CA2449614C - Fire extinguishing composition and process - Google Patents

Abstract

A process for extinguishing, preventing and/or controlling fires using a composition containing CHF3 is disclosed. CHF3 can be used in volume percentages with air as high as 80% without adversely affecting mammalian habitation, with no effect on the ozone in the stratosphere and with little effect on the global warming process.

Description

. CA 02449614 2003-11-28 Fire Extinguishing Composition and Process Field of Inver~,tion This invention relates to compositions for use in preventing and extinguishing fires based on the~~
combustion of combustible materials. More particularly, it relates to such compositions that are "safe" to use -- as safe for humans as cwrrently used extinguishants but absolutely safe for the environment.
Specifically, the compositions of this invention have little or no effect on the ozone layer depletion process; and make no or very little contribution to the global warming. process known as the "'greenhouse effect". Although these compositions have minimal effect in these areas, they are extremely effective in preventing and extinguishing fires, particularly fires in enclosed spaces.
' Back4round of the Invention and Pr_~or Art In preventing or extinguishing fires, two important elements. must be considered for success:
(1) separating the combustibles from air; and (2) avoiding or reducing the temperature necessary for combustion to proceed. Thus, one can smother small fires with blankets or with foams to cover the burning surfaces to isolate the combustibles from the oxygen.in the air. In the customary process of pouring water on the burning surfaces to put out the fire, the main element is reducing temperature ~to a point where combustion cannot proceed. obviously, some smothering or separation of combustibles from air also occurs in the water situation.
The particular process used to extinguish fires depends upon several items, e.g. the location of the fire, the combustibles involved, the size of the fire, etc. In fixed enclosures ouch as computer rooms, storage vaults, rare book library rooms, petroleum pipeline pumping stations and the like, halogenated hydrocarbon fire extinguishing agents are currently preferred. These halogenated hydrocarbon fire extinguishing agents are not only effective for such fires, but also cause little, if any, damage to the room or its contents. This contrasts to the well-Rnown "water damage" that can sometimes exceed the fire damage when the customary water pouring process is used.
The halogenated hydrocarbon fire extinguishing agents that are currently most popular are the bromine-containing halocarbons, e.g.
bromotrifluoromethane (CF3Hr, Halon x.301) and bromochlorodifluoromethane (CF2C18r, Halon 1211). It is believed that these bromine-containing fire extinguishing agents are highly effective in extinguishing fires in progress because, at the elevated temperatures involved in the combustion, these compounds decompose to form products containing bromine atoms which effectively interfere with the self-sustaining free radical combustion process and, thereby, extinguish the fire. These bromine-containing halocarbons may be dispensed from portable equipment or from an automatic room flooding system activated by a fire detector.
In many situations, enclosed spaces are involved. Thus, fires may occur in rooms, vaults, enclosed machines, ovens, containers, storage tanks, bins and like areas. The use of an effective amount of fire extinguishing agent in an atmosphere which would also permit human occupancy in the enclosed space involves two situations. In one situation,-the fire extinguishing agent is introduced into the enclosed space to extinguish an existing fire; the second situation is to provide an ever-present atmosphere containing, the fire "extinguishing" or, more accurately, the fire prevention agent in such an amount that fire cannot be initiated nor sustained. Thus, in U.S. Patent 3,844,354, Larsen suggests the use of chloropentafluoroethane (CF3-CF2C1) in a total flooding system (TFS) to extinguish fires in a fixed enclosure, the chloropentafluoroethane being introduced into the fixed enclosure to maintain its concentration at less than 15%. On the other hand, in U.S. Patent 3,715,438, Huggett discloses creating an atmosphere in a fixed enclosure which is habitable but, at the same time;
does not sustain combustion. Huggett provides an atmosphere consisting essential7.y of air, a perfluorocarbon selected from carbon tetrafluoride, hexafluoroethane, octafluoropropane and mixtures - thereof and make-up oxygen, as required.
It has also been known that bromine-containing halocarbons such as Halon 1301 can be used to provide a habitable atmosphere that will not support combustion. However, the high cost due to bromine content and the toxicity to humans i.e. cardiac sensitization at relatively low levels (e. g. Halon 1301 cannot be used above 7.5-10%) make the bromine-containing materials unattractive for long term use.
In recent years, even more serious objections to the use of brominated haloca:rbon fire extinguishants has arisen. The depletion of the stratospheric ozone -layer, and particularly the role: of chlorofluorocarbons (CFO's) have led to great interest in developing alternative refrigerants, solvents, blouting agents, etc. It is now believed that-bxomine-containing halocarbons such as Halon 1301 and Halon 1211 are at least as active as chlorofluorocarbons in the ozone layer. depletion process.
