Fire presents many challenges, not least due to the variables that determine which suppression medium is acceptable for a given fireplace scenario. Our objective on this two-part article is to offer guidance based on a hazard-specific method and allow you to make an informed choice 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 materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires usually related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting monitors, we specialise mainly within the Class B category: 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 the place water solely could not penetrate the fireplace load successfully.
Fire courses.
How will we make foam?
Finished foam solution includes a simple recipe of froth concentrate, water and air. Foam concentrate is typically combined in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge device – we are going to cowl proportioning later in this article and discharge methods in Part 2. At this point air is entrained by using units designed to naturally aspirate the solution. The amount of aspiration and the kind of concentrate determines the growth ratio. This is typically split between low, medium and excessive expansion. Low expansion is up to 20:1, medium is 200:1 and excessive enlargement is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated turbines are also used. The decision to decide on a selected expansion ratio is set by the hazard under evaluate.
Put simply, water and oil do not combine. Applying only water to Class B merchandise is not going to suppress the burning vapours. This is a crucial level 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 obtain success. Whatever technique is chosen to supply that blanket or movie, the target is identical.
Steps of foam era Images equipped by Author / Contributor
A little of the history of foam improvement
We can date the development of modern foam concentrates from the 1960s onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the base component). The main drawback was as a result of limited fuel tolerance, which meant it was vulnerable to fuel 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 higher fuel tolerance as properly as forming a vapour-sealing movie throughout 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 growth did not utterly substitute the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight gasoline pick-up (mixing) and provide a good resistance to warmth, outlined by the business as ‘burn-back resistance’.
Further improvement within the Nineteen 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 additionally 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 extra problem as they had been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar know-how also grew to become obtainable with the new era of AFFF-ARs.
In current years fluorine, one of many cornerstone components to all foams, has become an environmental problem, due to persistence in groundwater. The industry has been introduced with a significant problem to eliminate the ‘fluoro’ component of all of the completely different foam concentrate varieties. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of a whole range of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have become the new normal and first selection for operators changing current inventory or reviewing new projects. As a foam proportioner producer we should examine the bodily properties of froth rigorously (especially viscosity) as they influence decisions on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types 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 necessary to combat the small degree of water miscibility of the fuel.
All foam focus producers will naturally promote their product as being highly efficient. The best way of evaluating their claims is to familiarise your self with the empirically based mostly standard EN 1568 or UL162. The tests cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). ไดอะแฟรม ซีล and the extra demanding polar solvents are both included within the check protocols. This additionally covers contemporary and seawater as nicely as light and forceful software of the foam. Each foam is given a rating with IA being one of the best, IIID the worst. This means that you can problem foam suppliers in order to make an knowledgeable decision on the best foam in your needs.
Whilst EN 1568 is an excellent benchmark normal, consciousness of the consequences on foam performance from elements outside the standard checks ought to be noted. For instance, significantly aggressive solvents can challenge the firefighting effectiveness of certain foams. This can be exacerbated by different ambient air temperatures, the application method, fuel depth etc. Our advice could be to grasp the details of the checks and try to match them to the foam’s appropriateness in your particular person hazards. We would at all times recommend consulting individual foam producers as they can usually provide particular in-house fire-performance knowledge towards a variety of the more uncommon fuels.
However, despite diaphragm seal conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the enlargement ratio Images provided by Author / Contributor
Critical factors for achievement: the time and software price matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the speed at which finished foam is applied. Both are decided by empirically primarily based standards published by our bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ issue signifies that for a given dimension of fireside area it’s necessary to use the froth for long sufficient to achieve extinction and to prevent re-ignition. This is very critical in handbook intervention as firefighter’s will be at risk throughout post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the appliance time may be so long as 60 minutes for the most important tank diameters.
The utility fee refers to the amount of finished foam applied per square metre. This varies in accordance with the fuel and the froth kind but is at present a minimum of 4.0 litres per minute per square metre. One of the continued developments in foam efficiency is the likelihood that this might be reduced, however standards typically take time to recognise product development. Anything lower than the minimum software rate implies that fireplace control is unlikely to be achieved. This means that firefighting assets, significantly in a manual hearth attack, need to be assembled before firefighting commences and this takes time. The benefit in fitting mounted systems is that the resources are already designed and built into the system for immediate utility.
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 greatest to tackle their particular fireplace challenges, the next is an summary of the assorted foam proportioning methods.
Foam inductors:
Typically associated with fire service deployment and restricted fastened techniques functions. 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 stress drop created by the venturi draws the froth focus 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 fire appliance or fitted into a pipework system.
However, while it’s thought of to be the simplest technique, it has severe drawbacks: (i) models are manufacturing facility calibrated so any changes to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter changes will adversely affect proportioning accuracy and doubtlessly forestall any proportioning; (iii) changes in focus viscosity will undermine the flexibility of the venturi to draw focus into the downstream lines; (iv) stress loss is high, as a lot as 35%, so responsibility pump pressures must be excessive enough to permit for it, probably adding further price into the system; (v) foam supply units have to be sized in order to not restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices on account of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electric or a mix of electric and diesel pumps to produce foam focus 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 systems, the place disadvantages include: (i) further prices in hardware and design time; (ii) the foam 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 needs an extra power source, apart from water, so isn’t as reliably safe as a system with a possible single level of failure, such as a completely water-driven system; (iv) usually, these systems are very complex and trigger 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 break the foam focus and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal 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 foam crammed bladder so that foam concentrate could be proportioned with water using the identical supply. The venturi principle is again brought into play as it creates a pressure drop on the level of injection for the froth concentrate. Testing cannot be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs because of foam focus usage, which must 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 needed to avoid a broken bladder when commissioning a model new set up. It is rarely easy to work inside the metal strain vessel should problems happen, particularly if and when a alternative bladder could also be required: all of it provides to the problem and price.
Compressed air foam (CAFS):
This is not a proportioning technique within the typical sense as the froth is already proportioned utilizing one of many earlier strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth solution on the point of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces allowing better penetration and cooling. This is also a benefit in wildfire conditions by coating susceptible structures to mitigate hearth growth. The limited water provides related to distant wildfire areas implies that the useful resource could be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra level of failure is possible as a outcome of further CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is solely mechanical and extremely dependable. A water-driven rotor provides the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is equipped 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 accurately across a large working range. The purely mechanical system offers cost-efficient and eco-friendly proportioning fee testing, utterly with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embody:
Reduced prices: proportioning price is examined without using foam or creating premix or foam – value effective and eco-friendly.
Improved performance: constant proportioning price throughout a wide working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount 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 thus far the only FM permitted water motor coupled variable proportioners using FM permitted flow meters. Using the take a look at return line this presents the possibility to examine the proportioning fee during commissioning in addition to for annual tests, without creating any premix, which is a really huge benefit for the person and relieves the environment.
In the second a half of this function we will explore the results of viscosity on foam proportioning and typical foam software areas and recommended discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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