Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given fireplace state of affairs. Our goal on this two-part article is to supply guidance based on a hazard-specific method and allow you to make an informed decision on applicable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are classified as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires generally related to cooking similar to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise primarily within the Class B class: flammable liquids.
Foam is considered to be the simplest fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only could not penetrate the hearth load effectively.
Fire classes.
How will we make foam?
Finished foam solution comprises a easy recipe of froth focus, water and air. Foam focus is typically combined within the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge system – we will cover proportioning later on this article and discharge strategies in Part 2. At this level air is entrained through the use of devices designed to naturally aspirate the answer. The amount of aspiration and the kind of concentrate determines the expansion ratio. This is usually split between low, medium and high enlargement. Low growth is as much as 20:1, medium is 200:1 and excessive enlargement is greater than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated turbines are additionally used. The decision to choose a particular enlargement ratio is decided by the hazard under review.
Put simply, water and oil don’t combine. Applying only 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 enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to achieve success. Whatever technique is chosen to produce that blanket or movie, the objective is identical.
Steps of foam generation Images supplied by Author / Contributor
A little of the history of froth growth
We can date the event of modern foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the base component). The main downside was because of restricted fuel tolerance, which meant it was susceptible to gas 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 film throughout the floor of the gasoline. เกจวัดแรงดันปั๊มลม is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth didn’t completely replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat gasoline pick-up (mixing) and supply a good resistance to warmth, outlined by the business 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 each worlds: a film-forming foam that also had good burn-back resistance.
The 1980s 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 challenge as they have been water soluble and foam harmful. ที่วัดแรงดันน้ำ -AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical know-how additionally became out there with the brand new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone elements to all foams, has turn out to be an environmental problem, as a end result of persistence in groundwater. The business has been presented with a significant problem to remove the ‘fluoro’ element of all the completely different foam focus sorts. We have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of a whole vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have become the model new regular and first choice for operators changing current inventory or reviewing new tasks. As a foam proportioner producer we should study the physical properties of foam fastidiously (especially viscosity) as they affect selections 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, means that the alcohol-resistant high quality of SFFF/F3 is necessary to fight the small diploma of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being highly effective. The best way of comparing their claims is to familiarise your self with the empirically based normal 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 both included within the check protocols. This also covers recent and seawater in addition to light and forceful utility 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 knowledgeable determination on the most effective foam on your wants.
Whilst EN 1568 is a wonderful benchmark standard, consciousness of the effects on foam performance from elements exterior the usual tests should be famous. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by totally different ambient air temperatures, the application method, fuel depth etc. Our recommendation can be to understand the small print of the exams and try to match them to the foam’s appropriateness in your individual hazards. We would all the time advocate consulting individual foam manufacturers as they’ll usually present specific in-house fire-performance data towards a few of the extra unusual fuels.
However, despite the froth manufacturers’ sometimes conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the expansion ratio Images equipped by Author / Contributor
Critical factors for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the rate at which completed foam is applied. Both are determined by empirically primarily based requirements printed by bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor signifies that for a given size of fire area it’s needed to apply the foam for long sufficient to attain extinction and to stop re-ignition. This is especially important in guide intervention as firefighter’s will be in danger during post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the applying time may be as lengthy as 60 minutes for the largest tank diameters.
The utility fee refers to the amount of completed foam utilized per sq. metre. This varies according to the gasoline and the froth kind however is at present no much less than four.0 litres per minute per square metre. One of the continued developments in foam efficiency is the likelihood that this shall be reduced, however standards often take time to recognise product development. Anything lower than the minimum application rate signifies that fireplace management is unlikely to be achieved. This means that firefighting resources, notably in a manual fireplace assault, must be assembled before firefighting commences and this takes time. The advantage in fitting fixed systems is that the assets are already designed and built into the system for immediate software.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an informed decision on how best to tackle their specific fire challenges, the following is an summary of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with fireplace service deployment and restricted mounted systems functions. This makes use of the venturi precept to create a strain drop in a small aluminium or seawater materials suitable gadget with built-in focus pick-up tube. The stress drop created by the venturi draws the foam concentrate from a container where it mixes with water to create foam resolution. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fireplace equipment or fitted right into a pipework system.
However, whilst it’s considered to be the best method, it has extreme drawbacks: (i) models are manufacturing facility calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a changing quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are crucial as deviations brought on by pipe diameter changes will adversely affect proportioning accuracy and probably prevent any proportioning; (iii) adjustments in focus viscosity will undermine the power of the venturi to draw concentrate into the downstream strains; (iv) stress loss is high, as much as 35%, so obligation pump pressures have to be high sufficient to permit for it, probably including extra cost into the system; (v) foam delivery devices need to be sized so as to not restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to entire lifetime prices because of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced strain proportioners:
These use an electric or a combination of electrical and diesel pumps to provide foam focus into a proportioner at the next strain than the incoming water-line pressure. The proportioner is installed into the water line and regulates the mixing.
They are actually related to older techniques, the place disadvantages include: (i) further costs in hardware and design time; (ii) the foam pump is often restricted to a much tighter operating vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an additional power source, other than water, so is not as reliably secure as a system with a potential single point of failure, such as a wholly water-driven system; (iv) usually, these systems are very advanced and trigger 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 froth concentrate and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal strain vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam crammed bladder so that foam focus can be proportioned with water utilizing the identical supply. The venturi precept is again brought into play because it creates a strain drop on the point of injection for the foam focus. Testing can’t be achieved without creating premix and discharging finished foam. This will add to complete lifetime prices on account 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 spot as a result of nice care is required to keep away from a broken bladder when commissioning a new installation. It is never simple to work within the steel strain vessel should problems happen, particularly if and when a substitute bladder may be required: it all provides to the difficulty and price.
Compressed air foam (CAFS):
This isn’t a proportioning method within the standard sense as the froth is already proportioned using one of many previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth resolution on the point of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces permitting better penetration and cooling. This can additionally be a profit in wildfire situations by coating weak buildings to mitigate fire development. The limited water supplies associated with distant wildfire areas means that the useful resource may be fully optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is possible due to the extra CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is solely mechanical and extremely reliable. A water-driven rotor provides the motive force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and will proportion the froth focus precisely throughout a large working vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning fee testing, utterly without utilizing 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 accredited foam proportioners embody:
Reduced prices: proportioning fee is tested without utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: fixed proportioning price across a large operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in stress loss, in comparison with older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a special proportioning rate.
FM approved FireDos Gen III proportioners are to date the only FM permitted water motor coupled variable proportioners utilizing FM approved move meters. Using the test return line this presents the chance to examine the proportioning price throughout commissioning in addition to for annual exams, with out creating any premix, which is a very massive profit for the consumer and relieves the environment.
In the second part of this characteristic we will explore the effects of viscosity on foam proportioning and typical foam software areas and really helpful discharge devices.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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