Firefighting foam is a crucial tool for battling fires, especially those fueled by flammable liquids.
Unlike plain water, foam can smother and cool a fire more effectively by blanketing the flames and cutting off the fire’s oxygen supply.
Importantly, there are different classes of firefighting foam designed for different types of fires – it’s not a one-size-fits-all solution.
In this article, we explain what firefighting foam is, how it works, the various classes of foam, its benefits and downsides, and what alternatives exist for fire suppression.
Firefighting foam is a specialised fire suppression agent used by firefighters to extinguish fires,
It is particularly used for fires involving flammable liquids like oil or fuel.
It consists of a foam concentrate mixed with water and air to create a stable mass of small bubbles that can be sprayed onto a fire.
This foam is lighter than liquids like gasoline or water, allowing it to float and spread across the burning fuel’s surface.
When applied to a fire, the foam forms a thick blanket over the flames.
This blanket cools the fire and prevents oxygen from reaching the fuel, effectively smothering the combustion.
By sealing off flammable vapours and cutting off the oxygen, the foam helps to prevent re-ignition of the fire once it’s extinguished.
Firefighting foams are typically deployed using specialised equipment (such as foam nozzles or foam cannons) because they must be mixed and aerated properly before reaching the fire.
Firefighting foam is an essential fire-fighting tool, widely used in settings ranging from structural fires and wildfires to industrial and aviation fires.
Firefighting foam works by attacking the fire on multiple fronts.
A fire needs three elements to keep burning – heat, fuel, and oxygen.
It is often depicted as the ‘fire triangle’.
Foam interferes with all three elements to extinguish the flames.
First, when the foam is sprayed on a burning material, it cools the fuel by moistening it and lowering its temperature below the ignition point.
Second, the foam creates a physical barrier that separates the fuel from oxygen in the air, effectively suffocating the fire.
Third, the foam suppresses flammable vapours from the fuel, preventing those vapours from rising and feeding the fire or causing explosions.
In practice, as the foam spreads over the burning area, you can imagine it forming a foam blanket that both cools and smothers.
For example, aqueous film-forming foam (AFFF), a common firefighting foam for fuel fires, forms a film on the fuel’s surface that quickly cuts off oxygen, cools the fire, and prevents the fire from relighting.
By tackling the heat, oxygen, and fuel supply all at once, firefighting foam knocks down fires faster and helps keep them from reigniting.
Firefighting foams are broadly divided into two major classes: Class A foam and Class B foam.
Each class is formulated for a specific category of fire and has distinct applications.
Understanding the difference between Class A and Class B foams is important, as using the wrong foam for a given fire could reduce effectiveness or even be unsafe.
Below, we explain these classes and their typical uses.
Class A foam is designed to fight Class A fires, which are fires in ordinary combustible materials such as wood, paper, cloth, and vegetation.
This type of foam is commonly used in structural fire fighting and wildland firefighting, where materials like timber, brush, or furniture are burning.
The primary purpose of Class A foam is to enhance water’s ability to extinguish these solid-material fires.
It contains surfactants and wetting agents that reduce water’s surface tension, allowing the water and foam solution to soak into burning materials more deeply.
By penetrating into the embers and pores of materials, Class A foam makes water much more effective at quenching embers and cooling hot surfaces, even in deep-seated fires.
Firefighters will mix Class A foam concentrate with water (often in fire engine tanks or through special foam proportioning equipment) and then apply it through hoses or nozzles.
The resulting foam clings to surfaces like walls or tree trunks, helping to douse flames and prevent rekindling of the fire.
Class B foam is formulated to combat Class B fires, which involve flammable liquids or gases.
This includes gasoline, diesel fuel, oil, alcohol, or other volatile liquids.
These types of fires are especially dangerous because pouring water on them can sometimes make things worse.
Class B foams are therefore used in scenarios like fuel tanker accidents, industrial chemical fires, airport emergencies, or oil refinery fires.
This foam is often used by specialised firefighting teams in industrial, aviation, or military settings.
The key feature of Class B foam is its ability to spread across liquid surfaces and form a floating blanket.
Class B foams are formulated with agents (surfactants and other additives) that produce a film or a membrane over the surface of a burning liquid fuel.
For instance, Aqueous Film-Forming Foam (AFFF) is a common Class B foam that creates a thin film on top of the fuel, blocking oxygen and smothering the fire quickly.
