Fire presents many challenges, not least because of the variables that decide which suppression medium is acceptable for a given hearth scenario. Our goal on this two-part article is to offer guidance primarily based on a hazard-specific method and allow you to make an informed determination 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 flamable materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires generally associated with cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting monitors, we specialise mainly in the Class B class: 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 where water solely could not penetrate the fire load effectively.
Fire courses.
How will we make foam?
Finished foam answer includes a easy recipe of foam focus, water and air. Foam concentrate is often blended within 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’ll cover proportioning later in this article and discharge strategies in Part 2. At this point air is entrained by using units designed to naturally aspirate the answer. The amount of aspiration and the type of focus determines the enlargement ratio. This is often split between low, medium and high enlargement. Low expansion is as a lot as 20:1, medium is 200:1 and high growth 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 mills are additionally used. The determination to choose on a specific expansion ratio is decided by the hazard under review.
Put simply, water and oil don’t combine. Applying solely water to Class B products is not going to suppress the burning vapours. This is a vital level 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 similar.
Steps of foam era Images supplied by Author / Contributor
A little of the historical past of froth development
We can date the event of contemporary foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary disadvantage was as a outcome of restricted fuel 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 bottom product, synthetic detergents gave foam a larger gas tolerance in addition to forming a vapour-sealing film throughout the floor of the fuel. เกจวัดแรงดันลม10bar is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth didn’t completely substitute the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight fuel pick-up (mixing) and offer a good resistance to warmth, defined by the trade as ‘burn-back resistance’.
Further development in the Nineteen Eighties took FP to the next stage with film-forming fluoroprotein or FFFP. We now had the best 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 always offered a further problem as they have been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The identical know-how additionally became obtainable with the new technology of AFFF-ARs.
In recent years fluorine, one of many cornerstone components to all foams, has turn into an environmental issue, because of persistence in groundwater. The business has been introduced with a significant challenge to remove the ‘fluoro’ factor of all of the totally different foam focus types. 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 define these foams, which have turn into the new normal and first alternative for operators altering current inventory or reviewing new projects. As a foam proportioner manufacturer we should examine the physical properties of froth fastidiously (especially viscosity) as they affect decisions on the general proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more essential in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant high quality of SFFF/F3 is necessary to combat the small degree of water miscibility of the fuel.
All foam focus manufacturers will naturally promote their product as being highly effective. The best method of evaluating their claims is to familiarise your self with the empirically based mostly normal EN 1568 or UL162. The checks cover extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are each included in the take a look at protocols. This also covers recent and seawater in addition to light and forceful utility of the froth. Each foam is given a rating with IA being one of the best, IIID the worst. This means you could challenge foam suppliers to find a way to make an knowledgeable determination on the most effective foam in your wants.
Whilst EN 1568 is a superb benchmark commonplace, awareness of the consequences on foam efficiency from elements exterior the usual exams ought to be noted. For example, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by different ambient air temperatures, the application technique, gasoline depth etc. Our advice can be to grasp the small print of the checks and attempt to match them to the foam’s appropriateness on your individual hazards. We would at all times suggest consulting individual foam producers as they will often present particular in-house fire-performance knowledge in opposition to some of the extra unusual fuels.
However, despite the foam manufacturers’ generally conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the enlargement ratio Images equipped by Author / Contributor
Critical elements for success: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary elements: time and the rate at which completed foam is utilized. Both are determined by empirically based mostly requirements revealed by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ issue implies that for a given size of fireside area it’s needed to use the froth for long sufficient to achieve extinction and to forestall re-ignition. This is very crucial in guide intervention as firefighter’s shall be in danger throughout post-fire operations. When it involves mounted protection for hydrocarbon and polar solvent tanks, the applying time could be as lengthy as 60 minutes for the biggest tank diameters.
The software fee refers to the quantity of completed foam applied per sq. metre. This varies according to the gasoline and the foam kind however is at present no less than 4.zero litres per minute per square metre. One of the ongoing developments in foam efficiency is the probability that this shall be lowered, however standards often take time to recognise product improvement. Anything lower than the minimal application fee signifies that fire management is unlikely to be achieved. This means that firefighting assets, significantly in a handbook fire attack, must be assembled before firefighting commences and this takes time. The advantage in fitting fixed techniques is that the assets are already designed and constructed 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 best to tackle their specific fireplace challenges, the following is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and restricted mounted systems applications. This uses the venturi precept to create a pressure drop in a small aluminium or seawater materials appropriate gadget with built-in focus pick-up tube. The pressure drop created by the venturi attracts the foam focus from a container where it mixes with water to create foam resolution. 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’s considered to be the only methodology, it has severe drawbacks: (i) items are manufacturing facility calibrated so any adjustments to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge system or a altering quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter adjustments will adversely affect proportioning accuracy and doubtlessly prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to draw concentrate into the downstream traces; (iv) pressure loss is high, as a lot as 35%, so duty pump pressures must be excessive sufficient to permit for it, doubtlessly including extra cost into the system; (v) foam supply devices need to be sized in order not to prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime prices on account of foam focus 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 electrical or a mix of electrical and diesel pumps to supply foam concentrate into a proportioner at the next strain than the incoming water-line strain. The proportioner is installed into the water line and regulates the mixing.
They at the moment are related to older systems, where disadvantages embody: (i) further prices in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter operating vary, though the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs an additional energy supply, apart from water, so isn’t as reliably secure as a system with a potential single level of failure, corresponding to an entirely water-driven system; (iv) usually, these techniques are very advanced and cause high efforts on the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to damage the foam concentrate and entrain air, which in turn 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 focus proportioner similar to those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam crammed bladder so that foam focus may be proportioned with water utilizing the identical supply. The venturi principle is once more brought into play because it creates a pressure drop at the level of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs on account of foam focus usage, 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 rarely simple to work throughout the steel pressure vessel should problems happen, particularly if and when a replacement bladder may be required: all of it adds to the issue and price.
Compressed air foam (CAFS):
This just isn’t a proportioning technique within the conventional sense as the foam is already proportioned using one of the earlier methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam solution on 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 weak buildings to mitigate hearth development. The limited water supplies associated with distant wildfire areas signifies that the resource may be fully optimised. However, as with balanced strain proportioner foam pumps, an additional level of failure is feasible because of the further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is only mechanical and highly reliable. A water-driven rotor provides the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is supplied with foam focus through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning rate and can proportion the foam concentrate precisely throughout a wide working range. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, utterly with out utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The advantages of FireDos Gen III FM approved foam proportioners include:
Reduced prices: proportioning rate is tested with out using foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: fixed proportioning price across a wide working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in pressure loss, in comparison with older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning price.
FM accredited FireDos Gen III proportioners are to date the only FM approved water motor coupled variable proportioners using FM permitted circulate meters. Using the take a look at return line this offers the likelihood to check the proportioning fee throughout commissioning as well as for annual checks, with out creating any premix, which is a really massive profit for the person and relieves the environment.
In the second a half of this feature we will explore the consequences of viscosity on foam proportioning and typical foam software areas and recommended discharge devices.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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