FIRE EXTINGUISHING COMPOSITION
Field of the Invention This invention relates generally to fire extinguishing compositions, and more particularly to fire extinguishing compositions for application to hydrocarbon fires.
Background of the Invention
There is a continuing need to develop effective compositions for extinguishing fires. Particularly, there is a need for effective liquid fire extinguishing compositions. Liquid compositions are more easily transported, stored, and applied than pressurized canisters such as the traditional C02 canisters. Liquid compositions also have distinct advantages when fighting large fires, since the liquid can be dispersed over a wide area using a suitable dispensing nozzle or orifice. Water has long been used as an effective liquid fire extinguishing composition. Water has a number of disadvantages. Relatively large quantities of water are required to extinguish a fire, and large quantities of water may not be readily available or practical. Water is not a very good fire extinguishing composition for hydrocarbon fires, such as grease fires, oil fires, tar fires, and the like, because the hydrocarbons repel the water. Also, these "Class B" fuels fires burn hotter and faster than many other kinds of fires due to the efficiency of hydrocarbons as a fuel for oxidation reactions. Compositions for efficiently extinguishing out such fires are therefore desired.
A standard measure for the effectiveness of a fire extinguishing composition typically for hydrocarbon fires is Test Standard UL 162 as prescribed by Underwriters Laboratories Inc. , of Northbrook, IL. This test measures both the effectiveness of the composition at initially extinguishing the fire, as well as the ability of the composition to retard re-ignition of the fire, or "burn back". A fifty square foot pan is filled with four inches of water. A two inch layer of N-heptane is added, and floats on the surface of the water. The N-heptane is then ignited and allowed to burn for one minute. The fire extinguishing composition is then distributed across the surface of the pan at a rate of two gallons per minute. The fire must be extinguished within three minutes. A torch flame is applied about one inch from the surface of the foam from minutes four to five. No candle flame must be produced which can sustain itself for more than thirty seconds. The torch test is repeated from the sixth minute to the seventh minute. At eight minutes, a 12 inch stove pipe is placed vertically into the pan, two and one half feet from the corner of the pan with the least consistency of foam. The N-heptane within the pipe is reignited at nine minutes, and after one minute the pipe is removed. The tested composition must prevent the fire from spreading to more than 20% of the surface area of the pan between minute 10 and minute 15 in order to pass the test.
Many compositions are known for effectively extinguishing hydrocarbon fires. One class of such compounds are fluorinated polymers, which are applied to the fire with a
carrier. Ethanol is a common carrier, despite its flammability, as the flammability is insignificant relative to the amount of fire extinguishing composition that is being applied. The fluorinated polymer is typically applied with a surfactant, which helps to distribute the polymer across the surface of the fuel and to prevent agglomeration of the polymer. Agglomeration will result in gaps in the polymer layer, which will permit oxygen to reach the fuel and to allow the flame propagation. Fluorocarbon compounds have received increasing scrutiny for environmental concerns. It is therefore desired to reduce the amount of fluorocarbon compounds in products including fire extinguishing products.
Summary of the Invention It is an object of the invention to provide a fire extinguishing composition which will effectively extinguish hydrocarbon fires.
It is another object of the invention to provide a fire extinguishing composition which will pass Test Standard UL 162 of Underwriter's Laboratories, Inc.
It is still another object of the invention to provide a fire extinguishing composition which will require reduced amounts of fluorocarbon compounds.
These and other objects are provided by a fire extinguishing composition comprising a fluorinated polymer and a surfactant for the fluorinated polymer. The surfactant
comprises at least one of a sulfate or phosphate having the general formula
MRX
where M is a salt forming cation selected from the group consisting of Na, Li, K, and NH4; R is a straight chain alkyl having from 5 to about 8, and preferably less than 8 carbon atoms; and X is a sulfate or phosphate group.
Preferred surfactants are sodium hexyl sulfate and sodium octyl sulfate. These surfactants can be used alone or in combination, as well as in combination with other surfactants. A preferred fluorinated polymer is Forafac 1157 or 1157N, a trademark of Elf-Atochem North America, Inc. of Philadelphia, Pennsylvania. This product is polyfluorinated alkyl betaine, in a solvent of ethanol and water. Other fluorinated polymers are possible. Such products are described in EP621057A, the disclosure of which is incorporated by reference.
