US3475333A

US3475333A - Fire extinguishing

Info

Publication number: US3475333A
Application number: US681308A
Authority: US
Inventors: Donald N Meldrum; John R Williams
Original assignee: National Foam System Inc
Current assignee: Enterra Corp; National Foam System Inc
Priority date: 1967-11-01
Filing date: 1967-11-01
Publication date: 1969-10-28
Anticipated expiration: 1986-10-28

Description

Oct. 28, 1969 MELDRUM ET AL 3,475,333

FIRE EXTINGUISHING Filed Nov. 1, 1967 50L UTION INLET INVENTORS .Damlal MMe [drum Jolzrzg. Williams United States US. Cl. 252-3 17 Claims ABSTRACT OF THE DESCLOSURE Fire-fighting foam of the type stabilized by protein hydrolyzate is made more effective by the addition of a very small amount of fluorinated surfactant having a terminal perhalogenated chain of carbon atoms 6 to carbons long, not more than two of the halogens being chlorine and the remainder being fluorine. The quantity of fluorinated surfactant added is not enough to cause foaming by itself. Anionic, nonionic, amphoteric and cationic fluorinated surfactants can be so used, so long as they are compatible with the foam. The improved foam is much more effective in extinguishing fires of hydrophobic liquids in tanks into which the foams are introduced from below the surface of the burning liquid. It is also more effective in fighting fires in combination with powder-type extinguishers like potassium bicarbonate.

The presentapplication is in part a continuation of prior applications Ser. No. 556,595, filed June 10, 1966; Ser. No. 436,652, filed Mar. 2, 1965; and Ser. No. 343,- 454, filed Feb. 10, 1964. All of these prior applications have since been abandoned.

Fires in hydrophobic combustible liquids like gasoline can be among the most catastrophic of disasters. One of the key reasons for the seriousness of such fires is that prior art fire fighting techniques leave something to be desired. Even the use of fluorinated surfactant foams as described in US. Patent 3,258,423, granted June 28, 1966, does not solve many of the problems. In the first place such foams do not securely extinguish gasoline fires in tanks when the foam is introduced from below the surface of the burning liquid. Subsurface introduction is preferred for fighting tank fires. In addition, the fluorinated surfactants of the patent are extremely expensive.

Among the objects of the present invention is the provision of improved fire fighting methods and improved foams and foam-forming compositions for use therewith.

Additional objects of the present invention will be recognized from the following description of several of its exemplifications, reference being made to the accompanying drawings wherein:

FIG. 1 diagrammatically illustrates one arrangement for practicing the present invention; and

FIG. 2 is an enlarged view of a foam generator show in FIG. 1.

According to the present invention the extinguishing of all types of fires is made more effective when the extinguishing medium is the standard prior art type of protein hydrolyzate foam modified by including in the foam-forming liquid an exceedingly small amount of a fluorinated surfactant. Fluorinated surfactants in concentrations too small to support foam by themselves contribute to protein hydrolyzate foams a resistance to breaking which is even greater than that of foams based on the fluorinated surfactants alone. The foams of the present invention will for example rapidly extinguish by subsurface introduction a fire in a gasoline storage atet tank and effectively secure the gasoline against reignition from the hot tank walls even if the fire has burned several minutes before the foam introduction is commenced and the top has been heated by the fire to almost red heat. A foam stabilized only with fluorinated surfactants will not be as effective and will permit reignition.

The very small concentration of fluorinated surfactant in the protein hydrolyzate foams of the present invention also makes these foams much more resistant to breaking by fire extinguishing powders such as potassium bicarbonate.

The fluorinated surfactants used in accordance with the present invention have a terminal perhalogenated chain of carbon atoms 6 to 15 carbons long. Salts of per fluorocarboxylic acid are of outstanding effectiveness, especially lower alkylamine salts, and the substitution of a single chlorine in place of one of the fluorines in such compounds does not detract significantly from their effectiveness, particularly where that chlorine is in a onecarbon branch near a terminal position on the chain. The presence of two chlorines in the perhalogenated chain does appreciably lower the effectiveness but such compounds are still suitable for the purposes of the present invention. A single hydrogen substituted at the terminal position in a perfluorinated chain more sharply lowers the effectiveness but still leaves a material that is operative.

