A guide to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fireplace situation. Our objective on this two-part article is to provide steering based on a hazard-specific approach and assist 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 classified as follows:
Class A – carbonaceous or combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires usually related to cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting monitors, we specialise primarily in the Class B category: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only could not penetrate the fire load effectively.
Fire lessons.
How do we make foam?
Finished foam resolution comprises a simple recipe of froth focus, water and air. Foam focus is often combined in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge system – we are going to cowl proportioning later on this article and discharge strategies in Part 2. At this level air is entrained through the use of devices designed to naturally aspirate the answer. The amount of aspiration and the type of concentrate determines the growth ratio. This is often break up between low, medium and high expansion. Low expansion is as much as 20:1, medium is 200:1 and high growth is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to increase the froth adequately, although naturally aspirated mills are additionally used. The choice to choose a specific expansion ratio is determined by the hazard underneath evaluate.
Put simply, water and oil don’t mix. Applying only water to Class B products is not going to suppress the burning vapours. This is a crucial level to make as it is the vapours, not the liquid itself, that burns. We want a medium that allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever technique is chosen to supply that blanket or film, the objective is identical.
Steps of foam generation Images supplied by Author / Contributor
A little of the history of foam growth
We can date the development of modern foam concentrates from the 1960s onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The primary disadvantage was as a result of limited fuel tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, synthetic detergents gave foam a higher gas tolerance as properly as forming a vapour-sealing film throughout the surface of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement did not utterly substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight fuel pick-up (mixing) and supply a good resistance to warmth, defined by the industry as ‘burn-back resistance’.
Further growth within the 1980s took FP to the subsequent level with film-forming fluoroprotein or FFFP. We now had one of the best of both worlds: a film-forming foam that also had good burn-back resistance.
The 1980s 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 were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar know-how also turned obtainable with the model new technology of AFFF-ARs.
In current years fluorine, one of the cornerstone elements to all foams, has become an environmental concern, because of persistence in groundwater. The business has been introduced with a serious problem to eliminate the ‘fluoro’ factor of all the different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of a complete vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn into the brand new regular and first alternative for operators changing present stock or reviewing new tasks. As a foam proportioner producer we must examine the bodily properties of foam rigorously (especially viscosity) as they affect choices on the overall proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly necessary in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant high quality of SFFF/F3 is important to combat the small degree of water miscibility of the gas.
All foam focus manufacturers will naturally promote their product as being extremely efficient. The greatest method of evaluating their claims is to familiarise your self with the empirically based mostly normal 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 check protocols. This additionally covers recent and seawater as properly as mild and forceful application of the foam. Each foam is given a score with IA being one of the best, IIID the worst. This means that you can problem foam suppliers in order to make an knowledgeable decision on the most effective foam on your wants.
Whilst EN 1568 is a superb benchmark commonplace, awareness of the consequences on foam performance from components outdoors the standard checks ought to be famous. For instance, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by totally different ambient air temperatures, the application method, gas depth and so forth. Our advice can be to know the details of the tests and attempt to match them to the foam’s appropriateness on your particular person hazards. We would all the time advocate consulting particular person foam producers as they will typically present particular in-house fire-performance data against a variety of the extra unusual fuels.
However, regardless of the froth manufacturers’ typically 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 according to the expansion ratio Images provided by Author / Contributor
Critical elements for fulfillment: the time and utility fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the speed at which completed foam is applied. Both are determined by empirically based requirements published by our bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given size of fireside area it is essential to apply the foam for lengthy sufficient to attain extinction and to forestall re-ignition. This is particularly important in guide intervention as firefighter’s shall be at risk during post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the application time may be so lengthy as 60 minutes for the largest tank diameters.
The software fee refers back to the quantity of completed foam applied per sq. metre. This varies in accordance with the gas and the foam type however is currently no much less than litres per minute per square metre. One of the continuing developments in foam efficiency is the chance that this shall be lowered, but requirements typically take time to recognise product improvement. Anything lower than the minimal software rate implies that fireplace control is unlikely to be achieved. This implies that firefighting resources, particularly in a manual fireplace assault, need to be assembled earlier than firefighting commences and this takes time. The advantage in fitting fastened methods is that the assets are already designed and constructed into the system for quick utility.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to permit readers to make an knowledgeable determination on how best to sort out their explicit fire challenges, the next is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically related to fire service deployment and limited fastened systems purposes. This uses the venturi principle to create a strain drop in a small aluminium or seawater materials compatible system with built-in focus pick-up tube. The strain drop created by the venturi draws the froth focus from a container where it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a hearth appliance or fitted into a pipework system.
However, whilst it is thought-about to be the best methodology, it has severe drawbacks: (i) models are factory calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a changing quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter adjustments will adversely have an result on proportioning accuracy and probably forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to draw concentrate into the downstream strains; (iv) strain loss is high, as a lot as 35%, so duty pump pressures have to be excessive enough to allow for it, probably adding extra price into the system; (v) foam delivery gadgets have to be sized in order not to restrict design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices as a outcome of foam concentrate usage, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mixture of electric and diesel pumps to provide foam concentrate into a proportioner at a better stress than the incoming water-line pressure. The proportioner is put in into the water line and regulates the blending.
They are now associated with older systems, where disadvantages embody: (i) additional prices in hardware and design time; (ii) the foam pump is generally restricted to a a lot tighter operating range, although the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump needs a further power source, other than water, so is not as reliably secure as a system with a potential single point of failure, such as a wholly water-driven system; (iv) sometimes, these methods are very complicated and trigger high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to wreck the froth focus and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal stress vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner much like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam focus can be proportioned with water using the identical supply. The venturi precept is once more brought into play because it creates a strain drop at the level of injection for the froth concentrate. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs because 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 needed to avoid a damaged bladder when commissioning a new set up. It is never straightforward to work within the metal strain vessel should issues happen, particularly if and when a replacement bladder may be required: all of it provides to the difficulty and price.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology within the standard sense as the froth is already proportioned utilizing one of many previous strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As compound gauge ราคา identify suggests, CAFS injects compressed air into the froth solution at the level of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces permitting better penetration and cooling. This can also be a profit in wildfire situations by coating vulnerable structures to mitigate fireplace progress. The restricted water provides associated with remote wildfire areas signifies that the useful resource can be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an additional point of failure is possible as a end result of additional CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their unique water-driven foam proportioner. Now in its third era, the product is solely mechanical and highly dependable. A water-driven rotor provides the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is equipped with foam focus by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning fee and can proportion the foam concentrate accurately throughout a large working vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning fee testing, completely with out 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 approved foam proportioners embody:
Reduced prices: proportioning rate is tested without using foam or creating premix or foam – value effective and eco-friendly.
Improved efficiency: fixed proportioning fee throughout a wide working range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in pressure loss, in comparability with older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning fee.
FM approved FireDos Gen III proportioners are so far the only FM accredited water motor coupled variable proportioners using FM approved circulate meters. Using the test return line this offers the possibility to examine the proportioning price during commissioning in addition to for annual tests, with out creating any premix, which is a very huge benefit for the user and relieves the environment.
In the second part of this characteristic we will explore the results of viscosity on foam proportioning and typical foam software areas and recommended discharge devices.
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Written by
David Owen
Andreas Hulinsky