A guide to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is acceptable for a given fireplace scenario. Our goal on this two-part article is to supply steerage primarily based on a hazard-specific approach and help you make an knowledgeable choice on acceptable fire-suppression measures, particularly 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 usually associated with cooking similar 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 considered to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely may not penetrate the fire load effectively.
Fire courses.
How can we make foam?
Finished foam answer comprises a easy recipe of foam focus, water and air. Foam concentrate is usually 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’ll cowl proportioning later on this article and discharge methods in Part 2. At this point air is entrained by using units designed to naturally aspirate the answer. The quantity of aspiration and the kind of concentrate determines the growth ratio. This is often split between low, medium and high growth. Low growth is as a lot as 20:1, medium is 200:1 and excessive growth 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 turbines are additionally used. The decision to choose a specific growth ratio is determined by the hazard underneath evaluation.
Put simply, water and oil don’t mix. Applying solely water to Class B merchandise is not going to suppress the burning vapours. This is an important level 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 movie to be successful. Whatever technique is chosen to provide that blanket or movie, the target is similar.
Steps of foam generation Images equipped by Author / Contributor
A little of the historical past of foam improvement
We can date the event of recent 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 bottom component). The main downside was because of restricted 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 larger fuel tolerance in addition to forming a vapour-sealing film across the surface of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s development did not utterly replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight fuel pick-up (mixing) and offer a good resistance to warmth, defined by the business as ‘burn-back resistance’.
Further improvement in the Eighties took FP to the subsequent stage with film-forming fluoroprotein or FFFP. We now had one of the best of both worlds: a film-forming foam that additionally had good burn-back resistance.
The Eighties further added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented an additional challenge as they had been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar know-how also grew to become out there with the new generation of AFFF-ARs.
In latest years fluorine, one of many cornerstone ingredients to all foams, has turn out to be an environmental issue, because of persistence in groundwater. The industry has been offered with a serious problem to eliminate the ‘fluoro’ element of all of the totally different foam focus varieties. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of an entire 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 model new regular and first selection for operators altering present inventory or reviewing new projects. As a foam proportioner manufacturer we must study the physical properties of foam rigorously (especially viscosity) as they influence decisions on the general proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are increasingly necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small degree of water miscibility of the gasoline.
เกจวัดแก๊สlpg will naturally promote their product as being highly effective. The best method of comparing their claims is to familiarise yourself with the empirically primarily based standard EN 1568 or UL162. The checks cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included in the take a look at protocols. This also covers contemporary and seawater in addition to light 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 could challenge foam suppliers so as to make an knowledgeable determination on the most effective foam in your wants.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the effects on foam performance from elements outdoors the usual tests should 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 applying method, gasoline depth etc. Our advice can be to know the details of the tests and try to match them to the foam’s appropriateness in your particular person hazards. We would always advocate consulting particular person foam producers as they will usually present specific in-house fire-performance knowledge in opposition to a number of the extra uncommon fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on efficiency, 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 equipped by Author / Contributor
Critical elements for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary elements: time and the rate at which finished foam is applied. Both are determined 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 requirements.
The ‘time’ issue signifies that for a given size of fireside area it is needed to apply the foam for long sufficient to achieve extinction and to prevent re-ignition. This is particularly crucial in guide intervention as firefighter’s might be in danger throughout post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the application time can be as lengthy as 60 minutes for the largest tank diameters.
The application price refers back to the amount of finished foam utilized per sq. metre. This varies according to the fuel and the froth sort however is currently no less than four.zero litres per minute per square metre. One of the continued developments in foam efficiency is the chance that this might be lowered, but standards often take time to recognise product growth. Anything less than the minimum software fee means that hearth management is unlikely to be achieved. This means that firefighting resources, notably in a guide fireplace attack, need to be assembled earlier than firefighting commences and this takes time. The benefit in fitting fixed techniques is that the resources are already designed and built into the system for instant utility.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an knowledgeable determination on how best to sort out their particular hearth challenges, the next is an overview of the various foam proportioning methods.
Foam inductors:
Typically associated with fireplace service deployment and restricted mounted systems purposes. This makes use of the venturi precept to create a pressure drop in a small aluminium or seawater material appropriate device with built-in focus pick-up tube. The pressure drop created by the venturi attracts the foam 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 hearth equipment or fitted right into a pipework system.
However, while it’s thought-about to be the simplest methodology, it has extreme drawbacks: (i) models are manufacturing unit calibrated so any adjustments to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a altering amount of discharge devices) will probably require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter adjustments will adversely affect proportioning accuracy and potentially stop any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to draw focus into the downstream strains; (iv) stress loss is high, as a lot as 35%, so responsibility pump pressures have to be high enough to permit for it, doubtlessly including further price into the system; (v) foam delivery devices need to be sized in order not to limit design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to whole lifetime prices as a outcome of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced stress proportioners:
These use an electrical or a combination of electrical and diesel pumps to produce foam focus right into a proportioner at a better stress than the incoming water-line strain. The proportioner is put in into the water line and regulates the mixing.
They at the second are related to older techniques, where disadvantages embrace: (i) additional prices in hardware and design time; (ii) the froth pump is often restricted to a much tighter operating vary, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants a further power supply, apart from water, so just isn’t as reliably safe as a system with a potential single point of failure, corresponding to a completely water-driven system; (iv) sometimes, these techniques are very advanced and trigger high efforts on 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 froth focus and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal stress vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced stress proportioners. The incoming pressurised water compresses the froth filled bladder in order that foam focus may be proportioned with water using the same supply. The venturi principle is once more brought into play as it creates a strain drop at the point of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime prices 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 end result of nice care is required to avoid a broken bladder when commissioning a model new installation. It is rarely simple to work inside the steel stress vessel should issues happen, particularly if and when a substitute bladder could additionally be required: all of it adds to the difficulty and value.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology within the conventional sense as the foam is already proportioned utilizing one of many previous strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the foam answer on the point of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces allowing better penetration and cooling. This can be a profit in wildfire conditions by coating susceptible structures to mitigate hearth progress. The restricted water provides related to distant wildfire areas means that the useful resource may be absolutely optimised. However, as with balanced stress proportioner foam pumps, an extra point of failure is feasible as a end result of further CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is solely mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and can proportion the foam concentrate precisely across a wide operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate testing, fully without using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners embrace:
Reduced costs: proportioning price is tested with out using foam or creating premix or foam – value effective and eco-friendly.
Improved efficiency: fixed proportioning rate across a wide working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in pressure loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a different proportioning rate.
FM approved FireDos Gen III proportioners are thus far the only FM permitted water motor coupled variable proportioners using FM permitted flow meters. Using the take a look at return line this presents the chance to examine the proportioning fee during commissioning in addition to for annual tests, without creating any premix, which is a really huge benefit for the user and relieves the setting.
In the second part of this function we’ll discover the effects of viscosity on foam proportioning and typical foam utility areas and really helpful discharge gadgets.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share

Scroll to Top