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A information to foam and foam proportioning tools – Part 1

Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fire scenario. Our goal on this two-part article is to provide steering based mostly on a hazard-specific strategy 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 combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires usually related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily in the Class B class: flammable liquids.
Foam is considered to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are specifically for deep-seated Class A fires where water solely may not penetrate the hearth load successfully.
Fire classes.
How do we make foam?
Finished foam solution comprises a simple recipe of froth focus, water and air. Foam focus is often mixed 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 gadget – we will cover proportioning later in this article and discharge strategies in Part 2. At this point air is entrained by utilizing units 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 high growth. Low expansion is as much as 20:1, medium is 200:1 and high enlargement is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, although naturally aspirated turbines are also used. The determination to determine on a particular expansion ratio is set by the hazard underneath evaluation.
Put merely, water and oil don’t mix. Applying only water to Class B products is not going to suppress the burning vapours. This is an important 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 be successful. Whatever methodology is chosen to provide that blanket or film, the objective is identical.
Steps of froth era Images equipped by Author / Contributor
A little of the historical past of foam development
We can date the development of modern foam concentrates from the 1960s onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the base component). The primary disadvantage was as a result of restricted gasoline tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, synthetic detergents gave foam a higher gas tolerance in addition to forming a vapour-sealing film across the floor of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s development did not utterly exchange using protein-based foam. เกจวัดแรงดัน , or FP, meant that protein foam could each fight gas pick-up (mixing) and supply a great resistance to heat, outlined by the business as ‘burn-back resistance’.
Further improvement in the Eighties took FP to the following stage with film-forming fluoroprotein or FFFP. We now had one of 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 always introduced a further challenge as they had been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same expertise also grew to become obtainable with the new era of AFFF-ARs.
In recent years fluorine, one of the cornerstone elements to all foams, has turn out to be an environmental problem, as a outcome of persistence in groundwater. The trade has been introduced with a serious challenge to remove the ‘fluoro’ factor of all the completely different foam concentrate sorts. We have witnessed an period 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 become the model new regular and first selection for operators changing present stock or reviewing new projects. As a foam proportioner manufacturer we should examine the bodily properties of foam fastidiously (especially viscosity) as they affect selections on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are increasingly necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is necessary to fight the small diploma of water miscibility of the gasoline.
All foam concentrate producers will naturally promote their product as being extremely effective. The best way of comparing their claims is to familiarise yourself with the empirically based standard EN 1568 or UL162. The exams 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 also covers contemporary and seawater as nicely as light and forceful utility of the froth. Each foam is given a rating with IA being one of the best, IIID the worst. This means that you can problem foam suppliers in order to make an knowledgeable decision on one of the best foam on your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the results on foam performance from elements exterior the standard exams should be famous. For example, significantly aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by completely different ambient air temperatures, the applying methodology, gas depth and so forth. Our advice would be to grasp the small print of the checks and try to match them to the foam’s appropriateness on your particular person hazards. We would all the time suggest consulting individual foam manufacturers as they can typically present particular in-house fire-performance data towards a number of the more unusual fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on performance, the earlier 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 components for success: the time and application fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the rate at which finished foam is utilized. Both are determined by empirically based requirements revealed by our 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 measurement of fireplace space it’s necessary to apply the froth for lengthy sufficient to realize extinction and to forestall re-ignition. This is particularly 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 application time can be so long as 60 minutes for the biggest tank diameters.
The utility price refers to the amount of finished foam utilized per square metre. This varies according to the gasoline and the foam kind but is presently no much less than four.zero litres per minute per sq. metre. One of the continued developments in foam performance is the likelihood that this might be reduced, however requirements usually take time to recognise product growth. Anything less than the minimal software rate signifies that fire control is unlikely to be achieved. This means that firefighting sources, significantly in a handbook fireplace attack, must be assembled earlier than firefighting commences and this takes time. The benefit in becoming fixed methods is that the resources are already designed and built into the system for immediate software.
Principle of froth extinguishment Images provided 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 fireplace challenges, the following is an outline of the varied foam proportioning methods.
Foam inductors:
Typically associated with hearth service deployment and restricted fastened systems applications. This makes use of the venturi precept to create a pressure drop in a small aluminium or seawater material appropriate gadget with built-in concentrate pick-up tube. The stress drop created by the venturi attracts the froth focus from a container the place it mixes with water to create foam solution. Both the pick-up tube and body of the inductor are compact enough to be easily carried on a fire appliance or fitted right into a pipework system.
However, while it’s thought-about to be the simplest technique, it has severe drawbacks: (i) models are manufacturing unit calibrated so any modifications to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge gadget or a changing amount of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter changes will adversely affect proportioning accuracy and potentially stop any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to draw focus into the downstream traces; (iv) strain loss is high, as a lot as 35%, so obligation pump pressures have to be excessive sufficient to allow for it, doubtlessly adding extra price into the system; (v) foam delivery gadgets have to be sized in order not to prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging completed foam. This will add to entire lifetime costs as a outcome of foam focus usage, which needs to be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mix of electrical and diesel pumps to provide foam focus right into a proportioner at the next stress than the incoming water-line pressure. The proportioner is put in into the water line and regulates the blending.
They at the moment are related to older systems, where disadvantages embrace: (i) further prices in hardware and design time; (ii) the foam pump is normally restricted to a a lot tighter working vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an extra power source, aside from water, so just isn’t as reliably secure as a system with a possible single level of failure, similar to a completely 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 damage the foam concentrate and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner just like the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam concentrate could be proportioned with water using the same provide. The venturi principle is again brought into play as it creates a pressure drop on the level of injection for the froth focus. Testing can’t be achieved with out creating premix and discharging completed foam. This will add to entire lifetime prices as a end result of foam concentrate usage, which needs to 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 needed to avoid a broken bladder when commissioning a new installation. It is never easy to work inside the steel stress vessel ought to issues happen, particularly if and when a alternative bladder could also be required: it all provides to the issue and value.
Compressed air foam (CAFS):
This is not a proportioning methodology in the conventional sense as the froth is already proportioned utilizing one of the earlier strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth resolution at the point of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces permitting better penetration and cooling. This can be a benefit in wildfire situations by coating vulnerable buildings to mitigate fireplace growth. The restricted water provides related to remote wildfire areas implies that the resource could be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra point of failure is possible because of the extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn out to be 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 supplies the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning rate and can proportion the froth concentrate precisely across a wide operating range. เกจวัดแรงดันปั๊มลม supplies cost-efficient and eco-friendly proportioning fee testing, completely without utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners include:
Reduced costs: proportioning price is tested without utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved performance: fixed proportioning price across a wide working vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in pressure loss, in comparability with older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a different proportioning rate.
FM accredited FireDos Gen III proportioners are so far the only FM accredited water motor coupled variable proportioners utilizing FM accredited circulate meters. Using the take a look at return line this presents the chance to examine the proportioning rate throughout commissioning as nicely as for annual exams, without creating any premix, which is a very massive profit for the user and relieves the surroundings.
In the second a part of this characteristic we will explore the consequences of viscosity on foam proportioning and typical foam application areas and beneficial discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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