Compressed Air Foam Systems Explained

Compressed air foam systems have been around in some form or other since the 1930s. They have been used in the United States Navy for over 80 years in order to fight flammable liquid fires, and in the last few decades are becoming more popular in structural and wildfire fighting.  

Compressed air foam systems (CAFS) are fire fighting units that add injected, compressed air into a solution that creates a stream of foam to smother fires. Unlike plain water, which beads up, evaporates, and runs off quickly, the dense foam can cling to surfaces, insulate, and penetrate deep into a fire. This makes CAFS more effective at fire fighting than just water. 

The following article is all about the compressed air foam system, how they work, as well as pros and cons of using such a system, and what something like this might cost. 

How Compressed Air Foam Systems Work

Pressurized air is mixed with water and a foaming agent to deliver a consistent stream of fire-fighting foam. The foam battles the three factors that a fire needs to keep burning. The foam bubbles smother the fire—cutting off oxygen, it insulates the area—reducing heat, and coats surfaces—removing the fire’s fuel. So how does it all work in tandem?

Pressurized Air is Injected Into the Water

Pressurized air is injected into a stream of water in such a way that the air pressure remains much higher than the water pressure. This prevents the backflow of water into the airline which can cause vibrations and pulsations when air and water pressures meet.

Air, Water, And Foam Combine

Air and water then mix with the foam that gets pumped out of the containment. The air and water mixture can be altered with the foam to create a dryer, wetter, or denser foam depending on what is needed to combat the fire. 

As air and water mix with the foam solution, it creates a light foam that has much less surface tension than water alone. This means the lightweight foam can cling to overhead and vertical surfaces much better than plain water can. Water hits most surfaces, especially plastics and metal, beads up, and quickly runs off. 

Foam Solution Gets Sprayed Through Special Nozzles

When everything is properly mixed, compressed, and ready to flow, the solution is sent through flexible pressure hoses and out of special nozzles. Some nozzles spray the foam straight out in a pressurized jet, while others can create cones of spray or other shapes to help cover wide areas quicker. 

The compressed air foam solution combines the energy of the compressed air and the expansion of the foam to create a high energy foam spray.

This solution can be sprayed farther away with more accuracy and more fire coverage than water jets and sprays. The foam is then able to penetrate farther into the flames and hit the base of the fire easier than plain water. 

Advantages of Compressed Air Foam Systems

Compressed air foam systems have plenty of advantages to them. They use less water, are quicker acting on most fires, and can save lives. There are plenty of other advantages to these systems, so let’s get into them. 

Less Water Consumption

A typical fire truck with normal 2½ inch hoses can pump out hundreds of gallons of water per minute. In areas that are already struggling with drought, overpopulated water usage, and other water struggles, this much water usage can be problematic. 

A compressed air foam system uses air, a foam solution, and water to combat fires. Because of the air and foam solution and the expansion of the foam, these machines use up to 4 times less water than water-only fire trucks.  

Puts Out the Fire Quicker

In extremely hot fires, water can evaporate before it gets to the base of the flames. The more water that converts to steam before hitting the source, the more water is needed to put out the fire. 

CAFSs can create a wetter, dense foam that penetrates the boiling flames and gets to the base of the fire quicker. The foam then covers, coats, and smothers the flames putting them out faster. 

Fires need three things to stay active; oxygen, heat, and a fuel source. The compressed air foam battles all three sources better than water, allowing it to put out fires faster. In some instances, foam can put out a fire 2 to 3 times faster than water alone.  

Reduces Pollution

Compressed air foam systems reduce pollution in two ways. They use less water when battling blazes, so they reduce water pollution. Because the compressed air foam systems put out fires faster than water, they reduce the amount of heat and carbon being released into the air.

Water Pollution

When water is sprayed onto a building fire, for instance, it mixes not only with the smoke particles, but all the other contaminants that are present in a burning building. All the synthetic materials, chemicals, and other harmful agents could be present in the water as it runs into the ground and community wastewater systems. 

