What is firefighting foam?
Firefighting foam is used as a versatile fire suppression agent to fight multiple types of fires ranging from forest fires to petrochemical fires, as well as to prevent the ignition of materials that might cause a fire.
An obvious explanation for the increasing use of firefighting foam is that it can effectively lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid.
Firefighting foam is nothing more than a compound of foam concentrate, water, and air in which organic solvents (i.e. trimethylene glycol and hexylene glycol) are added as a formula to reinforce its firefighting capabilities.
To serve as an effective extinguishing agent, several different types of foam are produced and used for fighting fires caused by different types of fuels. Manufacturers also use stabilizers and corrosion inhibitors (Lauryl alcohol) to ensure that the foam expands steadily and effectively despite strong winds or down droughts.
Foams with different characteristics are used by fire departments for different purposes. For example, low-expansion foam, many believe, is the most common type of firefighting foam due to its rapid deployment and low viscosity that ensures a low expansion rate (less than 20-fold). The capability to cover large areas quickly is another reason why firefighters like to choose this type of foam.
Not only that, medium and high expansion foams have the expansion ratio of 20 to 100 and 200 to 1000, making the foam solution suitable for wide variety of applications ranging from fighting house fires to forest fires.
Despite their many applications, firefighting foams are generally classified as extinguishing agents for Class A (ordinary solid combustibles such as paper, wood, cloth, and some plastics) and Class B (flammable liquids such as alcohol, ether, oil, gasoline, and grease).
Other types of foams can also be used for the other two classes of fires (Class C and D), which is rare in the firefighting history.
As mentioned earlier, firefighting foams are designed to serve the purpose of lowering the surface tension. Therefore, Class A foam, developed in mid-1980s, is useful for fighting wildfires because it lowers the surface tension of the water, aids fire suppression, and prevents reignition.
This type of foam can penetrate the fuel to raise the moisture content, which assists in wetting and saturating Class A fires with water rather than using plain water. On the other hand, it is important to know about the downside of firefighting foams prior to any use. The ongoing investigation of PFOS contamination seems to suggest that they might be hazardous and need to be treated with caution.