Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fireplace scenario. Our objective in this two-part article is to offer steerage based mostly on a hazard-specific strategy and allow you to make an informed 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 supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires generally related to cooking similar to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting screens, we specialise primarily 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, certain kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only could not penetrate the hearth load effectively.
Fire courses.
How can we make foam?
Finished foam resolution includes a simple recipe of foam concentrate, water and air. Foam concentrate is usually combined within the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge gadget – we will cover proportioning later on this article and discharge methods in Part 2. At this point air is entrained by using units designed to naturally aspirate the solution. The amount of aspiration and the type of concentrate determines the growth ratio. This is often break up between low, medium and excessive expansion. Low growth is up to 20:1, medium is 200:1 and excessive expansion is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to broaden the foam adequately, although naturally aspirated generators are additionally used. The decision to choose a specific enlargement ratio is set by the hazard underneath review.
Put simply, water and oil do not mix. Applying only water to Class B products will not suppress the burning vapours. This is a crucial level to make as it’s the vapours, not the liquid itself, that burns. We want a medium that permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to be successful. Whatever technique is chosen to provide that blanket or film, the objective is similar.
Steps of foam generation Images equipped by Author / Contributor
A little of the historical past of foam development
We can date the event of modern foam concentrates from the Sixties onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The main downside was due to restricted gas tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, artificial detergents gave foam a larger fuel tolerance in addition to 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 exchange the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam could each fight gas pick-up (mixing) and offer a great resistance to heat, outlined by the trade as ‘burn-back resistance’.
Further development within the 1980s took FP to the next stage with film-forming fluoroprotein or FFFP. We now had the best of each 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 extra problem 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 similar expertise also grew to become out there with the new generation of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has become an environmental problem, due to persistence in groundwater. The trade has been presented with a major challenge to remove the ‘fluoro’ element of all of the different foam concentrate sorts. We have witnessed an era of manufacturers’ claims and counter claims relating to 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 turn into the new regular and first alternative for operators altering present stock or reviewing new initiatives. As a foam proportioner manufacturer we should study the bodily properties of foam fastidiously (especially viscosity) as they influence decisions on the overall proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are increasingly important in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, implies that the alcohol-resistant high quality of SFFF/F3 is necessary to combat the small diploma of water miscibility of the fuel.
All foam focus producers will naturally promote their product as being highly effective. The finest means of evaluating their claims is to familiarise your self with the empirically based mostly commonplace EN 1568 or UL162. The tests cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included in the check protocols. This additionally covers contemporary and seawater as properly as mild and forceful application of the foam. Each foam is given a ranking with IA being one of the best, IIID the worst. This means you could challenge foam suppliers so as to make an knowledgeable decision on one of the best foam on your needs.
Whilst EN 1568 is a superb benchmark standard, awareness of the results on foam efficiency from elements outside the standard checks ought to be noted. For instance, significantly aggressive solvents can problem the firefighting effectiveness of certain foams. This can be exacerbated by different ambient air temperatures, the applying methodology, gasoline depth etc. Our advice could be to grasp the small print of the checks and try to match them to the foam’s appropriateness in your particular person hazards. We would at all times recommend consulting particular person foam producers as they can usually present specific in-house fire-performance knowledge in opposition to some of the more uncommon fuels.
However, regardless of the foam manufacturers’ typically conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the growth ratio Images supplied by Author / Contributor
Critical elements for achievement: the time and application fee 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 determined by empirically primarily based standards revealed by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ factor signifies that for a given dimension of fireplace area it’s essential to use the foam for long enough to attain extinction and to forestall re-ignition. เกจวัดถังแก๊ส is especially crucial in guide intervention as firefighter’s will be at risk throughout post-fire operations. When it comes to fastened safety for hydrocarbon and polar solvent tanks, the application time could be as lengthy as 60 minutes for the biggest tank diameters.
The software rate refers again to the amount of completed foam utilized per square metre. This varies in accordance with the gas and the froth type however is presently no less than four.zero litres per minute per sq. metre. One of the continuing developments in foam performance is the likelihood that this shall be reduced, but standards typically take time to recognise product improvement. Anything lower than the minimal application price signifies that hearth control is unlikely to be achieved. This signifies that firefighting assets, notably in a handbook fire attack, have to be assembled earlier than firefighting commences and this takes time. The advantage in fitting fixed methods is that the resources are already designed and constructed into the system for quick utility.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to permit readers to make an informed choice on how finest to sort out their explicit hearth challenges, the following is an overview of the assorted foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and limited mounted techniques applications. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater materials suitable device with built-in concentrate pick-up tube. The strain drop created by the venturi draws the froth focus from a container the place 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 right into a pipework system.
However, whilst it’s thought of to be the best method, it has extreme drawbacks: (i) items are manufacturing facility calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge system or a altering quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are crucial as deviations brought on by pipe diameter adjustments will adversely affect proportioning accuracy and doubtlessly stop any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to draw concentrate into the downstream traces; (iv) stress loss is high, as much as 35%, so obligation pump pressures need to be excessive sufficient to allow for it, probably adding extra price into the system; (v) foam delivery gadgets must be sized so as not to prohibit design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs because of foam focus usage, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mix of electric and diesel pumps to produce foam focus into a proportioner at a higher strain than the incoming water-line stress. The proportioner is installed into the water line and regulates the blending.
They are now related to older methods, where disadvantages embody: (i) extra costs in hardware and design time; (ii) the froth pump is often restricted to a a lot tighter working vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants a further energy supply, aside from water, so is not as reliably secure as a system with a potential single level of failure, such as an entirely water-driven system; (iv) usually, these techniques are very complex and trigger excessive efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to damage the foam focus and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced stress proportioners. The incoming pressurised water compresses the froth filled bladder in order that foam concentrate can be proportioned with water using the same supply. The venturi precept is once more brought into play because it creates a pressure drop at the point of injection for the foam concentrate. Testing cannot be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs on account of foam concentrate usage, which must be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a outcome of nice care is needed to keep away from a damaged bladder when commissioning a model new set up. It is never straightforward to work throughout the steel strain vessel should issues occur, particularly if and when a substitute bladder could additionally be required: all of it adds to the issue and cost.
Compressed air foam (CAFS):
This just isn’t a proportioning method within the standard sense as the foam is already proportioned utilizing one of many previous 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 resolution at the point of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces permitting higher penetration and cooling. This can be a benefit in wildfire situations by coating weak structures to mitigate fire growth. The limited water provides associated with remote wildfire areas implies that the resource can be absolutely optimised. However, as with balanced strain proportioner foam pumps, a further level of failure is possible as a outcome of further CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is only mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam focus through an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning rate and will proportion the froth concentrate precisely across a wide working vary. The purely mechanical system supplies 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 benefits of FireDos Gen III FM accredited foam proportioners embrace:
Reduced costs: proportioning rate is tested without using foam or creating premix or foam – cost effective and eco-friendly.
Improved performance: constant proportioning fee throughout a wide working range.
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 special proportioning price.
FM permitted 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 presents the chance to verify the proportioning fee throughout commissioning as properly as for annual checks, with out creating any premix, which is a really massive benefit for the person and relieves the setting.
In the second part of this feature we are going to discover the consequences of viscosity on foam proportioning and typical foam utility areas and really helpful discharge devices.
For extra information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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