Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given hearth state of affairs. Our objective in this two-part article is to supply steerage based mostly on a hazard-specific approach and allow you to make an informed determination 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 materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires usually associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting displays, we specialise primarily within the Class B class: flammable liquids.
Foam is taken into account 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 the place water solely might not penetrate the fire load effectively.
Fire courses.
How do we make foam?
Finished foam solution includes a simple recipe of froth concentrate, water and air. Foam concentrate is typically combined in the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge device – we will cowl proportioning later in this article and discharge methods in Part 2. At this level air is entrained by utilizing gadgets designed to naturally aspirate the answer. The quantity of aspiration and the kind of concentrate determines the growth ratio. This is often break up between low, medium and high enlargement. Low expansion is as a lot as 20:1, medium is 200:1 and excessive expansion is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the foam adequately, although naturally aspirated turbines are also used. The choice to determine on a selected growth ratio is determined by the hazard under review.
Put simply, water and oil do not mix. Applying solely water to Class B merchandise will not suppress the burning vapours. This is a vital point to make as it’s the vapours, not the liquid itself, that burns. We need a medium that enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to achieve success. Whatever method is chosen to produce that blanket or movie, the target is the same.
Steps of froth generation Images supplied by Author / Contributor
A little of the historical past of froth growth
We can date the event of recent foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The major drawback was as a result of restricted fuel tolerance, which meant it was vulnerable to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, artificial detergents gave foam a larger fuel tolerance in addition to forming a vapour-sealing movie throughout the floor of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth did not completely exchange using protein-based foam. Fluoroprotein, or FP, meant that protein foam could both fight gas pick-up (mixing) and supply a great resistance to heat, outlined by the business as ‘burn-back resistance’.
Further improvement within the Eighties took FP to the following 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 1980s additional added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented a further challenge 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 identical expertise additionally became available with the new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone components to all foams, has become an environmental issue, due to persistence in groundwater. The trade has been offered with a serious problem to eliminate the ‘fluoro’ factor of all the completely different foam concentrate sorts. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of an entire 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 alternative for operators altering existing inventory or reviewing new tasks. As a foam proportioner producer we must look at the physical properties of froth fastidiously (especially viscosity) as they influence selections on the overall proportioning resolution. More of this later.
Multi-purpose foams such because 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, 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 manufacturers will naturally promote their product as being extremely efficient. The greatest method of comparing their claims is to familiarise your self with the empirically 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 check protocols. เกจวัดแรงดูด covers recent and seawater as nicely as light and forceful software of the foam. Each foam is given a rating with IA being the best, IIID the worst. This means you could challenge foam suppliers so as to make an knowledgeable decision on the most effective foam in your needs.
Whilst EN 1568 is an excellent benchmark normal, awareness of the results on foam efficiency from components outdoors the usual checks should be famous. For instance, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This may be exacerbated by totally different ambient air temperatures, the application technique, gas depth and so forth. Our recommendation could be to know the details of the exams and try to match them to the foam’s appropriateness in your individual hazards. We would always suggest consulting particular person foam producers as they can often present particular in-house fire-performance knowledge against some of the more unusual fuels.
However, despite the froth manufacturers’ generally conflicting claims on performance, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the growth ratio Images provided by Author / Contributor
Critical elements for fulfillment: the time and application rate matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary components: time and the rate at which finished foam is applied. Both are determined by empirically based standards published by our bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ factor implies that for a given measurement of fireplace space it is necessary to use the froth for long enough to realize extinction and to forestall re-ignition. This is particularly important in handbook intervention as firefighter’s will be at risk throughout post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the applying time may be so lengthy as 60 minutes for the most important tank diameters.
The software fee refers back to the amount of finished foam utilized per square metre. This varies according to the fuel and the foam type but is currently a minimal of 4.zero litres per minute per square metre. One of the ongoing developments in foam efficiency is the chance that this shall be decreased, however standards typically take time to recognise product improvement. Anything less than the minimum utility fee implies that fire 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 benefit in becoming mounted systems is that the sources are already designed and constructed into the system for immediate application.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an knowledgeable determination on how best to deal with their particular fireplace challenges, the next is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted fixed systems purposes. This uses the venturi precept to create a strain drop in a small aluminium or seawater material suitable gadget with built-in focus pick-up tube. The stress drop created by the venturi draws the froth concentrate 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 fireplace equipment or fitted right into a pipework system.
However, whilst it’s thought-about to be the best method, it has extreme drawbacks: (i) models are manufacturing facility calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge gadget or a changing quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter modifications will adversely have an result on proportioning accuracy and potentially stop any proportioning; (iii) adjustments in concentrate viscosity will undermine the power of the venturi to attract concentrate into the downstream lines; (iv) strain loss is excessive, as much as 35%, so duty pump pressures must be excessive enough to allow for it, doubtlessly including further value into the system; (v) foam delivery gadgets need to be sized so as not to prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices as a outcome of foam concentrate utilization, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electrical or a mix of electrical and diesel pumps to supply foam focus into a proportioner at a higher pressure than the incoming water-line stress. The proportioner is put in into the water line and regulates the mixing.
They are actually related to older systems, where disadvantages embrace: (i) extra prices in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter working range, though the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump needs an additional power supply, aside from water, so just isn’t as reliably safe as a system with a possible single level of failure, such as a wholly water-driven system; (iv) typically, these systems 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 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 versatile bladder (typically a butyl material) linked to a foam concentrate proportioner just like those fitted to balanced stress proportioners. The incoming pressurised water compresses the foam crammed bladder in order that foam concentrate can be proportioned with water using the identical provide. The venturi principle is again introduced into play as it creates a stress drop on the level of injection for the foam concentrate. Testing cannot be achieved without creating premix and discharging finished foam. This will add to complete lifetime prices as a end result of foam concentrate usage, which must be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of great care is needed to avoid a damaged bladder when commissioning a new set up. It is rarely easy to work within the metal pressure vessel ought to problems happen, especially if and when a replacement bladder may be required: all of it provides to the problem and cost.
Compressed air foam (CAFS):
This just isn’t a proportioning method in the conventional sense as the froth is already proportioned utilizing one of the 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 froth answer on the level of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces permitting better penetration and cooling. This is also a benefit in wildfire situations by coating vulnerable constructions to mitigate hearth growth. The limited water supplies related to distant wildfire areas means that the resource may be fully optimised. However, as with balanced pressure proportioner foam pumps, an additional level of failure is feasible as a outcome of further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is only mechanical and extremely dependable. A water-driven rotor supplies the driving force to drive a directly 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 price and can proportion the foam focus precisely across a large operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, fully without 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 accredited foam proportioners embrace:
Reduced prices: proportioning rate is tested with out utilizing foam or creating premix or foam – cost effective and eco-friendly.
Improved performance: fixed proportioning price throughout a wide operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in strain loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a different proportioning rate.
FM approved FireDos Gen III proportioners are thus far the one FM approved water motor coupled variable proportioners using FM approved move meters. Using the test return line this presents the chance to examine the proportioning rate during commissioning as properly as for annual exams, with out creating any premix, which is a really massive profit for the user and relieves the surroundings.
In the second a part of this function we are going to discover the results of viscosity on foam proportioning and typical foam software areas and really helpful discharge devices.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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