The purchase of firefighting foam can be a daunting task for fire service leaders and their staff. For many, a lack of knowledge about what foam can or cannot do for particular types of fires can unfortunately lead to avoidance. Some won’t carry foam and others will minimize it by buying one type of foam and expecting it to work on any fire.
Fire departments might have been successful with either of those strategies, but technology has finally caught up with us.
The complexity of today’s fire hazard in residential housing has grown beyond the combustion of wood and natural fibers with the proliferation of the use of synthetic materials like petroleum-based plastics and fibers. Those fires burn faster and hotter than those of previous generations.
The demand for these materials and the industrial processes to produce them has dramatically increased the potential for a fire that will require the use of the appropriate foam regardless of the size of a department.
How many communities have new chemical manufacturing facilities within their boundaries? What community doesn’t have a major transportation route running through it or nearby where chemicals and petroleum products are in transit?
A and B
Class A and Class B are the two primary foam types used by fire departments; these categories correspond to the types of fuels that the foams are designed to be used on. This is very important.
When choosing the right foam to purchase you have to follow the science. Class B foams were the first firefighting foams and came to the general fire service from the industrial firefighting world.
Class B foam works by creating a chemical barrier on the surface of the burning material, which inhibits the fuel’s ability to produce vapors. That’s why it is important to maintain the integrity of the foam blanket once it’s in place; break the barrier and the fuel produces vapors and if those vapors have an ignition source — you’re back to square one.
Class B fuels can be divided into two more classes: hydrocarbons like gasoline, kerosene and fuel oil that do not mix with water, and polar solvents like alcohols, ketones and ethers which will mix with water.
Class A foam came along later and was developed to increase water’s ability to absorb heat and provide better penetration of Class A fuels by reducing the surface tension of plain water.
Using Class A foam on a flammable liquids fire might extinguish the fire, but lead to catastrophic results because of its chemical inability to secure the explosive vapors.
Alphabet soup
Class B foams can be divided into two general categories — synthetic based and protein based; each has its advantages and disadvantages.
Synthetic foams are basically super soap with fire performance additives. They include high-expansion foam, aqueous film-forming foam, and alcohol-resistant aqueous film-forming foam (AR-AFFF).
Synthetic foams typically flow more freely and provide quick knockdown with limited need for actively replenishing the foam blanket, meaning they are durable.
Protein foams use natural proteins instead of a synthetic soap, and similar fire performance components are added. Protein-type foams include regular protein foam (P), fluoroprotein foam (FP), alcohol-resistant fluoroprotein foam (AR-FP), film-forming fluoroprotein (FFFP), and alcohol-resistant film-forming fluoroprotein (AR-FFFP).
In general, protein-based foams spread slightly slower than synthetic but produce a more heat resistant and a longer-lasting foam blanket.
Where to apply
Why so many types?
Each foam is the best choice for certain applications, but no foam is best for every application. For example, if you want to fill up a large volume area like a basement or an airplane hangar, high-expansion foam would be the best choice.
For an overturned tanker in a municipal environment where the fuel may accumulate into a deeper pool, FFFP may be your best choice. Have a chemical company in your response area that uses ethanol as part of its production? An alcohol-resistant, fluoroprotein foam may be your best choice.
What if your department doesn’t know what type of Class B fire you will encounter next? If that’s the case, a good option would be multi-purpose foam, like an alcohol-resistant FFFP or an alcohol-resistant AFFF, that is flexible enough to handle most Class B fires.
Always use a foam nozzle for Class B foam application because you need to expand the foam for it to work at its best.
It will work with a fog nozzle on regular hydrocarbons, but vapor suppression and post fire security are sacrificed with a standard fog nozzle. You want to make a thick foam blanket, not dish washing liquid.
Class A foam
Go back to the first issues of fire service trade journals and you will see ads for Class A foam.
The difference in Class A foam today is its formulations provide better wetting of Class A fuels, foam longevity (durability) and better heat resistance. Class A foam also is very versatile.
- Dump it into a water tank to produce a premix.
- Proportion it using a standard venturi educator.
- Meter it with a Class A foam injection system.
- Use it at concentrations of 0.1 percent to 3 percent.
- Apply it through compressed air foam systems, conventional fog nozzles, or low-, medium- or high-expansion foam nozzles.
- Use it for direct attack, indirect attack or to protect exposures.
- Use it for both wildland fires and structural firefighting.
Increasingly, the fire service has become aware of the negative impact that some of our past fire-extinguishing agents have had on the environment. Depletion of the earth’s ozone layer by fluorohydrocarbons like Halon is one.
In recent years foam manufacturers have been working to make improvements in not only the efficiency and effectiveness of their products, but also to lessen their negative environmental impact.
More than a decade after 3M stopped production of PFOS-based AFFF agents, there is continued discussion on the environmental impact and efficacy of firefighting foams. It is usually focused on foams that contain fluorochemicals, while the discussion of efficacy is usually focused on foams that do not contain fluorochemicals.
The Fire Fighting Foam Coalition has produced a fact sheet that provides accurate and up-to-date information about these issues.
