Classifications

• • A—HUMAN NECESSITIES
  • A62—LIFE-SAVING; FIRE-FIGHTING
  • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
  • A62D1/00—Fire-extinguishing compositions; Use of chemical substances in extinguishing fires
  • A62D1/0071—Foams
  • A62D1/0085—Foams containing perfluoroalkyl-terminated surfactant

Definitions

• the present invention relates to the field of fire extinguishing and more particularly relates to foam concentrates for portable water spray extinguishers.
• foaming base generally consists of a hydrolyzate of animal proteins (hair, horns, hooves, hemoglobin).
• fluorosurfactants to obtain a fluoroprotein foam concentrate; such emulsifiers are described, for example, in patents GB 1,280,508, GB 1,368,463, US 4,424,133, EP 49,958, US 4,460,480, FR 2,230,384, GB 2,011,784 and WO 8803425.
• the foaming base is composed of a mixture of hydrocarbon-based surfactants. Fluorinated film-forming surfactants can also be incorporated.
• AFFF emulsifiers the presence of the fluorinated surfactant makes it possible to produce a foam which, by decantation, forms an aqueous film floating above the surface of the hydrocarbon. The purpose of this aqueous film is not only to extinguish the fire, but also to prevent a possible re-ignition of the surface of the hydrocarbon.
• Emulsifiers of this type have been described in numerous patents, in particular the following: GB 1 258 299, US 5 085 786, FR 2 347 426, US 3 957 657, FR 2 040 316, US 4 350 206, FR 3 562 156, FR 2 148 442, FR 2 407 724, FR 2 385 413, US 3 772 195, FR 2 397 847, US 3 661 776, US 3 839 425, FR 2 103 669, US 3 957 657, US 3 963,776 and FR 2,296,625.
• the spreading coefficient must be positive, care must be taken that the interfacial tension ( Yi ) is not too low in order to avoid emulsification of the hydrocarbon by the extinguishing composition or too great thinning of the film aqueous.
• the emulsification of the hydrocarbon by the extinguishing composition risks in fact causing the entrainment of part of the hydrocarbon inside the extinguishing foam, of contaminating the latter and of igniting it.
• the thermal resistance of the aqueous film Another important factor vis-à-vis the re-ignition phenomenon is the thermal resistance of the aqueous film.
• an excessive spreading speed leads to the formation of a very thin film which is not very resistant to heat; conversely, the films most resistant to heat are those with the slowest speed of formation. It is therefore important to find a compromise between the spreading speed and the thermal resistance of the aqueous film, this property being essential for obtaining good resistance to re-ignition.
• the aqueous film which removes the hydrocarbon vapors can at any time, for example by stirring, be separated from the foam from which i is derived and be found directly in contact with an ignited part. If its thermal resistance is too low, the film can be destroyed and release hydrocarbon vapors which ignite immediately and continue to destroy the rest of the film.
• AFFF foam concentrates which are generally used with fire hoses are not suitable in a portable extinguisher designed to be carried and used by hand and which, in working order, has a mass less than or equal to 20 kg.
• the amount of water available to dilute the foam concentrate to the use concentration (0.5 to 6%, most often 1 to 3%) is limited and generally set at 6 or 9 liters , while in the application system by means of a lance the quantity of water available is not limited. Therefore, to meet the certification standards for foaming liquids for hydrocarbon fires, a foaming agent for portable fire extinguisher must be much more efficient than a conventional foaming agent for fire hoses.
• the portable extinguisher must extinguish with only 6 liters of foam concentrate solution diluted to 3% (French standard) S61-900), while in the case of extinction with a fire hose the maximum available quantity of foam concentrate solution diluted to 3% may be up to 28.5 liters (French standard S60-220) or 22 , 3 liters (UL 162 standard).
• the total content of fluorinated compounds a and b being between 5 and 25% (preferably between 7 and 18%) and the weight ratio (a + b) / (c + d) being between 1 and 2 (preferably between 1.3 and 1.7).
• the non-fluorinated surfactant (d) can be chosen from the compounds of the following formulas: in which R 4 represents an alkyl radical, linear or branched, containing from 8 to 18 carbon atoms, r is an integer ranging from 1 to 16, M denotes an alkali metal ion or quaternary ammonium and M 'an alkali metal ion.
