How Foam Extinguishers Combat Flammable Liquid Fires
When dealing with flammable liquid fires, foam is a highly effective tool. Understanding how foam works is crucial for ensuring appropriate use and maximizing its benefits. Foam serves as a barrier between the fuel and the air, breaking the fire’s element triangle and extinguishing the flames. This detailed explanation will delve into the mechanics of foam and its application in fire suppression.
The Mechanics of Foam
Foam is a mixture of liquid and gas air. In the case of extinguishing flammable liquid fires, foam is used to create an effective barrier. The mixture, being much lighter than the flammable liquid, floats on the surface, separating the fuel from air. This separation ruptures the fire’s critical elements: fuel, air, and heat. The air inside the foam bubbles remains encapsulated as long as the bubbles do not collapse, rendering it unavailable for further combustion. This oxygen exclusion can be achieved as long as the liquid is heavier than the foam, preventing the liquid fuel from destroying the foam bubbles.
Challenges with Polar Solvents and Foam
However, not all flammable liquids are created equal, particularly in the presence of polar solvents like unleaded gasoline. In such cases, foam bubbles rapidly dissolve into the fuel, leading to the depletion of the foam. For applications involving water-soluble fuels, a concentrate with specific additives is required to ensure the foam maintains its effectiveness. This concentrate is called Alcohol Resistant Concentrate (ARC) and is essential for extinguishing fuels with a high alcohol content, which are susceptible to mixing with water in the foam, causing it to fail.
Types of Foam Extinguishers
Aquas Film Forming Foam (AFFF)
AFFF is a versatile foam that can be used for both Class A and Class B fires. The primary function of AFFF is to provide a thick film at the surface of the flammable liquid, controlling the release of flammable vapors. This film suppresses the fire by smothering the vapors, which are the actual source of combustion. AFFF is particularly effective in extinguishing Class B fires, which include flammable liquids with a high alcohol content. These foams are designated as AR (Alcohol Resistant) to ensure they can handle the challenges posed by alcohol-rich fuels.
Specific Requirements for Class B Fuels
When dealing with Class B fuels—flammable liquids with a high alcohol content—the correct foam type is essential for effective suppression. For these fuels, Class B foam is required, which is specifically designed to resist the mixing of alcohol with water in the foam. This ensures the foam remains effective in extinguishing the fire.
Understanding Foam Blankets and Film Forming Mechanism
The primary function of foam in flammable liquid fires is to blanket the surface of the fuel, smothering the flammable vapors. This process effectively suppresses the fire because it is the vapors, not the fuel itself, that burn. However, the correct type of foam must be used for each fuel type to achieve this. Class A foams, designed for “normal” fuels like wood, can penetrate the surface of the fuel, making them ineffective in forming a vapor blanket. Class B foams, on the other hand, create this vapor blanket, and Class K foams, used for cooking grease fires, achieve a similar effect through a process called saponification, which forms a soapy layer to smother the vapors. This process is known as saponification and can be a valuable term to remember and use in conversation.
Understanding the mechanics and types of foam is crucial for safe and effective fire suppression. Whether it’s using AFFF for a wide range of flammable liquids, ensuring the use of AR foam for alcohol-rich fuels, or recognizing the specific functions of Class A, Class B, and Class K foams, knowing these details can save lives and prevent significant damage.