Fire presents many challenges, not least due to the variables that decide which suppression medium is suitable for a given fire situation. Our goal in this two-part article is to supply steerage based on a hazard-specific approach and help you make an informed determination on appropriate fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorised 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 generally associated with cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise primarily in the Class B class: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely could not penetrate the fireplace load effectively.
Fire courses.
How will we make foam?
Finished ราคาเกจวัดแรงดันน้ำ comprises a easy recipe of froth focus, water and air. Foam focus is often mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge gadget – we’ll cowl proportioning later in this article and discharge strategies in Part 2. At this level air is entrained by using units designed to naturally aspirate the answer. The quantity of aspiration and the type of concentrate determines the expansion ratio. This is typically cut up between low, medium and high growth. Low growth is up to 20:1, medium is 200:1 and excessive growth is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated mills are also used. The choice to choose a particular growth ratio is set by the hazard beneath evaluation.
Put simply, water and oil do not mix. Applying only water to Class B products is not going to suppress the burning vapours. This is a crucial point 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 methodology is chosen to provide that blanket or movie, the target is identical.
Steps of froth generation Images equipped by Author / Contributor
A little of the historical past of froth development
We can date the development of contemporary foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the bottom component). The major disadvantage was as a end result of restricted gas tolerance, which meant it was susceptible to gasoline pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, synthetic detergents gave foam a greater fuel tolerance as well as forming a vapour-sealing movie throughout the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s improvement did not completely replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam could both fight gasoline pick-up (mixing) and provide an excellent resistance to warmth, outlined by the business as ‘burn-back resistance’.
Further growth in the Nineteen Eighties took FP to the following level 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 Eighties further added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced an extra challenge as they had been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical technology additionally turned out there with the new technology of AFFF-ARs.
In latest years fluorine, one of the cornerstone ingredients to all foams, has turn out to be an environmental issue, as a end result of persistence in groundwater. The business has been offered with a serious problem to eliminate the ‘fluoro’ factor of all the completely different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of a whole range 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 into the new regular and first selection for operators changing present stock or reviewing new projects. As a foam proportioner manufacturer we must look at the physical properties of foam carefully (especially viscosity) as they affect decisions on the general proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more essential within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant high quality of SFFF/F3 is critical to fight the small diploma of water miscibility of the fuel.
All foam focus producers will naturally promote their product as being highly efficient. The best method of comparing their claims is to familiarise your self with the empirically primarily based commonplace EN 1568 or UL162. The exams cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included within the test protocols. This additionally covers fresh and seawater as properly as mild and forceful software of the froth. Each foam is given a score with IA being one of the best, IIID the worst. This means that you can challenge foam suppliers so as to make an informed decision on one of the best foam in your needs.
Whilst EN 1568 is an excellent benchmark normal, consciousness of the consequences on foam performance from components outdoors the standard tests should be famous. For example, notably aggressive solvents can problem the firefighting effectiveness of certain foams. This may be exacerbated by totally different ambient air temperatures, the application methodology, gas depth and so forth. Our advice could be to know the major points of the tests and attempt to match them to the foam’s appropriateness on your individual hazards. We would always suggest consulting individual foam producers as they will usually present particular in-house fire-performance knowledge towards a few of the more unusual fuels.
However, despite the froth manufacturers’ generally 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 enlargement ratio Images supplied by Author / Contributor
Critical components for achievement: the time and application rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary elements: time and the rate at which completed foam is applied. Both are determined by empirically based mostly standards published by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given size of fireplace space it is needed to apply the froth for lengthy sufficient to achieve extinction and to forestall re-ignition. This is particularly critical in manual intervention as firefighter’s might be at risk throughout post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the appliance time could be as long as 60 minutes for the most important tank diameters.
The utility fee refers to the amount of finished foam utilized per sq. metre. This varies based on the gas and the foam type but is presently a minimal of four.zero litres per minute per sq. metre. One of the continued developments in foam performance is the chance that this will be decreased, but standards often take time to recognise product growth. Anything lower than the minimum software fee means that fireplace control is unlikely to be achieved. This means that firefighting sources, significantly in a manual fire attack, need to be assembled before firefighting commences and this takes time. The benefit in becoming mounted systems is that the assets are already designed and constructed into the system for quick utility.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to allow readers to make an informed decision on how greatest to deal with their specific fireplace challenges, the following is an summary of the various foam proportioning methods.
Foam inductors:
Typically related to hearth service deployment and restricted fastened techniques functions. This uses the venturi principle to create a strain drop in a small aluminium or seawater materials compatible device with built-in concentrate pick-up tube. The stress drop created by the venturi draws the foam focus from a container the place it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a fire equipment or fitted right into a pipework system.
However, whilst it’s thought of to be the only technique, it has extreme drawbacks: (i) units are manufacturing unit calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a altering quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter modifications will adversely have an effect on proportioning accuracy and potentially prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to draw focus into the downstream lines; (iv) strain loss is high, as much as 35%, so obligation pump pressures need to be high sufficient to permit for it, probably including additional cost into the system; (v) foam delivery devices must be sized so as not to limit design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to entire lifetime prices on account of foam concentrate usage, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a combination of electrical and diesel pumps to produce foam concentrate right into a proportioner at a better stress than the incoming water-line stress. The proportioner is put in into the water line and regulates the mixing.
They are actually related to older methods, the place disadvantages embody: (i) extra prices in hardware and design time; (ii) the froth pump is generally restricted to a much tighter working range, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an additional energy supply, aside from water, so is not as reliably secure as a system with a possible single point of failure, such as an entirely water-driven system; (iv) usually, these techniques are very advanced and cause high efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to damage the froth concentrate and entrain air, which in flip can undermine correct 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 those fitted to balanced stress proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam focus could be proportioned with water utilizing the same provide. The venturi principle is again brought into play because 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 costs as a outcome of foam concentrate utilization, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot because nice care is needed to avoid a broken bladder when commissioning a model new set up. It isn’t simple to work inside the metal strain vessel ought to issues happen, particularly if and when a substitute bladder may be required: it all provides to the problem and value.
Compressed air foam (CAFS):
This just isn’t a proportioning technique in the standard sense as the foam is already proportioned using one of the earlier strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth solution at the point of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces permitting better penetration and cooling. This can additionally be a profit in wildfire conditions by coating vulnerable structures to mitigate hearth progress. The restricted water supplies related to remote wildfire areas signifies that the resource may be fully optimised. However, as with balanced stress proportioner foam pumps, an additional level of failure is possible because of the additional CAFS equipment.
Water driven 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 only mechanical and extremely reliable. A water-driven rotor provides the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is provided with foam concentrate via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning fee and will proportion the foam concentrate accurately across a large operating vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning fee testing, fully with out 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 include:
Reduced prices: proportioning rate is tested without utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: fixed proportioning rate across a large operating range.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in stress loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a unique proportioning rate.
FM approved FireDos Gen III proportioners are to date the only FM permitted water motor coupled variable proportioners utilizing FM approved flow meters. Using the test return line this provides the likelihood to verify the proportioning price throughout commissioning as properly as for annual exams, with out creating any premix, which is a really huge profit for the user and relieves the environment.
In the second part of this function we are going to discover the results of viscosity on foam proportioning and typical foam application areas and beneficial discharge devices.
For extra information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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