While perfluorocarbons, such,as those .
suggested by Huggett, cited above, are believed not to.
have as much effect upon the ozone depletion process as chlorofluorocarbons, their extraordinarily high stability makes them suspect in another environmentah area, that of "greenhouse effect". This effect. is caused by accumulation of gases that provide a shield against heat transfer and results in the undesirable warming of the earth's surface:
There is, therefore, a need for an effective fire extinguishing composition and process which can also provide safe human habitation and which composition contributes little or nothing to the stratospheric ozone depletion process or to the "greenhouse effectp.
It is an object of the present invention to provide such a fire extinguishing composition: and to provide a process for preventing and controlling fire in a fixed enclosure by introducing into said fixed enclosure, an effective amount of the composition.
Summary of Inventio In one aspect, the present invention is, based on the finding that an effective, amount of a composition consisting essentially of at least one fluoro-partially substituted ethane selected from the group of pentafluoroethane (CF3-CHF2), also known as FC-125, and the tetrafluoraethanes (CHF2-CHF2 and CF3-CH2F~, also j known as FC-134 and.FC-134a, will prevent and/or extinguish fire based on the combustion of combustible materials, particularly in an enclosed space, without adversely affecting the atmos.pl-iere from the standpoint of toxicity to humans, ozone depletion or "'greenhouse effect"'.
In a second aspect, the, present invention relates to a process for p~~~~, ro~-extinguishing fire in an enclosed air-containing area which is habitable by humans and other mammels and which contains combustible materials of the non-self-sustaining type, the process comprising the steps of introducing into the air in said enclosed area an amount of a gaseous composition comprising CHF3 sufficient to impart wheat , capacity per mol of total oxygen that will suppress combustion of the combustible materials in said enclosed area, without upsetting the mammelian habitability.
The trifluoromethane may be used in conjunction with as little as 1% of at least one halogenated hydrocarbon selected from the group of difluoromethane (HFC-32), chlorodifluoromethane (HCFC-22), 2,2-dichloro-1,1,1-trifluoroethane HCFC-123), 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a), 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124), 1-chloro-1,1,2,2-tetrafluoroethane (HCFC-124a), pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2-tetrafluoroethane (HFC-134a), 3,3-dichloro-1,1,1,2,2-pentafluoropropane (HCFC-225ca), 1,3-dichloro-1,1,2,2,3-pentafluoropropane (HCFC-225cb), 2,2-dichloro-1,1,1,3,3-pentafluoropropane (HCFC-225aa), 2,3-dichlorol,1,1,3,3-pentafluoropropane (HCFC-225da), 1,1,1,2,2,3,3-heptafluoropropane (HFC-227ca), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), _ 5a _ 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,2,2,3-hexafluoropropane (HFC-236cb), 1,1,2,2,3,3-hexafluoropropane (HFC-236ca), 3-chloro-1,1,2,2,3-pentafluoropropane (HCFC-235caj, 3-chloro-1,1,1,2,2-pentafluoropropane (HCFC-235cb), 1-chloro-1,1,2,2,3-pentafTuoropropane (HCFC-235cc), 3-chloro-1,1,1,3,3-pentafluoropropane (HCFC-235fa), 3-chloro T,1,.1,2,2,3-hexafluorapropane.(HCFC-226ca), 1'-chloro-1,1,2,2,3,3-hexafluoropropane (HCFC-226cb), 2-chloro-1,1,1,3,3,3-hexafluorop:ropane (HCFC-226da), 3-chloro-1,1,1,2,3,3-hexafluorop:ropane (HCFC-226ea), and 2-chloro-1,1,1,2,3,3-hexafluoropropane (HCFC-226ba) one particularly surprisingly effective application of the invention is :its use in providing a habitable atmosphere, as defined in Huggett U.S. Patent No. 3,715,438. Thus, the invention would comprise a habitable atmosphere, which does not sustain combustion of combustible materials of the non-self-sustaining type, i.e. a material which does not contain an oxidizer component capable of supporting combustion, and which is capable of sustaining mammalian life, consisting essentially of (a) ai:r; (b) the fluoroethane (FC125, 134 and/or 134a) in an amount sufficient to suppress combustion of the combustible materials present in an enclosed compartment containing said atmosphere; and, optionally if necessary, (c) make-up oxygen in an amount from zero to the amount required to provide; together with the oxygen in the air;
sufficient total oxygen to sustain mammalian life.
The invention also comprises a process for preventing and controlling fire in an enclosed air-containing mammalian-habitable compartment which contains combustible materials of the non self-containing type which consists essentially of:
(a) introducing at least one of 'the aforementioned fluoroethanes into the air in the enclosed compartment in an amount sufficient to suppress combustion of the combustible materials in the enclosed compartment; and (b) introducing oxygen in an amount from zero to the amount required to provide, together with the oxygen present in the air, sufficient total oxygen to sustain mammalian life.

