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A information to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least due to the variables that decide which suppression medium is suitable for a given fireplace state of affairs. Our goal in this two-part article is to supply guidance based mostly on a hazard-specific approach and assist you to make an knowledgeable decision on applicable 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 similar to magnesium

Class F – fires usually related to cooking corresponding to vegetable oils

Class E – electrical hazards.
As a producer of foam proportioners and firefighting screens, we specialise mainly in the Class B class: flammable liquids.
Foam is considered to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only might not penetrate the fireplace load successfully.
Fire courses.
How do we make foam?

Finished foam solution includes a simple recipe of foam concentrate, water and air. Foam focus is typically combined within 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 using gadgets designed to naturally aspirate the answer. The quantity of aspiration and the kind of concentrate determines the expansion ratio. This is typically cut up between low, medium and excessive growth. Low growth is up to 20:1, medium is 200:1 and excessive growth is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the froth adequately, although naturally aspirated turbines are also used. The choice to choose a particular enlargement ratio is set by the hazard under evaluation.
Put simply, water and oil do not mix. Applying only water to Class B products is not going to suppress the burning vapours. This is an important point 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 achieve success. Whatever technique is chosen to provide that blanket or movie, the target is the same.
Steps of froth generation Images supplied by Author / Contributor

A little of the historical past of foam improvement

We can date the event of modern foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary disadvantage was due to limited fuel tolerance, which meant it was vulnerable to gasoline pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, artificial detergents gave foam a higher fuel tolerance in addition to forming a vapour-sealing film across 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 development did not fully substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam may both combat gas pick-up (mixing) and provide a good resistance to warmth, outlined 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 the most effective of both worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always offered 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 same expertise also grew to become available with the model new generation of AFFF-ARs.
In current years fluorine, one of the cornerstone elements to all foams, has turn into an environmental concern, due to persistence in groundwater. The trade has been introduced with a significant challenge to get rid of the ‘fluoro’ element of all of the totally different foam focus types. diaphragm seal have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of a complete range of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have become the new normal and first alternative for operators changing present stock or reviewing new projects. As a foam proportioner manufacturer we must look at the physical properties of froth fastidiously (especially viscosity) as they influence selections on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more essential within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is important to combat the small diploma of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being highly efficient. The greatest method of evaluating their claims is to familiarise your self 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 in the test protocols. This also covers contemporary and seawater in addition to gentle and forceful utility of the foam. Each foam is given a score with IA being the best, IIID the worst. This means that you can challenge foam suppliers in order to make an knowledgeable determination on the most effective foam in your wants.
Whilst EN 1568 is an excellent benchmark standard, awareness of the consequences on foam efficiency from factors exterior the usual exams should be famous. For instance, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This can be exacerbated by totally different ambient air temperatures, the applying method, gas depth and so on. Our advice would be to grasp the details of the checks and try to match them to the foam’s appropriateness in your individual hazards. We would all the time advocate consulting individual foam producers as they will usually present specific in-house fire-performance knowledge towards a few of the extra unusual fuels.
However, despite the froth manufacturers’ typically conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams based on the expansion ratio Images supplied by Author / Contributor

Critical factors for fulfillment: the time and software 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 standards.
The ‘time’ issue means that for a given measurement of fireside space it is needed to apply the froth for lengthy sufficient to achieve extinction and to forestall re-ignition. This is particularly crucial in guide intervention as firefighter’s might be in danger throughout post-fire operations. When it involves fixed safety for hydrocarbon and polar solvent tanks, the applying time could be so lengthy as 60 minutes for the biggest tank diameters.
The software rate refers back to the amount of finished foam utilized per sq. metre. This varies in accordance with the gas and the froth kind but is presently no less than 4.0 litres per minute per sq. metre. One of the continuing developments in foam performance is the likelihood that this will be decreased, however standards usually take time to recognise product growth. Anything less than the minimum utility price signifies that hearth control is unlikely to be achieved. This implies that firefighting resources, notably in a manual fire assault, must be assembled earlier than firefighting commences and this takes time. The advantage in fitting fastened methods is that the assets are already designed and built into the system for quick application.
Principle of froth extinguishment Images provided by Author / Contributor

Foam proportioning strategies: mixing water with foam concentrate

In order to permit readers to make an informed decision on how greatest to tackle their specific hearth challenges, the following is an overview of the various foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and restricted fastened techniques functions. This uses the venturi principle to create a stress drop in a small aluminium or seawater materials appropriate device with built-in concentrate pick-up tube. The pressure 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 body of the inductor are compact sufficient to be simply carried on a hearth equipment or fitted into a pipework system.
However, while it is considered to be the only technique, it has extreme drawbacks: (i) units are manufacturing facility calibrated so any adjustments to the hydraulics (caused by size 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 prevent any proportioning; (iii) adjustments 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 responsibility pump pressures need to be excessive sufficient to permit for it, doubtlessly including extra value into the system; (v) foam delivery units need to be sized in order to not restrict design flows; (vi) testing can’t 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 must be changed, and the disposal of premix or foam.
Types of froth agentsImages supplied by Author / Contributor

Balanced stress proportioners:
These use an electrical or a mixture of electric and diesel pumps to supply foam concentrate into a proportioner at the next stress than the incoming water-line stress. The proportioner is put in into the water line and regulates the mixing.
They are now associated with older systems, where disadvantages include: (i) extra prices in hardware and design time; (ii) the foam pump is normally restricted to a a lot tighter operating vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants a further power supply, other than water, so isn’t as reliably secure as a system with a possible single level of failure, such as an entirely water-driven system; (iv) sometimes, these techniques are very complex and cause excessive efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to break 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 flexible bladder (typically a butyl material) linked to a foam focus proportioner much like the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the froth crammed bladder so that foam focus may be proportioned with water utilizing the identical provide. The venturi precept is again introduced into play because it creates a strain drop on the point of injection for the froth concentrate. Testing can’t be achieved without creating premix and discharging completed foam. This will add to complete lifetime costs as a result of foam focus utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a result of nice care is required to avoid a broken bladder when commissioning a new set up. It is rarely simple to work throughout the steel stress vessel should issues happen, especially 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 method within the typical sense as the foam is already proportioned utilizing one of many previous methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth answer at the point of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces permitting higher penetration and cooling. This is also a profit in wildfire situations by coating weak structures to mitigate fire progress. The restricted water supplies associated with remote wildfire areas signifies that the resource can be absolutely optimised. However, as with balanced stress proportioner foam pumps, a further level of failure is possible as a result of extra CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have turn into synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is purely mechanical and extremely reliable. A water-driven rotor supplies the motive force to drive a instantly coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning fee and will proportion the froth focus precisely throughout a wide operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, fully without using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor

The benefits of FireDos Gen III FM accredited foam proportioners include:
Reduced prices: proportioning fee is tested without using foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: fixed proportioning fee across a large working vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in stress loss, in comparison with older generations, via hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a different proportioning price.
FM permitted FireDos Gen III proportioners are so far the only FM approved water motor coupled variable proportioners using FM accredited circulate meters. Using the check return line this provides the possibility to examine the proportioning price during commissioning in addition to for annual exams, without creating any premix, which is a really big benefit for the user and relieves the surroundings.
In the second a half of this feature we’ll explore the effects of viscosity on foam proportioning and typical foam software areas and recommended discharge devices.
For more information, go to www.firedos.com

Written by

David Owen

Andreas Hulinsky

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