Foam Suppression Systems – What You Need To Know
Whether it is protecting high-risk assets or an emergency situation, foam hardware has evolved since its commercial introduction in the 1950s to meet the needs of fire safety professionals, risk managers, fire service brigades, and industrial fire suppression for industries worldwide.
Foam hardware components can generally be divided into four categories: tank systems; proportioning devices; discharge devices; and mobile equipment. The applications for foam hardware are governed by safety codes and standards usually under the direction of an authority having jurisdiction, for the intended purpose to prevent or mitigate the chance of costly property loss and business interruption, as well as reduction of risk.
Examples of such guidelines are National Fire Protection Association (NFPA) 11: Standard for Low, Medium and High Expansion Foam; NFPA 16: Standard For The Installation of Foam-Water Sprinkler and Foam-Water Spray Systems; NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems; NFPA 30 Flammable and Combustible Liquids Code; NFPA 409: Standard On Aircraft Hangars; NFPA 412: Standard For Evaluating Aircraft Rescue and Fire-Fighting Foam Equipment; NFPA 418: Standard For Heliports and EN13565-2: Fixed Fire Fighting Systems – Foam Systems Design, Construction and Maintenance and FM Global Property Loss Prevention Data Sheets.
So what exactly is a foam system? NFPA Standard 11, Section 3.3.6 defines foam-water sprinkler systems as “a special system that is pre-connected to a source of foam concentrate and to a water supply. The system is equipped with appropriate discharge devices for extinguishing agent discharge and for distribution over the area to be protected. The piping system is connected to a water supply through a control valve that usually is actuated by operation of automatic detection equipment that is installed in the same area as the sprinklers. When the valve opens, water flows into the piping system, foam concentrate is injected into the water, and the resulting foam solution discharging through the discharge device generates and distributes foam. Upon exhaustion of the foam concentrate supply, water discharge follows and continues until shut off manually. Systems can be used for discharge of water first, followed by discharge of foam for a specified period, and then followed by water until manually shut off.”
Foam-water systems can take different forms like deluge, wet pipe, dry pipe, pre-action, spray and pre-primed systems depending on the type of risk requiring protection.
Fixed foam systems are designed to protect single and multiple high-hazard, high-risk applications and can utilise either Class A or B foam concentrate. In the case of Class B foam, there are various foam concentrate types with the most common being Aqueous Film Forming Foam (AFFF), Alcohol-Resistant Aqueous Film Forming Foam (AR-AFFF) and detergent (High-Expansion) based foam.
Foam Hardware Systems
Bladder Tank System
A Bladder tank is the main component in this type balanced pressure proportioning system. It requires no outside power source other than an adequate water supply. The bladder tank is a carbon steel pressure vessel with a nylon reinforced neoprene rubber bladder inside that stores the foam concentrate. During operation the foam concentrate is discharged from the tank by the water supply, collapsing the bladder around a perforated centre tube until the concentrate is depleted. Bladder tank systems include various component parts such as proportioners, discharge devices, swing check valves, ball valves and hydraulic actuating ball valves. Typical sizes tanks range from 189 litres to 12492 litres.
Most manufacturers of bladder tanks offer them in standard and pre-piped configurations, vertical and horizontal versions. Selection of any specific tank configuration is dependent on the available space where the installation is to occur. Two different types of proportioners can be used in bladder tank systems; they are a variable range proportioner or a conventional (between the flanges) proportioner. The variable range proportioner is used in a closed head foam-water sprinkler system where both a minimum litres-a-minute and maximum litres-a-minute flow is required. A conventional (between the flanges) proportioner is typically used in a deluge system where discharge devices such as foam chambers, foam makers, monitors or sprinkler heads are incorporated into the design.
Positive Displacement Foam Pump System
Positive displacement foam pump skids are typically found in two different type systems they are: balanced pressure (BP) foam pump skids and in-line balanced pressure proportioner (ILBP) foam pump skids. Both systems use the same components such as an atmospheric tank, positive displacement foam pump (electric and diesel), balancing valve, and full service control panel (electric/diesel).