-Preferred Embodiments The tri-fluoroalkane, CHF3, when added in adequate amounts to the air in a confined space, eliminates the combustion-sustaining properties of the air and suppresses the combustion of flammable materials, such as paper, cloth, wood, flammable liquids, and plastic items, which may be present in the enclosed compartment, without detriment to normal mammalian activities.
Tri-fluoromethane is extremely stable and chemically inert. CHF3 does not decompose at temperatures as high as 400°C to produce corrosive or toxic products and cannot be ignited even in pure oxygen so that they continue to be effective as a flame suppressant at the ignition temperatures of the combustible items present in the compartment. CHF3 is also physiologically inert.
Tri-fluoromethane is additionally advantageous because of its low boiling points, i:e.
a boiling point at normal atmospheric pressure of 82.1°C. Thus, at any low environmental temperature likely to be encountered, this gas will not liquefy and will not, thereby, diminish the fire preventive properties of the modified air. In fact, any material having such a low boiling point. would be suitable as a refrigerant.
Tri-fluoromethane is also characterized by an extremely low boiling point anal a high vapor pressure, i.e. about 635 psig at 21°C. This permits CHF3 to act as its own propellant in "hand-~held'° fire extinguishers. It may also be used with other materials such as those disclosed on pages 5 and 6 of this specification to act as the propellant and co-extinguishant for these materials of lower vapor pressure. Its lack of toxicity (comparable to -nitrogen) and its short atmospheric lifetime (with little effect on the global warming potential) compared to the perfluoroalkanes (with lifetimes of over 500 years) make CHF3 ideal for this portable fire-extinguisher use.
As the propellant in a hand-held or other portable platform system (wheeled unit, truck-mounted unit, etc.) the trifluoromethane may comprise anywhere from 0.5 weight percent to 99 weight percent of the mixture with one or more of the compounds listed on pages 5 and 6. When it acts as its own propellant, of course, it comprises 100% of the propellant-extinguisher mixture.
To eliminate the combu~aion-sustaining ' properties of the air in the confined space situation, the gas should be added in an amount which will impart to the modified air a heat capacity per mole of total oxygen present, including any make-up oxygen required, sufficient to suppress or prevent combustion of the flammable, non-self-sustaining materials present in the enclosed environment. Surprisingly, we have found that with the use of CHF3, the quantit:y of CHF3 required to suppress combustion is sufficiently low as to eliminate the requirement for make-up oxygen.
The minimum heat capacity required to suppress combustion varies with t:he combustibility of the particular flammable materials present in the confined space. It is well known that the combustibility of materials, namely their capability for igniting and maintaining sustained combustion under a given set of environmental conditions, varies according to chemical composition and certain physical properties, such as surface area relative to volume;