In general the concentration of the fluorinated surfactant in the foam can range from about to about /s by weight, the smaller concentrations being used for the most effective surfactants such as those in which all the halogens in the perhalogenated chain are fluorine or all but one are fluorine and that one is a chlorine located in a chlorodifluoro methyl branch on a penultimate carbon in the chain.

Turning now to the figures, in FIG. 1 there are shown tanks 10 and 11 which may be of the usual type in the so-called tank farms for storage of gasoline, kerosene, jet fuel, fuel oil, or other combustible hydrophobic liquid. The tanks are provided with pipe connections 20, 21 valved as at 30, 31, through which the tanks can be filled and emptied. While a plurality of such connections is generally provided on each tank, only one is shown inasmuch as no more are necessary for the fire extinguishing of the present invention when the tanks have a diameter of not more than about 60 feet. Tanks of larger diameter should have two or more introduction sites well spaced from each other to enable the introduced foam to more rapidly reach all portions of the burning surface.

Each tank to be protected has its connector running to the foam generator 40, but two or more tanks may have their connectors manifolded to the same pipe 36 for example so that a single foam generator can service more than one tank either simultaneously or singly. The piping, including pipe 36, is generally most conveniently exposed above ground as indicated in the figure, so that it is readily accessible for maintenance or the like. Valves 30, 31 can also be made remotely controllable so that they can each be operated from a central location remote .from the tanks.

Foam generator 40 is preferably located as close to the tanks as convenient, but outside the usual dikes such as shown at 38 which surround the individual tanks for confining the contents in the event of massive rupture. The farther away the foam generator is from the tanks, the longer it will take to begin to get the foam into any tank when needed. However, even a foot separation is perfectly feasible inasmuch as the foam can be pumped this distance in as little as 30 seconds or less. Distances as much as 300 feet can also be used.

The foam generator 40 of FIG. 1 is more clearly shown in FIG. 2 and has a water supply in the form of a pond 50 into which an intake tube 52 dips to supply a solution pump 53 which has its outlet connected to a venturi-type injector 55. The injector has an air inlet 56 that is merely open to the atmosphere. An auxiliary pump 54 discharges into the intake of solution-pump '53 and has its intake connected to a container 57 of foam-generating concentrate. This concentrate is of the type that is based on protein hyd-rolyzate as the foam stabilizer, but it also contains the afore-mentioned fluorinated surfactant.

Solution pump 53 is arranged to provide an outlet pressure adequate to pump the foam against the hydrostatic head of the contents of the tank, and at a rate of at least about 0.1 gallon per minute of foam-forming solution for each square foot of liquid surface in a tank. For tanks 25 feet high the outlet pressure of pump 53 should be at least about 100 pounds per square inch.

Venturi 55 is arranged to cause the pumped solution to suck in air through opening 56 at a rate suflicient to produce foam having an expansion of from about 2 to 6 and impelled towards the storage tanks 10, 11 under a pressure of at least about 25 pounds per square inch. For the more volatile liquids like gasoline the preferred expansion should be not over about 4.

Auxiliary pump 54 is operated to supply the foam concentrate to the liquid drawn from pond 50 in a proportion suitable to make the desired foam. The pipe 36 and all other interconnecting conduits should have a cross-sectional area adequate for the desired purpose. For tanks having a diameter of 25 feet the piping should be at least 2 inches in internal diameter, and for larger tanks proportionately larger.

The following examples give specific illustrations of how the present invention is practiced.

EXAMPLE I The foam concentrate used had the following composition:

Water to make 100.0%.

