Application of firefighting foam concentrate in low, medium and high expansion
The foam blanket contains firefighting foam concentrate and water (premix solution) combined with air.
The expansion ratio is the volume of finished foam produced versus the volume of premix solution supplied. The more air is introduced, the higher expansion ratio you get. For example: when a foam generator supplied with 100 litres of water + foam solution produces 1000 litres of foam, the expansion ratio is therefore 1000/100 = 10.
There are 3 expansion ratios depending on the foam proportioning and discharge devices used:
Foam expansion ratio <20
Low expansion is commonly used on widespread hydrocarbon fires such as in tank storage, refineries, airports and onbroad ships. A high density foam allows long projection distances and heights using fixed/mobile nozzles or monitors, allowing firefighting from a safe distance. Bubbles are very small, dense and heavy. The foam blanket is stable and provides a strong cover. Low expansion foam has a good flowability. It spreads quickly above the fuels and adheres to vertical surfaces. It separates the fuel from oxygen supply by forming an aqueous or polymer film. Moreover, its high ratio of water guarantees significant cooling effect. Low Expansion foam is not sensitive to atmospheric conditions such as wind or rain.
Foam expansion ratio ≥ 20 to < 200
Medium Expansion is mostly used by municipal fire brigades, for small surfaces such as road traffic accident, solvent storage or to control hazardous chemicals spill. A large amount of finished foam is produced with minimum quantity of premix solution and within a short time. The thick foam blanket quickly spreads above the fuel, separating the fuel from oxygen supply and resulting in fire extinguishment. The water contained provides additional cooling effect to control fire faster and prevent reignition. Low density makes it a bit sensitive to wind and bad weather.
Expansion ratio of foam ≥ 200
High Expansion is mostly used on dry product fires or enclosed areas to drawn large volume surfaces and fill cavities such as warehouse, cellars, aircraft hangar or engine/pump rooms aboard ships. Less water used produces a very large amount of foam in a short time, resulting in fire extinguishment by smothering. In high expansion, bubbles are very light and large, they contain a high proportion of air. Foam bubbles are achieved by spraying the solution onto a wide screen while a lot of air is introduced naturally or in a forced manner. High expansion foam is not suitable for outdoor use. High expansion foam fire extinguishing systems must be installed in the immediate area of the potential fires.
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