Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given fireplace situation. Our goal in this two-part article is to supply guidance based on a hazard-specific approach and help you make an informed determination on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are classified as follows:
Class A – carbonaceous or combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires usually associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting screens, we specialise mainly in the Class B category: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely might not penetrate the hearth load effectively.
Fire courses.
How will we make foam?
Finished foam answer comprises a simple recipe of foam focus, water and air. Foam concentrate is often 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 are going to cowl proportioning later on this article and discharge methods in Part 2. At this level air is entrained by using devices designed to naturally aspirate the answer. The quantity of aspiration and the type of focus determines the expansion ratio. This is often split between low, medium and high enlargement. Low expansion is up to 20:1, medium is 200:1 and high enlargement is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to broaden the froth adequately, although naturally aspirated mills are additionally used. The decision to determine on a selected growth ratio is set by the hazard under review.
Put merely, water and oil do not mix. Applying solely water to Class B merchandise is not going to 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 enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to achieve success. Whatever method is chosen to provide that blanket or movie, the target is the same.
Steps of froth era Images equipped by Author / Contributor
A little of the history of foam growth
We can date the development of recent foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the base component). The major drawback was due to restricted fuel tolerance, which meant it was susceptible 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 higher gas tolerance in addition to forming a vapour-sealing movie across the floor of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s improvement didn’t completely replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam might both fight gas pick-up (mixing) and supply a good resistance to warmth, defined by the industry as ‘burn-back resistance’.
Further development in the Eighties took FP to the following stage with film-forming fluoroprotein or FFFP. We now had the most effective of each worlds: a film-forming foam that also had good burn-back resistance.
The Eighties further added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always offered a further challenge as they have been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same expertise additionally became obtainable with the new technology of AFFF-ARs.
In recent years fluorine, one of many cornerstone ingredients to all foams, has turn into an environmental problem, due to persistence in groundwater. The business has been introduced with a major problem to get rid of the ‘fluoro’ element of all of the completely different foam concentrate sorts. We have witnessed an era of manufacturers’ claims and counter claims concerning the efficacy of a complete range of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the model new normal and first choice for operators changing existing inventory or reviewing new initiatives. As a foam proportioner manufacturer we should study the physical properties of foam carefully (especially viscosity) as they influence choices on the general proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more important within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, implies that the alcohol-resistant high quality of SFFF/F3 is important to combat the small diploma of water miscibility of the gas.
All foam focus producers will naturally promote their product as being extremely efficient. The finest method of evaluating their claims is to familiarise yourself with the empirically based mostly standard EN 1568 or UL162. The exams 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 test protocols. This also covers contemporary and seawater as nicely as mild and forceful utility of the foam. Each foam is given a ranking with IA being the most effective, IIID the worst. This means that you could challenge foam suppliers to find a way to make an informed choice on the most effective foam on your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the results on foam performance from elements outdoors the standard exams ought to be noted. For instance, particularly aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the appliance methodology, gas depth etc. Our advice would be to understand the primary points of the exams and try to match them to the foam’s appropriateness in your particular person hazards. We would always recommend consulting individual foam producers as they can typically provide particular in-house fire-performance information in opposition to a few of the more uncommon fuels.
However, regardless of the foam manufacturers’ typically conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the growth ratio Images supplied by Author / Contributor
Critical components for achievement: the time and utility fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the speed at which finished foam is utilized. Both are determined 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 implies that for a given size of fire area it’s needed to apply the foam for long sufficient to attain extinction and to stop re-ignition. This is especially crucial in guide intervention as firefighter’s shall be at risk during post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the appliance time could be as lengthy as 60 minutes for the largest tank diameters.
The utility rate refers to the amount of finished foam applied per square metre. This varies in accordance with the gas and the froth sort however is presently no much less than four.0 litres per minute per sq. metre. One of the continued developments in foam efficiency is the likelihood that this might be lowered, however requirements often take time to recognise product growth. Anything lower than the minimal application rate signifies that fireplace management is unlikely to be achieved. This implies that firefighting sources, notably in a guide fireplace assault, need to be assembled earlier than firefighting commences and this takes time. The advantage in becoming mounted systems is that the sources are already designed and constructed into the system for immediate software.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to allow readers to make an informed determination on how best to tackle their specific fireplace challenges, the next is an outline of the various foam proportioning methods.
Foam inductors:
Typically associated with hearth service deployment and restricted mounted systems functions. This uses the venturi precept to create a strain drop in a small aluminium or seawater material appropriate gadget with built-in concentrate pick-up tube. The pressure drop created by the venturi draws the froth concentrate from a container the place it mixes with water to create foam resolution. Restricted -up tube and body of the inductor are compact sufficient to be simply carried on a fire appliance or fitted into a pipework system.
However, while it is thought of to be the best technique, it has extreme 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 quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations caused by pipe diameter changes will adversely affect proportioning accuracy and probably stop any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to attract concentrate into the downstream lines; (iv) pressure loss is high, as a lot as 35%, so obligation pump pressures need to be excessive enough to permit for it, potentially including additional price into the system; (v) foam delivery units have to be sized so as to not limit design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs because of foam concentrate utilization, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a mixture of electrical and diesel pumps to provide foam concentrate right into a proportioner at a better pressure than the incoming water-line strain. The proportioner is put in into the water line and regulates the mixing.
They at the second are related to older techniques, the place disadvantages embrace: (i) further prices in hardware and design time; (ii) the froth pump is normally restricted to a much tighter working vary, though the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump wants an extra power supply, aside from water, so is not as reliably safe as a system with a possible single level of failure, such as a completely water-driven system; (iv) usually, these methods are very complex and cause excessive efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to damage the foam concentrate 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 concentrate proportioner just like those fitted to balanced stress proportioners. The incoming pressurised water compresses the froth filled bladder so that foam concentrate can be proportioned with water using the same provide. The venturi principle is once more introduced into play as it creates a stress drop at the point of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to complete lifetime prices as a end result of foam concentrate usage, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a outcome of great care is needed to keep away from a broken bladder when commissioning a brand new installation. It is rarely easy to work throughout the steel strain vessel should issues occur, especially if and when a alternative bladder could also be required: all of it adds to the issue and cost.
Compressed air foam (CAFS):
This just isn’t a proportioning method in the conventional sense as the froth is already proportioned utilizing one of the earlier strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam resolution at the point of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces permitting better penetration and cooling. This is also a profit in wildfire situations by coating vulnerable constructions to mitigate fireplace progress. The restricted water supplies related to distant wildfire areas signifies that the useful resource may be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an additional level of failure is feasible because of the extra CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is solely mechanical and highly dependable. A water-driven rotor supplies the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and will proportion the froth focus accurately across a wide operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning fee testing, fully without using 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 embrace:
Reduced prices: proportioning rate is examined without using foam or creating premix or foam – price effective and eco-friendly.
Improved performance: constant proportioning fee across a large operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in stress loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a special proportioning rate.
FM accredited FireDos Gen III proportioners are so far the only FM approved water motor coupled variable proportioners using FM permitted move meters. Using the test return line this presents the chance to check the proportioning rate throughout commissioning as properly as for annual exams, without creating any premix, which is a very huge profit for the user and relieves the setting.
In the second part of this feature we will explore the results of viscosity on foam proportioning and typical foam utility areas and recommended discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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