GB2278120A

GB2278120A - Foaming agents

Info

Publication number: GB2278120A
Application number: GB9310099A
Authority: GB
Inventors: Simon Howard Horwell
Original assignee: WARNSTAR Ltd
Current assignee: WARNSTAR Ltd
Priority date: 1993-05-17
Filing date: 1993-05-17
Publication date: 1994-11-23
Also published as: GB9310099D0

Abstract

Foaming agents for use in foam compositions comprise compounds of general formula I: R<1>-(OCH2)nR<2>R<3> (I> wherein R<1> represents a straight or branched chain -(C12-C28 alkyl,-(C12-C28 alkyl)C=O- or a -(C12-C28 alkyl) phenyl group; -SO2-,-SO-,-CO- or -PO3-; R<3> represents a 5 or 6 membered saturated or partially saturated heterocyclic ring, optionally containing more than one hetero atoms and optionally substituted with one or more electronegative substituents; n is an integer from 1 to 300 which form stable foams with greatly reduced quantities of additives such as stabilisers and foam boosters. The invention also relates to foam compositions useful for extinguishing fires and blanketing toxic materials.

Description

FOAMING AGENTS The present invention relates to foaming compositions, particularly fire suppressing compositions, and to compounds capable of forming a high stablility foam for inclusion in such compositions. The invention relates in particular to foams for suppressing fires and blanketing toxic materials.

There are many different types of fire suppressing agent currently available on the market. Probably the simplest fire suppressing material is water which extinguishes fires by removing heat energy. However the use of water is limited to 'Class A' fires which involve carbonaceous fuels and to some types of 'Class B' fires. Class B fires are those which involve flammable liquids or liquifiable solids but water can only be used on fuels with very high flash points or low densities and is then applied as a fog spray. In fact, it is generally recommended that water is not used on flammable liquids.

The use of water on live electrical apparatus poses the risk of electric shock to the fire fighter and the use of water on chemical fires is often also extremely hazardous.

Carbon dioxide is also frequently used to suppress fires in classes A and B and some fires in Class C involving flammable gases or high voltage electrical apparatus. It may also be used for most chemical fires. Carbon dioxide has the advantages of being inexpensive and clean but one disadvantage is that heavy walled cylinders are needed to contain it because of its high vapour pressure and this makes carbon dioxide based extinguishing systems extremely bulky and heavy. Also, carbon dioxide extinguishers require special apparatus to fill them and need regular testing. In addition, the carbon dioxide is discharged as a 'snow' which, because of its low temperature, can cause cold burns and the concentration of carbon dioxide needed for effective fire extinguishing cannot sustain life and is therefore dangerous to the operator.

The type of fire suppressants known as 'dry powder' are also in common use. These can be used on all types of fires except class D fires where special types of compounds are needed. Multipurpose dry powder for use on fires of classes A, B and C may consist of monoammonium phosphate, silicon fluids and, often, urea. Other powders are based on sodium or potassium bicarbonate, urea or graphite. The main disadvantages of dry powders are that they are messy and often corrosive.

Other types of fire suppressing materials include the halocarbons or Halons such as dichlordifluoromethane, bromotrifluoromethane (Halon 1301) which is used in fixed systems and bromochlorodifluoromethane (Halon 1211) which is used in portable extinguishers. Halons may be used on all types of fire except those involving very high flash point liquids, oxidising agents and Class D fires which are those involving flammable metals.

The halons are very powerful fire suppressants but have many disadvantages. They extinguish fires via a radical inhibition mechanism and when applied to a fire, a small proportion decomposes to form hydrogen halides and, in the case of Halon 1211, carbonyl chloride. Free halogens may also be formed and all of these substances are toxic and corrosive. In additon, halons are very stable and persist in in the atmosphere for a long time. They have been implicated in the depletion of the ozone layer and because of this there is a worldwide search for ways of reducing the amounts of the compounds which are used or, preferably replacing the compounds with alternatives which are less harmful to the environment.

A further common type of fire suppressant is foam. Foams can be used to deliver fire suppressing compounds to the site of use. In this way, the dispersion of the compound can be controlled and, therefore, this is one way in which the quantities of fire suppressing compounds can be limited. Foams containing water allow water to be more widely used as a fire suppressing agent and water damage to be minimised. Foams can be used on Class A and Class B fires and also on many chemical fires.