Detailed Description of the Preferred Embodiments The fluorinated polymer can be selected from a number of different polymers suitable for extinguishing fires, and particularly hydrocarbon fires. A currently preferred fluorinated polymer is that produced under the trademark Forafac 1157 and 1157N, a product of Elf-Atochem North America, Inc. of Philadelphia, Pennsylvania. Forafac 1157N is an amphoteric perfluoroalkyl surfactant manufactured as a 27%
active solution of RFCH2CH2S02NHCH2CH2CH2N(+) (CH3) 2CH21COO(-) .
The solvent medium of Forafac 1157 and 1157N is a mixture of ethanol and water. A 27% active solution of Forafac 1157N contains 27% of fluoroalkyl betaine, 11% ethanol and the balance water. The fluorinated polymer is preferably carried by a suitable solvent medium. The fluorinated polymer can also be mixed with a combination of solvents for the polymer.
Surfactants suitable for the invention include those having formula MRX
where M is selected from Na, Li, K and NH4; R is a straight chain alkyl having between 5 and 8 carbons, and preferably having less than 8 carbons; and X is a sulfate group or a phosphate group. Currently preferred surfactants are sodium hexyl sulfate and sodium octyl sulfate. Also, as the number of carbons is reduced, free alcohol will accumulate in the product and must be stripped out of the polymer product by suitable stripping processes known in the art. The stripping processes will remove water with the alcohol, which can have the added advantage of permitting the product to be shipped in a dry or reduced-weight condition. The water can be added at the desired location where the final composition is prepared.
The polymer, solvent, and surfactant are mixed together in proportions which will vary depending on the particular polymers, solvents, and surfactants that are used. The final,
mixed solution is diluted in water. In general, the fewer the number of carbons in the straight chain surfactant, the less of the surfactant that will be necessary. Suitable compositions are illustrated as follows where all percentages, unless indicated otherwise are by weight of the composition.
Example 1 A fire extinguishing composition was prepared having the formula:
(Forafac 1157N™) 2 lbs.
Sodium octyl sufate 12.125 lbs.
Water 87.875 lbs.
Example 2 A fire extinguishing composition was prepared having the formula:
(Forafac 1157N™) 2 lbs.
Sodium octyl sufate 6.6 lbs.
Water 93.4 lbs.
Example 3
A fire extinguishing composition was prepared having the formula:
(Forafac 1157N™) 2 lbs. Sodium hexyl sulfate 5.0 lbs.
Water 95 lbs.
Example 4
A fire extinguishing composition can be prepared having the formula: (Forafac 1157N™) 1 lbs.
Sodium pentyl sulfate 12.125 lbs.
Water 87.875 lbs.
Example 5 The composition of Example 1 was applied as a 3% solution (by weight) with water to extinguish a fire under the procedures described in Test Standard UL 162 of Underwriter's Laboratories, Inc., as described above. The solution extinguished the fire in approximately one minute and thirty five seconds, and passed the Test 162 requirements that the fire not spread to more than 20% of the surface area of the panin minutes 10 to 15.
Several other surfactants known in the art are possible for use with the invention. Several surfactants are described in Collier et al, U.S. Patent No. 4,007,124 and Barrat, et al, U.S. Patent No. 4,111,855. The disclosures of these patents are incorporated fully by reference. The preferred compositions according to the invention have between about 0.5% and about 4% (by weight) of fluorinated polymer (Forafac 1157N) , between about 5.5 and about 16% surfactant, and between about 80 and about 94% water.
The solution can be applied to a fuel which is under combustion in any suitable manner. The solution can be
sprayed, dumped, injected or otherwise distributed in any manner suitable for a liquid and such that the composition will cover the surface of the fuel. The composition will form a foam on the top of the fuel, which will prevent oxygen from reaching the fuel and thereby will prevent flame propogation and extinguish the fire.
The fluorinated polymer is heat resistant and floats on a top of fuels such as oil. The surfactant holds the polymer together so that a substantially continuous layer is formed over the fuel to prevent oxygen from reaching the fuel and thus prevent flame propagation. The higher the number of carbons in the surfactant, generally the more of the surfactant will be necessary to put out the same fire. Ethanol, if present as a solvent for the fluorinated polymer, will flash upon reaching the hot fire.
The invention provides a composition which preferably has less than 0.5% fluorine, based on the weight of the total composition. The composition ca be shipped as a concentrate. Water is added at the place where the final composition is desired, preferably to 97% by weight of the total composition. The invention can be provided in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be had to the following claims, rather than to the foregoing specification as indicating the scope thereof.