A information to foam and foam proportioning tools – Part 1

Fire presents many challenges, not least because of the variables that decide which suppression medium is suitable for a given hearth scenario. Our objective in this two-part article is to provide steerage based mostly on a hazard-specific strategy and allow you to make an knowledgeable choice on applicable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or combustible 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 producer of foam proportioners and firefighting screens, we specialise primarily within the Class B category: flammable liquids.
Foam is considered 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 might not penetrate the fire load effectively.
Fire courses.
How can we make foam?
Finished foam resolution comprises a simple recipe of foam concentrate, water and air. Foam concentrate is typically mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge device – we’ll cowl proportioning later on this article and discharge methods in Part 2. At this level air is entrained through the use of gadgets designed to naturally aspirate the solution. The quantity of aspiration and the sort of concentrate determines the expansion ratio. This is often cut up between low, medium and high enlargement. Low enlargement is up to 20:1, medium is 200:1 and excessive expansion is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to broaden the froth adequately, although naturally aspirated mills are additionally used. The choice to decide on a selected enlargement ratio is decided by the hazard under review.
Put simply, water and oil do not mix. Applying only water to Class B merchandise will not 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 permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to achieve success. Whatever method is chosen to supply that blanket or film, the target is identical.
Steps of foam era Images provided by Author / Contributor
A little of the history of froth growth
We can date the event of modern foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the base component). The primary disadvantage was as a end result of limited gas tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a greater fuel tolerance in addition to forming a vapour-sealing movie throughout the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth didn’t fully exchange the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam may both combat gas pick-up (mixing) and offer a great resistance to warmth, outlined by the trade as ‘burn-back resistance’.
Further improvement within 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 also had good burn-back resistance.
The Eighties additional added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented an additional problem as they had been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same know-how additionally became obtainable with the new technology of AFFF-ARs.
In current years fluorine, one of the cornerstone elements to all foams, has turn into an environmental issue, because of persistence in groundwater. The business has been offered with a significant challenge to remove the ‘fluoro’ component of all of the totally different foam concentrate types. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of an entire range of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn out to be the new regular and first selection for operators changing existing inventory or reviewing new projects. As a foam proportioner manufacturer we should look at the bodily properties of foam carefully (especially viscosity) as they influence decisions on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are increasingly essential 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 critical to fight the small degree of water miscibility of the gas.
All foam concentrate manufacturers will naturally promote their product as being extremely efficient. The best method of comparing their claims is to familiarise your self with the empirically primarily based standard EN 1568 or UL162. The exams cover 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 within the take a look at protocols. This additionally covers contemporary and seawater in addition to mild and forceful software of the foam. Each foam is given a ranking with IA being the best, IIID the worst. This means you could challenge foam suppliers to find a way to make an knowledgeable determination on the best foam in your wants.
Whilst EN 1568 is a wonderful benchmark commonplace, consciousness of the effects on foam performance from factors exterior the standard tests ought to be noted. For instance, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the applying method, fuel depth and so on. Our advice can be to understand the small print of the checks and try to match them to the foam’s appropriateness in your individual hazards. We would always suggest consulting individual foam producers as they can often present particular in-house fire-performance knowledge against a few of the more unusual fuels.
However, despite the foam manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the growth ratio Images supplied by Author / Contributor
Critical factors for success: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the rate at which completed foam is utilized. Both are determined by empirically based standards published by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given dimension of fireplace area it is necessary to use the froth for long sufficient to achieve extinction and to forestall re-ignition. This is especially important in manual intervention as firefighter’s might be at risk during post-fire operations. When it involves mounted protection for hydrocarbon and polar solvent tanks, the applying time may be so long as 60 minutes for the largest tank diameters.
The application rate refers back to the amount of completed foam applied per sq. metre. This varies based on the gasoline and the froth kind however is at present no less than 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 standards typically take time to recognise product improvement. Anything less than the minimum application fee means that fireplace management is unlikely to be achieved. This means that firefighting resources, particularly in a guide fireplace attack, need to be assembled before firefighting commences and this takes time. The benefit in fitting fixed systems is that the sources are already designed and built into the system for quick application.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to permit readers to make an knowledgeable decision on how best to sort out their explicit fire challenges, the following is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically associated with fireplace service deployment and limited fastened systems purposes. This uses the venturi principle to create a strain drop in a small aluminium or seawater material suitable device 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 resolution. Both the pick-up tube and body of the inductor are compact enough to be easily carried on a hearth equipment or fitted right into a pipework system.
However, whilst it is considered to be the best method, it has severe drawbacks: (i) units are factory calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are crucial as deviations attributable to pipe diameter changes will adversely have an effect on proportioning accuracy and potentially prevent any proportioning; (iii) changes in concentrate viscosity will undermine the ability of the venturi to draw focus into the downstream strains; (iv) pressure loss is excessive, as much as 35%, so responsibility pump pressures have to be high enough to permit for it, probably including extra cost into the system; (v) foam supply gadgets must be sized so as not to restrict design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime costs because of foam concentrate usage, which needs to be changed, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced strain proportioners:
These use an electric or a mixture of electric and diesel pumps to produce foam concentrate right into a proportioner at a higher strain than the incoming water-line strain. The proportioner is put in into the water line and regulates the mixing.
They at the moment are associated with older techniques, where disadvantages embody: (i) additional costs in hardware and design time; (ii) the foam pump is normally restricted to a much tighter working vary, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump wants a further power supply, 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) usually, these techniques are very complex and trigger excessive 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 turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner much like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth filled bladder so that foam concentrate can be proportioned with water utilizing the identical supply. The venturi precept is once more brought into play as it creates a stress drop at the level of injection for the froth focus. Testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs because of foam focus utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is needed to avoid a broken bladder when commissioning a brand new set up. It isn’t simple to work inside the steel strain vessel ought to issues occur, especially if and when a replacement bladder may be required: it all adds to the problem and price.
Compressed air foam (CAFS):
This just isn’t a proportioning method within the typical sense as the froth is already proportioned using one of the previous strategies. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth answer on 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 conditions by coating vulnerable buildings to mitigate hearth progress. The limited water provides related to remote wildfire areas signifies that the resource may be fully optimised. However, as with balanced strain proportioner foam pumps, a further level of failure is possible because of the additional CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in เกจวัดแรงกด , the product is purely mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and can proportion the froth focus accurately throughout a large working range. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, fully with out using any foam concentrate 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 embrace:
Reduced costs: proportioning rate is tested without using foam or creating premix or foam – value effective and eco-friendly.
Improved performance: constant proportioning rate across a large operating range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in stress loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a unique proportioning fee.
FM approved FireDos Gen III proportioners are thus far the only FM permitted water motor coupled variable proportioners using FM approved flow meters. Using the test return line this offers the chance to examine the proportioning price during commissioning as nicely as for annual exams, without creating any premix, which is a really big profit for the user and relieves the surroundings.
In the second part of this function we will discover the results of viscosity on foam proportioning and typical foam utility areas and recommended discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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