ไดอะแฟรม LOGO.png

Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given hearth state of affairs. Our goal on this two-part article is to offer steering based mostly on a hazard-specific strategy and help you make an knowledgeable decision 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 materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires typically related to cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise mainly within the Class B category: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain kinds of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely could not penetrate the fire load effectively.
Fire courses.
How do we make foam?
Finished foam solution includes a easy recipe of foam focus, water and air. Foam concentrate is often mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge system – we are going to cowl proportioning later on this article and discharge methods in Part 2. At this point air is entrained through the use of devices designed to naturally aspirate the answer. The quantity of aspiration and the sort of focus determines the growth ratio. This is usually break up between low, medium and high enlargement. Low enlargement is as a lot as 20:1, medium is 200:1 and high expansion is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the froth adequately, though naturally aspirated turbines are also used. The choice to choose a particular growth ratio is determined by the hazard underneath evaluate.
Put simply, water and oil do not combine. Applying solely water to Class B products is not going to suppress the burning vapours. This is a crucial level to make as it is the vapours, not the liquid itself, that burns. We need a medium that enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to achieve success. Whatever technique is chosen to produce that blanket or film, the objective is the same.
Steps of froth generation Images provided by Author / Contributor
A little of the historical past of foam growth
We can date the development of contemporary foam concentrates from the Sixties onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The major drawback was as a end result of limited gasoline tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, artificial detergents gave foam a greater gasoline tolerance as properly as forming a vapour-sealing film across the surface of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement did not utterly substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both fight gas pick-up (mixing) and supply an excellent resistance to warmth, outlined by the trade as ‘burn-back resistance’.
Further improvement in the 1980s took FP to the next 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 Eighties additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always presented an additional problem as they were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar expertise additionally grew to become obtainable with the brand new generation of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has become an environmental concern, because of persistence in groundwater. The trade has been offered with a serious problem to eliminate the ‘fluoro’ factor of all of the totally different foam concentrate types. We have witnessed an period of manufacturers’ claims and counter claims relating to 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 become the new normal and first choice for operators changing current stock or reviewing new initiatives. As a foam proportioner manufacturer we must examine the physical properties of foam rigorously (especially viscosity) as they affect selections on the overall proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant sorts are more and more necessary within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant high quality of SFFF/F3 is important to fight the small degree of water miscibility of the gas.
All foam focus producers will naturally promote their product as being extremely efficient. The best means of comparing their claims is to familiarise yourself with the empirically primarily 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 more demanding polar solvents are both included in the test protocols. This also covers fresh and seawater as well as light and forceful utility of the foam. Each foam is given a rating with IA being the best, IIID the worst. This means that you could challenge foam suppliers so as to make an knowledgeable decision on one of the best foam in your wants.
Whilst EN 1568 is a superb benchmark standard, consciousness of the results on foam performance from elements outside the usual exams must be noted. For example, significantly aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the applying methodology, fuel depth and so forth. Our recommendation would be to know the primary points 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 producers as they will usually provide particular in-house fire-performance data in opposition to a few of the more unusual fuels.
However, despite the froth manufacturers’ typically conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the expansion ratio Images supplied by Author / Contributor
Critical elements for fulfillment: the time and software rate matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the speed at which finished foam is utilized. Both are decided by empirically based mostly standards printed by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ issue implies that for a given dimension of fireside space it’s essential to use the froth for lengthy enough to realize extinction and to forestall re-ignition. This is very crucial in guide intervention as firefighter’s might be in danger during post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the applying time can be so long as 60 minutes for the largest tank diameters.
The utility rate refers to the amount of finished foam utilized per sq. metre. This varies in accordance with the gasoline and the foam kind but is currently no less than 4.0 litres per minute per square metre. One of the ongoing developments in foam efficiency is the chance that this might be lowered, however requirements usually take time to recognise product improvement. Anything lower than the minimum application fee implies that fire management is unlikely to be achieved. This signifies that firefighting assets, particularly in a manual hearth assault, must be assembled before firefighting commences and this takes time. The benefit in fitting fastened methods is that the resources are already designed and constructed into the system for immediate utility.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to allow readers to make an knowledgeable determination on how greatest to sort out their explicit fireplace challenges, the following is an outline of the various foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and limited mounted methods purposes. This uses the venturi precept to create a pressure drop in a small aluminium or seawater material suitable gadget with built-in focus pick-up tube. The stress drop created by the venturi attracts the froth concentrate from a container where it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fire equipment or fitted right into a pipework system.
However, while it’s considered to be the simplest method, it has severe drawbacks: (i) items are factory calibrated so any changes to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter adjustments will adversely affect proportioning accuracy and probably forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to draw concentrate into the downstream lines; (iv) stress loss is excessive, as much as 35%, so responsibility pump pressures have to be high enough to allow for it, doubtlessly including extra price into the system; (v) foam delivery devices have to be sized in order not to limit design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to complete lifetime prices on account of foam concentrate usage, which must be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a mixture of electric and diesel pumps to supply foam focus into a proportioner at the next pressure than the incoming water-line strain. The proportioner is put in into the water line and regulates the mixing.
They at the second are associated with older techniques, where disadvantages include: (i) further prices in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter operating range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an additional energy supply, apart from water, so isn’t as reliably safe as a system with a possible single point of failure, such as an entirely water-driven system; (iv) typically, these systems are very complicated and cause excessive efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to damage the foam focus and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel stress vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner similar to the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam focus could be proportioned with water using the same provide. The venturi precept is once more brought into play because it creates a stress drop at the level of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs on account of foam concentrate utilization, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a result of nice care is required to keep away from a damaged bladder when commissioning a new installation. It isn’t straightforward to work within the metal strain vessel should problems occur, particularly if and when a substitute bladder may be required: it all provides to the problem and price.
Compressed air foam (CAFS):
This is not a proportioning technique within the typical sense as the froth is already proportioned utilizing one of the 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 foam answer on the point of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces allowing better penetration and cooling. This is also a profit in wildfire conditions by coating vulnerable constructions to mitigate fireplace growth. The limited water supplies associated with distant wildfire areas implies that the useful resource can be fully optimised. However, as with balanced strain proportioner foam pumps, a further point of failure is possible as a outcome of extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is solely mechanical and extremely dependable. A water-driven rotor supplies the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is supplied with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and will proportion the foam focus precisely throughout a wide operating vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, utterly with out utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The advantages of FireDos Gen III FM accredited foam proportioners embrace:
Reduced costs: proportioning rate is tested with out using foam or creating premix or foam – cost efficient and eco-friendly.
Improved performance: constant proportioning fee across a large operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in pressure loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a different proportioning price.
FM permitted FireDos Gen III proportioners are to date the only FM permitted water motor coupled variable proportioners utilizing FM approved circulate meters. Using เกจวัดแรงดันน้ำ10บาร์ take a look at return line this provides the possibility to check the proportioning price during commissioning as well as for annual tests, with out creating any premix, which is a very huge benefit for the user and relieves the setting.
In the second a half of this function we are going to discover the consequences of viscosity on foam proportioning and typical foam software areas and beneficial discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share