In general, conventional fire suppressing foams consist of a foam forming agent, viscosity modifiers, solvents, stabilisers and protein or fluorinated surfactants together with a fire suppressing agent. In prior art foams, the foaming agent comprises a compound of the general formula: RSO3-M+; R(CH2CH2O)nH; or

wherein R is a C12-C28 fatty alcohol or fatty acid residue, M is an alkali metal, ammonium or an ammonium derivative such as triethylammonium and n is an integer of from 4 to 20.

Materials used in these foams to improve their fire suppressing properties include inorganic salts such as zinc chloride, iron (II) sulphate, sodium phosphate, potassium phosphate, zinc chloride and sodium chloride.

One disadvantage of including these salts in foam compositions is that several of them, particularly the phosphates, are toxic and harmful to the environment.

In addition, the detergents of the alkyl benzene type shown above, especially those with long alkyl chains, are prohibited in the UK because thay are very stable and tend to persist in the environment.

There is therefore a need for foam forming agents which produce foams which are stable with greatly reduced amounts of stabilising agents.

In a first aspect of the present invention, there is provided a compound of general formula I: Rl-(ocH2cH2)nR2R3 wherein R1 represents a straight or branched chain -(Cl2-c28 alkyl, -(C12-C28 alkyl)C=O- or a -(C12-C28 alkyl) phenyl group; R2 represents -SO2-, -SO-, -CO- or -PO3-; R3 represents a 5 or 6 membered saturated or partially saturated heterocyclic ring, optionally containing more than one hetero atoms and optionally substituted with one or more electronegative substituents; fl is an integer from 1 to 300.

The compounds of the invention are useful as foam forming and boosting agents, particularly for fire suppression and have the advantage that when they are included in a foam composition, a stable foam is formed with greatly reduced quantities of stabilisers. It is thought that the reason for this may be that the presence of the electronegative heterocyclic ring exerts an attractive force on the polyoxyethylene backbone thus increasing its rigidity. However, it should be stressed that the usefulness of the present invention does not depend on the accuracy or otherwise of this rationalisation.

The stability of the foam formed by the compounds of the present invention is so high over a wide pH range that high concentrations of various agents can be incorporated into the foam formulations without adversely affecting their foaming ablility. This means that foaming compositions containing the compounds of the present invention can be used as blanketing materials to cover spillages of corrosive or toxic materials such as chlorine and sulphuric and hydrochloric acids. The materials disperse into the foam without destroying its structure. In addition, because of the high stability of the foams it may also be possible to incorporate into the foam composition agents which react with the toxic materials and convert them into harmless products.Foams containing such chemicals are known in the art but, because of the high stability of foams containing the compounds of the present invention, much greater quantities can be included in the compositions.

The compounds of the present invention have the further advantages that they can be used in lower concentrations than conventional foam forming agents and that they are readily biodegradable. These factors mean that when the compounds are included in a foam effective at suppressing fires, they will help to protect the environment from harmful combustion products and aquatic toxins.

In the context of the present invention, the term Cl2-C28 alkyl refers to a straight or branched saturated hydrocarbon chain having from 12 to 28 carbon atoms.

Examples include cetyl, lauryl and stearyl groups.

The group R3 may include 5 or 6 membered heterocyclic rings such as furan, 2H-pyrrole, 2-pyrroline, 3 pyrroline, 1,3-dioxolane, oxazole, thiazole, imidazole, 2-imidazoline, pyrazole, 2-pyrazoline, isoxazole, 1,2,3oxadiazole, 1,2,3-triazole, 2H-pyran, 4H-pyran, pyridine pyrrolidine, piperidine, 1,4-dioxane, morpholine, pyridazine, pyrimidine, pyrazine and 1,3,5-triazine rings and the electronegative substituents which are optionally present in these rings may be carbonyl, -OH, phenyl or substituted phenyl.

It has been found that the most stable foams are formed when: R1 represents a straight alkyl chain, preferably a C14-C20 alkyl- or a (C14-C20 alkyl)CO- group; R2 represents an SO2 group; R3 represents a pyrrolidine or pyrrolidone group; n is an integer from 6 to 200, and more preferably from 6 to 120.

Particularly preferred compounds are those of general formula II:

A compound which has proved to be particularly suitable is that which has the formula:

Compounds of general formula I may be prepared by any suitable process known to those skilled in the art or by the following process which itself forms part of the invention.

