A guide to foam and foam proportioning equipment – Part 1

Fire presents many challenges, not least due to the variables that decide which suppression medium is suitable for a given fireplace situation. Our objective in this two-part article is to provide guidance based mostly on a hazard-specific strategy 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 usually related to cooking similar 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 taken into account to be the best fire-extinguishing medium for both 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 only may not penetrate the hearth load effectively.
Fire lessons.
How will we make foam?
Finished foam answer contains a easy recipe of foam focus, water and air. Foam focus is usually combined in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge system – we are going to cowl proportioning later in this article and discharge methods in Part 2. At this level air is entrained by using units designed to naturally aspirate the solution. The quantity of aspiration and the kind of concentrate determines the enlargement ratio. This is often break up between low, medium and high enlargement. Low expansion is up to 20:1, medium is 200:1 and high growth is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated turbines are also used. The decision to choose a selected enlargement ratio is decided by the hazard beneath review.
Put merely, water and oil do not mix. Applying solely water to Class B products is not going to suppress the burning vapours. This is a crucial 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 film to be successful. Whatever methodology is chosen to provide that blanket or movie, the objective is similar.
Steps of froth technology Images supplied by Author / Contributor
A little of the history of foam improvement
We can date the event of contemporary foam concentrates from the Sixties onwards. Up to that time foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the base component). The primary disadvantage was because of limited fuel tolerance, which meant it was susceptible to gasoline pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, synthetic detergents gave foam a higher gasoline tolerance as properly as forming a vapour-sealing film throughout the floor of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth did not completely exchange using protein-based foam. Fluoroprotein, or FP, meant that protein foam might both fight gasoline pick-up (mixing) and supply a great resistance to warmth, defined by the trade as ‘burn-back resistance’.
Further growth within the Nineteen Eighties took FP to the subsequent degree with film-forming fluoroprotein or FFFP. We now had the most effective of both worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s additional added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always introduced an extra problem as they had been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar know-how also became obtainable with the new generation of AFFF-ARs.
In ตัววัดแรงดันน้ำ , one of the cornerstone ingredients to all foams, has turn into an environmental problem, as a result of persistence in groundwater. The business has been introduced with a major challenge to eliminate the ‘fluoro’ component of all of the different foam focus varieties. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of a complete range of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn out to be the brand new normal and first alternative for operators changing existing stock or reviewing new projects. As a foam proportioner producer we must look at the physical properties of froth carefully (especially viscosity) as they influence decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are more and more essential within the fuel-storage arena. 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 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 way of comparing their claims is to familiarise yourself with the empirically based mostly 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 more demanding polar solvents are both included within the test protocols. This additionally covers fresh and seawater as well as mild and forceful application of the froth. Each foam is given a ranking with IA being the most effective, IIID the worst. This means that you can problem foam suppliers to have the ability to make an knowledgeable decision on one of the best foam in your needs.
Whilst EN 1568 is a superb benchmark standard, awareness of the consequences on foam performance from factors outdoors the usual checks ought to be famous. For example, particularly aggressive solvents can problem the firefighting effectiveness of sure foams. This may be exacerbated by totally different ambient air temperatures, the applying method, fuel depth etc. Our advice can be to know the details of the tests and attempt to match them to the foam’s appropriateness in your individual hazards. We would at all times suggest consulting particular person foam manufacturers as they’ll typically provide particular in-house fire-performance data against some of the more unusual fuels.
However, despite the foam manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the expansion 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 elements: time and the rate at which finished foam is applied. Both are determined by empirically based mostly requirements printed by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ factor signifies that for a given measurement of fireplace space it is needed to use the foam for lengthy sufficient to realize extinction and to prevent re-ignition. This is very critical in manual intervention as firefighter’s will be at risk throughout post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the application time may be so lengthy as 60 minutes for the most important tank diameters.
The application price refers back to the quantity of finished foam applied per square metre. This varies based on the gasoline and the foam kind but is presently a minimum of four.zero litres per minute per sq. metre. One of the ongoing developments in foam performance is the likelihood that this will be lowered, but requirements often take time to recognise product growth. Anything lower than the minimal utility rate means that fireplace control is unlikely to be achieved. This implies that firefighting assets, significantly in a handbook fire assault, must be assembled earlier than firefighting commences and this takes time. The benefit in becoming mounted systems is that the resources are already designed and built into the system for quick application.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to allow readers to make an informed choice on how best to tackle their particular hearth challenges, the next is an overview of the assorted foam proportioning methods.
Foam inductors:
Typically related to fireplace service deployment and restricted mounted methods purposes. This uses the venturi principle to create a stress drop in a small aluminium or seawater materials suitable device with built-in concentrate pick-up tube. The stress drop created by the venturi attracts the froth focus from a container where it mixes with water to create foam resolution. Both the pick-up tube and body of the inductor are compact enough to be easily carried on a fireplace appliance or fitted into a pipework system.
However, whilst it is thought-about to be the best method, it has severe drawbacks: (i) items are factory calibrated so any adjustments to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a altering quantity of discharge devices) will likely 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 probably forestall any proportioning; (iii) changes in concentrate viscosity will undermine the ability of the venturi to draw focus into the downstream lines; (iv) stress loss is excessive, as a lot as 35%, so obligation pump pressures must be excessive enough to allow for it, potentially including additional price into the system; (v) foam delivery gadgets need to be sized in order not to limit design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices on account of foam focus usage, which needs 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 mixture of electric and diesel pumps to supply foam concentrate right into a proportioner at a better pressure 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 systems, the place disadvantages embrace: (i) additional costs in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter working vary, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump wants an extra power source, aside from water, so is not as reliably secure as a system with a possible single level of failure, similar to an entirely water-driven system; (iv) usually, these techniques are very complicated and trigger excessive efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to break the froth focus and entrain air, which in turn can undermine correct 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 pressure proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam concentrate can be proportioned with water using the identical supply. The venturi principle is again introduced into play as it creates a stress drop at the level of injection for the froth concentrate. Testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime costs as a result of foam focus utilization, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of nice care is required to keep away from a broken bladder when commissioning a new set up. It is rarely easy to work inside the steel stress vessel should issues occur, particularly if and when a alternative bladder may be required: all of it provides to the issue and value.
Compressed air foam (CAFS):
This is not a proportioning methodology within the conventional sense as the froth is already proportioned using one of the earlier strategies. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam resolution at the level of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces allowing higher penetration and cooling. This can additionally be a profit in wildfire situations by coating susceptible buildings to mitigate fire growth. The limited water provides related to distant wildfire areas signifies that the useful resource could be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra point of failure is possible due to the additional CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is solely mechanical and extremely dependable. A water-driven rotor provides the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is supplied 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 precisely across a wide working vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, utterly with out utilizing any foam concentrate or creating premix or firefighting foam.
เกจวัดแก๊สหุงต้ม . Images provided by Author / Contributor
The benefits of FireDos Gen III FM approved foam proportioners embrace:
Reduced prices: proportioning price is examined without utilizing foam or creating premix or foam – cost effective and eco-friendly.
Improved efficiency: constant proportioning fee across a wide operating vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning fee.
FM approved FireDos Gen III proportioners are thus far the only FM approved water motor coupled variable proportioners utilizing FM approved move meters. Using the take a look at return line this provides the likelihood to verify the proportioning price during commissioning as nicely as for annual tests, without creating any premix, which is a very big benefit for the user and relieves the setting.
In the second a half of this function we’ll explore the consequences of viscosity on foam proportioning and typical foam software areas and beneficial discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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