Fire presents many challenges, not least because of the variables that determine which suppression medium is acceptable for a given hearth scenario. Our goal in this two-part article is to supply steering primarily based on a hazard-specific approach and help you make an informed choice on acceptable fire-suppression measures, particularly 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 corresponding to magnesium
Class F – fires usually associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily within the Class B class: flammable liquids.
Foam is considered to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only might not penetrate the fire load successfully.
Fire lessons.
How can we make foam?
Finished foam answer comprises a simple recipe of foam focus, water and air. Foam focus is typically combined within the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge device – we’ll cowl proportioning later in this article and discharge methods in Part 2. At this level air is entrained by using units designed to naturally aspirate the answer. The quantity of aspiration and the type of concentrate determines the expansion ratio. This is typically split between low, medium and high expansion. Low expansion is up to 20:1, medium is 200:1 and excessive expansion is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to increase the froth adequately, although naturally aspirated mills are additionally used. The decision to decide on a particular enlargement ratio is decided by the hazard beneath review.
Put merely, water and oil don’t combine. Applying only water to Class B products is not going to suppress the burning vapours. This is an important point to make as it’s 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 obtain success. Whatever technique is chosen to provide that blanket or film, the target is the same.
Steps of froth era Images provided by Author / Contributor
A little of the historical past of foam improvement
We can date the event of recent 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 base component). The major disadvantage was as a outcome of restricted gasoline 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, synthetic detergents gave foam a larger gasoline tolerance in addition to forming a vapour-sealing film throughout the surface of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth did not utterly replace the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight gasoline pick-up (mixing) and provide a good resistance to heat, outlined by the business as ‘burn-back resistance’.
Further growth in the Nineteen Eighties took FP to the next degree 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 record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always introduced an additional challenge as they were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The same know-how also turned out there with the new technology of AFFF-ARs.
In latest years fluorine, one of many cornerstone ingredients to all foams, has turn out to be an environmental issue, because of persistence in groundwater. The industry has been offered with a significant problem to get rid of the ‘fluoro’ factor of all the completely different foam focus varieties. We have witnessed an era of manufacturers’ claims and counter claims concerning 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 become the model new normal and first choice for operators altering present stock or reviewing new tasks. As a foam proportioner manufacturer we must study the physical properties of foam carefully (especially viscosity) as they affect choices on the overall proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant sorts are more and more necessary within 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 necessary to fight the small degree of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being highly effective. The greatest way of comparing their claims is to familiarise your self with the empirically primarily based standard 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 each included in the take a look at protocols. This also covers contemporary and seawater as nicely as gentle 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 could problem foam suppliers so as to make an informed decision on the best foam on your needs.
Whilst EN 1568 is an excellent benchmark commonplace, consciousness of the consequences on foam efficiency from factors outside the standard checks ought to be noted. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by different ambient air temperatures, the applying method, gas depth and so on. Our advice could be to understand the details of the checks and attempt to match them to the foam’s appropriateness in your particular person hazards. We would all the time suggest consulting individual foam manufacturers as they can typically present particular in-house fire-performance data in opposition to some of the extra uncommon fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on performance, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the growth ratio Images supplied by Author / Contributor
Critical factors for success: the time and software price matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary factors: time and the speed at which finished foam is applied. Both are determined by empirically based mostly requirements printed by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ factor implies that for a given size of fireplace area it is essential to apply the foam for long sufficient to achieve extinction and to prevent re-ignition. This is especially important in handbook intervention as firefighter’s shall be in danger throughout post-fire operations. When it comes to fastened safety for hydrocarbon and polar solvent tanks, the appliance time can be as lengthy as 60 minutes for the most important tank diameters.
The utility price refers to the amount of completed foam utilized per square metre. This varies based on the gasoline and the froth type however is at present at least 4.0 litres per minute per sq. metre. One of the continued developments in foam efficiency is the likelihood that this might be reduced, but requirements typically take time to recognise product development. Anything lower than the minimum software fee implies that fire management is unlikely to be achieved. This means that firefighting resources, notably in a manual fire attack, need to be assembled earlier than firefighting commences and this takes time. The advantage in becoming fixed methods is that the resources are already designed and built into the system for instant application.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an knowledgeable choice on how best to sort out their specific fire challenges, the following is an overview of the varied foam proportioning strategies.
Foam inductors:
Typically related to fire service deployment and restricted fixed systems functions. This makes use of the venturi precept to create a pressure drop in a small aluminium or seawater materials compatible gadget with built-in focus pick-up tube. เกจ์แรงดัน created by the venturi draws the froth concentrate from a container where 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 fire equipment or fitted into a pipework system.
However, whilst it’s thought-about to be the best methodology, it has extreme drawbacks: (i) models are manufacturing facility calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge gadget or a altering quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter modifications will adversely have an result on proportioning accuracy and probably prevent any proportioning; (iii) modifications in focus viscosity will undermine the flexibility of the venturi to attract focus into the downstream traces; (iv) stress loss is high, as much as 35%, so duty pump pressures have to be excessive sufficient to allow for it, potentially adding extra cost into the system; (v) foam supply devices have to be sized so as not to restrict design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices on account of foam concentrate usage, which must be changed, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mixture of electrical and diesel pumps to supply foam focus into a proportioner at a better stress than the incoming water-line stress. The proportioner is put in into the water line and regulates the blending.
They are actually associated with older methods, where disadvantages embody: (i) further costs in hardware and design time; (ii) the foam pump is normally restricted to a much tighter working range, although the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump wants an additional power supply, other than water, so just isn’t as reliably secure as a system with a possible single point of failure, similar to a wholly water-driven system; (iv) usually, these techniques are very complex and trigger excessive efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to damage the froth concentrate and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel stress vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner just like those fitted to balanced strain proportioners. The incoming pressurised water compresses the froth stuffed bladder in order that foam focus may be proportioned with water using the identical supply. The venturi precept is once more introduced into play as it creates a strain drop on the point of injection for the froth focus. Testing can’t be achieved with out creating premix and discharging finished foam. This will add to complete lifetime prices as a end result of foam focus usage, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a end result of great care is needed to keep away from a broken bladder when commissioning a new set up. It isn’t straightforward to work inside the steel pressure vessel ought to issues happen, especially if and when a replacement bladder could also be required: it all provides to the problem and price.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology 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 foam resolution on the point of discharge. The consensus view is that CAFS enhances the finished foam’s ability to cling to vertical surfaces allowing higher penetration and cooling. This is also a benefit in wildfire conditions by coating susceptible buildings to mitigate fire progress. The limited water supplies associated with distant wildfire areas means that the resource may be fully optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is feasible as a outcome of 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 technology, the product is purely mechanical and highly reliable. A water-driven rotor provides the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning fee and can proportion the foam concentrate accurately throughout a wide operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning fee testing, utterly with out using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The benefits of FireDos Gen III FM approved foam proportioners embody:
Reduced costs: proportioning fee is tested without using foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: constant proportioning fee across a wide working vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% reduction in strain loss, in comparability with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a special proportioning fee.
FM approved FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners using FM permitted move meters. Using the test return line this offers the chance to examine the proportioning rate throughout commissioning in addition to for annual exams, without creating any premix, which is a very big benefit for the consumer and relieves the setting.
In the second part of this feature we will discover the consequences of viscosity on foam proportioning and typical foam application areas and beneficial discharge devices.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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