A information to foam and foam proportioning equipment – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is appropriate for a given fireplace state of affairs. Our objective in this two-part article is to supply steerage based on a hazard-specific strategy and assist you to make an knowledgeable decision on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are classified as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires generally related to cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise mainly within the Class B class: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are specifically for deep-seated Class A fires where water solely might not penetrate the fire load effectively.
Fire lessons.
How will we make foam?
Finished foam solution includes a easy recipe of foam concentrate, water and air. Foam focus is typically mixed 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 device – 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 answer. The quantity of aspiration and the sort of focus determines the growth ratio. This is often break up between low, medium and high enlargement. Low growth is as a lot as 20:1, medium is 200:1 and excessive enlargement 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 generators are additionally used. The choice to choose on a specific expansion ratio is determined by the hazard under evaluation.
Put simply, water and oil don’t mix. Applying solely water to Class B merchandise won’t 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 film to achieve success. Whatever technique is chosen to provide that blanket or film, the objective is similar.
Steps of foam technology Images equipped by Author / Contributor
A little of the historical past of foam growth
We can date the development of modern foam concentrates from the 1960s onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the base component). The main disadvantage was because of restricted gas 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 bottom product, synthetic detergents gave foam a greater gasoline tolerance as nicely as forming a vapour-sealing movie throughout the surface of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth did not fully substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat fuel pick-up (mixing) and offer an excellent resistance to warmth, outlined by the business as ‘burn-back resistance’.
Further growth in the Nineteen Eighties took FP to the next level with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that also had good burn-back resistance.
The Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented an additional challenge as they had been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical expertise also grew to become available with the new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone ingredients to all foams, has turn out to be an environmental issue, due to persistence in groundwater. The industry has been offered with a major problem to remove the ‘fluoro’ element of all of the completely different foam focus types. We have witnessed an era of manufacturers’ claims and counter claims concerning the efficacy of a whole vary of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the model new normal and first alternative for operators changing present inventory or reviewing new tasks. As a foam proportioner producer we should look at the physical properties of froth rigorously (especially viscosity) as they affect selections on the general proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant sorts are more and more essential in the fuel-storage enviornment. 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 focus producers will naturally promote their product as being highly effective. The best method of comparing their claims is to familiarise your self with the empirically based normal EN 1568 or UL162. The checks 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 in the check protocols. This additionally covers recent and seawater as nicely as gentle and forceful software of the foam. Each foam is given a ranking with IA being the best, IIID the worst. This means that you can problem foam suppliers to find a way to make an informed decision on the best foam in your needs.
เกจ์วัดแรงดันลม is a superb benchmark commonplace, consciousness of the consequences on foam performance from factors outdoors the standard exams must be noted. For instance, notably aggressive solvents can problem the firefighting effectiveness of certain foams. This may be exacerbated by different ambient air temperatures, the application method, gasoline depth etc. Our advice can be to grasp the small print of the checks and attempt to match them to the foam’s appropriateness on your particular person hazards. We would at all times recommend consulting individual foam producers as they can usually provide specific in-house fire-performance knowledge in opposition to a few of the extra unusual fuels.
However, despite the froth manufacturers’ typically conflicting claims on performance, the earlier fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the enlargement ratio Images supplied by Author / Contributor
Critical components for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the speed at which finished foam is applied. Both are decided by empirically based standards revealed by our bodies such as 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 size of fireside space it is needed to use the froth for long enough to achieve extinction and to forestall re-ignition. This is very crucial in guide intervention as firefighter’s will be in danger throughout post-fire operations. When it involves fixed safety for hydrocarbon and polar solvent tanks, the appliance time could be as lengthy as 60 minutes for the most important tank diameters.
The software fee refers again to the quantity of completed foam utilized per square metre. This varies in accordance with the gasoline and the foam sort but is presently a minimum of four.zero litres per minute per square metre. One of the continued developments in foam performance is the likelihood that this will be decreased, however requirements typically take time to recognise product growth. Anything lower than the minimal application fee signifies that fireplace control is unlikely to be achieved. This means that firefighting sources, particularly in a handbook fireplace assault, must be assembled earlier than firefighting commences and this takes time. The advantage in becoming fastened systems is that the assets are already designed and built into the system for immediate software.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an knowledgeable decision on how greatest to deal with their explicit hearth challenges, the next is an outline of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with hearth service deployment and restricted fastened systems purposes. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater materials appropriate system with built-in focus pick-up tube. The stress drop created by the venturi draws the froth focus from a container where it mixes with water to create foam resolution. Both the pick-up tube and body of the inductor are compact enough to be simply carried on a fireplace appliance or fitted right into a pipework system.
However, while it is thought of to be the only technique, it has extreme drawbacks: (i) items are manufacturing unit calibrated so any modifications 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 probably require a system re-design; (ii) system design and sign-off are critical as deviations brought on by pipe diameter adjustments will adversely affect proportioning accuracy and potentially stop any proportioning; (iii) adjustments in focus viscosity will undermine the flexibility of the venturi to attract concentrate into the downstream lines; (iv) stress loss is excessive, as much as 35%, so duty pump pressures need to be excessive sufficient to permit for it, doubtlessly adding additional value into the system; (v) foam delivery gadgets have to be sized so as not to prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices because 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 mix of electric and diesel pumps to provide foam focus right into a proportioner at the next strain than the incoming water-line strain. The proportioner is installed into the water line and regulates the mixing.
They at the second are associated with older techniques, the place disadvantages include: (i) further prices in hardware and design time; (ii) the froth pump is normally restricted to a much tighter working range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an extra energy source, aside from water, so just isn’t as reliably secure as a system with a potential single point of failure, similar to a wholly water-driven system; (iv) usually, these techniques are very complex and trigger high efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to damage the foam focus and entrain air, which in flip can undermine correct 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 similar to the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the froth stuffed bladder in order that foam focus may be proportioned with water using the same supply. The venturi precept is once more brought into play as it creates a strain drop at the point of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs as a end result of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a end result of nice care is needed to avoid a broken bladder when commissioning a brand new installation. It is rarely straightforward to work inside the steel stress vessel should problems happen, particularly if and when a substitute bladder could additionally be required: it all provides to the difficulty and cost.
Compressed air foam (CAFS):
This is not a proportioning methodology 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 identify suggests, CAFS injects compressed air into the foam resolution on the point of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces allowing better penetration and cooling. This is also a profit in wildfire situations by coating weak structures to mitigate hearth progress. The limited water supplies associated with distant wildfire areas signifies that the resource could be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra level of failure is feasible because of the extra CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third generation, 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 supplied with foam focus via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning rate and can proportion the foam concentrate precisely across a wide working range. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, completely without utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The advantages of FireDos Gen III FM approved foam proportioners embody:
Reduced costs: proportioning fee is examined with out utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved performance: constant proportioning price across a wide working range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in strain loss, in comparability with older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a different proportioning rate.
FM accredited FireDos Gen III proportioners are thus far the only FM accredited water motor coupled variable proportioners using FM accredited move meters. Using the test return line this offers the chance to check the proportioning price throughout commissioning in addition to for annual tests, with out creating any premix, which is a very huge benefit for the person and relieves the surroundings.
In the second part of this function we’ll discover the results of viscosity on foam proportioning and typical foam application areas and recommended discharge devices.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky

Scroll to Top