Fire presents many challenges, not least because of the variables that decide which suppression medium is suitable for a given hearth state of affairs. Our objective on this two-part article is to supply steering primarily based on a hazard-specific approach and help you make an knowledgeable decision 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 generally associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting screens, we specialise mainly in the Class B category: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only could not penetrate the hearth load successfully.
Fire classes.
How can we make foam?
Finished foam resolution contains a easy recipe of froth concentrate, water and air. Foam focus is typically mixed in the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge system – we will cowl proportioning later in this article and discharge methods in Part 2. At this point air is entrained by utilizing units designed to naturally aspirate the solution. The amount of aspiration and the kind of concentrate determines the growth ratio. This is often cut up between low, medium and excessive growth. Low enlargement is up to 20:1, medium is 200:1 and high growth 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 turbines are also used. The decision to choose on a selected growth ratio is determined by the hazard beneath review.
Put merely, water and oil do not 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’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 be successful. Whatever methodology is chosen to provide that blanket or film, the target is similar.
Steps of foam technology Images provided by Author / Contributor
A little of the historical past of froth improvement
We can date the development of recent foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the base component). The main downside was as a result of limited gas tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the base product, artificial detergents gave foam a larger fuel tolerance in addition to forming a vapour-sealing film throughout the surface of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’ เพรสเชอร์เกจวัดแรงดันน้ำ didn’t completely substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight gas pick-up (mixing) and provide an excellent resistance to warmth, defined by the industry as ‘burn-back resistance’.
Further growth in the Eighties took FP to the next stage with film-forming fluoroprotein or FFFP. We now had one of the best of both worlds: a film-forming foam that also had good burn-back resistance.
The Nineteen Eighties further added to our listing 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 foam blanket from early destruction. The identical know-how also became available with the brand new technology of AFFF-ARs.
In latest years fluorine, one of the cornerstone elements to all foams, has turn out to be an environmental issue, as a end result of persistence in groundwater. The trade has been offered with a serious problem to get rid of the ‘fluoro’ factor of all the different foam focus varieties. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a complete vary 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 tasks. As a foam proportioner manufacturer we must look at the physical properties of froth fastidiously (especially viscosity) as they affect choices on the general proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more necessary within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant high quality of SFFF/F3 is critical to fight the small diploma of water miscibility of the gas.
All foam concentrate manufacturers will naturally promote their product as being extremely efficient. The greatest method of comparing their claims is to familiarise yourself with the empirically primarily based normal 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 more demanding polar solvents are each included in the test protocols. This additionally covers contemporary and seawater in addition to mild and forceful application of the froth. Each foam is given a ranking with IA being one of the best, IIID the worst. This means that you can problem foam suppliers so as to make an informed determination on one of the best foam in your wants.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the results on foam performance from components exterior the standard exams must be noted. For example, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by different ambient air temperatures, the application technique, fuel depth and so on. Our recommendation could be to know the small print of the exams and attempt to match them to the foam’s appropriateness in your particular person hazards. We would always suggest consulting individual foam producers as they will often present particular in-house fire-performance data in opposition to a number of the more unusual fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the enlargement ratio Images provided by Author / Contributor
Critical elements for achievement: the time and software fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the speed at which completed foam is utilized. Both are decided by empirically based mostly standards printed by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor implies that for a given dimension of fire space it is necessary to use the froth for lengthy sufficient to attain extinction and to prevent re-ignition. This is especially crucial in guide intervention as firefighter’s might be in danger throughout post-fire operations. When it involves mounted protection for hydrocarbon and polar solvent tanks, the application time can be as lengthy as 60 minutes for the most important tank diameters.
The software fee refers again to the quantity of completed foam utilized per sq. metre. This varies in accordance with the fuel and the foam kind but is currently no much less than 4.0 litres per minute per sq. metre. One of the continued developments in foam performance is the chance that this will be lowered, but requirements often take time to recognise product improvement. Anything less than the minimum application rate signifies that fire management is unlikely to be achieved. This means that firefighting sources, notably in a guide fireplace assault, have to be assembled before firefighting commences and this takes time. The benefit in fitting fixed techniques is that the assets are already designed and built into the system for immediate application.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an knowledgeable determination on how finest to tackle their specific hearth challenges, the following is an outline of the various foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted fixed techniques purposes. This uses the venturi precept to create a strain drop in a small aluminium or seawater material appropriate system with built-in focus pick-up tube. The stress drop created by the venturi attracts the froth focus from a container the place 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 fireplace equipment or fitted into a pipework system.
However, whilst it’s thought of to be the only method, it has severe drawbacks: (i) items are manufacturing unit calibrated so any adjustments to the hydraulics (caused by size 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 caused by pipe diameter changes will adversely affect proportioning accuracy and potentially prevent any proportioning; (iii) adjustments in focus viscosity will undermine the flexibility of the venturi to attract focus into the downstream traces; (iv) stress loss is excessive, as a lot as 35%, so responsibility pump pressures need to be high sufficient to permit for it, probably including extra price into the system; (v) foam supply gadgets need to be sized so as to not restrict design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs on account of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced stress proportioners:
These use an electrical or a mix of electrical and diesel pumps to provide foam concentrate into a proportioner at the next stress than the incoming water-line pressure. The proportioner is put in into the water line and regulates the mixing.
They are actually associated with older techniques, the place disadvantages include: (i) extra costs in hardware and design time; (ii) the froth pump is normally restricted to a much tighter working vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump wants an additional power supply, aside from water, so is not 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 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 break the foam concentrate and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner much like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth crammed bladder so that foam concentrate may be proportioned with water utilizing the identical provide. The venturi principle is again introduced into play because it creates a strain 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 whole lifetime prices as a result of foam focus 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 result of great care is required to avoid a damaged bladder when commissioning a brand new set up. It is rarely easy to work inside the steel stress vessel ought to issues happen, especially if and when a alternative bladder may be required: it all adds to the difficulty and value.
Compressed air foam (CAFS):
This is not a proportioning method within the typical sense as the foam is already proportioned using one of many earlier strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth solution at the point of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces allowing better penetration and cooling. This is also a benefit in wildfire situations by coating susceptible constructions to mitigate hearth development. The restricted water supplies related to remote wildfire areas implies that the resource could be fully optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is feasible because of the additional CAFS equipment.
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 extremely reliable. A water-driven rotor provides the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is equipped with foam focus via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning fee and will proportion the foam concentrate precisely across a wide operating range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning price testing, utterly with out using 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 embrace:
Reduced costs: proportioning price is examined without utilizing foam or creating premix or foam – value effective and eco-friendly.
Improved efficiency: fixed proportioning fee throughout a wide operating vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in strain loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a special proportioning rate.
FM accredited FireDos Gen III proportioners are so far the only FM accredited water motor coupled variable proportioners using FM accredited move meters. Using the take a look at return line this provides the possibility to check the proportioning price during commissioning in addition to for annual checks, with out creating any premix, which is a really massive benefit for the person and relieves the setting.
In the second part of this feature we’ll explore the effects of viscosity on foam proportioning and typical foam software areas and recommended discharge units.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share