formula:

CHrCH- L (IJRJX wherein x can range from about 1200 to about 5000, preferably 1600 to 3000, and wherein R represents hydrogen-, methyl-, ethyl-, acetyl-, propionyl-, butyryl-, hydroxyl-, or carboxyl-substituted methyl or ethyl, or halogenor hydroxyl-substituted acetyl, propional or butyryl, and wherein at least 50% of said R groups are hydrogen. The water-soluble vinyl alcohol polymers of the instant invention can have molecular weights ranging from about 50,000 to about 450,000, and preferably from about 70,000 to 200,000. As above indicated, preferably at least of said R groups will be hydrogen. Most preferably, the vinyl alcohol polymer is of low enough molecular weight that it will dissolve readily to the extent of at least 5.0 weight percent in water at room temperature without heating.

Vinyl alcohol polymers are conventionally obtained by polymerizing esters of vinyl alcohol followed, where appropriate, by saponification of the ester groups. To prepare the polymers of the instant invention, wherein up to about 50% of the R groups are acyl, one polymerizes the corresponding vinyl ester to afford the polyvinyl ester having all R groups acyl and then partially saponify said polyvinyl ester and thereby remove 50% or more of the acyl groups. For example, to prepare polyvinyl alcohol containing 20% acetyl groups, polyvinyl acetate would be 80% saponified and the remaining 20% acetyl groups be left unsaponified. To prepare the methoxy and ethoxy ether derivatives of polyvinyl alcohol, a fully saponified material, i.e., polyvinyl alcohol having substantially 100% hydroxy groups, as would be obtained by total saponifi-cation of a polyvinyl ester, is etherified up to the desired degree, that is, up to about a maximum of 50% of the hydroxyl groups can be etheried using conventional etherification agents such as diazomethane, dimethyl sulfate or diethyl sulfate.

The preferred concentration of alkali metal borate and vinyl alcohol polymer in the fireretardant solutions of this invention range from about 1.0 to 3.5% by weight of each.

The term water-soluble polyol as used in the instant application connotes a C to C polyhydroxy nonaromatic hydrocarbon, i.e., alkane, alkene, cycloalkane or cycloalkene, having from 2 to 6 hydroxyl groups. The term water soluble, as applied to such polyols, connotes that the polyol is soluble in water to the extent of at least 25 weight percent at 25 C.

Examples of suitable water-soluble C to C polyhydroxy nonaromatic hydrocarbons include, for example, ethylene glycol, diethylene glycol, triethylene glycol, trimethylene glycol, monoand dipropylene gycol, glycerol, erythritol, pentaerythritol, trimethylol ethane and propane, arabitol, adonitol, xylitol, mannitol, sorbitol, iditol, dulcitol, and the various isomeric cyclohexane triols and n-hexane triols. The preferred polyols are liquids at room temperature. Most preferred are ethylene glycol, propylene glycol, and glycerol. As hereinbefore indicated, the preferred concentration of triol in the fire-retardant solution ranges from 1.0 to 10.0 weight percent, most preferably 3.0 to 7.0 weight percent.

If desired, the fire-retardant solutions of this invention need not be prepared until immediately prior to use. Such solutions can most easily be prepared by simultaneous or consecutive addition of the desired quantities of alkali metal borate and vinyl alcohol polymer and, where desired, polyol and/ or urea, to agitated, heated water. Alternatively, a mixture of borate and vinyl alcohol polymer and polyol and/or urea in the desired proportion may be added to heated, agitated water. With cold watersoluble vinyl alcohol polymer, the water need not be heated. Alternatively, separate aqueous solutions of polyvinyl alcohol and borate, urea and/or polyol may be prepared and combined to afford the desired fireretardant solution. It is thus apparent that the polyvinyl alcohol, borate, polyol and urea constituents of the solution can all be stored and the fire-retardant solution prepared therefrom immediately before use. Such a storage procedure, of course, conserves space and the polyvinyl alcohol, borate, urea and polyol are substantially indefinitely storage stable under ordinary storage conditions.

As heretofore indicated, the fire-retardant solutions of the instant invention are applied to, i.e., deposited upon, a band of vegetation in front of an advancing fire. Such application may be by means of hand-carried or vehiclemounted pressure sprayers or by dumping or spraying from aircraft. The preferred method of application will depend upon the terrain and the nature of the vegetation being covered.

A suitable application rate will depend upon the thickness and height of the vegetation being covered. In general, from /2 to 10 gallons of fire-retardant solution per 100 square feet of vegetation is suitable. Obviously, the thicker is the vegetation to be covered with solution, the greater is the amount of solution that should be used to significantly reduce the combustibility of said vegetation. In most circumstances, from 1 to 5 gallons of solution per 100 square feet of vegetation will render the vegetation substantially noncombustible.

The invention can be more fully understood by reference to the following examples. All parts are parts by weight unless otherwise expressly noted.

