Fire presents many challenges, not least because of the variables that decide which suppression medium is suitable for a given fireplace situation. Our goal on this two-part article is to supply steering based on a hazard-specific strategy and assist you to make an informed decision on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are classified 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 generally related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily in the Class B category: flammable liquids.
Foam is considered to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely could not penetrate the fire load effectively.
Fire lessons.
How do we make foam?
Finished foam resolution comprises a easy recipe of foam concentrate, water and air. Foam focus is typically blended within the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge system – we will cowl proportioning later on this article and discharge strategies in Part 2. At this level air is entrained by using devices designed to naturally aspirate the answer. The quantity of aspiration and the kind of concentrate determines the enlargement ratio. This is often break up between low, medium and high expansion. 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 generators are also used. The determination to choose a particular growth ratio is decided by the hazard beneath review.
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 point to make as it’s the vapours, not the liquid itself, that burns. We want a medium that allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to obtain success. Whatever methodology is chosen to produce that blanket or movie, the objective is the same.
Steps of froth generation Images supplied by Author / Contributor
A little of the history of foam growth
We can date the event of modern foam concentrates from the Sixties onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the base component). The main downside was as a result of limited gasoline tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, artificial detergents gave foam a higher fuel tolerance as nicely as forming a vapour-sealing movie across the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s growth did not utterly exchange the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight fuel pick-up (mixing) and offer an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further improvement within the 1980s took FP to the following degree with film-forming fluoroprotein or FFFP. We now had the best of each worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s additional added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. เกจวัดแรงดันลมขนาดเล็ก or polar solvents had at all times introduced a further challenge as they were water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar know-how additionally became available with the model new era of AFFF-ARs.
In recent years fluorine, one of many cornerstone elements to all foams, has turn out to be an environmental concern, because of persistence in groundwater. The industry has been offered with a significant challenge to remove the ‘fluoro’ factor of all the totally different foam concentrate sorts. 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 time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the new normal and first selection for operators altering current inventory or reviewing new initiatives. As a foam proportioner manufacturer we should look at the bodily properties of foam carefully (especially viscosity) as they affect choices on the general proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are increasingly important within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant high quality of SFFF/F3 is important to fight the small diploma of water miscibility of the gasoline.
All foam concentrate producers will naturally promote their product as being extremely effective. The best means of comparing their claims is to familiarise yourself with the empirically based commonplace EN 1568 or UL162. The exams cover 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 within the test protocols. This also covers recent and seawater in addition to light and forceful utility of the froth. 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 decision on the best foam for your needs.
Whilst EN 1568 is a wonderful benchmark normal, awareness of the consequences on foam efficiency from components outdoors the standard checks must be famous. For example, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This can be exacerbated by completely different ambient air temperatures, the appliance technique, gas depth etc. Our advice could be to understand the main points of the exams and attempt to match them to the foam’s appropriateness in your particular person hazards. We would all the time suggest consulting individual foam producers as they’ll usually provide specific in-house fire-performance data against some of the extra uncommon fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the expansion ratio Images equipped by Author / Contributor
Critical factors for achievement: the time and software fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the speed at which completed foam is applied. Both are decided by empirically based requirements revealed by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor means that for a given measurement of fireside area it is needed to apply the froth for long sufficient to attain extinction and to forestall re-ignition. This is very important in guide intervention as firefighter’s might be at risk throughout post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the applying time may be as long as 60 minutes for the biggest tank diameters.
The software rate refers to the quantity of finished foam utilized per sq. metre. This varies based on the gas and the froth kind but is currently no much less than four.zero litres per minute per square metre. One of the continuing developments in foam efficiency is the likelihood that this will be reduced, but requirements usually take time to recognise product growth. Anything lower than the minimum utility fee signifies that hearth control is unlikely to be achieved. This signifies that firefighting sources, particularly in a guide fireplace assault, have to be assembled before firefighting commences and this takes time. The advantage in fitting mounted techniques is that the resources are already designed and built into the system for immediate software.
Principle of foam extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to allow readers to make an knowledgeable choice on how greatest to sort out their particular hearth challenges, the following is an outline of the varied foam proportioning methods.
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Typically associated with fire service deployment and limited fixed systems functions. This uses the venturi precept to create a strain drop in a small aluminium or seawater materials appropriate system with built-in concentrate pick-up tube. The strain drop created by the venturi draws the foam focus from a container the place it mixes with water to create foam resolution. Both the pick-up tube and body of the inductor are compact sufficient to be easily carried on a fire appliance or fitted right into a pipework system.
However, while it’s thought of to be the simplest technique, it has severe drawbacks: (i) units are manufacturing unit calibrated so any modifications to the hydraulics (caused by size 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 critical as deviations attributable to pipe diameter changes will adversely affect proportioning accuracy and potentially forestall any proportioning; (iii) adjustments in concentrate viscosity will undermine the ability of the venturi to draw focus into the downstream traces; (iv) stress loss is high, as much as 35%, so duty pump pressures need to be high enough to allow for it, probably including further cost into the system; (v) foam delivery units must be sized in order to not prohibit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs on account of foam concentrate usage, which has to be changed, and the disposal of premix or foam.
Types of froth agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electrical or a mix of electrical and diesel pumps to produce foam focus right into a proportioner at a higher pressure than the incoming water-line strain. The proportioner is installed into the water line and regulates the mixing.
They at the moment are associated with 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 range, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump wants an extra energy supply, apart from water, so just isn’t as reliably safe as a system with a potential single point of failure, similar to an entirely water-driven system; (iv) typically, these methods are very complex and trigger high efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to wreck the froth focus and entrain air, which in flip can undermine accurate 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 just like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth crammed bladder so that foam focus may be proportioned with water using the same supply. The venturi precept is once more brought into play because it creates a pressure 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 usage, which has 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 required to avoid a damaged bladder when commissioning a model new set up. It isn’t simple to work within the steel strain vessel should issues happen, particularly if and when a alternative bladder could additionally be required: all of it provides to the issue and cost.
Compressed air foam (CAFS):
This isn’t a proportioning methodology within the conventional sense as the foam is already proportioned utilizing one of many previous strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the foam answer on the point of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces allowing higher penetration and cooling. This can be a benefit in wildfire situations by coating vulnerable buildings to mitigate fireplace development. The restricted water provides associated with distant wildfire areas means that the useful resource may be totally optimised. However, as with balanced strain proportioner foam pumps, a further point of failure is possible due to the extra 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 purely mechanical and highly dependable. A water-driven rotor supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam focus through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and can proportion the foam focus precisely across a large working range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, completely without using 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 permitted foam proportioners embrace:
Reduced costs: proportioning price is examined without using foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: constant proportioning fee across a large working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in pressure loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a unique proportioning rate.
FM permitted FireDos Gen III proportioners are so far the one FM approved water motor coupled variable proportioners using FM accredited circulate meters. Using the test return line this provides the possibility to examine the proportioning fee throughout commissioning in addition to for annual checks, without creating any premix, which is a very huge profit for the consumer and relieves the setting.
In the second a part of this feature we will explore the results of viscosity on foam proportioning and typical foam utility areas and recommended discharge gadgets.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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November 3, 2023
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