In a second aspect of the invention, there is provided a process for the preparation of a compound of general formula I, the process comprising reacting a compound of general formula III: R1(OCH2CH2)=R2O- III wherein R1, R2 and n are as defined in general formula I; with a compound of general formula IV: R3H IV The reaction is preferably carried out under dry conditions.

Compounds of general formula III are well known in the art and may be prepared from compounds of general formula V R1O-(CH2CH2O),H V wherein R1 and n are as defined in general formula I; by methods known to those skilled in the art. When R2 is SO2, the compound of general formula III may be prepared by reacting a compound of general formula V with pyridinium-l-sulphonate which is the addition compound of pyridine and sulphur trioxide and has the formula:

This compound is well known to those skilled in the art and may be prepared by adding sulphur trioxide to pyridine under cold dry conditions.

Compounds of general formula IV are well known in the art and may be prepared by methods known to those skilled in the art.

Compounds of general formula V are also well known in the art but may be prepared by reacting a compound of general formula VI R1OH VI wherein R1 is as defined for general formula I; with ethylene oxide. The amount of ethylene oxide used depends on the number of units required in the chain.

In this reaction, which is well known, an excess of ethylene oxide is added to the compound of general formula VI.

As discussed above, the compounds of general formula I are particularly useful as foam forming agents since they form very stable foams which require only minimal amounts of stabilising agent. The invention therefore relates to the use of a compound of general formula I as a foam forming agent.

In a third aspect of the invention, there is provided a foam composition comprising a compound of general formula I as a foam forming agent.

The composition will generally comprise from 0.01 to 45% by volume of the compound of general formula I. However, it is preferred that the amount of the compound of general formula I is from 9.05 to 20% and most preferably from 0.1 to 10% by volume of the foam composition.

In order to reduce the cost of the foam compositions of the present invention, they may also contain additional foaming agents which will generally be conventional foaming agents such as polyether sulphates or alkyl sulphates. Particularly suitable conventional foaming agents which may be included are sodium stearyl sulphate and octadecanol-40-ethoxy sulphate. In general, conventional foaming agents will comprise from 1 to 44% of the composition and the combined volume of compound of general formula I and conventional foaming agent will not exceed 45% of the volume of the composition. One of the great advantages of the compounds of the present invention is that they can be included in relatively small amounts in foam compositions and will greatly improve the stability and quality of the foam produced by those compositions.

The foam composition may be caused to form a foam by the addition of air to the mixture at the site of use. In this case, the foam composition will generally be diluted with water and the dilute formulation pumped under pressure to a foam generator where air is added.

However, in some circumstances, it may be advantageous to provide a composition which will form a foam in the absence of air, for example when it is not possible to add air and/ or water and in these circumstances it may be desirable to provide a foam formulation which also includes a blowing agent which expands spontaneously as soon as the composition is released from a container so that a foam is formed. The blowing agent will generally be present in an amount of from 1 to 25% by volume of the composition and preferably from 5 to 15%.

Suitable blowing agents include chlorofluorocarbons or perfluorocarbons, particularly perfluorinated alkanes, perfluorinated cycloalkanes, chlorofluoroalkanes and mixtures thereof. Examples of suitable compounds include trichlorofluoromethane, dichlorodifluoromethane, monochlorotrifluoromethane, monochlorodifluoromethane, trifluoromethane, trichlorotrifluoroethane, 1,2 -dichloro- 1,1,1,2-tetrafluoroethane or decafluorobutane. It is particularly preferred that the blowing agent comprises a perfluorocycloalkane, and especially octafluorocyclobutane since it has now been found that this compound forms an inert layer above a fire being treated with the foam and thus starves the fire of oxygen.In addition, it seems that octafluorocyclobutane may act as a free radical sponge since it appears to suppress fire not only by oxygen starvation but also when there appears to be sufficient oxygen present to support combustion. However the effectiveness of the present invention does not depend on the accuracy or otherwise of this rationalisation. In addition, the presence in a foam composition of octafluorocyclobutane increases the stability of the foam against the fire front.

When octafluorocyclobutane is used as a blowing agent, it may be mixed with a perfluoroalkane such as decafluorobutane in a ratio of octafluorocyclobutane: decafluorobutane of from 1:9 to 7:3.

As mentioned above, the foams of the present invention are extremely stable and are suitable for blanketing or neutralising spills of toxic or corrosive substances such as bromine, chlorine, fuming acids, particularly sulphuric and hydrochloric acids and volatile liquids such as titanium tetrachloride and thionyl chloride. The blanketing or neutralising agent to be used will, of course depend on the substance to be blanketed or neutralised but such agents are well known to those skilled in the art. For example, when the substance to be neutralised is bromine, the foam composition may include from 5 to 50% of a compound such as sodium thiosulphate which is capable of reacting with bromine.

