A guide 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 situation. Our objective in this two-part article is to supply steerage based on a hazard-specific method and allow you to make an informed determination on appropriate fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires typically associated with cooking such as vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting displays, we specialise mainly in 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, certain forms of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely might not penetrate the fire load successfully.
Fire classes.
How will we make foam?
Finished foam solution includes a easy recipe of foam concentrate, water and air. เกจวัดความดันแก๊ส is typically 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 gadget – we will cover proportioning later in 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 kind of concentrate determines the expansion ratio. This is often split between low, medium and high growth. Low enlargement is as a lot as 20:1, medium is 200:1 and high expansion 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 generators are additionally used. The choice to decide on a specific growth ratio is determined by the hazard under evaluate.
Put simply, water and oil don’t combine. Applying only water to Class B products won’t suppress the burning vapours. This is a crucial level 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 achieve success. Whatever method is chosen to provide that blanket or movie, the target is the same.
Steps of froth era Images provided by Author / Contributor
A little of the historical past of foam development
We can date the development of modern foam concentrates from the Sixties onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the base component). The major drawback was due to restricted fuel tolerance, which meant it was vulnerable to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, synthetic detergents gave foam a higher gas tolerance as properly as forming a vapour-sealing film across the floor of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s improvement did not completely substitute the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each combat fuel pick-up (mixing) and provide a good resistance to heat, outlined by the trade as ‘burn-back resistance’.
Further improvement in the 1980s took FP to the subsequent degree with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that also had good burn-back resistance.
The Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time offered a further challenge as they had been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar technology also turned available with the brand new era of AFFF-ARs.
In recent years fluorine, one of the cornerstone ingredients to all foams, has become an environmental issue, because of persistence in groundwater. The industry has been offered with a serious challenge to eliminate the ‘fluoro’ component of all of the different foam focus types. We have witnessed an period of manufacturers’ claims and counter claims relating to the efficacy of a complete vary of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn into the model new regular and first selection for operators altering current stock or reviewing new projects. As a foam proportioner producer we must study the physical properties of froth rigorously (especially viscosity) as they influence choices on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are increasingly necessary in 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 gas.
All foam focus manufacturers will naturally promote their product as being extremely efficient. The greatest method of evaluating their claims is to familiarise yourself with the empirically based commonplace EN 1568 or UL162. The tests cover 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 in the check protocols. This also covers fresh and seawater as nicely as mild and forceful software of the foam. Each foam is given a score with IA being the best, IIID the worst. This means you could problem foam suppliers in order to make an informed determination on the most effective foam for your wants.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the effects on foam efficiency from components exterior the standard exams ought to be noted. For instance, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by completely different ambient air temperatures, the application methodology, gas depth and so on. Our advice can be to understand the details of the exams and try to match them to the foam’s appropriateness for your particular person hazards. We would always suggest consulting particular person foam manufacturers as they’ll often provide specific in-house fire-performance information in opposition to a number of the more unusual fuels.
However, regardless of the froth manufacturers’ sometimes conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the enlargement ratio Images supplied by Author / Contributor
Critical components for success: the time and software rate matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary factors: time and the rate 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 implies that for a given dimension of fire space it’s needed to apply the froth for lengthy sufficient to realize extinction and to stop re-ignition. This is especially critical in manual intervention as firefighter’s might be in danger during post-fire operations. When it involves fixed protection for hydrocarbon and polar solvent tanks, the appliance time can be so long as 60 minutes for the most important tank diameters.
The application price refers again to the quantity of completed foam utilized per sq. metre. This varies in accordance with the fuel and the froth type however is at present no much less than four.0 litres per minute per sq. metre. One of the continued developments in foam efficiency is the probability that this will be lowered, however requirements typically take time to recognise product improvement. Anything lower than the minimal application fee means that hearth control is unlikely to be achieved. This signifies that firefighting resources, significantly in a guide hearth assault, need to be assembled before firefighting commences and this takes time. The advantage in fitting fastened systems is that the assets are already designed and constructed into the system for immediate application.
Principle of foam extinguishment Images provided 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 hearth challenges, the following is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically associated with fire service deployment and limited mounted methods applications. This uses the venturi precept to create a stress drop in a small aluminium or seawater materials appropriate system with built-in focus pick-up tube. The stress drop created by the venturi draws the froth 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 hearth appliance or fitted right into a pipework system.
However, while it’s thought-about to be the best technique, it has extreme drawbacks: (i) items are manufacturing unit calibrated so any changes 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 likely require a system re-design; (ii) system design and sign-off are critical as deviations brought on by pipe diameter changes will adversely affect proportioning accuracy and probably prevent any proportioning; (iii) modifications in focus viscosity will undermine the ability of the venturi to attract concentrate into the downstream lines; (iv) strain loss is high, as a lot as 35%, so responsibility pump pressures need to be high enough to permit for it, probably including further cost into the system; (v) foam supply devices must be sized in order to not restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs because of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
Types of froth agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electrical or a combination of electrical and diesel pumps to produce foam focus into a proportioner at a better stress than the incoming water-line stress. The proportioner is installed into the water line and regulates the blending.
They at the moment are associated with older methods, where disadvantages include: (i) additional 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 wide ranges in flows; (iii) the froth pump wants an extra power supply, apart from water, so just isn’t as reliably secure as a system with a potential single level of failure, similar to a completely water-driven system; (iv) typically, these systems are very complicated and cause high efforts at 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 froth focus and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel pressure vessel containing a flexible 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 filled bladder so that foam concentrate could be proportioned with water utilizing the same supply. The venturi principle is once more introduced into play because it creates a strain drop at the point of injection for the foam concentrate. Testing can’t be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices on account 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 result of great care is needed to keep away from a broken bladder when commissioning a new installation. It isn’t simple to work inside the metal strain vessel should problems happen, especially if and when a substitute bladder could additionally be required: it all adds to the problem and price.
Compressed air foam (CAFS):
This is not a proportioning method in the typical sense as the froth is already proportioned using one of many previous strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth solution on the level of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces permitting better penetration and cooling. This can be a profit in wildfire conditions by coating susceptible structures to mitigate fireplace growth. The restricted water provides associated with remote wildfire areas means that the resource may be totally optimised. However, as with balanced strain proportioner foam pumps, an additional point of failure is feasible because of the further CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into 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 focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and can proportion the foam concentrate precisely throughout a wide operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning price testing, completely without using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners embody:
Reduced prices: proportioning price is examined with out using foam or creating premix or foam – cost efficient and eco-friendly.
Improved performance: fixed proportioning rate across a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% discount in pressure loss, in comparability with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a unique proportioning rate.
FM approved FireDos Gen III proportioners are so far the only FM permitted water motor coupled variable proportioners utilizing FM approved move meters. Using the check return line this offers the possibility to verify the proportioning rate during commissioning as nicely as for annual tests, with out creating any premix, which is a really huge profit for the user and relieves the setting.
In the second a half of this feature we are going to explore the effects of viscosity on foam proportioning and typical foam application areas and really helpful discharge devices.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share

Scroll to Top