Fire presents many challenges, not least due to the variables that determine which suppression medium is appropriate for a given hearth scenario. Our goal in this two-part article is to offer steering based mostly on a hazard-specific method and allow you to make an knowledgeable determination 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 combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires typically related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise primarily in the Class B class: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain forms of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only might not penetrate the hearth load effectively.
Fire lessons.
How can we make foam?
Finished foam solution comprises a easy recipe of froth focus, water and air. Foam focus is typically blended in 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 system – we’ll cowl proportioning later in this article and discharge strategies in Part 2. At this point air is entrained through the use of gadgets designed to naturally aspirate the answer. The quantity of aspiration and the sort of concentrate determines the expansion ratio. This is usually cut up between low, medium and high growth. Low growth is as much as 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 turbines are additionally used. The decision to choose a selected expansion ratio is decided by the hazard underneath evaluation.
Put simply, water and oil do not combine. Applying solely water to Class B products will not suppress the burning vapours. This is an important level to make as it is the vapours, not the liquid itself, that burns. We need a medium that permits 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 target is similar.
Steps of froth era Images supplied by Author / Contributor
A little of the history of froth growth
We can date the development of modern foam concentrates from the 1960s 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 as a result of limited fuel tolerance, which meant it was vulnerable to gas pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, synthetic detergents gave foam a larger fuel tolerance in addition to forming a vapour-sealing film throughout the floor of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s growth didn’t fully exchange the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight gasoline pick-up (mixing) and supply an excellent resistance to warmth, defined by the industry as ‘burn-back resistance’.
Further development within the Eighties took FP to the subsequent level 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 record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always introduced an additional problem as they have been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar expertise also turned obtainable with the new technology of AFFF-ARs.
In recent years fluorine, one of many cornerstone components to all foams, has turn out to be an environmental problem, due to persistence in groundwater. The trade has been presented with a serious challenge to eliminate the ‘fluoro’ element of all the different foam focus sorts. We have witnessed an era of manufacturers’ claims and counter claims relating to the efficacy of an entire 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 brand new regular and first choice for operators changing present inventory or reviewing new projects. As a foam proportioner manufacturer we must study the bodily properties of foam fastidiously (especially viscosity) as they affect selections on the general proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more important within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant quality of SFFF/F3 is important to fight the small degree of water miscibility of the fuel.
หลักการทำงานของเกจ์วัดแก๊ส will naturally promote their product as being highly effective. The best way of evaluating their claims is to familiarise yourself with the empirically based normal EN 1568 or UL162. The checks cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included within the take a look at protocols. This also covers contemporary and seawater as properly as mild and forceful application of the froth. Each foam is given a ranking with IA being the best, IIID the worst. This means that you can problem foam suppliers in order to make an informed determination on the most effective foam for your needs.
Whilst EN 1568 is a superb benchmark commonplace, consciousness of the results on foam performance from components exterior the usual checks must be noted. For example, particularly aggressive solvents can challenge the firefighting effectiveness of certain foams. This could be exacerbated by completely different ambient air temperatures, the appliance methodology, gasoline depth etc. Our recommendation can be to grasp the small print of the exams and attempt to match them to the foam’s appropriateness for your particular person hazards. We would always suggest consulting particular person foam producers as they can typically provide particular in-house fire-performance information in opposition to a variety of the extra unusual fuels.
However, regardless of the foam 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 in accordance with the expansion ratio Images supplied by Author / Contributor
Critical elements for achievement: the time and application price matrix
Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the speed at which completed foam is applied. Both are decided by empirically based requirements printed by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given measurement of fireplace area it’s essential to apply the foam for lengthy enough to realize extinction and to stop re-ignition. This is very critical in handbook intervention as firefighter’s will be in danger throughout post-fire operations. When it involves fixed safety for hydrocarbon and polar solvent tanks, the appliance time can be so lengthy as 60 minutes for the biggest tank diameters.
The application price refers to the quantity of finished foam applied per sq. metre. This varies according to the gas and the froth sort however is currently no much less than four.zero litres per minute per square metre. One of the ongoing developments in foam efficiency is the probability that this might be reduced, however standards usually take time to recognise product improvement. Anything lower than the minimal software fee signifies that hearth management is unlikely to be achieved. This signifies that firefighting sources, particularly in a handbook hearth assault, must be assembled earlier than firefighting commences and this takes time. The advantage in fitting fixed systems is that the assets are already designed and constructed into the system for instant application.
Principle of froth extinguishment Images provided by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to allow readers to make an informed determination on how best to tackle their particular fire challenges, the next is an overview of the various foam proportioning strategies.
Foam inductors:
Typically associated with hearth service deployment and limited fastened systems functions. This makes use of the venturi precept to create a pressure drop in a small aluminium or seawater materials suitable system with built-in focus pick-up tube. The strain 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 enough to be easily carried on a hearth equipment or fitted right into a pipework system.
However, whilst it’s thought-about to be the best methodology, it has severe drawbacks: (i) units are manufacturing facility calibrated so any modifications 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 probably require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter changes will adversely have an effect on proportioning accuracy and potentially forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the flexibility of the venturi to draw concentrate into the downstream strains; (iv) strain loss is high, as much as 35%, so obligation pump pressures have to be high enough to allow for it, probably including additional cost into the system; (v) foam supply units have to be sized in order not to limit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices because of foam focus utilization, which needs to be replaced, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced strain proportioners:
These use an electric or a mix of electric and diesel pumps to supply foam concentrate into a proportioner at a better strain than the incoming water-line strain. The proportioner is put in into the water line and regulates the blending.
They are now related to older methods, where disadvantages embody: (i) additional costs in hardware and design time; (ii) the froth pump is often restricted to a a lot tighter working vary, though 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 safe as a system with a potential single point of failure, similar to a completely water-driven system; (iv) sometimes, these techniques are very complex and cause excessive efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to wreck the froth focus and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel strain vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner similar to the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the foam crammed bladder so that foam concentrate could be proportioned with water using the identical provide. The venturi principle is again introduced into play as it creates a pressure drop on the level of injection for the froth focus. Testing cannot be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs because of foam focus utilization, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a outcome of nice care is required to avoid a broken bladder when commissioning a model new set up. It is rarely simple to work throughout the steel stress vessel should problems occur, especially if and when a substitute bladder may be required: it all adds to the issue and value.
Compressed air foam (CAFS):
This is not a proportioning technique in the typical sense as the froth is already proportioned using one of many earlier methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam solution at the point of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces allowing higher penetration and cooling. This is also a benefit in wildfire conditions by coating susceptible structures to mitigate fire development. The limited water supplies associated with remote wildfire areas signifies that the resource may be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an additional point of failure is feasible due to the extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn into synonymous with their unique water-driven foam proportioner. Now in its third era, the product is solely mechanical and extremely dependable. A water-driven rotor provides the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is supplied 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 price and can proportion the froth focus accurately across a large working vary. The purely mechanical system supplies 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 benefits of FireDos Gen III FM approved foam proportioners embody:
Reduced prices: proportioning fee is tested with out utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: constant proportioning rate throughout a large operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in strain loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a special proportioning price.
FM approved FireDos Gen III proportioners are to date the one FM permitted water motor coupled variable proportioners utilizing FM accredited circulate meters. Using the test return line this provides the likelihood to verify the proportioning rate throughout commissioning as well as for annual exams, without creating any premix, which is a very massive benefit for the person and relieves the setting.
In the second a half of this feature we are going to explore the effects of viscosity on foam proportioning and typical foam utility areas and really helpful discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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