A guide to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least due to the variables that decide which suppression medium is acceptable for a given hearth situation. Our objective in this two-part article is to offer steerage primarily based on a hazard-specific approach and assist you to make an knowledgeable determination on applicable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or flamable materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires generally associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting monitors, we specialise primarily within the Class B category: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only may not penetrate the hearth load effectively.
Fire courses.
How can we make foam?
Finished foam answer contains a simple recipe of foam focus, water and air. Spoiler is usually combined within 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 device – we will 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 solution. The quantity of aspiration and the kind of concentrate determines the expansion ratio. This is often split between low, medium and excessive growth. Low growth is up to 20:1, medium is 200:1 and excessive growth is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to broaden the froth adequately, although naturally aspirated turbines are additionally used. The determination to choose a selected expansion ratio is determined by the hazard under review.
Put merely, water and oil do not combine. Applying solely water to Class B products is not going to suppress the burning vapours. This is a crucial point to make as it is the vapours, not the liquid itself, that burns. We want a medium that permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever method is chosen to produce that blanket or film, the target is the same.
Steps of froth era Images equipped by Author / Contributor
A little of the history of foam improvement
We can date the development of recent foam concentrates from the Sixties onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the base component). The main downside was because of limited fuel tolerance, which meant it was susceptible to gasoline pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, artificial detergents gave foam a larger fuel tolerance as properly as forming a vapour-sealing movie across the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement didn’t completely substitute the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat gasoline pick-up (mixing) and provide a good resistance to warmth, defined by the industry as ‘burn-back resistance’.
Further growth within the Eighties took FP to the following degree with film-forming fluoroprotein or FFFP. We now had one of the best of both worlds: a film-forming foam that additionally 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 at all times presented a further challenge as they were water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar expertise additionally turned out there with the new generation of AFFF-ARs.
In recent years fluorine, one of many cornerstone elements to all foams, has turn out to be an environmental issue, due to persistence in groundwater. The business has been presented with a serious challenge to eliminate the ‘fluoro’ factor of all of the totally different foam concentrate types. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a whole 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 inventory or reviewing new tasks. As a foam proportioner producer we must examine the physical properties of froth rigorously (especially viscosity) as they affect decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are increasingly essential in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant high quality of SFFF/F3 is important to combat the small diploma of water miscibility of the gas.
All foam concentrate producers will naturally promote their product as being extremely effective. The greatest method of comparing their claims is to familiarise your self with the empirically primarily based normal EN 1568 or UL162. The checks cover extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are both included in the test protocols. This also covers recent and seawater as nicely as light and forceful application of the foam. Each foam is given a score with IA being the most effective, IIID the worst. This means you could problem foam suppliers so as to make an informed decision on one of the best foam on your wants.
Whilst EN 1568 is an excellent benchmark commonplace, awareness of the consequences on foam efficiency from components exterior the usual tests ought to be famous. For example, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This may be exacerbated by totally different ambient air temperatures, the appliance technique, gasoline depth and so forth. Our advice would be to grasp the small print of the checks and attempt to match them to the foam’s appropriateness on your individual hazards. We would always recommend consulting particular person foam producers as they will often present particular in-house fire-performance knowledge towards a variety of the more uncommon fuels.
However, regardless of 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 completed foam.
Foams based on the expansion ratio Images provided by Author / Contributor
Critical factors for success: the time and application price matrix
Successful extinction of flammable liquid fires depends on two converging and complementary elements: time and the rate at which completed foam is applied. Both are decided by empirically primarily based requirements revealed by bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ issue means that for a given size of fire space it’s needed to apply the foam for long sufficient to realize extinction and to prevent re-ignition. This is especially critical in guide intervention as firefighter’s shall be at risk throughout post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the application time could be so long as 60 minutes for the biggest tank diameters.
The application fee refers to the quantity of completed foam utilized per square metre. This varies according to the fuel and the froth sort however is presently at least four.0 litres per minute per sq. metre. One of the continued developments in foam performance is the likelihood that this might be reduced, but standards typically take time to recognise product improvement. Anything lower than the minimal utility rate implies that fireplace control is unlikely to be achieved. This signifies that firefighting resources, particularly in a guide fire attack, have to be assembled before firefighting commences and this takes time. The advantage in fitting fixed methods is that the resources are already designed and constructed into the system for quick software.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to allow readers to make an informed determination on how greatest to tackle their particular hearth challenges, the next is an overview of the varied foam proportioning methods.
Foam inductors:
Typically related to fireplace service deployment and limited fastened systems applications. This makes use of the venturi principle to create a strain drop in a small aluminium or seawater material compatible device 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 answer. Both the pick-up tube and body of the inductor are compact enough to be simply carried on a fireplace appliance or fitted right into a pipework system.
However, whilst it is considered to be the best methodology, it has extreme drawbacks: (i) models are factory calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a changing amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter changes will adversely affect proportioning accuracy and doubtlessly prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to draw concentrate into the downstream traces; (iv) stress loss is excessive, as a lot as 35%, so obligation pump pressures need to be high enough to permit for it, potentially adding further cost into the system; (v) foam delivery units have to be sized so as not to limit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to complete lifetime costs because of foam focus usage, 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 mix of electrical and diesel pumps to supply foam focus into a proportioner at a better stress than the incoming water-line stress. The proportioner is put in into the water line and regulates the mixing.
They at the moment are associated with older systems, the place disadvantages include: (i) extra costs in hardware and design time; (ii) the foam pump is often restricted to a much tighter operating vary, although the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump needs an additional power supply, apart from water, so just isn’t as reliably safe as a system with a potential single point of failure, similar to a wholly water-driven system; (iv) sometimes, these methods are very complex 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 break the foam concentrate and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal stress vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner much like the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth filled bladder in order that foam focus could be proportioned with water using the identical provide. The venturi principle is once more introduced into play as it creates a stress drop on the level of injection for the foam concentrate. Testing can’t be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs because of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a end result of nice care is required to keep away from a damaged bladder when commissioning a model new installation. It is rarely simple to work inside the steel strain vessel should problems happen, especially if and when a replacement bladder may be required: it all provides to the difficulty and value.
Compressed air foam (CAFS):
This just isn’t a proportioning method in the conventional sense as the froth is already proportioned utilizing one of many earlier strategies. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the foam answer at the point 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 is also a profit in wildfire conditions by coating vulnerable structures to mitigate fire development. The limited water provides associated with distant wildfire areas implies that the useful resource may be fully optimised. However, as with balanced strain proportioner foam pumps, an extra level of failure is possible because of the further CAFS equipment.
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 purely mechanical and extremely 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 focus via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and can proportion the foam focus accurately across a large working vary. 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 advantages of FireDos Gen III FM permitted foam proportioners include:
Reduced costs: proportioning fee is tested without utilizing foam or creating premix or foam – price efficient and eco-friendly.
Improved efficiency: constant proportioning rate throughout a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, in comparison with older generations, via hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a unique proportioning rate.
FM approved FireDos Gen III proportioners are thus far the one FM approved water motor coupled variable proportioners using FM permitted flow meters. Using the test return line this offers the possibility to verify the proportioning fee throughout commissioning in addition to for annual checks, without creating any premix, which is a very big profit for the user and relieves the environment.
In the second part of this function we’ll explore the consequences of viscosity on foam proportioning and typical foam application areas and beneficial discharge gadgets.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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