Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fireplace situation. Our goal in this two-part article is to provide steering primarily based on a hazard-specific method and help you make an informed choice on applicable 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 typically associated with cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting screens, we specialise mainly within the Class B class: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only may not penetrate the fire load successfully.
Fire courses.
How can we make foam?
Finished foam solution contains a simple recipe of froth focus, water and air. Foam focus is often mixed in the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge system – we’ll cover proportioning later in this article and discharge strategies in Part 2. At this level air is entrained by using units designed to naturally aspirate the solution. The amount of aspiration and the sort of concentrate determines the expansion ratio. This is often cut up between low, medium and excessive growth. Low growth is up to 20:1, medium is 200:1 and excessive enlargement is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to increase the froth adequately, though naturally aspirated turbines are also used. The decision to choose on a specific growth ratio is determined by the hazard under evaluate.
Put simply, water and oil do not combine. Applying solely water to Class B products won’t suppress the burning vapours. This is a crucial 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 methodology is chosen to provide that blanket or film, the target is the same.
Steps of froth technology Images equipped by Author / Contributor
A little of the historical past of froth growth
We can date the development of modern foam concentrates from the Sixties onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary downside was due to restricted gas tolerance, which meant it was susceptible to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, synthetic detergents gave foam a higher gasoline tolerance in addition to forming a vapour-sealing film throughout the surface of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s development did not completely exchange the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight gas pick-up (mixing) and supply a great resistance to warmth, outlined by the trade as ‘burn-back resistance’.
Further development within the 1980s took FP to the following stage with film-forming fluoroprotein or FFFP. We now had the best of both 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 at all times offered a further problem as they had been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The same expertise additionally grew to become obtainable with the new generation of AFFF-ARs.
In recent years fluorine, one of the cornerstone components to all foams, has become an environmental problem, due to persistence in groundwater. The industry has been presented with a major problem to get rid of the ‘fluoro’ factor of all the totally different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of an entire vary of newly formulated fluorine-free foam. pressure gauge 10 bar ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn into the brand new normal and first alternative for operators changing present stock or reviewing new projects. As a foam proportioner manufacturer we must examine the bodily properties of froth fastidiously (especially viscosity) as they influence choices on the overall proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are more and more necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant quality of SFFF/F3 is important to combat the small diploma of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being extremely effective. The best method of comparing their claims is to familiarise yourself with the empirically primarily based standard EN 1568 or UL162. The tests 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 additionally covers fresh and seawater in addition to mild and forceful application of the foam. Each foam is given a rating with IA being one of the best, IIID the worst. This means that you can problem foam suppliers in order to make an knowledgeable choice on one of the best foam in your needs.
Whilst EN 1568 is a wonderful benchmark normal, awareness of the results on foam performance from factors exterior the usual tests must be noted. For instance, significantly aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by different ambient air temperatures, the application technique, fuel depth and so on. Our advice could be to know the details of the tests and attempt to match them to the foam’s appropriateness for your particular person hazards. We would all the time suggest consulting particular person foam producers as they’ll usually provide particular in-house fire-performance information towards a few of the extra unusual fuels.
However, despite the froth manufacturers’ sometimes conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the growth ratio Images equipped by Author / Contributor
Critical components for success: the time and application fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the rate at which completed foam is applied. Both are decided by empirically based 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’ factor implies that for a given dimension of fire area it’s needed to use the froth for lengthy sufficient to attain extinction and to forestall re-ignition. This is especially important in handbook intervention as firefighter’s will be in danger during post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the application time may be as long as 60 minutes for the biggest tank diameters.
The application fee refers again to the quantity of finished foam utilized per square metre. This varies according to the gasoline and the froth sort but is currently a minimum of 4.zero litres per minute per sq. metre. One of the continuing developments in foam efficiency is the probability that this will be reduced, however requirements often take time to recognise product improvement. Anything lower than the minimum utility price implies that fireplace management is unlikely to be achieved. This signifies that firefighting assets, notably in a manual fireplace assault, have to be assembled earlier than firefighting commences and this takes time. The advantage in fitting fastened systems is that the assets are already designed and built into the system for quick application.
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 tackle their specific hearth challenges, the next is an outline of the assorted foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted mounted techniques applications. This uses the venturi principle to create a strain drop in a small aluminium or seawater material appropriate gadget with built-in focus pick-up tube. The stress drop created by the venturi draws the foam 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 into a pipework system.
However, whilst it’s considered to be the only method, it has severe drawbacks: (i) items are manufacturing unit calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are important as deviations caused by pipe diameter adjustments will adversely affect proportioning accuracy and potentially prevent any proportioning; (iii) modifications in focus viscosity will undermine the power of the venturi to draw focus into the downstream strains; (iv) pressure loss is excessive, as a lot as 35%, so obligation pump pressures must be excessive sufficient to permit for it, potentially including further price into the system; (v) foam supply gadgets have to be sized so as to not limit design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to whole lifetime prices because of foam concentrate utilization, 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 electric or a mixture of electrical and diesel pumps to produce foam concentrate into a proportioner at a higher stress than the incoming water-line strain. The proportioner is put in into the water line and regulates the mixing.
They are actually associated with older techniques, the place disadvantages embrace: (i) additional costs in hardware and design time; (ii) the foam pump is generally restricted to a a lot tighter operating vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump wants a further power source, other than water, so isn’t as reliably safe as a system with a potential single point of failure, similar to a wholly water-driven system; (iv) sometimes, these techniques are very complex and cause 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 froth concentrate and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner similar to those fitted to balanced stress proportioners. The incoming pressurised water compresses the froth crammed bladder in order that foam concentrate may be proportioned with water utilizing the same supply. The venturi principle is once more introduced into play as it creates a strain drop on the level of injection for the foam concentrate. Testing can’t be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs as a end result of foam focus usage, which needs to be changed, 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 rarely easy to work throughout the steel pressure vessel ought to problems occur, particularly if and when a replacement bladder may be required: it all provides to the problem and price.
Compressed air foam (CAFS):
This isn’t a proportioning methodology within the conventional sense as the froth is already proportioned using one of the previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth solution on the level of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces permitting better penetration and cooling. This can be a benefit in wildfire conditions by coating weak constructions to mitigate fireplace growth. The restricted water supplies related to remote wildfire areas implies that the resource could be absolutely optimised. However, as with balanced strain proportioner foam pumps, a further level of failure is feasible because of 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 generation, the product is purely mechanical and highly reliable. A water-driven rotor provides the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam focus via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and will proportion the foam concentrate accurately across a wide operating vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, utterly without utilizing 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 accredited foam proportioners embody:
Reduced prices: proportioning rate is examined with out using foam or creating premix or foam – value effective and eco-friendly.
Improved efficiency: constant proportioning price across a large working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress 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 permitted FireDos Gen III proportioners are so far the only FM approved water motor coupled variable proportioners utilizing FM permitted circulate meters. Using the take a look at return line this presents the likelihood to verify the proportioning rate during commissioning as nicely as for annual exams, with out creating any premix, which is a very massive benefit for the person and relieves the surroundings.
In the second part of this characteristic we’ll discover the consequences of viscosity on foam proportioning and typical foam application areas and recommended discharge gadgets.
For extra information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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