• monoalkyl ethers there may be mentioned the monoethyl or monobutyl ether of ethylene glycol and the monobutyl ether of diethylene glycol, the latter being preferred.
• the foam concentrates according to the invention can be prepared by simple mixing of the various constituents until homogenization. To accelerate the homogenization, one can operate by heating to a temperature between room temperature and that of boiling of the mixture, preferably at a temperature between 30 and 60 ° C.
• the pH of the foam concentrate is advantageously stabilized at a value at least equal to 7 (preferably between 8 and 10) by means of a weak base, for example ammonia or an organic base such as diethanolamine, triethanolamine, urea.
• a weak base for example ammonia or an organic base such as diethanolamine, triethanolamine, urea.
• the foam concentrates according to the invention can be used in a portable fire extinguisher in an amount of 0.5 to 6 parts by weight (preferably 1 to 3 parts) of foam concentrate per 100 parts by weight of water.
• This test which indicates the speed of formation of the aqueous film on the surface of the hydrocarbon, is carried out by pouring 50 ml of hydrocarbon (heptane) into a Petri dish (diameter: 11.5 cm), the outer face of which is painted black so that you can watch the film.
• hydrocarbon heptane
• Petri dish diameter: 11.5 cm
• 0.1 ml of a 3% aqueous emulsifier solution is deposited using a micropipette.
• the solution should be applied dropwise starting from the center and making an eccentric movement.
• the stopwatch is started when the first drop is deposited and stopped when the film has covered the entire surface of the hydrocarbon. We note the time. If the total recovery is not obtained in less than a minute, the percentage of surface covered after one minute is noted.
• the spreading is satisfactory if the total recovery is obtained in less than 30 seconds, preferably between 5 and 25 seconds.
• the evaluation of the thermal resistance of the aqueous film is obtained by measuring the Limit Temperature of Film Stability (TLSF).
• TLSF Limit Temperature of Film Stability
• a good foam concentrate should lead to a TLSF higher than 35 ° C, preferably higher than around 40 ° C
• the overrun (or expansion rate) is the ratio of the volume of foam produced from a 3% aqueous solution of foam concentrate to the initial volume.
• 100 ml of 3% aqueous emulsifier solution is introduced into a 1 liter test tube, then the solution is beaten for one minute at the rate of one beat per second using a perforated circular piston (30 holes of 5 mm in diameter representing 25% of the surface) and fixed in its center to a metal rod.
• a satisfactory foam concentrate must lead to an expansion at least equal to 8.
• the surface tension (y s ) with tap water and the interfacial tension ( ⁇ ) with heptane are measured using a LAUDA tensiometer in accordance with ISO 304 and ISO 6889 standards, but operating at 25 ° C.
• an emulsifier according to the invention is prepared, the active ingredient contents of which are as follows:
• the foam concentrates (b1) and (b2) prove to be less efficient than the foam concentrate of example 1-a.
• Example 1-a is repeated, but the proportions of the various constituents are modified and / or the surfactant D1 is replaced by the compound D2.
• Example 1-a The procedure is as in Example 1-a, but a part of the ether E is replaced by monoethylene glycol (hereinafter MEG) and the proportions of the various surfactants are varied.
• MEG monoethylene glycol
• Example 1-a The procedure is as in Example 1-a, but a part of the ether E is replaced by monoethylene glycol and at least one of the surfactants D2, D3 and D4 is used in place of D1 and / or instead of alkylglucoside C.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Business, Economics & Management (AREA)
• Emergency Management (AREA)
• Fire-Extinguishing Compositions (AREA)
• Emulsifying, Dispersing, Foam-Producing Or Wetting Agents (AREA)

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Citations (3)

• 1994
  • 1994-04-13 DK DK94400801T patent/DK0621057T3/da active
  • 1994-04-13 EP EP19940400801 patent/EP0621057B1/de not_active Expired - Lifetime
  • 1994-04-13 ES ES94400801T patent/ES2094028T3/es not_active Expired - Lifetime
  • 1994-04-13 DE DE1994600885 patent/DE69400885T2/de not_active Expired - Lifetime
  • 1994-04-19 CA CA 2121654 patent/CA2121654A1/fr not_active Abandoned
  • 1994-04-20 AU AU60595/94A patent/AU658341B2/en not_active Ceased
  • 1994-04-22 JP JP6084383A patent/JP2575289B2/ja not_active Expired - Lifetime

Patent Citations (3)

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