Fire presents many challenges, not least due to the variables that decide which suppression medium is appropriate for a given fire situation. Our goal on this two-part article is to provide steering based on a hazard-specific method and assist you to make an knowledgeable determination on acceptable fire-suppression measures, particularly 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 generally related to cooking such as vegetable oils
Class E – electrical hazards.
As Unusual of froth proportioners and firefighting monitors, we specialise primarily in the Class B class: flammable liquids.
Foam is considered to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only might not penetrate the hearth load successfully.
Fire courses.
How do we make foam?
Finished foam solution comprises a easy recipe of foam concentrate, water and air. Foam focus is usually blended in the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge device – we’ll cover proportioning later on this article and discharge methods in Part 2. At this level air is entrained by using units designed to naturally aspirate the solution. The quantity of aspiration and the sort of concentrate determines the growth ratio. This is often break up between low, medium and excessive expansion. Low expansion is as much as 20:1, medium is 200:1 and excessive growth is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the foam adequately, although naturally aspirated generators are additionally used. The determination to choose a particular growth ratio is decided by the hazard under evaluation.
Put merely, water and oil do not combine. Applying only water to Class B merchandise will not suppress the burning vapours. This is an important level to make as it’s 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 film to be successful. Whatever methodology is chosen to supply that blanket or movie, the target is the same.
Steps of froth generation Images equipped by Author / Contributor
A little of the historical past of froth development
We can date the event of modern 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 primary downside was because of limited 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 utilizing protein as the bottom product, artificial detergents gave foam a higher fuel tolerance as properly as forming a vapour-sealing movie throughout the surface 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 substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both fight fuel pick-up (mixing) and offer a good resistance to warmth, outlined by the industry as ‘burn-back resistance’.
Further growth within the Eighties took FP to the subsequent degree with film-forming fluoroprotein or FFFP. We now had one of the best of both worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented an additional challenge as they were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar know-how additionally grew to become available with the model new generation of AFFF-ARs.
In latest years fluorine, one of many cornerstone elements to all foams, has become an environmental problem, due to persistence in groundwater. The business has been introduced with a serious problem to eliminate the ‘fluoro’ element of all of the completely different foam concentrate sorts. We have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of a complete vary of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn out to be the new normal and first alternative for operators altering current inventory or reviewing new tasks. As a foam proportioner producer we should look at the physical properties of foam fastidiously (especially viscosity) as they affect choices on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are increasingly important within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant high quality of SFFF/F3 is critical to combat the small diploma of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being extremely efficient. The best method of comparing their claims is to familiarise yourself with the empirically based commonplace 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 both included in the test protocols. This additionally covers fresh and seawater as nicely as gentle and forceful software of the froth. Each foam is given a ranking with IA being the best, IIID the worst. This means that you can challenge foam suppliers in order to make an knowledgeable decision on the best foam in your needs.
Whilst EN 1568 is an excellent benchmark standard, awareness of the consequences on foam performance from factors exterior the usual tests should be noted. For instance, significantly aggressive solvents can problem the firefighting effectiveness of certain foams. This could be exacerbated by totally different ambient air temperatures, the application method, gasoline depth etc. Our advice could be to understand the primary points of the exams and try to match them to the foam’s appropriateness for your particular person hazards. We would always recommend consulting particular person foam manufacturers as they’ll usually provide specific in-house fire-performance information in opposition to a number of the more uncommon fuels.
However, despite 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 based on the growth ratio Images supplied by Author / Contributor
Critical factors for achievement: the time and software fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the rate at which completed foam is utilized. Both are determined by empirically based standards printed by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor means that for a given dimension of fire space it’s needed to use the foam for long sufficient to attain extinction and to prevent re-ignition. This is especially important in guide intervention as firefighter’s might be in danger throughout post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the applying time can be so lengthy as 60 minutes for the most important tank diameters.
The software price refers to the quantity of completed foam applied per square metre. This varies according to the gas and the froth type but is currently a minimum of four.zero litres per minute per square metre. One of the continuing developments in foam efficiency is the chance that this will be decreased, however standards often take time to recognise product improvement. Anything lower than the minimal application fee means that fire control is unlikely to be achieved. This signifies that firefighting assets, notably in a guide fire assault, must be assembled before firefighting commences and this takes time. The benefit in becoming fastened techniques is that the sources are already designed and built into the system for quick utility.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an informed determination on how finest to deal with their explicit fire challenges, the next is an summary of the varied foam proportioning methods.
Foam inductors:
Typically associated with hearth service deployment and restricted fixed techniques purposes. This uses the venturi principle to create a stress drop in a small aluminium or seawater materials compatible system with built-in focus pick-up tube. The stress drop created by the venturi draws the froth concentrate 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 easily carried on a fireplace appliance or fitted right into a pipework system.
However, while it’s considered to be the only methodology, it has severe drawbacks: (i) models are factory calibrated so any changes to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a changing amount of discharge devices) will probably require a system re-design; (ii) system design and sign-off are critical as deviations attributable to pipe diameter changes will adversely have an effect on proportioning accuracy and probably prevent any proportioning; (iii) changes in concentrate viscosity will undermine the flexibility of the venturi to attract focus into the downstream traces; (iv) strain loss is high, as much as 35%, so obligation pump pressures have to be excessive sufficient to permit for it, doubtlessly adding additional cost into the system; (v) foam delivery devices must be sized in order not to restrict design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices because of foam concentrate utilization, which needs to be replaced, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mixture 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 put in into the water line and regulates the blending.
They are actually related to older systems, where disadvantages embrace: (i) additional prices in hardware and design time; (ii) the foam pump is normally 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, other than water, so is not as reliably safe as a system with a potential single point of failure, corresponding to a completely water-driven system; (iv) usually, these techniques are very advanced and cause high efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to wreck the froth concentrate and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel stress vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner much like the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth filled bladder in order that foam focus may be proportioned with water using the same provide. The venturi precept is again brought into play as it creates a stress drop on the point of injection for the froth focus. Testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime costs as a result of foam focus utilization, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is required to keep away from a broken bladder when commissioning a new set up. It isn’t easy to work within the steel strain vessel ought to problems happen, especially if and when a substitute bladder could also be required: it all provides to the problem and cost.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology within the typical sense as the froth is already proportioned using one of the previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth resolution on the point 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 benefit in wildfire situations by coating vulnerable constructions to mitigate hearth growth. The limited water supplies associated with remote wildfire areas means that the resource could be fully optimised. However, as with balanced pressure proportioner foam pumps, a further point of failure is feasible because of the additional CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is solely mechanical and highly dependable. A water-driven rotor provides the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning price and will proportion the froth concentrate accurately across a large working vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, utterly without using 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 accredited foam proportioners embrace:
Reduced prices: proportioning fee is examined without utilizing foam or creating premix or foam – value effective and eco-friendly.
Improved performance: constant proportioning rate throughout a large working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in strain loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a special proportioning rate.
FM accredited FireDos Gen III proportioners are to date the only FM permitted water motor coupled variable proportioners using FM approved circulate meters. Using the take a look at return line this offers the possibility to verify the proportioning rate during commissioning as properly as for annual exams, without creating any premix, which is a very huge benefit for the consumer and relieves the environment.
In the second part of this feature we will discover the results of viscosity on foam proportioning and typical foam utility areas and really helpful discharge gadgets.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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