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كتاب جديد
كل ما تريد معرفته عن مظام اطفايْ الحريق بالرغوه
التصميم
حساب الكميات
انواع الفوم المختلفه
انواع الادوات المسخدمه في الفوم
حساب الخزان
ABOUT FOAM
Firefighting foam is a foam used for fire suppression. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion. Fire-fighting foam was invented by the Russian engineer and chemist Aleksandr Loran in 1902.
The surfactants used must produce foam in concentration of less than 1%. Other components of fire-retardant foams are organic solvents (e.g., trimethyl-trimethylene glycol and hexylene glycol),
foamstabilizers (e.g., lauryl alcohol), and corrosion inhibitors.
foamstabilizers (e.g., lauryl alcohol), and corrosion inhibitors.
Overview
- Low-expansion foams such as AFFF, have an expansion rate less than 20 times are low-viscosity, mobile, and can quickly cover large areas.
- Medium-expansion foams have an expansion ratio of 20–100.
- High-expansion foams have an expansion ratio over 200–1000 and are suitable for enclosed spaces such as hangars, where quick filling is needed.
- Alcohol-resistant foams contain a polymer that forms a protective layer between the burning surface and the foam, preventing foam breakdown by alcohols in the burning fuel. Alcohol-resistant foams are used in fighting fires of fuels containing oxygenates, e.g. MTBE, or fires of liquids based on or containing polar solvents.
Class A foams
Class A foams were developed in mid-1980s for fighting wildfires. Class A foams lower the surface tension of the water, which assists in the wetting and saturation of Class A fuels with water. This aids fire suppression and can prevent reignition. Favorable experiences led to its acceptance for fighting other types of class A fires, including structure fires.
Class B foams
Class B foams are designed for class B fires — flammable liquids. The use of class A foam on a class B fire may yield unexpected results, as class A foams are not designed to contain the explosive vapors produced by flammable liquids. Class B foams have two major subtypes.
Synthetic foams
Synthetic foams are based on synthetic surfactants. They provide better flow and spreading over the surface of hydrocarbon-based liquids, for faster knockdown of flames. They have limited post-fire security and are toxic groundwater contaminants.
- Aqueous film forming foams (AFFF) are water-based and frequently contain hydrocarbon-based surfactant such as Sodium alkyl sulfate, and fluorosurfactant, such as fluorotelomers, perfluorooctanoic acid (PFOA), or perfluorooctanesulfonic acid (PFOS).
- Alcohol-resistant aqueous film-forming foams (AR-AFFF) are foams resistant to the action of alcohols and can form a protective film.
Protein foams
Protein foams contain natural proteins as the foaming agents. Unlike synthetic foams, protein foams are bio-degradable. They flow and spread slower, but provide a foam blanket that is more heat-resistant and more durable.
Protein foams include regular protein foam(P), fluoroprotein foam(FP), film-forming fluoroprotein(FFFP), alcohol-resistant fluoroprotein foam (AR-FP), and alcohol-resistant film-forming fluoroprotein (AR-FFFP).
Protein foam from non-animal sources is preferred, because of the possible threats of biological contaminants such as prions.
Applications
Every type of foam has its application. High-expansion foams are used when an enclosed space, such as a basement or hangar, must be quickly filled. Low-expansion foams are used on burning spills. AFFF is best for spills of jet fuels, FFFP is better for cases where the burning fuel can form deeper pools, and AR-AFFF is suitable for burning alcohols. The most flexibility is achieved by AR-AFFF or AR-FFFP. AR-AFFF must be used in areas where gasolines are blended with oxygenates, since the alcohols prevent the formation of the film between the FFFP foam and the gasoline, breaking down the foam, rendering the FFFP foam virtually useless.
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