CA1116386A

CA1116386A - Fighting fire

Info

Publication number: CA1116386A
Application number: CA000305737A
Authority: CA
Inventors: Peter J. Chiesa, Jr.
Original assignee: Enterra Corp
Current assignee: Enterra Corp
Priority date: 1977-06-21
Filing date: 1978-06-19
Publication date: 1982-01-19
Also published as: JPS549497A; BR7803892A; HK58883A; DE2826224A1; FR2395044B1; BE868270A; AU3593678A; FR2395044A2; GB1601537A; AU520410B2

Abstract

FIGHTING FIRE

Abstract of the Disclosure Fire-fighting foam effective against burning hydro-philic or polar liquids like lower alcohols, ketones, etc.
is made from concentrate containing thixotropic thickener dissolved in large amount, yet has a tolerable viscosity particularly when stirred. Heteropolysaccharide-7 or chain-shortened modifications of it are suitable for this purpose. The concentrate can also be made suitable for fighting fires on hydrophobic liquids by adding surfactants that cause aqueous film formation over such liquids.

Description

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The present invention relates primarily to the fighting' , of fires o,n hydrophilic liquids.
Among the objects of the present invention is the provision of novel compos~tions with which to fight such fires, i as well as novel fire-fighting processes that make use of such ~ compositions. Il !
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~ ~ tion will be more fully expoundad in the following descrlption ,1 of several of its examplifications~ ¦ .
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3~f;i i The fighting oE fires on hydrophilic li~uids such as isopropyl alcohol, acetone, and the like, has heretofore not reached the advanced state that has been attained in the art of fighting fires on hydrophobic liquids. Aqueous foams are considered the most desirable materials for fighting fires on large bodies of flammable liquids, such as in storage tanks, but hydrophilic liquids have an undesirable effect on such foams.
U.S. Patent Nos. 4,060,489 and 4,060,132 show that the presence of a thixotropic polysaccharide in dissolved condition in the aqueous liquid from which the foam is prepared, causes the foam to gel and become a bubble-containina mat when it contacts the hydrophilic liquid. Such mat floats on the burning liquid and protects the ~oam above it so that the fire is fairly rapidly extinguished.
Because the Eoams are generated by Eoaming an aqueous concentrate that is diluted with many times its volume of water, the concentration of the thixotropic polysaccharide in the diluted solution is quite small so that it is difficult to develop a very good, stable mat formation. Moreover it is not too practical to merely dissolve a very high concentration of the thixotropic polysaccharide in the aqueous concentrate, inasmuch as this produces a concentrate that is too stiff a gel to ~e rapidly diluted to foaming dilution or to be suitable for use with the proportioning foamers that have been developed. As a result special solvents have been used to make the concentrates, or thic~eners have been incorporated in such a way that the concentrat~s themselves are not too stable.

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According to the present invention very desirable i fire-fighting concentrates are in the form of solutions essen-; tially in water~ which solutions have dissolved in them a thixotropic polysaccharide thickener that increases their Brookfield spindle 4 viscosity at 20C to not over about 3,000 centipoises at 60 rpm spindle speed, and the concentration of the thickener in the concentrates being at least about 1% by weight.
A particularly desirable thixotropic polysaccharide is heteropolysaccharide-7 described in U. S. Patent 3,915,B00, as well as somewhat degraded forms of heteropolysaccharide-7.
Among other advantages these polysaccharides yield more effective foams when such foams are made with the help of sea water, as compared to fresh water. I ~ -Some working examples illustrate the present invention.

Exam~le 1 The following ingredients are combined: ¦
Water 9,240 ml.
; Chlorinated metaxylenol 3.6 gO
Urea 93 g ' /CH2~
Il I,~'CH2cH2cH2cO~a li OH C 2 ! .;
(30% in water)357 ml.

HeteropolysaccharidF-7 122 g.
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2 CH2cH2ocH2cooNa (30% in water) 675 ml.
30% aqueous solution of equimolecular mixture of sodium decylsulfate and .:
sodium octylsulfate 795 ml.
Monobutyl ether of diethylene glycol 300 ml.

