Fire presents many challenges, not least due to the variables that decide which suppression medium is appropriate for a given fireplace scenario. Our goal in this two-part article is to supply steering primarily based on a hazard-specific approach and assist you to make an informed choice on applicable 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 such as magnesium

Class F – fires typically related to cooking similar to vegetable oils

Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting screens, we specialise primarily in the Class B category: flammable liquids.
Foam is taken into account 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 specifically for deep-seated Class A fires where water solely may not penetrate the hearth load effectively.
Fire lessons.
How can we make foam?

Finished foam solution contains a simple recipe of froth focus, water and air. Foam concentrate is often combined in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge system – we’ll cover proportioning later on this article and discharge strategies in Part 2. At this level air is entrained through the use of devices designed to naturally aspirate the solution. The quantity of aspiration and the sort of focus determines the expansion ratio. This is typically split between low, medium and excessive enlargement. Low growth is up to 20:1, medium is 200:1 and excessive growth is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the foam adequately, although naturally aspirated mills are also used. The determination to choose a selected enlargement ratio is decided by the hazard underneath evaluate.
Put merely, water and oil do not combine. Applying only water to Class B products won’t suppress the burning vapours. This is a crucial level 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 obtain success. Whatever digital pressure gauge is chosen to produce that blanket or movie, the target is the same.
Steps of foam era Images provided by Author / Contributor

A little of the history of foam growth

We can date the development of recent foam concentrates from the Sixties onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the base component). The major disadvantage was as a outcome of restricted 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 utilizing protein as the base product, artificial detergents gave foam a larger gas tolerance as well as forming a vapour-sealing movie across 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 development did not fully exchange using protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat gas pick-up (mixing) and offer a great resistance to heat, outlined by the industry as ‘burn-back resistance’.
Further improvement within the Nineteen Eighties took FP to the next stage with film-forming fluoroprotein or FFFP. We now had the best of each worlds: a film-forming foam that also had good burn-back resistance.
The Nineteen Eighties additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time introduced an additional challenge as they had been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar expertise also turned obtainable with the brand new era of AFFF-ARs.
In current years fluorine, one of many cornerstone ingredients to all foams, has turn into an environmental concern, as a end result of persistence in groundwater. The industry has been introduced with a significant problem to eliminate the ‘fluoro’ component of all of the different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of a whole range of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the new regular and first alternative for operators altering current stock or reviewing new tasks. As a foam proportioner producer we must study the bodily properties of foam fastidiously (especially viscosity) as they affect choices on the overall proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly essential within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant high quality of SFFF/F3 is necessary to fight the small diploma of water miscibility of the gas.
All foam concentrate manufacturers will naturally promote their product as being highly effective. The finest way of comparing their claims is to familiarise your self with the empirically primarily based standard EN 1568 or UL162. The tests cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included in the test protocols. This additionally covers contemporary and seawater in addition to light and forceful application of the foam. Each foam is given a ranking with IA being the most effective, IIID the worst. This means you could problem foam suppliers to find a way to make an informed choice on one of the best foam on your needs.
Whilst EN 1568 is a superb benchmark standard, consciousness of the effects on foam performance from components outside the usual tests should be noted. For instance, notably aggressive solvents can challenge the firefighting effectiveness of certain foams. This can be exacerbated by completely different ambient air temperatures, the application method, gas depth etc. Our advice could be to know the primary points of the tests and try to match them to the foam’s appropriateness for your particular person hazards. We would at all times recommend consulting particular person foam producers as they can typically present particular in-house fire-performance knowledge towards a few of the more uncommon fuels.
However, despite the foam 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 finished foam.
Foams based on the growth ratio Images equipped by Author / Contributor

