Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fire scenario. Our objective in this two-part article is to offer guidance based on a hazard-specific strategy and allow you to make an informed choice 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 combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires typically related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting screens, we specialise primarily within the Class B class: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are specifically 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 answer includes a easy recipe of froth concentrate, water and air. Foam focus is typically blended in 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 device – we will cover proportioning later on this article and discharge strategies in Part 2. At this point air is entrained through the use of units designed to naturally aspirate the answer. The quantity of aspiration and the kind of focus determines the enlargement ratio. This is typically cut up between low, medium and excessive enlargement. Low expansion is as a lot as 20:1, medium is 200:1 and high enlargement is greater than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to expand the foam adequately, though naturally aspirated turbines are also used. The determination to choose a specific growth ratio is determined by the hazard beneath evaluation.
Put merely, water and oil don’t combine. Applying only water to Class B merchandise won’t suppress the burning vapours. This is a vital level to make as it’s 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 film to obtain success. Whatever technique is chosen to produce that blanket or film, the target is the same.
Steps of froth era Images equipped by Author / Contributor
A little of the history of foam improvement
We can date the event of modern 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 major downside was because of limited gasoline tolerance, which meant it was vulnerable to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, artificial detergents gave foam a greater gasoline tolerance as nicely as 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 devices are fitted.
Nevertheless, AFFF’s growth didn’t completely replace the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat gas pick-up (mixing) and provide a great resistance to heat, defined by the business as ‘burn-back resistance’.
How-to within the Nineteen Eighties took FP to the subsequent stage 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 Nineteen 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 a further challenge as they were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same technology additionally grew to become out there with the brand new generation of AFFF-ARs.
In recent years fluorine, one of many cornerstone ingredients to all foams, has turn into an environmental issue, because of persistence in groundwater. The business has been introduced with a significant problem to get rid of the ‘fluoro’ component of all the completely different foam concentrate sorts. We have witnessed an period 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 become the new normal and first choice for operators altering existing inventory or reviewing new tasks. As a foam proportioner manufacturer we must study the physical properties of froth fastidiously (especially viscosity) as they influence selections on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant high quality of SFFF/F3 is necessary to fight the small diploma of water miscibility of the gasoline.
All foam focus manufacturers will naturally promote their product as being highly effective. The best way of evaluating their claims is to familiarise your self with the empirically based mostly standard EN 1568 or UL162. The checks cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included in the take a look at protocols. This additionally covers recent and seawater in addition to light and forceful software of the froth. 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 informed decision on the best foam on your wants.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the results on foam performance from factors exterior the usual exams should be noted. For example, particularly aggressive solvents can problem the firefighting effectiveness of sure foams. This can be exacerbated by totally different ambient air temperatures, the application technique, fuel depth etc. Our advice can be to grasp the small print of the tests and attempt to match them to the foam’s appropriateness for your individual hazards. We would all the time advocate consulting particular person foam manufacturers as they’ll typically provide particular in-house fire-performance data towards some of the more unusual fuels.
However, despite the froth manufacturers’ sometimes conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the expansion ratio Images provided by Author / Contributor
Critical elements for success: the time and application rate matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary components: time and the rate at which completed foam is applied. Both are decided by empirically primarily based requirements printed by our bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor implies that for a given dimension of fireside space it is needed to use the foam for long enough to realize extinction and to stop re-ignition. This is especially important in manual intervention as firefighter’s might be in danger during post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the appliance time may be so lengthy as 60 minutes for the biggest tank diameters.
The application fee refers to the quantity of completed foam utilized per square metre. This varies based on the gas and the foam kind however is at present a minimum of four.0 litres per minute per sq. metre. One of the continuing developments in foam performance is the likelihood that this shall be lowered, but requirements typically take time to recognise product growth. Anything less than the minimum utility fee implies that hearth management is unlikely to be achieved. This signifies that firefighting assets, notably in a manual fireplace assault, need to be assembled earlier than firefighting commences and this takes time. The benefit in becoming mounted systems is that the resources are already designed and constructed into the system for instant software.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to allow readers to make an informed determination on how finest to tackle their particular fireplace challenges, the next is an overview of the assorted foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and restricted mounted techniques applications. This uses the venturi principle to create a stress drop in a small aluminium or seawater material appropriate system with built-in concentrate pick-up tube. The strain drop created by the venturi draws the froth concentrate from a container the place it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a fire equipment or fitted right into a pipework system.
However, while it is thought of to be the only methodology, it has extreme drawbacks: (i) models are manufacturing unit calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge system or a altering amount of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations caused by pipe diameter modifications will adversely have an result on proportioning accuracy and potentially stop any proportioning; (iii) changes in concentrate viscosity will undermine the power of the venturi to draw concentrate into the downstream traces; (iv) pressure loss is high, as much as 35%, so responsibility pump pressures need to be high sufficient to permit for it, probably adding extra value into the system; (v) foam supply units have to be sized in order to not limit design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to complete lifetime prices on account of foam concentrate utilization, which needs to be replaced, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced strain proportioners:
These use an electric or a combination of electric and diesel pumps to supply foam concentrate right into a proportioner at a better stress than the incoming water-line pressure. The proportioner is installed into the water line and regulates the blending.
They are now related to older systems, the place disadvantages embrace: (i) extra prices in hardware and design time; (ii) the foam pump is normally restricted to a much tighter operating range, though the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump wants an extra energy source, aside from water, so just isn’t as reliably secure as a system with a possible single level of failure, such as a completely water-driven system; (iv) sometimes, these techniques 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 concentrate and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner much like the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the froth filled bladder in order that foam focus may be proportioned with water using the same provide. The venturi precept is once more introduced into play as it creates a pressure drop on the level of injection for the froth focus. Testing cannot be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs as a result of foam focus utilization, which has to be changed, 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 keep away from a damaged bladder when commissioning a brand new set up. It isn’t easy to work within the metal pressure vessel should problems occur, especially if and when a alternative bladder could additionally be required: it all adds to the difficulty and price.
Compressed air foam (CAFS):
This isn’t a proportioning method in the standard sense as the foam is already proportioned utilizing one of many earlier strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam answer at the level of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces allowing better penetration and cooling. This is also a profit in wildfire situations by coating vulnerable constructions to mitigate fireplace growth. The limited water supplies related to distant wildfire areas means that the useful resource may be absolutely optimised. However, as with balanced strain proportioner foam pumps, an additional point of failure is possible as a result 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 technology, the product is only 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 concentrate through an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning fee and can proportion the foam focus precisely across a wide operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, completely 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 embody:
Reduced prices: proportioning price is examined without utilizing foam or creating premix or foam – value effective and eco-friendly.
Improved efficiency: fixed proportioning price across a large working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in strain loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a different proportioning fee.
FM accredited FireDos Gen III proportioners are thus far the only FM accredited water motor coupled variable proportioners utilizing FM accredited flow meters. Using the check return line this offers the possibility to check the proportioning price throughout commissioning as nicely as for annual checks, with out creating any premix, which is a really massive benefit for the user and relieves the surroundings.
In the second a half of this feature we’ll explore the results of viscosity on foam proportioning and typical foam application areas and beneficial discharge devices.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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