Foam Systems
Fire-Fighting foams are used in both portable and fixed fire extinguishing systems. They are primarily used to combat flammable and combustible liquid fuel fires. The National Fire Protection Association (NFPA) has many standards and guidelines that address foam application for tank / dike protection, aviation spill hazards, aircraft hangar protection and liquids warehousing applications. Foams do differ in chemical composition. This difference affects the rate of application and appropriateness for use on particular liquid fuel hazards. Foams are sometimes used in combination with dry chemicals. This provides a solution for both two-dimensional pool and three-dimensional spilling fuel fire scenarios. Foam is created by proportioning the foam concentrate with water. This is done by different types of portable and fixed proportioning devices. Different devices are available for foam discharge such as sprinklers, nozzles and foam monitors.
Low expansion foam is used principally to extinguish burning flammable or combustible liquid spill or tank fires by application to develop a cooling, coherent blanket. This blanket can prevent vapor transmission for some time, depending on stability and depth of the foam. The blanket may be removed after a suitable period of time. It has no detrimental effect on the product with which it comes into contact with. Foam can also be used to diminish or halt the generation of flammable vapors from non- burning liquids and solids and may be used to fill cavities or enclosures where toxic or flammable gases may collect. In aircraft fueling and service applications, foam plays a significant role as large fuel spills due to accidents or mal-functioning is expected. It can also be used in flammable liquid warehousing applications. Medium or high expansion foam may be used to fill enclosures. In such case, it halts convection and access to air for combustion. Their water content is also used to cool and diminish oxygen by steam displacement. These types of foams may also be used to control liquified natural gas (LNG) spill fires and help disperse the resulting vapor cloud. Foam generated from solutions of low surface tension and characteristics may be used in Class A fires. In such case, the water solution draining from the foam cools and wets the solid combustibles.
There are different causes that lead to improper functioning of foams unless it has been taken into consideration during system design. Foam breaks down and vaporizes its water content under attack by heat and flame. There for, the sufficient volume and rate must be applied to burning surfaces to account for this loss. Foam is also unstable thus it can be broken easily by physical and mechanical force (e.g. use of water hose stream). It is also subjected to severe breakdown when used in conjunction with certain other extinguishing agents. Turbulent air or violently uprising combustion gases from fire may divert foam from the burning area.
Many types of foam concentrates are available in the market. These types do differ in chemical composition, mixing ration and the hazard in which they are used to protect as well as the system type used to apply the foam. The following are the common types available in the markets:
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Aqueous Film-Forming Foam (AFFF)
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Type: synthetic foam concentrate
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Proportioning Rate: 1%, 3%, 6%
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Expansion Ration Classification: low expansion foam concentrate
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Characteristics:
- It has low viscosity
- It has fast spreading and leveling characteristics
- It develops a continuous layer of solution (film) under the foam, maintain a floating film on hydrocarbon fuel surfaces to help suppress combustible vapors and cool the fuel substrate
- The film can spread on surfaces partially covered with foam
- This film is self-healing following mechanical disruption
- Suitable for aircraft fuel spill fires due to its fluidity and fast spreading on Kerosene fuel
- Sophisticated discharge devices are not required because of the inherent rapid and easy forming capabilities
Can be used in conjunction with dry chemical extinguishing agent
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Alcohol Resistant Aqueous Film-Forming Foam (AR-AFFF)
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Type: synthetic foam concentrate
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Proportioning Rate: 1x3%, 3x3%, 3x6%
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Expansion Ration Classification: low expansion foam concentrate
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Characteristics:
- It exhibits AFFF foam concentrate characteristics
- It is suitable for use with polar solvent, water soluble and water miscible fuels by forming a floating gel-like mass for foam build up on these types of fuels.
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Protein (P) Foaming Agent
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Type: organic foam concentrate
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Proportioning Rate: 3%, 6%
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Expansion Ration Classification: low expansion foam concentrate
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Characteristics:
- It produces dense, viscous foams of high stability, high heat resistant and good resistant to burn back.
- It produces foams of less resistant to breakdown by fuel saturation than are AFFF and Fluor protein foams
- It produces non-toxic and biodegradable foams
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Fluoroprotein (FP) Foaming Agent
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Type: organic foam concentrate
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Proportioning Rate: 3%, 6%
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Expansion Ration Classification: low expansion foam concentrate
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Characteristics:
- It contains fluorinated surface-active agents that confer a fuel shedding property.
- Suitable for subsurface injection
- Suitable for nozzle and monitor foam applications
- Suitable for in-depth crude oil fires
- More compatible with dry chemical than other protein- based type foam concentrat
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Film-Forming Fluoroprotein (FFFP)
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Type: organic foam concentrate
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Proportioning Rate: 3%, 6%
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Expansion Ration Classification: low expansion foam concentrate
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Characteristics:
- It contains film forming fluorinated surface-active agents that confer a fuel shedding property as well as forming water solution on most of hydrocarbon fuels surfaces (film).
- It has fast spreading and leveling characteristics
- This film is self-healing following mechanical disruption
- It may be used with spray devices due to the rapid and easy forming capabilities
- It has less burn back resistance than other protein- based type foam concentrate
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High Expansion Foam
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Type: synthetic foam concentrate
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Proportioning Rate: 2%
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Expansion Ration Classification: high expansion foam concentrate
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Characteristics:
- It is used to control and extinguish Class A and some class B fires
- It suits total flooding of confined or inaccessible spaces and for volumetric displacement of vapor, heat and smoke.
- It can be used in conjunction with water from automatic sprinklers
- It can be used for control of fire and reduction of vaporization from LNG spills.