In most cases, the foam compositions of the present invention will contain water in an amount of from 10 to 95% by volume of the composition. More preferably, the amount of water in the composition will vary from 25 to 75% of the composition.

Other constituents which may be included in the foam composition include stabilisers and suspending agents such as sodium carboxymethyl cellulose, sodium alginate, carbomer and polyvinylpyrrolidone (K90); foam stabilisers such as polyvinyl alcohol, high molecular weight polysaccharides, oxystearin and propylene glycol alginate; solvent aids such as glycols, aqueous ammonia, propan-2-ol. and methylpolysiloxane; foam improvers, for example iron (II) sulphate, magnesium sulphate, magnesium chloride and sodium chloride; foam boosters and/or air entraining agents such as cobalt chloride, alkyl ether sulphates or alkyl esters; fire suppression aids such as fluorinated surfactants, zinc stearate and potassium acetate; polymeric membrane formation aids such as chlorohexanediol and hexan-1,6-diamine; preservatives such as 2'-hydroxybiphenyl and trichlorophenol; buffer systems such as ammonium bicarbonate and ammonium chloride and colouring agents such as phenolphthalein.

A particularly preferred foam of the present invention has the composition: Ingredient % ranee Foaming agent of 1-45 General Formula I octafluorocyclobutane 1-15 decafluorobutane 1-30 water and other ingredients 10-95 The percentage ranges given are on a volume/volume basis.

The foam forming compositions of the present invention may be prepared simply by mixing the ingredients.

However, it is particularly preferred to provide a concentrate comprising from 1 to 25% of a compound of general formula I and, optionally other foam forming agents, stabilisers, solvent aids, foam improvers etc such as those mentioned above and to add water, blowing agents and neutralising agents for harmful substances in appropriate amounts when required.

Therefore, in a further aspect of the present invention, there is provided a concentrate for the formation of a foam forming composition, the concentrate comprising a compound of general formula I.

Some of the perfluorocarbons used as blowing agents in the foams have also proved to be very effective in suppressing fires even when not included in a foam composition and, therefore, in a further aspect of the invention there is provided the use of a perfluorocarbon compound as a fire suppressing agent.

The most effective compounds have boiling points in the range of -10" to 45"C, preferably -1" to 150C and most preferably about 1"C.

Although it is not essential, it is preferred that the perfluoro compound is a component of a foam composition, preferably a composition containing, as foaming agent, a compound of general formula I.

The perfluoro compounds of this aspect of the invention are especially useful because they are likely to be replacements for chlorofluorocarbons which are used at present but which are known to be damaging to the environment and, in particular, to the ozone layer. The perfluorocarbons are much more stable than chlorofluorocarbons and are correspondingly far less likely to react with ozone.

The invention will now be further described with reference to the following examples.

Example la Freshly prepared sulphur trioxide (80g, 1 mol) was added to pyridine (79g, 1 mol) at a temperature of -20C. The mixture was stirred and the temperature allowed to rise to about 120C. The resulting liquid, pyridinium sulphonate, was added to CH3(CH2)14O(CH2CH2)20H (1109g, 1 mol) in dry pyridine (200 ml) at a rate of about 10 ml/minute. When all of the pyridinium sulphonate had been added to the mixture, the solvent was removed to leave a cream solid product which was not purified further.

Example lb Preparation of foaming agent of formula:

The crude product from Example la was dissolved in 1,2dichloroethane (350 ml) and stirred and cooled to a temperature of OOC. Pyrrolidine (63 ml, 1 mol) was added to the solution at a rate of about 5 ml per minute. When the addition was complete, water (100 ml) was added to the flask and the mixture stirred for 1 minute. Excess solvent was decantered and the product filtered.

Analysis of the compound showed it to have the formula shown above.

Example 2 Preparation of Foam Composition A foam concentrate was prepared having the following ingredients.

