A information to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given fireplace situation. Our goal on this two-part article is to supply steering based on a hazard-specific method and allow you to make an knowledgeable choice on appropriate fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires generally associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily in the Class B class: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely might not penetrate the fire load effectively.
Fire courses.
How can we make foam?
Finished foam answer includes a easy recipe of froth concentrate, water and air. Foam concentrate is often blended in the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge system – we’ll cover proportioning later in this article and discharge methods in Part 2. At this point air is entrained by utilizing units designed to naturally aspirate the answer. The quantity of aspiration and the kind of focus 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 high enlargement is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated generators are also used. The choice to choose on a particular enlargement ratio is determined by the hazard underneath review.
Put merely, water and oil don’t mix. Applying solely water to Class B products will not suppress the burning vapours. This is an important 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 movie to be successful. Whatever technique is chosen to supply that blanket or film, the objective is similar.
Steps of foam generation Images provided by Author / Contributor
A little of the history of foam growth
We can date the development of recent foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the bottom component). The main drawback was as a outcome of restricted fuel tolerance, which meant it was susceptible 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, artificial detergents gave foam a higher gasoline tolerance in addition to forming a vapour-sealing movie throughout the floor of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth didn’t completely substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight 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 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 Nineteen Eighties additional added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always presented an additional problem as they had been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The identical technology also turned out there with the new technology of AFFF-ARs.
In current years fluorine, one of many cornerstone components to all foams, has turn out to be an environmental concern, as a result of persistence in groundwater. The industry has been presented with a serious problem to remove the ‘fluoro’ factor of all of the completely different foam concentrate types. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a whole range of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the new regular and first choice for operators changing present inventory or reviewing new initiatives. As a foam proportioner manufacturer we must look at the physical properties of foam carefully (especially viscosity) as they affect selections on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more important within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant high quality of SFFF/F3 is critical to combat the small diploma of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being extremely effective. The finest way of evaluating their claims is to familiarise yourself with the empirically based normal EN 1568 or UL162. The checks cowl 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 within the check protocols. This additionally covers fresh and seawater as nicely as mild and forceful utility of the froth. Each foam is given a ranking with IA being the most effective, IIID the worst. This means that you can problem foam suppliers in order to make an informed choice on the best foam on your wants.
Whilst EN 1568 is a superb benchmark standard, consciousness of the consequences on foam efficiency from factors exterior the standard tests must be famous. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of certain foams. This may be exacerbated by completely different ambient air temperatures, the applying technique, fuel depth and so on. Our recommendation could be to know the primary points of the tests and attempt to match them to the foam’s appropriateness on your individual hazards. We would always recommend consulting particular person foam manufacturers as they can usually provide particular in-house fire-performance information in opposition to a few of the more uncommon fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the growth ratio Images provided by Author / Contributor
Critical elements for achievement: the time and software rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the rate at which finished foam is applied. Both are determined by empirically based standards printed by our bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor signifies that for a given measurement of fireside area it’s necessary to use the foam for lengthy sufficient to attain extinction and to stop re-ignition. This is particularly important in guide intervention as firefighter’s might be at risk throughout post-fire operations. When it involves mounted safety for hydrocarbon and polar solvent tanks, the appliance time can be as long as 60 minutes for the biggest tank diameters.
The software rate refers again to the quantity of completed foam utilized per sq. metre. This varies according to the fuel and the froth sort but is presently no less than 4.0 litres per minute per square metre. One of the continued developments in foam performance is the likelihood that this shall be lowered, but standards often take time to recognise product improvement. เกจวัดแรงดันสูญญากาศ than the minimal application rate means that fireplace control is unlikely to be achieved. This implies that firefighting sources, particularly in a manual hearth attack, have to be assembled earlier than firefighting commences and this takes time. The benefit in becoming fastened techniques is that the resources are already designed and built into the system for immediate software.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an informed decision on how best to tackle their explicit fireplace challenges, the following is an summary of the assorted foam proportioning strategies.
Foam inductors:
Typically related to fire service deployment and limited fastened systems purposes. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater materials suitable gadget with built-in focus pick-up tube. The stress drop created by the venturi attracts the foam concentrate from a container where it mixes with water to create foam resolution. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a hearth appliance or fitted right into a pipework system.
However, while it’s thought-about to be the only method, it has extreme drawbacks: (i) models are factory calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a altering quantity 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 have an result on proportioning accuracy and probably forestall any proportioning; (iii) modifications in focus viscosity will undermine the power of the venturi to draw focus into the downstream lines; (iv) strain loss is excessive, as a lot as 35%, so duty pump pressures must be high enough to permit for it, probably adding further price into the system; (v) foam delivery devices need to be sized in order to not prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime prices on account of foam concentrate utilization, which must be replaced, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electric or a combination of electric and diesel pumps to produce foam concentrate into a proportioner at a better pressure than the incoming water-line pressure. The proportioner is put in into the water line and regulates the blending.
They are actually related to older techniques, the place disadvantages include: (i) additional prices in hardware and design time; (ii) the foam pump is generally restricted to a a lot tighter operating vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants an extra energy supply, other than water, so just isn’t as reliably secure as a system with a possible single level of failure, similar to a wholly water-driven system; (iv) typically, these systems are very advanced and trigger excessive efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless 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 steel pressure vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner similar to those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam concentrate could be proportioned with water utilizing the identical supply. The venturi precept is again brought into play because it creates a strain drop on the point of injection for the foam concentrate. Testing can’t be achieved with out creating premix and discharging completed foam. This will add to entire lifetime prices because of foam concentrate usage, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is required to keep away from a broken bladder when commissioning a brand new installation. It is rarely straightforward to work throughout the steel pressure vessel ought to problems occur, especially if and when a replacement bladder could also be required: all of it adds to the issue and value.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology within the conventional sense as the foam is already proportioned using one of many earlier strategies. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth resolution at the level of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces allowing higher penetration and cooling. This can be a profit in wildfire situations by coating weak constructions to mitigate fire progress. The limited water supplies related to distant wildfire areas means that the resource could be fully optimised. However, as with balanced strain proportioner foam pumps, a further level of failure is possible because of the extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is purely mechanical and highly dependable. A water-driven rotor provides the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied 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 precisely across a large operating range. The purely mechanical system offers cost-efficient and eco-friendly proportioning fee testing, fully with out using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The benefits of FireDos Gen III FM approved foam proportioners include:
Reduced prices: proportioning fee is tested without using foam or creating premix or foam – cost effective and eco-friendly.
Improved efficiency: fixed proportioning fee throughout a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in stress loss, in comparison with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a different proportioning rate.
FM accredited FireDos Gen III proportioners are thus far the only FM approved water motor coupled variable proportioners utilizing FM permitted flow meters. Using the test return line this offers the possibility to check the proportioning fee throughout commissioning as properly as for annual exams, with out creating any premix, which is a very big profit for the person and relieves the environment.
In the second part of this function we are going to explore the effects of viscosity on foam proportioning and typical foam application areas and beneficial discharge units.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky

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