Fire presents many challenges, not least due to the variables that determine which suppression medium is suitable for a given hearth situation. Our objective in this two-part article is to provide guidance primarily based on a hazard-specific strategy and help you make an informed determination on appropriate fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are classified 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 such as vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting monitors, we specialise primarily in the Class B category: flammable liquids.
Foam is considered to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only may not penetrate the hearth load successfully.
Fire lessons.
How can we make foam?
Finished foam solution contains a simple recipe of froth focus, water and air. Foam concentrate is typically combined 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 device – we’ll cowl proportioning later in this article and discharge strategies in Part 2. At this point air is entrained through the use of devices designed to naturally aspirate the answer. The quantity of aspiration and the sort of focus determines the expansion ratio. This is typically break up between low, medium and high enlargement. Low expansion is up to 20:1, medium is 200:1 and high enlargement is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to increase the froth adequately, though naturally aspirated mills are additionally used. The determination to choose on a particular enlargement ratio is set by the hazard under review.
Put merely, water and oil don’t combine. Applying only water to Class B products is not going to suppress the burning vapours. This is an important point 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 achieve success. Whatever methodology is chosen to supply that blanket or film, the target is identical.
Steps of froth technology Images equipped by Author / Contributor
A little of the history of foam improvement
We can date the event of contemporary foam concentrates from the Sixties onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the base component). The main disadvantage was because of limited 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 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 further enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s improvement did not completely replace the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight gasoline pick-up (mixing) and offer an excellent resistance to heat, outlined by the industry as ‘burn-back resistance’.
Further growth in the Nineteen Eighties took FP to the following level with film-forming fluoroprotein or FFFP. We now had the best of each worlds: a film-forming foam that additionally 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 always offered an extra problem as they were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same know-how also became available with the new generation of AFFF-ARs.
In recent years fluorine, one of many cornerstone ingredients to all foams, has turn into an environmental concern, because of persistence in groundwater. The trade has been presented with a major challenge to get rid of the ‘fluoro’ element of all the totally different foam concentrate sorts. เกจวัดแรงดันแก๊สอาร์กอน have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of a complete vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the brand new regular and first selection for operators changing current stock or reviewing new tasks. As a foam proportioner manufacturer we should examine the bodily properties of foam rigorously (especially viscosity) as they influence selections on the overall proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly necessary in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, implies that the alcohol-resistant quality of SFFF/F3 is important to combat the small degree of water miscibility of the gas.
All foam concentrate manufacturers will naturally promote their product as being highly effective. The greatest method of evaluating their claims is to familiarise your self with the empirically 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 both included in the take a look at protocols. This also covers recent and seawater as properly as gentle and forceful software of the froth. Each foam is given a ranking with IA being one of the best, IIID the worst. This means you could problem foam suppliers to have the ability to make an knowledgeable choice on the most effective foam in your needs.
Whilst EN 1568 is an excellent benchmark commonplace, awareness of the results on foam efficiency from components exterior the standard checks must be famous. For example, significantly aggressive solvents can challenge the firefighting effectiveness of certain foams. This can be exacerbated by completely different ambient air temperatures, the applying technique, fuel depth and so forth. Our advice would be to know the details of the exams and try to match them to the foam’s appropriateness for your individual hazards. We would at all times advocate consulting individual foam manufacturers as they’ll typically provide particular in-house fire-performance knowledge against a few of the extra uncommon fuels.
However, regardless of the foam manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the expansion ratio Images equipped by Author / Contributor
Critical components for fulfillment: the time and software price matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary elements: time and the rate at which finished foam is utilized. Both are decided by empirically based requirements revealed by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ factor implies that for a given dimension of fireplace space it’s needed to apply the froth for lengthy sufficient to attain extinction and to prevent re-ignition. This is very crucial in guide intervention as firefighter’s might be in danger throughout post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the applying time can be so long as 60 minutes for the biggest tank diameters.
The software price refers to the quantity of finished foam utilized per square metre. This varies according to the fuel and the froth type but is currently no less than four.zero litres per minute per sq. metre. One of the continuing developments in foam performance is the likelihood that this shall be lowered, but standards usually take time to recognise product improvement. Anything lower than the minimum utility price implies that fire control is unlikely to be achieved. This signifies that firefighting resources, significantly in a manual hearth attack, need to be assembled earlier than firefighting commences and this takes time. The advantage in becoming mounted systems is that the assets are already designed and constructed into the system for instant software.
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 knowledgeable determination on how best to deal with their explicit hearth challenges, the following is an overview of the varied foam proportioning strategies.
Foam inductors:
Typically related to fire service deployment and restricted mounted systems functions. This makes use of the venturi precept to create a strain drop in a small aluminium or seawater material appropriate device with built-in concentrate pick-up tube. The strain drop created by the venturi attracts the foam concentrate from a container where it mixes with water to create foam resolution. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a fireplace equipment or fitted into a pipework system.
However, whilst it is thought-about to be the only method, it has extreme drawbacks: (i) units are manufacturing facility calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge system or a changing quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter modifications will adversely affect proportioning accuracy and probably prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to draw concentrate into the downstream traces; (iv) strain loss is excessive, as much as 35%, so responsibility pump pressures have to be high enough to permit for it, doubtlessly adding extra value into the system; (v) foam supply gadgets have to be sized so as not to prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime prices on account of foam concentrate utilization, which has to be changed, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electrical or a mix of electric and diesel pumps to supply foam concentrate into a proportioner at a better pressure than the incoming water-line strain. The proportioner is put in into the water line and regulates the blending.
They at the second are related to older methods, where disadvantages embody: (i) extra costs in hardware and design time; (ii) the froth pump is normally restricted to a much tighter operating vary, though the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump wants an extra power supply, apart from water, so is not as reliably secure as a system with a possible single level of failure, corresponding to an entirely water-driven system; (iv) sometimes, these systems are very complex and trigger high efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to damage the froth concentrate and entrain air, which in flip can undermine accurate 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 focus proportioner similar to the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the froth filled bladder so that foam concentrate can be proportioned with water using the identical provide. The venturi principle is once more introduced into play as it creates a stress drop at the level of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices on account of foam focus usage, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is required to keep away from a broken bladder when commissioning a brand new set up. It is rarely simple to work inside the steel stress vessel should problems happen, particularly if and when a alternative bladder may be required: it all adds to the difficulty and price.
Compressed air foam (CAFS):
This isn’t a proportioning method within 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 solution on the level of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces permitting better penetration and cooling. This can also be a profit in wildfire situations by coating vulnerable constructions to mitigate hearth progress. The limited water provides associated with remote wildfire areas signifies that the resource could be fully optimised. However, as with balanced strain proportioner foam pumps, an extra level of failure is possible because of the extra CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third era, the product is solely mechanical and extremely reliable. A water-driven rotor supplies the motive force to drive a immediately 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 rate and will proportion the froth concentrate precisely across a large working vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, completely with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners embody:
Reduced prices: proportioning rate is tested with out using foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: fixed proportioning fee across a wide working range.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in pressure loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a special proportioning price.
FM accredited FireDos Gen III proportioners are thus far the one FM accredited water motor coupled variable proportioners using FM permitted move meters. Using the take a look at return line this presents the chance to check the proportioning rate throughout commissioning as nicely as for annual checks, without creating any premix, which is a really big benefit for the user and relieves the environment.
In the second part of this function we’ll discover the consequences of viscosity on foam proportioning and typical foam utility areas and really helpful discharge gadgets.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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