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Fire presents many challenges, not least due to the variables that determine which suppression medium is appropriate for a given fireplace situation. Our objective on this two-part article is to provide steerage based on a hazard-specific strategy and allow you to make an informed determination on applicable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires usually related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise mainly within the Class B category: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only could not penetrate the fireplace load successfully.
Fire courses.
How will we make foam?
Finished foam solution comprises a simple recipe of foam concentrate, water and air. Foam concentrate is often mixed in the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge system – we will cover proportioning later on this article and discharge strategies in Part 2. At this point air is entrained by utilizing gadgets designed to naturally aspirate the answer. The amount of aspiration and the sort of focus determines the growth ratio. This is typically split between low, medium and high expansion. Low enlargement is as a lot as 20:1, medium is 200:1 and high expansion is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated mills are also used. The decision to choose a specific expansion ratio is determined by the hazard under evaluate.
Put merely, water and oil don’t mix. Applying only water to Class B products will not suppress the burning vapours. This is an important point to make as it’s the vapours, not the liquid itself, that burns. We need a medium that allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to obtain success. Whatever method is chosen to produce that blanket or film, the objective is the same.
Steps of foam generation Images equipped by Author / Contributor
A little of the history of foam development
We can date the development of contemporary foam concentrates from the Sixties onwards. Up to that time foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the base component). The primary drawback was as a end result of limited gas tolerance, which meant it was vulnerable to gasoline pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a greater gasoline tolerance in addition to forming a vapour-sealing movie across the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth did not fully replace the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight gasoline pick-up (mixing) and provide a great resistance to warmth, defined by the trade as ‘burn-back resistance’.
Further development in the Nineteen Eighties took FP to the subsequent stage with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that also had good burn-back resistance.
The Nineteen Eighties further added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time introduced an extra challenge as they have been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same expertise additionally grew to become out there with the new technology of AFFF-ARs.
In current years fluorine, one of the cornerstone ingredients to all foams, has turn into an environmental concern, because of persistence in groundwater. The industry has been presented with a serious problem to eliminate the ‘fluoro’ element of all of the totally different foam focus types. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a whole vary of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have become the new normal and first alternative for operators changing current inventory or reviewing new tasks. As a foam proportioner manufacturer we must look at the bodily properties of foam fastidiously (especially viscosity) as they influence choices on the overall proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are increasingly necessary within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small degree of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being extremely effective. The best way of evaluating their claims is to familiarise your self with the empirically based mostly standard EN 1568 or UL162. The exams cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are each included within the take a look at protocols. This also covers contemporary and seawater as well as light and forceful software of the froth. Each foam is given a ranking with IA being the most effective, IIID the worst. This means that you could challenge foam suppliers so as to make an knowledgeable decision on the most effective foam for your wants.
Whilst EN 1568 is an excellent benchmark normal, awareness of the results on foam efficiency from components outdoors the usual exams must be noted. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by completely different ambient air temperatures, the application technique, fuel depth etc. Our advice would be to understand the small print of the checks and attempt to match them to the foam’s appropriateness on your individual hazards. We would all the time recommend consulting particular person foam manufacturers as they will typically present specific in-house fire-performance data towards a few of the extra uncommon fuels.
However, despite the froth manufacturers’ typically conflicting claims on performance, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the expansion ratio Images equipped by Author / Contributor
Critical factors for achievement: the time and software rate matrix
Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the rate at which completed foam is utilized. Both are decided by empirically based mostly requirements published by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ issue signifies that for a given measurement of fireside area it’s essential to use the froth for long enough to attain extinction and to stop re-ignition. This is especially important in manual intervention as firefighter’s shall be at risk throughout post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the appliance time can be so lengthy as 60 minutes for the most important tank diameters.
The software price refers back to the amount of finished foam applied per square metre. This varies based on the gasoline and the froth type but is at present at least four.0 litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the likelihood that this might be decreased, but requirements typically take time to recognise product development. Anything lower than the minimum utility fee implies that hearth control is unlikely to be achieved. This implies that firefighting sources, significantly in a handbook fire assault, need to be assembled earlier than firefighting commences and this takes time. The benefit in becoming mounted methods is that the assets are already designed and built into the system for quick utility.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an knowledgeable decision on how finest to sort out their particular fire challenges, the following is an overview of the varied foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and restricted fixed systems applications. เกจวัดแรงดัน4นิ้วราคา makes use of the venturi principle to create a strain drop in a small aluminium or seawater material suitable gadget with built-in concentrate pick-up tube. The pressure drop created by the venturi draws the froth 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 sufficient to be easily carried on a hearth appliance or fitted into a pipework system.
However, while it is thought of to be the simplest methodology, it has severe drawbacks: (i) models are manufacturing unit calibrated so any modifications to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a altering amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations attributable to pipe diameter adjustments will adversely affect proportioning accuracy and doubtlessly prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to attract concentrate into the downstream lines; (iv) strain loss is excessive, as a lot as 35%, so responsibility pump pressures must be excessive sufficient to permit for it, doubtlessly adding further price into the system; (v) foam delivery units have to be sized so as to not restrict design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs on account of foam focus usage, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a mix of electric and diesel pumps to provide foam focus into a proportioner at a higher pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the mixing.
They are actually associated with older techniques, where disadvantages embrace: (i) additional prices in hardware and design time; (ii) the froth pump is often restricted to a much tighter working range, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs an extra power supply, apart from water, so is not as reliably safe as a system with a potential single level of failure, similar to an entirely water-driven system; (iv) typically, these systems are very complicated and cause excessive efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to wreck the froth concentrate and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner much like the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the froth stuffed bladder so that foam concentrate could be proportioned with water using the identical provide. The venturi principle is once more introduced into play because it creates a strain drop on the point of injection for the froth concentrate. Testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime prices because of foam concentrate usage, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a end result of great care is needed to avoid a damaged bladder when commissioning a new set up. It is never simple to work within the metal strain vessel should problems occur, especially if and when a replacement bladder could also be required: all of it adds to the difficulty and cost.
Compressed air foam (CAFS):
This isn’t a proportioning technique within the typical sense as the foam is already proportioned utilizing one of many earlier methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth solution on the level of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces allowing higher penetration and cooling. This is also a profit in wildfire situations by coating weak buildings to mitigate hearth progress. The limited water supplies related to remote wildfire areas means that the resource could be fully optimised. However, as with balanced strain proportioner foam pumps, a further level of failure is feasible due to the additional CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is purely mechanical and extremely reliable. A water-driven rotor supplies the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning fee and will proportion the froth focus accurately across a wide working vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning price testing, completely with out using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The advantages of FireDos Gen III FM approved foam proportioners embody:
Reduced costs: proportioning rate is tested with out using foam or creating premix or foam – cost effective and eco-friendly.
Improved efficiency: constant proportioning fee throughout a large working vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in strain loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a special proportioning rate.
FM accredited FireDos Gen III proportioners are thus far the only FM accredited water motor coupled variable proportioners using FM accredited circulate meters. Using the test return line this offers the chance to verify the proportioning price during commissioning as well as for annual exams, without creating any premix, which is a very big benefit for the consumer and relieves the surroundings.
In the second a half of this feature we will discover the consequences of viscosity on foam proportioning and typical foam utility areas and beneficial discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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