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.
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
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.
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.
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: