Foam Vs Combustion

In order to understand how foam suppresses fire, it is first necessary to understand the process of combustion.

Combustion is a process where fuel undergoes a rapid exothermic chemical reaction (release of heat) with an oxidizing agent, usually air, resulting in the formation of products of combustion and energy (fire).


A fuel is any material that can be oxidized; it can be a solid, liquid, or gas and is generally organic in nature, i.e., composed mostly of carbon, hydrogen, or oxygen. The products of combustion of an organic fuel (assuming complete combustion) are carbon dioxide and water. The energy released may be in the form of heat or light, or the combination of heat and light (fire).

The chemical reaction is not a simple one-step reaction, but is a chain reaction resulting in a number of interdependent chemical reactions. Figure 1-1 depicts the four requirements for combustion using the “fire tetrahedron.”


It follows that any method for extinguishing fire must involve one or more of the following techniques:

  1. Remove heat at a faster rate than it is released.
  2. Separate the fuel from the oxidizing agent.
  3. Dilute the vapour-phase concentration of the fuel and/or oxidizing agent below that necessary for combustion.
  4. Terminate the chemical chain-reaction sequence.

Fire fighting foam is an aggregate of gas-filled bubbles (Figure 1-2) formed from aqueous solutions of specially formulated, liquid agent concentrates. The gas used is usually air, but certain applications use an inert gas.

Since foam is lighter than flammable and combustible liquids, it floats on the fuel surface producing a continuous blanket that suppresses fire by separating flammable vapours and oxygen as shown in Figure 1-2. Because foam is a water-bearing material, it also cools the fuel surface.


Designing a Foam System

In today’s society oil and its petrochemical derivatives play an ever-increasing role in our day to day life. New materials and chemicals are constantly being developed to meet the needs of an expanding and developing market place. Global economies are affected by the supply and demand of these commodities. In recent years, one major refinery fire incident in America had a massive impact, overnight, on oil prices internationally. With this back­ground it has become even more vital for Loss Prevention Engineers to ensure that flammable liquid assets are protected to the best degree possible.

Indeed, the protection philosophy applied must not only consider the consequences of an incident within a facility but also the effects on the environment and society outside.

In many cases the only effective solution to a major flammable liquid fire or unignited spill incidents is the use of foam – correctly selected and applied. Often, especially with decreasing plant manpower levels, this requires a fixed system. Nowadays there is a greater choice of foam agents and hardware available for this purpose, thus making the task of optimum system design much more complex.

In Control Fire Protection now have access to the most comprehensive range of foam equipment available from both Ansul and Skum, can assist and advise in the design process and make the task easier.

What is the risk protected

Before any system design can be carried out, it is obviously necessary to define the risk to be protected. This does not just mean finding out the dimensions of the hazard. The fuel type, availability of power supplies, area classifications, ambient conditions, water supply and site valve/pipework specifications may all have some bearing on final system design.

The most important point to remember is that the hazard to be protected should not be looked at in isolation. Even when the risk appears to be remote from others, a system designer should consider all relevant outside factors such as the local availability of compatible back-up foam stocks from neighbouring facilities. When several risks are present on one site it is particularly important to look at the worst possible fire scenario and make sure resources are available to tackle it.

All recognised international standards make it very clear that sufficient foam concentrate and application equipment must be available for the largest incident so the fire protection engineer must decide whether a fire in one hazard could escalate to others – or more importantly, can good system design with fast detection and rapid actuation prevent this happening?

Also, of course, it is often possible to provide more cost effective fire protection by serving several hazards from one central proportioning unit and foam concentrate supply. It is in these areas, with their wide range of experience of risk assessment and system design in all industry sectors that In Control Fire Protection can provide the most cost­ effective solutions to fire protection problems.

Although foam systems can be used for protection of combustible solids such as paper, by far the most com­mon use of foam is for the protection of flammable liquids. The type of liquid and its physical properties affect the type of foam to be used and the system running time required to assure extinguishment.

What foam should be used

In recent years there have been many new foams developed and introduced. Different generic types are available such as "protein" and "synthetic" based foams.

Undoubtedly the general trend is towards multipurpose foam concentrates that can be used on all types of fuel, but these may not be the most cost-effective in all cases.

Foam liquid manufacturers have increased the confusion by continuing the debate on what generic type is best. The truth of the matter is that the important thing is not what raw material a foam is made from but how the end product performs!