The main difference between an ILBP and the BP pump skid is that the BP pump skid utilises a conventional (between the flanges) proportioner located on the foam pump skid. Whereas, ILBP pumps skid allows the use of in-line balance pressure proportioner which can be remotely located away from the foam pump skid.
The Foam pump is primarily driven by three common power sources: electric motor, water motor (Pelton wheel) or diesel engine. Foam pumps are typically positive displacement rotary type to ensure that any viscosity foam concentrate can be used. Foam concentrate is typically supplied by an atmospheric storage tank.
Foam Concentrate Proportioning System
A foam concentrate proportioning system is a self-contained, preassembled proportioning system with a positive displacement water motor powered pump. These systems require no outside power source other than an adequate water supply. A foam concentrate proportioning system will also require the use of an atmospheric tank (contains the foam concentrate) and can be recharged without stopping the flow of the system.
The atmospheric storage tanks itself is typically manufactured of high-density, cross-linked polyethylene in a vertical configuration. Storage tank assemblies are equipped with a suction connection, return connection, drain/fill connection, and domed top. Typical sizes range from 18 litres to 37854 litres.
High Expansion Foam System
A high expansion foam system is designed for total flood or local application hazards and incorporates the same hardware components and devices as describe for bladder tank and proportioning foam systems. A high expansion foam generator is an air-aspirated discharge device that is typically water powered and requires no other outside power to deliver expanded foam solution in volumes ranging from 200:1 to 1000:1.
Foam Ratio Controller
Ratio controllers are a modified venturi device designed to meter the correct amount of foam concentrate into a water stream over a specified range of flow and pressure rates with minimal pressure loss. The ratio controller consists of three components: the body with water inlet, metering orifice located in the foam concentrate inlet, and throat (nozzle) located downstream from the water inlet.
Inline Balanced Pressure Proportioners
Inline balanced pressure (ILBP) proportioner are a complete self-contained device that incorporates the necessary components including ratio controller, duplex gauge, balancing valve, check valve, ball valve, and associated brass piping. ILBPs are designed to balance the incoming foam concentrate pressure with the incoming fire-water pressure, and meter the correct amount of foam concentrate to fire-water stream over a wide range of flow rates and pressures. The ILBP system works with a positive displacement foam pump, to supply foam concentrate to the ILBP. A pressure sustaining valve, located in the return line, carries excess foam concentrate not needed by the device back to the atmospheric storage tank.
Threaded proportioners are modified venturi ratio controllers that accurately mix and meter foam concentrate into fire-water streams. Each proportioner consists of the following components: body, inlet nozzle, and metering orifice constructed out of bronze material. During operation, water flows through the modified venturi to create an area of lower pressure which is directly affected by the water velocity as it flows through the ratio controller.
Variable Range Proportioner
Variable range proportioner is a low foam solution proportioning device, designed to accurately proportion the foam concentrate into the water stream at both high and low system flow rates. The variable range proportioner is designed as an integral component of a bladder tank proportioning system, used with foam concentrates in foam-water sprinkler systems. Use of a variable range proportioner complies with NFPA 30, the flammable and combustible liquids code, Paragraph 188.8.131.52.2, which states “foam/water sprinkler systems are to provide foam solution to operating sprinklers with 4 sprinklers flowing.”
Continuous Flow Hose Reel
Continuous flow hose reel assemblies are typically manufactured with magna-cast aluminium supports and brass waterway. Hose reels typically feature non-collapsible booster hose and brass 90-degree elbow inlet swivel with male NST outlet. The carbon steel reel is designed to store and deploy continuous flow hose, which allows liquid to flow while the hose is still on the reel. Hose reels are used for remote protection of assets or where manual foam firefighting is required.
