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Fire presents many challenges, not least due to the variables that determine which suppression medium is acceptable for a given fireplace situation. Our goal in this two-part article is to offer steering based on a hazard-specific strategy and assist you to make an knowledgeable choice on appropriate fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires generally related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise primarily within the Class B class: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are specifically for deep-seated Class A fires where water solely may not penetrate the fireplace load effectively.
Fire courses.
How will we make foam?
Finished foam resolution contains a simple recipe of foam focus, water and air. Foam focus is typically mixed within 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 system – we will cover proportioning later in this article and discharge methods in Part 2. At this level air is entrained by using devices designed to naturally aspirate the solution. The amount of aspiration and the type of concentrate determines the expansion ratio. This is often split between low, medium and high expansion. Low growth is as much as 20:1, medium is 200:1 and high enlargement is greater than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to increase the foam adequately, though naturally aspirated turbines are also used. The decision to choose on a selected expansion ratio is determined by the hazard beneath review.
Put simply, water and oil do not mix. Applying solely water to Class B products won’t 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 movie to obtain success. Whatever methodology is chosen to produce that blanket or film, the objective is similar.
Steps of froth generation Images supplied by Author / Contributor
A little of the history of foam growth
We can date the event of contemporary foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary disadvantage was due to restricted gasoline 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 greater fuel tolerance as properly as forming a vapour-sealing film across the floor of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s development did not completely substitute the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat fuel pick-up (mixing) and supply an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further growth in the 1980s took FP to the subsequent degree 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 list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced a further challenge as they had been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar technology additionally became obtainable with the new generation of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has turn into an environmental issue, as a outcome of persistence in groundwater. The trade has been offered with a major problem to eliminate the ‘fluoro’ factor of all of the completely different foam focus varieties. We have witnessed an era of manufacturers’ claims and counter claims concerning the efficacy of an entire 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 brand new normal and first selection for operators altering current stock or reviewing new projects. As a foam proportioner manufacturer we must look at the bodily properties of froth rigorously (especially viscosity) as they affect choices on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant sorts are increasingly necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, implies that the alcohol-resistant quality of SFFF/F3 is important to combat the small degree of water miscibility of the gasoline.
All foam concentrate manufacturers will naturally promote their product as being highly effective. The best means of comparing their claims is to familiarise yourself with the empirically primarily based normal EN 1568 or UL162. The checks cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the more demanding polar solvents are each included in the check protocols. This additionally covers contemporary and seawater in addition to gentle and forceful application of the foam. Each foam is given a score with IA being the best, IIID the worst. This means you could problem foam suppliers in order to make an informed choice on one of the best foam in your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the results on foam efficiency from components outside the standard checks ought to be famous. For example, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the application method, gasoline depth etc. Our advice can be to know the primary points of the exams and try to match them to the foam’s appropriateness on your particular person hazards. We would all the time suggest consulting particular person foam manufacturers as they will often provide particular in-house fire-performance knowledge against some of the extra uncommon fuels.
However, regardless of the foam manufacturers’ generally conflicting claims on performance, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams based on the growth ratio Images supplied by Author / Contributor
Critical factors for fulfillment: the time and utility price matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary factors: time and the speed at which completed foam is utilized. Both are determined by empirically based requirements revealed by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue signifies that for a given dimension of fireplace space it is essential to use the froth for lengthy sufficient to achieve extinction and to prevent re-ignition. This is particularly crucial in handbook intervention as firefighter’s shall be at risk throughout post-fire operations. When it comes to mounted protection for hydrocarbon and polar solvent tanks, the appliance time can be as lengthy as 60 minutes for the biggest tank diameters.
The application rate refers again to the quantity of finished foam utilized per square metre. This varies according to the gas and the foam type however is currently no less than four.0 litres per minute per square metre. One of the continued developments in foam efficiency is the probability that this shall be lowered, however requirements typically take time to recognise product development. Anything less than the minimum application price implies that hearth control is unlikely to be achieved. This implies that firefighting resources, notably in a manual fire attack, need to be assembled before firefighting commences and this takes time. The advantage in becoming fastened techniques is that the sources are already designed and built into the system for immediate utility.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an knowledgeable decision on how finest to sort out their particular hearth challenges, the following is an outline of the assorted foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted fastened techniques purposes. This uses the venturi precept to create a pressure drop in a small aluminium or seawater materials suitable gadget with built-in concentrate pick-up tube. The stress drop created by the venturi attracts the froth focus from a container where it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a hearth equipment or fitted into a pipework system.
However, whilst ตัววัดแรงดันน้ำ thought-about to be the best methodology, it has severe drawbacks: (i) units are factory calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge gadget or a changing quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations brought on by pipe diameter adjustments will adversely affect proportioning accuracy and doubtlessly forestall any proportioning; (iii) changes in focus viscosity will undermine the ability of the venturi to attract concentrate into the downstream lines; (iv) pressure loss is high, as much as 35%, so obligation pump pressures have to be excessive enough to permit for it, potentially including additional price into the system; (v) foam supply devices have to be sized so as to not prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices on account of foam focus usage, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electric or a mixture of electrical and diesel pumps to provide foam concentrate right into a proportioner at the next pressure than the incoming water-line pressure. The proportioner is installed into the water line and regulates the blending.
They at the second are related to older systems, where disadvantages include: (i) additional costs in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter working vary, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants a further energy source, aside from water, so just 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 excessive efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to damage the froth concentrate and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner much like the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the foam crammed bladder in order that foam concentrate could be proportioned with water using the same supply. The venturi principle is again brought into play as it creates a stress drop on the point of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to entire lifetime prices as a outcome of foam concentrate utilization, which must be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a result of great care is required to keep away from a broken bladder when commissioning a new set up. It is rarely easy to work within the steel pressure vessel ought to problems occur, particularly if and when a alternative bladder could also be required: it all adds to the difficulty and price.
Compressed air foam (CAFS):
This just isn’t 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 quite than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam solution at the level of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces permitting better penetration and cooling. This can additionally be a profit in wildfire conditions by coating susceptible constructions to mitigate hearth development. The restricted water supplies related to remote wildfire areas signifies that the useful resource could be totally optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is possible as a end result of extra CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into 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 immediately coupled positive-displacement plunger or piston pump. This is provided with foam concentrate through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and will proportion the froth concentrate accurately throughout a wide working vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate testing, fully without using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners embrace:
Reduced costs: proportioning fee is tested without using foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: constant proportioning price throughout a large working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in strain loss, in comparison with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a different proportioning price.
FM approved FireDos Gen III proportioners are thus far the one FM approved water motor coupled variable proportioners utilizing FM permitted flow meters. Using the test return line this presents the possibility to verify the proportioning price during commissioning as nicely as for annual tests, with out creating any premix, which is a really big benefit for the user and relieves the environment.
In the second part of this characteristic we are going to discover the effects of viscosity on foam proportioning and typical foam utility areas and really helpful discharge gadgets.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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