_ g _ heat capacity, porosity, and the like. Thus, thin, porous paper such as tissue paper is considerably more combustible than a block of wood.
In general, a heat capacity of about 40 cal./°C and constant pressure per mole of oxygen is more than adequate to prevent or suppress the combustion of materials of relatively moderate combustibility, such as wood and plastics. More combustible materials, such as paper, cloth, and some volatile flammable liquids, generally require that the CHF3 be added in an amount sufficient to impart a higher heat capacity. 3t is also desirable to provide an extra margin of safety by imparting a heat capacity in excess of minimum requirements for the particular flammable materials. A minimum heat capacity of 45 cal./°C per mole of oxygen is generally adequate for moderately combustible materials and a minimum of about 50 cal./°C per mole of oxygen for highly flammable materials. More can be added if desired but, in general, an amount imparting w heat capacity higher than about 55 cal./°C per mole of total oxygen adds substantially to the cost and may create unnecessary physical discomfort without any substantial further ' increase in the fire safety factor.
Heat capacity per mole of total oxygen can be determined by the formula:
Cp * _ ( Cp ) o + p;a ( Cp ) z 2 z Po2 wherein:
Cp* = total heat capacity per mole of oxygen at constant pressure;
Po = partial pressure of oxygen;

PZ = partial pressure of other gas;

(Cp)Z = heat capacity of other gas at constant pressure.
The boiling points of CHF3 and the mole percent required to impart to air heat capacities (Cp) of 40 and 50 cal./°C at a temperature of 25°C and constant pressure while maintaining a 21% oxygen content are tabulated below:
Boiling point, Cp=40 Cp=50 °C. percent percent CHF3 -82.1 21.5 62.0 It will be noted from Example 2 that CHF3 is not toxic at concentration up to about 80%.
The concentration of oxygen available in the confined air space should be sufficient to sustain mammalian life. The amount of make-up oxygen, if required, is determined by such factors as degree of air dilution by the CHFg gas and depletion of the available oxygen in the air by human respiration. The amount of oxygen required to sustain human, and therefore mammalian life in general, at atmospheric, subatmospheric, and superatmospheric pressures, is well known and the necessary data are readily available.
See, for example, Paul Webb, Bioastronautics Data Book, NASA SP-3006, National Aeronautics and Space Administration, 1964, p. 5. The minimum oxygen partial pressure is considered to be about 1.8 p.s.i.a., with amounts above 8.2 p.s.i.a. causing oxygen toxicity. At normal atmospheric pressures at sea level, the unimpaired performance zone is in the range of about 16 to 36 volume percent of oxygen. The normal amount of oxygen maintained in a confined space is about 16% to about 21% at normal atmospheric pressure.
In most applications using CHF3, no make-up oxygen will be required initial7Ly or even thereafter, since the CHF3 volume requirement even when the starting oxygen amount of 21o ds~creased to 16%, is extremely small. However, habitation for extended periods of tune will generally n-equire addition of oxygen to make up the depletion caused by respiration.
Introduction of the CHF3 gas and any oxygen is easily provided for by metering appropriate quantities of the gas or gases .into the enclosed air-containing compartment.
The air in the compartment can be treated at any time that it appears desirable. The modified air can be used continuously if a threat of fire is constantly present or the particular environment is such that fire hazard must be kept at an absolute minimum, or it can be used as an emergency measure if a threat of fire develops.
As stated previously, small amounts of one or more of the compounds set forth on pages 5 and 6 may be used along with the CHF3 gas wii~hout upsetting the mammalian habitability or losing the other advantages of the CHF3.
The invention will be more clearly understood by referring to the examples which follow. The unexpected effects of CHF3, and CHF3 in the aforementioned blends, in suppressing and combatting fire, as well as its compatabil:ity with the ozone layer and its relatively low °'greenhouse effect°', when compared to other fire-combatting gases, particularly the perfluoroalkanes, are shown in the examples.