Sl(C~3)3- ~~~ ~1 - O - -Si(C~3)3 -.
,C3H6 .
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C,~2 .
~-C2H4SO3~a 3 :

(40 weight percent in 1:1 isopropyl-water mixture ~: by volume) 213 ml.
(C~3)2CF~CF2)nC NH3C2~5 where 20% of the n is 2, 30% of the n is 4, ~ 30% of the n is 6,and .' ;; . 20% of the n is 8 102 g.
~ MgSO4 204 g-: ;

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The heteropolysaccharide-7 is difficult to dissolve directly in water in the abovc-specified amount, and it is pre-ferred to begin by mixing together the first five ingredients;
', using only 12 ml. of the fourth ingredient (the Cg-substituted imidazoline) and adding the fifth in small portions with stirring, followed by pumping this pre-mix through a recirculating pump until smooth. The remaining ingredients are then added and the resulting mixture thoroughly mixedO Its pH should be about 7.1 to 8, and if necessary it is adjusted to that pH with acetic acid -~
or ammonia. Upon completion oflthe stirring associated with the mixing, the product rapidly gels, but the gel is easily liquefied by a little agitation. With a bit of stirring it flows fairly easily. Under the influence of a suction of several inches of mercury produced at the intake of a venturi jet, the gel flows smoothly up into such a suction intake.
When ~e foregoing concentrate is diluted with ten times¦
its volume of water it is readily foamed with air to produce a very effective fire-fighting foam having an expansion of 6 to 8.
When foamed with the apparatus of U. 5. Patent 2,868,301 the foam can be projected a substantial distance. Projected onto a burning liquid as hydrophilic or as polar as ethanol or acetone, the majority of foam thus applied is not broken, but some forms a gel-like mat that does not dissolve in cuch liquid rapidly enough to significantly diminish the spreading of the projected foam over the burning surface and the e~tinguishing of the fire by the foam. The formation of the mat involves geIation of the liquid contained in the foam and loss of water from the gelled 1, 6.

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liquid to the hydrophilic liquid through syneresis, and takes place so rapidly that the foam bubbles are trapped in the mat causing it to float on the hydrophilic liquid. This action takes place with about eqllal effectiveness when the diluting water is tap water or sea water or any combination of these two waters, and resulting diluates have about the same fire-fighting effective-ness.
Also when used to fight fires on hydrophobic liquids, the foregoing foam shows about the same good results as the foams of British Patent 1,381,953 and U.S. Patent No. 3,849,315.
Example 2 The formulation of Example 1 is modified in two respects. Instead of the 122 grams of heteropolysaccharide-7, there is added 138 grams of a degraded form of that polysaccharide, . e~ /G f~ c and instead of 102 grams of the ethyamine salt of the perfluorinated mixed acids, 100 grams of the free mixed acids CF 3 ( CH 2 )mCOOH are used, where 40% of the m is 4, ` 35~ of the m is 6, and 25% of the m is ~.
The degraded form of the polysaccharide is prepared by adding a little HCl to the fermentation broth in which it is formed to brlng its pH to 6.5, and then heating the acidified broth to 90C for thirty minut~es. The degraded product is then recovered by the same technique used to recover the unde~raded material.

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ll 1., Other hydrolysis techniques can ~e used to degrads the fermentation pxoduct if desired. Alternatively degradation can be effected by heat alo~e or by oxidative attack. Thus a one hour boiling of the fermentation broth causes degradation, or the fermentation broth can be treated with 1/20 its volume of 30% H2O2 at 70DC for 30 minutes, and a similar degradation can be effected with 1/10 its volume of acidified 2% potassium permanganate at 50~C. The degradation is not major and the degraded product is still quite insoluble in lower alcohols so ~.
-i that the recovery technique does not have to be modified~ It is estimated that the degrading step shortens the polymer chains about twenty to thirty percent and has no other significant effe~l .
The viscosity of a 1% aqueous solution of the polymer at low shear is generally reduced about 1/3, and this is the important result that is desired.
Because of the viscosity reduction the formulation of Example 2 contains more of the polysaccharide and when diluted and foamed it is somewhat more effective in extinguishing fires on hydrophilic liquids. Thus when a typical concentrate of Example 2 has its viscosity measured with a Brookfield LVF
viscometer using a ~o. 4 spindle, it gives the folIowing readings at the designated spindle speeds:

'~Spindle Speed in Viscosity I_evolutions ~ r Minute in Centipoises 0 3 142,000 0.6 95~000 i 1.5 53,600 3.0 32,000 6.0 17,700 12.0 9 450 ' 30.0 4,200 6~.0 2,130 8.

