Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given fireplace scenario. Our objective on this two-part article is to provide guidance primarily based on a hazard-specific method and assist you to make an knowledgeable choice on acceptable 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 materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires typically associated with cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting monitors, we specialise mainly within the Class B class: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely may not penetrate the fire load effectively.
Fire courses.
How can we make foam?
Finished foam solution contains a easy recipe of froth concentrate, water and air. Foam concentrate is usually 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’ll cover proportioning later in this article and discharge methods in Part 2. At this level air is entrained by utilizing units designed to naturally aspirate the answer. The amount of aspiration and the kind of concentrate determines the enlargement ratio. This is usually cut up between low, medium and excessive expansion. Low enlargement is as much 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 increase the froth adequately, though naturally aspirated mills are additionally used. The determination to decide on a selected expansion ratio is decided by the hazard underneath evaluate.
Put merely, water and oil do not combine. Applying solely water to Class B merchandise 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 need a medium that enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to achieve success. Whatever method is chosen to supply that blanket or movie, the target is the same.
Steps of froth era Images equipped by Author / Contributor
A little of the history of foam development
We can date the event of modern foam concentrates from the Sixties onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary drawback was because of restricted gas tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a higher gasoline tolerance in addition to forming a vapour-sealing movie throughout the floor of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s development did not fully substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight gasoline pick-up (mixing) and supply a good resistance to heat, outlined by the business as ‘burn-back resistance’.
Further improvement in the Nineteen Eighties took FP to the next degree with film-forming fluoroprotein or FFFP. We now had the most effective of both worlds: a film-forming foam that additionally had good burn-back resistance.
The Nineteen Eighties additional added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times offered an additional challenge as they were water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical know-how also turned out there with the new technology of AFFF-ARs.
In recent years fluorine, one of the cornerstone ingredients to all foams, has become an environmental concern, because of persistence in groundwater. The trade has been offered with a major challenge to eliminate the ‘fluoro’ factor of all the different foam concentrate varieties. We have witnessed an period of manufacturers’ claims and counter claims regarding 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 regular and first selection for operators changing present inventory or reviewing new projects. As เกจวัดแรงดันถังแก๊ส must study the physical properties of foam fastidiously (especially viscosity) as they influence decisions on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are increasingly essential within the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant quality of SFFF/F3 is critical to fight the small degree of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being highly efficient. The best method of evaluating their claims is to familiarise your self with the empirically primarily based standard EN 1568 or UL162. The checks cowl extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the more demanding polar solvents are both included within the take a look at protocols. This additionally covers fresh and seawater in addition to mild and forceful utility of the foam. Each foam is given a rating with IA being the most effective, IIID the worst. This means that you can problem foam suppliers so as to make an informed choice on one of the best foam for your needs.
Whilst EN 1568 is an excellent benchmark commonplace, awareness of the results on foam performance from factors exterior the standard tests must be noted. For instance, significantly aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by different ambient air temperatures, the application methodology, gas depth and so on. Our recommendation would 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 advocate consulting individual foam producers as they will often provide particular in-house fire-performance knowledge in opposition to some of the extra uncommon fuels.
However, despite the froth manufacturers’ generally conflicting claims on performance, the sooner fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the expansion ratio Images equipped by Author / Contributor
Critical components for success: the time and application fee matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary factors: time and the rate at which completed foam is utilized. Both are decided by empirically based standards revealed by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given measurement of fire space it is necessary to apply the froth for lengthy sufficient to achieve extinction and to forestall re-ignition. This is particularly critical in manual intervention as firefighter’s will be at risk during post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the applying time may be so lengthy as 60 minutes for the most important tank diameters.
The utility fee refers again to the quantity of completed foam utilized per sq. metre. This varies in accordance with the fuel and the froth kind but is presently at least four.0 litres per minute per square metre. One of the continuing developments in foam performance is the likelihood that this shall be reduced, however requirements usually take time to recognise product growth. Anything less than the minimum utility price implies that fireplace management is unlikely to be achieved. This signifies that firefighting resources, notably in a guide fire assault, have to be assembled before firefighting commences and this takes time. The advantage in fitting fixed techniques is that the sources are already designed and built into the system for immediate software.
Principle of foam extinguishment Images equipped 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 fireplace challenges, the next is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with fireplace service deployment and limited mounted methods purposes. This uses 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 strain 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 body of the inductor are compact sufficient to be simply carried on a fire appliance or fitted into a pipework system.
However, while it is thought-about to be the simplest methodology, it has extreme drawbacks: (i) units are manufacturing facility calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a changing amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter modifications will adversely have an effect on proportioning accuracy and doubtlessly stop any proportioning; (iii) changes in concentrate viscosity will undermine the flexibility of the venturi to attract concentrate into the downstream traces; (iv) pressure loss is excessive, as much as 35%, so obligation pump pressures have to be excessive enough to allow for it, potentially including extra value into the system; (v) foam delivery gadgets need to be sized in order not to limit design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices as a outcome of foam concentrate usage, 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 supply foam concentrate into a proportioner at the next strain than the incoming water-line pressure. The proportioner is installed into the water line and regulates the blending.
They at the moment are related to older techniques, the place disadvantages embrace: (i) further prices in hardware and design time; (ii) the foam pump is generally restricted to a a lot tighter operating range, though the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump wants a further power source, apart from water, so is not as reliably secure as a system with a potential single point of failure, similar to an entirely water-driven system; (iv) usually, these systems are very advanced and cause excessive 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 damage the foam focus 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 flexible 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 filled bladder so that foam focus can be proportioned with water utilizing the same provide. The venturi principle is once more brought into play as it creates a pressure drop on the level of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to entire lifetime prices as a outcome of foam focus utilization, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a outcome of nice care is needed to keep away from a damaged bladder when commissioning a brand new set up. It isn’t simple to work throughout the steel strain vessel ought to issues happen, especially if and when a substitute bladder could also be required: it all provides to the problem and price.
Compressed air foam (CAFS):
This just isn’t a proportioning technique within the standard sense as the foam is already proportioned utilizing one of many previous methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth solution on the level of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces allowing better penetration and cooling. This can be a benefit in wildfire conditions by coating weak constructions to mitigate hearth growth. The restricted water provides related to distant wildfire areas means that the useful resource can be absolutely optimised. However, as with balanced strain proportioner foam pumps, an additional point of failure is feasible as a result of additional CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is solely mechanical and highly dependable. 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 by way of 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 focus precisely across a wide operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, fully without using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners embrace:
Reduced costs: proportioning price is examined with out using foam or creating premix or foam – price efficient and eco-friendly.
Improved efficiency: fixed proportioning fee throughout a large operating vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in pressure loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a unique proportioning price.
FM accredited FireDos Gen III proportioners are so far the one FM approved water motor coupled variable proportioners using FM permitted circulate meters. Using the check return line this provides the likelihood to examine the proportioning rate throughout commissioning as properly as for annual exams, without creating any premix, which is a very huge benefit for the person and relieves the setting.
In the second a half of this feature we will discover the results of viscosity on foam proportioning and typical foam software areas and really helpful discharge units.
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Written by
David Owen
Andreas Hulinsky