The first design step is identifying the fuel. Hydrocarbons such as petrol, diesel and jet fuel need a different foam from polar solvents such as alcohols and ketones, and the wrong foam breaks down quickly on a polar solvent. We calculate application rates and discharge times to NFPA 11 and TS EN 13565-2, then select the proportioner, concentrate storage and discharge devices to suit the hazard.
ATypes and components
Low expansion foam
Expansion ratio up to 20, giving a heavy blanket that stands up to hot fuel surfaces. Used on storage tanks, bunded areas, loading racks and foam-water sprinkler systems.
Medium and high expansion foam
Medium expansion runs from 20 to 200, high expansion above 200. High expansion generators fill large volumes such as aircraft hangars, warehouses and cable tunnels in a short time, while medium expansion is effective for vapour suppression on spill pools.
AFFF and AR-AFFF concentrates
AFFF forms a thin aqueous film on hydrocarbon fuel and knocks fire down quickly. AR-AFFF contains a polymer that also leaves a protective membrane on polar solvents; both are typically used at 1, 3 or 6 per cent.
Fluorine-free foams
With environmental restrictions on PFAS-containing foams, fluorine-free concentrates are increasingly the default on new projects. When switching, check that the proportioner and discharge devices, not just the concentrate, have been tested and approved with that foam.
Proportioners
In-line inductors suit small, fixed-flow applications; balanced pressure and ratio controller proportioners suit systems with variable flow. Accurate proportioning directly determines extinguishing performance.
Bladder tank
Foam concentrate is held in a rubber bladder inside a steel tank. Water entering the tank squeezes the bladder and pushes concentrate to the proportioner, with no separate foam pump or electrical supply needed.
Foam chambers and tank protection
On fixed-roof tanks, foam chambers deliver foam gently down the tank wall onto the fuel surface. On floating-roof tanks, foam is applied to the rim seal area; monitors and foam-water sprinklers cover bunds and loading areas.
BHow it works
- The detection system or an operator opens the foam system section valve.
- As fire water passes through the proportioner, concentrate is injected at the set ratio to form foam solution.
- The solution reaches the foam chamber, monitor, sprinkler or generator and mixes with air to form foam.
- The foam covers the fuel surface, stops vapour release and cools the surface to extinguish the fire.
CAdvantages
- Far more effective than water on flammable liquids
- Lasting blanket against re-ignition
- High expansion fills large volumes quickly
- Bladder tank option with no electrical supply
- Works alongside sprinkler and deluge systems
DApplications
- Fuel and chemical tank farms
- Road and rail tanker loading racks
- Aircraft hangars
- Refineries and petrochemical plants
- Solvent and paint stores
- Helidecks and helipads
EFrequently asked questions
Which foam concentrate is right for our site?
If only hydrocarbon fuels are present, AFFF or a fluorine-free foam approved for hydrocarbons may be enough. If polar solvents such as alcohols, acetone or methanol are present, an alcohol-resistant (AR) foam is essential. The fuel list, the approval status of existing equipment and PFAS restrictions all need to be considered together.
How long does foam concentrate last, and how is it checked?
Shelf life depends on the type of concentrate and storage conditions, and under the right conditions it can be many years. Performance matters more than date, so NFPA 11 calls for an annual sample to be sent for laboratory analysis. If results fall outside the acceptance limits, the concentrate is replaced.
Can we convert an AFFF system to fluorine-free foam just by changing the concentrate?
Usually not. Fluorine-free foams have different viscosity and expansion behaviour, so the proportioner setting, discharge devices and application rate all need to be revalidated. Cleaning PFAS residues out of tanks and pipework that held the old foam is a separate part of the conversion project.