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Because the 60 rpm viscosity is below 3000 centipoises, such a concentrate is well s~lited for use with standard propor- ¦
tioning foamers. Because of the high content of the poly- !
saccharide, over 1.1% by weight of the concentrate, it can be diluted with more than 10 times its volume of water and still do a very good job of extinguishing fires. A typical fire test gives the following results on a burning batch of 60 gallons 9g%
isopropyl alcohol in a round pan providing a 40 square foot surface. I
Preburn time 3 minutes -~*

Dilution with 16 2/3 its volume of tap water Application rate 0.15 gallons of diluate per minute per square foot of surface Expansion 8.8 Control 2 minutes 20 seconds Extinguishment 2 minutes 50 seconds Sealability (the application of the foam is continued for 1 minute after extinguishment) 11 minutes 30 seconds A feature of heteropolysaccharide-7 as well as of the thixotropic polysaccharides into which it can be degraded, is that they~are more effective in extinguishing fires on hydrophili~
liquids when they are usea with sea water, as compared to their I ,;

use with fresh water. This appears to be largely due to the e presence of maynesium ions in sea water, and the addition of magnesium ions in the foregoing formulations, in a proportion of at least about 1/6 the weight of the polysaccharide shortens ~ ~1 . .. ..
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~'-their fire extinguishing times when they are diluted with fresh water. It has no significant effect on the fire extinguishing when sea water is the diluent.
Increasing the magnesium ion content to a~out 1/3 the weight of the polysaccharide heightens the improvement, but further increases in magnesium ion content do not further add significantly to the effectiveness.

Adding too much magnesium ion can also produce problems such as the precipitation of magnesium compound when the concentrate is subjected to very low temperatures. Such precipitation could interfere with the use of the concentrate in standard proportioning foamers in extremely cold weatherO
~agnesium sulfate in a proportion of about 1.3 to about 1.7 times the weight of the polysaccharide is a preferred choice and gives magnesium ions in a proportion of about 1/4 to about 1/3 the weight of the polysaccharide. However, magnesium chloride, nitrate, and/or acetate can be substituted for some or all of the magnesium sulfate, if desired. Other metallic ions such as of calcium, chromium and the others listed in U.S. Patent 3,915,800 (Table VII) can be substituted for the magnesium but are ~not as good at equalizing the effects of sea water and fresh water dilution.
The urea in the foregoing examples can be reduced in .;
amount or entire]y eliminatea, inasmuch as its principal effect is to speed up the solution of the polysaccharlde in th~ water. 7Or th- deyraded forms of hetero7Olysaccharide-7 j lOo ~
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, the optimum urea content of the water in which the polysaccharide is to be dissolved is not as high as for the undegraded hetero-polysaccharide-7, From about 1/2% to about 5% urea in the water, by weight, is a preferred range of concentration regardless of the type of heteropolysaccharide-7, and the same concentration is suitable for other viscosity-increasing thickeners such as scleroglucan, mannan gum, etc. The increase in polysaccharide dissolution rate makes itself felt however, even with lesser concentrations of urea, and its effect is not changed much over wide variations in the amount of polysaccharide being dissolved.
The urea also helps reduce the freezing point of the concentrate. As little as 1/2% urea based on the weight of the concentrate produces a noticeable improvement, particularly when the concentrate also contains at least about 2% of a glycol or an etherified glycol freezing point depressant.
The urea can be partially or completely replaced by thiourea or even ammonium thiocyanate or ammonium cyanate, without much change in effectiveness. All of these additives rapidly dissolve in water to greatly improve lts solvent action on the polysaccharide, even when the additive and the polysaccharide are added to the water simultaneously.The stabilizing effect of urea as noted in German Auslegeschrift 1,169,302 for protein hydroly-zates, is not noticeable with the polysaccharides of the present invention.
The diethylene glycol monobutyl ether in the above examples can also be omitted, although it helps boost the expan- ¦
sion obtainable when the concentrate is foamed, and also helps shorten the time required to extinguish a fire, particularly on hydrophilic liquids. Only about 2 to 5% of such additive based ,' 11.

