Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given hearth state of affairs. Our objective on this two-part article is to supply steerage primarily based on a hazard-specific method and help you make an knowledgeable determination 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 combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires generally related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting monitors, we specialise primarily 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 could not penetrate the fireplace load effectively.
Fire lessons.
How will we make foam?
Finished foam answer includes a simple recipe of froth concentrate, water and air. Foam concentrate is usually blended 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 device – we will cowl proportioning later in this article and discharge methods in Part 2. At this level air is entrained through the use of gadgets designed to naturally aspirate the solution. The amount of aspiration and the kind of concentrate determines the expansion ratio. This is often break up between low, medium and excessive enlargement. Low growth is up to 20:1, medium is 200:1 and high growth is greater than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to expand the foam adequately, although naturally aspirated turbines are also used. The choice to choose a specific enlargement ratio is determined by the hazard under review.
Put simply, water and oil don’t mix. Applying solely water to Class B products is not going to suppress the burning vapours. This is a vital 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 movie to be successful. Whatever method is chosen to produce that blanket or movie, the objective is the same.
Steps of froth generation Images equipped by Author / Contributor
A little of the historical past of foam improvement
We can date the event of contemporary foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary downside was due to limited fuel tolerance, which meant it was prone to fuel pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, synthetic detergents gave foam a greater gas tolerance in addition to forming a vapour-sealing film across the floor of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement did not utterly substitute the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat fuel pick-up (mixing) and provide an excellent resistance to warmth, defined by the industry as ‘burn-back resistance’.
Further growth within the Eighties took FP to the following 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 Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time introduced a further challenge as they have been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same technology additionally grew to become available with the new generation of AFFF-ARs.
In latest years fluorine, one of many cornerstone components to all foams, has become an environmental problem, as a outcome of persistence in groundwater. The business has been presented with a serious problem to eliminate the ‘fluoro’ element of all the completely different foam focus types. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a complete vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn out to be the new normal and first alternative for operators altering current inventory or reviewing new projects. As a foam proportioner manufacturer we must study the bodily properties of froth rigorously (especially viscosity) as they influence choices on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more necessary in 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 gasoline.
เกจวัดแรงดันลมราคา concentrate producers will naturally promote their product as being extremely effective. The best method of evaluating their claims is to familiarise your self with the empirically primarily based normal 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 both included within the take a look at protocols. This additionally covers recent and seawater as properly as light and forceful application of the foam. Each foam is given a ranking with IA being the best, IIID the worst. This means that you can problem foam suppliers to find a way to make an informed determination on the most effective foam on your wants.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the effects on foam efficiency from elements outdoors the usual tests should be famous. For example, significantly aggressive solvents can problem the firefighting effectiveness of certain foams. This may be exacerbated by completely different ambient air temperatures, the applying methodology, gasoline depth and so on. Our advice can be to grasp the primary points of the checks and attempt to match them to the foam’s appropriateness in your particular person hazards. We would at all times recommend consulting individual foam producers as they will often provide specific in-house fire-performance information against a few of the more unusual fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on performance, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the growth ratio Images supplied by Author / Contributor
Critical components for achievement: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the rate at which completed foam is applied. Both are determined by empirically based standards revealed by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given measurement of fireplace area it’s essential to use the foam for lengthy enough to realize extinction and to stop re-ignition. This is particularly important in handbook intervention as firefighter’s shall be at risk during post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the application time could be so lengthy as 60 minutes for the largest tank diameters.
The software price refers back to the amount of completed foam utilized per square metre. This varies based on the gas and the foam sort however is currently a minimum of 4.0 litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the probability that this shall be reduced, but requirements usually take time to recognise product development. Anything less than the minimum application rate implies that hearth control is unlikely to be achieved. This means that firefighting resources, significantly in a manual fireplace attack, must be assembled before firefighting commences and this takes time. The advantage in fitting fastened techniques is that the sources are already designed and built into the system for instant application.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an informed determination on how finest to sort out their explicit fireplace challenges, the next is an summary of the assorted foam proportioning methods.
Foam inductors:
Typically related to hearth service deployment and restricted fastened methods functions. This makes use of the venturi precept to create a stress drop in a small aluminium or seawater material compatible gadget with built-in focus pick-up tube. The stress drop created by the venturi draws the foam focus from a container the place 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 hearth equipment or fitted right into a pipework system.
However, whilst it’s thought of to be the best method, it has extreme drawbacks: (i) units are manufacturing facility calibrated so any adjustments to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge system or a changing amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are crucial as deviations attributable to pipe diameter modifications will adversely affect proportioning accuracy and potentially stop any proportioning; (iii) changes in focus viscosity will undermine the ability of the venturi to draw concentrate into the downstream lines; (iv) pressure loss is high, as much as 35%, so duty pump pressures must be high enough to allow for it, probably including additional cost into the system; (v) foam delivery units must be sized so as not to restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs because of foam concentrate usage, which needs to be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electric or a combination of electrical and diesel pumps to produce foam concentrate into a proportioner at a better strain than the incoming water-line strain. The proportioner is installed into the water line and regulates the mixing.
They at the moment are related to older methods, where disadvantages embrace: (i) further prices in hardware and design time; (ii) the foam pump is normally restricted to a much tighter working range, though the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump needs a further power supply, other than water, so isn’t as reliably safe as a system with a possible single point of failure, such as an entirely water-driven system; (iv) sometimes, these systems are very advanced and cause high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to damage the froth focus and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel stress vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner similar to the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the froth filled bladder so that foam focus may be proportioned with water using the same supply. The venturi principle is again introduced into play as it creates a strain drop at the level of injection for the froth concentrate. Testing can’t be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs because of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because nice care is needed to avoid a damaged bladder when commissioning a new installation. It isn’t simple to work inside the steel stress vessel should issues happen, particularly if and when a substitute bladder could also be required: all of it provides to the problem and cost.
Compressed air foam (CAFS):
This just isn’t a proportioning technique within the standard sense as the froth is already proportioned using one of the earlier methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam solution on the level of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces permitting better penetration and cooling. This can be a benefit in wildfire conditions by coating vulnerable buildings to mitigate hearth progress. The restricted water supplies associated with distant wildfire areas implies that the resource may be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra level of failure is feasible because of the additional CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is only mechanical and highly reliable. A water-driven rotor provides the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is equipped with foam focus via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning price and will proportion the froth focus precisely throughout a wide operating vary. 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 provided by Author / Contributor
The benefits of FireDos Gen III FM approved foam proportioners embrace:
Reduced prices: proportioning fee is examined without utilizing foam or creating premix or foam – price efficient and eco-friendly.
Improved performance: constant proportioning price throughout a wide operating range.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a unique proportioning price.
FM approved FireDos Gen III proportioners are to date the only FM permitted water motor coupled variable proportioners utilizing FM approved flow meters. Using the test return line this provides the chance to verify the proportioning price throughout commissioning as well as for annual exams, with out creating any premix, which is a really massive profit for the consumer and relieves the environment.
In the second a part of this characteristic we will discover the consequences of viscosity on foam proportioning and typical foam application areas and really helpful discharge devices.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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