To perform effectively, several properties are needed from a foam. These depend on the accuracy of proportioning and method of application as well as on the foam concentrate.

The most important properties that a foam requires for effective fire extinguishing are:

  • Cohesion – to form a stable blanket on the fuel surface
  • Heat resistance
  • Burnback resistance – to prevent remaining fire burning off the foam blanket
  • Adhesion – to give sealing against hot objects in the fire
  • Vapour suppression – to prevent vapours rising through the foam blanket
  • Stability – to provide security against re-ignition. Stability is often measured in terms of "25% drainage time" which is the time taken for 25% of the foam solution required to make a given foam sample to drain from that foam. Longer drainage times mean greater stability
  • Flowability – to move rapidly across a fuel surface and around any obstacles in its path
  • Flame knockdown – to quickly control the fire
  • Fuel tolerance – to ensure that the foam is not broken down by contamination with the fuel. This is particularly important in the case of water soluble fuels such as alcohols, gasohols, ketones etc. as they break down standard types of foam.

Stages in foam production

There are two basic stages in the generation of foam. The first is when "foam concentrate" is added to water in a given concentration to form "foam solution". This stage is called proportioning. It is a very critical stage because it is vital that the correct percentage concentration is formed if the foam is to perform properly.

The next stage is when air is mixed with the solution to produce bubbles of foam or "finished foam".

Of course, producing bubbles is not all there is to a foam system. There are many different types of foam concent­rate available, many types of proportioners and many different types of foam generating and application equipment.

For every flammable liquid fire protection problem there is an optimum combination of equipment, concentrate and application technique. Many factors including cost and environmental impact must be taken into account. In Control Fire Protection can provide this optimum combination in every case.

To produce a reliable and cost-effective foam system, detailed hazard and fuel information is required and several vital decisions have to be made:

    • What is the risk protected?

    • Which foam is the best for the task?

    • What proportioning system is most appropriate?

    • What is the best application method?

    • What standard of protection should be applied?

    • What foam solution flow rate is required?

    • How long should the system run for?

    • How much foam concentrate is required?

    Fire Fighting Foam


    Fire fighting foam is a collection of bubbles formed by the aeration of a solution of foam concentrate with water.

    Foam is made up of three components – foam concentrate (a liquid produced by chemical manufacturers and supplied in drums or bulk) water and air. The finished product, foam, floats on a fuel surface to extinguish a flammable liquid fire by separating the fuel from oxygen.

    Because of its high water content it also helps cool the fuel surface and any hot objects in the fire area. Foam expansion is classified into three headings – Low, Medium and High.

    Expansion is defined as the ratio of the volume of foam produced to the volume of foam solution required to make it. Expansion ratios up to 20:1 are usually considered to be low expansion foams; 20:1 – 200:1 medium, and above 200:1 high. Each expansion ratio has different uses.

    A well formulated foam applied correctly will exhibit a range of properties including stability, cohesion, rapid fire knockdown, heat resistance and vapour suppression that will ensure that a fire is extinguished efficiently and securely so that re ignition does not occur.

    Foam concentrates are available from a number of manufacturers within the Tyco Group including an extensive line of ANSUL® premium foam concentrates for both Class A and B fires. We can also supply foam concentrates from the Towalex and Sabo range.

    The product range includes Protein, Flouroprotein, and AFFF foams suitable for most types of flammable liquids including Polar Solvents.

    Foam concentrates are available in 1%, 3% or 6% concentrations. We can also provide foam for vapour suppression / neutralising and where require we can provide training foam. Product Datasheets and Material Safety Data Sheets are available for all foam agents – see the links on each product page.

    Foam Types

    There are numerous types of foams that are selected for specific applications according to their properties and performance. Some foams are thick, viscous, and form tough, heat-resistant blankets over burning liquid surfaces; other foams are thinner and spread more rapidly. Some foams are capable of producing a vapour sealing film of surface active water solution on a liquid surface. Others, such as medium and high expansion foams, are used as large volumes to flood surfaces and fill cavities.

    Chemical Foam

    Foams have been classified in different ways over the years. The earliest foams were based upon a chemical reaction occurring between aluminium sulphate (Al2 (SO4)3) and sodium bicarbonate (NaHCO3). The energy used to create the foam bubbles came from the chemical reaction. This type of foam is now largely obsolete.