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on the total weight of the concentrate is all that is needed for this purpose. This addit;ve also helps reduce the freezing point of the concentrate, but this i9 not important. The concentrates of the present invention ara freeze-thaw stable so that they are not damaged by freezing, and as they cool to freezing temperature their gelled condition becomes too stiff before they actually freeze. They should accordingly be stored for use at temperatures no lower than about 35F, unless the concentrates are to be pumped through a diluting apparatus by a positive displacement pump.
It will be further noted that the dissolved magnesium salt significantly reduces the freezing point of the concentrates, whether or not other freeze-preventing additives are used.
Additives such as ethylene glycol and hexylene glycol can be used in place of some or all of the diethylene glycol monobutyl ether, if desired, but are not preferred inasmuch as they are considered toxic to marine life and fire-fighting liquids can eventually run off into streams.
The silicone surfactant and/or the fluorocarbon sur-factant can also be omitted if desired. As noted in the parent applications, their presence maXes the formulations, after dilution and foaming, extremely effective in extinguishing fires on hydrophobic liquids such as gasoline, so that these formula-tions can be used for fighting fires involv mg either type of liquid with excellent results. The silicone surfactant and the fluorocarbon surfactant cause aqueous films to form over burning hydrophobic liquids, and this greatly assists the fighting o~
fires on such liquids. ~owever, either of these two aqueous film formers can be reduced in quantity or entirely eliminated, and good aqueous film formation generally effected by increasing the concentration of the other. Also as pointed out in ~he parent applications other fluorocarbon surfactants and other ¦

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silicone surfactants can be used to provide the aqueous film formation. For sueh result the diluated concentrate should have a surface tension of 19 or less dynes per centimeter, preferably 18 dynes or less. Higher surface tensions do not eause signifi-eant aqueous film formation.
The omission of all fluorocarbon surfaetant from the foregoing formulations also lowers the effectiveness with whieh t};ey fight fires on hydrophilie liquids. At least about 0~03%
fluorocarbon surfactant, or better still 0.05% is particularly desired to give sueh increased effeetiveness to the diluted eon *
centrate. The undiluted concentrate ean then have at least ten times these amounts.
The formulation of Example 2 with its relatively high eoncentration of thixotropic polysaccharide does a very good job of extinguishing fires on hydrophilic liquids, even when diluted with 16 2~3 times its volume of fresh or sea water. On the other hand the formulation of Example 1 is best used when diluted with only about 10 times its volume of fresh or sea water.
The formulations of both examples do not inelude the resinous film~formers normally used in foam eoncentrates as deseribed in the parent applications. Such film-formers ean be added as for instance in eoncentrations that add about 1/2% to about 1 1/2% solids based on the total weight of the eoncentrate.j A partieularly good resinous film-former is the reaetion produet of 3-dimethylaminopropylamine-1 with an equivalent amount of i ethylene-maleicanhydride eopolymer, described in Example I of British Patent 1,3~31,952.
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The chlorinated metaxylenol of the formulations of the present examples is a biocide that prevents the growth of mold, bacteria, etc. in the concentrates. Other biocides or preserva-tives, such as methyl parahydroxybenzoate or any o~ those designated in the prior applications can be used instead oE or combined with the chlorinated metaxylenol, preferably in a total concentration of 0.0l to about 0.~3~ by weight of the concen-trate.
When the concentrate is made by a sequence of steps extending over a number of hours, as fcr instance when the polysaccharide solution in the water is prepared and stirred or permitted to stand overnight before the remaining ingredients are added, the preservative should be added in the first stage of the preparation.
It will be noted that the formulations of Examples l and 2 not only have fluorocarbon and silicone surfactants in small amounts but they also have additional surfactants that are not of the fluorocarbon or silicone types and are in larger amounts to impart the desired formability to the compositions.
; Those foamability-improving surfactants are largely of the type that ha~e a hydrophilic moièty weighing at least 80~ more than the lipophilic moiety, and thus follow the teachings of U.S.
Patent No. 3,849,315.
The foamed compositions of the present invention do a very good job of extinguishing fires when applied by projection from foam-delivering nozzlesj~ either portable or fixed as for example on towers, or from line-proportioning foamers, or foam chambers. In each case standard equipment can be used without modification.