Alcohol-resistant AFFF (AR-AFFF) is a variant used for fuels like ethanol or other polar solvents.
It generates a thicker, more resilient foam layer to deal with those alcohol-based fires that would otherwise break down normal foam.
Class B foams float on the surface of burning liquids and prevent flammable vapours from escaping.
By doing so, they not only extinguish the flames but also keep the fuel from reigniting as long as the foam blanket remains intact.
Firefighting foam offers several important benefits over plain water or other extinguishing methods when it comes to suppressing fires:
Foam can quench fires faster than water in many cases.
When applied, it forms a thick blanket that smothers flames and stops the fire from re-igniting.
This rapid suppression limits the damage a fire can do and improves safety by quickly knocking down intense flames.
Foam is particularly useful for fires that water alone cannot easily put out.
Its ability to float and spread means it can cover flammable liquid surfaces or penetrate porous materials.
This makes foam a very versatile agent, capable of tackling a wide range of fire types.
When using foam, firefighters can often extinguish a fire with less water overall.
The foam solution is lighter and more efficient at suppression, so it requires a smaller volume of liquid to achieve the same effect as plain water.
Using less water not only conserves water but also reduces water damage to property and minimises the runoff of contaminated water.
A good foam blanket stays in place on a fuel surface and resists breaking down quickly.
This means it provides a long-lasting barrier that prevents the fire from getting oxygen.
In practical terms, foam can secure a fire scene by ensuring the fire stays out once extinguished.
Firefighting foam has a cooling effect on burning materials.
By cooling the fuel and surrounding structures, foam helps to limit heat damage and slows the fire’s spread.
Despite its effectiveness, firefighting foam has several downsides and concerns that firefighters and safety officials must consider:
Some older types of firefighting foam contain chemicals that can be harmful to the environment.
In particular, some older Class B foams have used perfluorinated compounds (PFAS) which do not break down easily in nature.
If foam runoff enters waterways or soil, it can contaminate the water and harm wildlife and ecosystems.
This has become a serious concern, leading to a shift in recent years toward fluorine-free foams that are less damaging to the environment.
Some older types of firefighting foams can pose health risks to firefighters and anyone exposed.
Skin contact or inhalation of foam mist can potentially lead to issues like skin irritation or respiratory problems over time.
There is also worry about long-term exposure to certain chemicals in foam being linked to more serious health conditions for firefighters.
Proper protective gear and decontamination after foam use are important to mitigate these risks.
After a fire is out, the foam residue itself becomes a waste product that needs to be cleaned up.
Foam can be difficult and costly to remove from surfaces, and used foam (along with the contaminated water it creates) must be disposed of properly so it doesn’t pollute the environment.
The cleanup process can be labour-intensive.
This includes foam left on runways or equipment that needs thorough washing, and contaminated runoff might need to be collected and treated as hazardous waste.
Using foam is generally more expensive than using water or basic fire extinguishing powders.
Fire departments must purchase foam concentrate and maintain specialised foam-capable equipment.
Over time, the cost of foam concentrate and the upkeep of foam systems, foam tanks, and nozzles can add up.
This means foam might be conserved for situations where it’s really needed, rather than used on every routine fire.
Firefighters need special training to use firefighting foam effectively.
Deploying foam isn’t as straightforward as spraying water; one must know the proper mixing ratio and application techniques (such as ‘rain-down’ or ‘roll-on’ methods).
Additionally, not all fire engines have firefighting equipment for foam..
Those that are, have to carry foam concentrate and have foam mixing systems or attachments.
Improper use of foam can reduce its effectiveness, so departments invest in training to ensure it’s used correctly.
All this adds complexity to firefighting operations when foam is involved.
Firefighting foam is a versatile and powerful tool in modern firefighting, with a crucial role in suppressing fires that would be difficult to handle with water alone.
Understanding the different classes of foam is essential for effective fire suppression.
Firefighters must also weigh the advantages of foam against its potential downsides.
Choosing the right firefighting method comes down to the situation: the type of fire, the environment, and the resources available all play a part.
In some cases, foam will clearly be the best choice for quickly controlling a dangerous blaze.
In other cases, a different approach might be safer or more practical.
By being informed about the classes of firefighting foam and their proper use, firefighters and emergency responders can make smart decisions that maximise fire suppression.
Every tool has its place, and the knowledge of when and how to use each one is what truly keeps fires at bay and communities safe.
