Fire presents many challenges, not least due to the variables that decide which suppression medium is suitable for a given fire state of affairs. Our objective in this two-part article is to supply steerage based on a hazard-specific strategy and help you 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 combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires usually associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of foam 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 kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only could not penetrate the hearth load successfully.
Fire classes.
How will we make foam?
Finished foam solution includes a easy recipe of froth concentrate, water and air. Foam focus is usually mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge device – we will cover proportioning later in this article and discharge strategies in Part 2. At this point air is entrained by utilizing units designed to naturally aspirate the answer. The quantity of aspiration and the kind of concentrate determines the growth ratio. This is often cut up between low, medium and excessive expansion. Low growth is up to 20:1, medium is 200:1 and excessive enlargement is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to expand the foam adequately, though naturally aspirated turbines are additionally used. The choice to decide on a specific expansion ratio is decided by the hazard beneath review.
Put simply, water and oil don’t combine. Applying solely water to Class B merchandise will not suppress the burning vapours. This is a crucial 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 film to be successful. Whatever technique is chosen to produce that blanket or movie, the target is identical.
Steps of froth generation Images supplied by Author / Contributor
A little of the historical past of foam development
We can date the development of modern foam concentrates from the 1960s onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the base component). The main drawback was as a result of restricted gas tolerance, which meant it was prone 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 higher fuel tolerance in addition to forming a vapour-sealing movie throughout the surface of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s improvement did not utterly replace the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam could each fight gasoline pick-up (mixing) and provide an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further growth within 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 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 always presented a further challenge 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 turned available with the brand new era of AFFF-ARs.
In recent years fluorine, one of many cornerstone elements to all foams, has turn out to be an environmental issue, as a end result of persistence in groundwater. The trade has been introduced with a serious challenge to remove the ‘fluoro’ component of all the totally different foam concentrate types. We have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of an entire vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn out to be the model new normal and first choice for operators changing current inventory or reviewing new tasks. As a foam proportioner manufacturer we must look at the physical properties of froth carefully (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 essential in the fuel-storage enviornment. 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 gas.
All foam concentrate producers will naturally promote their product as being extremely effective. The finest means of evaluating their claims is to familiarise your self with the empirically based mostly standard EN 1568 or UL162. The tests cover 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 additionally covers fresh and seawater in addition to gentle and forceful utility of the froth. Each foam is given a score with IA being the best, IIID the worst. This means you could problem foam suppliers in order to make an knowledgeable decision on the best foam on your needs.
Whilst EN 1568 is a superb benchmark normal, consciousness of the results on foam efficiency from elements exterior the usual exams ought to be famous. For instance, particularly aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by totally different ambient air temperatures, the applying technique, gasoline depth etc. Our recommendation could be to know the primary points of the tests and attempt to match them to the foam’s appropriateness for your particular person hazards. We would always advocate consulting individual foam manufacturers as they can typically provide particular in-house fire-performance information towards some of the extra unusual fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams based on the expansion ratio Images provided by Author / Contributor
Critical factors for success: the time and utility price matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary elements: time and the speed at which completed foam is applied. Both are decided by empirically primarily based standards published by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor means that for a given size of fire space it’s necessary to use the froth for lengthy enough to achieve extinction and to forestall re-ignition. This is particularly important in handbook intervention as firefighter’s will be at risk during post-fire operations. When it involves mounted protection for hydrocarbon and polar solvent tanks, the application time could be as long as 60 minutes for the biggest tank diameters.
เกจวัดแรงดันเบนซิน refers to the quantity of completed foam utilized per square metre. This varies in accordance with the gas and the foam type however is currently no much less than four.0 litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the probability that this might be reduced, however standards often take time to recognise product improvement. Anything lower than the minimum utility price means that fireplace management is unlikely to be achieved. This implies that firefighting sources, particularly in a handbook fireplace attack, have to be assembled before firefighting commences and this takes time. The benefit in fitting fixed techniques is that the resources are already designed and built into the system for instant software.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an informed determination on how greatest to tackle their specific fire challenges, the following is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with hearth service deployment and restricted fixed methods purposes. This makes use of the venturi precept to create a stress drop in a small aluminium or seawater materials suitable system with built-in focus pick-up tube. The strain drop created by the venturi draws the froth 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 easily carried on a fire appliance or fitted right into a pipework system.
However, while it is thought of to be the best technique, it has severe drawbacks: (i) models are manufacturing facility calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter changes will adversely have an result on proportioning accuracy and probably prevent any proportioning; (iii) adjustments in concentrate viscosity will undermine the ability of the venturi to attract focus into the downstream lines; (iv) strain loss is high, as a lot as 35%, so responsibility pump pressures must be excessive sufficient to permit for it, doubtlessly adding additional value into the system; (v) foam supply units need to be sized so as to not prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to complete lifetime costs as a result of foam concentrate usage, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages supplied by Author / Contributor
Balanced stress proportioners:
These use an electrical or a mix of electrical and diesel pumps to produce foam focus into a proportioner at a higher stress than the incoming water-line strain. The proportioner is installed into the water line and regulates the blending.
They are actually related to older methods, where disadvantages include: (i) extra prices in hardware and design time; (ii) the froth pump is normally restricted to a much tighter operating vary, although the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump wants a further power supply, other than water, so just isn’t as reliably safe as a system with a potential single level of failure, similar to an entirely water-driven system; (iv) sometimes, these methods are very advanced 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 damage the foam focus and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner similar to those fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth crammed bladder in order that foam focus could be proportioned with water utilizing the identical provide. The venturi principle is again introduced into play as it creates a pressure drop on the point of injection for the froth concentrate. Testing can’t be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices because of foam focus utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness because nice care is needed to avoid a damaged bladder when commissioning a model new set up. It isn’t easy to work throughout the steel strain vessel should issues happen, particularly if and when a replacement bladder could also be required: it all provides to the issue and cost.
Compressed air foam (CAFS):
This is not a proportioning method within the typical sense as the foam is already proportioned using one of many previous methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth answer on the point 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 is also a profit in wildfire conditions by coating weak buildings to mitigate fire progress. The limited water provides related to distant wildfire areas implies that the resource could be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra point of failure is feasible because of the extra CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is solely mechanical and extremely reliable. A water-driven rotor supplies the driving force to drive a instantly 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 rate and can proportion the froth concentrate precisely across a large operating vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, utterly without using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The benefits of FireDos Gen III FM approved foam proportioners embrace:
Reduced costs: proportioning rate is tested with out utilizing foam or creating premix or foam – price efficient and eco-friendly.
Improved performance: constant proportioning fee across a wide operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in pressure loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a special proportioning rate.
FM accredited FireDos Gen III proportioners are to date the only FM approved water motor coupled variable proportioners utilizing FM approved flow meters. Using the check return line this provides the likelihood to check the proportioning price throughout commissioning as nicely as for annual exams, without creating any premix, which is a really huge benefit for the user and relieves the environment.
In the second a half of this function we are going to explore the results of viscosity on foam proportioning and typical foam utility areas and beneficial discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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