In the above formulation the ethylamine salt was a mixture of salts prepared by neutralizing with ethylamine a perhalo acid cut in which analysis showed the n value to range from about 3 to about 13 as follows:

Percent n=3 or lower 0.5 5 16.0

13 and over 0.5

Solution pump 53 has an outlet pressure of 135 pounds per square inch and pumps solution at the rate of 50 gallons per minute. Tanks and 11 have diameters of feet and a height of 25 feet with the nearest tank connected by a 150-foot length of 2 /2 inch I.D. conduit to the outlet of the foam maker. The foam maker was arranged to provide foam having an expansion of about 2.6 (measured at atmospheric pressure) against a hydrostatic head back pressure of 25 pounds per square inch, and the auxiliary pump 54 supplied one part of concentrate by volume for every 25 parts of water from pond 50. With this arrangement a test was run with the top of the tank removed and 80,000 gallons of gasoline filling the tank to a depth of 22 feet. The venturi injector was 150 feet from this tank and after one minute of burning the valve at the tank was opened and foam introduction commenced, the foam flowing at the rate of 5.6 feet per second. Forty-five seconds after the foam began entering the tank it was evident that the flame was subsiding and after another fifteen seconds the fire was definitely under control. The introduction of foam was continued for four and one-half minutes beyond that and the last small flame flickers were all gone about fifteen seconds after the foam introduction was stopped. There was no attempt to cool the hot metal of the tank around the rim where the burning had taken place, and notwithstanding this there were no subsequent reignitions. A total of about eleven gallons of foam concentrate was consumed.

EXAMPLE II A steel tank twenty feet in diameter and five feet high with no top (for test purposes) was charged with 9,000 gallons of a mixture of diesel fuel and gasoline. The foam maker was arranged to provide foam having an expansion of about 3.5 against a hydrostatic head back pressure of ten pounds per square inch. The foam liquid concentrate of Example I was inducted into the water stream by means of a venturi line proportioner to give one part of concentrate by volume for every twenty parts of water. Water under pressure was supplied by a fire truck, and the solution flow at the foam maker was about thirty gallons per minute. Foam was injected at the base of the tank fifty feet from the foam maker (venturi injector). After about one minute of burning, foam introduction was started and the fire was extinguished two minutes and forty seconds thereafter. The tank rim was not cooled by water streams or anything else, and for thirty minutes after extinguishment by the subsurface foam injection a lighted torch applied to the top of the tanks contents did not cause reignition, because of the protective effect of the foam blanket on the fuel surface.

EXAMPLE III pressure) is introduced at a linear velocity of 2. feet per second from a solution pumped at a rate of 10 gallons per minute. The solution is made by diluting the following concentrate with 25 times its volume of water:

Percent The protein hydrolyzate made by substituting pounds of feathers for the 100 pounds of horn and hoof meal in Example I of US. Patent 2,361,057 74.0 Sodium bisulfite 0.8 Ferrous chloride 2.0 Propylene glycol 9.0 Diethylene glycol 1.5 (CF CF(CF -COO*NH C H 0.4

Water to make 100.0%.

The ethylamine salt has the following distribution for the values of n:

Percent Control of the fire takes about one minute and complete extinguishment about 3% minutes.

The control of fires according to the present invention is several times as effective as obtained when the foam used does not have the above-identified fluorinated surfactants. Moreover the foam of the present invention contains so little fiuorinated material that it does not appreciably contaminate the liquid being extinguished. After a while the foam breaks into watery droplets that settle out leaving the liquid that burned ready for use for most purposes, with in many cases no more than a filtration to remove such things as soot formed during the burning.

The conduits through which the foam is introduced into the tank can be special ones provided for fire extinguishing alone, or they can be the same conduits used for other purposes such as the filling and emptying of the tanks in the normal operations. Introducing the foam at a linear speed of at least about two feet a second is desirable to keep the contents of the tank from backing out through the foam-introduction line. If such backing out does take place however, the liquid thus moving into the conduit comes from the bottom of the tank where no burning takes place. Should the level of the tank become so low as to bring the burning liquid near its internal foam discharge, then the hydrostatic head Within the tank would also be low and there would be very little tendency for the contents to back out. Indeed, it is desirable in some cases of fire to immediately start pumping out the contents at the bottom of the tank through a different conduit either before or after foam introduction is established.

