Fire presents many challenges, not least due to the variables that decide which suppression medium is appropriate for a given fireplace state of affairs. Our goal in this two-part article is to offer steering based on a hazard-specific approach and assist you to make an knowledgeable choice on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires usually related to cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily within the Class B category: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely might not penetrate the fireplace load successfully.
Fire courses.
How will we make foam?
Finished foam answer contains a simple recipe of foam focus, water and air. Foam concentrate is often combined in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge device – we will cowl proportioning later on this article and discharge methods in Part 2. At this level air is entrained by utilizing devices designed to naturally aspirate the solution. The amount of aspiration and the sort of concentrate determines the enlargement ratio. This is usually cut up between low, medium and excessive expansion. Low expansion is up to 20:1, medium is 200:1 and excessive growth is greater than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to increase the foam adequately, although naturally aspirated turbines are also used. The determination to choose a specific expansion ratio is set by the hazard under review.
Put simply, water and oil don’t mix. Applying solely water to Class B products will not suppress the burning vapours. This is a vital level to make as it’s the vapours, not the liquid itself, that burns. We need a medium that permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to be successful. Whatever methodology is chosen to provide that blanket or movie, the target is similar.
Steps of froth technology Images supplied by Author / Contributor
A little of the history of foam growth
We can date the development of recent foam concentrates from the 1960s onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the base component). The primary disadvantage was due to limited fuel tolerance, which meant it was susceptible to gas 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 larger gasoline tolerance as well as forming a vapour-sealing film throughout the surface of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s development didn’t utterly replace the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each combat gas pick-up (mixing) and provide a great resistance to warmth, outlined by the industry as ‘burn-back resistance’.
Further improvement in the 1980s took FP to the next stage with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that additionally 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 presented a further challenge as they have been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar expertise also turned available with the model new generation of AFFF-ARs.
In recent years fluorine, one of many cornerstone ingredients to all foams, has become an environmental problem, because of persistence in groundwater. The trade has been offered with a major problem to eliminate the ‘fluoro’ element of all the different foam concentrate sorts. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of an entire vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn out to be the model new regular and first selection for operators changing present stock or reviewing new tasks. As a foam proportioner manufacturer we should examine the bodily properties of foam rigorously (especially viscosity) as they affect selections on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more necessary in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant quality of SFFF/F3 is important to combat the small diploma of water miscibility of the fuel.
All foam concentrate producers will naturally promote their product as being highly effective. The finest means of evaluating their claims is to familiarise yourself with the empirically based normal EN 1568 or UL162. The checks cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included within the test protocols. This additionally covers recent and seawater as nicely as light and forceful software of the foam. Each foam is given a score with IA being the best, IIID the worst. This means that you could problem foam suppliers to be able to make an informed determination on the most effective foam on your wants.
Whilst EN 1568 is an excellent benchmark standard, consciousness of the consequences on foam performance from factors outdoors the usual checks must be noted. For instance, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by completely different ambient air temperatures, the application methodology, gas depth and so on. Our recommendation can be to understand the details of the checks and try to match them to the foam’s appropriateness in your individual hazards. We would always recommend consulting particular person foam manufacturers as they can typically provide specific in-house fire-performance knowledge against a few of the extra unusual fuels.
However, despite the froth manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the enlargement ratio Images provided by Author / Contributor
Critical factors for success: the time and software price matrix
Successful extinction of flammable liquid fires depends on two converging and complementary elements: time and the speed at which finished foam is utilized. เกจวัดแรงดันsumo are determined by empirically based mostly standards revealed by our bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given measurement of fireplace space it is necessary to apply the foam for lengthy sufficient to achieve extinction and to stop re-ignition. This is especially important in guide intervention as firefighter’s might be in danger throughout post-fire operations. When it comes to mounted safety for hydrocarbon and polar solvent tanks, the appliance time may be so lengthy as 60 minutes for the largest tank diameters.
The utility rate refers again to the quantity of completed foam utilized per sq. metre. This varies based on the gasoline and the froth kind however is at present no less than four.zero litres per minute per sq. metre. One of the continuing developments in foam performance is the probability that this might be reduced, however standards typically take time to recognise product development. Anything less than the minimal application price means that fire control is unlikely to be achieved. This means that firefighting resources, particularly in a manual fireplace attack, need to be assembled before firefighting commences and this takes time. The advantage in fitting mounted systems is that the sources are already designed and constructed into the system for instant software.
Principle of foam extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to permit readers to make an informed determination on how finest to tackle their explicit fire challenges, the next is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with fire service deployment and limited fixed techniques applications. This uses the venturi precept to create a strain drop in a small aluminium or seawater materials compatible gadget with built-in focus pick-up tube. The stress drop created by the venturi attracts the froth focus from a container the place it mixes with water to create foam resolution. Both the pick-up tube and physique of the inductor are compact sufficient to be easily carried on a fireplace equipment or fitted into a pipework system.
However, while it’s thought of to be the only method, it has severe drawbacks: (i) units are manufacturing facility calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a changing amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter changes will adversely affect proportioning accuracy and probably forestall any proportioning; (iii) adjustments in concentrate viscosity will undermine the ability of the venturi to attract concentrate into the downstream lines; (iv) stress loss is high, as a lot as 35%, so obligation pump pressures must be high sufficient to permit for it, doubtlessly including extra price into the system; (v) foam delivery gadgets must be sized so as not to restrict design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime costs as a outcome of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
Types of froth agentsImages supplied by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a combination of electrical and diesel pumps to supply foam concentrate into a proportioner at a higher strain than the incoming water-line pressure. The proportioner is put in into the water line and regulates the mixing.
They are actually associated with older systems, the place disadvantages embody: (i) further prices in hardware and design time; (ii) the foam pump is generally restricted to a much tighter operating vary, though the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump needs an extra power supply, aside from water, so isn’t as reliably secure as a system with a possible single level of failure, similar to a completely water-driven system; (iv) sometimes, these techniques are very complex and trigger high efforts at the buyer 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 flip can undermine correct 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 just like the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam focus can be proportioned with water utilizing the identical supply. The venturi principle is once more brought into play because it creates a strain 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 complete lifetime costs because of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of nice care is needed to avoid a broken bladder when commissioning a model new set up. It is rarely easy to work inside the metal pressure vessel ought to issues occur, especially if and when a replacement bladder could also be required: it all provides to the difficulty and value.
Compressed air foam (CAFS):
This is not a proportioning method within the typical sense as the froth is already proportioned utilizing one of the previous strategies. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth resolution at the point of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces permitting better penetration and cooling. This can be a benefit in wildfire conditions by coating susceptible buildings to mitigate fire development. The limited water supplies associated with remote wildfire areas implies that the resource could be totally optimised. However, as with balanced stress proportioner foam pumps, a further point of failure is feasible due to the further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is purely mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning price and can proportion the foam concentrate accurately throughout a large operating range. The purely mechanical system offers cost-efficient and eco-friendly proportioning price testing, fully without utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners embrace:
Reduced prices: proportioning fee is examined without using foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: constant proportioning fee throughout a large working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a unique proportioning rate.
FM accredited FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners utilizing FM permitted flow meters. Using the take a look at return line this provides the possibility to check the proportioning fee throughout commissioning as nicely as for annual checks, without creating any premix, which is a very huge benefit for the consumer and relieves the surroundings.
In the second part of this function we’ll explore the consequences of viscosity on foam proportioning and typical foam application areas and really helpful discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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