Components Percentage Compound of Example 1 10% Octadecanol-40 ethoxy sulphate 20% sodium stearyl sulphate 10% ethylene glycol (solvent) 40% sodium chloride (viscosity modifier) 1% sodium carboxymethyl cellulose (stabiliser) 1% soluble starch (stabiliser) 5% polyvinyl alchohol (solvent) 1% zinc stearate (stabiliser) 5% propan-2 -ol (solvent) 1% 2-hydroxybiphenyl (preservative) 0.1k polyvinylpyrollidone (preservative) 2% magnesium sulphate (viscosity modifier) 0.9k ammonium bicarbonate (buffer) 0.5k ammonium chloride (buffer) 0.5k sodium stearate (stabiliser) 2% phenolphthalein (colour) 0.2W y-butyrolactone (stabiliser) 0.4 cobalt chloride (foam booster) 100 ppm In order to prepare the concentrate, the above materials were added in order with mixing after each addition.

The quantities of stabiliser used in the foam concentrate of this example are considerably lower than the amounts of stabiliser used in prior art foams.

Example 3 Preparation of Foaming Compositions Example 3a - Foaming Composition To 1 volume of the concentrate of Example 2, half a volume of water was added to give a foaming composition.

Example 3b - Spontaneously foaming Composition In order to prepare a spontaneously foaming composition, the following components were mixed together: Concentrate of Example 2 10% Octafluorocyclobutane 5% Decafluorobutane 10% Water 75% Example 3c - Foam Composition for Control of Bromine Spills Concentrate of Example 2 10% Sodium thiosulphate 40% Sodium bicarbonate 0.5% Phenolphthalein 0.5W 25% aqueous ammonia 2% Water 47% Example 4 Use of Foam Composition of Example 3a to Suppress Fires Fire tests were carried out by floating No 2 fuel oil on water in a pan with a 1:1 ratio of oil to water. The fuel was ignited and allowed to burn for one minute. The foam of Example 3a was then applied to the fire by deflection from a back plate. The results of the test are shown in Table 1.

Table 1

Conditions 1 2 3 mean Discharge Rate 3.2 3.2 3.2 3.2 Expansion Ratio 8.2 8.4 8.2 8.3 DTsa (mins) 22 20 21 21 Foam temp ("C) 15 15 15 15 Air temp (OC) 16 16 16 16 90% Control time (s) 61 61 58 60 Extinction time (s) 88 104 106 97 Burn back time (min) 22 22 21 22 Fuel temp at extinction OC 69 69 69 69 Where DTso is the time for 50% of the foam to break down to form a liquid.

The expansion ratio is the ratio of the volume of foam to volume of solution required to produce that volume of foam. In the table, the mean value of expansion ratio is 8.3 and therefore, on average, 1 volume of solution produced 8.3 volumes of foam.

Example 5 Fire Suppression with Foam of Example 3b The foam formulation of Example 3b was also tested for its ability to extinguish fire. The test used was similar to the test of Example 4 except that this time the No 2 fuel oil was mixed in a 1:1 ratio with benzene rather than water. The results of this test are shown in Table 2.

Table 2

li I --1 1 1 Conditions 1 2 3 mean Expansion Ratio 60 60 60 60 DT50 (mins) 20 20 20 20 Foam temp ("C) 8 7 9 8 Air temp ("C) 16 16 16 16 90% Control time (s) 21 21 20 21 Extinction time (s) 32 32 33 32 Fuel temp at extinction OC 70 70 70 70 Where DTSo is the time for 50% of the foam to break down to form a liquid.

The expansion ratio is the ratio of the volume of foam to volume of solution required to produce that volume of foam. In the table, the mean value of expansion ratio is 60 and therefore, on average, 1 volume of solution produced 60 volumes of foam.

It is impossible to test burn-back with standard methods because the fuel, once extiguished using the foam of Example 3b, cannot be reignited. This may be because of the presence in the foam of octafluorocyclobutane which forms a layer above the fuel and prevents it from being reignited. As discussed above, it is also possible that octafluorocyclobutane has a free radical supressing effect which adds to its fire extinguishing capabilities.

The tests show that both the foam formulations of the present invention are extremely effective in extinguing fire even though they contain far lower quantities of additives such as stabilisers and preservatives than conventional foams.

Claims

1. A compound of general formula I: R1- (OCH2CH2) R2R3 I wherein R1 represents a straight or branched chain -(C12-C28 alkyl, -(Cl2-C28 alkyl)C=O- or a -(Cl2-C28 alkyl) phenyl group; -SO2-, --SO-, -CO- or -PO3-; R3 represents a 5 or 6 membered saturated or partially saturated heterocyclic ring, optionally containing more than one hetero atoms and optionally substituted with one or more electronegative substituents; n is an integer from 1 to 300.

