A information to foam and foam proportioning equipment – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is suitable for a given fire state of affairs. Our goal on this two-part article is to provide steerage based mostly on a hazard-specific method and allow you to make an knowledgeable choice on appropriate 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 similar to magnesium
Class F – fires generally associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting displays, we specialise primarily within the Class B category: flammable liquids.
Foam is considered to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely might not penetrate the fire load effectively.
Fire classes.
How can we make foam?
Finished foam solution contains a easy recipe of foam focus, water and air. Foam concentrate is often mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge device – we’ll cover proportioning later on this article and discharge methods in Part 2. At this point air is entrained by using gadgets designed to naturally aspirate the answer. The amount of aspiration and the sort of concentrate determines the growth ratio. This is usually break up between low, medium and excessive enlargement. Low growth is up to 20:1, medium is 200:1 and high expansion is greater than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to expand the foam adequately, though naturally aspirated generators are additionally used. The determination to choose a particular expansion ratio is determined by the hazard under review.
Put simply, water and oil don’t combine. Applying only water to Class B products 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 need a medium that allows 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 foam era Images supplied by Author / Contributor
A little of the historical past of foam growth
We can date the event of recent foam concentrates from the 1960s onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the base component). The major downside was because of limited gas 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 fuel tolerance as well as forming a vapour-sealing film across the floor of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s development didn’t completely replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight fuel pick-up (mixing) and supply an excellent resistance to warmth, outlined by the business as ‘burn-back resistance’.
Further growth in the 1980s 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 additionally 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 at all times introduced a further challenge as they have been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The identical technology additionally turned obtainable with the new era of AFFF-ARs.
In latest years fluorine, one of many cornerstone ingredients to all foams, has turn out to be an environmental problem, due to persistence in groundwater. The business has been presented with a serious problem to remove the ‘fluoro’ element of all of the completely different foam focus sorts. Savings have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of an entire 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 turn out to be the model new normal and first alternative for operators changing current inventory or reviewing new projects. As a foam proportioner producer we should look at the bodily properties of foam rigorously (especially viscosity) as they affect decisions on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more important in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant 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 highly efficient. The best method of evaluating 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 both included within the check protocols. This additionally covers recent and seawater in addition to gentle and forceful utility of the froth. Each foam is given a ranking with IA being the best, IIID the worst. This means that you can problem foam suppliers in order to make an knowledgeable determination on the most effective foam in your wants.
Whilst EN 1568 is a superb benchmark normal, consciousness of the consequences on foam efficiency from factors exterior the standard checks must be famous. For example, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by totally different ambient air temperatures, the appliance method, gasoline depth and so forth. Our advice could be to understand the details of the checks and attempt to match them to the foam’s appropriateness in your individual hazards. We would all the time advocate consulting particular person foam producers as they can often present specific in-house fire-performance information against a variety of the extra uncommon fuels.
However, despite the froth manufacturers’ generally 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 growth ratio Images provided by Author / Contributor
Critical components for fulfillment: the time and software fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the speed at which finished foam is utilized. Both are decided by empirically based standards published 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 means that for a given dimension of fire space it is necessary to use the foam for lengthy sufficient to realize extinction and to prevent re-ignition. This is very important in manual intervention as firefighter’s will be in danger throughout post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the applying time can be so long as 60 minutes for the most important tank diameters.
The software rate refers to the amount of finished foam applied per sq. metre. This varies according to the gas and the froth type but is at present at least four.zero litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the probability that this shall be reduced, but requirements typically take time to recognise product improvement. Anything lower than the minimal application price signifies that fireplace control is unlikely to be achieved. This means that firefighting assets, significantly in a manual fire attack, have to be assembled before firefighting commences and this takes time. The advantage in fitting mounted techniques is that the assets are already designed and constructed into the system for instant software.
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 knowledgeable decision on how finest to sort out their particular hearth challenges, the next is an overview of the varied foam proportioning methods.
Foam inductors:
Typically related to fireplace service deployment and restricted fastened techniques purposes. This makes use of the venturi principle to create a strain drop in a small aluminium or seawater materials compatible device with built-in concentrate pick-up tube. The pressure drop created by the venturi draws the foam concentrate from a container where it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a hearth equipment or fitted right into a pipework system.
However, while it is considered to be the only technique, it has severe drawbacks: (i) units are manufacturing facility calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a changing amount of discharge devices) will probably require a system re-design; (ii) system design and sign-off are critical as deviations attributable to pipe diameter changes will adversely affect proportioning accuracy and potentially stop any proportioning; (iii) adjustments in concentrate viscosity will undermine the power of the venturi to attract focus into the downstream traces; (iv) pressure loss is excessive, as a lot as 35%, so obligation pump pressures have to be high enough to permit for it, probably including additional value into the system; (v) foam supply devices must be sized in order to not prohibit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs as a outcome of foam focus usage, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced strain proportioners:
These use an electric or a mix of electric and diesel pumps to produce foam focus into a proportioner at a better pressure than the incoming water-line strain. The proportioner is installed into the water line and regulates the blending.
They are actually related to older systems, the place disadvantages include: (i) additional costs in hardware and design time; (ii) the foam pump is often restricted to a much tighter working range, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an additional power source, aside from water, so just isn’t as reliably safe as a system with a potential single point of failure, corresponding to a completely water-driven system; (iv) usually, these systems are very advanced and trigger excessive efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to damage the foam 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 focus proportioner just like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam crammed bladder so that foam focus could be proportioned with water utilizing the same supply. The venturi precept is once more introduced into play because it creates a strain drop at the point of injection for the froth focus. Testing cannot be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices as a outcome of foam focus usage, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a end result of nice care is needed to avoid a broken bladder when commissioning a new set up. It is rarely easy to work inside the steel stress vessel should problems happen, especially if and when a replacement bladder may be required: it all adds to the problem and value.
Compressed air foam (CAFS):
This isn’t a proportioning methodology in the standard sense as the foam is already proportioned using one of many earlier strategies. However, pressurised air is then added forcefully quite 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 capacity to cling to vertical surfaces permitting higher penetration and cooling. This can be a profit in wildfire conditions by coating vulnerable constructions to mitigate hearth development. The limited water provides associated with remote wildfire areas means that the resource can be fully 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 become synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is solely mechanical and extremely reliable. A water-driven rotor supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate through an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and will proportion the foam focus accurately throughout a wide working range. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, utterly with out utilizing 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 embrace:
Reduced prices: proportioning rate is tested with out using foam or creating premix or foam – cost effective and eco-friendly.
Improved performance: fixed proportioning rate across a wide working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in pressure loss, in comparison with older generations, through hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a unique proportioning fee.
FM permitted FireDos Gen III proportioners are thus far the only FM approved water motor coupled variable proportioners utilizing FM permitted circulate meters. Using the take a look at return line this offers the possibility to examine the proportioning price during commissioning as well as for annual tests, without creating any premix, which is a really huge profit for the person and relieves the setting.
In the second a part of this characteristic we are going to explore the consequences of viscosity on foam proportioning and typical foam application areas and really helpful discharge devices.
For extra information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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