Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given fireplace situation. Our objective in this two-part article is to supply steerage based on a hazard-specific approach and help you make an knowledgeable determination on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires generally associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting monitors, we specialise primarily in the Class B category: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only may not penetrate the fireplace load successfully.
Fire lessons.
How can we make foam?
Finished foam solution includes a simple recipe of foam concentrate, water and air. Foam concentrate is often mixed in 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 are going to cowl proportioning later in this article and discharge strategies in Part 2. At this level air is entrained through the use of units designed to naturally aspirate the solution. The amount of aspiration and the kind of concentrate determines the enlargement ratio. This is usually break up between low, medium and excessive growth. Low enlargement is as a lot as 20:1, medium is 200:1 and high 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 turbines are additionally used. The choice to choose a specific expansion ratio is set by the hazard beneath review.
Put simply, water and oil don’t mix. Applying solely water to Class B products won’t suppress the burning vapours. This is a vital 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 be successful. Whatever methodology is chosen to supply that blanket or movie, the target is similar.
Steps of foam technology Images equipped by Author / Contributor
A little of the history of foam growth
We can date the development of contemporary foam concentrates from the Sixties onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the base component). The primary drawback was due to limited gas tolerance, which meant it was vulnerable to gasoline pick-up (mixing). เกจวัดแรงดันเบนซิน came 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 movie throughout the floor of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth did not utterly replace the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat gasoline pick-up (mixing) and offer an excellent resistance to heat, outlined by the industry as ‘burn-back resistance’.
Further improvement in the 1980s took FP to the following degree with film-forming fluoroprotein or FFFP. We now had the most effective of each worlds: a film-forming foam that also had good burn-back resistance.
The Eighties additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced an additional problem as they were 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 available with the new generation of AFFF-ARs.
In current years fluorine, one of many cornerstone ingredients to all foams, has become an environmental issue, as a outcome of persistence in groundwater. The industry has been presented with a serious problem to remove the ‘fluoro’ element of all of the totally different foam concentrate types. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of a whole range 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 choice for operators changing present stock or reviewing new initiatives. As a foam proportioner manufacturer we must look at the bodily properties of froth rigorously (especially viscosity) as they influence choices on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are increasingly important in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant quality of SFFF/F3 is critical to combat the small degree of water miscibility of the gasoline.
All foam concentrate manufacturers will naturally promote their product as being extremely efficient. The finest way of evaluating their claims is to familiarise your self with the empirically primarily based commonplace EN 1568 or UL162. The exams cover extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are both included within the test protocols. This also covers recent and seawater as nicely as mild 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 challenge foam suppliers so as to make an knowledgeable decision on the most effective foam for your wants.
Whilst EN 1568 is an excellent benchmark normal, consciousness of the consequences on foam performance from factors exterior the standard exams must be famous. For example, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by completely different ambient air temperatures, the applying methodology, gasoline depth etc. Our recommendation would be to know the details of the exams and attempt to match them to the foam’s appropriateness for your individual hazards. We would all the time recommend consulting particular person foam manufacturers as they can often present particular in-house fire-performance information in opposition to a variety of the more uncommon fuels.
However, despite the froth manufacturers’ typically conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the enlargement ratio Images supplied by Author / Contributor
Critical components for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the rate at which finished foam is applied. Both are decided by empirically primarily based standards published by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given measurement of fire area it is needed to use the foam for lengthy sufficient to realize extinction and to prevent re-ignition. This is very important in manual intervention as firefighter’s might be at risk during post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the appliance time may be as lengthy as 60 minutes for the largest tank diameters.
The utility rate refers again to the amount of completed foam applied per sq. metre. This varies in accordance with the fuel and the froth sort but is presently no less than four.zero litres per minute per square metre. One of the continuing developments in foam performance is the probability that this shall be reduced, but requirements often take time to recognise product improvement. Anything less than the minimal software fee means that fireplace control is unlikely to be achieved. This means that firefighting sources, significantly in a handbook fire assault, have to be assembled before firefighting commences and this takes time. The advantage in becoming mounted methods is that the sources are already designed and constructed into the system for immediate application.
Principle of froth extinguishment Images supplied 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 tackle their explicit hearth challenges, the following is an summary of the various foam proportioning methods.
Foam inductors:
Typically associated with fire service deployment and restricted mounted methods functions. This makes use of the venturi principle 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 attracts the froth focus from a container where it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a fireplace appliance or fitted right into a pipework system.
However, while it’s thought of to be the simplest methodology, it has extreme drawbacks: (i) items are factory calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a changing amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are important as deviations caused by pipe diameter adjustments will adversely have an result on proportioning accuracy and doubtlessly prevent any proportioning; (iii) modifications in focus viscosity will undermine the ability of the venturi to attract focus into the downstream lines; (iv) pressure loss is high, as much as 35%, so obligation pump pressures have to be excessive sufficient to permit for it, doubtlessly including extra cost into the system; (v) foam supply gadgets have to be sized so as not to limit design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to whole lifetime costs on account of foam concentrate usage, which needs to be changed, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced stress proportioners:
These use an electrical or a combination of electric and diesel pumps to produce foam focus right into a proportioner at a higher pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the mixing.
They are now related to older methods, the place disadvantages embody: (i) further costs in hardware and design time; (ii) the foam pump is often restricted to a much tighter working vary, although the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump needs an additional energy source, aside from water, so is not as reliably safe as a system with a possible single level of failure, similar to an entirely water-driven system; (iv) sometimes, these techniques are very complicated and trigger high efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to wreck the foam concentrate and entrain air, which in turn can undermine accurate 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 similar to those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam concentrate may be proportioned with water utilizing the identical provide. The venturi principle is again brought into play as it creates a stress drop at the level of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime prices as a result of foam focus usage, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a result of great care is required to avoid a broken bladder when commissioning a new set up. It is rarely easy to work inside the metal pressure vessel should issues occur, particularly if and when a alternative bladder may be required: all of it provides to the problem and price.
Compressed air foam (CAFS):
This is not 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 quite than naturally entrained or aspirated. As the name 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 capability to cling to vertical surfaces allowing higher penetration and cooling. This can be a benefit in wildfire situations by coating vulnerable buildings to mitigate fireplace progress. The restricted water provides related to distant wildfire areas implies that the useful resource can be fully optimised. However, as with balanced pressure proportioner foam pumps, a further point of failure is feasible because of the further CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is solely mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and can proportion the foam focus accurately across a large working range. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate testing, fully without utilizing 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 permitted foam proportioners include:
Reduced prices: proportioning price is examined without utilizing foam or creating premix or foam – price efficient and eco-friendly.
Improved efficiency: constant proportioning price across a large working vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in strain loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a different proportioning price.
FM accredited FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners utilizing FM permitted move meters. Using the test return line this presents the possibility to examine the proportioning fee during commissioning as properly as for annual exams, with out creating any premix, which is a really huge benefit for the consumer and relieves the setting.
In the second a part of this characteristic we will discover the consequences of viscosity on foam proportioning and typical foam software areas and beneficial discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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