Fire presents many challenges, not least due to the variables that decide which suppression medium is appropriate for a given hearth situation. Our objective in this two-part article is to offer steering based mostly on a hazard-specific method 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 typically related to cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting monitors, we specialise mainly within the Class B class: flammable liquids.
Foam is taken into account to be the most effective 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 fireplace load effectively.
Fire courses.
How do we make foam?
Finished foam answer comprises a easy recipe of foam concentrate, water and air. Foam focus is typically blended in 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 will cover proportioning later in this article and discharge strategies in Part 2. At this level air is entrained through the use of gadgets designed to naturally aspirate the solution. The quantity of aspiration and the type of concentrate determines the enlargement ratio. This is usually split between low, medium and high enlargement. Low expansion is up to 20:1, medium is 200:1 and high expansion is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the froth adequately, although naturally aspirated mills are also used. The choice to choose a selected expansion ratio is set by the hazard underneath evaluate.
Put simply, water and oil don’t mix. Applying solely water to Class B products won’t suppress the burning vapours. This is a crucial point to make as it is the vapours, not the liquid itself, that burns. We want a medium that enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever technique is chosen to supply that blanket or film, the objective is the same.
Steps of froth generation Images equipped by Author / Contributor
A little of the historical past of foam improvement
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 ground hoof and horn is the base component). The primary downside was due to restricted gasoline tolerance, which meant it was vulnerable 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 gas tolerance as properly as forming a vapour-sealing film throughout the surface of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth didn’t utterly replace the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat fuel pick-up (mixing) and offer a great resistance to heat, defined by the industry as ‘burn-back resistance’.
Further growth within the Eighties took FP to the next level with film-forming fluoroprotein or FFFP. We now had the most effective of each worlds: a film-forming foam that also had good burn-back resistance.
The Nineteen Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented an extra 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 out there with the new generation of AFFF-ARs.
In latest years fluorine, one of the cornerstone components to all foams, has turn into an environmental issue, due to persistence in groundwater. The industry has been presented with a significant problem to remove the ‘fluoro’ factor of all the totally different foam concentrate varieties. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of a whole range 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 selection for operators altering present inventory or reviewing new tasks. As a foam proportioner producer we should examine the physical properties of froth fastidiously (especially viscosity) as they influence decisions on the overall proportioning resolution. More of this later.
เครื่องมือวัดความดัน -purpose foams such as the F3 alcohol-resistant varieties are increasingly necessary in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant high quality of SFFF/F3 is critical to combat the small degree of water miscibility of the gas.
All foam focus producers will naturally promote their product as being extremely effective. The finest means of comparing their claims is to familiarise yourself with the empirically based normal EN 1568 or UL162. The exams cowl extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included in the take a look at protocols. This also covers contemporary and seawater as well as light and forceful utility of the froth. Each foam is given a ranking with IA being one of the best, IIID the worst. This means that you can problem foam suppliers in order to make an informed determination on the best foam for your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the consequences on foam performance from elements outside the usual tests ought to be noted. For example, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by completely different ambient air temperatures, the application technique, fuel depth and so on. Our recommendation would be to grasp the major points of the exams and try to match them to the foam’s appropriateness in your individual hazards. We would at all times advocate consulting particular person foam producers as they can usually provide particular in-house fire-performance information against a few of the extra uncommon fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the enlargement ratio Images supplied by Author / Contributor
Critical factors for success: the time and utility rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the speed at which completed foam is applied. Both are determined by empirically based requirements published by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor means that for a given dimension of fireside space it is essential to use the foam for long sufficient to achieve extinction and to forestall re-ignition. This is particularly critical in manual intervention as firefighter’s shall be in danger throughout post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the applying time could be so lengthy as 60 minutes for the biggest tank diameters.
The utility rate refers again to the amount of finished foam utilized per sq. metre. This varies in accordance with the gas and the froth sort but is presently no much less than 4.zero litres per minute per square metre. One of the ongoing developments in foam efficiency is the likelihood that this shall be reduced, however standards usually take time to recognise product development. Anything less than the minimum application rate implies that hearth control is unlikely to be achieved. This implies that firefighting sources, significantly in a guide fire assault, have to be assembled earlier than firefighting commences and this takes time. The benefit in fitting mounted systems is that the resources are already designed and built into the system for immediate software.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an knowledgeable choice on how finest to sort out their particular hearth challenges, the following is an outline of the varied foam proportioning methods.
Foam inductors:
Typically associated with fireplace service deployment and limited fastened systems applications. 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 pressure drop created by the venturi draws the foam 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 sufficient to be simply carried on a hearth appliance or fitted into a pipework system.
However, while it’s thought-about to be the best technique, it has extreme drawbacks: (i) items are factory calibrated so any adjustments to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a changing quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter modifications will adversely affect proportioning accuracy and potentially forestall any proportioning; (iii) changes in focus viscosity will undermine the power of the venturi to attract focus into the downstream traces; (iv) pressure loss is high, as a lot as 35%, so responsibility pump pressures need to be high enough to permit for it, doubtlessly including further price into the system; (v) foam supply gadgets have to be sized in order to not restrict design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime prices as a result of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced strain proportioners:
These use an electric or a mix of electric and diesel pumps to produce foam concentrate right into a proportioner at the next strain than the incoming water-line stress. The proportioner is installed into the water line and regulates the blending.
They are actually associated with older techniques, where disadvantages embrace: (i) extra prices in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter operating range, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump needs an additional energy supply, other than water, so just isn’t as reliably safe as a system with a possible single point of failure, corresponding to an entirely water-driven system; (iv) sometimes, these techniques are very complex and trigger excessive 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 break the froth focus and entrain air, which in flip 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 much like those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam concentrate may be proportioned with water utilizing the same supply. The venturi precept is again brought into play as it creates a pressure drop at the point of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to entire lifetime costs because of foam concentrate usage, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a end result of great care is needed to keep away from a damaged bladder when commissioning a model new set up. It isn’t easy to work inside the steel strain vessel ought to issues happen, particularly if and when a substitute bladder could also be required: it all provides to the difficulty and value.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology within the conventional sense as the foam is already proportioned utilizing one of the earlier 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 at the level of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces permitting higher penetration and cooling. This can be a benefit in wildfire situations by coating susceptible constructions to mitigate fireplace progress. The limited water provides associated with distant wildfire areas means that the useful resource could be totally optimised. However, as with balanced stress proportioner foam pumps, an extra point of failure is feasible as a end result of additional CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is solely mechanical and highly reliable. A water-driven rotor provides the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is supplied with foam focus by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning rate and will proportion the foam concentrate precisely across a wide working range. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate 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 permitted foam proportioners include:
Reduced costs: proportioning price is examined without utilizing foam or creating premix or foam – value effective and eco-friendly.
Improved performance: constant proportioning price throughout a wide operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a special proportioning rate.
FM permitted FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners utilizing FM permitted flow meters. Using the test return line this presents the likelihood to examine the proportioning fee during commissioning in addition to for annual checks, with out creating any premix, which is a really massive benefit for the consumer and relieves the environment.
In the second a half of this characteristic we are going to explore the consequences of viscosity on foam proportioning and typical foam application areas and beneficial discharge units.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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