    Mechanical Foams

    Mechanical foam is produced by mixing a foam concentrate with water at the appropriate concentration, and then aerating and agitating the solution to form a bubble structure. Therefore, unlike chemical foams, the energy used to create the foam bubbles of a mechanical foam comes from an outside source. There are several types of mechanical foams: – Protein – Fluoroprotein – Film-Forming Fluoroprotein (FFFP) – Aqueous Film-Forming Foam (AFFF) – Alcohol-Resistant Concentrate (ARC) – Synthetic Detergent (High/Medium Expansion) The differences between these foam concentrates depend on: – whether the concentrate is based upon naturally occurring materials or synthetic chemicals. – whether the synthetic chemicals are fluorinated or nonfluoronated. – the type of fuel being protected. – the expansion ratio. – whether they will form an aqueous film on certain fuels.

    Protein Foam

    Protein Foam is derived from naturally-occurring sources of protein such as hoof and horn meal or feather meal. The protein meal is hydrolyzed in the presence of lime and converted to a protein hydrolysate which is neutralized and to which other components are added such as foam stabilizers, corrosion inhibitors, antimicrobial agents, and freezing point depressants. Foams derived from protein foam concentrates generally have very good heat stability and resist burnback, but are not as mobile or fluid on the fuel surface as other types of low expansion foams. Protein foams are susceptible to fuel pickup; consequently, care should be taken to minimize submergence.

    Fluoroprotein Foam

    Fluoroprotein Foam is derived from protein foam concentrates to which small amounts of fluorochemical surfactants are added. The fluorochemical surfactants are similar to those developed for AFFF foam agents but used in much lower concentrations. The addition of these chemicals produces an easier flowing foam. Because of these chemicals, fluoroprotein foams are said to be oleophobic (oil shedding) and are well suited for sub-surface injection.

    Aqueous Film Forming Foam (AFFF)

    FireFightingFoams1Aqueous Film-Forming Foam (AFFF) is a completely synthetic foam. It consists of combinations of fluorochemical and hydrocarbon surfactants combined with high boiling point solvents and water. Surfactants are chemicals that have the ability to alter the surface properties of water. Fluorochemical surfactants alter these properties in such a way that a thin film (Figure 1-7) can spread on a hydrocarbon fuel (such as gasoline) even though the aqueous film is more dense than the fuel.



    Film Forming Fluoroprotein (FFFP)

    Film-Forming Fluoroprotein (FFFP) is a protein base foam concentrate to which quantities of fluorochemical surfactants (similar to those used in AFFF foam agents) are added. This improves the mobility of the foam to the point where it begins to approach the quick extinguishment that is characteristic of AFFF foam agents. On some fuels, it also forms an aqueous film like the AFFF foam agents. However, this reduces the burnback resistance that is characteristic of protein-based foams. Film-forming fluoroprotein foams tend to be a compromise between AFFF and fluoroprotein foam agents.

    Synthetic detergent foam

    Synthetic Detergent type foam agents are based on mixtures of non-fluorochemical, hydrocarbon type surfactants along with solvents and water. These foam agents do not form aqueous films or polymeric membranes. Instead, they function by forming an aggregate of foam bubbles on the surface of the fuel. They are used most frequently with high expansion foam generators yielding expansion ratios of 200 to 1000:1 (see Figure 1-9). The reduced water content of high expansion foams makes them suitable for use in total flooding applications and on cryogenic type fuels such as liquefied natural gas (LNG). Some of these foam agents are specially formulated to be used with low, medium, and high expansion foam hardware at different proportioning ratios and are referred to as multiple expansion foam agents.

    Alcohol Resistant foams (AR)

    FireFightingFoams2Alcohol-Resistant Concentrate (ARC) produces a foam that is effective on fuels such as methyl alcohol, ethyl alcohol, and acetone which have appreciable water solubility or miscibility. Standard foam agents are mixtures of chemicals (natural or synthetic) whose bubbles collapse when applied to water soluble fuels. These fuels are said to be foam destructive. The early alcohol-resistant foams were based on mixtures of protein foams and chemicals called metal soaps. These chemicals are hydrophobic or water repellent. The most current alcohol-resistant concentrates are based on AFFF concentrates to which a water soluble polymer (polysaccharide) has been added. When these foam agents are applied to a water soluble fuel such as methyl alcohol, a polymeric membrane (Figure 1-8) is formed between the foam and the water soluble fuel. When this foam agent is used on a conventional (water insoluble) hydrocarbon fuel, it functions as an AFFF foam by forming an aqueous film at the fuel/air interface. Since the polymer is a naturally occurring chemical, small amounts of an antimicrobial agent are added to prevent biological degradation.