A check valve can be used in the foam supply conduit to prevent backflow, and with such a valve the foam introduction speed can be as low as desired.

The venturi injector 55 is of the high-back-pressure type and this is particularly desirable since it is suitable for pumping foam against high hydrostatic heads while taking its air directly from the atmosphere. There is accordingly no need to supply a separate source of compressed air that would otherwise be needed to cause the air to foam with the foaming solution under the high pressure required. A typical high-back-pressure device of this type for use with an outlet line 2 /2 inches in internal diameter has an injector nozzle 61 0.640 inch in diameter with its outlet radially spaced 0.625 inch from a surrounding or mixing chamber 62, the air inlet 56 having a diameter of 0.625 inch and being 1.5 inches upstream of the injector outlet. The rapid extinguishing action of the present invention is obtained even when other foam generators are used with or Without having the air supplied from a pump.

The process of the present invention is best practiced with the foam generator started before the tank valves are opened. Thus the foam generator can be started and the tank valve-opening delayed until foam is forced out of the air intake 56, indicating that the conduit between the foam mixer and the tank valve is filled with foam. Alternatively, the tank valve can be of by-pass type which when closed, closes the outflow from the tank but opens pipe 36 to an auxiliary or bleed outlet. The tank valve can then have its opening delayed until observation shows that foam is flowing out of that outlet.

It is also possible to open the tank valve before the foam reaches it, but this involves some risk in the event that something goes wrong with the foam producer or there is an undetected leak in the line. In the interest of safety the tank valves are not only operated from remote locations, but can be under the control of a pressureresponsive switch in the pipe 36 that causes the tank valve to close when the pressure in that pipe is below that which is suitable for introducing foam into the tank.

In general the subsurface introduction of foam can be arranged to supply the foam at the same rates (gallons per minute) as that used for application of foam by any other technique. About one gallon of foam per minute for every square feet of surface of the burning liquid is quite effective, even in tanks having diameters of 180 feet or more. The linear velocity of the introduced foam has a critical maximum which should not be exceeded. For burning gasoline or liquids having similar viscosity such as benzol, the foam introduction should be at a linear velocity of less than ten feet per second. If the velocity is higher the control of the fire is less effective and its extinguishment delayed or completely prevented. For extinguishing fires of more viscous liquids like furnace oils, the injection velocity can be as high as twenty feet per second. The lower the injection velocity the more effective the foam is in rapidly controlling the fire so that it is desirable to introduce the foam through a large diameter tank connection. Two parallel streams can be introduced through separate connections to even further reduce the introduction velocity, and three or more connections are desirable where a large quantity of foam is to be rapidly introduced, as in tanks having diameters of feet or so.

Fire extinguishing, as in the above examples, is also obtained when the protein hydrolyzate is made from other protein sources including feathers and fish meal. Also the fiuorinated surfactants of the above examples can be replaced by any of the following without significantly changing the effectiveness of the foam:

Sodium perfluorooctanoate Monomethylarnine perfluoroisooctanoate Ammonium perfiuorodecanoate Potassium omega-chloroperfiuorodecanoate Salt of diisopropylamine and perfiuoro-S-ethylheptyl su fonic acid Sodium salt of perfiuoroisoheptyl sulfonic acid Sodium salt of p-(perfluorododecyl)phenol Ethylene diamine double salt of 8,8-dichloroperfluorodecanoic acid Phosphoric acid triester of CF (CF CH OH Tetramethyl ammonium salt of delta-(chlorodifiuoromethyl)perfluorinated nonanoic acid Perfluorohexylsulfonic acid The great variety of different chemical structures that the foregoing fiuorinated surfactants can have established quite clearly that it is the. perhalogenated terminal carbon chain at least six carbons long that contributes the superior characteristics of the present invention. When these perhalogenated chains get up to more than 15 carbons long they impart so much hydrophobicity to any chemical structure that the Water solubility of the resulting compound tends to be too low to permit the desired amount of surfactants to be included in a concentrate or to be dissolved in the diluted concentrate.

