Film-forming Fire Fighting Composition

Abstract

Aqueous foam film-forming fire fighting compositions based on mixtures of fluorocarbon and siloxane surfactants, are improved for sub-surface introduction into burning hydrophobic liquids by the addition of a different surfactant that increases foamability and has a hydrophilic moiety weighing at least 80 percent more than its lipophilic moiety.

Description

The present invention relates to fire fighting, and particularly to the use of film-forming compositions in the fighting of fires.

Application Ser. No. 131,763 filed Apr. 6, 1971, discloses aqueous foam compositions that spread films over hydrophobic liquids and in this way extinguish flames on such liquids. While those compositions do an admirable job in controlling fires in hydrophobic liquids, even when the foams do not cover the entire burning surface, one of the objects of the present invention is the provision of even more effective fire fighting film-forming compositions and methods.

The foregoing as well as additional objects of the present invention will be more completely understood from the following description of several of its exemplifications.

It has been discovered that the fire-fighting compositions of application Ser. No. 131,763, the contents of which application are incorporated herein as though fully set forth, are improved by substituting for at least about 40 percent of the foam-ability-improving surfactant, one that has a hydrophilic moiety whose weight is at least 80 percent greater and better still at least 120 percent greater than the weight of its lipophilic moiety. In other words, in an aqueous film-forming liquid containing dissolved fluorocarbon and silicone surfactants in amounts that give the liquid a surface tension at least as low as 19 dynes per centimeter but do not give it good foamability, improvement is made pursuant to the present invention by having the liquid also contain a different surfactant that has a hydrophilic moiety whose weight is at least 80 percent greater and more desirably at least 120 percent greater than its lipophilic moiety, and is contained in an amount at least about 40 percent of that which provides good foamability to the liquid.

Preferred lipophilic moieties for the last mentioned surfactant are hydrocarbon chains not over 10 carbons long, or better still only 7 or 8 carbons long. Also the best hydrophilic moieties contain at least 3 hydrophile units such as hydroxyl, carboxyl, sulfo and nitrogen. Particularly effective surfactants are those of the imidazoline type containing a quaternized nitrogen hydroxide carrying two short carboxylated chains. Others falling within the foregoing definition and providing very good results include disodium n-octyl amine di-propionate.

A feature of the present invention is that the fire-fighting foams thus produced are very effective for extinguishing fires in burning hydrophobic liquids by introducing the foam into the burning liquid below the liquid's surface. Such sub-surface introduction is a particularly desirable technique for fighting fires in storage tanks, for example, inasmuch as less vulnerable and less expensive foam-supplying installations can be used.

The fire-fighting composition of the present invention can also contain other ingredients such as anti-freeze agents, hydrophilic resins, buffers, sequestering agents such as those for the cations of sea water, preservatives, the acetylene glycols of Ser. No. 131,763, etc. The new composition can also be prepared from concentrates which are diluted with tap or sea water when needed to be applied to a fire.

The following examples show typical compositions pursuant to the present invention.

EXAMPLE I

55 grams (CF.sub.3).sub.2 CF(CF.sub.2).sub.n COO.sup.-.sup.+NH.sub.3 C.sub.2 H.sub.5 where n is 4, a minor amount of which can be replaced by compounds where n is 2, 6 and 8,

128 grams of a 40 percent by weight solution in 1:1 by volume water-isopropanol, of ##SPC1##

a minor amount of which can be replaced by compounds in which the bracketed portion occurs 2, 4 and 5 times, rather than three,

400 ml of a 48 percent by weight solution in water of ##SPC2##

215 ml of a 10 percent by weight solution in water of the condensation product of 3-dimethylamino-propylamine-1 with an equivalent amount of an ethylene-maleic anhydride copolymer having 3 molar proportions of ethylene for every mol of maleic acid and having a viscosity of 7 cps. at normal pH as a 2 percent solution in water, a softening temperature of 170.degree.C. and a melting temperature of 235.degree.C. The condensation reaction which is slightly exothermic takes place in water solution at room temperature and opens each acid anhydride group to make one carboxyl and one amide of 3-dimethylamino-propylamine-1,

340 ml diethyleneglycol monobutyl ether,

20 g tris hydroxymethylamino methane, and

water to make 1 gallon.

The foregoing ingredients are mixed in any order and the final product is a so-called 6 percent fire-fighting concentrate. It can be stored for many months, and is used for fire-fighting by mixing it with 162/3 times its volume of water and also with sufficient air to foam with an expension of 3 to 6. This expansion is generally considered adequate for fire fighting. Such mixing is conveniently effected with a high-back-pressure venturi as shown in U.S. Pat. No. 3,475,333 granted Oct. 28, 1969, for sub-surface introduction into the usual types of storage tanks.

EXAMPLE II

68 g of the fluorocarbon surfactant of Example I,

127 g of the same 40 percent solution of silicone surfactant described in Example I,

370 ml ethylene glycol,

467 ml of a 30 percent by weight aqueous solution of about a 1:1 mixture of sodium n-octyl and n-decyl sulfates,

467 ml of a 28 percent by weight aqueous solution of ##SPC3##

31 g tris hydroxymethylamino methane,

6 g sodium nitrilotriacetate,

340 ml diethylene glycol monobutyl ether, and

water to make up 1 gallon.

This mixture can be used interchangeably with that of Example I, but by reason of the sequestering action of the nitrilotriacetate it works better than that of Example I when diluted with sea water.

