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 offer steerage primarily based on a hazard-specific strategy and help you make an informed decision on applicable 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 similar to magnesium
Class F – fires usually associated with cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting screens, 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 forms of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only might not penetrate the fireplace load successfully.
Fire classes.
How will we make foam?
Finished foam resolution comprises a easy recipe of froth focus, water and air. Foam focus is usually 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 cover proportioning later in this article and discharge methods in Part 2. At this level air is entrained through the use of units designed to naturally aspirate the answer. The quantity of aspiration and the kind of focus determines the growth ratio. This is often split between low, medium and high growth. Low growth is up to 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 increase the foam adequately, though naturally aspirated generators are additionally used. The choice to choose on a specific growth ratio is determined by the hazard underneath review.
Put simply, water and oil do not combine. Applying only water to Class B products is not going to 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 enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to achieve success. Whatever technique is chosen to supply that blanket or movie, the objective is similar.
Steps of froth generation Images equipped by Author / Contributor
A little of the history of foam improvement
We can date the development of modern foam concentrates from the Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the bottom component). The main disadvantage was due to restricted fuel tolerance, which meant it was susceptible to gas pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, artificial detergents gave foam a greater fuel tolerance as well as forming a vapour-sealing film across the floor of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth did not completely substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both fight gasoline pick-up (mixing) and supply a great resistance to heat, defined by the trade as ‘burn-back resistance’.
Further development within the Eighties took FP to the subsequent level 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 1980s additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times offered an additional problem as they were water soluble and foam harmful. เกจวัดแรงดันแก๊ส -AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical technology also grew to become obtainable with the new generation of AFFF-ARs.
In recent years fluorine, one of the cornerstone components to all foams, has turn out to be an environmental concern, because of persistence in groundwater. The trade has been presented with a significant challenge to remove the ‘fluoro’ component of all of the different foam concentrate sorts. We have witnessed an period of manufacturers’ claims and counter claims relating to the efficacy of a whole vary 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 model new regular and first choice for operators altering present inventory or reviewing new tasks. As a foam proportioner manufacturer we must examine the bodily properties of froth carefully (especially viscosity) as they influence choices on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are increasingly necessary within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small degree of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being highly efficient. The best way of evaluating their claims is to familiarise yourself with the empirically based standard 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 more demanding polar solvents are each included in the take a look at protocols. This additionally covers recent and seawater in addition to mild and forceful utility of the froth. Each foam is given a score with IA being one of the best, IIID the worst. This means you could problem foam suppliers to be able to make an knowledgeable determination on one of the best foam for your wants.
Whilst EN 1568 is a wonderful benchmark normal, awareness of the effects on foam performance from elements outside the usual checks should be noted. For example, significantly aggressive solvents can problem the firefighting effectiveness of certain foams. This can be exacerbated by completely different ambient air temperatures, the applying method, gas depth and so on. Our recommendation could be to know the major points of the checks and try to match them to the foam’s appropriateness for your individual hazards. We would always advocate consulting individual foam producers as they will typically provide specific in-house fire-performance knowledge in opposition to a variety of the more uncommon fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on performance, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the enlargement ratio Images equipped by Author / Contributor
Critical elements for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary elements: time and the speed at which completed foam is applied. Both are decided by empirically primarily based standards revealed by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue signifies that for a given size of fireside area it is necessary to use the froth for long sufficient to attain extinction and to stop re-ignition. This is especially important in handbook intervention as firefighter’s shall be in danger throughout post-fire operations. When it involves fixed protection for hydrocarbon and polar solvent tanks, the applying time could be as long as 60 minutes for the biggest tank diameters.
The utility rate refers to the amount of completed foam applied per square metre. This varies according to the gasoline and the foam type however is currently no much less than four.0 litres per minute per square metre. One of the continuing developments in foam efficiency is the probability that this will be reduced, but standards usually take time to recognise product improvement. Anything less than the minimum software price means that fire control is unlikely to be achieved. This means that firefighting sources, significantly in a guide fireplace attack, have to be assembled before firefighting commences and this takes time. The benefit in fitting fastened methods is that the resources are already designed and built into the system for quick utility.
Principle of foam extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to permit readers to make an knowledgeable determination on how best to deal with their specific hearth challenges, the following is an summary of the varied foam proportioning methods.
Foam inductors:
Typically associated with hearth service deployment and limited mounted techniques purposes. This uses the venturi principle to create a pressure drop in a small aluminium or seawater material compatible system with built-in focus pick-up tube. The strain 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 body of the inductor are compact enough to be easily carried on a hearth appliance or fitted into a pipework system.
However, while it is thought-about to be the only methodology, it has extreme drawbacks: (i) units are manufacturing unit calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a changing amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter adjustments will adversely affect proportioning accuracy and potentially stop any proportioning; (iii) adjustments in concentrate viscosity will undermine the flexibility of the venturi to draw focus into the downstream traces; (iv) stress loss is high, as a lot as 35%, so duty pump pressures need to be high enough to permit for it, doubtlessly including extra cost into the system; (v) foam delivery devices must be sized so as to not restrict 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 must be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electrical or a mix of electrical and diesel pumps to supply foam concentrate right into a proportioner at the next pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the mixing.
They are actually related to older methods, where disadvantages embody: (i) additional prices in hardware and design time; (ii) the froth pump is generally restricted to a much tighter working range, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump needs an extra energy 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 techniques are very complex and trigger high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to break the foam focus and entrain air, which in flip can undermine correct 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 concentrate proportioner just like those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam focus can be proportioned with water using the same provide. The venturi precept is again brought into play because it creates a stress drop on the point of injection for the froth focus. Testing cannot be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs because of foam focus utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot because great care is needed to keep away from a damaged bladder when commissioning a new set up. It isn’t straightforward to work within the metal stress vessel ought to problems occur, particularly if and when a alternative bladder may be required: it all provides to the difficulty and value.
Compressed air foam (CAFS):
This just isn’t a proportioning technique in the standard sense as the froth is already proportioned utilizing one of the earlier strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam answer on the level of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces permitting higher penetration and cooling. This can be a profit in wildfire situations by coating susceptible buildings to mitigate fireplace development. The restricted water provides related to distant wildfire areas signifies that the useful resource can be fully optimised. However, as with balanced strain proportioner foam pumps, an additional level of failure is possible as a end result of further CAFS equipment.
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 solely mechanical and highly reliable. A water-driven rotor supplies the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and can proportion the foam concentrate accurately across a wide working vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate testing, completely without utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embody:
Reduced prices: proportioning price is examined with out using foam or creating premix or foam – value effective and eco-friendly.
Improved performance: fixed proportioning price across a wide working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a different proportioning price.
FM permitted FireDos Gen III proportioners are so far the one FM accredited water motor coupled variable proportioners using FM permitted flow meters. Using the test return line this provides the chance to examine the proportioning price during commissioning in addition to for annual checks, without creating any premix, which is a very massive benefit for the person and relieves the setting.
In the second part of this characteristic we will discover the consequences of viscosity on foam proportioning and typical foam software areas and really helpful discharge gadgets.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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