Fire presents many challenges, not least because of the variables that determine which suppression medium is acceptable for a given fire situation. Our goal on this two-part article is to offer steerage based on a hazard-specific strategy and assist you to make an informed choice on acceptable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires usually associated with cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting displays, we specialise mainly in the Class B class: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only might not penetrate the fireplace load successfully.
Fire courses.
How can we make foam?
Finished foam answer comprises a easy recipe of foam concentrate, water and air. Foam focus is often combined in the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge device – we will cowl proportioning later on this article and discharge methods in Part 2. At this point air is entrained through the use of devices designed to naturally aspirate the answer. The amount of aspiration and the kind of focus determines the growth ratio. This is often split between low, medium and high growth. Low expansion is up to 20:1, medium is 200:1 and excessive growth is more than 200:1. Only เกจวัดแรงดันลม10bar -expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated mills are additionally used. The decision to choose a particular growth ratio is decided by the hazard underneath evaluate.
Put merely, water and oil don’t combine. Applying only water to Class B products will not suppress the burning vapours. This is an important point to make as it’s 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 be successful. Whatever method is chosen to supply that blanket or movie, the objective is the same.
Steps of froth era Images provided by Author / Contributor
A little of the historical past of foam growth
We can date the development of contemporary foam concentrates from the 1960s onwards. Up to that time foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The major disadvantage was as a outcome of limited fuel tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the bottom product, synthetic detergents gave foam a larger gas tolerance in addition to forming a vapour-sealing film across the floor of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s development didn’t utterly exchange using protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight fuel pick-up (mixing) and offer an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further improvement in the Nineteen 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 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 all the time introduced an extra challenge as they were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical technology additionally grew to become available with the model new era of AFFF-ARs.
In recent years fluorine, one of the cornerstone ingredients to all foams, has become an environmental problem, as a end result of persistence in groundwater. The business has been introduced with a significant problem to eliminate the ‘fluoro’ component of all the different foam concentrate varieties. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of a whole 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 alternative for operators changing present inventory or reviewing new projects. As a foam proportioner producer we must examine the bodily properties of foam carefully (especially viscosity) as they influence choices on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant 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 efficient. The best method of evaluating their claims is to familiarise yourself with the empirically primarily 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 additionally covers fresh and seawater in addition to gentle and forceful software 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 in order to make an informed determination on the most effective foam for your needs.
Whilst EN 1568 is a superb benchmark standard, consciousness of the consequences on foam performance from components outdoors the standard checks should be famous. For example, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by completely different ambient air temperatures, the appliance technique, fuel depth and so on. Our advice could be to understand the details of the checks and try to match them to the foam’s appropriateness on your individual hazards. We would always recommend consulting particular person foam producers as they can usually present specific in-house fire-performance knowledge against a variety of the more uncommon fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on performance, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the growth ratio Images supplied by Author / Contributor
Critical factors for fulfillment: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the speed at which completed foam is utilized. Both are decided by empirically based requirements published by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given dimension of fireside area it is necessary to apply the froth for long sufficient to attain extinction and to forestall re-ignition. This is especially critical in manual intervention as firefighter’s will be at risk during post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the applying time can be so long as 60 minutes for the most important tank diameters.
The utility fee refers again to the quantity of completed foam utilized per sq. metre. This varies according to the gas and the froth type but is at present at least 4.0 litres per minute per square metre. One of the continuing developments in foam efficiency is the probability that this shall be reduced, however requirements often take time to recognise product improvement. Anything less than the minimal utility fee signifies that fireplace management is unlikely to be achieved. This means that firefighting assets, particularly in a manual fireplace attack, need to be assembled earlier than firefighting commences and this takes time. The benefit in becoming mounted techniques is that the sources are already designed and constructed into the system for quick software.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an knowledgeable determination on how greatest to deal with their explicit hearth challenges, the following is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically associated with fire service deployment and restricted fixed systems applications. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater material appropriate device with built-in focus pick-up tube. The strain drop created by the venturi draws the froth focus 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, whilst it’s thought-about to be the simplest method, it has severe drawbacks: (i) units are manufacturing unit calibrated so any changes 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 caused by pipe diameter changes will adversely have an effect on proportioning accuracy and doubtlessly prevent any proportioning; (iii) changes in concentrate viscosity will undermine the ability of the venturi to attract concentrate into the downstream lines; (iv) stress loss is excessive, as a lot as 35%, so obligation pump pressures have to be excessive sufficient to permit for it, doubtlessly including extra cost into the system; (v) foam delivery gadgets must be sized in order to not limit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to complete lifetime costs as a end result of foam focus usage, which must be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electrical or a mix of electric and diesel pumps to supply foam focus right into a proportioner at a higher stress 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, the place disadvantages include: (i) further costs in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter operating range, although the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump needs an extra energy source, other than water, so isn’t as reliably secure as a system with a potential single level of failure, corresponding to a completely water-driven system; (iv) sometimes, these techniques are very complex and cause high efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to wreck the foam concentrate and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal stress vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner much like the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam concentrate could be proportioned with water using the same provide. The venturi principle is once more introduced into play because it creates a pressure drop on the point of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime costs as a outcome of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a end result of nice care is required to keep away from a damaged bladder when commissioning a new installation. It is never simple to work inside the steel strain vessel should problems occur, particularly if and when a replacement bladder could additionally be required: all of it provides to the difficulty and cost.
Compressed air foam (CAFS):
This isn’t a proportioning methodology within the standard sense as the foam is already proportioned using one of many previous strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam resolution at the level 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 profit in wildfire conditions by coating vulnerable buildings to mitigate hearth development. The limited water provides associated with distant wildfire areas implies that the resource can be fully optimised. However, as with balanced stress proportioner foam pumps, an extra point of failure is feasible because of the further CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is only mechanical and extremely dependable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam focus via 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 focus accurately across a wide working range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, fully without using 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 accredited foam proportioners embody:
Reduced prices: proportioning fee is examined with out utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: fixed proportioning price throughout a wide operating range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in strain loss, in comparability with older generations, via 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 one FM permitted water motor coupled variable proportioners utilizing FM approved move meters. Using the check return line this offers the chance to verify the proportioning rate during commissioning in addition to for annual exams, without creating any premix, which is a very big profit for the consumer and relieves the environment.
In the second a half of this function we will explore the effects of viscosity on foam proportioning and typical foam application areas and recommended discharge devices.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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