A guide to foam and foam proportioning tools – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is acceptable for a given hearth state of affairs. Our objective on this two-part article is to supply guidance based on a hazard-specific approach and allow you to make an informed decision on appropriate fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are classified 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 usually related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting displays, we specialise mainly 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 kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water solely could not penetrate the fireplace load effectively.
Fire classes.
How will we make foam?
Finished foam solution includes a simple recipe of foam focus, water and air. Foam concentrate is often 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 gadget – we will cover proportioning later on this article and discharge strategies in Part 2. At this point air is entrained through the use of units designed to naturally aspirate the solution. The quantity of aspiration and the sort of concentrate determines the enlargement ratio. This is often cut up between low, medium and excessive enlargement. Low enlargement is as a lot as 20:1, medium is 200:1 and excessive enlargement is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated turbines are additionally used. The decision to decide on a particular expansion ratio is determined by the hazard beneath evaluation.
Put simply, water and oil don’t combine. Applying only 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 obtain success. Whatever method is chosen to supply that blanket or movie, the target is similar.
Steps of froth generation Images equipped by Author / Contributor
A little of the history of froth improvement
We can date the development of contemporary foam concentrates from the 1960s onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The main drawback was as a result of limited 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 base product, artificial detergents gave foam a greater gas tolerance as nicely as forming a vapour-sealing movie across 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 development did not utterly exchange the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat gasoline pick-up (mixing) and provide an excellent resistance to warmth, outlined by the trade as ‘burn-back resistance’.
Further growth within the Eighties took FP to the next stage 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 additional added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time introduced a further problem 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 similar expertise also grew to become available with the model new era of AFFF-ARs.
In latest years fluorine, one of many cornerstone components to all foams, has turn out to be an environmental problem, because of persistence in groundwater. The industry has been presented with a significant challenge to get rid of the ‘fluoro’ component of all of the totally different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims concerning 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 become the new regular and first selection for operators altering existing inventory or reviewing new initiatives. As a foam proportioner manufacturer we must look at the physical properties of foam fastidiously (especially viscosity) as they influence selections on the general proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are increasingly necessary in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant high quality of SFFF/F3 is necessary to fight the small degree of water miscibility of the fuel.
All foam focus manufacturers will naturally promote their product as being extremely efficient. The greatest method of comparing their claims is to familiarise your self with the empirically based mostly normal EN 1568 or UL162. The tests 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 in addition to light and forceful application of the froth. Each foam is given a score with IA being the best, IIID the worst. This means you could problem foam suppliers to have the ability to make an knowledgeable decision on the best foam on your needs.
Whilst EN 1568 is a superb benchmark commonplace, awareness of the effects on foam performance from components outside the usual tests should be noted. For instance, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This could be exacerbated by different ambient air temperatures, the appliance methodology, fuel depth and so forth. Our advice can be to understand the small print of the exams and try to match them to the foam’s appropriateness on your individual hazards. We would always recommend consulting individual foam manufacturers as they can typically provide particular in-house fire-performance data in opposition to a number of the more uncommon fuels.
However, regardless of the foam manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the expansion ratio Images equipped by Author / Contributor
Critical elements for success: the time and utility price matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary elements: time and the speed at which completed foam is utilized. Both are determined by empirically primarily based standards revealed by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor signifies that for a given size of fire space it is essential to apply the froth for lengthy sufficient to achieve extinction and to forestall re-ignition. This is especially critical in handbook intervention as firefighter’s might be at risk during post-fire operations. When it comes to fastened safety for hydrocarbon and polar solvent tanks, the application time may be so long as 60 minutes for the largest tank diameters.
The application price refers back to the quantity of finished foam applied per square metre. This varies in accordance with the fuel and the froth type however is presently a minimal of four.zero litres per minute per sq. metre. One of the continuing developments in foam performance is the probability that this might be decreased, however standards usually take time to recognise product development. Anything lower than the minimal application fee implies that fireplace management is unlikely to be achieved. This implies that firefighting assets, significantly in a manual fire attack, have to be assembled earlier than firefighting commences and this takes time. The benefit in becoming mounted techniques is that the sources are already designed and constructed into the system for quick application.
Principle of foam extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to allow readers to make an knowledgeable determination on how greatest to deal with their particular fire challenges, the next is an summary of the varied foam proportioning methods.
Foam inductors:
Typically related to fireplace service deployment and restricted fastened methods functions. เพรสเชอร์เกจคือ makes use of the venturi precept to create a strain drop in a small aluminium or seawater material appropriate device with built-in focus pick-up tube. The strain drop created by the venturi draws the froth concentrate 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 simply carried on a fire equipment or fitted into a pipework system.
However, whilst it’s considered to be the simplest technique, it has extreme drawbacks: (i) items are manufacturing facility 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 amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations brought on by pipe diameter adjustments will adversely affect proportioning accuracy and probably forestall any proportioning; (iii) adjustments in concentrate viscosity will undermine the ability of the venturi to draw focus into the downstream traces; (iv) strain loss is high, as a lot as 35%, so obligation pump pressures must be excessive sufficient to permit for it, potentially adding additional value into the system; (v) foam supply gadgets need to be sized so as to not limit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs as a outcome of foam concentrate utilization, 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 electrical or a mix of electric and diesel pumps to supply foam focus into a proportioner at a higher 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 systems, where disadvantages include: (i) further prices in hardware and design time; (ii) the foam pump is normally restricted to a much tighter operating range, although the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump wants an additional energy source, apart from water, so just isn’t as reliably safe as a system with a potential single point of failure, corresponding to an entirely water-driven system; (iv) usually, these systems are very complex and trigger excessive efforts on 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 foam focus and entrain air, which in turn can undermine accurate 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 concentrate proportioner much like the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the froth filled bladder so that foam concentrate could be proportioned with water using the same provide. The venturi principle is once more brought into play because it creates a stress drop at the level of injection for the froth focus. Testing can’t be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices on account of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because nice care is needed to keep away from a damaged bladder when commissioning a brand new set up. It is rarely straightforward to work throughout the metal pressure vessel ought to issues occur, particularly if and when a alternative bladder may be required: all of it adds to the difficulty and price.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology within the standard sense as the froth is already proportioned utilizing one of the previous methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam solution on the level of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces allowing better penetration and cooling. This can be a profit in wildfire conditions by coating susceptible constructions to mitigate hearth growth. The restricted water provides associated with distant wildfire areas signifies that the resource may be absolutely optimised. However, as with balanced strain proportioner foam pumps, a further level of failure is feasible as a end result 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 technology, the product is only mechanical and extremely dependable. A water-driven rotor provides the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning price and will proportion the froth concentrate accurately throughout a wide operating range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning fee testing, completely without utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners embrace:
Reduced costs: proportioning price is tested without utilizing foam or creating premix or foam – cost effective and eco-friendly.
Improved performance: constant proportioning fee throughout a large working range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% discount in pressure loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning price.
FM permitted FireDos Gen III proportioners are thus far the one FM accredited water motor coupled variable proportioners utilizing FM permitted circulate meters. Using the check return line this offers the chance to check the proportioning price throughout commissioning in addition to for annual checks, with out creating any premix, which is a very massive profit for the user and relieves the environment.
In the second part of this characteristic we are going to explore the effects of viscosity on foam proportioning and typical foam application areas and recommended discharge gadgets.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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