How to use firefighting foam on fire
How does foam stop a fire?
A fire is extinguished by removing or interfering with one of the 3 elements of the fire triangle: heat, fuel and oxygen (air).
Applying firefighting foam on the burning fuel results in suppressing the oxygen supply.
Depending on the foam concentrate type and fire risk faced, firefighting foam formulation is different. Every firefighting foam includes surfactants. Surfactants are responsible for the foaming action, foam quality and wetting ability.
Foam concentrates composition and its Critical Micellar Concentration (CMC) offer two main properties:
- Wetting property: It lowers the surface tension of water which spreads quickly over the fuels and penetrates faster in solids than plain water will. It will deeply cool the solids from inside. Foam concentrate makes water more effective to suppress a solid fire. The use of foam concentrate also induces using far less water in class A and class B fire suppression.
- Foaming property: by adding air inside the foam solution, it forms foam. Surfactants in the foam produce a lot of bubbles and creates a stable foam blanket. The firefighting foam produced is very fluid and spreads quickly and uniformly over the fuel surface. The foam blanket holds in place for an extended period of time. Water stored in the foam blanket provides a long cooling effect and reduces the chance of reignition. The foam blanket separates the fuel and flammable vapors from the air, so it helps to remove oxygen from the fire and cut off air supply.
Fluorosurfactants are responsible for the film forming in AFFF (Aqueous Film Forming Foam) and AR-AFFF (Alcohol Resistant) foams.
On hydrocarbon fires, AFFF foam used generates an aqueous film on the surface of the fuel. This film is very fluid, it floats and spreads quickly above the fuel surface. It provides rapid fire control and extinguishment.
On polar solvent fires, AFFF-AR foams are used. Polar solvents fuels are miscible with water and destroy the foam blanket. That’s why AR-AFFF foams contain polymers to form a barrier between the fuel surface and the foam blanket. This barrier protects the foam blanket from destruction by the polar solvent.
Fluorine-free foams (FFF) are composed of hydrocarbons surfactants and are totally free of any fluorosurfactant. There is no film forming property on hydrocarbon fires. Non-fluorinated foams are composed of an amount of bubbles that create the foam blanket. The foam blanket quickly controls and extinguishes the fire. It also forms a polymer barrier to protect the foam blanket from destruction by the polar solvent.
Drain time is measuring how durable or quick the foam solution will be released. Longer drain times are required for maximal fuel insulation and effective suppression.
Firefighting foam quality and performances are tested and approved by international standards such as EN1568, UL162, NFPA18, LASTFIRE, GESIP, ICAO, IMO.
Comparison of ECOPOL F3HC FFF and AFFF foams application during EN1568-3 fire test pan.
Forceful foam application.
What is necessary when applying firefighting foam?
Several factors are critical when applying firefighting foam.
First, you must identify the type of fuel and fire risks.
- Classes of fire mostly faced by firefighters:
- Class A fires: ordinary solid combustibles such as wood, paper, plastics…
- Class B fires: flammable liquids
- Water immiscible fuels – hydrocarbon fuels (heptane, oil, gasoline)
- Water miscible fuels – polar solvent fuels (acetone, alcohol, isopropanol)
- Fire structure and size: for example
- Structural fires such as solid combustibles must be deeply penetrated by the foam
- Tank: require specific foam equipment (foam pourer or long-range nozzle or monitor), the foam needs to stick to vertical surfaces
- Bund area: the foam needs to spread quickly above the fuel surface
BIOFOR class A/B foam on tyre fire, compared to plain water only
Second, what type of means and equipment do you have? The quality of the foam generated is strongly related to hardware and different parameters.
- Foam equipment: Foam concentrate must be compatible with foam proportioning (venturi proportioner, water driven proportioner, around the pump system) and foam discharge devices (nozzle, monitor, sprinkler, deluge system) to produce a quality foam blanket inducted with the good flow rate at the accurate proportioning rate.
- Water quality used: foam concentrates react reacting differently depending on the water quality used (fresh water, sea water or brackish water)
- Type of foam concentrate: firefighting foam concentrates are designed to be efficient at a certain proportioning rate on fuels (such as 1%, 3% or 6%), following a defined application rate depending on the size of the fire and the flow rate.
- Foam properties: each foam has individual properties in terms of viscosity, freeze protection, compatibility, certifications…
Then, foam application and effect expected?
