Fire presents many challenges, not least due to the variables that determine which suppression medium is appropriate for a given fireplace state of affairs. Our objective in this two-part article is to supply steerage based on a hazard-specific strategy and assist you to make an knowledgeable determination on applicable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are classified as follows:
Class A – carbonaceous or flamable materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires typically associated with cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise mainly within 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 types of foam (known as wetting agents) are particularly for deep-seated Class A fires where water solely might not penetrate the fire load successfully.
Fire classes.
How will we make foam?
Finished foam resolution includes a easy recipe of foam concentrate, water and air. Foam concentrate is typically combined in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge system – we are going to cover proportioning later on this article and discharge methods in Part 2. At this point air is entrained through the use of gadgets designed to naturally aspirate the answer. The quantity of aspiration and the sort of focus determines the expansion ratio. This is often split between low, medium and excessive expansion. Low growth 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 froth adequately, though naturally aspirated generators are also used. เครื่องมือใช้วัดความดัน to determine on a selected growth ratio is determined by the hazard under review.
Put simply, water and oil do not mix. Applying solely water to Class B merchandise 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 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 method is chosen to produce that blanket or film, the objective is similar.
Steps of froth era Images provided by Author / Contributor
A little of the historical past of foam improvement
We can date the development of contemporary foam concentrates from the 1960s onwards. Up to that time foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The major drawback was because of restricted gasoline tolerance, which meant it was susceptible to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, artificial detergents gave foam a higher gasoline tolerance as properly as forming a vapour-sealing film throughout the surface of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth didn’t fully exchange the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight fuel pick-up (mixing) and offer a good resistance to heat, defined by the trade as ‘burn-back resistance’.
Further growth in the Nineteen Eighties took FP to the next 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 1980s further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always introduced an additional 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 identical technology additionally turned out there with the brand new generation of AFFF-ARs.
In recent years fluorine, one of the cornerstone ingredients to all foams, has turn out to be an environmental concern, as a result of persistence in groundwater. The business has been presented with a significant challenge to eliminate the ‘fluoro’ factor of all the totally 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 regular and first alternative for operators altering existing stock or reviewing new projects. As a foam proportioner producer we should study the physical properties of froth fastidiously (especially viscosity) as they affect selections on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more necessary within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant 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 highly effective. The greatest method of comparing their claims is to familiarise yourself with the empirically based commonplace EN 1568 or UL162. The tests 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 within the check protocols. This additionally covers contemporary and seawater in addition to gentle and forceful software of the foam. Each foam is given a rating with IA being the most effective, IIID the worst. This means that you can challenge foam suppliers to have the ability to make an informed decision on one of the best foam in your needs.
Whilst EN 1568 is an excellent benchmark commonplace, consciousness of the consequences on foam performance from components outdoors the usual exams must be famous. For instance, notably aggressive solvents can problem the firefighting effectiveness of certain foams. This can be exacerbated by totally different ambient air temperatures, the appliance technique, gasoline depth etc. Our recommendation could be to grasp the major points of the checks and attempt to match them to the foam’s appropriateness in your particular person hazards. We would always advocate consulting particular person foam manufacturers as they will often provide specific in-house fire-performance data in opposition to some of the more unusual fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on performance, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the enlargement ratio Images supplied by Author / Contributor
Critical factors for fulfillment: the time and application price matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the rate at which finished foam is utilized. Both are determined by empirically based requirements revealed by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ factor means that for a given measurement of fireside space it’s necessary to apply the foam for lengthy enough to realize extinction and to stop re-ignition. This is especially critical in manual intervention as firefighter’s shall be at risk during post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the applying time could be as lengthy as 60 minutes for the most important tank diameters.
The application fee refers to the quantity of completed foam utilized per sq. metre. This varies in accordance with the fuel and the froth sort however is currently a minimum of 4.0 litres per minute per sq. metre. One of the continued developments in foam efficiency is the chance that this shall be reduced, however requirements typically take time to recognise product development. Anything lower than the minimal utility fee signifies that fireplace control is unlikely to be achieved. This means that firefighting sources, significantly in a handbook fire assault, have to be assembled before firefighting commences and this takes time. The benefit in fitting fastened techniques is that the assets are already designed and built into the system for instant application.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an informed determination on how finest to deal with their particular fire challenges, the next is an summary of the various foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and limited fixed techniques applications. This uses the venturi principle to create a stress drop in a small aluminium or seawater materials appropriate device with built-in focus pick-up tube. The stress drop created by the venturi attracts the froth 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 fireplace equipment or fitted into a pipework system.
However, whilst it is thought of to be the only methodology, it has extreme drawbacks: (i) units are manufacturing facility calibrated so any adjustments 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 doubtless require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter adjustments will adversely have an effect on proportioning accuracy and potentially prevent any proportioning; (iii) adjustments in focus viscosity will undermine the power of the venturi to attract focus into the downstream lines; (iv) strain loss is excessive, as a lot as 35%, so duty pump pressures have to be excessive enough to allow for it, potentially including further price into the system; (v) foam supply gadgets must be sized in order to not limit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs because of foam concentrate utilization, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mix of electrical and diesel pumps to supply foam concentrate right into a proportioner at a higher pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the mixing.
They are now associated with older systems, the place disadvantages embody: (i) additional prices in hardware and design time; (ii) the foam pump is often restricted to a much tighter operating vary, though the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs an additional energy source, aside from water, so is not as reliably safe as a system with a possible single level of failure, such as a wholly water-driven system; (iv) typically, these methods are very complex and trigger excessive efforts on 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 flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner just like the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the froth crammed bladder in order that foam concentrate could be proportioned with water using the same provide. The venturi principle is again introduced into play because it creates a strain drop on the level of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs as a end result of foam focus usage, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a result of nice care is required to avoid a damaged bladder when commissioning a new set up. It is rarely easy to work within the steel stress vessel should issues happen, especially if and when a substitute bladder may be required: it all adds to the problem and value.
Compressed air foam (CAFS):
This isn’t a proportioning method within the typical sense as the foam is already proportioned utilizing one of the earlier methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth answer at the level 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 also be a benefit in wildfire situations by coating vulnerable structures to mitigate fireplace growth. The limited water provides associated with remote wildfire areas implies that the useful resource can be fully optimised. However, as with balanced pressure proportioner foam pumps, a further level of failure is possible due to the extra CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have become 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 supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning price and will proportion the froth concentrate precisely throughout a wide working vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate testing, fully with out using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embrace:
Reduced prices: proportioning fee is examined without using foam or creating premix or foam – cost effective and eco-friendly.
Improved performance: constant proportioning fee throughout a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in stress loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a unique proportioning fee.
FM accredited FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners utilizing FM approved move meters. Using the test return line this presents the chance to check the proportioning price throughout commissioning in addition to for annual exams, with out creating any premix, which is a really big benefit for the consumer and relieves the surroundings.
In the second part of this feature we are going to explore the results of viscosity on foam proportioning and typical foam utility areas and beneficial discharge gadgets.
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Written by
David Owen
Andreas Hulinsky