Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given hearth scenario. Our objective on this two-part article is to supply steering based on a hazard-specific approach and help you make an informed decision on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires usually related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise mainly within the Class B class: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are specifically for deep-seated Class A fires where water solely could not penetrate the hearth load effectively.
Fire lessons.
How will we make foam?
Finished foam solution comprises a simple recipe of froth focus, water and air. Foam concentrate is usually mixed in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge device – we will cover proportioning later in this article and discharge strategies in Part 2. At this point air is entrained through the use of gadgets designed to naturally aspirate the answer. The amount of aspiration and the kind of concentrate determines the enlargement ratio. This is often split between low, medium and excessive enlargement. Low growth is up to 20:1, medium is 200:1 and high expansion is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to broaden the froth adequately, though naturally aspirated turbines are also used. The decision to choose on a specific growth ratio is set by the hazard beneath review.
Put merely, water and oil don’t mix. Applying solely water to Class B merchandise will not suppress the burning vapours. This is a vital level to make as it is the vapours, not the liquid itself, that burns. We want a medium that permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever methodology is chosen to provide that blanket or movie, the objective is the same.
Steps of froth generation Images provided by Author / Contributor
A little of the historical past of froth development
We can date the development of contemporary foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the base component). The major 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 using protein as the bottom product, synthetic detergents gave foam a larger fuel tolerance as well as forming a vapour-sealing movie throughout the floor of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement didn’t fully substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat gas pick-up (mixing) and supply a great resistance to heat, defined by the business as ‘burn-back resistance’.
Further growth in the Eighties took FP to the next degree 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 1980s further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times offered an extra challenge as they have been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar technology additionally grew to become obtainable with the new era of AFFF-ARs.
In current years fluorine, one of the cornerstone elements to all foams, has turn into an environmental issue, as a result of persistence in groundwater. The trade has been introduced with a major challenge to eliminate the ‘fluoro’ factor of all of the completely different foam focus varieties. We have witnessed an period of manufacturers’ claims and counter claims relating to the efficacy of a complete range of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn into the new regular and first alternative for operators changing present stock or reviewing new tasks. As a foam proportioner producer we should look at the physical properties of froth fastidiously (especially viscosity) as they affect choices on the overall proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are increasingly important in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is critical to fight the small degree of water miscibility of the gasoline.
All foam concentrate producers will naturally promote their product as being extremely effective. The greatest way of evaluating their claims is to familiarise your self with the empirically based standard EN 1568 or UL162. The tests cover extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are each included within the test protocols. This additionally covers contemporary and seawater as nicely as mild and forceful application of the foam. Each foam is given a rating with IA being the most effective, IIID the worst. This means you could problem foam suppliers in order to make an knowledgeable choice on the most effective foam in your wants.
Whilst EN 1568 is a superb benchmark commonplace, consciousness of the effects on foam efficiency from factors exterior the usual exams should be noted. For instance, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by totally different ambient air temperatures, the appliance methodology, gasoline depth and so forth. Our recommendation can be to know the small print of the checks and attempt to match them to the foam’s appropriateness on your individual hazards. We would at all times recommend consulting particular person foam manufacturers as they will usually provide specific in-house fire-performance information towards some of the extra uncommon fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the growth ratio Images provided by Author / Contributor
Critical elements for fulfillment: the time and application fee matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary elements: time and the rate at which finished foam is utilized. Both are determined by empirically based standards printed by our bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ issue signifies that for a given dimension of fireside space it is essential to use the froth for lengthy sufficient to attain extinction and to prevent re-ignition. This is particularly critical in manual intervention as firefighter’s might be at risk during post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the applying time can be so long as 60 minutes for the largest tank diameters.
The application rate refers back to the quantity of finished foam applied per sq. metre. This varies based on the fuel and the froth kind however is presently no less than 4.zero litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the probability that this shall be lowered, however standards often take time to recognise product development. Anything lower than the minimum application fee signifies that fireplace management is unlikely to be achieved. This signifies that firefighting assets, particularly in a guide fireplace assault, must be assembled earlier than firefighting commences and this takes time. The advantage in becoming fixed methods is that the assets are already designed and built into the system for quick software.
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 decision on how best to deal with their specific fire challenges, the next is an summary of the various foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and restricted fastened systems purposes. This uses the venturi principle to create a stress drop in a small aluminium or seawater materials compatible system with built-in concentrate pick-up tube. pressure gauge trerice ราคา created by the venturi attracts the foam focus from a container the place it mixes with water to create foam solution. Both the pick-up tube and body of the inductor are compact enough to be simply carried on a hearth equipment or fitted right into a pipework system.
However, while it is thought of to be the simplest technique, it has severe drawbacks: (i) models are factory calibrated so any adjustments 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 probably require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter adjustments will adversely have an effect on proportioning accuracy and doubtlessly prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the flexibility of the venturi to attract focus into the downstream traces; (iv) stress loss is high, as a lot as 35%, so duty pump pressures need to be high sufficient to allow for it, doubtlessly adding extra cost into the system; (v) foam supply devices must be sized so as to not restrict design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to complete lifetime prices because of foam concentrate usage, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced stress proportioners:
These use an electrical or a mix of electric and diesel pumps to provide foam concentrate right 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 at the second are associated with older techniques, the place disadvantages include: (i) further prices in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter working vary, although the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump wants an extra energy supply, apart from 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) usually, these methods are very complex and trigger excessive efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to damage the foam focus and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain 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 froth stuffed bladder so that foam concentrate could be proportioned with water utilizing the same provide. The venturi precept is again brought into play as it creates a pressure drop at the point of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs as a end result of foam focus utilization, which must be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a result of nice care is required to avoid a damaged bladder when commissioning a model new installation. It is rarely simple to work throughout the metal stress vessel should issues occur, particularly if and when a replacement bladder could also be required: all of it adds to the difficulty and value.
Compressed air foam (CAFS):
This is not a proportioning technique within the typical sense as the froth is already proportioned utilizing one of many earlier methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth resolution on the point of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces permitting higher penetration and cooling. This is also a benefit in wildfire conditions by coating weak structures to mitigate fire growth. The limited water supplies associated with remote wildfire areas means that the useful resource may be absolutely optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is feasible due to the further CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is only mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning fee and will proportion the foam focus accurately across a large operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning price testing, fully without utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners include:
Reduced prices: proportioning price is examined without utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: fixed proportioning fee throughout a wide operating range.
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 different proportioning rate.
FM approved FireDos Gen III proportioners are to date the one FM approved water motor coupled variable proportioners using FM accredited move meters. Using the take a look at return line this presents the chance to examine the proportioning price throughout commissioning in addition to for annual tests, without creating any premix, which is a really big benefit for the user and relieves the surroundings.
In the second a half of this characteristic we will discover the effects of viscosity on foam proportioning and typical foam application areas and really helpful discharge gadgets.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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