It is a feature of the present invention that the desirable effects of the fiuorinated surfactants is not associated with the foaming effects that these surfactant sometimes contribute. The best foaming tendencies are shown by perhalogenated carbon chains that are 7 to 8 carbon atoms long, and rapidly falls off to the point where such chains 11 carbons long can exhibit no foaming tendencies even in a 1% solution in water. Such chains only 6 carbons long have a relatively small foaming effect yet for the most effective fire extinguishing of the present invention the 6 carbon chains and the 11 carbon chains are just as suitable as the 7 and 8 carbon chains.

Similarly, some of the fiuorinated surfactants such as This lack of dependence on foaming of the fluorinated material is further emphasized by the fact that the following ethylamine salt,

gives better results for the purposes of the present invention than the corresponding ammonium salt, yet the ethylamine salt has much less foaming ability than the ammonium salt.

Whether the fluorinated surfactants of the present invention are anionic, nonionic, amphoteric or cationic, they still sharply improve the effectiveness of the fire extinguishing. Some protein hydrolyzate formulations are incompatible with cationic surfactants whether they be halogenated or not halogenated, and this compatibility is an essential aspect of the invention.

The perhalogenated carbon chain length of the present invention is counted without considering any branches that are present in the chain. In a branched structure the chain of carbons for the purposes of the present invention is the longest chain that can be traced in that structure. Thus the perhalogenated chain length of the first surfactant listed above is 7. Any substitution in the chain that produces a branch having a carbon not fully halogenated, greatly lowers the effectiveness of the surfactant for the purposes of the present invention unless the substitution is on a carbon that need not be counted to make a perhalogenated chain having at least 6 carbons.

As mentioned earlier, the foams of the present invention are also particularly effective in fighting fires that have first been extinguished with potassium bicarbonate powder or similar dry powder fire extinguishers. An eX- ample of a particularly effective concentrate for this purpose is:

EXAMPLE IV Percent The dried blood protein hydrolyzate specifically described in US. Patent No. 2,697,691 37.0 Ferrous sulfate 1.1 Ethylene glycol 12.0 Sodium tetrachlorophenate 0.1 Ammonium salt of perfluorooctanoic acid 0.3 Water to make 100.0%.

The composition of Example IV will form a very stable and effective foam when diluted with 16 /3 times its volume of water and the resulting diluate mechanically mixed with eight times its volume of air in a mixing nozzle of the type described in US. Patent 3,122,327, granted Feb. 25, 1964. In a test over gasoline, a cylindrical layer of this foam one inch thick and three inches in diameter took approximately 35 minutes to burn off with a downwardly directed flame normally 1 /2 inches long and under which the' foam-covered gasoline was rotated on a rotating mount. It took 46 minutes, or 11 minutes after the foam had completely broken, before the surface of the gasoline became completely involved in burning.

The other surfactants listed above show similar results when tested the same way, the complete involvement time varying down to about 25 minutes. Foam-forming compositions that omit the surfactant but are otherwise identical, break and the gasoline becomes completely involved in a tot-a1 time of about 2 minutes, and the presence of unhalogenated surfactants in the foam reduces that time even further.

When the foam produced as above indicated from the concentrate of Example IV is applied to a gasoline fire that has been first knocked down with potassium bicarbonate powder, the foam effectively prevents reignition. For instance it keeps the gasoline from ignition by a torch flame pointed down into the foam at least about twice as long as the same foam without the fluorinated surfactant.

Similar increases in ignition prevention are obtained when the foams of the present invention are used with sodium bicarbonate or ammonium phosphate powder extinguishing. For instance the concentrate of Example I diluted with 33 times its volume of water and foamed with 10 times its volume of air works very well with all of the above powders. Another highly effective foam for use with the above powders pursuant to the present invention is made by diluting the concentrate of Example III with 33 /3 times its volume of water and then foaming it to an expansion of six to twelve.

