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Aqueous foams are typically used in controlling and extinguishing flammable liquids fires. In some cases, however, the foam is used to fill an entire compartmentThis type of foam is known as high expansion, and expands water up to 1,000 times. When using high expansion foam, the level to which the hazard has to be "covered" has to be calculated. Typical applications are rolled paper warehouses and the hold of a cargo ship.. Thus, foam is hazard-specific.
Foam is a mass of bubbles that are formed by providing a foaming agent – foam concentrate solution diluted with water – and a way to inject air into the mixture. Because the resultant "foam" is lighter than the flammable liquids to which it is applied, a continuous layer is formed over the surface of the flammable liquid. Some foam concentrates are thick and viscousThese will spread a tough heat resistant blanket over the surface of a burning liquid., and some are light and thin.
The use of foam requires some acute attention to the way it works and its characteristics. As foam generally forms a blanket, it is imperative that the blanket not be broken, either mechanicallyIn many fires, other means, such as the application of hose streams, may be part of the plan. If this is the case, the force of a hose stream may impact the foam's ability to form a blanket. Careful planning is a must. or chemicallyCertain chemical vapors and some types of liquids can easily destroy the foam. There is also the chance that vapor release from burning chemicals may divert the foam away from its intended area.. In the case of a fire, foam applied to the fire may be, at first, broken down, causing the water content to vaporize under attack by heat and flame. Thus, there must be a continuous applicationThe rate and volume has to be sufficient to make up for any breakdown or loss in a fire situation. for a designated period of time, or the foam will be ineffective. There also has to be enough concentrate to do the entire job. Partial application is not an option, as the foam will be destroyed quickly as the fire burns if enough foam is not applied for an extended period.
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