The silicone surfactant is somewhat more stable in a solution that contains isopropyl alcohol. It is accordingly helpful to increase the amount of isopropyl alcohol in the 6 percent concentrates of Examples I and II. As much as 5 percent by weight isopropyl alcohol can thus be present in those concentrates. Larger concentrations are undesirable inasmuch as they tend to unduly lower the flash point of the concentrates. The silicone surfactants are also more stable if kept from acid media and as in Ser. No. 131,763 a pH of about 7.8 is preferred for the concentrates of the present invention. The tris hydroxymethylamino methane helps buffer the concentrates of the foregoing Examples at about that pH, even when they are mixed with other concentrates that are acid. There is however no need to preserve the pH when the concentrates are diluted for application to a fire inasmuch as the diluted fire-fighting liquid does not lose any significant fire-fighting ability if it is on the acid side for the relatively few minutes needed to control the fire.

Any of the fluorocarbon surfactants disclosed in Ser. No. 131,763 can be used in place of those of Examples I and II. Other anionic, cationic or amphoteric fluocarbon surfactants such as those shown to be effective in U.S. Pat. No. 3,655,555, granted Apr. 11, 1972, can also be so used. Similarly any of the silicone surfactants of that prior application can be used in place of those of Examples I and II. A fungicide such as formaldehyde or the sodium salt of o-phenyl-phenol can also be added to the concentrates to inhibit mold growth and the like.

The concentrates of the present invention can also be prepared for dilution in proportions other than the 162/3:1 ratio given above. Another widely used dilution ratio is 331/3:1 and for such use the concentrates can be prepared to have double the strength shown in Examples I and II. Other dilutions take correspondingly modified concentrates, although it is not necessary to accurately proportion the dilution. As much as a plus or minus 50 percent departure from the target dilution proportion can be tolerated. One reason for such tolerance is that the fire-fighting effectiveness of the diluted mixtures is not dependent to any significant degree on good foaming. Even a foam of the present invention with an expansion of 2 will do a good job of rapidly extinguishing a gasoline fire by subsurface introduction.

It will be noted that in the foregoing Example II the imidazoline surfactant is so effective that it is diluted with more than an equal amount of less effective surfactant composition outside the scope of the present invention. That example can be substantially improved by replacing the less effective surfactant composition by an additional quantity of the imidazoline surfactant of Examples I or II, or any other imidazoline surfactant such as ##SPC4##

In the foregoing surfactants the long unsubstituted alkyl chain of 7 to 9 carbons is the lipophilic moiety. The balance of the molecule is the hydrophilic moiety and contains a multiplicity of hydrophile units. The quaternary hydroxylated nitrogen is one such unit, the other nitrogen is a second, and the alcohol, carboxy and sulfo groups are additional ones. A chain of two carbons will not detract from the hydrophilic character even if such chain is fully hydrogenated and also carries a methyl branch. Oxygen or nitrogens should therefore interrupt carbon chains to leave chain lengths not more than two carbons long. Thus the two carbons connected together in the imidazoline ring are counted as part of the hydrophilic moiety, as is the CH.sub.2 CH.sub.2 OCH.sub.2 portion of the imidazoline of Example I. Similarly the ring carbon to which the lipophilic moiety is connected has two nitrogens also directly connected to it and for that reason is considered part of the hydrophilic moiety.

In place of the imidazoline type surfactant of Examples I and II there can be used the di-sodium, di-potassium or mixed sodium-potassium salt of n-octyl amine di-propionic acid, e.g., C.sub.8 H.sub.17 N(CH.sub.2 CH.sub.2 --COONa).sub.2, or the corresponding salts of n-octyl amine di-2-methyl propionic acid although they are somewhat less effective. Because of the prohibitive expense it is impractical to use a fluorocarbon or siloxane type surfactant as a foamability-improving material.

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 scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims

What is claimed is:

1. In an aqueous film-forming fire-fighting foamable liquid containing dissolved fluorocarbon and silicone surfactants in amounts that give the liquid a surface tension at least as low as 19 dynes per centimeter but do not give it good foamability and also containing one or more foamability-increasing surfactants that are neither fluorocarbons nor silicones, to bring the foamability of the liquid up to the level needed for a fire-fighting foam, the improvement according to which at least 40 percent of the foamability-increasing surfactants is an imidazoline or amine di-propionate surfactant with hydrophilic and lipophilic moieties of which the hydrophilic moiety has at least three hydrophile units selected from the class consisting of hydroxyl, carboxyl, sulfo and nitrogen, and weighs at least 80 percent more than the lipophilic moiety.

2. The combination of claim 1 in which the lipophilic moiety is in the form of a hydrocarbon chain not over 10 carbons long.

3. The combination of claim 1 in which the imidazoline has one of its ring nitrogens quaternized with two carboxylated carbon chains each having not over two hydrophobic carbons connected together.

4. The combination of claim 1 in which the hydrophilic moiety weighs at least 120 percent more than the lipophilic moiety.

5. The combination of claim 1 in which the imidazoline surfactant is: ##SPC5##

where R is a C.sub.7 to C.sub.9 alkyl, and the amine di-propionate surfactant is C.sub.8 H.sub.17 N(CH.sub.2 CH.sub.2 --COONa).sub.2 or ##SPC6##

6. In the method of fighting a fire in a body of liquid hydrocarbon held in a container by introducing an aqueous foam into the body of liquid from a location below the surface of that body, the improvement according to which the aqueous foam is the foamed composition of claim 1.

7. In the method of fighting a fire in a body of liquid hydrocarbon held in a container by introducing an aqueous foam into the body of liquid from a location below the surface of that body, the improvement according to which the aqueous foam is the foamed composition of claim 4.