Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fireplace scenario. Our objective on this two-part article is to provide steering based on a hazard-specific approach and allow you to make an informed choice on acceptable fire-suppression measures, particularly 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 such as magnesium
Class F – fires usually related to cooking similar to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise mainly in the Class B class: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely may not penetrate the hearth load effectively.
Fire lessons.
How do we make foam?
Finished foam resolution includes a easy 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 solution (premix) is created, it is pumped to the chosen discharge system – we will cover proportioning later on this article and discharge methods in Part 2. At this point air is entrained by using gadgets designed to naturally aspirate the solution. The amount of aspiration and the type of concentrate determines the expansion ratio. This is typically break up between low, medium and excessive growth. Low expansion is up to 20:1, medium is 200:1 and high enlargement is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated generators are also used. The choice to choose on a particular expansion ratio is determined by the hazard under evaluation.
Put merely, water and oil don’t combine. Applying solely water to Class B products won’t suppress the burning vapours. This is an important level to make as it is the vapours, not the liquid itself, that burns. We need a medium that enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to be successful. Whatever methodology is chosen to produce that blanket or film, the objective is identical.
Steps of foam era Images equipped by Author / Contributor
A little of the historical past of froth development
We can date the event of modern foam concentrates from the Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the bottom component). The main disadvantage was as a outcome of 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 bottom product, synthetic detergents gave foam a larger fuel tolerance as properly as forming a vapour-sealing film across the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s development didn’t utterly substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat fuel pick-up (mixing) and offer a great resistance to warmth, defined by the business as ‘burn-back resistance’.
Further improvement in the Nineteen 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 also had good burn-back resistance.
The 1980s additional 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 destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar know-how also grew to become available with the new generation of AFFF-ARs.
In latest years fluorine, one of the cornerstone ingredients to all foams, has turn out to be an environmental problem, because of persistence in groundwater. The trade has been offered with a serious challenge to remove the ‘fluoro’ factor of all of the different foam focus types. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of a complete range of newly formulated fluorine-free foam. Bonus ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn out to be the new normal and first alternative for operators changing current inventory or reviewing new projects. As a foam proportioner producer we must examine the physical properties of foam fastidiously (especially viscosity) as they affect decisions on the overall proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are more and more important in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant quality of SFFF/F3 is critical to combat the small degree of water miscibility of the gasoline.
All foam focus manufacturers will naturally promote their product as being highly efficient. The greatest way of evaluating their claims is to familiarise your self with the empirically based standard EN 1568 or UL162. The tests cover 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 test protocols. This also covers recent and seawater in addition to light and forceful software of the froth. Each foam is given a ranking with IA being the best, IIID the worst. This means that you could problem foam suppliers so as to make an knowledgeable determination on the most effective foam for your needs.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the effects on foam efficiency from factors outside the standard exams ought to be noted. For example, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This could be exacerbated by different ambient air temperatures, the appliance methodology, fuel depth and so on. Our recommendation could be to know the small print of the checks and attempt to match them to the foam’s appropriateness on your particular person hazards. We would at all times recommend consulting particular person foam producers as they can typically provide specific in-house fire-performance data towards some of the extra unusual fuels.
However, regardless of the foam manufacturers’ typically conflicting claims on performance, the earlier 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 supplied by Author / Contributor
Critical components for achievement: the time and software fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the speed at which finished foam is utilized. Both are determined by empirically 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’ factor implies that for a given dimension of fireplace space it’s necessary to apply the froth for lengthy sufficient to attain extinction and to forestall re-ignition. This is particularly important in guide intervention as firefighter’s might be in danger throughout 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 most important tank diameters.
The software rate refers to the quantity of completed foam applied per square metre. This varies in accordance with the gas and the froth kind but is at present no less than four.0 litres per minute per sq. metre. One of the continued developments in foam efficiency is the chance that this will be reduced, however standards typically take time to recognise product improvement. Anything less than the minimal software price signifies that fire management is unlikely to be achieved. This signifies that firefighting resources, particularly in a manual fireplace assault, must be assembled earlier than firefighting commences and this takes time. The advantage in becoming fastened techniques is that the sources are already designed and built into the system for instant application.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an knowledgeable determination on how finest to deal with their specific hearth challenges, the next is an overview of the various foam proportioning methods.
Foam inductors:
Typically related to hearth service deployment and restricted fixed techniques purposes. This uses the venturi principle to create a pressure drop in a small aluminium or seawater material compatible device with built-in focus pick-up tube. The stress drop created by the venturi attracts the foam focus from a container the place it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fire equipment or fitted into a pipework system.
However, whilst it’s considered to be the best methodology, it has extreme drawbacks: (i) models are manufacturing unit calibrated so any changes to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a altering quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter adjustments will adversely have an effect on proportioning accuracy and probably prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to draw focus into the downstream lines; (iv) strain loss is high, as much as 35%, so obligation pump pressures need to be high sufficient to permit for it, potentially adding further price into the system; (v) foam supply units have to be sized so as to not prohibit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs as a result of foam focus usage, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced stress proportioners:
These use an electrical or a mix of electrical and diesel pumps to provide foam focus right into a proportioner at the next pressure than the incoming water-line pressure. The proportioner is installed into the water line and regulates the mixing.
They are now related to older systems, the place disadvantages embody: (i) extra prices in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter working range, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump needs a further power source, aside from water, so just isn’t as reliably secure as a system with a potential single level of failure, such as a wholly water-driven system; (iv) sometimes, these techniques are very advanced and trigger high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to wreck the foam concentrate and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam focus may be proportioned with water utilizing the same provide. The venturi principle is once more introduced into play as it creates a strain drop on the point of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs because of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a end result of nice care is required to keep away from a damaged bladder when commissioning a new set up. It is never easy to work inside the steel pressure vessel should problems happen, especially if and when a replacement bladder may be required: all of it adds to the difficulty and price.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology in the typical sense as the foam is already proportioned using one of the previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title 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 allowing higher penetration and cooling. This can be a profit in wildfire situations by coating vulnerable structures to mitigate hearth development. The restricted water provides related to remote wildfire areas implies that the useful resource could be totally optimised. However, as with balanced pressure proportioner foam pumps, an additional point of failure is feasible because of the further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn into synonymous with their unique water-driven foam proportioner. Now in its third era, the product is solely mechanical and extremely dependable. A water-driven rotor supplies the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning price and can proportion the foam focus accurately throughout a wide operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning fee testing, fully with out utilizing 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 approved foam proportioners embrace:
Reduced prices: proportioning fee is tested without utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved performance: fixed proportioning fee across a wide working range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% discount in pressure loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a unique proportioning fee.
FM permitted FireDos Gen III proportioners are so far the one FM accredited water motor coupled variable proportioners using FM approved circulate meters. Using the check return line this presents the possibility to examine the proportioning rate during commissioning in addition to for annual exams, without creating any premix, which is a really massive profit for the person and relieves the setting.
In the second a part of this feature we are going to explore the results of viscosity on foam proportioning and typical foam application areas and really helpful discharge devices.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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