Fire presents many challenges, not least due to the variables that decide which suppression medium is suitable for a given fire state of affairs. Our objective on this two-part article is to offer guidance primarily based on a hazard-specific approach and help you make an informed decision 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 such as magnesium
Class F – fires typically related to cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily in the Class B class: flammable liquids.
Foam is considered to be the simplest fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water solely could not penetrate the fire load effectively.
How can we make foam?
Finished foam solution includes a simple recipe of foam concentrate, water and air. Foam concentrate is often blended within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge system – we are going to cowl proportioning later in this article and discharge methods in Part 2. At this point air is entrained through the use of devices designed to naturally aspirate the solution. The amount of aspiration and the sort of focus determines the enlargement ratio. This is often cut up between low, medium and high enlargement. Low enlargement is as a lot as 20:1, medium is 200:1 and excessive enlargement is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to increase the foam adequately, though naturally aspirated turbines are additionally used. The choice to decide on a specific enlargement ratio is set by the hazard under evaluate.
Put merely, water and oil do not mix. Applying solely water to Class B merchandise is not going to 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 film to achieve success. Whatever method is chosen to produce that blanket or film, the objective is the same.
Steps of froth era Images supplied by Author / Contributor
A little of the historical past of froth growth
We can date the development of contemporary foam concentrates from the Sixties onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The primary downside was due to restricted fuel tolerance, which meant it was susceptible to gas 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 additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth didn’t utterly replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat gas pick-up (mixing) and provide a great resistance to warmth, defined by the trade as ‘burn-back resistance’.
Further development in the 1980s 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 a further problem as they have been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The same know-how additionally turned out there with the new generation of AFFF-ARs.
In latest years fluorine, one of the cornerstone components to all foams, has become an environmental issue, because of persistence in groundwater. The industry has been offered with a significant problem to remove the ‘fluoro’ component of all of the different foam focus types. We have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of an entire range of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn out to be the model new normal and first alternative for operators altering current inventory or reviewing new tasks. As a foam proportioner manufacturer we must examine the physical properties of foam carefully (especially viscosity) as they influence choices on the overall proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly essential within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant high quality of SFFF/F3 is critical to fight the small degree of water miscibility of the fuel.
All foam concentrate producers will naturally promote their product as being extremely efficient. The finest way of evaluating 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 extra demanding polar solvents are each included in the check protocols. This additionally covers contemporary and seawater as properly as gentle and forceful software of the froth. Each foam is given a ranking with IA being the most effective, IIID the worst. This means that you can problem foam suppliers in order to make an knowledgeable determination on one of the best foam on your needs.
Whilst EN 1568 is a superb benchmark normal, consciousness of the consequences on foam efficiency from elements outside the standard checks ought to be noted. For instance, notably aggressive solvents can challenge the firefighting effectiveness of certain foams. This can be exacerbated by different ambient air temperatures, the application technique, gas depth and so forth. Our recommendation would be to grasp the small print of the tests and attempt to match them to the foam’s appropriateness in your individual hazards. We would all the time suggest consulting individual foam manufacturers as they can often provide particular in-house fire-performance information in opposition to some of the more uncommon fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the enlargement ratio Images supplied by Author / Contributor
Critical factors for fulfillment: the time and utility fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary elements: time and the rate at which finished foam is applied. Both are decided by empirically based requirements revealed by bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given dimension of fireside space it is essential to use the froth for lengthy enough to attain extinction and to forestall re-ignition. digital pressure gauge is very important in handbook intervention as firefighter’s shall be in danger throughout post-fire operations. When it involves fixed protection for hydrocarbon and polar solvent tanks, the applying time can be as long as 60 minutes for the biggest tank diameters.
The application price refers again to the amount of finished foam utilized per square metre. This varies in accordance with the fuel and the foam sort however is currently at least four.0 litres per minute per sq. metre. One of the continued developments in foam efficiency is the probability that this shall be reduced, however standards often take time to recognise product development. Anything less than the minimal utility price signifies that hearth management is unlikely to be achieved. This means that firefighting resources, significantly in a manual fireplace assault, must be assembled earlier than firefighting commences and this takes time. The advantage in becoming mounted techniques is that the assets are already designed and built into the system for instant software.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to allow readers to make an informed choice on how finest to deal with their particular fireplace challenges, the following is an overview of the assorted foam proportioning methods.
Typically related to hearth service deployment and limited mounted methods applications. This uses the venturi precept to create a strain drop in a small aluminium or seawater materials suitable gadget with built-in concentrate 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 body of the inductor are compact sufficient to be simply carried on a hearth appliance or fitted into a pipework system.
However, whilst it’s thought of to be the best methodology, it has extreme drawbacks: (i) units are factory calibrated so any modifications to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge system or a changing quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are crucial as deviations attributable to pipe diameter adjustments will adversely affect proportioning accuracy and potentially prevent any proportioning; (iii) modifications in focus viscosity will undermine the ability of the venturi to draw concentrate into the downstream traces; (iv) stress loss is high, as a lot as 35%, so duty pump pressures must be excessive sufficient to allow for it, potentially including additional value into the system; (v) foam supply units have to be sized so as to not restrict design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to whole lifetime prices on account of foam focus utilization, which must be replaced, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electric or a combination of electric and diesel pumps to supply foam focus right into a proportioner at a better strain than the incoming water-line stress. The proportioner is put in into the water line and regulates the blending.
They are now associated with older methods, the place disadvantages include: (i) further prices in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter operating range, although the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump needs an extra energy source, aside from water, so just isn’t as reliably safe as a system with a possible single point of failure, similar to a completely water-driven system; (iv) typically, these systems are very complex and trigger high 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 froth concentrate and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Comprised of a metal strain vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner similar to those fitted to balanced stress proportioners. The incoming pressurised water compresses the foam filled bladder so that foam concentrate could be proportioned with water utilizing the same provide. The venturi principle is once more brought into play because it creates a stress drop on the point of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to entire lifetime costs as a end result of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a end result of nice care is needed to avoid a broken bladder when commissioning a model new set up. It is never simple to work throughout the metal stress vessel ought to problems occur, particularly if and when a substitute bladder could additionally be required: all of it provides to the issue and value.
Compressed air foam (CAFS):
This isn’t a proportioning methodology in the typical sense as the froth is already proportioned using one of many earlier methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the foam answer at the point of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces permitting better penetration and cooling. This can be a profit in wildfire situations by coating susceptible constructions to mitigate fireplace progress. The restricted water provides associated with remote wildfire areas means that the resource may be absolutely optimised. However, as with balanced pressure proportioner foam pumps, a further level of failure is possible due to the further 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 technology, the product is purely mechanical and extremely dependable. A water-driven rotor provides the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is provided with foam concentrate via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning price and can proportion the froth focus accurately throughout a large working vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning fee testing, utterly 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 permitted foam proportioners embrace:
Reduced prices: proportioning fee is tested without using foam or creating premix or foam – value effective and eco-friendly.
Improved performance: constant proportioning rate throughout a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in stress loss, in comparability with older generations, by way of hydraulic optimisation.
Improved pressure gauge cut-off for simple and quick adjustment to a special proportioning rate.
FM permitted FireDos Gen III proportioners are thus far the only FM approved water motor coupled variable proportioners using FM permitted move meters. Using the check return line this presents the possibility to check the proportioning rate during commissioning as properly as for annual checks, without creating any premix, which is a really huge benefit for the consumer and relieves the setting.
In the second a part of this feature we’ll explore the consequences of viscosity on foam proportioning and typical foam software areas and recommended discharge devices.
For extra info, go to www.firedos.com
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