The process of producing and applying fire fighting air-foams to hazards require three separate operations each of which consumes energy, they are:
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The proportioning process
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The foam generation phase
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The distribution method
There are many types of proportioning devices and systems. These types include the following:
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Nozzle Eductor
A device that incorporates a venturi to draw foam concentrate through a short length of pipe and/or flexible tubing connected to the foam supply.
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In-Line Eductor (Inductor)
A Venturi-type proportioning device that meters foam concentrate at a fixed or variable concentration into the water stream at a point between the water source and a nozzle or other discharge device.
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Around the Pump Proportioner
A system that uses a venturi eductor installed in a bypass line between the discharge and suction side of a water pump and suitable variable or fixed orifices to induct foam concentrate from a tank or container into the pump suction line.
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Pressure Proportioning Tank
A foam concentrate tank with no bladder that uses water flow through an orifice to displace a foam concentrate, having a specific gravity of at least 1.15, in the tank with water to add foam concentrate through an orifice into a water line at a specified rate.
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Coupled Water Motor-Pump Proportioner
A correctly designed positive displacement water motor in the water supply line coupled to a positive displacement foam concentrate pump to provide proportioning.
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Balanced Pressure Proportioner
A foam proportioning system that utilizes either a bladder tank or foam pump and valve(s) to balance foam and water pressures at a modified venturi- type proportioner located in the foam solution delivery piping; a foam concentrate metering orifice is fitted in the foam inlet section of the proportioner.
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Variable Orifice, Variable Flow Demand Proportioner
A direct injection proportioning system that utilizes flow meters for foam concentrate and water in conjunction with a variable output foam pump control system.
There are many foam equipment and systems types. These include the following:
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Foam Equipment
A device that incorporates a venturi to draw foam concentrate through a short length of pipe and/or flexible tubing connected to the foam supply.
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Foam and Foam Water Monitors
A device that delivers a large foam stream and is mounted on a stationary support that either is elevated or is at grade.
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Portable Monitor (Cannon)
A device that delivers a foam monitor stream and is mounted on a movable support or wheels so it can be transported to the fire scene.
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High Back-Pressure Foam Maker
A foam maker utilizing the Venturi principle for aspirating air into a stream of foam solution forms foam under pressure.
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High Expansion Foam-Generating Devices
There are two principal methods used for the generation of these types of fire-fighting foams. One method uses a modified venturi action with air aspiration flow, whereas the other requires use of a blower and screen to form the finished foam. The latter system produces high-expansion foam containing sufficient residual kinetic energy to enable it to be forced through large tubes and passageways.
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Water Fog or Spray Nozzles
A specially designed hose line nozzle or fixed foam maker designed to aspirate air that is connected to a supply of foam solution. Several types of adjustable water fog or spray nozzles for portable use provide an acceptable fire-fighting foam of adequate characteristics when supplied with certain foam concentrates.
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Foam-Generating Equipment and systems
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Open Dip Tank, Quench Tank System
This system consists of a small, aspirating foam-maker supplied by a water line and foam concentrate educted to the foam-maker. Foam discharges into a mixing box, which also acts as a surface distributor for gentle foam application.
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Foam Chambers for Large Storage Tanks
Fire protection of large outdoor fuel storage tanks requires that several foam chambers with foam-makers be installed at equally spaced positions slightly below the curb angle on the top periphery of the tanks. These chambers are connected to lines on the ground that supply foam solution to each foam-maker simultaneously in case of ignition of the flammable contents of the tank. Frangible seals at the discharge outlet of the foam chamber
prevent vapor from entering the foam piping. These seals are designed to burst when foam pressure is applied. A screen for the air inlet to the aspirating foam-maker prevents clogging from foreign matter, such as bird nesting material. A universal or swing pipe joint is installed at ground level in the foam solution inlet pipe to prevent fracturing of the supply piping if an explosion precedes a tank fire.
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Internal Tank Foam Distributing Devices
Devices that have been developed to gently apply foam from one point, regardless of burning fuel level. These devices are required for some alcohol- type foams.
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Central Foam House Distributing Systems
These systems, consist of an enclosure housing a foam concentrate supply tank and a proportioning device of an automatic or balanced pressure type. Foam solution is supplied under adequate pressure from this foam house to the piping system and controlled by appropriate valves so that the foam chambers with foam-makers on the burning tank receive foam solution.
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Intermediate Back-Pressure System
Similar to the preceding central foam house distributing systems, it utilizes strong and well-braced foam delivery pipes on the side of the tank, which act as supports to prevent buckling of the tank from heat. This system also uses a foam truck to proportion and pump foam solution to the piping outside the dike or firewall of the burning tank.
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Subsurface Foam-Injection Systems
The subsurface foam-injection system accomplishes this by injecting foam under the pressure of the head of fuel in the tank, using the high back- pressure foam-maker
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Portable foam devices for Tank Protection
Mobile foam monitors of high-capacity discharge (foam cannon) may be used to direct a stream of foam over the open top rim of a burning tank so foam will fall into the burning area. These devices waste foam because of crosswinds, fire updrafts, and inability to place the equipment in an advantageous position.
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Foam Water Sprinkler System
A piping network employing automatic sprinklers, nozzles or other discharge devices, connected to a source of foam concentrate and to a water supply.
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High Expansion Foam System
High-expansion foam is an aggregation of bubbles resulting from the mechanical expansion of a foam solution by air or by other gases, with expansion ratios in the range of from 20:1 to approximately 1000:1. There are three types of systems:
(1) total flooding, (2) local application, and (3) portable.
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Compressed Air Foam System
A system employing compressed air foam discharge devices or hoses attached to a piping system through which foam is transported from a mixing chamber.
All previously discussed systems and components are provided by Bavaria to satisfy the customers' needs. Please check our products technical datasheets for more information or contact us.
