A information to foam and foam proportioning equipment – Part 1

Fire presents many challenges, not least because of the variables that decide which suppression medium is suitable for a given hearth scenario. Our objective in this two-part article is to offer guidance based mostly on a hazard-specific method and assist you to make an informed decision on appropriate fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires typically associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise primarily in the Class B category: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only could not penetrate the fireplace load effectively.
Fire classes.
How will we make foam?
Finished foam solution comprises a easy recipe of foam focus, water and air. Foam focus is typically blended 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 gadget – we’ll cover proportioning later on 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 enlargement ratio. This is usually cut up between low, medium and excessive expansion. Low growth is up to 20:1, medium is 200:1 and high enlargement is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to broaden the foam adequately, although naturally aspirated mills are additionally used. The choice to choose a specific 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 is 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 be successful. Whatever technique is chosen to produce that blanket or movie, the objective is identical.
Steps of froth technology Images supplied by Author / Contributor
A little of the historical past of foam growth
We can date the development of modern foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the base component). The main disadvantage was as a outcome of restricted gasoline 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 utilizing protein as the bottom product, synthetic detergents gave foam a larger fuel tolerance in addition to 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 units are fitted.
Nevertheless, AFFF’s improvement did not completely substitute the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat gas pick-up (mixing) and supply a good resistance to heat, outlined by the trade as ‘burn-back resistance’.
Further development within the 1980s took FP to the next level 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 Nineteen Eighties additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time introduced a further challenge 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 identical technology also turned obtainable with the model new generation of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has turn into an environmental problem, due to persistence in groundwater. The business has been offered with a major challenge to eliminate the ‘fluoro’ element of all the completely different foam focus sorts. We have witnessed an era of manufacturers’ claims and counter claims concerning the efficacy of a whole vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the new regular and first alternative for operators changing current stock or reviewing new tasks. As a foam proportioner manufacturer we must look at the bodily properties of froth fastidiously (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 increasingly necessary within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant high quality of SFFF/F3 is necessary to combat the small diploma of water miscibility of the gasoline.
All foam concentrate producers will naturally promote their product as being highly effective. The best way of comparing their claims is to familiarise your self with the empirically based mostly commonplace EN 1568 or UL162. The checks 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 in the take a look at protocols. This also covers fresh and seawater in addition to light and forceful application of the froth. Each foam is given a rating with IA being one of the best, IIID the worst. This means that you could problem foam suppliers so as to make an knowledgeable decision on the best foam in your needs.
Whilst EN 1568 is a superb benchmark commonplace, consciousness of the results on foam performance from components exterior the usual checks should be famous. For example, notably aggressive solvents can challenge the firefighting effectiveness of certain foams. This may be exacerbated by completely different ambient air temperatures, the applying method, gas depth etc. Our recommendation could be to grasp the details of the checks and try to match them to the foam’s appropriateness for your individual hazards. We would all the time advocate consulting individual foam manufacturers as they will often provide specific in-house fire-performance information against a few of the extra uncommon fuels.
However, despite the foam manufacturers’ generally conflicting claims on performance, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the growth ratio Images supplied by Author / Contributor
Critical factors for achievement: the time and utility price matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary elements: time and the speed at which finished foam is applied. Both are determined by empirically based mostly standards revealed by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ issue means that for a given size of fireside space it is essential to use the foam for long enough to achieve extinction and to forestall re-ignition. This is particularly crucial in handbook intervention as firefighter’s will be in danger throughout post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the application time can be as long as 60 minutes for the biggest tank diameters.
The software price refers again to the quantity of finished foam applied per sq. metre. This varies based on the gas and the froth type but is presently a minimum of four.0 litres per minute per square metre. One of the continued developments in foam performance is the chance that this might be decreased, but requirements often take time to recognise product growth. Anything lower than the minimum application price implies that fire control is unlikely to be achieved. This means that firefighting sources, notably in a guide fire assault, need to be assembled earlier than firefighting commences and this takes time. The benefit in becoming fastened techniques is that the sources are already designed and constructed into the system for instant application.
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 decision on how best to sort out their particular hearth challenges, the following is an summary of the various foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted fastened systems functions. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater material appropriate device with built-in focus pick-up tube. The pressure drop created by the venturi draws the froth focus from a container where it mixes with water to create foam resolution. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fireplace appliance or fitted right into a pipework system.
However, whilst it is considered to be the only method, it has extreme drawbacks: (i) units are factory calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a altering amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter adjustments will adversely affect proportioning accuracy and doubtlessly stop any proportioning; (iii) changes in focus viscosity will undermine the flexibility of the venturi to draw concentrate into the downstream traces; (iv) strain loss is high, as much as 35%, so responsibility pump pressures must be high enough to permit for it, probably adding further cost into the system; (v) foam supply gadgets have to be sized in order not to prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs on account of foam concentrate utilization, which must be replaced, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced stress proportioners:
These use an electrical or a mix of electric and diesel pumps to produce foam focus into a proportioner at a higher pressure than the incoming water-line pressure. The proportioner is installed into the water line and regulates the mixing.
They are now associated with older techniques, the place disadvantages include: (i) extra costs in hardware and design time; (ii) the foam pump is generally restricted to a much tighter operating vary, although the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump wants an additional energy supply, aside from water, so is not as reliably secure as a system with a possible single level of failure, such as a completely water-driven system; (iv) usually, these methods are very advanced and cause excessive efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to break the foam concentrate and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel strain vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced stress proportioners. The incoming pressurised water compresses the froth crammed bladder so that foam focus may be proportioned with water using the identical provide. The venturi principle is again introduced into play because it creates a strain drop on the point of injection for the froth focus. Testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs because of foam focus utilization, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a result of great care is required to avoid a broken bladder when commissioning a model new installation. It is never easy to work inside the metal stress vessel should problems happen, especially if and when a replacement bladder may be required: it all adds to the issue and value.
Compressed air foam (CAFS):
This isn’t a proportioning method within the standard sense as the froth is already proportioned utilizing one of the previous methods. However, Hurry is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth resolution on the point of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces permitting higher penetration and cooling. This can also be a profit in wildfire situations by coating vulnerable constructions to mitigate fire development. The limited water provides associated with remote wildfire areas implies that the useful resource may be fully optimised. However, as with balanced pressure proportioner foam pumps, an additional level of failure is feasible as a outcome of extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is solely mechanical and highly reliable. A water-driven rotor provides the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning rate and can proportion the foam concentrate precisely throughout a wide operating range. The purely mechanical system provides 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 supplied by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners embody:
Reduced prices: proportioning fee is tested with out using foam or creating premix or foam – cost efficient and eco-friendly.
Improved performance: fixed proportioning fee throughout a large working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, in comparability with older generations, via hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a special proportioning fee.
FM permitted FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners utilizing FM permitted move meters. Using the test return line this provides the possibility to verify the proportioning rate throughout commissioning as nicely as for annual checks, with out creating any premix, which is a really huge profit for the user and relieves the setting.
In the second part of this feature we will discover the consequences of viscosity on foam proportioning and typical foam utility areas and beneficial discharge gadgets.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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