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,' i The formulation of Example 2 meets all commercial , standards when used to extinguish fires after dilution with ¦l 16 2/3 times its volume of fresh or sea water, which is a ' standard dilution provided by standard foaming equipment~ At ;! this dilution it is preferred to apply it to fires on the fol-lowing liquids at the designated rates in gallons of diluted ..
liquid per minute per square foot of surface on the burning liquid, using a fixed applicator such as a foam chambero Methanol .16 .
Isopropanol .20 n-propanol u 10 n-Butanol .10 t-gutyl Alcohol 35 Isodecanol .10 SDA-1-200 PF (Ethanol) .16 Ethyl Acetate .10 .
n-propyl Acetate .10 Butyl Acetate .10 .
ethyl ~nyl Acetate .10 Methyl Acrylate .10 ~ Acetone .20 Methyl Ethyl Ketone .20 Methyl Isobutyl Ketone : .10 . Propionaldehyde .10 : Hexane .10 I Heptane .10 : Aut~motive Gasoline .10 ::~ Lactol Spirits (Naphtha Solvent) .10 Mineral Spirits (Petroleum Spirit) .10 : Toluene .10 ~ Petroleum Distillate .10 l Methyl Cellosolve .10 . ~ .
: j; The foregoing application rates are preferably increased by about one-fourth when using movable discharge .;
nozzles to spread the applied foam ar.d speed the extinguishment. .
~owever, it is not desirable to increase~the rate of ~application to t-butyl alcohol (on which fires are always difficult to i extinguish) or to have a movable nozzle application rate less I! than about 0.16 gallons per minute per square footO

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, The formulations of Examples 1 and 2 can be applied when diluted with 10 times their volume of fresh or sea waterO
The preferred application rates of the Example 2 formulation when so diluted are about one-fifth less than listed above, except that application rates lower than about 0.10 gallons per minute per square foot are not desirable whether from fixed ;
or movable foam applicators. Also the tenfold dilution is not recommended for fires on hydrophobic liquids where the 16 2/3 dilution has been a time-honored and widespread standard proven to be highly effective and built into standard fire-fighting -~, . equipment.
The formulations of the present invention can be further varied. Thus the formulation of ~xample 2 can use the fluorinated surfactant of Example 1, or major variations can be made such as shown in the following exemplifications:

Example 3 ....
ID this example some of the heteropolysaccharide-7 is replaced by xanthan gum and good results are obtained, although there is some loss of burnback resistance. The formulation is water 6155 mls.
urea 62 g.
the degraded heteropolysaccharide-7 of Example 2 41 g.
xanthan gum 41 g.
o-phenoxy phenol 5.8 g.
the Cg substituted imidazoline surfactant solution of Example 1 460 mls.
the mixed alcohol sulfates solution of Example 1 530 mls.
I the silicone surfactant solution d,, of Example 1 142 mls.
- the fluorinated surfactant of Example 1 68 g, acetic acid 35 mls.

