Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fire state of affairs. Our objective in this two-part article is to offer steerage based on a hazard-specific method and allow you to make an informed determination on applicable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorized 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 related to cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise primarily within the Class B category: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water solely could not penetrate the hearth load successfully.
Fire classes.
How can we make foam?
Finished foam answer includes a simple recipe of froth focus, water and air. Foam concentrate is typically blended 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 gadget – we are going to cover proportioning later in this article and discharge strategies in Part 2. At this level air is entrained by utilizing units designed to naturally aspirate the answer. The quantity of aspiration and the type of focus determines the enlargement ratio. This is typically cut up between low, medium and excessive expansion. Low growth is as much as 20:1, medium is 200:1 and high expansion is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to increase the foam adequately, although naturally aspirated generators are also used. The decision to choose a particular enlargement ratio is decided by the hazard underneath evaluation.
Put merely, water and oil do not combine. Applying solely water to Class B merchandise is not going to suppress the burning vapours. This is a crucial point 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 obtain success. Whatever methodology is chosen to produce that blanket or movie, the objective is identical.
Steps of foam technology Images supplied by Author / Contributor
A little of the history of foam improvement
We can date the development of recent foam concentrates from the 1960s onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the base component). The major downside was due to restricted fuel tolerance, which meant it was prone to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, artificial detergents gave foam a greater gas tolerance as nicely as forming a vapour-sealing film across the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s growth didn’t fully replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight gasoline pick-up (mixing) and provide a good resistance to warmth, outlined by the industry as ‘burn-back resistance’.
Further growth in the 1980s took FP to the subsequent stage with film-forming fluoroprotein or FFFP. We now had the most effective of both worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s further added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always presented an extra 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 identical expertise also became obtainable with the new era of AFFF-ARs.
In current years fluorine, one of many cornerstone ingredients to all foams, has turn into an environmental concern, as a end result of persistence in groundwater. The trade has been presented with a major challenge to remove the ‘fluoro’ element of all the totally different foam concentrate sorts. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of an entire 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 into the new normal and first alternative for operators changing existing inventory or reviewing new tasks. As a foam proportioner producer we must examine the bodily properties of foam rigorously (especially viscosity) as they affect choices on the overall proportioning answer. More of this later.
Multi-purpose foams such as 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, signifies that the alcohol-resistant high quality of SFFF/F3 is important to fight the small degree of water miscibility of the gas.
All foam concentrate producers will naturally promote their product as being highly effective. The best way of evaluating their claims is to familiarise yourself with the empirically primarily based standard EN 1568 or UL162. The tests 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 within the check protocols. This also covers recent and seawater as well as light and forceful utility of the foam. Each foam is given a ranking with IA being one of the best, IIID the worst. This means you could challenge foam suppliers to find a way to make an informed determination on the most effective foam on your needs.
Whilst EN 1568 is an excellent benchmark normal, consciousness of the results on foam performance from elements outdoors the standard tests should be famous. For example, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the appliance technique, fuel depth and so forth. Our recommendation can be to know the details of the exams and attempt to match them to the foam’s appropriateness on your individual hazards. We would always suggest consulting individual foam producers as they can usually provide particular in-house fire-performance data towards a few of the more uncommon fuels.
However, regardless of the froth manufacturers’ typically 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 in accordance with the expansion ratio Images supplied by Author / Contributor
Critical factors for fulfillment: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the speed at which completed foam is utilized. Both are determined by empirically primarily based requirements published by our bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given measurement of fireplace space it’s necessary to use the foam for long sufficient to achieve extinction and to prevent re-ignition. This is especially crucial in guide intervention as firefighter’s shall be in danger throughout post-fire operations. When it comes to fastened safety for hydrocarbon and polar solvent tanks, the application time can be so long as 60 minutes for the most important tank diameters.
The utility price refers to the amount of finished foam utilized per sq. metre. This varies in accordance with the gasoline and the foam type but is currently a minimal of 4.0 litres per minute per square metre. One of the continued developments in foam efficiency is the likelihood that this will be lowered, but requirements usually take time to recognise product improvement. Anything less than the minimal application fee means that fire control is unlikely to be achieved. This signifies that firefighting assets, significantly in a manual fire assault, have to be assembled earlier than firefighting commences and this takes time. The advantage in fitting fastened techniques is that the resources are already designed and constructed into the system for quick software.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to allow readers to make an knowledgeable choice on how finest to sort out their explicit fire challenges, the following is an overview of the varied foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and limited fixed techniques functions. This makes use of the venturi principle to create a strain drop in a small aluminium or seawater material suitable device with built-in focus pick-up tube. The strain drop created by the venturi attracts the foam 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 sufficient to be simply carried on a fire appliance or fitted right into a pipework system.
However, while it’s thought of to be the only method, it has severe drawbacks: (i) models are manufacturing unit 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 doubtless require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter modifications will adversely affect proportioning accuracy and doubtlessly forestall any proportioning; (iii) adjustments in concentrate viscosity will undermine the power of the venturi to draw focus into the downstream lines; (iv) pressure loss is excessive, as a lot as 35%, so duty pump pressures must be high sufficient to allow for it, potentially including further cost into the system; (v) foam supply gadgets have to be sized in order to not limit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices on account of foam focus usage, which has to be changed, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electric or a mix of electrical and diesel pumps to provide foam concentrate right into a proportioner at a higher stress than the incoming water-line strain. The proportioner is put in 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 froth pump is normally restricted to a a lot tighter operating range, although the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump needs an additional energy source, aside from water, so isn’t as reliably safe as a system with a potential single point of failure, similar to a wholly water-driven system; (iv) usually, these systems are very advanced and cause 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 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 pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner just like the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth crammed bladder in order that foam concentrate can be proportioned with water utilizing the same provide. The venturi precept is again introduced into play as it creates a strain drop on the level of injection for the foam concentrate. Testing can’t be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs as a end result of foam concentrate utilization, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of great care is needed to avoid a damaged bladder when commissioning a model new installation. It isn’t simple to work within the steel strain vessel ought to issues occur, especially if and when a substitute bladder may be required: all of it adds to the issue and price.
Compressed air foam (CAFS):
This isn’t a proportioning method in 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 title suggests, CAFS injects compressed air into the foam resolution on the level of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces allowing higher penetration and cooling. This can additionally be a benefit in wildfire situations by coating weak constructions to mitigate fire growth. เกจวัดแรงดันดิจิตอล associated with remote wildfire areas signifies that the useful resource may be totally optimised. However, as with balanced pressure proportioner foam pumps, an additional point of failure is possible as a end result of further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is purely mechanical and highly dependable. A water-driven rotor provides the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is provided with foam focus via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning price and will proportion the froth concentrate precisely across a large operating vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, utterly without using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The advantages of FireDos Gen III FM approved foam proportioners include:
Reduced prices: proportioning fee is examined without using foam or creating premix or foam – cost efficient and eco-friendly.
Improved performance: fixed proportioning price throughout a large working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in pressure loss, in comparison with older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a special proportioning fee.
FM approved FireDos Gen III proportioners are thus far the one FM approved water motor coupled variable proportioners using FM permitted flow meters. Using the test return line this provides the likelihood to examine the proportioning price during commissioning as well as for annual tests, with out creating any premix, which is a really big benefit for the person and relieves the setting.
In the second a half of this characteristic we’ll explore the effects of viscosity on foam proportioning and typical foam application areas and recommended discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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