Fire Fighting Foam Products
In the deluge system, all sprinklers are open and normally there is no water in the piping. When fire occurs, a supplementary detection system senses the fire and automatically
opens a water control valve. This allows water to flow through the piping system to all sprinklers.
In a preaction system, all sprinklers are closed and normally there is no water in the piping. A preaction system is used when faster response is desired (versus a dry pipe system). When fire occurs, a supplementary detection system (more sensitive than the sprinkler elements) senses the fire and automatically opens a water control valve which
allows water to flow into the piping system. Subsequent water discharge occurs from individual sprinklers as they respond to the heat of the fire. The system shown below uses HAD’s (Heat Actuated Detectors) and a dropweight release to open the preaction valve. Alternate detection systems can also be used. Pre-priming foam solution is not needed as foam will be proportioned into the piping during operation.
Dry pipe systems use automatic sprinklers that are attached to a piping system containing air under pressure. When the air is released from the opening of the sprinklers, the water pressure overcomes the lessened air pressure and opens the dry pipe valve. The dry pipe valve is designed so that a moderate air pressure prevents a higher water pressure from opening the valve.
Once the valve is opened, the water flows into the piping system and out the opened sprinklers. This system provides protection in areas subject to below freezing temperatures. Piping must be drained of water or foam solution following operation to prevent freezing.
Typically, upright sprinklers are used to allow drainage. Otherwise, approved dry pendent sprinklers must be used to prevent freezing. Dry pipe systems are inherently slower in operating and should be considered less desirable for applications using AFFF.
This system uses automatic closed-head sprinklers that are attached to a piping system containing water. Water discharges immediately from those sprinklers opened by a fire. A flow of water through the valve sounds an alarm.
Wet pipe systems should not be used where freezing conditions are likely to damage piping. In systems using AFFF concentrate, the piping to the sprinkler heads can be pre-primed with foam solution to enable immediate effective foam discharge. AFFF solution in contact with steel pipe may gradually lose its fire effectiveness. Samples of this solution should be checked on an annual basis and replenished as needed. A test discharge connection is recommended downstream from the proportioner and should be located to fill a maximum portion of the sprinkler system piping. The test connection should be of sufficient size to meet the minimum flow rate for the particular proportioner. This type of system is the most reliable, simplest, and fastest responding of all closed-head sprinkler systems. Conversions of water systems to foam can usually be accomplished easily. (Local codes and regulations should be investigated prior to conversion.)
An automatic sprinkler system is designed to distribute water or foam solution to a specific hazard area. The application rate, commonly referred to as ‘‘ density,’’ is frequently expressed in units of gallons per minute per square foot ( gpm/ ft2) or liters per minute per square meter (Lpm/m2) of area.
The worst potential fire situation is generally used to determine the number of sprinkler heads discharging. This, in turn, determines the water supply demand; and in the case
of foam sprinkler systems, the required amount of foam liquid concentrate. Characteristics of some flammable products may require higher densities and special foam liquid
concentrates.
Areas protected by sprinkler systems are usually given a class of occupancy (light, ordinary, or high hazard). The class of occupancy relates to the probable number of sprinkler
heads that may operate in a particular fire situation and governs the maximum spacing allowed between sprinkler heads. The sprinkler head provides for a nearly uniform distribution of water or expanded foam over a given area. The solution strikes a deflector and is broken into a circular pattern of distribution. Spacing of sprinkler heads results in overlapping patterns to ensure uniform coverage and effective fire control.
Pipe sizing to the sprinkler heads is commonly determined by hydraulic calculations to assure an adequate supply of water and uniform distribution from the sprinkler heads. The standard addressing sprinkler system design is NFPA Standard 13 or BS EN12845. Additional guidance for foam systems design is contained within NFPA Standards 11, 16, and 30.
Conventional sprinklers heads are available for either upright or pendent installation. A heat sensitive element, consisting of either a fusible link or frangible glass bulb, is rated for a specific operating temperature. A standard orifice sprinkler is 15mm; however, various small and large orifice sprinklers are available to achieve the desired density with the available water supply pressure.
Conventional open sprinkler heads, without the heat-sensitive element, are used for total area flooding “deluge” systems. In applications using AFFF concentrates, the conventional sprinkler is acceptable. The UL listing directory should be consulted to ensure the sprinkler head is listed with the manufacturer’s foam concentrate.
Acceptable foam quality is expected from conventional sprinkler heads of similar design to those listed. These sprinklers cannot be used with protein or fluoroprotein base foam concentrates which require air aspirated discharge devices.
Foam/water sprinkler heads are open type and generate air aspirated foam by drawing air into the foam solution stream. The sprinkler head is available for either
upright or pendent mounting and may be used with either foam or water. Patterns of coverage are similar to conventional sprinkler heads; however, only a 3/8 in. orifice is
available corresponding to a K-Factor of 3.0.
Sprinkler systems can be either closed-head or open-head (deluge) systems using conventional sprinkler heads. Sprinkler systems using foam/water sprinkler heads can
only be open-head systems as these sprinklers are not available with heat-sensitive elements. Closed-head sprinkler systems can be of three different types: wet pipe, dry pipe, or preaction. An AFFF foam can be used in any closed-head sprinkler system as covered by NFPA Standard 16 – Foam/ Water Sprinkler Systems.
The following types of system are generally used
Wet Pipe System - click here for further information
Dry Pipe System – click here for further information
Preaction System – click here for further information
Deluge System – click here for further information
Approved Sprinkler Head list for Foam Concentrates
Bladder Tanks are the most common type of balanced pressure proportioning systems. The system uses a pressure rated tank with an internal rubber bladder. The foam concentrate is stored within the bladder and system water pressure is used to squeeze the bladder and provide pressurised concentrate to the proportioner.
Bladder tanks come in a wide range of sizes from 300 us gallons to 3000 usgal in the Ansul Product Range and from 400 litres to 25000 litres in the SKUM range.Bladder Tanks provide a self contained balanced pressure proportioning system requiring no external power or foam pumping.
Recent developments by SKUM have enhanced the advantages of using a bladder tank as the means of providing a balanced pressure proportioning system – see News items for details
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