Fire presents many challenges, not least due to the variables that determine which suppression medium is acceptable for a given hearth scenario. Our objective in this two-part article is to provide steering primarily based on a hazard-specific approach and help you make an informed determination 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 materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires generally associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily within the Class B category: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely may not penetrate the fireplace load successfully.
How do we make foam?
Finished foam answer comprises a easy recipe of froth concentrate, water and air. Foam focus is often blended within 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 cowl proportioning later on this article and discharge strategies in Part 2. At this point air is entrained by utilizing units designed to naturally aspirate the solution. The quantity of aspiration and the type of focus determines the enlargement ratio. This is typically split between low, medium and excessive enlargement. Low enlargement is as much as 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 increase the froth adequately, although naturally aspirated turbines are additionally used. The determination to decide on a selected enlargement ratio is set by the hazard underneath evaluation.
Put simply, water and oil do not combine. Applying solely water to Class B merchandise 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 need a medium that allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to obtain success. Whatever technique is chosen to provide that blanket or film, the target is the same.
Steps of froth technology Images supplied by Author / Contributor
A little of the historical past of froth development
We can date the event of contemporary foam concentrates from the Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary downside was due to limited gasoline tolerance, which meant it was vulnerable to gas pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, synthetic detergents gave foam a higher gasoline tolerance in addition to 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 units are fitted.
Nevertheless, AFFF’s development didn’t fully exchange the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both fight gasoline pick-up (mixing) and supply an excellent resistance to heat, outlined by the industry as ‘burn-back resistance’.
Further development in the Eighties took FP to the next degree 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 Eighties additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented an extra challenge as they have been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar know-how also became obtainable with the brand new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone elements to all foams, has turn into an environmental problem, due to persistence in groundwater. The industry has been introduced with a significant challenge to remove the ‘fluoro’ factor of all of the totally different foam concentrate types. 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 model new normal and first choice for operators altering present stock or reviewing new initiatives. As a foam proportioner producer we must examine the physical properties of foam carefully (especially viscosity) as they affect decisions on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more essential 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 combat the small diploma of water miscibility of the fuel.
All foam concentrate producers will naturally promote their product as being highly effective. The best method of evaluating their claims is to familiarise yourself with the empirically primarily based standard 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 each included within the take a look at protocols. This additionally covers recent and seawater in addition to mild and forceful application of the froth. Each foam is given a score with IA being one of the best, IIID the worst. This means you could problem foam suppliers in order to make an knowledgeable choice on the most effective foam on your wants.
Whilst EN 1568 is a superb benchmark normal, consciousness of the consequences on foam performance from factors outside the standard tests ought to be noted. For example, notably aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by different ambient air temperatures, the application method, gas depth and so on. Our recommendation could be to understand the primary points of the exams and attempt to match them to the foam’s appropriateness on your individual hazards. We would at all times suggest consulting individual foam producers as they’ll usually provide particular in-house fire-performance knowledge against some of the extra unusual fuels.
However, despite the foam manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams based on the growth ratio Images equipped by Author / Contributor
Critical components for achievement: the time and application fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the speed at which finished foam is utilized. Both are determined by empirically primarily based standards revealed by bodies such as 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 fireplace space it’s necessary to apply the froth for lengthy sufficient to attain extinction and to forestall re-ignition. This is particularly critical in handbook intervention as firefighter’s shall be in danger throughout post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the applying time could be so long as 60 minutes for the most important tank diameters.
The utility rate refers to the amount of completed foam utilized per sq. metre. This varies based on the gasoline and the foam type however is presently at least four.0 litres per minute per sq. metre. เกจ์วัดแรงดันน้ำ of the ongoing developments in foam performance is the probability that this might be decreased, however requirements often take time to recognise product improvement. Anything less than the minimal utility rate signifies that hearth control is unlikely to be achieved. This means that firefighting resources, significantly in a guide hearth attack, must be assembled earlier than firefighting commences and this takes time. The advantage in fitting mounted methods is that the sources are already designed and constructed into the system for quick utility.
Principle of froth extinguishment Images equipped 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 deal with their specific hearth challenges, the next is an outline of the assorted foam proportioning strategies.
Typically associated with fire service deployment and restricted mounted methods functions. This uses the venturi precept to create a stress drop in a small aluminium or seawater materials appropriate system with built-in focus pick-up tube. The strain drop created by the venturi attracts the froth concentrate from a container where it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fire equipment or fitted right into a pipework system.
However, while it is considered to be the best methodology, it has severe drawbacks: (i) items are manufacturing unit calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a altering amount of discharge devices) will probably require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter changes will adversely have an result on proportioning accuracy and potentially forestall any proportioning; (iii) changes in focus viscosity will undermine the ability of the venturi to attract concentrate into the downstream strains; (iv) stress loss is high, as much as 35%, so duty pump pressures must be excessive sufficient to permit for it, potentially including additional price into the system; (v) foam supply gadgets must be sized so as to not prohibit design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to complete lifetime prices as a outcome of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced strain proportioners:
These use an electrical or a combination of electrical and diesel pumps to produce foam focus into a proportioner at a better pressure than the incoming water-line stress. The proportioner is put in into the water line and regulates the mixing.
They are actually associated with older systems, where disadvantages embrace: (i) further costs in hardware and design time; (ii) the froth pump is generally restricted to a much tighter working vary, though the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump wants an additional energy source, other than water, so is not as reliably secure as a system with a possible single level of failure, similar to a wholly water-driven system; (iv) sometimes, these systems are very complicated and cause high efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary 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.
Comprised of a steel pressure vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner much like those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam crammed bladder so that foam concentrate could be proportioned with water using the identical provide. The venturi principle is again introduced into play because it creates a pressure drop on the level of injection for the foam focus. Testing cannot be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices on account of foam focus utilization, 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 broken bladder when commissioning a new installation. It is rarely simple to work throughout the metal stress vessel ought to problems occur, particularly if and when a replacement bladder could also be required: all of it adds to the difficulty and price.
Compressed air foam (CAFS):
This is not a proportioning technique in the conventional sense as the foam is already proportioned using one of many earlier methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the foam solution at the level of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces permitting higher penetration and cooling. This is also a benefit in wildfire conditions by coating vulnerable structures to mitigate fire development. The limited water provides related to remote wildfire areas means that the resource could be totally optimised. However, as with balanced pressure proportioner foam pumps, an additional level of failure is possible as a outcome of additional CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is solely mechanical and highly dependable. A water-driven rotor provides the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and will proportion the foam focus accurately across a large working vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, utterly with out using 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 approved foam proportioners include:
Reduced prices: proportioning fee is examined without utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: constant proportioning rate across a large operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a unique proportioning price.
FM accredited FireDos Gen III proportioners are so far the one FM approved water motor coupled variable proportioners using FM permitted flow meters. Using the take a look at return line this presents the possibility to check the proportioning price throughout commissioning as nicely as for annual exams, without creating any premix, which is a very huge benefit for the user and relieves the surroundings.
In the second a part of this characteristic we’ll explore the effects of viscosity on foam proportioning and typical foam software areas and really helpful discharge units.
For more information, go to www.firedos.com
The authorities of Sudan has launched tender in search of consultants to assist within the implementation of an irrigation challenge