A guide to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given hearth state of affairs. Our objective in this two-part article is to offer guidance based on a hazard-specific method and help you make an knowledgeable determination on applicable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are classified as follows:
Class A – carbonaceous or combustible supplies

Class B – flammable liquids

Class C – flammable gases

Class D – metals similar to magnesium

Class F – fires usually related to cooking similar to vegetable oils

Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise primarily within 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, certain types of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water only might not penetrate the hearth load successfully.
Fire lessons.
How can we make foam?

Finished foam solution comprises a easy recipe of froth concentrate, water and air. Foam focus is usually combined in 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 gadget – we are going to cover proportioning later on this article and discharge strategies in Part 2. At this level air is entrained by utilizing devices designed to naturally aspirate the solution. The quantity of aspiration and the kind of concentrate determines the enlargement ratio. This is usually split between low, medium and high enlargement. Low expansion is as a lot as 20:1, medium is 200:1 and high growth is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, although naturally aspirated generators are additionally used. The choice to choose a particular enlargement ratio is set by the hazard under review.
Put simply, water and oil don’t combine. Applying solely water to Class B products won’t suppress the burning vapours. This is an important level to make as it’s the vapours, not the liquid itself, that burns. We want a medium that permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever method is chosen to provide that blanket or film, the target is identical.
Steps of foam era Images supplied by Author / Contributor

A little of the history of foam improvement

We can date the development of contemporary foam concentrates from the 1960s onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary disadvantage was because of limited gasoline tolerance, which meant it was vulnerable to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, synthetic detergents gave foam a higher gas tolerance as well as forming a vapour-sealing film across the surface of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth didn’t utterly substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight fuel pick-up (mixing) and provide an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further development in the 1980s took FP to the subsequent stage with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s 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 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 same know-how also grew to become available with the model new technology of AFFF-ARs.
In latest years fluorine, one of many cornerstone elements to all foams, has turn out to be an environmental problem, because of persistence in groundwater. The trade has been introduced with a significant problem to get rid of the ‘fluoro’ factor of all the 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 normal and first choice for operators changing current inventory or reviewing new projects. As a foam proportioner producer we should look at the bodily properties of foam fastidiously (especially viscosity) as they affect decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are more and more important within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant high quality of SFFF/F3 is necessary to combat the small diploma of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being extremely effective. The best way of evaluating their claims is to familiarise your self with the empirically based mostly standard EN 1568 or UL162. The exams cowl extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included in the test protocols. This also covers recent and seawater as properly as 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 challenge foam suppliers in order to make an knowledgeable choice on one of the best foam in your wants.
Whilst EN 1568 is an excellent benchmark commonplace, consciousness of the effects on foam performance from components outside the standard exams must be famous. For example, particularly aggressive solvents can challenge the firefighting effectiveness of certain foams. This may be exacerbated by completely different ambient air temperatures, the appliance technique, gas depth and so on. Our advice would be to understand the major points of the tests and attempt to match them to the foam’s appropriateness in your particular person hazards. We would always suggest consulting particular person foam manufacturers as they’ll often provide particular in-house fire-performance knowledge against some of the extra uncommon fuels.
However, despite the foam manufacturers’ generally conflicting claims on performance, the sooner fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the enlargement ratio Images provided by Author / Contributor

Critical elements for achievement: the time and application rate 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 determined by empirically based requirements published by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ issue implies that for a given size of fireside space it’s necessary to use the foam for long sufficient to achieve extinction and to prevent re-ignition. This is particularly crucial in handbook intervention as firefighter’s will be in danger throughout post-fire operations. When it involves mounted safety for hydrocarbon and polar solvent tanks, the applying time could be so long as 60 minutes for the most important tank diameters.
The utility rate refers to the quantity of finished foam applied per sq. metre. This varies based on the fuel and the froth sort but is at present no much less than four.zero litres per minute per sq. metre. One of the continued developments in foam efficiency is the likelihood that this shall be reduced, but requirements often take time to recognise product improvement. Anything less than the minimal software fee implies that fire control is unlikely to be achieved. This implies that firefighting sources, particularly in a guide fireplace attack, have to be assembled earlier than firefighting commences and this takes time. The benefit in fitting mounted techniques is that the resources are already designed and constructed into the system for immediate 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 knowledgeable determination on how greatest to sort out their specific fireplace challenges, the following is an summary of the assorted foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted mounted techniques purposes. This uses the venturi principle to create a strain drop in a small aluminium or seawater materials compatible system with built-in concentrate pick-up tube. The strain drop created by the venturi attracts the foam concentrate from a container the place it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fireplace equipment or fitted right into a pipework system.
However, whilst it’s thought-about to be the simplest method, 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 changing amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are crucial as deviations brought on by pipe diameter adjustments will adversely have an result on proportioning accuracy and potentially forestall any proportioning; (iii) changes in focus viscosity will undermine the flexibility of the venturi to attract concentrate into the downstream lines; (iv) strain loss is excessive, as a lot as 35%, so obligation pump pressures must be high enough to allow for it, potentially adding extra price into the system; (v) foam delivery gadgets must be sized so as not to prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime costs as a result of foam concentrate usage, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor

Balanced pressure proportioners:
These use an electric or a mixture of electrical and diesel pumps to produce foam focus into a proportioner at a higher stress than the incoming water-line stress. The proportioner is installed into the water line and regulates the blending.
They are now associated with older systems, the place disadvantages include: (i) extra costs in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter working range, though the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump needs a further power supply, aside from water, so just isn’t as reliably safe as a system with a potential single level of failure, similar to a wholly water-driven system; (iv) usually, these techniques are very complex and cause high efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to damage the foam concentrate 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 similar to the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam filled bladder so that foam focus could be proportioned with water utilizing the same supply. The venturi principle is once more brought into play because it creates a stress drop on the level of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to complete lifetime costs because of foam concentrate usage, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a end result of nice care is required to keep away from a damaged bladder when commissioning a new installation. It isn’t simple to work inside the steel stress vessel ought to problems happen, particularly if and when a replacement bladder may be required: it all adds to the problem and cost.
Compressed air foam (CAFS):
This is not a proportioning method within the typical sense as the foam is already proportioned utilizing one of the previous methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth solution 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. เพรสเชอร์เกจ is also a benefit in wildfire conditions by coating weak buildings to mitigate hearth growth. The limited water provides related to distant wildfire areas implies that the resource may be fully optimised. However, as with balanced strain proportioner foam pumps, an extra level of failure is feasible due to the further 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 only mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate through 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 foam focus accurately across 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 provided by Author / Contributor

The advantages of FireDos Gen III FM permitted foam proportioners embrace:
Reduced costs: proportioning rate is tested without using foam or creating premix or foam – price efficient and eco-friendly.
Improved performance: fixed proportioning fee throughout a wide operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% discount in strain loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a special proportioning fee.
FM accredited FireDos Gen III proportioners are to date the one FM approved water motor coupled variable proportioners using FM accredited move meters. Using the check return line this presents the chance to check the proportioning rate throughout commissioning in addition to for annual checks, without creating any premix, which is a really massive profit for the user and relieves the environment.
In the second a part of this function we are going to explore the results of viscosity on foam proportioning and typical foam software areas and beneficial discharge devices.
For more information, go to www.firedos.com

Written by

David Owen

Andreas Hulinsky


Leave a Comment