A guide to foam and foam proportioning equipment – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is appropriate for a given fireplace situation. Our goal on this two-part article is to supply steering based mostly on a hazard-specific method and allow you to make an knowledgeable determination on acceptable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or flamable materials

Class B – flammable liquids

Class C – flammable gases

Class D – metals such as magnesium

Class F – fires generally related to cooking such as vegetable oils

Class E – electrical hazards.
As a producer of froth proportioners and firefighting monitors, we specialise primarily within the Class B category: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are specifically for deep-seated Class A fires where water solely may not penetrate the fire load successfully.
Fire courses.
How will we make foam?

Finished foam answer comprises a easy recipe of froth focus, water and air. Foam focus is often combined within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge system – we will cover proportioning later in 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 focus determines the growth ratio. This is usually cut up between low, medium and high growth. Low enlargement is up to 20:1, medium is 200:1 and high growth is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to expand the foam adequately, though naturally aspirated mills are additionally used. The choice to choose a selected growth ratio is determined by the hazard underneath evaluation.
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 an important point to make as it’s 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 movie to achieve success. Whatever methodology is chosen to produce that blanket or film, the target is the same.
Steps of foam technology Images supplied by Author / Contributor

A little of the history of froth development

We can date the event of contemporary foam concentrates from the 1960s onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary drawback was as a result of limited gasoline tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, synthetic detergents gave foam a larger fuel tolerance in addition to forming a vapour-sealing film throughout the floor of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth did not utterly replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight gas pick-up (mixing) and provide a good resistance to heat, outlined by the trade as ‘burn-back resistance’.
Further improvement in the Eighties took FP to the following level with film-forming fluoroprotein or FFFP. We now had the best of each 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 presented 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 same expertise additionally turned out there with the model new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone components to all foams, has turn into an environmental issue, as a outcome of persistence in groundwater. The trade has been introduced with a significant challenge to eliminate the ‘fluoro’ factor of all the totally different foam concentrate varieties. We have witnessed an period of manufacturers’ claims and counter claims relating to the efficacy of a whole 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 into the new normal and first choice for operators altering current stock or reviewing new projects. As a foam proportioner producer we should examine the physical properties of foam fastidiously (especially viscosity) as they affect choices on the general proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are more and more important in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant high quality of SFFF/F3 is important to fight the small degree of water miscibility of the gasoline.
All foam focus manufacturers will naturally promote their product as being extremely effective. The best method of comparing their claims is to familiarise yourself with the empirically based normal EN 1568 or UL162. The checks cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are each included within the test protocols. This also covers contemporary and seawater in addition to mild and forceful software of the froth. Each foam is given a rating with IA being one of the best, IIID the worst. This means you could challenge foam suppliers to be able to make an knowledgeable determination on the best foam on your wants.
Whilst EN 1568 is a superb benchmark normal, awareness of the effects on foam efficiency from factors outdoors the standard exams ought to be noted. For instance, notably aggressive solvents can problem the firefighting effectiveness of certain foams. This could be exacerbated by totally different ambient air temperatures, the applying technique, gasoline depth etc. Our recommendation could be to understand the main points of the exams and attempt to match them to the foam’s appropriateness in your particular person hazards. We would all the time suggest consulting individual foam manufacturers as they’ll usually present particular in-house fire-performance information towards some of the more uncommon fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on performance, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the growth ratio Images supplied by Author / Contributor

Critical factors for success: the time and application price matrix

Successful extinction of flammable liquid fires is decided by two converging and complementary factors: time and the rate at which completed foam is applied. Both are decided by empirically based mostly requirements printed by our bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given measurement of fire area it’s necessary to apply the foam for long sufficient to realize extinction and to forestall re-ignition. This is particularly crucial in guide intervention as firefighter’s might be in danger during post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the applying time may be so lengthy as 60 minutes for the biggest tank diameters.
The software rate refers to the quantity of completed foam applied per square metre. This varies based on the gasoline and the froth sort but is presently at least 4.0 litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the probability that this will be lowered, but standards usually take time to recognise product improvement. Anything lower than the minimum utility rate signifies that hearth management is unlikely to be achieved. This signifies that firefighting sources, notably in a handbook hearth assault, have to be assembled earlier than firefighting commences and this takes time. The advantage in becoming fastened methods is that the resources are already designed and built into the system for immediate utility.
Principle of froth extinguishment Images provided by Author / Contributor

