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Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given hearth scenario. Our goal in this two-part article is to supply guidance primarily based on a hazard-specific method and allow you to make an informed choice 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 combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires usually related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting monitors, we specialise primarily within the Class B category: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely could not penetrate the hearth load successfully.
Fire courses.
How will we make foam?
Finished Copy contains a easy recipe of foam concentrate, water and air. Foam concentrate is often combined within the ratio of 1% or 3% to either 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 methods in Part 2. At this point air is entrained by utilizing units designed to naturally aspirate the answer. The amount of aspiration and the kind of focus determines the enlargement ratio. This is often split between low, medium and excessive growth. Low expansion is up to 20:1, medium is 200:1 and high enlargement is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated mills are additionally used. The determination to choose a selected expansion ratio is decided by the hazard underneath evaluate.
Put simply, water and oil don’t combine. Applying only water to Class B products is not going to suppress the burning vapours. This is an important 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 obtain success. Whatever method is chosen to produce that blanket or movie, the objective is the same.
Steps of froth technology Images equipped by Author / Contributor
A little of the historical past of froth improvement
We can date the development of recent foam concentrates from the Sixties onwards. Up to that time foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary downside was as a outcome of restricted gas tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, artificial detergents gave foam a greater gas tolerance in addition to forming a vapour-sealing movie across the surface of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s improvement didn’t utterly substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam could each fight gasoline pick-up (mixing) and provide an excellent resistance to warmth, outlined by the industry as ‘burn-back resistance’.
Further improvement in the Eighties took FP to the subsequent level with film-forming fluoroprotein or FFFP. We now had the most effective of each worlds: a film-forming foam that additionally had good burn-back resistance.
The Nineteen Eighties additional 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 problem as they were water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar technology also grew to become available with the new technology of AFFF-ARs.
In recent years fluorine, one of the cornerstone elements to all foams, has become an environmental issue, because of persistence in groundwater. The business has been introduced with a major challenge to get rid of the ‘fluoro’ element of all the completely different foam focus varieties. We have witnessed an period of manufacturers’ claims and counter claims regarding 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 become the model new regular and first selection for operators changing current inventory or reviewing new initiatives. As a foam proportioner manufacturer we should look at the bodily properties of froth rigorously (especially viscosity) as they influence selections on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more important in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant quality of SFFF/F3 is critical to fight the small degree of water miscibility of the gas.
All foam focus manufacturers will naturally promote their product as being highly efficient. The greatest method of evaluating their claims is to familiarise your self with the empirically primarily based normal EN 1568 or UL162. The tests cowl extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the more demanding polar solvents are both included within the test protocols. This additionally covers contemporary and seawater in addition to light and forceful application of the froth. Each foam is given a ranking with IA being the best, IIID the worst. This means you could challenge foam suppliers in order to make an informed decision on the most effective foam for your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the effects on foam performance from elements outdoors the usual checks should be famous. For example, particularly aggressive solvents can problem the firefighting effectiveness of sure foams. This may be exacerbated by totally different ambient air temperatures, the appliance technique, fuel depth etc. Our advice would be to grasp the details of the exams and attempt to match them to the foam’s appropriateness for your individual hazards. We would all the time advocate consulting particular person foam manufacturers as they can usually present particular in-house fire-performance data in opposition to a variety of the extra unusual fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on performance, the earlier fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the enlargement ratio Images provided by Author / Contributor
Critical elements for success: the time and application fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the speed at which finished foam is utilized. Both are decided by empirically based requirements published 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 signifies that for a given size of fire area it is essential to apply the foam for long enough to realize extinction and to stop re-ignition. This is especially important in manual intervention as firefighter’s shall be at risk throughout post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the appliance time could be as lengthy as 60 minutes for the biggest tank diameters.
The software price refers again to the quantity of completed foam applied per square metre. This varies in accordance with the fuel and the froth kind but is presently no much less than 4.zero litres per minute per square metre. One of the ongoing developments in foam performance is the probability that this will be lowered, however requirements often take time to recognise product development. Anything lower than the minimum utility rate means that fireplace management is unlikely to be achieved. This signifies that firefighting assets, significantly in a handbook fire attack, need to be assembled earlier than firefighting commences and this takes time. The benefit in fitting fixed methods is that the assets are already designed and built into the system for quick application.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to permit readers to make an informed choice on how best to sort out their specific fireplace challenges, the following is an outline of the varied foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and limited mounted methods applications. This makes use of the venturi principle to create a stress drop in a small aluminium or seawater materials compatible 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 solution. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fireplace appliance or fitted right into a pipework system.
However, whilst it’s thought of to be the best method, it has severe drawbacks: (i) models are manufacturing unit calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a altering amount of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter changes will adversely have an effect on proportioning accuracy and probably prevent any proportioning; (iii) changes in concentrate viscosity will undermine the flexibility of the venturi to draw focus into the downstream lines; (iv) pressure loss is excessive, as a lot as 35%, so obligation pump pressures need to be high sufficient to permit for it, potentially including extra value into the system; (v) foam supply devices need to be sized in order to not prohibit design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs as a result of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced pressure proportioners:
These use an electric or a combination of electric and diesel pumps to provide foam focus into a proportioner at a higher 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 related to older systems, where disadvantages embrace: (i) additional prices in hardware and design time; (ii) the foam pump is normally restricted to a much tighter working vary, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump needs a further energy supply, aside from water, so is not as reliably secure as a system with a possible single level of failure, similar to an entirely water-driven system; (iv) usually, these methods are very complicated and trigger excessive efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to wreck the foam concentrate 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 flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam concentrate can be proportioned with water using the same provide. The venturi principle is again introduced into play as it creates a stress drop at the point of injection for the froth concentrate. Testing cannot be achieved without creating premix and discharging finished foam. This will add to whole lifetime prices 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 because great care is needed to avoid a damaged bladder when commissioning a brand new installation. It is rarely easy to work inside the metal strain vessel should problems happen, especially if and when a substitute bladder may be required: it all provides to the problem and value.
Compressed air foam (CAFS):
This just isn’t a proportioning technique in the conventional sense as the foam is already proportioned using one of the previous methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam resolution on the point of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces allowing higher penetration and cooling. This can be a profit in wildfire conditions by coating weak structures to mitigate fire development. The limited water provides related to remote wildfire areas means that the useful resource could be totally optimised. However, as with balanced strain proportioner foam pumps, an additional level of failure is possible as a outcome of further CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is purely mechanical and highly reliable. A water-driven rotor provides the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and can proportion the froth focus precisely throughout a large working vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, completely with out using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM approved foam proportioners embody:
Reduced costs: proportioning rate is tested without utilizing foam or creating premix or foam – value effective and eco-friendly.
Improved performance: fixed proportioning price across a wide working range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in pressure loss, in comparability with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a special proportioning rate.
FM permitted FireDos Gen III proportioners are so far the only FM permitted water motor coupled variable proportioners using FM permitted circulate meters. Using the test return line this presents the likelihood to verify the proportioning rate during commissioning in addition to for annual exams, with out creating any premix, which is a very massive benefit for the consumer and relieves the setting.
In the second part of this characteristic we’ll discover the effects of viscosity on foam proportioning and typical foam application areas and really helpful discharge devices.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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