According to the present invention there is provided a fire extinguishant solution comprising a modified aqueous fire fighting foam and a salt selected from a group containing potassium lactate, a glycollic acid salt, a lactic acid salt, a hydroxybutyric acid salt, a tartaric acid salt, potassium glycollate, potassium hydroxybutyrate and potassium tartrate, wherein the aqueous fire fighting foam is modified by the exclusion of an anionic hydrocarbon surfactant such as sodium octyl sulphate.

According to the invention, there is also provided a fire extinguishant solution consisting of a salt selected from a group containing potassium lactate, a glycollic acid salt, a lactic acid salt, a hydroxybutyric acid salt, a tartaric acid salt, potassium glycollate, potassium hydroxybutyrate and potassium tartrate in a proportion from 5 weight % to 60 weight %, a fluorosurfactant in a proportion from 0.02 weight % to 1 weight %, a hydrocarbon surfactant in a proportion from 0.05 weight % to 0.5 weight %, a foam booster such as diethylene glycol monobutyl ether in a proportion from 0.1 weight % to 2.0 weight % and a trace of biocide, the remainder being water.

Fire extinguishant solutions in accordance with the invention will now be described by way of example.

It is desirable to combine the benefits of foam extinguishants with the fast fire knock- down effect of fire extinguishing powders. However, an extinguishant combining a salt such as potassium lactate or citrate with a fluorosurfactant has been found to be unstable and unsatisfactory.

An alternative approach is to combine an aqueous foam fire fighting compound (AFFF) with a salt such a potassium lactate. This is also unsatisfactory since the resulting solution is unclear and unstable and has an increased viscosity.

It has been found, however, in accordance with the invention that an AFFF which has been modified by the removal or alteration of a hydrocarbon surfactant (typically an anionic surfactant) provides a highly effective fire extinguishant when combined with a salt such as potassium lactate. Furthermore, the resulting water-based compound has a low freeze temperature (being usable at temperatures less than-40° C) and provides a cost-effective method of producing small particles of extinguishant within a fire for more effective fire-fighting. Furthermore, the fire extinguishant has an approximately neutral PH, is non-toxic, and it improves on powder base extinguishants in that it is easier to distribute through pipework without clogging and is easier to clean up after discharge.

It also provides a more effective fire extinguishant than water or a foam/water mix.

Although potassium lactate is the preferred salt, salts of glycollic acid, lactic acid, hydroxybutyric acid and tartaric acid may be used. Also potassium glycollate, potassium hydroxybutyrate or potassium tartrate salts may be used.

The preferred composition is 5 weight % to 60 weight % (most preferably 45 weight % to 55 weight %) potassium lactate, 0.02 weight % to 1 weight % (most preferably 0.08 weight % to 1.0 weight % fluorosurfactant (Atochem Forarfac 1157N), 0.05 weight % to 0.5 weight % (most preferably 0.2 weight % to 0.3 weight %) hydrocarbon surfactant (Henkel APG 325N), 0.1 weight % to 2.0 weight % (most preferably 0.4 weight % to 0.6 weight %) foam booster (Diethylene glycol monobutyl ether [butyl carbiton/butyl diglycol]) and a trace of biocide (Nippon Bactrachem W15), the remainder being water.

The foam booster is optional but its inclusion improves the performance of the extinguishant.

Comparative tests have been conducted on a lm3 test rig with all sides covered apart from the front. An obstruction in the form of a car engine was placed in the centre of the rig and the extinguishant agents were discharged via horizontal jets or overhead sprays. Five litres of diesel with 1 litre of petrol floating on a water base was used as the fuel. The fire was allowed to burn for 30 seconds to allow for full fire involvement of the diesel before extinguishant actuation.

The following results were obtained: AGENT EXTINCTION TIME DISCHARGE TIME COMMENTS (Seconds) (Seconds) PREFERRED COMPOSITION 250 ml (210gms) 1.6 Fire almost extinguished 500 ml (420gms)--Fire extinguished 1 Litre (0.83kg) 2.89 8.17 Fire extinguished 1 Litre (0.83kg) 0.51 3.58 Fire extinguished easily COMPARATIVE TESTS 9 It (9kg) AFFF premix 45 106 Fire extinguished 0.25 kg Halon 1211 1.63 4.17 Fire extinguished 0.5 kg Halon 1211 1.38 2.89 Fire extinguished 0.5 kg FM200 2.90 5.46 Fire just extinguished 0.5 kg FE36-5.63 Fire was not extinguished Tests have also been conducted to compare the effect of the preferred composition and AFFF on polar-solvent fires.

Tests were conducted on a fire tray as described in MoD Defence standard 42-41/Issue 1,0.25m2 fire tray. Comparative tests were conducted with a 3 Itr. portable fire extinguisher filled with AFFF and the preferred composition respectively. DESCRIPTION RESULTS Test 1 Fire extinguished in 5 seconds. 9 ltrs of isopropanol poured into tray. Pre-burn for 1 minute prior to discharge of hand held extinguisher filled with the preferred composition. Test 2 Fire not extinguished. As Test 1 but filled with AFFF. Test 3 Fire extinguished in 5 seconds. As Test 1 but with 9 ltrs of acetone with a 2 minute pre-burn. Test 4 Fire not extinguished. As Test 3 but filled with AFFF. These tests show that the preferred composition has a better performance than AFFF premix, FM200 and FE36. The performance approaches that of Halon 1211.

The preferred extinguishant may be used for fixed systems and portable appliances.

Potassium lactate is non-toxic and generally harmless.

In operation, the various components of the extinguishant contribute to the extinguishing action. Thus, the water cools the flammable liquid to below its ignition temperature and the fire goes out. The limiting factor is the droplet size; hence the success of mist and fog systems as compared to jets of water. The smaller the droplet size the greater the surface area, and the more effective the spray. The water droplets absorb heat as they boil and turn to water vapour. This water vapour also takes up significantly more volume, thus diluting the local oxygen level. The addition of the modified AFFF reduces the surface tension of the water to below 20mN/m, and the water forms smaller droplets. The greater surface area of the smaller droplets increases the speed of operation of the extinguishant.

Finally, the potassium lactate is broken down by the fire. Heat is absorbed as the compound breaks down and potassium ions are liberated which break the'fire chain'.

Potassium lactate absorbs more energy as it breaks down than potassium bicarbonate which has been used as an extinguishant. The solution droplets entering the combustion zone and impinging on the hot surfaces will release the potassium lactate from the solution.