WHAT IS CLASS A FOAM AND HOW DOES IT WORK?
There are many theories and views of what makes Class A foam work. Some have described it as a completely new way of extinguishing fire, and others have gone so far as to say it must be some type of “black magic.”
The truth is that Class A foam is nothing magic or nothing new. Since the 1950s, fire service personnel have been adding similar mixtures to water to make it more effective. Since 1986 there has been an increase in the attention and emphasis placed on the particular additive Class A foam.
Class A foam can be best described as a “water enhancer.” It is a chemical additive that enhances and changes the capabilities of water. The addition of Class A foam to water, in the correct percentages, reduces the surface tension of water, thereby allowing it to be absorbed into a material.
Class A foam is manufactured by a variety of foam suppliers. It is defined as a synthetic detergent foam. It is a neutral on the pH scale and is normally a clear liquid that has a sweet, waxy smell. Its freezing point is identified as – 13°C, and it is 100 percent soluble in water. It is generically named Class A foam, as it is used primarily on Class A material such as wood and paper products, versus Class B or C materials. At this time, there is no UL standard on Class A foam. If you plan to buy Class A foam, you should bin only USDA-approved foam or foam that meets NFPA 298, Foam Chemicals for Wildland Fire Control.
Often, Class A foam is referred to as soap. It actually is not a soap. Class A foam is a synthetic water-soluble organic preparation that is chemically different from soap. However, it resembles soap in its ability to emulsify oils and hold dirt (or carbon) in suspension.
The reason Class A foam works is best explained by understanding its molecular structure. According to Ron Rochna of the Bureau of Land Management, foam is composed of a molecule that bonds to water on one side and to carbon on the other. In a simplified format, the same thing happens when you wash your hands with a detergent. If you wash your hands with water only, some dirt rinses off. If you wash your hands w ith a detergent, they wash clean. In a fire, one side of the foam molecule bonds with water, the odier with the carbon that is created by the fire. This results in the fire being extinguished quickly and greatly reduces the chance of a rekindle. Because the surface tension of the water is reduced, the water, with the additive, is soaked into the material quickly with only a limited amount of steam being produced. In a typical fire involving Class A materials on which 100 percent water is applied, the majority of that water is converted to steam, and the heat is reduced.
