Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given fireplace state of affairs. Our objective in this two-part article is to supply steering primarily based on a hazard-specific method and allow you to make an knowledgeable decision on appropriate fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorized 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 typically related to cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting monitors, we specialise mainly within the Class B class: flammable liquids.
Foam is considered to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only might not penetrate the hearth load effectively.
Fire classes.
How will we make foam?
Finished foam resolution comprises a easy recipe of froth focus, water and air. Foam focus is usually blended in the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge gadget – we are going to cover proportioning later in this article and discharge strategies in Part 2. At this level air is entrained by utilizing devices designed to naturally aspirate the solution. The quantity of aspiration and the type of focus determines the growth 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 high expansion is greater than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to expand the froth adequately, though naturally aspirated generators are additionally used. The determination to choose a particular expansion ratio is decided by the hazard underneath evaluate.
Put merely, water and oil don’t mix. Applying only water to Class B products is not going to suppress the burning vapours. This is a vital point to make as it’s the vapours, not the liquid itself, that burns. We need a medium that enables 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 movie, the objective is identical.
Steps of froth era Images provided by Author / Contributor
A little of the history of foam development
We can date the event of contemporary foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the base component). The main downside was because of limited fuel tolerance, which meant it was vulnerable to fuel pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, synthetic detergents gave foam a larger gas tolerance in addition to forming a vapour-sealing film throughout the floor of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s development did not utterly substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat gas pick-up (mixing) and supply an excellent resistance to warmth, outlined by the business as ‘burn-back resistance’.
Further improvement within the Eighties took FP to the next level with film-forming fluoroprotein or FFFP. We now had the best of each worlds: a film-forming foam that also 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 always presented an additional problem as they have been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same technology also became out there with the new generation of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has become an environmental issue, because of persistence in groundwater. The trade has been introduced with a significant challenge to get rid of the ‘fluoro’ component of all of the totally different foam focus varieties. We have witnessed an period of manufacturers’ claims and counter claims concerning 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 selection for operators changing existing stock or reviewing new tasks. As a foam proportioner producer we should examine the physical properties of froth rigorously (especially viscosity) as they influence selections on the overall proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are more and more essential within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant 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 finest way of comparing their claims is to familiarise yourself with the empirically based normal EN 1568 or UL162. เกจวัดแรงดันแก๊สlpg , foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the more demanding polar solvents are each included in the check protocols. This additionally covers fresh and seawater as properly as gentle and forceful utility of the foam. Each foam is given a rating with IA being the best, IIID the worst. This means you could challenge foam suppliers to have the ability to make an informed decision on the best foam on your wants.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the results on foam efficiency from factors exterior the usual tests 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 application technique, gasoline depth and so forth. Our recommendation could be to grasp the details of the tests and attempt to match them to the foam’s appropriateness for your individual hazards. We would always suggest consulting individual foam producers as they can often present particular in-house fire-performance data in opposition to some of the more uncommon fuels.
However, regardless of the foam manufacturers’ typically conflicting claims on performance, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the expansion ratio Images supplied by Author / Contributor
Critical factors for fulfillment: the time and application rate 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 mostly requirements printed by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor signifies that for a given dimension of fire area it’s essential to apply the foam for lengthy sufficient to achieve 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 involves fixed protection for hydrocarbon and polar solvent tanks, the appliance time can be as lengthy as 60 minutes for the largest tank diameters.
The utility rate refers to the quantity of finished foam utilized per sq. metre. This varies according to the fuel and the froth type but is at present a minimal of 4.0 litres per minute per sq. metre. One of the ongoing developments in foam performance is the likelihood that this shall be decreased, however requirements usually take time to recognise product improvement. Anything less than the minimum utility price signifies that fire control is unlikely to be achieved. This implies that firefighting sources, particularly in a manual fireplace assault, must be assembled earlier than firefighting commences and this takes time. The benefit in fitting fixed methods is that the sources are already designed and built into the system for quick application.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to permit readers to make an informed determination on how finest to deal with their explicit fireplace challenges, the next is an summary of the various foam proportioning strategies.
Foam inductors:
Typically related to fire service deployment and restricted fastened systems functions. This makes use of the venturi principle to create a strain drop in a small aluminium or seawater material suitable 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 solution. Both the pick-up tube and body of the inductor are compact sufficient to be simply carried on a fire equipment or fitted into a pipework system.
However, whilst it’s thought-about to be the only method, it has extreme drawbacks: (i) items are factory calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a altering quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter modifications will adversely have an effect on proportioning accuracy and probably prevent any proportioning; (iii) changes in focus viscosity will undermine the flexibility of the venturi to attract focus into the downstream traces; (iv) stress loss is excessive, as a lot as 35%, so responsibility pump pressures must be high sufficient to allow for it, probably including additional price into the system; (v) foam supply units need to be sized in order not to restrict design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices as a outcome of foam focus utilization, which must be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electric or a mixture of electric and diesel pumps to supply foam focus right into a proportioner at a higher pressure than the incoming water-line strain. The proportioner is installed into the water line and regulates the mixing.
They are actually associated with older methods, where disadvantages include: (i) further costs in hardware and design time; (ii) the foam pump is generally restricted to a a lot tighter working range, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs an additional energy supply, apart from water, so isn’t as reliably secure as a system with a possible single level of failure, similar to a wholly water-driven system; (iv) usually, these techniques are very advanced and cause excessive efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to break the froth focus and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth filled bladder so that foam focus may be proportioned with water utilizing the same provide. The venturi precept is again brought into play because it creates a strain drop at the point of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs on account of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a result of nice care is required to keep away from a broken bladder when commissioning a new set up. It is rarely straightforward to work throughout the steel stress vessel ought to problems happen, particularly if and when a replacement bladder could also be required: it all adds to the difficulty and value.
Compressed air foam (CAFS):
This isn’t a proportioning method within the standard sense as the foam is already proportioned utilizing one of many previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam answer on the point of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces allowing higher penetration and cooling. This can be a profit in wildfire conditions by coating vulnerable structures to mitigate fireplace development. The limited water provides associated with distant wildfire areas means that the useful resource can be absolutely optimised. However, as with balanced stress proportioner foam pumps, an additional point of failure is possible as a result of further CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is purely mechanical and highly reliable. A water-driven rotor provides the motive force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam focus through an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning rate and will proportion the froth focus precisely throughout a large operating vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning fee testing, fully without utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners embody:
Reduced costs: proportioning fee is examined with out utilizing foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: constant proportioning fee throughout a wide operating range.
Optimised delivery 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 straightforward and fast adjustment to a special proportioning fee.
FM permitted FireDos Gen III proportioners are thus far the only FM permitted water motor coupled variable proportioners using FM permitted move meters. Using the check return line this presents the likelihood to examine the proportioning price throughout commissioning as properly as for annual exams, without creating any premix, which is a really huge benefit for the person and relieves the setting.
In the second a half of this function we will discover the consequences of viscosity on foam proportioning and typical foam application areas and beneficial discharge gadgets.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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