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The formulation of Example 3 can also be modified by the addition of 0.3% trls-hydroxymethyl aminomethane, about 0,07% of the disodium salt of nitrilotriacetic acid, and about 3% butyl carbitol, based ~n the total weight of concentrate, Other very effective mixtures of perfluorocarboxylic acids useful for the formulations of the present invention, are those in which by weight about 55 to about 70% is C8, about 14 to about 23% is C10, about 6 to about ~/v is C12, about 2 to about 7% j is C14, and any balance is C6. Such a mixture in a concentration i of 30 grams/gallon in a formulation also having 25 grams/gallon , ~r of the silicone surfactant solution of E~ample 1 and 600 mls./
gallon of the mixed imidazolines of Example 1, 150 mls./gallon of 30% solution of the corresponding Cll-substituted imidazoline surfactant, 295 mls./gallon of propylene glycol monobutyl ether and 268 mls./gallon of butyl cellosolve, makes a very effective fire extinguisher whether or not the heteropolysaccharide-7 is added to it.
Instead of degrading the normal polymeric chains of heteropolysaccharide-7 their formation by fermentation can be stopped when it has proceeded about half to three-quarters the extent practiced to produce the undegraded heterop~lysaccharide-7.
This early termination lowers the yield but also produces a shorter polymer that can be considered a degraded form of hetero-polysaccharide-7 in accordance with the present invention. The undegraded polymer seems to resist degradation by high-shear stirring. -The degree of chain-shortening is best dete~nined by measuring the viscosity of aqueous solutions of the chain-shortened material. A 20~C viscosity of over 3,000 centipoises for a 10% solution measured at 60 rpm of a number 4 spindle in a Rrookfield viscometer, shows inadequate chain-shortening~

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Conducting the chain-shorteniny on a 1~ solution of the polysaccharide permits convenient measurement of the viscosity as the chain-shortening reaction is taking place.
As shown, non-thixotropic thickeners for aqueous systems can also be used in amounts up to about half the total thickcners in the formulations of the present invention. Thus, ]ocust bean gum can be used in an amount about 1/3 that of the thixotropic polysaccharide. Some thickeners such as guar yum and its derivatives impart to the concentrates a free-thaw instability that is not desired, Special solvents such as the N-methyl pyrrolidone-2 are not needed in the formulations of the present invention, so that these formulations are inexpensive to manufacture, Moreover N-methyl pyrrolidone-2 has an adverse effect on fire fighting with heteropolysaccharide-7 or its degraded forms.
However, such solvents can be used in small amoun-ts, e.g. up to about 10%
by weight, to further reduce the viscosity of the concentrate.
It is helpful to buffer the concentrate as by the addition of some tris-hydroxymethyl aminomethane in a quantity of 1/8 to 1/2% by weight, unless the silicone surfactant is omitted.

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~ 3~-3 The concentrates of the present invention can be stored in mild steel containers that have their interiors uncoated, or in plastic containers. No serious corrosion of the mild steel is , produced after many months of storage in such a container, They can be used very effectively to fight non-polar liquid fires in tanks by introducing the foamed diluted concentrate below the liquid surface in the tanX, This so-called sub-surface intro-duction technique is particularly desirable in tanks of gasoline or other petroleum products, and is not suitable for fighting fires on polar, that is hydrophilic liquids~

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Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the 1l scope of the appended claims the invention may be practiced : ¦ otherwise than as specifically described. .:
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An aqueous pumpable fire-fighting concentrate for dilution with at least about ten times its volume of water and foaming with air to produce a fire-fighting foam having an expansion of at least about 3, the concentrate being a solution in essentially water and having dissolved in it a thixotropic polysaccharide thickener that increases its Brookfield spindle 4 viscosity at 20°C to not over about 3,000 centipoises at 60 rpm spindle speed, and the concentration of the thickner in the concentrate being at least about 1% by weight, and wherein the concentrate also contains from about 1/2 to about 5% of an additive selected from the group consisting of urea, thiourea, ammonium cyanate and ammonium thiocyanate.

2. The concentrate of Claim 1 in which the polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7.

3. The concentrate of Claim 2 in which the polysaccharide is a degraded heteropolysaccharide-7 and the additive is urea.

4. The concentrate of Claim 1 in which the polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7, and the concentrate having also dissolved in it a magnesium salt that contributes magnesium ions in a quantity at least about 1/6 the weight of the polysaccharide.

5. The process of fighting a fire on a body of hydrophilic liquid by applying to the burning surface of that liquid a foamed aqueous solution of a thixotropic polysaccharide selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7, the polysaccharide being dissolved in that solution in an amount that causes the foam to form a gel blanket when it contacts the hydrophilic liquid, and the solution containing a dissolved magnesium salt that contributes magnesium ions in an amount at least about 1/6 the weight of the polysaccharide, and the foamed aqueous solution being derived from a concentrate according to the concentrate of claim 1 in which the polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7, and the concentrate having also dissolved in it a magnesium salt that contributes magnesium ions in a quantity at least about 1/6 the weight of the polysaccharide.