Example 5 CHF-~ as a Propellant (compared to nitrogen) The discharge propertiE~s of 2,2-dichloro-1,1;1-trifluoroethane were measured first pressurized with nitrogen as a control example and then pressurized with trifluoromethane as Example 5:
Control - 1182.2 grams of 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) was added to a container serving as an extinguisher. The container was then pressurized to 151 psig with 5.3 grams of nitrogen. Then, the exi=inguisher contained 99.5% HCFC-123 and 0.5% nitrogen..
Example - 1014 grams of HCFC-123 was added to a container serving as an extinguisher. The container was then pressurized to 150 psig (equivalent to the Control) with 108.5 grams of CHF;;. Thus, the extinguisher contained 90.3% HCFC-123 and 9.7% CHF3.
Both extinguishers werea discharged in short bursts and the reduced pressures between bursts recorded in Tables 5 and 5A. It will be noted that the pressure was lost very rapidly in the Control example even with only 12.5 wt.% of the contents discharged;
whereas the propellant (CHF3) in Example 5 maintains over 67% of the original pressurca even after'almost 87 wt.% of the contents have been discharged. Compare the 21st burst in Table 5 to the fir:at burst in Table 5A.
Although this example discloses the use of CHF3 as a propellant for portable fire extinguishers at an initial pressure of 150 psig (approximately 10.5 bars), it should be understood that lower pressures can be used. Thus, at room temperature (20°C), it would not be advisable to pressurize the extinguisher with CHF3 above 2.5 bars for a glass container, nor above 4.5 bars for one composed of tin.

It is also understood that, although the starting weight percent of the CHF3 propellant in the example was about 10%, anywhere from 0.5 to 100 weight percent of CHF3 may be used in this invention.

Burst Total Wt. Weight Discharge Pressure Pressure (gms) Change (%) (psig) Change (9ms) (Psig) 0 2798.8 -0.0 150.0 1 2753.5 45.3 4.0 148.0 2.0 2 2713.0 40.5 7.6 146.0 2.0 3 2669.3 43.7 11.5 145.0 1.0 4 2624:5 44.8 15.5 144.0 1.0 25.75.3 49.2 19.9 142.0 2.0 6 2528.9 46.4 24.0 140.0 2.0 7 2487.4 41.5 27.7 138x0 2.0 8 2448.3 39.1 31.2 136.0 2.0 9 2390.5 57.8 36.4 134.0 2.0 2348.1 42.4 40.2 133.0 1.0 ' 11 2304.0 44.1 44.1 130.0 3.0 12 2256.0 48.0 48.4 128.0 2.0 13 2210.3 45.7 52.4 127.0 1.0 14 2161.6 48.T 56.8 125.0 2.~

2108.8 52.8 61.5 123.0 2.0 16 2063.7 45.1 65.5 120.0 3.0 17 2021.7 42.0 69.2 118.0 2.0 18 1961.7 60.0 74.6 115.0 3.0 19 1915.0 46.7 78.7 113.0 2.0 1854.5 60.5 84.1 109:0 4.0 21 1824.7 29.8 86.8 103.0 6.0 22 1793.5 31.2 89.6 80.0 23.0 23 1744.1 49.4 94.0 0.0 80.0 Burst Total Wt. Weight Discharge Pressure Pressure (gms) Change (~) (psig) Change (gms) (pslg) 0 2863.8 -0.0 151.0 1 2715.3 148.5 12.5 90.0 61.0 2 2601.9 113.4 22.1 70.0 20:0 3 2521.5 80.4 28.8 62.0 8.0 4 2446.7 74.8 35.1 56.0 6.0 5 2358.5 88.2 42.6. 51.0 5.0 6 2271.2 87.3 49.9 46.0 5.0 7 2179.0 92.2 57.7 43.0 3.0 8 2065.2 113.8 67.3 39.0 4.0 9 1924.7 140.5 79.1 36.0 3.0 10 1812.6 112.1 88.5 30.0 6.0 11 1791.6 21.0 90.3 15.0 15.0

Claims (2)

What is Claimed is:

1. A process for extinguishing fire in an enclosed air-containing area which is habitable by humans and other mammals and which contains combustible materials of the non-self-sustaining type, the process comprising the steps of introducing into the air in said enclosed area an amount of a gaseous composition comprising at least one fluoro-substituted ethane selected from the group consisting of CF3-CHF2, CHF2-CHF2 and CF3-CH2F sufficient to impart a heat capacity per mol of total oxygen that will suppress combustion of the combustible materials in said enclosed area, without upsetting the mammalian habitability.

2. A process as in Claim 1 wherein make-up oxygen is also introduced into said enclosed area in an amount from zero to the amount required to provide, together with the oxygen present in said air, sufficient total oxygen to sustain mammalian life.