Some of the main characteristics against which foam types are compared and differentiated are vapor suppression, heat resistance, knockdown, fuel and alcohol tolerance. There is no one type of foam which covers all the characteristics in one, in this sense there is no one size fits all solution. As the different types of foam excel in some and have lower tolerance towards other characteristics it is very important to pre- evaluate the conditions in which the foam will be used.
In order to have a better understanding of the different characteristics and properties of the different foams lets have a more detailed look at the different characteristics, starting with heat resistance.
- The heat resistance property relates to the ability of the bubbles comprising the foam to withstand the direct contact with open flames or surfaces with highly elevated temperature levels. The harder the bubbles are destroyed the better the quality of the foam, the better and faster will it put out the fire.
- Foams vapor suppression properties are expressed by the foams ability to suppress flame vapors and thus prevent them from spreading and igniting in the air. This particular feature of the foam is used in the extinguishing of highly flammable liquids, as well as the prevention of the aforementioned to ignite.
- The knockdown ability of the foam shows how quickly the foam blanket can spread across the burning surface. The rapid spread of the foam solution across the fire fuel results in a quicker knockdown. Generally the faster the knockdown- the higher the extinguishing efficiency.
- Fuel resistance is the ability of the foams bubbles to withstand the fuel entering into them. In this way the foam can enter the fuel and re-surface without bringing up any flammable particles. In the case it does bring back fuel to the top, it will just reignite the fire and the whole procedure will be ineffective.
- The alcohol tolerance of the foam is expressed by its ability to form a film separating the alcoholic liquid from the foam blanket. This film which forms on the surface of the liquid is quite important as it firstly suppresses any fumes spreading into the air and secondly ‘suffocates’ the fire and thus extinguishes it.
Types of Foam
One can find several types of foam on the market, they are all different in their characteristics and are used in the extinguishing of different types of materials. Generally there are five types of foams from which to choose from.
To begin with the earliest and most basic types of firefighting foam are the Protein and Fluroprotein types of foams.
Protein foam is the earliest and most basic type of foam. It is essentially produced by the hydrolysis of protein material such as animal hoof and horn, which is also the main reason to be very outdated and barely used anymore. Most manufacturers refuse producing it due to the ingredients and unpleasant manufacturing process.
- Fluroprotein foams is the upgraded version of the protein foam, with the addition of special fluoro- chemical surfactants which cause the surface tension of the protein-based concentrate to be reduced and thus allow more fluid movement of the foam.
The more advanced and wide spread types of foam are the AFFF and FFFP types of foams.
- AFFF or Aqueous Film Forming Foam, which is the most universal and commonly used type of foam. It consists of synthetic foaming agents added to fluoro- chemical surfactants.
- FFFP or Film Forming Fluroprotein Foam is a protein based foam which has a higher extinguishing ability than the AFFF type of foams.
The last type of foam from which to choose from depending on your needs is the AR- AFFF, which is also the most advanced type of foam. Nevertheless it is not as wide spread as the AFFF mainly due to the higher price, but also because most situations do not require this type of protection, in a way it is an overkill to use AR instead of a normal AFFF foam.
- AR- AFFF or Alcohol-Resistant foam consists of fluorochemicals, foaming agents, synthetic stabilizers, and synthetic polymers designed for use on polar solvents.