The protein hydrolyzate foam stabilization lends itself admirably to the aforementioned improvements by the fluorinated surfactants, other types of foam stabilization, such as with hydrocarbon (unfluorinated) surfactants or synthetic or natural polymers, do not provide a heat resistance as good as described above, whether or not the fluorinated surfactants of the present invention are also incorporated in them.

As pointed out above, the surfactants of the present invention can be used in mixtures, and this is particularly desirable where the mixtures are more easily produced than individual compounds, as in the case of the alkanoic acids. The perhaloiso acids and similarly branched structures referred to above are readily made by the techniques described in US. Patent 3,311,566, granted Mar. 28, 1967, and columns 7 and 8 of US. Patent 3,156,732, granted Nov. 10, 1964, or in column 8 of US. Patent 3,116,337, granted Dec. 31, 1963. U8. Patents 3,130,221, granted April 21, 1964, and 3,134,816, granted May 26, 1964, describe methods for preparing sulfonic acid salts and amines suitable for use pursuant to the present invention. The other structures are also old or obvious. For example, the salts are readily made by simple neutralization. By-product isomers and homologues that result from manufacturing processes such as the electrolytic treatment in HF electrolytes, as described for example in Fluorine Chemistry, edited by I. H. Simons, vol. I, pages 414 17, published by Academic Press, Inc., New York, NY. (1950), need not be separated out.

There is some variation in the effectiveness of the various fluorinated surfactants of the present invention. In general those in which the perhalogenated chain is 9 or 10 carbons long seem to be somewhat better than those with shorter chains, but this difference in effectiveness is not as great as that produced when a chlorine replaces a fluorine in the chain. The surfactants of the present invention need be used in a concentration no higher than shown by the foregoing examples of use with dry powder extinguishers, which amounts to about 0.017% in the liquid phase of the final foam. Higher concentrations up to /s% can be used particularly with the surfactants of lesser effectiveness, but tend to make the foams unnecessarily expensive. As in the conventional use of prior art protein foams, expansion of the foam about 2 to about 20 can be used in general or with the powder extinguishers.

For subsurface introduction into bodies of burning liquids, the expansion should be not greater than 6, as pointed out above, and is preferably even less with the more volatile burning liquids. Also the concentration of fluorinated surfactant in the foaming solution used for such subsurface foam introduction preferably ranges as high as 0.05% to provide the greatest effectiveness.

While concentrates for dilution with between about 16 /3 to 33 /3 times their volume of water, can have from 0.3 to 0.5% of the fluorinated surfactants of the present invention and be suitable for any of the above kinds of fire extinguishing including the subsurface introduction, they can also be very effective for general use with from about 0.1 to about 1% of the fluorinated surfactant of the present invention.

Further features of the present invention are that the foams stabilized with hydrolyzed protein and containing the small amount of fluorinated surfactant have a high degree of cohesiveness and adhesiveness, are stable for longer periods of time, and are prepared just as readily from sea water or other high mineral content water, as from fresh water. Foams stabilized with protein-free fluorinated surfactants with or without other types of stabilizers tend to be blown away fairly readily by winds, and cannot be prepared with sea water. The minerals in such water sharply reduce the foaming caused by the fluorinated surfactants, yet they do not detract appreciably from the desirable characteristics of the fluorinated surfactants when in small concentrations in the foams stabilized with protein hydrolyzate.

What is claimed is:

1. In the process of extinguishing a burning hydrophobic liquid in a tank by the introduction of aqueous foam to the lower portion of the liquid in the tank to cause the foam to rise to the surface of the burning liquid, the improvement according to which the introduced foam is prepared from an aqueous solution containing protein hydrolyzate in a concentration sufiicient to almost completely stabilize the foam, and the solution also contains in dissolved condition about V to about by weight of at least one compatible surfactant having a terminal perhalogenated chain of carbon atoms 6 to 15 carbons long, no more than two of the halogens being chlorine, the remainder being fluorine to further stabilize the foam and reduce the reignition of combustible material by hot surfaces, without making the foam susceptible to winds or lessen the foamability with sea water.

