Fire presents many challenges, not least because of the variables that determine which suppression medium is suitable for a given hearth scenario. Our objective in this two-part article is to provide guidance based on a hazard-specific method and help you make an knowledgeable determination on appropriate fire-suppression measures, especially 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 corresponding to magnesium
Class F – fires generally related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting screens, we specialise mainly within the Class B category: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only might not penetrate the hearth load effectively.
Fire lessons.
How can we make foam?
Finished foam resolution includes a simple recipe of foam concentrate, water and air. Foam concentrate is usually blended 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 device – we will cover proportioning later in this article and discharge strategies in Part 2. At this level air is entrained by using gadgets designed to naturally aspirate the solution. The amount of aspiration and the type of concentrate determines the expansion ratio. This is typically cut up between low, medium and excessive expansion. Low enlargement is as much as 20:1, medium is 200:1 and high expansion is greater 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 determination to decide on a particular enlargement ratio is determined by the hazard beneath evaluate.
Put simply, water and oil don’t combine. Applying only water to Class B merchandise won’t suppress the burning vapours. This is a crucial point to make as it is the vapours, not the liquid itself, that burns. We want 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 movie, the target is similar.
Steps of froth era Images supplied by Author / Contributor
A little of the history of foam growth
We can date the event of contemporary foam concentrates from the 1960s onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary drawback was as a outcome of limited gas 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 bottom product, artificial detergents gave foam a larger gasoline tolerance in addition to forming a vapour-sealing film throughout the surface of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth did not utterly substitute the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat gas pick-up (mixing) and offer a good resistance to warmth, defined by the business as ‘burn-back resistance’.
Further improvement within the Eighties took FP to the subsequent level with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that additionally had good burn-back resistance.
The Nineteen Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced a further problem 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. เกจวัดแรงดันco2 turned out there with the new generation of AFFF-ARs.
In recent years fluorine, one of the cornerstone ingredients to all foams, has turn out to be an environmental issue, as a outcome of persistence in groundwater. The industry has been introduced with a serious challenge to eliminate the ‘fluoro’ factor of all the totally different foam concentrate sorts. We have witnessed an period of manufacturers’ claims and counter claims relating to the efficacy of an entire 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 into the new regular and first selection for operators changing existing inventory or reviewing new tasks. As a foam proportioner producer we should look at the bodily properties of froth carefully (especially viscosity) as they affect decisions on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are more and more essential in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small diploma of water miscibility of the fuel.
All foam focus manufacturers will naturally promote their product as being highly effective. The finest method of comparing their claims is to familiarise yourself with the empirically based normal EN 1568 or UL162. The tests cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included in the check protocols. This additionally covers contemporary and seawater as properly as mild and forceful utility of the foam. Each foam is given a rating with IA being the best, IIID the worst. This means that you can problem foam suppliers so as to make an informed determination on the best foam on your needs.
Whilst EN 1568 is an excellent benchmark standard, awareness of the results on foam performance from components outdoors the usual tests ought to be noted. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of certain foams. This could be exacerbated by completely different ambient air temperatures, the applying technique, fuel depth etc. Our recommendation would be to grasp the details of the checks and try to match them to the foam’s appropriateness on your individual hazards. We would all the time advocate consulting individual foam manufacturers as they’ll typically provide specific in-house fire-performance information in opposition to some of the more unusual fuels.
However, despite the froth manufacturers’ generally conflicting claims on performance, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the enlargement ratio Images provided by Author / Contributor
Critical components for success: the time and application rate matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary components: time and the rate at which completed foam is utilized. Both are determined by empirically based mostly requirements printed by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue means that for a given size of fireplace area it is necessary to apply the foam for lengthy sufficient to attain extinction and to forestall re-ignition. This is very crucial in handbook intervention as firefighter’s might be at risk throughout post-fire operations. When it involves fixed safety for hydrocarbon and polar solvent tanks, the appliance time may be as long as 60 minutes for the most important tank diameters.
The utility fee refers again to the amount of completed foam applied per square metre. This varies based on the gasoline and the foam sort but is currently no less than four.zero litres per minute per square metre. One of the continued developments in foam performance is the likelihood that this will be decreased, but standards typically take time to recognise product development. Anything lower than the minimal software rate signifies that fire control is unlikely to be achieved. This implies that firefighting sources, particularly in a guide hearth attack, need to be assembled before firefighting commences and this takes time. The benefit in fitting fastened techniques is that the sources are already designed and built into the system for instant software.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an knowledgeable decision on how greatest to deal with their particular fire challenges, the next is an overview of the various foam proportioning methods.
Foam inductors:
Typically associated with fire service deployment and limited mounted techniques purposes. This uses the venturi precept to create a strain drop in a small aluminium or seawater material suitable gadget with built-in concentrate pick-up tube. The pressure drop created by the venturi attracts the foam concentrate from a container the place it mixes with water to create foam solution. Both the pick-up tube and body of the inductor are compact sufficient to be easily carried on a fireplace equipment or fitted right into a pipework system.
However, while it is thought-about to be the simplest methodology, it has severe drawbacks: (i) items are manufacturing unit calibrated so any adjustments 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 probably require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter modifications will adversely have an effect on proportioning accuracy and doubtlessly prevent any proportioning; (iii) changes in concentrate viscosity will undermine the power 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 high enough to permit for it, potentially adding further value into the system; (v) foam delivery gadgets must be sized so as not to restrict design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs because of foam concentrate utilization, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced stress proportioners:
These use an electric or a combination of electric and diesel pumps to supply foam concentrate right into a proportioner at a higher stress than the incoming water-line pressure. The proportioner is put in into the water line and regulates the mixing.
They are now associated with older systems, the place disadvantages include: (i) additional costs in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter operating range, although the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump wants an additional power supply, aside from water, so just isn’t as reliably safe as a system with a potential single level of failure, such as a completely water-driven system; (iv) typically, these systems are very complex and trigger excessive efforts on 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 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 concentrate proportioner similar to the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam concentrate can be proportioned with water using the identical supply. The venturi precept is again brought into play as it creates a strain drop at the point of injection for the froth focus. Testing can’t be achieved with out creating premix and discharging completed foam. This will add to complete lifetime prices because of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is required to keep away from a damaged bladder when commissioning a model new set up. It is never easy to work within the metal strain vessel should issues happen, particularly if and when a alternative bladder could also be required: it all adds to the difficulty and cost.
Compressed air foam (CAFS):
This just isn’t a proportioning method within the conventional sense as the foam is already proportioned utilizing one of the previous methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth answer at the point of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces permitting better penetration and cooling. This is also a benefit in wildfire conditions by coating vulnerable constructions to mitigate fire development. The limited water provides associated with distant wildfire areas implies that the useful resource may be fully optimised. However, as with balanced stress proportioner foam pumps, an extra point of failure is feasible due to the extra CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is only mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning rate and can proportion the froth focus precisely throughout a wide working range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, fully without using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embody:
Reduced prices: proportioning fee is tested without using foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: fixed proportioning rate across a large working range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a different proportioning rate.
FM permitted FireDos Gen III proportioners are thus far the one FM approved water motor coupled variable proportioners using FM approved move meters. Using the test return line this offers the chance to examine the proportioning rate during commissioning in addition to for annual exams, without creating any premix, which is a very big benefit for the consumer and relieves the environment.
In the second a half of this characteristic we’ll discover the consequences of viscosity on foam proportioning and typical foam software areas and beneficial discharge devices.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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