6. The process of fighting a fire on a body of hydrophilic liquid by applying to the burning surface of that liquid a foamed aqueous solution of a thixotropic polysaccharide selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropoly-saccharide-7, the polysaccharide being dissolved in that solution in an amount that causes the foam to form a gel blanket when it contacts the hydrophilic liquid, and the solution being essentially in sea water, and the foamed aqueous solution being derived from a concentrate according to the concentrate of claim 1 in which the polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7.

7. An aqueous pumpable fire fighting concentrate for dilution with at least about ten times its volume of water and foaming with air to produce a fire-fighting foam having an expansion of at least about 3, the concentrate consisting essentially of water having dissolved therein a foaming agent that provides the foainability, and a thixotropic polysaccharide thickner that increases the Brookfield spindle 4 viscosity of thc concentrate at 20°C to not over about 3,000 centipoises at 60 rpm spindle speed and causes the fire-fighting foam to form an insoluble gel blanket when placed on a burning hydrophilic liquid, the concentration of the thickener in the concentrate being at least about 1% by weight, and wherein the concentrate also contains from about ? to about 5% of an additive selected from the group consisting of urea, thiourea, ammonium cyanate and ammonium thiocyanate.

8. The concentrate of Claim 7 in which the polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7.

9. The concentrate of Claim 8 in which the polysaccharide is a degraded heteropolysaccharide-7 and the additive is urea.

10. The process of fighting a fire on a body of hydro-philic liquid, which process comprises applying to the burning surface of that liquid a foam having an expansion of at least about 3 foamed from an aqueous solution of a foaming agent and thixotropic polysaccharide selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropoly-saccharide-7, the polysaccharide being dissolved in that solution in an amount that causes the foam to form a gel blanket when it contacts the hydrophilic liquid, and the solution being essentially in sea water, and the formed aqueous solution being derived from a concentrate according to Claim 8.

11. The concentrate of Clalms 7, 8 or 9 in which the concentration of the polysaccharide is over 1.1% by weight.

12. The concentrate of Claim 7 in which the polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7, and the concentrate also contains magnesium sulfate dissolved in a proportion at least about 1/6 the weight of the polysaccharide and sufficient to improve the fire-fighting effectiveness of the concentrate when it is diluted with fresh water.

13. An aqueous pumpable fire-fighting concentrate for dilution with at least about ten times its volume of water and foaming with air to produce a fire-fighting foam having an expansion of at least about 3, the concentrate being a solution in essentially water and having dissolved in it a thixotropic polysaccharide thickener that increases its Brookfield spindle 4 viscosity at 20°C to not over about 3,000 centipoises at 60 rpm spindle speed, and the concentration of the thickener in the concentrate being at least about 1%
by weight.

14. The concentrate of Claim 13 in which the poly-saccharide is selected from the class consisting of hetero-polysaccharide-7 and degraded forms of heteropolysaccharide-7.

15. The concentrate of Claim 14 in which the poly-saccharide is a degraded heteropolysaccharide-7.

16. An aqueous pumpable fire-fighting concentrate for dilution with at least about ten times its volume of water and foaming with air to produce a fire-fighting foam having an expansion of at least about 3, the concentrate consisting essentially of water having dissolved therein a foaming agent that provides the foamability, and a thixotropic polysaccharide thickener that increases the Brookfield spindle 4 viscosity of the concentrate at 20°C to not over about 3,000 centipoises at 60 rpm spindle speed and causes the fire-fighting foam to form an insoluble gel blanket when placed on a burning hydrophilic liquid, the concentration of the thickener in the concentrate being at least about 1% by weight.

17. The concentrate of Claim 16 in which the poly-saccharide is selected from the class consisting of hetero-polysaccharide-7 and degraded forms of heteropolysaccharide-7.

18. The concentrate of Claim 17 in which the poly-saccharide is a degraded heteropolysaccharide-7.