Fire presents many challenges, not least due to the variables that determine which suppression medium is suitable for a given fire situation. Our goal on this two-part article is to offer steering based mostly on a hazard-specific approach and assist 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 classified as follows:
Class A – carbonaceous or combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires usually associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise primarily within the Class B class: flammable liquids.
Foam is considered to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain kinds of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water only could not penetrate the fire load effectively.
Fire lessons.
How do we make foam?
Finished foam answer comprises a easy recipe of foam focus, 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 system – we will cowl proportioning later in this article and discharge methods in Part 2. At this level air is entrained by utilizing gadgets designed to naturally aspirate the solution. The amount of aspiration and the sort of concentrate determines the expansion ratio. This is often break up between low, medium and high growth. Low enlargement is as a lot as 20:1, medium is 200:1 and excessive expansion is more 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 decision to choose on a selected expansion ratio is determined by the hazard beneath evaluate.
Put simply, water and oil do not combine. Applying solely water to Class B merchandise won’t suppress the burning vapours. This is an important level to make as it’s 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 movie to obtain success. Whatever methodology is chosen to produce that blanket or film, the target is similar.
Steps of froth era Images provided by Author / Contributor
A little of the history of froth growth
We can date the development of contemporary 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 base component). The primary disadvantage was due to limited gasoline tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using pressure gauge nuova fima ราคา as the bottom product, artificial detergents gave foam a higher gasoline tolerance as nicely as forming a vapour-sealing film throughout the surface of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s development didn’t fully replace the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight fuel pick-up (mixing) and offer a good resistance to warmth, defined by the business as ‘burn-back resistance’.
Further growth within the Eighties 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 Nineteen Eighties additional added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always offered an extra problem as they have been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar expertise additionally turned out there with the model new technology of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has turn into an environmental concern, due to persistence in groundwater. The trade has been introduced with a major problem to get rid of the ‘fluoro’ factor of all the totally different foam concentrate varieties. 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 outline these foams, which have turn out to be the new normal and first choice for operators changing present stock or reviewing new tasks. As a foam proportioner producer we must look at the physical properties of foam carefully (especially viscosity) as they influence decisions on the overall proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are increasingly important in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, implies that the alcohol-resistant quality of SFFF/F3 is important to fight the small diploma of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being extremely efficient. The greatest method of comparing their claims is to familiarise yourself with the empirically based mostly commonplace EN 1568 or UL162. The checks 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 additionally covers fresh and seawater as nicely as gentle and forceful application of the foam. Each foam is given a rating with IA being the most effective, IIID the worst. This means you could problem foam suppliers to have the ability to make an knowledgeable choice on one of the best foam in your wants.
Whilst EN 1568 is an excellent benchmark commonplace, awareness of the consequences on foam efficiency from factors outdoors the usual checks ought to be famous. For instance, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This can be exacerbated by totally different ambient air temperatures, the appliance technique, gasoline depth and so on. Our recommendation can be to grasp the main points of the checks and attempt to match them to the foam’s appropriateness on your individual hazards. We would always advocate consulting individual foam manufacturers as they can often present particular in-house fire-performance information against some of the more unusual fuels.
However, despite the foam manufacturers’ typically conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the expansion ratio Images provided by Author / Contributor
Critical factors for success: the time and software rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the speed at which finished foam is applied. Both are decided by empirically based requirements revealed by our bodies such because 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 is essential to apply the foam for lengthy sufficient to attain extinction and to forestall re-ignition. This is very crucial in manual intervention as firefighter’s might be at risk during post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the applying time could be so lengthy as 60 minutes for the largest tank diameters.
The software rate refers to the quantity of completed foam utilized per sq. metre. This varies according to the gasoline and the froth type but is at present at least 4.zero litres per minute per sq. metre. One of the continued developments in foam performance is the chance that this will be reduced, but standards often take time to recognise product improvement. Anything lower than the minimal software price implies that hearth management is unlikely to be achieved. This means that firefighting assets, significantly in a handbook hearth assault, must be assembled before firefighting commences and this takes time. The advantage in fitting fixed techniques is that the sources are already designed and constructed into the system for quick utility.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to allow readers to make an informed decision on how greatest to deal with their specific hearth challenges, the next is an outline of the varied foam proportioning strategies.
Foam inductors:
Typically related to fire service deployment and restricted mounted techniques applications. This uses the venturi principle to create a strain drop in a small aluminium or seawater materials suitable system with built-in focus pick-up tube. The pressure drop created by the venturi attracts the froth concentrate from a container the place it mixes with water to create foam answer. Both the pick-up tube and body of the inductor are compact enough to be simply carried on a fireplace equipment or fitted into a pipework system.
However, while it’s thought of to be the simplest technique, it has extreme drawbacks: (i) units are factory calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a altering amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are important as deviations caused by pipe diameter changes will adversely have an effect on proportioning accuracy and doubtlessly stop any proportioning; (iii) modifications in focus viscosity will undermine the flexibility of the venturi to draw focus into the downstream strains; (iv) strain loss is high, as much as 35%, so obligation pump pressures have to be excessive enough to permit for it, doubtlessly including additional cost into the system; (v) foam supply units need to be sized in order to not prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime costs as a result of foam focus utilization, which must be changed, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced strain proportioners:
These use an electrical or a mix of electrical and diesel pumps to produce foam concentrate right into a proportioner at a higher stress than the incoming water-line pressure. The proportioner is put in into the water line and regulates the mixing.
They are now related to older systems, where disadvantages embrace: (i) further costs in hardware and design time; (ii) the foam pump is generally restricted to a much tighter working vary, although the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump wants an additional power source, other than water, so isn’t as reliably safe as a system with a possible single point of failure, corresponding to an entirely water-driven system; (iv) sometimes, these techniques are very advanced and trigger high efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to damage the froth concentrate and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel pressure vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner just like the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam focus may be proportioned with water using the identical supply. The venturi precept is once more introduced into play as it creates a strain drop at 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 whole lifetime prices as a outcome of foam concentrate utilization, which must be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a end result of nice care is needed to keep away from a broken bladder when commissioning a brand new installation. It is never straightforward to work inside the steel pressure vessel should problems happen, especially if and when a substitute bladder could additionally be required: all of it adds to the difficulty and value.
Compressed air foam (CAFS):
This isn’t a proportioning methodology within the typical sense as the foam is already proportioned utilizing one of the earlier strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth 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 susceptible buildings to mitigate fire development. The limited water supplies associated with distant wildfire areas means that the resource can be fully optimised. However, as with balanced pressure proportioner foam pumps, an additional level of failure is feasible because of the extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is only mechanical and highly dependable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is equipped with foam focus via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning fee and will proportion the froth concentrate accurately throughout a large operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, completely with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The advantages of FireDos Gen III FM approved foam proportioners embody:
Reduced costs: proportioning fee is tested without using foam or creating premix or foam – cost effective and eco-friendly.
Improved efficiency: fixed proportioning price throughout a large operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in pressure loss, in comparison with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a different proportioning price.
FM accredited FireDos Gen III proportioners are so far the only FM permitted water motor coupled variable proportioners utilizing FM approved move meters. Using the test return line this provides the chance to verify the proportioning fee throughout commissioning in addition to for annual exams, without creating any premix, which is a very massive profit for the person and relieves the environment.
In the second a part of this characteristic we’ll discover the effects of viscosity on foam proportioning and typical foam application areas and really helpful discharge gadgets.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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