Sometimes this contaminated water can get washed into streams and local waterways. These contaminants can be fatal to local fish and other wildlife that is dependent on these waterways. 

Since air foam systems use so much less water per fire, fewer contaminants are likely to end up in the environment. When the foam does break down, it stays in place better than plain water. Even though the foam solution itself can be a form of pollution, it doesn’t travel as far.

Air Pollution

The smoke that comes off of fires is made up of tiny particles of burnt material and carbon that can get into the atmosphere. The smoke and particulates can travel for miles before settling down where they can contaminate soil, and water, and affect people’s health. 

When fires are put out faster, obviously less air pollution is formed. Compressed air foam systems can put out fires much quicker than only water. Again, CAFSs can help reduce both water and air pollution. 

Firefighters Stay Safer 

One of the biggest causes of firefighter injury and death comes from overexertion and exhaustion. Fighting fires is a stressful, physically demanding job. Especially when you add in all the heavy equipment they must carry to stay safe from heat and toxic smoke. 

Anything that can make it easier for them to do their job should be a welcome relief. One way the CAFS helps to make it easier on firefighters is because the hoses are much smaller and lighter, leading to less fatigue. 

The hoses are much smaller in diameter than typical, heavy, fire hoses. Even when the CAFS hoses are full of fire fighting material, it’s mostly lightweight foam, not heavy, dense water. They are also more maneuverable than typical water hoses, also reducing strenuous activity and fatigue. 

Reduces Heat and Puts Out Fires Faster

Since the foam can put out fires in a more timely manner, and it reduces the heat, it means that fires don’t reach the critical flashover stage nearly as much. Again, putting fewer firefighters at risk of injury. 

Disadvantages of Compressed Air Foam Systems

With everything, there are advantages and disadvantages to consider. Compressed air foam systems are no different. 

Cost is a Major Factor

Probably the biggest disadvantage in the CAFS is the initial cost, then the recurring cost of the foaming solution.

These are big machines that require complicated computerized equipment, air compressors, and foam proportioners. To add a machine to a large pump truck the cost could amount to $30,000 to $40,000.

This cost can only go up when adding more discharge outlets, and foam proportioners. More complicated machines can easily reach upwards of $100,000. Then foam solvents have to be purchased each time it is used. While some material costs can be minimal, they are a constant cost issue.

Not For All Fires

Compressed air foam is not rated for electrical fires. The foam works wonders on Class A and Class B fires, but since it mixes with water, it is not rated for Class C electrical fires. 

The Foam Can be Hazardous

Depending on the foam solution and what is added to it, the foams can be corrosive to some materials such as metal and leather. Of course, water can also cause rust and when it’s mixed with ash and soot, it can become caustic and damaging as well. 

The foam has been known to cause eye, skin, and respiratory irritation. The foams can contain solvents, surfactants, and hydrocarbons mixed in. All of these things can be irritating to people if they come in close contact with them. 

Foam can also become a slip hazard on some surfaces. On smooth surfaces such as tile, polished wood, or other common flooring choices, the thick foam can become slippery. This can make it difficult for firefighters to move around without slipping and causing injury. 

Complicated Machinery

While the interfaces on CAFS machines can be quite user friendly—the push of a button or two and the unit is ready to go—they are big, complicated pieces of equipment. There are a lot of moving parts that will need maintenance and care, and with more moving parts, comes more possibilities of equipment failure. 

Possible User Error

There are different types of foam used for different classes of fire, and if they get mixed up, or if the wrong foam type gets accidentally added to the wrong tank, it could potentially cause large repair costs. 


Compressed air foam systems are nothing new, but they have come a long way since they first started being used to fight fires.

They have a lot of advantages to their use such as reduced pollution and water usage and putting out fires much faster than traditional water. They can also be safer for firefighters, which is a huge concern. 

CAFSs also have their own set of disadvantages. The cost of these machines can be significant as the machines can be quite complicated, and the foam can be destructive to property.

But if the fire can be put out quicker and safer with fewer injuries and few resources, maybe they have a more significant place in firefighting.  

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