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June 08, 2018


One of the most misunderstood aspects of firefighting is fire suppressants and foam. Why is that? Well one of the problems is that most people, firefighting personnel included, don’t really understand the properties of foam and how it should be used.

Foam can be used in many ways for dealing with chemicals and synthetic materials. Think about it like this: today’s house fires can be more complex than in the past, with newer construction often incorporating synthetic materials like petroleum-based plastics and fibers, as opposed to traditional wood and other natural elements.

What does this mean? It means that today’s fires also burn hotter and faster than ever before, meaning every possible tool that can be brought to bear must be deployed and utilized quickly.

Another misconception about foam is that all foams are the same – that is, that there’s only one type of foam and it can be used for anything and everything. All of these issues can lead to avoidance of foam and therefore a loss of a potentially excellent firefighting tool.

Class B and Class A Fires

There are two types of fires we’ll be talking about and therefore two types of foams to deal with them.

Class B fires are those which are fueled by flammable or combustible liquids. They include sources like gasoline, fuel oil, kerosene, and alcohol, among others.

Class A fires are those which consist of natural combustibles like paper, wood, natural fabrics, and other such items.

Types of Foam

The two most common types of foam used in firefighting are Class B and Class A. Note that these two types of foam correspond with the type of fire hazard they’re designed to fight – Class B or Class A.

A Class B foam is designed to fight a Class B fire, and Class B fuels can be divided into two additional classes:

  • Hydrocarbons that don’t mix with water, including:

o    Gasoline

o    Kerosene

o    Fuel Oil

  • Polar solvents that do mix with water, including:

o    Ketones

o    Ethers

o    Alcohols

So how do they work? Class B foams create a barrier on a burning surface, thus inhibiting the fuel’s ability to produce vapors. The integrity of the foam blanket must be maintained once it has been applied, otherwise the fuel can produce more vapors and those vapors in combination with an ignition source mean you’re right back where you started.

Class B foams can also be broken down into two more main categories – synthetic-based and protein-based – each having distinct advantages and disadvantages.

Synthetic-based foam

This type of foam utilizes compounds which “lower the surface tension between two liquids, between a gas and a liquid, or between a liquid and a solid.” They include high-expansion foam, aqueous film-forming foam (AFFF) and alcohol-resistant aqueous film-forming foam (AR-AFFF).

The main advantages are that they spread and flow better, while also providing a fast knockdown time for flames. Their durability can be measured by the fact that there is little need to actively replenish the foam blanket once it’s been deployed.

Protein-based foam

Instead of using synthetic compounds, protein-based foams utilize natural proteins with added fire performance components.

They include the following:

  • Regular protein foam (P)
  • Fluoroprotein foam (FP)
  • Alcohol-resistant fluoroprotein foam (AR-FP)
  • Film-forming fluoroprotein (FFFP)
  • Alcohol-resistant film-forming fluoroprotein (AR-FFFP)

The main difference between synthetic and protein is that synthetic spread slightly faster, but protein produce a generally more heat-resistant foam blanket.

Class A Foam

Class A foam was developed after Class B, and works by helping water’s ability to absorb heat and help reduce the surface tension of plain water, thus providing better penetration of those Class A fuels we talked about earlier – wood and other natural elements.

Class A foam is known for its versatility, as it can be used for both a direct and indirect attack on a fire, as well as to protect exposures. It’s also used for both structural and wildland firefighting.

It is important to note that Class A foam can be used on flammable liquids and work to extinguish the fire, however, it does not possess the chemical ability to deal with the associated vapors, and therefore can lead to disastrous results if used on the wrong type of fire.

Considerations – What type of foam to choose?

In determining which type of foam you should select for your department, remember that each type works best for certain applications, and that there is really no single best foam for everything – i.e. no one-size-fits-all foam.

However, you can make an informed decision based on the types of Class B and Class A fires you’re likely to encounter most often.

For instance, if you’re department is in a rural or small community, away from large highways where chemical spills are a concern, then you may not need to invest in Class B foam, but instead focus on Class A foam for common house and structure fires.

Conversely, if you live in a community with a large capacity of Class B fuel storage – e.g. refineries, tank farms, and chemical plants – or near a busy highway where chemical spills are possible, then Class B foam is a wise choice.

Cost effectiveness

It’s important to conduct comprehensive and effective research on the types of fires and hazards you’re likely to face, and the type of foam best suited to your needs, so that you’re department is spending the communities’ tax dollars in the most cost-effective way possible. It does you no good to have a large quantity of Class B foam on hand if there’s little to no chance you’re ever going to need it.

On the same topic, you don’t want cost to necessarily be the sole or determining factor in choosing a foam. If you simply opt for the least expensive choice, it can very well end up costing you more in the long run if you make the wrong choice and have to purchase a different class anyway. Cost can and should be one of the factors to consider, but not the only one.

Environmental-impact concerns

A small note on an issue that is ongoing and complex, yet is important and shouldn’t be overlooked, and that is the environmental impacts of foam. It is indeed a consideration that should be taken into account. Is the foam you’re using safe or toxic to the environment, and what kind of long-term effects will it have on the environment – not just for plant and animal life, but for issues like ground seepage and drinking water.

Foams used in the past were not at all environmentally friendly, mainly due to the use of fluorochemicals in their makeup; however, many of today’s manufacturers are thinking about the environment and taking steps to move away from producing foams with fluorochemicals that are toxic to the environment, and making what are referred to as “fluorine-free” foams.

Much like cost, this should not be the only factor you consider, but it should be one of them.

When you’ve done the necessary thought and research and are ready to invest in the foam you need to keep your community safe, we offer a vast array of foams and fire suppressants for all of your needs.

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