2. A compound as claimed in Claim 1, wherein R3 comprises a furan, 2H-pyrrole, 2-pyrroline, 3-pyrroline, 1,3-dioxolane, oxazole, thiazole, imidazole, 2imidazoline, pyrazole, 2-pyrazoline, isoxazole, 1,2,3oxadiazole, 1,2,3-triazole, 2H-pyran, 4H-pyran, pyridine pyrrolidine, piperidine, 1,4-dioxane, morpholine, pyridazine, pyrimidine, pyrazine or 1,3,5-triazine ring.

3. A compound as claimed in claim 1 or claim 2 wherein R1 represents a straight chain C14-C20 alkyl- or a (Cl4-C20 alkyl)CO- group.

4. A compound as claimed in any one of claims 1 to 3, wherein R2 represents an SO2 group.

5. A compound as claimed in any one of claims 1 to 4 wherein R3 represents a pyrrolidine or pyrrolidone group.

6. A compound as claimed in any one of claims 1 to 5, wherein n is an integer from 6 to 120.

7. A compound as claimed in any one of claims 1 to 6 which is of general formula II:

wherein Rl and n are as defined in claim 1.

8. A compound of the formula:

9. A process for the preparation of a compound of general formula I, the process comprising reacting a compound of general formula III: R1 (OCH2CH2) nR2H III wherein Rl, R2 and n are as defined in general formula I; with a compound of general formula IV: R3H IV

10. The use of a compound as defined in any one of claims 1 to 8 as a foaming agent in a foam composition.

11. A foam composition comprising a compound of general formula I as a foam forming agent.

12. A foam composition as claimed in claim 11 wherein the compound of general formula I is present in an amount of from 0.05 to 45% by volume.

13. A foam composition as claimed in claim 11 or claim 12, further including one or more additional foam forming agents.

14. A foam composition as claimed in any one of claims 1 to 14, further including from 1 to 25% by volume of a blowing agent such as a chlorofluorocarbon or perfluorocarbon, particularly a perfluorinated alkane, perfluorinated cycloalkane, chlorofluoroalkane or a mixture thereof.

15. A foam composition as claimed in any one of claims 11 to 14, wherein the blowing agent comprises trichlorofluoromethane, dichlorodifluoromethane, monochlorotrifluoromethane, monochlorodifluoromethane, trifluoromethane, trichlorotrifluoroethane, 1, 2-dichloro- 1,1,1,2-tetrafluoroethane or decafluorobutane or a perfluorocycloalkane such as octafluorocyclobutane, optionally mixed with a perfluoroalkane such as decafluorobutane.

16. A compound as claimed in claim 15, wherein the blowing agent is octafluorocyclobutane mixed with decafluorobutane in a ratio of octafluorocyclobutane: decafluorobutane of from 1:9 to 7:3.

17. A composition as claimed in any one of claims 11 to 16, further including from 5 to 50% by volume of an agent capable of reacting with a toxic or harmful substance to produce a less harmful product.

18. A composition as claimed in any one of claims 11 to 17, further including from 10 to 50% water.

19. A foam composition as claimed in any one of claims 11 to 18, further including one or more other constituents chosen from: stabilisers and suspending agents such as sodium carboxymethyl cellulose, sodium alginate, carbomer and polyvinylpyrrolidone (K90); foam stabilisers such as polyvinyl alcohol, high molecular weight polysaccharides, oxystearin and propylene glycol alginate; solvent aids such as glycols, aqueous ammonia, propan-2-o. and amethylpolysiloxane; foam improvers, for example iron (II) sulphate, magnesium chloride and sodium chloride; foam boosters and/or air entraining agents such as alkyl ether sulphates or alkyl esters; fire suppression aids such as fluorinated surfactants, zinc stearate and potassium acetate; polymeric membrane formation aids such as chlorohexanediol and hexan-1,6-diamine; and preservatives such as 2'-hydroxybiphenyl and trichlorophenol.

20. A concentrate for the preparation of a foam composition as claimed in any one of claims 11 to 19, the concentrate comprising from 1 to 25% of a compound of general formula I and, optionally, other foam forming agents.

21. The use of a perfluoroalkane or a perfluorocycloalkane as a fire suppressing agent.

22. The use as claimed in Claim 21 wherein the perfluorocycloalkane is octofluorocyclobutane.

23. A fire extinguishing composition comprising a perfluoroalkane or a perfluorocycloalkane or a mixture thereof.