A guide to foam and foam proportioning tools – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is suitable for a given hearth state of affairs. Our goal on this two-part article is to supply guidance based on a hazard-specific approach and help you make an informed choice on acceptable 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 corresponding to magnesium
Class F – fires usually associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting screens, we specialise mainly 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 forms of foam (known as wetting agents) are specifically 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 foam concentrate, water and air. Foam focus is usually combined within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge gadget – we are going to cowl proportioning later on this article and discharge methods in Part 2. At this point air is entrained through the use of units designed to naturally aspirate the solution. The amount of aspiration and the sort of focus determines the expansion ratio. This is usually cut up between low, medium and excessive enlargement. Low growth is as much as 20:1, medium is 200:1 and high enlargement is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to expand the froth adequately, though naturally aspirated turbines are additionally used. The choice to choose a specific growth ratio is set by the hazard under evaluation.
Put simply, water and oil don’t combine. Applying only water to Class B products is not going to suppress the burning vapours. This is a vital level to make as it is the vapours, not the liquid itself, that burns. We need a medium that allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to achieve success. Whatever technique is chosen to provide that blanket or film, the target is identical.
Steps of froth era Images supplied by Author / Contributor
A little of the historical past of foam growth
We can date the event of modern foam concentrates from the Sixties onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The primary downside was due to limited gasoline tolerance, which meant it was susceptible to gasoline pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, artificial detergents gave foam a higher gas tolerance as well as forming a vapour-sealing movie across the floor of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s improvement did not fully substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat fuel pick-up (mixing) and provide an excellent resistance to warmth, defined by the business as ‘burn-back resistance’.
Further improvement within the Eighties took FP to the following degree with film-forming fluoroprotein or FFFP. We now had the most effective of both worlds: a film-forming foam that also had good burn-back resistance.
The Eighties additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always offered an extra challenge as they have been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The same know-how also grew to become available with the model new generation of AFFF-ARs.
In current years fluorine, one of many cornerstone elements to all foams, has turn into an environmental issue, because of persistence in groundwater. The trade has been offered with a major problem to get rid of the ‘fluoro’ factor of all the totally different foam concentrate types. We have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of an entire 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 turn out to be the new regular and first selection for operators altering existing stock or reviewing new initiatives. As a foam proportioner producer we must examine the physical properties of froth fastidiously (especially viscosity) as they influence decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are more and more essential in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is important to fight the small diploma of water miscibility of the gasoline.
All foam concentrate manufacturers will naturally promote their product as being highly efficient. The greatest method of comparing their claims is to familiarise yourself with the empirically based mostly commonplace EN 1568 or UL162. The exams cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the more demanding polar solvents are both included in the test protocols. This also covers recent and seawater in addition to light and forceful utility of the foam. Each foam is given a rating with IA being the best, IIID the worst. This means you could problem foam suppliers to find a way to make an informed choice on the best foam in your needs.
Whilst EN 1568 is a superb benchmark normal, consciousness of the effects on foam performance from components outdoors the usual tests must be noted. For instance, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by totally different ambient air temperatures, the applying method, gas depth etc. Our advice could be to understand the primary points 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 manufacturers as they’ll typically provide particular in-house fire-performance knowledge against a number of the more uncommon fuels.
However, despite the froth manufacturers’ sometimes conflicting claims on performance, the sooner 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 factors for fulfillment: the time and application fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the rate at which completed foam is utilized. Both are decided by empirically based requirements printed by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given size of fireside space it’s necessary to apply the froth for long enough to attain extinction and to forestall re-ignition. This is particularly important in manual intervention as firefighter’s will be in danger during post-fire operations. When it involves mounted safety for hydrocarbon and polar solvent tanks, the application time could be so long as 60 minutes for the most important tank diameters.
The utility fee refers back to the quantity of finished foam utilized per sq. metre. This varies in accordance with the fuel and the foam type however is currently a minimal of four.0 litres per minute per sq. metre. One of the continuing developments in foam performance is the chance that this will be reduced, however requirements typically take time to recognise product growth. Anything lower than the minimum application price means that fireplace control is unlikely to be achieved. This implies that firefighting sources, significantly in a handbook fire attack, have to be assembled earlier than firefighting commences and this takes time. The benefit in becoming mounted methods is that the assets are already designed and built into the system for instant application.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an informed choice on how greatest to tackle their particular hearth challenges, the following is an summary of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with fireplace service deployment and limited fastened techniques applications. This uses the venturi principle to create a strain drop in a small aluminium or seawater materials suitable gadget with built-in focus pick-up tube. The pressure drop created by the venturi attracts the froth concentrate from a container where it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a hearth equipment or fitted into a pipework system.
However, whilst it’s considered to be the best technique, it has extreme drawbacks: (i) units are factory calibrated so any changes 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 caused by pipe diameter modifications will adversely affect proportioning accuracy and doubtlessly forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the flexibility of the venturi to draw focus into the downstream traces; (iv) pressure loss is high, as much as 35%, so responsibility pump pressures have to be high sufficient to permit for it, potentially including further cost into the system; (v) foam supply devices have to be sized in order not to restrict design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs because of foam concentrate usage, which has to be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electrical or a combination of electric and diesel pumps to provide foam concentrate into a proportioner at the next strain than the incoming water-line pressure. The proportioner is installed into the water line and regulates the blending.
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 often restricted to a much tighter working range, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants an extra power supply, aside from water, so isn’t as reliably safe as a system with a possible single level of failure, corresponding to a wholly water-driven system; (iv) typically, these methods are very complicated and cause 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 wreck the froth concentrate and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel stress vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner much like those fitted to balanced strain proportioners. เกจปรับแรงดันแก๊ส compresses the froth filled bladder in order that foam concentrate may be proportioned with water utilizing the same provide. The venturi principle is again brought into play because it creates a pressure drop at the point of injection for the froth concentrate. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime costs on account of foam focus usage, which must be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because nice care is needed to keep away from a broken bladder when commissioning a brand new set up. It isn’t straightforward to work inside the steel stress vessel should issues happen, especially if and when a substitute bladder could additionally be required: all of it provides to the issue and price.
Compressed air foam (CAFS):
This isn’t a proportioning methodology within the standard sense as the froth is already proportioned utilizing one of the earlier 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 resolution on the level 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 can also be a profit in wildfire conditions by coating vulnerable structures to mitigate fire development. The restricted water supplies associated with remote wildfire areas means that the useful resource may be absolutely optimised. However, as with balanced stress proportioner foam pumps, an additional level of failure is possible because of the extra CAFS equipment.
Water pushed 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 solely mechanical and highly dependable. A water-driven rotor supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped 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 will proportion the froth concentrate precisely throughout a large operating range. The purely mechanical system offers cost-efficient and eco-friendly proportioning price testing, completely without 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 accredited foam proportioners embrace:
Reduced prices: proportioning fee is examined with out using foam or creating premix or foam – value effective and eco-friendly.
Improved performance: fixed proportioning fee across a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% discount in stress loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a special proportioning rate.
FM permitted FireDos Gen III proportioners are so far the only FM permitted water motor coupled variable proportioners using FM approved move meters. Using the check return line this offers the chance to verify the proportioning price throughout commissioning in addition to for annual checks, without creating any premix, which is a very massive profit for the person and relieves the environment.
In the second a half of this characteristic we’ll discover the consequences of viscosity on foam proportioning and typical foam software areas and really helpful discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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