A information to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is appropriate for a given hearth state of affairs. Our objective in this two-part article is to provide guidance based on a hazard-specific method 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 categorised as follows:
Class A – carbonaceous or combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires generally related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting monitors, we specialise mainly 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 solely might not penetrate the hearth load successfully.
Fire lessons.
How can we make foam?
Finished foam resolution includes a simple recipe of froth focus, water and air. Foam concentrate is usually combined in the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge system – we will cowl proportioning later in this article and discharge strategies in Part 2. At this level air is entrained by using devices designed to naturally aspirate the answer. The amount of aspiration and the type of focus determines the expansion ratio. This is often break up between low, medium and excessive enlargement. Low enlargement is up to 20:1, medium is 200:1 and excessive expansion is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated generators are additionally used. The determination to decide on a specific expansion ratio is decided by the hazard beneath review.
Put merely, water and oil do not combine. Applying only water to Class B products won’t 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 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 produce that blanket or movie, the objective is identical.
Steps of foam era Images provided by Author / Contributor
A little of the history of froth growth
We can date the development of modern foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the bottom component). The primary drawback was because of limited fuel tolerance, which meant it was prone to gasoline 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 greater gasoline tolerance in addition to forming a vapour-sealing movie across 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 didn’t completely exchange the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight gasoline pick-up (mixing) and supply a good resistance to warmth, outlined by the business as ‘burn-back resistance’.
Further growth in the Eighties took FP to the following level 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 Nineteen Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times offered a further problem as they have been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The identical technology also grew to become available with the new technology of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has become an environmental concern, due to persistence in groundwater. The industry has been presented with a major challenge to get rid of the ‘fluoro’ factor 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 term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn out to be the new regular and first alternative for operators changing existing inventory or reviewing new projects. As เกจวัดแรงดันดิจิตอลราคา must study the physical properties of froth rigorously (especially viscosity) as they affect decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more necessary in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant high quality of SFFF/F3 is critical to combat the small degree of water miscibility of the gasoline.
All foam concentrate manufacturers will naturally promote their product as being extremely effective. The greatest means of comparing their claims is to familiarise your self with the empirically based normal EN 1568 or UL162. The checks cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the more demanding polar solvents are both included in the check protocols. This also covers contemporary and seawater in addition to mild and forceful application of the foam. Each foam is given a rating with IA being the best, IIID the worst. This means that you can challenge foam suppliers in order to make an informed determination on one of the best foam on your wants.
Whilst EN 1568 is a wonderful benchmark standard, consciousness of the results on foam efficiency from elements outdoors the standard tests must be famous. For example, notably aggressive solvents can challenge the firefighting effectiveness of certain foams. This could be exacerbated by different ambient air temperatures, the appliance technique, gas depth etc. Our recommendation would be to understand the details of the exams and attempt to match them to the foam’s appropriateness on your individual hazards. We would all the time suggest consulting individual foam manufacturers as they’ll often provide particular in-house fire-performance knowledge towards a variety of the extra uncommon fuels.
However, despite the froth manufacturers’ sometimes conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the enlargement ratio Images provided by Author / Contributor
Critical elements for success: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary elements: time and the speed at which completed foam is applied. Both are determined by empirically based requirements published by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor signifies that for a given dimension of fireside area it’s necessary to use the froth for long enough to attain extinction and to forestall re-ignition. This is particularly important in manual intervention as firefighter’s shall be at risk during post-fire operations. When it comes to mounted safety for hydrocarbon and polar solvent tanks, the applying time could be as long as 60 minutes for the most important tank diameters.
The application fee refers back to the quantity of completed foam utilized per sq. metre. This varies based on the gas and the froth type however is currently a minimum of four.0 litres per minute per sq. metre. One of the continuing developments in foam efficiency is the likelihood that this will be reduced, however requirements often take time to recognise product development. Anything lower than the minimum utility fee signifies that hearth management is unlikely to be achieved. This means that firefighting assets, significantly in a manual fire assault, need to be assembled before firefighting commences and this takes time. The advantage in fitting mounted systems is that the assets are already designed and built 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 determination on how best to sort out their particular hearth challenges, the following is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically associated with fire service deployment and limited fixed methods applications. This uses the venturi principle to create a stress drop in a small aluminium or seawater material appropriate gadget 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 solution. Both the pick-up tube and body of the inductor are compact sufficient to be easily carried on a hearth appliance or fitted into a pipework system.
However, while it’s thought of to be the only technique, it has extreme drawbacks: (i) items are manufacturing facility calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter modifications will adversely have an result on proportioning accuracy and probably prevent any proportioning; (iii) adjustments in focus viscosity will undermine the flexibility of the venturi to draw focus into the downstream strains; (iv) stress loss is excessive, as a lot as 35%, so obligation pump pressures need to be high sufficient to permit for it, doubtlessly including additional price into the system; (v) foam supply devices have to be sized in order not to restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs on account of foam focus utilization, which needs to be replaced, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced strain proportioners:
These use an electric or a mixture of electrical and diesel pumps to supply foam concentrate right into a proportioner at the next pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the blending.
They are now related to older methods, the place disadvantages embrace: (i) extra costs in hardware and design time; (ii) the froth pump is often restricted to a a lot tighter operating range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump wants an additional energy supply, aside from water, so is not as reliably secure as a system with a potential single point of failure, corresponding to a wholly water-driven system; (iv) sometimes, these systems are very complicated and cause excessive efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to wreck the foam focus and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal stress vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner similar to the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam focus may be proportioned with water utilizing the same supply. The venturi principle is again introduced into play as it creates a strain drop on the point of injection for the froth focus. 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 focus utilization, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot because great care is needed to keep away from a damaged bladder when commissioning a new installation. It is rarely simple to work within the metal pressure vessel should issues occur, especially if and when a replacement bladder could additionally be required: all of it provides to the issue and cost.
Compressed air foam (CAFS):
This isn’t a proportioning method within the conventional sense as the froth is already proportioned utilizing one of the previous strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the foam resolution at the level of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces allowing better penetration and cooling. This can be a benefit in wildfire conditions by coating susceptible constructions to mitigate fire progress. The restricted water provides related to remote wildfire areas signifies that the resource may be fully optimised. However, as with balanced stress proportioner foam pumps, a further point of failure is possible as a outcome of additional CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is purely mechanical and extremely reliable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning fee and can proportion the foam concentrate precisely across a large operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, fully without utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The advantages of FireDos Gen III FM accredited foam proportioners embrace:
Reduced prices: proportioning rate is tested with out utilizing foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: fixed proportioning price throughout a wide operating range.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in strain loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a special proportioning rate.
FM permitted FireDos Gen III proportioners are so far the one FM accredited water motor coupled variable proportioners using FM permitted flow meters. Using the check return line this provides the likelihood to examine the proportioning fee throughout commissioning in addition to for annual exams, without creating any premix, which is a very big profit for the person and relieves the environment.
In the second part of this function we’ll explore the consequences of viscosity on foam proportioning and typical foam utility areas and really helpful discharge gadgets.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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