A information to foam and foam proportioning equipment – Part 1

Fire presents many challenges, not least due to the variables that decide which suppression medium is acceptable for a given fire situation. Our goal in this two-part article is to supply steering based mostly on a hazard-specific strategy and assist you to make an informed determination on applicable 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 materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires typically related to cooking such as vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting displays, we specialise primarily within the Class B category: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water only might not penetrate the fireplace load successfully.
Fire classes.
How will we make foam?
Finished foam resolution comprises a easy recipe of froth concentrate, water and air. Foam concentrate is often blended in the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge gadget – we’ll cowl proportioning later on this article and discharge strategies in Part 2. At this level air is entrained through the use of gadgets designed to naturally aspirate the solution. The quantity of aspiration and the type of focus determines the enlargement ratio. This is typically split between low, medium and excessive growth. Low enlargement is as a lot as 20:1, medium is 200:1 and excessive expansion is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated generators are additionally used. The choice to determine on a particular enlargement ratio is determined by the hazard underneath evaluate.
Put merely, water and oil do not combine. Applying solely water to Class B merchandise won’t suppress the burning vapours. This is a vital point to make as it’s 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 film to obtain success. Whatever methodology is chosen to produce that blanket or film, the objective is similar.
Steps of foam era Images provided by Author / Contributor
A little of the history of foam development
We can date the development of modern 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 primary drawback was because of limited gasoline tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, artificial detergents gave foam a greater gasoline tolerance as well as forming a vapour-sealing movie throughout the surface of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating units 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 gas pick-up (mixing) and offer a great resistance to heat, defined by the business as ‘burn-back resistance’.
Further improvement in the Eighties took FP to the next degree 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 further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented a further problem as they were water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical technology additionally turned obtainable with the new era of AFFF-ARs.
In recent years fluorine, one of the cornerstone components to all foams, has turn into an environmental concern, due to persistence in groundwater. The trade has been presented with a serious challenge to remove the ‘fluoro’ factor of all of the totally different foam concentrate 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 time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have become the new normal and first choice for operators altering present stock or reviewing new tasks. As a foam proportioner manufacturer we must examine the physical properties of froth carefully (especially viscosity) as they affect selections on the general proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more essential within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, implies that the alcohol-resistant high quality of SFFF/F3 is critical to combat the small degree of water miscibility of the fuel.
All foam focus producers will naturally promote their product as being highly efficient. The greatest way of evaluating their claims is to familiarise yourself with the empirically based mostly commonplace EN 1568 or UL162. The tests cowl 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 take a look at protocols. This additionally covers fresh and seawater as properly as mild and forceful application of the froth. Each foam is given a rating with IA being the best, IIID the worst. This means you could challenge foam suppliers to find a way to make an knowledgeable decision on the best foam in your needs.
Whilst EN 1568 is a superb benchmark commonplace, awareness of the results on foam performance from factors outside the standard tests ought to be famous. For instance, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by completely different ambient air temperatures, the appliance method, fuel depth etc. Our advice would be to understand the major points of the tests and try to match them to the foam’s appropriateness on your individual hazards. We would all the time recommend consulting individual foam producers as they can typically provide particular in-house fire-performance knowledge in opposition to some of the more uncommon fuels.
However, despite the froth manufacturers’ generally conflicting claims on performance, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the enlargement ratio Images supplied by Author / Contributor
Critical elements for fulfillment: the time and utility fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the rate at which finished foam is applied. Both are decided by empirically based mostly requirements revealed by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ issue implies that for a given dimension of fireside area it is essential to apply the froth for long sufficient to realize extinction and to stop re-ignition. This is especially important in manual intervention as firefighter’s shall be in danger throughout post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the applying time can be as long as 60 minutes for the biggest tank diameters.
The utility fee refers to the quantity of completed foam utilized per sq. metre. This varies in accordance with the gasoline and the froth type but is presently at least four.0 litres per minute per sq. metre. One of the ongoing developments in foam performance is the chance that this shall be decreased, however standards usually take time to recognise product development. Anything less than the minimal utility rate implies that fire control is unlikely to be achieved. This implies that firefighting sources, significantly in a guide fireplace attack, must be assembled before firefighting commences and this takes time. The advantage in becoming fixed methods is that the assets are already designed and built into the system for instant utility.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an knowledgeable choice on how finest to sort out their particular fire challenges, the next is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with fire service deployment and restricted fastened techniques functions. This uses the venturi precept to create a pressure drop in a small aluminium or seawater materials suitable gadget with built-in concentrate pick-up tube. The strain drop created by the venturi draws the foam concentrate from a container the place 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 hearth appliance or fitted into a pipework system.
However, while it is thought-about to be the simplest methodology, it has extreme drawbacks: (i) models are factory calibrated so any modifications to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge gadget or a altering amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are critical as deviations brought on by pipe diameter changes will adversely affect proportioning accuracy and doubtlessly forestall any proportioning; (iii) modifications in focus viscosity will undermine the power of the venturi to draw concentrate into the downstream strains; (iv) stress loss is high, as a lot as 35%, so responsibility pump pressures have to be excessive enough to permit for it, probably adding extra cost into the system; (v) foam delivery gadgets need to be sized so as not to restrict design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime costs as a result of foam focus usage, which needs to be changed, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced stress proportioners:
These use an electric 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 blending.
They are now related to older techniques, where disadvantages include: (i) further costs in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter working vary, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump needs an additional energy supply, apart from water, so is not as reliably safe as a system with a potential single level of failure, corresponding to a wholly water-driven system; (iv) sometimes, these methods are very complex and cause high efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to break the foam focus and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel strain vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced pressure proportioners. เกจวัดแรงดันภาษาอังกฤษ compresses the froth crammed bladder in order that foam concentrate may be proportioned with water utilizing the same supply. The venturi principle is once more brought into play as it creates a strain drop at the level of injection for the froth concentrate. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to complete lifetime costs because of foam focus usage, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a outcome of great care is required to keep away from a damaged bladder when commissioning a new set up. It is never simple to work inside the metal stress vessel ought to problems occur, especially if and when a replacement bladder could additionally be required: it all adds to the issue and cost.
Compressed air foam (CAFS):
This is not a proportioning technique within the standard sense as the foam is already proportioned using one of many earlier methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth solution on the level of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces allowing better penetration and cooling. This can be a profit in wildfire situations by coating vulnerable constructions to mitigate fireplace progress. The limited water provides related to distant wildfire areas implies that the resource can be absolutely optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is possible as a end result of further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is only mechanical and extremely reliable. A water-driven rotor supplies the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and will proportion the foam focus accurately throughout a large working range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, completely without using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners include:
Reduced costs: proportioning rate is examined with out using foam or creating premix or foam – price effective and eco-friendly.
Improved performance: fixed proportioning price throughout a wide working range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% discount in stress loss, in comparability with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a special proportioning price.
FM approved FireDos Gen III proportioners are to date the one FM permitted water motor coupled variable proportioners using FM accredited move meters. Using the check return line this provides the possibility to examine the proportioning rate throughout commissioning in addition to for annual exams, with out creating any premix, which is a really massive benefit for the person and relieves the environment.
In the second part of this feature we’ll explore the results of viscosity on foam proportioning and typical foam software areas and really helpful discharge devices.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky

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