A guide to foam and foam proportioning tools – Part 1

Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given fire situation. Our objective on this two-part article is to provide steerage based mostly on a hazard-specific method and assist you to make an knowledgeable determination on applicable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorized 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 usually associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting screens, we specialise mainly in the Class B class: flammable liquids.
Foam is taken into account to be the most effective 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 could not penetrate the fire load effectively.
Fire lessons.
How do we make foam?
Finished foam solution includes a simple recipe of foam concentrate, water and air. Foam concentrate is typically mixed within the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge device – we will cover proportioning later in this article and discharge strategies in Part 2. At this point air is entrained by utilizing gadgets designed to naturally aspirate the answer. The quantity of aspiration and the kind of focus determines the enlargement ratio. This is typically split between low, medium and high growth. Low growth is as much as 20:1, medium is 200:1 and excessive expansion is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to increase the froth adequately, though naturally aspirated mills are additionally used. The decision to choose on a selected enlargement ratio is set by the hazard beneath evaluation.
Put merely, water and oil do not combine. Applying solely water to Class B products will not suppress the burning vapours. This is a crucial level to make as it is 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 produce that blanket or film, the objective is similar.
Steps of froth era Images provided by Author / Contributor
A little of the historical past of foam development
We can date the event of recent 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 base component). เกจวัดแรงดันไอน้ำ was due to restricted fuel tolerance, which meant it was prone 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 higher gasoline tolerance in addition to forming a vapour-sealing movie across the surface of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s development didn’t utterly replace the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat fuel pick-up (mixing) and offer a good resistance to heat, defined by the business as ‘burn-back resistance’.
Further improvement within the Eighties took FP to the following stage 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 1980s further added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced an additional challenge as they were water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar expertise also grew to become obtainable with the model new technology of AFFF-ARs.
In recent years fluorine, one of the cornerstone ingredients to all foams, has turn into an environmental issue, due to persistence in groundwater. The trade has been offered with a major problem to get rid of the ‘fluoro’ component of all of the different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims regarding 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 define these foams, which have turn out to be the brand new normal and first choice for operators changing current stock or reviewing new tasks. As a foam proportioner manufacturer we must examine the bodily properties of foam fastidiously (especially viscosity) as they influence decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are more and more important in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant quality of SFFF/F3 is important to fight the small degree of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being extremely effective. The greatest method of comparing their claims is to familiarise your self with the empirically based mostly standard EN 1568 or UL162. The exams cover extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included within the take a look at protocols. This additionally covers contemporary and seawater as well as gentle and forceful software of the froth. Each foam is given a ranking with IA being the most effective, IIID the worst. This means you could challenge foam suppliers so as to make an knowledgeable decision on the best foam for your needs.
Whilst EN 1568 is a wonderful benchmark standard, awareness of the effects on foam performance from elements exterior the standard exams ought to be famous. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by different ambient air temperatures, the application technique, gasoline depth and so on. Our recommendation would be to grasp the small print of the exams and attempt to match them to the foam’s appropriateness in your individual hazards. We would all the time advocate consulting individual foam producers as they’ll often provide specific in-house fire-performance knowledge against a variety of the more unusual fuels.
However, despite the froth manufacturers’ typically 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 according to the enlargement ratio Images equipped by Author / Contributor
Critical elements for fulfillment: the time and software price matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the speed at which completed foam is applied. Both are determined by empirically based mostly requirements printed by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ issue means that for a given measurement of fire area it is needed to apply the foam for long enough to achieve extinction and to stop re-ignition. This is particularly critical in handbook intervention as firefighter’s might be at risk throughout post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the appliance time may be as long as 60 minutes for the most important tank diameters.
The software rate refers back to the quantity of finished foam utilized per square metre. This varies according to the gasoline and the froth kind however is currently no less than 4.zero litres per minute per square metre. One of the ongoing developments in foam performance is the chance that this shall be lowered, however standards typically take time to recognise product improvement. Anything lower than the minimal utility rate signifies that fireplace control is unlikely to be achieved. This means that firefighting sources, notably in a manual fireplace assault, need to be assembled before firefighting commences and this takes time. The advantage in becoming mounted methods is that the resources are already designed and constructed into the system for instant software.
Principle of foam extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an informed determination on how best to sort out their specific fireplace challenges, the following is an outline of the varied foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and restricted fixed methods functions. This uses the venturi precept to create a pressure drop in a small aluminium or seawater materials appropriate device with built-in concentrate pick-up tube. The strain drop created by the venturi draws 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 easily carried on a fireplace equipment or fitted right into a pipework system.
However, whilst it’s thought-about to be the only method, it has severe drawbacks: (i) items are factory calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter changes will adversely affect proportioning accuracy and doubtlessly prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to attract focus into the downstream traces; (iv) stress loss is high, as a lot as 35%, so responsibility pump pressures must be excessive sufficient to permit for it, potentially adding further value into the system; (v) foam delivery devices need to be sized in order not to restrict design flows; (vi) testing cannot be achieved with out creating premix and discharging completed foam. This will add to complete lifetime prices on account of foam concentrate usage, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced strain proportioners:
These use an electric or a mixture of electric and diesel pumps to supply foam focus right into a proportioner at a better stress than the incoming water-line pressure. The proportioner is installed into the water line and regulates the mixing.
They are now associated with older methods, the place disadvantages embody: (i) additional prices in hardware and design time; (ii) the froth pump is normally restricted to a a lot tighter operating vary, though the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump wants an additional energy supply, aside from water, so is not as reliably safe as a system with a possible single point of failure, such as an entirely water-driven system; (iv) sometimes, these systems are very complex and cause high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to wreck the foam concentrate and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner much like those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam concentrate may be proportioned with water utilizing the same supply. The venturi principle is again brought into play because it creates a strain drop on the point of injection for the foam concentrate. Testing can’t be achieved with out creating premix and discharging finished foam. This will add to whole 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 weakness as a end result of great care is needed to avoid a damaged bladder when commissioning a new installation. It is never easy to work throughout the steel pressure vessel ought to issues occur, especially if and when a replacement bladder may be required: all of it adds to the problem and price.
Compressed air foam (CAFS):
This is not a proportioning method within the typical sense as the froth is already proportioned utilizing one of many earlier strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam resolution on the point of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces allowing higher penetration and cooling. This can additionally be a benefit in wildfire conditions by coating vulnerable buildings to mitigate fire growth. The limited water supplies associated with remote wildfire areas means that the resource may be fully optimised. However, as with balanced pressure proportioner foam pumps, a further point of failure is possible because of the extra CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have become 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 supplies the motive force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam focus via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and will proportion the froth concentrate accurately across a wide operating vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, completely without utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners embody:
Reduced costs: proportioning rate is tested without utilizing foam or creating premix or foam – cost effective and eco-friendly.
Improved efficiency: fixed proportioning price throughout a wide working vary.
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 fast adjustment to a unique proportioning rate.
FM accredited FireDos Gen III proportioners are thus far the one FM approved water motor coupled variable proportioners utilizing FM permitted circulate meters. Using the test return line this presents the likelihood to verify the proportioning fee during commissioning as well as for annual exams, without creating any premix, which is a really massive benefit for the consumer and relieves the surroundings.
In the second part of this characteristic we are going to discover the results of viscosity on foam proportioning and typical foam application areas and recommended discharge devices.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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