EXAMPLE 1 175 grams of polyvinyl alcohol (molecular weight about 100,000) was added with stirring to 7000 cc. of water heated to 95 C. forming a homogeneous solution. There was added with agitation 175 grams of borax to 1400 cc. of water heated to 95 C. forming a homogeneous solution. The borate and polyvinyl alcohol solutions were then combined to form a single homogeneous solution, and after cooling to about 40 C. charged to 2 /2- gallon fire extinguisher and pressurized with nitrogen to 120 p.s.i. A fiat, rectangular area of bare ground 10 x 20' was covered with a 6-inch deep layer of vegetation comprising of leaves, twigs and branches up to 1 inch in diameter. A 2-foot wide band of this vegetation running between approximately the midpoints of the two opposite long sides of the rectangle, i.e., a 20-sq. ft. area of vegetation, was uniformly sprayed by means of the fire extinguisher with about 2700 cc. of the solution. After a wait of 2 hours, an upwind corner of the vegetation was ignited. Wind velocity was approximately 5 knots. All brush contiguous to the point of ignition was eventually consumed by fire up to the treated band. The treated band did not burn nor did the untreated vegetation on the other side of the band from the fire ignite. Two hours after the ignited portion had completely burned, the treated band could still not be ignited with burning newspaper.

EXAMPLE 2 Simulated natural brush consisting of douglas fir pine needles was used to test a number of other solutions for fire retardance. The test consisted of covering a 2' x 5'- rectangular steel plate with a 2-inch thick layer of pine needles. A 4-inch wide band of needles completely across the pine needles at about the midpoint of the 5 sides of the needle layer was sprayed with a variety of solutions in the amounts shown in the table below. After standing for 2 hours, a corner of the needle bed was ignited. In all cases, the area of needles contiguous to the point of ignition up to the treated band was completely burned up. In all cases, the treated band did not ignite and the fire did not cross the treated band to the area of needles on the other side thereof.

The following solutions were used. In all cases sufficient water was used to yield 100 grams of solution.

Weight percent Approximate grams solution Polyvinyl alcohol 1 Borate 2 in deposited in solution solution on band 1 See following table:

Molecular Polyvinyl alcohol weight;

A=l00% polyvinyl alcohol (100% saponified polyvinyl acetate) 85, 000 B =100% polyvinyl alcohol (100% saponificd polyvinyl acetate) 175, 000 C saponlficd polyvinyl aceta 100, 000 D =50% saponified polyvinyl acetate 125, 000 E Polyvinyl alcohol 30% ethoxylated 93, 000

Z Borate: A=Borax; B=Potassium tetraboratc pentahydrate; C= Sodium mctaborate (NaBOg); D=Sodium ortlioborate; E=N 2213204.

7 EXAMPLE 3 Approximate Weight percent grams solution deposited Polyol l Urea on band 1 A: Glycerol; B= Ethylene glycol; C=propylene glycol; D=cyc1ohexane triol.

The enhanced effectiveness of the polyol-containing solution was shown by the fact that treatment of a band with solutions (1) and (7) rendered the band an efiective barrier for a period of 3 days. No rain fell during the period, but each morning extensive due was present on the needles which was allowed to evaporate before ignition. The band treated with solution (8) was not fully effective as a barrier for longer than about 36 hours.

The enhanced effectiveness of the urea-containing solution was demonstrated by the fact that a band of needles treated with solutions (25) and (9-11), inclusive, retained more eifectiveness as a fire barrier even after all the water in the fire-retardant solution deposited thereon had completely evaporated than did those where urea was absent, i.e., solutions (1), (7) and (8).

Various modifications will be apparent to one skilled in the art, and it is not intended that this invention be limited to the details in the specific examples presented by way of illustration. Accordingly, the scope of the invention is limited only by the appended claims.

I claim:

1. A process for rendering vegetation substantially noncombustible, comprising applying to said vegetation a fire retardant aqueous solution consisting essentially of (a) water; (b) from about 0.5 to about 5.0 weight percent of an alkali metal borate; and (c) from about 0.5

to about 5.0 weight percent of a water soluble vinyl alcohol polymer, said solution being applied at a rate ranging from about 0.5 to about 10.0 gallons per 100 square feet of vegetation.

2. A process in accordance with claim 1 wherein said aqueous solution is applied at a rate ranging from 1 to 5 gallons per 100 square feet of vegetation.

3. A process in accordance with claim 1 wherein said alkali metal borate and said vinyl alcohol polymer are each independently present in said solution at a concentration ranging from about 1.0 to about 3.5 weight percent.

4. A process in accordance with claim 1 wherein said alkali metal borate is sodium tetraborate decahydrate.

5. A process in accordance with claim 1 wherein at least about of the hydroxyl groups of said vinyl alcohol polymer are unsubstituted.

6. A process in accordance with claim 1 wherein said fire retardant solution additionally contains from about 1.0 to about 10.0 weight percent of C to C polyol.

7. A process in accordance with claim 1 wherein said fire retardant solution additionally contains at least about 0.5 weight percent urea.

8. A process in accordance with claim 7 wherein said urea is present in an amount of up to about 20.0 weight percent.

9. A process in accordance with claim 7 wherein said solution contains as an additional component from about 1.0 to about 10.0 weight percent C to C polyol.

References Cited UNITED STATES PATENTS 2,526,083 10/1950 Nielson 1173 2,681,326 6/1954 Christianson. 2,809,949 10/1957 Orth l17137 X 2,917,476 12/1959 Peterson et al. 117-137 X 2,935,471 5/1960 Aarons et al 117137 X 3,157,964 11/1964 Ferguson et al 117-3 X 3,178,855 4/1965 Siegel 1173 X FOREIGN PATENTS 584,717 1'0/1959 Canada.

WILLIAM D. MARTIN, Primary Examiner H. I. GWINNELL, Assistant Examiner US. Cl. X.R. 117137