    Hazardous material "HAZMAT" foams

    Specialist foams for toxic vapour suppression of fuels and other chemicals are now available. Such foams often require resistance to chemical reaction. Usually they are applied at medium expansions to form a long lasting and deep blanket of foam on the chemical surface.

    Balanced Proportioning

    Proportioning1Balanced Pressure Proportioning is the most common method used for fixed system applications where pressure or flow can vary with demand. There are two basic types – Bladder Tanks and Pump Systems using Balanced Pressure Proportioners. All balanced pressure systems use a modified venturi device called a proportioner or ratio controller. The proportioners are available in a variety of sizes and styles to match required flow ranges and pipe sizes. As water flows through the proportioner nozzle, a low pressure area is created. It is in this low pressure area that the pressurized concentrate mixes with the water stream. A metering orifice, at the concentrate inlet, regulates the rate of concentrate flow and thus determines the percentage of concentrate in the foam solution. Balanced pressure proportioning systems require the foam concentrate pressure to be balanced with the water pressure at the proportioner inlets. This balance meters the proper amount of foam concentrate into the water stream.

    Bladder Tank System

    VertBladTnkInstal Balanced pressure bladder tank systems use a pressure-rated tank with an internal nylonreinforced elastomeric bladder. System water pressure is used to squeeze the bladder containing the foam concentrate providing pressurized concentrate to the proportioner. The resulting foam solution is piped to discharge devices protecting the hazard area. A distinct advantage of bladder tanks is that no external power supply is required other than a pressurized water source. However, because the bladder tank is pressurized during operation, it cannot be conveniently recharged during discharge. Because of their simple design, bladder tanks require very little maintenance.  



    Balance Pressured  Pump Proportioning

    Balance pressure pump proportioning systems use atmospheric foam concentrate storage tanks The tank is not pressure rated and may be constructed of mild steel, fiberglass-reinforced plastic, or polyethylene plastic.PumpSkid Instead of using pressurized water as with bladder tanks, the foam liquid is pumped to the proportioner. An automatic pressure balancing valve regulates the foam concentrate pressure to match the water pressure. A duplex pressure gauge provides continuous monitoring of both water and concentrate pressures. The system can also be operated manually to control the pressures and isolate the automatic balancing valve. Positive displacement pumps are used with these systems to allow maximum efficiency for liquids of varying viscosity. The size of pumps and drivers will vary depending on the application and the type of foam concentrate used.

    In-Line Balanced Pressure Proportioner

    PPW-200_80 The in-line balanced pressure proportioner is similar to the pump skid previously described except that it is a separate assembly that offers the advantage of proportioning the foam concentrate at a location remote from the tank and pump. Like the pump skid, the proportioner assembly incorporates an automatic pressure balancing valve, duplex gauge, and hand-operated valves for optional manual pressure regulation. A pressure control valve, located in the return line to the foam concentrate storage tank, maintains constant pressure in the supply manifold that is 15 to 20 psi (103 to 138 kPa) higher than the water pressure to the proportioner. Multiple in-line balanced pressure proportioners can be supplied from a single foam pump to protect several hazard areas. By adding an automated valve to each proportioner, either foam discharge or water only discharge can be selected.

    Inline Inductors

    To Follow

    Premix Foam Systems

    The simplest means of proportioning is accomplished by pre-mixing. With this method, pre-measured portions of water and foam concentrate are mixed in a container. In most cases, pre-mixed solutions are discharged from a pressure-rated tank using an inert gas such as carbon dioxide or nitrogen. An alternate method of discharge uses a pump and on-pressure-rated, atmospheric storage tank. The pump transfers the foam solution (under pressure) through piping or hose to the discharge devices.

    Only AFFF concentrates can be used with the premix or dump-in methods. Protein base foams do not mix as readily as AFFF and will gradually settle out of the premixed solution. Specially diluted alcohol-resistant concentrates are used in specific pre-mix units. In dump-in applications, ANSULITE alcohol-resistant AFFF concentrate should only be used when the booster tank is equipped with a circulation pump and complete mixing can be accomplished through the recycle line.

