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Fire presents many challenges, not least because of the variables that decide which suppression medium is appropriate for a given hearth state of affairs. Our goal on this two-part article is to provide steerage based on a hazard-specific strategy and help you make an informed choice on appropriate fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorised 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 associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise primarily in the Class B class: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely might not penetrate the fireplace load successfully.
Fire courses.
How can we make foam?
Finished foam answer comprises a easy recipe of froth focus, water and air. Foam concentrate is typically mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge device – we are going to cowl proportioning later on this article and discharge strategies in Part 2. At this point air is entrained by utilizing devices designed to naturally aspirate the answer. The amount of aspiration and the sort of concentrate determines the enlargement ratio. This is usually split between low, medium and high growth. Low growth is as a lot as 20:1, medium is 200:1 and excessive growth is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the foam adequately, though naturally aspirated generators are additionally used. The choice to choose a selected growth ratio is set by the hazard beneath review.
Put simply, water and oil do not mix. Applying solely water to Class B products won’t suppress the burning vapours. This is an important level to make as it’s 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 achieve success. Whatever method is chosen to produce that blanket or film, the objective is the same.
Steps of foam era Images equipped by Author / Contributor
A little of the history of foam improvement
We can date the development of contemporary foam concentrates from the 1960s onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the base component). The primary drawback was as a result of limited gas tolerance, which meant it was vulnerable to gasoline pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a larger gas tolerance as nicely as 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 units are fitted.
Nevertheless, AFFF’s improvement did not fully exchange using protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat gasoline pick-up (mixing) and supply an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further growth within the Nineteen Eighties took FP to the next stage with film-forming fluoroprotein or FFFP. We now had the most effective of each worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented a further challenge as they have 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 additionally turned obtainable with the new generation of AFFF-ARs.
In latest years fluorine, one of the cornerstone elements to all foams, has become an environmental concern, as a outcome of persistence in groundwater. The trade has been offered with a significant challenge to remove the ‘fluoro’ component of all the totally different foam concentrate sorts. We have witnessed an era of manufacturers’ claims and counter claims relating to 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 turn out to be the brand new regular and first selection for operators changing present inventory or reviewing new tasks. As a foam proportioner manufacturer we must study the bodily properties of froth carefully (especially viscosity) as they affect selections on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more necessary in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant high quality of SFFF/F3 is critical to fight the small diploma of water miscibility of the gasoline.
All foam focus manufacturers will naturally promote their product as being highly effective. The greatest way of comparing their claims is to familiarise yourself with the empirically primarily based standard EN 1568 or UL162. The checks cowl extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included within the check protocols. This additionally covers fresh and seawater as nicely as gentle and forceful utility of the foam. Each foam is given a score with IA being one of the best, IIID the worst. This means that you can problem foam suppliers to be able to make an informed decision on the most effective foam on your wants.
Whilst EN 1568 is an excellent benchmark normal, awareness of the consequences on foam efficiency from elements exterior the standard exams must be noted. For example, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This can be exacerbated by completely different ambient air temperatures, the appliance methodology, gasoline depth and so forth. Our advice could be to understand the small print of the checks and try to match them to the foam’s appropriateness on your individual hazards. We would at all times advocate consulting individual foam manufacturers as they can typically provide specific in-house fire-performance information 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 finished foam.
Foams according to the growth ratio Images equipped by Author / Contributor
Critical elements for fulfillment: the time and application price matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary elements: time and the speed at which completed foam is utilized. Both are decided by empirically primarily based requirements revealed by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor implies that for a given dimension of fire area it is needed to apply the foam for long sufficient to attain extinction and to prevent re-ignition. This is very important in manual intervention as firefighter’s will be in danger throughout post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the appliance time could be so lengthy as 60 minutes for the largest tank diameters.
The utility rate refers to the quantity of completed foam applied per sq. metre. This varies based on the gas and the foam kind however is presently at least 4.zero litres per minute per sq. metre. One of the ongoing developments in foam performance is the chance that this shall be reduced, but requirements usually take time to recognise product growth. Anything less than the minimal application fee means that fireplace control is unlikely to be achieved. This signifies that firefighting resources, notably in a handbook fire assault, need to be assembled before firefighting commences and this takes time. The advantage in becoming mounted methods is that the assets are already designed and built into the system for instant 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 informed decision on how greatest to tackle their explicit hearth challenges, the following is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and limited fastened methods functions. This makes use of the venturi principle to create a stress 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 froth focus from a container the place 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 hearth equipment or fitted right into a pipework system.
However, while it is thought of to be the simplest technique, it has extreme drawbacks: (i) units 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 altering 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 adjustments will adversely have an effect on proportioning accuracy and potentially stop any proportioning; (iii) adjustments in focus viscosity will undermine the flexibility of the venturi to attract focus into the downstream lines; (iv) pressure loss is excessive, as a lot as 35%, so obligation pump pressures have to be excessive sufficient to allow for it, probably including additional price into the system; (v) foam delivery units have to be sized in order to not limit design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to entire lifetime costs on account of foam concentrate utilization, which has to be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced stress proportioners:
These use an electric or a mixture of electric and diesel pumps to produce foam concentrate into a proportioner at the next stress than the incoming water-line pressure. The proportioner is installed into the water line and regulates the blending.
They at the moment are related to older techniques, where disadvantages embrace: (i) extra costs in hardware and design time; (ii) the froth pump is generally restricted to a much tighter working vary, though the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump wants an extra power supply, apart from water, so is not as reliably safe as a system with a possible single point of failure, such as a completely water-driven system; (iv) usually, these methods are very complicated and cause excessive efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to break the foam focus and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal stress vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner just like the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam focus could be proportioned with water utilizing the same provide. The venturi principle is once more brought into play because it creates a stress drop on the point of injection for the foam focus. เกจอาร์กอน cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices because of foam concentrate utilization, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of nice care is required to keep away from a broken bladder when commissioning a new installation. It is rarely easy to work inside the steel strain vessel ought to problems occur, particularly if and when a replacement bladder could additionally be required: all of it adds to the difficulty and value.
Compressed air foam (CAFS):
This is not a proportioning methodology within the standard sense as the foam is already proportioned using one of many 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 foam answer at the level 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 also be a benefit in wildfire situations by coating vulnerable buildings to mitigate fire growth. The restricted water supplies related to distant wildfire areas signifies that the resource can be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra level of failure is feasible as a result of additional CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in its third era, the product is only mechanical and highly dependable. A water-driven rotor supplies the motive force to drive a instantly coupled positive-displacement plunger or piston pump. This is supplied with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and will proportion the froth focus precisely throughout a wide operating range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, utterly with out using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The advantages of FireDos Gen III FM accredited foam proportioners embrace:
Reduced prices: proportioning price is examined without using foam or creating premix or foam – cost efficient and eco-friendly.
Improved performance: constant proportioning fee throughout a wide operating range.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in stress loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning rate.
FM permitted FireDos Gen III proportioners are so far the only FM permitted water motor coupled variable proportioners utilizing FM approved circulate meters. Using the test return line this presents the possibility to examine the proportioning price during commissioning as well as for annual tests, without creating any premix, which is a really big benefit for the consumer and relieves the setting.
In the second part of this characteristic we are going to explore the consequences of viscosity on foam proportioning and typical foam software areas and recommended discharge gadgets.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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