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Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given fire situation. Our objective in this two-part article is to provide guidance based on a hazard-specific approach and help you make an informed decision on appropriate fire-suppression measures, especially with regard to the processing and storage of flammable liquids. As a manufacturer of foam proportioners and firefighting monitors, we specialise mainly in the Class B category: flammable liquids.
How do we make foam?
Steps of foam generation A little of the history of foam developmentprotein-based and synthetic foam agentsWe can date the development of modern foam concentrates from the 1960s onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the base component). The main drawback was due to limited fuel tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a greater fuel tolerance as well as forming a vapour-sealing film across the surface of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating devices are fitted. Nevertheless, AFFF’s development did not completely replace the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat fuel pick-up (mixing) and offer a good resistance to heat, defined by the industry as ‘burn-back resistance’. filmforming fluorprotein foam agents (FFFP)Further development in the 1980s took FP to the next level with film-forming fluoroprotein or FFFP. We now had the best of both worlds: a film-forming foam that also had good burn-back resistance. The 1980s further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always presented an additional challenge as they were water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same technology also became available with the new generation of AFFF-ARs. fluorine free foam agents In recent years fluorine, one of the cornerstone ingredients to all foams, has become an environmental issue, due to persistence in groundwater. The industry has been presented with a major challenge to eliminate the ‘fluoro’ element of all the different foam concentrate types. We have witnessed an era
of manufacturers’ claims and counter claims regarding the efficacy of a whole range of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have become the new normal and first choice for operators changing existing stock or reviewing new projects. As a foam proportioner manufacturer we must examine the physical properties of foam carefully Multi-purpose foams such as the F3 alcohol-resistant types are increasingly important in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small degree of water miscibility of the fuel. comparison of foam agents: EN 1568 and UL162All foam concentrate manufacturers will naturally promote their product as being highly effective. The best way of comparing their claims is to familiarise yourself with the empirically based standard EN 1568 or UL162. The tests cover extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are both included in the test protocols. This also covers fresh and seawater as well as gentle and forceful application of the foam. Each foam is given a rating with IA being the best, IIID the worst. This means that you can challenge foam suppliers in order to make an informed decision on the best foam for your needs. Whilst EN 1568 is an excellent benchmark standard, awareness of the effects on foam performance from factors outside the standard tests should be noted. For example, particularly aggressive solvents can challenge the firefighting effectiveness of certain foams. This can be exacerbated by different ambient air temperatures, the application method, fuel depth etc. Our advice would be to understand the details of the tests and try to match them to the foam’s appropriateness for your individual hazards. We would always recommend consulting individual foam manufacturers as they can often provide specific in-house fire-performance data against some of the more unusual fuels. However, despite the foam manufacturers’ sometimes conflicting claims on performance, the earlier fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam. About the authors David Owen has 35+ years experience in the UK fire protection industry specialising Andreas Hulinsky has been a Design Engineer at FireDos since 2009. He focuses on the development of proportioning systems, specialising in the proportioning of foam concentrates. Critical factors for success: the time and application rate matrix
uccessful extinction of flammable liquid fires depends on two converging and complementary factors: time and the rate at which finished foam is applied. Both are determined by empirically based standards published by bodies such as the National Fire Protection Association (NFPA) in
This means that firefighting resources, particularly in a manual fire attack, need to be assembled before firefighting commences and this takes time. The advantage in fitting fixed systems is that the resources are already designed and built into the system for immediate application. Foam proportioning methods: mixing water with foam concentrateIn order to allow readers to make an informed decision on how best to tackle their particular fire challenges, the following is an overview of the various foam proportioning methods. foam inductorsTypically associated with fire service deployment and limited fixed systems applications. This uses the venturi principle to create a pressure drop in a small aluminium or seawater material compatible device with built-in concentrate pick-up tube. The pressure drop created by the venturi draws the foam concentrate from a container where it mixes with water to create foam solution. Both the pick-up tube and body of the inductor are compact enough to be easily carried on a fire appliance or fitted into a pipework system. However, whilst it is considered to be the simplest method, it has severe drawbacks:
balanced pressure proportionersThese use an electric or a combination of electric and diesel pumps to supply foam concentrate into a proportioner at a higher pressure than the incoming water-line pressure. The proportioner is installed into the water line and regulates the mixing. They are now associated with older systems, where disadvantages include:
bladder tanks Comprised of a steel pressure vessel containing a flexible bladder (typically
a butyl material) linked to a foam concentrate proportioner similar to the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam filled bladder so that foam concentrate can be proportioned with water using the same supply. The venturi principle is again brought into play as it creates a pressure drop at the point of injection for the foam concentrate. Testing cannot be achieved without creating premix and discharging finished foam. This will add to
whole lifetime costs as a result of foam concentrate usage, which has to be replaced, and the disposal of premix or foam. However, the bladder itself is seen as Compressed air foam (CAFS)This is not a proportioning method in the conventional sense as the foam is already proportioned using one of the previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam solution at the point of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces allowing better penetration and cooling. This is also a benefit in wildfire situations by coating vulnerable structures to mitigate fire growth. The limited water supplies associated with remote wildfire areas means that the resource can be fully optimised. However, as with balanced pressure proportioner foam pumps, an additional point of failure is possible due to the additional CAFS apparatus. water driven or turbine foam proportionersFireDos have become synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is purely mechanical and highly reliable. A water-driven rotor supplies the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and will proportion the foam concentrate accurately across a wide operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, completely without using any foam concentrate or creating premix or firefighting foam. 1 = water motor 2 = proportioning pump 3 = coupling 4 = ball valve 'flushing' 5 = ball valve 'reutrning / proportioning' The benefits of FireDos Gen III FM approved foam proportioners include:
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How does a foam proportioner work?Watch this video to learn more about the working principle. View moreWhich of the following is a method by which foam extinguishes a fire?Vapor suppression is the ability of the foam blanket to suppress flammable vapors and prevent their release. Vapor suppression is necessary to extinguish fires involving flammable liquids and to prevent ignition of unignited flammable liquid spills.
Which type of foam is particularly well suited for gasoline spills?Aqueous Film-Forming Foam (AFFF) suppresses and secures fires involving petroleum-based products such as liquid natural gas and rubber; and flammable and combustible liquids such as diesel fuel, crude oil, and gasoline.
Which type of foam proportioner relies on the Venturi effect?National Foam Proportioners utilize the water flowing through them to produce a venturi effect that induces foam concentrate into the water stream.
When using low energy portable foam application systems the aeration and discharge functions are completed by 503?When using low energy portable foam application systems, the aeration and discharge functions are completed by: the master stream appliances.
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