Fire presents many challenges, not least due to the variables that determine which suppression medium is suitable for a given fire scenario. Our objective on this two-part article is to offer steering primarily based on a hazard-specific method and allow you to make an knowledgeable decision on applicable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are classified as follows:
Class A – carbonaceous or flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires generally related to cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting screens, we specialise mainly within the Class B class: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only could not penetrate the fireplace load successfully.
Fire lessons.
How can we make foam?
Finished foam solution comprises a simple recipe of froth concentrate, water and air. Foam concentrate is often mixed in the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge system – we will cover proportioning later on this article and discharge strategies in Part 2. At this point air is entrained through the use of devices designed to naturally aspirate the solution. The quantity of aspiration and the sort of concentrate determines the growth ratio. This is usually cut up between low, medium and excessive enlargement. Low enlargement 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 increase the froth adequately, though naturally aspirated mills are additionally used. The choice to determine on a specific enlargement ratio is decided by the hazard under evaluate.
Put merely, water and oil do not combine. Applying solely water to Class B products will not suppress the burning vapours. diaphragm seal is a crucial point to make as it is the vapours, not the liquid itself, that burns. We want a medium that enables 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 objective is identical.
Steps of froth generation Images provided by Author / Contributor
A little of the historical past of froth development
We can date the event of modern foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the base component). The major disadvantage was due to 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 using protein as the base product, artificial detergents gave foam a greater fuel tolerance in addition to forming a vapour-sealing movie across the floor of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s improvement didn’t fully substitute the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight gas pick-up (mixing) and provide a good resistance to heat, outlined by the business as ‘burn-back resistance’.
Further improvement within the Nineteen Eighties took FP to the following stage with film-forming fluoroprotein or FFFP. We now had the best of each worlds: a film-forming foam that also had good burn-back resistance.
The Nineteen Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented an additional problem 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 identical know-how additionally turned out there with the model new era of AFFF-ARs.
In recent years fluorine, one of many cornerstone ingredients to all foams, has turn out to be an environmental concern, as a end result of persistence in groundwater. The industry has been presented with a significant challenge to get rid of the ‘fluoro’ element of all the totally different foam focus types. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of an entire 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 model new normal and first alternative for operators changing present stock or reviewing new projects. As a foam proportioner producer we should study the bodily properties of foam carefully (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 within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant high quality of SFFF/F3 is critical to fight the small degree of water miscibility of the fuel.
All foam focus manufacturers will naturally promote their product as being extremely effective. The finest method of evaluating their claims is to familiarise your self with the empirically primarily based standard EN 1568 or UL162. The exams 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 check protocols. This additionally covers contemporary and seawater as well as light and forceful application of the froth. Each foam is given a rating with IA being the best, IIID the worst. This means that you could problem foam suppliers in order to make an knowledgeable determination on the best foam for your needs.
Whilst EN 1568 is an excellent benchmark standard, consciousness of the results on foam efficiency from factors outside the usual exams must 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, gas depth and so on. Our advice can be to understand the primary points of the checks and try to match them to the foam’s appropriateness for your individual hazards. We would at all times advocate consulting individual foam manufacturers as they’ll usually present specific in-house fire-performance information against a number of the more uncommon fuels.
However, despite the foam manufacturers’ typically conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the growth ratio Images equipped by Author / Contributor
Critical factors for success: the time and application price matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary components: time and the speed at which finished foam is utilized. Both are decided by empirically based mostly standards revealed by our bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor means that for a given size of fire area it is needed to apply the froth for long sufficient to attain extinction and to stop re-ignition. This is especially important in manual intervention as firefighter’s shall be at risk during post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the appliance time may be as lengthy as 60 minutes for the biggest tank diameters.
The utility rate refers back to the quantity of finished foam utilized per sq. metre. This varies in accordance with the gas and the foam kind but is at present at least four.zero litres per minute per sq. metre. One of the continued developments in foam efficiency is the chance that this might be reduced, however standards often take time to recognise product improvement. Anything lower than the minimum utility fee means that fireplace control is unlikely to be achieved. This means that firefighting assets, particularly in a handbook fireplace attack, have to be assembled before firefighting commences and this takes time. The advantage in becoming fixed methods is that the assets are already designed and constructed into the system for instant application.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to permit readers to make an informed determination on how greatest to sort out their specific fireplace challenges, the following is an overview of the varied foam proportioning methods.
Foam inductors:
Typically associated with fireplace service deployment and limited fastened techniques applications. This makes use of the venturi precept to create a pressure drop in a small aluminium or seawater materials appropriate device with built-in concentrate pick-up tube. The pressure drop created by the venturi draws the foam focus from a container where it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a fireplace equipment or fitted right into a pipework system.
However, whilst it is thought of to be the best technique, it has severe drawbacks: (i) items are factory 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 quantity of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter adjustments will adversely have an effect on proportioning accuracy and potentially forestall any proportioning; (iii) changes in focus viscosity will undermine the ability of the venturi to draw focus into the downstream strains; (iv) pressure loss is excessive, as much as 35%, so duty pump pressures must be excessive enough to allow for it, probably adding further cost into the system; (v) foam delivery gadgets have to be sized in order to not prohibit design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to whole lifetime prices on account of foam focus utilization, which must be replaced, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a mix of electric and diesel pumps to provide foam focus right into a proportioner at a higher pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the blending.
They are actually associated with older methods, where disadvantages include: (i) further costs in hardware and design time; (ii) the foam pump is normally restricted to a much tighter working vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump wants a further power source, apart from water, so is not as reliably safe as a system with a possible single level of failure, corresponding to a wholly water-driven system; (iv) sometimes, these techniques are very complicated and trigger excessive efforts at 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 froth focus and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner just like those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam filled bladder so that foam focus could be proportioned with water using the identical supply. The venturi precept is again brought into play because it creates a strain drop on the point of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs on account of foam concentrate usage, which has 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 nice care is required to avoid a broken bladder when commissioning a model new installation. It is never simple to work within the metal pressure vessel should problems occur, especially if and when a alternative bladder may be required: it all provides to the problem and price.
Compressed air foam (CAFS):
This is not a proportioning technique in the standard sense as the foam is already proportioned using one of many earlier methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth answer on the level of discharge. ไดอะแฟรม ซีล is that CAFS enhances the completed foam’s ability to cling to vertical surfaces allowing better penetration and cooling. This is also a benefit in wildfire situations by coating vulnerable constructions to mitigate hearth progress. The limited water provides related to distant wildfire areas means that the resource may be totally optimised. However, as with balanced pressure proportioner foam pumps, a further point of failure is possible due to the additional 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 purely mechanical and extremely dependable. A water-driven rotor supplies the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning price and will proportion the foam focus precisely across a large operating range. The purely mechanical system offers cost-efficient and eco-friendly proportioning price 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 embrace:
Reduced prices: proportioning price is examined with out using foam or creating premix or foam – value efficient and eco-friendly.
Improved performance: constant proportioning rate throughout a large operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, in comparability with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a unique proportioning price.
FM permitted FireDos Gen III proportioners are so far the only FM accredited water motor coupled variable proportioners utilizing FM permitted flow meters. Using the test return line this offers the chance to verify the proportioning fee throughout commissioning in addition to for annual tests, with out creating any premix, which is a really big benefit for the person and relieves the environment.
In the second part of this function we’ll explore the consequences of viscosity on foam proportioning and typical foam utility areas and really helpful discharge gadgets.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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