Critical elements for achievement: the time and software fee matrix

Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the speed at which completed foam is applied. Both are determined by empirically primarily based standards revealed by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
pressure gauge signifies that for a given measurement of fireside area it is necessary to use the froth for lengthy enough to realize extinction and to prevent re-ignition. This is particularly crucial in handbook intervention as firefighter’s might be in danger during post-fire operations. When it involves mounted safety for hydrocarbon and polar solvent tanks, the application time can be as long as 60 minutes for the largest tank diameters.
The utility fee refers to the quantity of completed foam utilized per sq. metre. This varies based on the fuel and the froth sort but is presently at least litres per minute per sq. metre. One of the ongoing developments in foam performance is the likelihood that this might be decreased, but standards typically take time to recognise product development. Anything less than the minimum application price means that fire control is unlikely to be achieved. This implies that firefighting resources, notably in a manual fire attack, have to be assembled earlier than firefighting commences and this takes time. The advantage in fitting fixed methods is that the sources are already designed and built into the system for immediate utility.
Principle of foam extinguishment Images equipped by Author / Contributor

Foam proportioning strategies: mixing water with foam concentrate

In order to allow readers to make an knowledgeable decision on how best to tackle their explicit hearth challenges, the following is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically associated with fire service deployment and restricted fastened methods applications. This makes use of the venturi precept to create a stress drop in a small aluminium or seawater materials suitable gadget with built-in focus pick-up tube. The strain drop created by the venturi draws the froth focus from a container where 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 fireplace appliance or fitted into a pipework system.
However, whilst it is considered to be the simplest 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 gadget or a changing quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations brought on by pipe diameter modifications will adversely have an effect on proportioning accuracy and potentially prevent any proportioning; (iii) adjustments in focus viscosity will undermine the ability of the venturi to attract focus into the downstream strains; (iv) pressure loss is excessive, as a lot as 35%, so responsibility pump pressures must be excessive sufficient to allow for it, potentially including additional price into the system; (v) foam supply devices have to be sized so as not to prohibit design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to entire lifetime costs on account of foam focus usage, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor

Balanced pressure proportioners:
These use an electrical or a mix of electric and diesel pumps to produce foam concentrate right into a proportioner at the next pressure than the incoming water-line pressure. The proportioner is put in into the water line and regulates the blending.
They are now related to older methods, the place disadvantages embody: (i) extra prices in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter operating vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump wants an additional energy supply, aside from water, so isn’t as reliably secure as a system with a potential single point of failure, such as a wholly water-driven system; (iv) sometimes, these techniques are very advanced and trigger excessive efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to wreck the froth concentrate and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner much like the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam focus could be proportioned with water using the identical provide. The venturi principle is once more brought into play as it creates a stress 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 prices on account of foam focus usage, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of nice care is needed to avoid a damaged bladder when commissioning a new installation. It is rarely simple to work throughout the metal pressure vessel ought to problems happen, especially if and when a alternative bladder could also be required: it all provides to the difficulty and value.
Compressed air foam (CAFS):
This isn’t a proportioning method within the typical sense as the foam is already proportioned using one of the previous methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth answer on the point of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces permitting higher penetration and cooling. This is also a profit in wildfire situations by coating susceptible buildings to mitigate hearth development. The restricted water supplies associated with distant wildfire areas signifies that the resource may be absolutely optimised. However, as with balanced stress proportioner foam pumps, an additional level of failure is feasible as a result of further CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is purely 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 provided with foam concentrate through an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and can proportion the froth concentrate precisely across a wide working range. The purely mechanical system offers cost-efficient and eco-friendly proportioning fee testing, fully with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor

The benefits of FireDos Gen III FM accredited foam proportioners include:
Reduced prices: proportioning rate is tested with out utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: constant proportioning rate across a large operating vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in stress loss, in comparison with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a special proportioning rate.
FM approved FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners utilizing FM accredited circulate meters. Using the take a look at return line this provides the chance to check the proportioning fee during commissioning in addition to for annual exams, with out creating any premix, which is a really huge benefit for the person and relieves the surroundings.
In the second part of this characteristic we’ll explore the effects of viscosity on foam proportioning and typical foam application areas and recommended discharge devices.
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Written by

David Owen

Andreas Hulinsky


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