Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given fire state of affairs. Our goal in this two-part article is to provide guidance primarily based on a hazard-specific strategy and allow you to make an informed choice on appropriate 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 typically associated with cooking such as vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting displays, we specialise primarily in 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 may not penetrate the hearth load effectively.
Fire courses.
How do we make foam?
Finished foam solution contains a simple recipe of foam concentrate, water and air. Foam focus is often mixed within the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge gadget – we will cowl proportioning later on this article and discharge strategies in Part 2. At this point air is entrained by using devices designed to naturally aspirate the solution. The amount of aspiration and the kind of focus determines the enlargement ratio. This is typically split between low, medium and excessive expansion. Low expansion is as much as 20:1, medium is 200:1 and high growth is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the froth adequately, though naturally aspirated generators are additionally used. The decision to decide on a specific enlargement ratio is determined by the hazard under evaluation.
Put merely, เกจวัดแรงดันเบนซิน and oil do not combine. Applying solely water to Class B products is not going to suppress the burning vapours. This is a crucial level to make as it is the vapours, not the liquid itself, that burns. We need a medium that allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever methodology is chosen to produce that blanket or movie, the target is the same.
Steps of froth generation Images provided by Author / Contributor
A little of the history of foam development
We can date the development 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 disadvantage was because of limited gasoline tolerance, which meant it was susceptible to gasoline pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, artificial detergents gave foam a larger gasoline tolerance in addition to forming a vapour-sealing movie throughout the surface of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s development did not fully exchange the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat fuel pick-up (mixing) and provide an excellent resistance to warmth, outlined by the industry as ‘burn-back resistance’.
Further growth in the Eighties took FP to the next level with film-forming fluoroprotein or FFFP. We now had the best of both worlds: a film-forming foam that also had good burn-back resistance.
The 1980s further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented a further problem as they had been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The same technology additionally turned available with the new technology of AFFF-ARs.
In latest years fluorine, one of the cornerstone ingredients to all foams, has turn out to be an environmental issue, due to persistence in groundwater. The industry has been presented with a major challenge to remove the ‘fluoro’ factor of all the completely different foam concentrate types. We have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of an entire vary 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 new normal and first choice for operators altering present inventory or reviewing new initiatives. As a foam proportioner producer we must look at the physical properties of froth fastidiously (especially viscosity) as they influence decisions on the overall proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant sorts are increasingly important within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant quality of SFFF/F3 is important to fight the small diploma of water miscibility of the gas.
All foam focus producers will naturally promote their product as being extremely efficient. The finest means of evaluating their claims is to familiarise your self with the empirically primarily based normal EN 1568 or UL162. The tests cover 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 within the take a look at protocols. This also covers recent and seawater as well as mild and forceful application of the froth. Each foam is given a rating with IA being the best, IIID the worst. This means that you can challenge foam suppliers to be able to make an knowledgeable determination on the most effective foam in your needs.
Whilst EN 1568 is an excellent benchmark standard, consciousness of the results on foam performance from components outdoors the usual checks should be noted. For example, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This can be exacerbated by totally different ambient air temperatures, the appliance methodology, gasoline depth etc. Our recommendation would be to understand the major points of the checks and attempt to match them to the foam’s appropriateness for your individual hazards. We would all the time advocate consulting individual foam producers as they can typically provide specific in-house fire-performance information towards a variety of the more unusual fuels.
However, despite the froth manufacturers’ typically conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams based on the enlargement ratio Images provided by Author / Contributor
Critical elements for fulfillment: the time and utility price matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary factors: time and the speed at which finished foam is utilized. Both are determined by empirically based mostly requirements published by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ issue signifies that for a given size of fire space it’s needed to apply the foam for lengthy sufficient to realize extinction and to stop re-ignition. This is especially crucial in handbook intervention as firefighter’s shall be in danger throughout post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the appliance time could be so lengthy as 60 minutes for the biggest tank diameters.
The utility price refers to the quantity of completed foam applied per square metre. This varies based on the fuel and the foam type however is at present a minimal of four.0 litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the probability that this might be lowered, however standards usually take time to recognise product improvement. Anything lower than the minimal utility fee implies that hearth control is unlikely to be achieved. This implies that firefighting resources, notably in a guide fire assault, need to be assembled before firefighting commences and this takes time. The advantage in fitting fastened systems is that the resources are already designed and constructed into the system for instant application.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an informed choice on how finest to tackle their explicit fireplace challenges, the next is an summary of the assorted foam proportioning methods.
Foam inductors:
Typically associated with hearth service deployment and restricted mounted systems purposes. This makes use of the venturi precept to create a stress drop in a small aluminium or seawater material appropriate system with built-in focus pick-up tube. The pressure drop created by the venturi draws the foam concentrate from a container the place it mixes with water to create foam answer. Both the pick-up tube and body of the inductor are compact sufficient to be easily carried on a fire equipment or fitted right into a pipework system.
However, while it is thought-about to be the simplest method, 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 device or a altering quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are critical as deviations attributable to pipe diameter modifications will adversely have an effect on proportioning accuracy and potentially prevent any proportioning; (iii) adjustments in concentrate viscosity will undermine the flexibility of the venturi to attract focus into the downstream lines; (iv) stress loss is high, as much as 35%, so duty pump pressures need to be high sufficient to permit for it, potentially including further value into the system; (v) foam supply gadgets need to be sized so as not to limit design flows; (vi) testing cannot be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs on account of foam concentrate usage, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a mixture of electric and diesel pumps to provide foam concentrate into a proportioner at the next strain than the incoming water-line strain. The proportioner is put in into the water line and regulates the mixing.
They are actually associated with older techniques, where disadvantages embody: (i) further costs in hardware and design time; (ii) the froth pump is generally restricted to a much tighter working range, although the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump wants an additional energy source, aside from water, so isn’t as reliably secure as a system with a potential single level of failure, corresponding to an entirely water-driven system; (iv) sometimes, these systems are very complicated and trigger excessive efforts on 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 froth concentrate 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 similar to those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam focus may be proportioned with water utilizing the same supply. The venturi principle is again brought into play as it creates a strain drop on the point of injection for the foam concentrate. Testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime costs because of foam concentrate utilization, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because nice care is needed to keep away from a broken bladder when commissioning a model new set up. It is never easy to work within the steel stress vessel should issues happen, especially if and when a replacement bladder could also be required: all of it adds to the difficulty and value.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology within the typical sense as the froth is already proportioned using one of many earlier 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 resolution on the level of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces permitting better penetration and cooling. This can also be a profit in wildfire situations by coating susceptible buildings to mitigate fire growth. The restricted water supplies associated with remote wildfire areas signifies that the useful resource may be totally optimised. However, as with balanced pressure proportioner foam pumps, a further level of failure is feasible because of the additional CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is purely mechanical and highly reliable. A water-driven rotor supplies the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning price and can proportion the foam concentrate accurately throughout a wide operating vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, fully without using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners include:
Reduced costs: proportioning rate is tested with out using foam or creating premix or foam – cost effective and eco-friendly.
Improved efficiency: constant proportioning price throughout a wide operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a unique proportioning fee.
FM permitted FireDos Gen III proportioners are so far the only FM approved water motor coupled variable proportioners using FM accredited move meters. Using the check return line this offers the possibility to verify the proportioning rate throughout commissioning as properly as for annual tests, without creating any premix, which is a really big benefit for the person and relieves the surroundings.
In the second a part of this feature we’ll discover the consequences of viscosity on foam proportioning and typical foam utility areas and really helpful discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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