Compressed Air Foam Systems (CAFS): How They Work & Dry Chemical Comparison
A compressed air foam system (CAFS) injects air into foam solution under pressure before it reaches the hose, producing a dense foam that travels farther, sticks to vertical surfaces and uses less water than a conventional hose line. CAFS is effective on Class A fires and for securing Class B pool fires, while dry chemical is faster for pressure-fed, three-dimensional and energized electrical hazards. Understanding the differences helps industrial sites choose the right suppression system or determine when both are needed.
How a compressed air foam system works
A CAFS unit combines water, foam concentrate and compressed air. A water pump supplies the solution, a proportioner adds the required foam concentrate, and a compressor introduces air into the solution. The air and solution are mixed before reaching the hose, creating the finished foam structure.
Foam expansion can be adjusted depending on the application. Wetter foam flows easily and penetrates fuel, while drier foam produces a more stable blanket that adheres to vertical surfaces and provides longer exposure protection. The system therefore gives operators control over both discharge characteristics and water usage.
What CAFS does well
CAFS provides good reach, reduced water consumption and strong adhesion. The foam can cling to vessel shells, structures and other exposed surfaces, creating a cooling and heat-shielding layer before or during fire exposure.
On Class A fires, this combination of penetration, cooling and adhesion makes CAFS particularly useful. With an appropriate Class B concentrate, it can also create a foam blanket over a hydrocarbon pool fire and help prevent reignition.
CAFS is therefore most useful when the hazard has a surface that foam can cover. Tank farms, loading areas, warehouses and other locations where pool or surface fires are expected can benefit from its water-saving characteristics.
Where CAFS has limitations
CAFS is water-based and depends on supporting equipment. A typical system requires a water supply, pump, foam concentrate, proportioning equipment and an air compressor. A failure in any of these components can reduce or eliminate the system's suppression capability.
CAFS is also not the preferred solution for energized electrical equipment. Foam solution is conductive, creating an electrical hazard when applied to live switchgear, motors or other energized equipment.
Three-dimensional and pressure-fed fires present another limitation. A leaking pump seal, flange fire or pressurized gas release does not provide a stable surface for foam to cover. In these situations, dry chemical can attack the flame directly and provide substantially faster knockdown.
Dry chemical skids: a different suppression approach
A dry chemical skid replaces the water and compressor infrastructure with an agent tank and nitrogen cylinders. Salus Global dry chemical skids are available in 350, 1,000 and 2,000 lb capacities, with agent tanks built and tested to ASME Section VIII and nitrogen stored separately.
When activated, nitrogen pressurizes and fluidizes the dry chemical before driving it through the hose and nozzle. The system requires no external water supply or electrical power for agent discharge, making self-contained dry chemical systems useful at remote industrial and oilfield locations.
Dry chemical works directly on the flame through chemical interruption of the combustion reaction. This makes it particularly effective for Class B and C hazards, including pressure-fed liquid fires, gas jets and three-dimensional hydrocarbon fires.
The trade-off is that dry chemical provides little lasting cooling or surface protection. A hot pump, vessel or other ignition source can cause reignition after the powder cloud dissipates. The agent also leaves residue that requires cleanup.
CAFS vs dry chemical
| Property | CAFS | Dry Chemical Skid |
|---|---|---|
| Fire classes | A, B with suitable Class B concentrate | B, C; Class A with ABC agent |
| Pool fire | Good; foam blanket secures the pool | Fast knockdown; no lasting barrier |
| Three-dimensional fire | Limited | Highly effective |
| Pressure-fed fire | Limited | Highly effective |
| Energized electrical | Not suitable | Suitable when properly rated |
| Cooling | Yes | No |
| Reignition protection | Foam blanket provides ongoing protection | Limited; no lasting blanket |
| Water supply | Required | Not required for agent discharge |
| Compressor | Required | Not required |
| Residue | Foam and water runoff | Dry chemical residue |
| Best application | Class A and pool/surface fires | Three-dimensional, pressure-fed and electrical hazards |
When to choose CAFS
CAFS is a strong choice where the expected fire has a surface that foam can cover and where water conservation is important. Tank farms, loading areas, warehouses, conveyor galleries and similar hazards can benefit from its combination of cooling, adhesion and reduced water consumption.
CAFS can also be useful where a foam blanket is required after initial knockdown. Unlike dry chemical, foam can remain over a fuel surface and reduce the likelihood of reignition.
When dry chemical is the better choice
Dry chemical is generally better suited to pump rows, compressor areas, LNG transfer areas, wellsites and other process hazards where a fire may involve a spray, jet, leak or energized electrical equipment.
For remote sites, the independence from a fire-water system is another advantage. A self-contained nitrogen-expelled dry chemical skid can be positioned close to the hazard and operated without an external water supply or compressor.
Why some sites use both
CAFS and dry chemical address different failure modes. Dry chemical can rapidly knock down a three-dimensional fire, while foam can subsequently secure a pool and provide continued cooling and reignition protection.
For a process area containing both pressure-fed equipment and potential liquid pools, using both systems can therefore provide broader protection than relying on either agent alone. The final selection should be based on the specific fuel, hazard geometry, required discharge performance and applicable listing or design requirements.
Frequently asked questions
Can CAFS be used with fluorine-free foam?
Yes, provided the foam concentrate and CAFS equipment are compatible and the system is designed or listed for that combination. Concentrate characteristics and proportioning requirements should be confirmed with the equipment and foam manufacturers.
Does CAFS work on a gas fire?
CAFS is generally not effective for a pressure-fed gas jet because there is no fuel surface for the foam blanket to cover. Isolation of the fuel source is the primary consideration, with dry chemical available where extinguishment is required.
Is dry chemical better than CAFS?
Neither is universally better. Dry chemical is faster for three-dimensional and pressure-fed fires, while CAFS provides cooling and lasting surface protection. The correct system depends on the hazard.
Can a site use CAFS and dry chemical together?
Yes. Using dry chemical for rapid knockdown and foam for pool-fire control can address the different limitations of the two agents. The systems should be selected and designed for the specific hazards present.
Compare CAFS and Dry Chemical for Your Hazard
Salus Global supplies dry chemical suppression systems for industrial, petrochemical and oilfield applications.