Foam chambers are NFPA-11 Type II air aspirating foam discharge devices that provide protection for open top floating and cone roof flammable liquid storage tanks. Foam chambers are a combination of a foam mixing chamber and a foam maker with an air inlet. A removable orifice plate is located between the flange inlet and solution pipe flange, and is sized to deliver the required foam solution at a specified pressure. A frangible vapour seal located in the foam chamber body prevents product vapours from entering the foam chamber body. The vapour seal will break once the foam solution enters, filling the foam chamber body with expanded foam. The foam flows to a deflector plate, which directs the foam to the inside of the storage tank wall and fuel surface, only allowing minimum foam submergence and fuel agitation.
A Foam maker is a stainless steel discharge tube incorporates a mixing barrel, an orifice plate (sized for the required flow at a given pressure) and an air inlet to allow air into the foam solution stream to generate expanded foam. The foam maker is normally installed in the line of a semi-fixed or fixed foam fire protection system. Foam makers are air-aspirating foam discharge devices used primarily for the protection of the seal area of open top floating roof storage tanks and dike areas around storage tanks. Additional applications include protection of spill hazards and diked flammable liquid storage areas.
The Foam station is a quick knock down fixed hardware device. The unit is typically self-contained, consisting of stainless steel concentrate tank, eductor, hand-line nozzle and non-collapsible hose. When in operation, water is introduced from a dedicated water source through the supply hose to the educator. While water is passing through the eductor a vacuum is created, which draws foam concentrate out of the tank, up to the eductor and into the water stream, delivering the foam solution. Some foam stations may be as simple as connecting a monitor with self-educting foam-water nozzles to a hydrant with placement of a tote or drum of foam next to it.
High Back Pressure Foam Maker
High back pressure foam maker is a discharge tube (bronze, carbon steel or stainless steel) with flange inlets and outlets and has air induction holes placed 90 degrees apart to allow air into the foam solution stream to generate expanded foam. These special foam makers are to inject foam into a fuel storage tank at the base of the tank. The foam then floats to the surface of the tank to extinguish the fire.
Mobile products are designed to provide quick, mobile foam fire protection for hazards consisting of flammable liquids. These types of hazards can be defined but not limited to tank farms, loading racks (both truck and rail), chemical processing plants, and marine loading terminals. Mobile products greatly increase the firefighting ability of emergency first responders. Mobile foam devices can be used with either Class A or Class B foam concentrates.
A mobile foam cart is designed and constructed for one person operation. This foam station can function at its full potential quickly in an emergency situation. Foam concentrate is stored in a polyethylene or stainless steel tank equipped with an eductor and pick-up tube. The pick-up tube is connected to the tank and utilises a metering device to determine what percentage of foam concentrate is introduced into the water stream. On the inlet of the eductor, a supply fire hose is connected that delivers water from an independent source.
A fire hose and discharge nozzle are connected to the outlet. When in operation, water flows through the eductor creating a vacuum that draws foam concentrate out of the tank to the metering valve of the eductor and into the water stream, delivering foam solution to the nozzle.
Typically used to protect against liquid spills, diked areas, storage tanks, loading racks or storage facilities in general that contain combustible or flammable liquids, a foam trailer is a complete mobile platform consisting of a trailer constructed with frame, wheels, and axles, non-slid decking, utility boxes, water inlet connections and monitor capable of carrying the total charged weight of the trailer assembly and the foam concentrate.
Trailers utilise either one of two foam storage vessel designs: polyethylene tote(s), single, dual, or multiple, or a rigidly constructed metal foam tank. Monitor utilised are typically of the self-educting type with flow ranges varying from 1893 litres-a-minute to 11,356 litres-a-minute.
Ultimately selection of any firefighting tool should be governed by product(s) being “fit for purpose” and having the appropriate third-party certifications for the intended application. Foam systems prevent or mitigate the chance of costly property loss and business interruption, as well as reduction of risk. Foam hardware, fixed suppression systems and mobile products have met the needs of fire safety professionals, risk managers, fire service brigades, and industrial fire suppression for high-hazard high-risk industries and continue to do so under the guidance of a “balance fire protection plan.”
For further information, go to www.solbergfoam.com