Foam proportioning strategies: mixing water with foam concentrate

In order to allow readers to make an knowledgeable decision on how finest to tackle their specific fire challenges, the following is an overview of the assorted foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and restricted mounted systems applications. This makes use of the venturi precept to create a strain drop in a small aluminium or seawater materials compatible gadget with built-in concentrate pick-up tube. The stress drop created by the venturi attracts the foam concentrate from a container where it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a fire appliance or fitted right into a pipework system.
However, while it’s thought-about to be the simplest technique, it has extreme drawbacks: (i) items are manufacturing unit calibrated so any changes to the hydraulics (caused by size 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 caused by pipe diameter changes will adversely affect proportioning accuracy and potentially prevent any proportioning; (iii) changes in focus viscosity will undermine the flexibility of the venturi to draw focus into the downstream lines; (iv) stress loss is high, as a lot as 35%, so obligation pump pressures must be excessive enough to permit for it, doubtlessly including additional cost into the system; (v) foam delivery units have to be sized so as to not prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime costs because of foam focus usage, which has to be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor

Balanced pressure proportioners:
These use an electric or a mix of electric and diesel pumps to supply foam concentrate right into a proportioner at a higher pressure than the incoming water-line strain. The proportioner is put in into the water line and regulates the mixing.
They are now related to older techniques, the place disadvantages embrace: (i) extra prices in hardware and design time; (ii) the froth pump is generally restricted to a much tighter working vary, though the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump needs an extra power supply, apart from water, so just isn’t as reliably safe as a system with a potential single level of failure, such as a wholly water-driven system; (iv) typically, these methods are very complex and trigger high 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 break 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 concentrate proportioner just like those fitted to balanced strain proportioners. The incoming pressurised water compresses the froth filled bladder so that foam concentrate may be proportioned with water using the identical provide. The venturi precept is once more introduced into play as it creates a pressure drop at the level of injection for the foam focus. Testing can’t be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices as a end result of foam focus usage, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of nice care is needed to keep away from a damaged bladder when commissioning a brand new installation. It is never easy to work throughout the steel stress vessel ought to issues occur, particularly if and when a alternative bladder could additionally be required: all of it adds to the problem and value.
Compressed air foam (CAFS):
This isn’t a proportioning technique in the typical sense as the foam is already proportioned using one of the previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the identify 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 allowing higher penetration and cooling. This can additionally be a benefit in wildfire situations by coating weak structures to mitigate fireplace progress. The limited water supplies associated with remote wildfire areas signifies that the useful resource can be absolutely optimised. However, as with balanced pressure proportioner foam pumps, a further level of failure is possible because of the further CAFS equipment.
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 purely mechanical and extremely reliable. A water-driven rotor provides the motive force to drive a instantly coupled positive-displacement plunger or piston pump. This is supplied with foam focus via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and will proportion the froth focus accurately across a large operating range. The purely mechanical system offers cost-efficient and eco-friendly proportioning price testing, utterly without using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor

The advantages of FireDos Gen III FM accredited foam proportioners include:
Reduced prices: proportioning rate is tested with out utilizing foam or creating premix or foam – cost efficient and eco-friendly.
Improved digital pressure gauge ราคา : fixed proportioning price throughout a wide working range.
Optimised delivery 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 straightforward and fast adjustment to a special proportioning price.
FM accredited FireDos Gen III proportioners are thus far the one FM permitted water motor coupled variable proportioners using FM permitted flow meters. Using the take a look at return line this presents the likelihood to examine the proportioning price during commissioning in addition to for annual tests, without creating any premix, which is a very huge benefit for the consumer and relieves the environment.
In the second part of this feature we’ll explore the results of viscosity on foam proportioning and typical foam application areas and beneficial discharge units.
For more data, go to www.firedos.com

Written by

David Owen

Andreas Hulinsky

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