    A disadvantage with premix systems is that all the water is converted to foam solution. Other types of proportioning systems store the foam concentrate separately from the water supply so that either foam or water discharge is possible.

    A Premix system is ideal for protection of small hazards where suitable continuous water supplies are not available. Typical risks include Pump Rooms, Dip Tanks and Engine Rooms.


    • Self Contained
    • Does not need continuous water supply
    • Does not need external power for operation
    • Relatively inexpensive


    • Premix storage life is limited – needs to be replaced every 1 to 3 years
    • Only suitable for small risks

    Foam Proportioning Equipment


    Foam Proportioning refers to the introduction of a foam concentrate into a volume or flowing stream of water. Proper proportioning is essential to ensure the optimum performance from the foam liquid concentrate.

    Various types of proportioning systems are available, each with advantages and disadvantages depending on the site conditions and specific application


    The simplest means of proportioning is accomplished by premixing. With this method, pre-measured portions of water and foam concentrate are mixed in a container. In most cases, premixed solutions are discharged from a pressure-rated tank using an inert gas such as carbon dioxide or nitrogen. An alternate method of discharge uses a pump and on-pressure-rated, atmospheric storage tank. The pump transfers the foam solution (under pressure) through piping or hose to the discharge devices.

    Inline Inductors (Proportioners)Foam EductorZ-2

    These are also know as eductors and are probably the most common type of proportioning devices. They are used extensively by municipal and industrial brigades for portable equipment as well as being used in simple fixed systems



    Balanced Pressure Proportioning Systems

    HorizontalBladderTankBalanced Pressure Proportioning is the most common method used for fixed system applications where pressure or flow can vary with demand.There are two basic types – Bladder Tanks and Pump Systems using Balanced Pressure Proportioners.

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    Ansulite 3×3 Low-Viscosity AR-AFFF

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    Download MSDS Sheet

    Ansulite3x3ANSULITE® 3×3 Low-Viscosity AR-AFFF (Alcohol-Resistant Aqueous Film-Forming Foam) Concentrate is formulated using a newly patented and proprietary technology. The foam concentrate has a dramatically reduced viscosity as compared to other listed polar-solvent type AR-AFFF concentrates on the market. This reduced viscosity enhances performance in all types of foam proportioning equipment including inline eductors, balanced pressure systems, and built-in systems aboard CFR vehicles.

    ANSULITE 3×3 Low-Viscosity AR-AFFF Concentrate is unique among the ANSULITE AFFF agents in that it can be used on either conventional Class B fuel or the polar solvent type Class B fuels. Its excellent wetting characteristics make it useful in combating Class A fires as well.

    Because of the low energy required to make foam, it can be used with both aspirating and nonaspirating discharge devices. To provide even greater fire protection capability, it may be used with dry chemical extinguishing agents without regard to the order of application.

    Due to the velocity of the dry chemical discharge, care must be taken not to submerge the polymeric membrane below the fuel surface.

    A unique application for ANSULITE 3×3 Low-Viscosity AR-AFFF Concentrate is vapor mitigation for hazardous fuming compounds including fuming acids. Recent tests on oleum and chlorosulfonic acids conducted in conjunction with DuPont at a DOE testing facility in Nevada found the foam to be very effective when applied through medium expansion nozzles such as the ANSUL® Model KR-M2 and KRM4.

    In addition, the concentrate is ideally suited for situations involving flammable liquid spills where prolonged vapor suppression is desirable in advance of the spill clean up.

    Ansulite 3% (AFC-3A) AFFF


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    Download MSDS Sheet

    ANSULITE 3% (AFC-3A) AFFF Concentrate is intended for use on Class B hydrocarbon fuel fires having low water solubility such as various crude oils, gasolines, diesel fuels, aviation fuels, etc. It is not suitable for use on fuels having appreciable water solubility (polar solvents), i.e., methyl and ethyl alcohol, acetone, and methyl ethyl ketone.

    It can be used with both aspirating and non-aspirating discharge devices because of the low energy required to make it foam.Its excellent wetting characteristics make it useful in combating Class A
    fires as well. It can be used with dry chemical extinguishing agents without regard to the order of application to provide even greater fire protection capability.