- Foam expansion: the foam expansion ratio indicates the volume of foam produced with a quantity of foam solution when mixed with air
- Low expansion (<20): the foam is highly dense, which allow long projection distances and heights
- Medium expansion (>20 and <200): used to produce a large amount of foam within a short time.
- High expansion (>200): a lot of air is introduced in the foam; bubbles are very light and large. It provides a maximum amount of foam, ideal to drown a large volume such as warehouses, cellars, aircraft hangars or engine rooms
- Foam application: gentle application or forceful application, the foam application must be continuous and uninterrupted until extinguishment
- forceful application
- gentle application
Gentle BIOFILM foam application on hydrocarbon fire
The longer the foam blanket drainage time is, the longer the oxygen supply will be cut off, thus maximal thermal insulation and effective cooling will result. Therefore, it results in better burnback resistance and vapor suppression post-extinguishment.
Which foam is used for ethanol fire?
Ethanol is a flammable liquid, more precisely a polar solvent. Ethanol fuel is miscible with water, it has hydrophilic properties.
When applied, a traditional AFFF or standard Fluorine-free foam, the foam blanket will be destroyed by the solvent. That is why we use specific firefighting foams: class B Alcohol-Resistant (AR) foams , which can be AFFF-AR or Fluorine Free Foam-AR.
Class B AR foams include a polymer which creates a protective barrier between the polar solvent and the foam blanket. AR foams are mostly viscous (pseudoplastic).
Class B AR foams can be fluorinated and non-fluorinated.
- AR-AFFF: Alcohol-Resistant Aqueous Film Forming Foam. The film property of AR-AFFF creates a membrane between the solvent and the foam blanket, and quickly spreads above the fuel surface.
- AR-FFF: Alcohol-Resistant Fluorine-free foam. Polymer added in FFF foams create a barrier between the solvent and the foam blanket, and quickly spreads above the fuel surface.
ECOPOL PREMIUM FFF firefighting foam application on 100m² ethanol fire
Is firefighting foam safe?
Firefighting foams have been used for decades to help firefighters rapidly extinguish fires.
Recent concerns have been raised about PFAS fluorosurfactants (Per- and polyfluoroalkyl substances) contained in AFFF and AFFF-AR firefighting foams.
PFAS are a wide family of chemicals widely used throughout society. They contain carbon-fluorine bonds, which are one of the strongest chemical bonds in organic chemistry. This means that they resist to degradation when disposed in the environment. Most PFAS are also easily transported in the environment covering long distances away from the source of their release. They are known as “forever chemicals”, as they stay permanently in the human body and in the environment. Some of them have been observed in soil and ground water contamination. PFAS are potentially highly Persistent and Pollutants. It’s technically difficult and costly to decontaminate sites that are polluted.
Regulations across the world are limiting or phasing out the use of PFAS, especially in firefighting foam. Since 2009, PFOS (Perfluorooctane sulfonic acid) and its derivatives have been added in the Stockholm Convention to eliminate their use. PFOS has already been restricted in the EU for more than 10 years, under the EU’s Persistent Organic Pollutants (POPs) Regulation. In addition, the Stockholm Convention regulates the global elimination of PFOA and its salts (Perfluorooctanoic acid). PFOA have been banned under the POPs Regulation since July 2020. PFAS compounds will be considered in the next European legislation which is expected by October 2021.
The fire industry is mostly aware of this high concern. Some industries and fire departments already have or are in the process of transitioning to fluorine-free foams for their fire protection.
GreenScreen is an independent organization which certified safe firefighting foams that do not contain hazardous chemicals. GreenScreen analyze and approve firefighting foams which are safe for humans and the environment.
Fluorine-free foams are viable alternatives. BIOEX developed a wide range of highly efficient fluorine-free foams that do not use fluorochemicals. BIOEX non fluorinated foams are tested on fire and approved by international standards such as EN1568, UL162, ICAO, IMO, USDA. They are used by major fire services across the world. BIOEX fluorine-free foams are safe for humans (including firefighters) and the environment, entirely biodegradable and GreenScreen approved. BIOEX supports its customer transition to fluorine-free foams.
ECOPOL F3HC fluorine-free foam used to extinguish hydrocarbon fire
Is fire fighting foam corrosive?
BIOEX firefighting foams are not corrosive when used with usual foam equipment materials.
BIOEX recommends foam concentrate storage in Stainless steel (type 316L or 304L), Polyethylene (PE) , Polypropylene (PP), Polyurethane or epoxy coating tank.
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