Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given hearth situation. Our goal on this two-part article is to supply steering based on a hazard-specific approach and help you make an informed decision 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 combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires usually related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting displays, we specialise mainly in the Class B category: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely may not penetrate the fire load successfully.
Fire lessons.
How do we make foam?
Finished foam answer includes a easy recipe of froth focus, water and air. Foam concentrate is often mixed within the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge device – we are going to cowl proportioning later on this article and discharge methods in Part 2. At this point air is entrained by using units designed to naturally aspirate the answer. The amount of aspiration and the sort of focus determines the enlargement ratio. This is typically break up between low, medium and high expansion. Low enlargement is up to 20:1, medium is 200:1 and excessive enlargement is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the froth adequately, although naturally aspirated turbines are additionally used. The choice to choose a particular growth ratio is decided by the hazard beneath evaluate.
Put simply, water and oil don’t combine. Applying solely water to Class B merchandise will not 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 allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever technique is chosen to produce that blanket or film, the objective is the same.
Steps of foam era Images provided by Author / Contributor
A little of the history of froth development
We can date the development of recent foam concentrates from the 1960s onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the base component). The primary disadvantage was because of restricted gas tolerance, which meant it was susceptible to gasoline pick-up (mixing). A breakthrough got here 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 surface of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth didn’t completely replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight fuel pick-up (mixing) and offer an excellent resistance to heat, outlined by the industry as ‘burn-back resistance’.
Further development in the 1980s took FP to the subsequent level with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that additionally had good burn-back resistance.
The Nineteen Eighties additional added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented an additional problem as they had been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same technology also grew to become out there 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, due to persistence in groundwater. The trade has been introduced with a major challenge to get rid of the ‘fluoro’ element of all of the different foam focus varieties. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of an entire 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 become the new regular and first selection for operators changing existing stock or reviewing new initiatives. As a foam proportioner producer we must look at the physical properties of froth rigorously (especially viscosity) as they influence choices on the general proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly necessary within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is important to fight the small degree of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being extremely effective. The finest method of evaluating their claims is to familiarise your self with the empirically primarily based standard EN 1568 or UL162. The exams cowl extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the more demanding polar solvents are each included in the take a look at protocols. This also covers fresh and seawater in addition to light and forceful utility of the foam. Each foam is given a ranking with IA being the best, IIID the worst. This means that you could challenge foam suppliers so as to make an informed choice on one of the best foam for your wants.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the effects on foam performance from elements exterior the usual tests ought to be famous. For example, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the appliance methodology, gas depth etc. Our recommendation would be to know the primary points of the tests and try to match them to the foam’s appropriateness on your individual hazards. We would all the time advocate consulting particular person foam manufacturers as they will typically provide particular in-house fire-performance data towards a variety of the extra uncommon fuels.
However, despite the froth manufacturers’ generally conflicting claims on performance, the earlier fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the growth ratio Images supplied by Author / Contributor
Critical elements for achievement: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the rate at which completed foam is applied. Both are decided by empirically based mostly standards 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 is needed to use the foam for long sufficient to attain extinction and to stop re-ignition. This is very crucial in manual 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 may be as lengthy as 60 minutes for the biggest tank diameters.
The application fee refers to the quantity of completed foam applied per sq. metre. This varies according to the gasoline and the froth type however is presently at least 4.0 litres per minute per square metre. One of the continuing developments in foam performance is the chance that this will be reduced, but requirements often take time to recognise product improvement. Anything less than the minimal software fee means that fire management is unlikely to be achieved. เกจวัดแรงดันคือ implies that firefighting assets, significantly in a handbook fire attack, need to be assembled earlier than firefighting commences and this takes time. The advantage in fitting mounted methods is that the sources are already designed and built into the system for instant utility.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to permit readers to make an informed determination on how best to deal with their specific fireplace challenges, the next is an summary of the various foam proportioning strategies.
Foam inductors:
Typically related to fire service deployment and restricted fastened methods applications. This uses the venturi principle to create a strain drop in a small aluminium or seawater material appropriate device with built-in concentrate pick-up tube. The pressure drop created by the venturi draws the foam concentrate from a container where 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 appliance or fitted right into a pipework system.
However, while it’s considered to be the best technique, it has severe drawbacks: (i) units are manufacturing facility calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a changing quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations caused by pipe diameter adjustments will adversely affect proportioning accuracy and doubtlessly prevent any proportioning; (iii) adjustments in concentrate viscosity will undermine the ability of the venturi to attract concentrate into the downstream traces; (iv) pressure loss is excessive, as much as 35%, so obligation pump pressures have to be excessive enough to allow for it, potentially adding further value into the system; (v) foam delivery units have to be sized so as to not prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices because of foam focus usage, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electric or a combination of electrical and diesel pumps to supply foam concentrate right into a proportioner at the next pressure than the incoming water-line strain. The proportioner is installed into the water line and regulates the blending.
They are actually associated with older techniques, where disadvantages embrace: (i) further prices in hardware and design time; (ii) the foam pump is often restricted to a much tighter working range, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs an extra power supply, aside from water, so just isn’t as reliably safe as a system with a potential single level of failure, similar to a wholly water-driven system; (iv) sometimes, these systems are very complicated and trigger high efforts at 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 froth focus and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner just like those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam crammed bladder in order that foam focus may be proportioned with water using the same provide. The venturi precept is again brought into play because it creates a stress drop on the level of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs on account of foam concentrate utilization, which must 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 damaged bladder when commissioning a new set up. It is rarely easy to work inside the metal pressure vessel should problems occur, especially if and when a substitute bladder could additionally be required: all of it adds to the issue and cost.
Compressed air foam (CAFS):
This isn’t a proportioning technique within the conventional sense as the froth is already proportioned utilizing one of many earlier methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam resolution on the level of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces permitting better penetration and cooling. This is also a profit in wildfire situations by coating weak structures to mitigate fire growth. The restricted water supplies related to remote wildfire areas signifies that the resource can be totally optimised. However, as with balanced stress proportioner foam pumps, an additional point of failure is possible due to the further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is purely mechanical and highly dependable. A water-driven rotor supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate 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 will proportion the froth focus precisely throughout a large working vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, fully with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM permitted 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 rate throughout a wide operating vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in strain loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning fee.
FM permitted FireDos Gen III proportioners are thus far the only FM permitted water motor coupled variable proportioners utilizing FM permitted circulate meters. Using the take a look at return line this presents the chance to check the proportioning fee during commissioning as properly as for annual exams, without creating any premix, which is a really massive benefit for the person and relieves the surroundings.
In the second part of this function we will discover the consequences of viscosity on foam proportioning and typical foam application areas and recommended discharge gadgets.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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