2. The combination of claim 1 in which the introduced foam has an expansion of from about 2 to about 4.

3. The combination of claim 1 in which the fluorinated surfactant is at least one lower alkylamine salt of a perhalocarboxylic acid.

4. The combination of claim 1 in which the hydrophobic liquid is gasoline and the foam is introduced at a linear speed of less than feet per second.

5. The combination of claim 1 in which the surfactant is present in a concentration of no more than about 0.017 percent by weight of the solution.

6. The combination of claim 3 in which the perhalogenated chain has only one chlorine atom and that atom is in a chlorodifluoromethyl branch on a penultimate carbon in the chain.

7. In the method of extinguishing a fire by applying to the fire an aqueous-air foam stabilized by protein hydrolyzate, the improvement according to which the foam is prepared from an aqueous solution containing protein hydrolyzate in a concentration suflicient to almost completely stabilize the foam, and the solution also contains in dissolved condition from about 3 to about Vs percent by weight of at least one surfactant compatible with the foam and having a terminal perhalogenated chain of carbon atoms 6 to carbons long, no more than one of the halogens being chlorine and the remainder being fluorine to further stabilize the foam, increase its compatibility with dry fire-extinguishing chemicals and reduce the reignition of combustible material by hot surfaces without making the foam susceptible to winds or lessen the foamability with sea water.

8. The combination of claim 7 in which the chain has a chlorodifluoromethyl branch on a penultimate carbon.

9. The combination of claim 7 in which the surfactants are salts of perfiuorocarboxylic acids.

10. In the method of extinguishing a fire on a body of inflammable liquid with a dry powder fire-extinguishing material, and then preventing reignition by covering the inflammable liquid with an aqueous-air foam stabilized with protein hydrolyzate, the improvement according to which the foam is prepared from an aqueous solution containing protein hydrolyzate in a concentration sufiicient to almost completely stabilize the foam, and the solution also contains in dissolved condition from about A to about 0.017 percent by weight of at least one surfactant compatible with the foam and having a terminal perhalogenated chain of carbon atoms 6 to 15 carbons long, no more than one of the halogens being chlorine and the remainder being fluorine to further stabilize the foam, increase its compatibility with dryextinguishing chemicals and reduce the reignition of combustible material by hot surfaces without making the foam susceptible to winds or lessen the foama'bility with sea water.

11. The combination of claim 10 in which the surfactants are salts of perhalocarboxylic acids.

12. The combination of claim 10 in which the surfactants are salts of perfluorocarboxylic acids.

13. The combination of claim 9 in which the salts are lower alkylamine salts.

14. In a protein hydrolyzate aqueous foam-forming concentrate for making a fire-fighting foam after dilution with from 16 /3 to 33 times its volume of water, the improvement according to which the concentrate is a water solution of protein hydrolyzate containing enough of such hydrolyzate to almost completely stabilize the foam produced after the dilution, and also contains in dissolved condition from about 5 to about 1 percent of at least one compatible surfactant having a terminal perhalogenated chain of carbon atoms 6 to 15 carbons long, not more than one of the halogens being chlorine and the remainder being fluorine to further stabilize the foam, increase its compatibility with dry-extinguishing chemicals and reduce the reignition 0f combustible material by hot surfaces without making the foam susceptible to winds or lessen the foamability with sea water.

15. The combination of claim 14 in which one of the halogens is chlorine and it is on a chlorodifluoromethyl branch on a penultimate carbon of the chain.

16. The combination of claim 14 in which the surfactants are salts of perhalocarboxylic acids.

17. The combination of claim 16 in which the salts are lower alkylamine salts.

References Cited UNITED STATES PATENTS 3,258,423 6/ 1966 Tuve et al 252-3 FOREIGN PATENTS 568,811 4/1945 Great Britain.

MAYER WEINBLATI, Primary Examiner US. Cl. X.R.