Fire presents many challenges, not least due to the variables that decide which suppression medium is appropriate for a given fire situation. Our objective in this two-part article is to supply steerage primarily based on a hazard-specific approach 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 combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires generally associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise mainly within the Class B category: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for each 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 may not penetrate the fireplace load effectively.
Fire lessons.
How will we make foam?
Finished foam solution comprises a easy recipe of froth focus, water and air. Foam concentrate is typically combined in 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 device – we will cowl proportioning later in this article and discharge strategies in Part 2. At this point air is entrained through the use of units designed to naturally aspirate the answer. The quantity of aspiration and the kind of concentrate determines the growth ratio. This is often cut up between low, medium and high enlargement. Low enlargement is as a lot as 20:1, medium is 200:1 and excessive growth is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to increase the froth adequately, though naturally aspirated generators are also used. The choice to choose a selected growth ratio is determined by the hazard underneath evaluate.
Put merely, water and oil do not combine. Applying solely water to Class B merchandise won’t 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 allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to obtain success. Whatever technique is chosen to supply that blanket or movie, the target is similar.
Steps of froth era Images provided by Author / Contributor
A little of the historical past of foam growth
We can date the event of recent foam concentrates from the 1960s onwards. Up to that time foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the base component). The primary disadvantage was due to limited gas tolerance, which meant it was vulnerable to gas 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 gasoline tolerance as well as forming a vapour-sealing film throughout the surface of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s growth didn’t fully replace the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight gasoline pick-up (mixing) and offer a good resistance to heat, outlined by the industry 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 most effective of each worlds: a film-forming foam that also 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 at all times presented an additional 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 know-how additionally turned out there with the brand new technology of AFFF-ARs.
In current years fluorine, one of the cornerstone elements to all foams, has become an environmental problem, due to persistence in groundwater. The trade has been introduced with a serious challenge to eliminate the ‘fluoro’ element of all of the completely different foam focus varieties. We have witnessed an era of manufacturers’ claims and counter claims concerning the efficacy of an entire range 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 model new normal and first alternative for operators changing present inventory or reviewing new tasks. As a foam proportioner manufacturer we should examine the bodily properties of froth carefully (especially viscosity) as they affect selections on the general proportioning solution. เครื่องมือที่ใช้วัดความดันโลหิต of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are increasingly necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies 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 producers will naturally promote their product as being extremely efficient. The best means of comparing their claims is to familiarise yourself with the empirically primarily based commonplace 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 more demanding polar solvents are both included in the take a look at protocols. This additionally covers contemporary and seawater in addition to mild and forceful software of the foam. 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 one of the best foam on your needs.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the effects on foam efficiency from components exterior the standard checks should be famous. For instance, significantly aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by different ambient air temperatures, the application method, gasoline depth and so forth. Our advice would be to know the details of the exams and try to match them to the foam’s appropriateness for your individual hazards. We would all the time recommend consulting particular person foam manufacturers as they will usually provide particular in-house fire-performance information against some of the more unusual fuels.
However, regardless of the foam manufacturers’ generally conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the enlargement ratio Images provided by Author / Contributor
Critical factors for success: the time and software price matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the rate at which finished foam is utilized. Both are determined by empirically based mostly 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’ factor means that for a given measurement of fire area it is needed to apply the froth for long sufficient to realize extinction and to prevent re-ignition. This is particularly important in guide intervention as firefighter’s shall be in danger during post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the applying time can be so lengthy as 60 minutes for the biggest tank diameters.
The application price refers back to the amount of finished foam utilized per square metre. This varies based on the gasoline and the foam sort but is at present a minimum of four.0 litres per minute per sq. metre. One of the continuing developments in foam performance is the probability that this shall be lowered, however standards often take time to recognise product development. Anything less than the minimum application rate signifies that hearth control is unlikely to be achieved. This signifies that firefighting assets, notably in a guide fireplace attack, need to be assembled before firefighting commences and this takes time. The benefit in becoming fastened systems is that the resources are already designed and built into the system for instant software.
Principle of foam 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 finest to sort out their explicit fire challenges, the next is an outline of the varied foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and limited fixed systems functions. This uses the venturi precept to create a strain drop in a small aluminium or seawater material compatible gadget with built-in focus pick-up tube. The pressure drop created by the venturi draws the froth concentrate from a container the place it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fireplace equipment or fitted right into a pipework system.
However, while it is thought of to be the only technique, it has severe drawbacks: (i) units are manufacturing unit calibrated so any modifications to the hydraulics (caused by size 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 caused by pipe diameter modifications will adversely have an effect on proportioning accuracy and probably stop any proportioning; (iii) adjustments in focus viscosity will undermine the power of the venturi to attract focus into the downstream traces; (iv) stress loss is high, as a lot as 35%, so obligation pump pressures must be excessive enough to allow for it, doubtlessly including further value into the system; (v) foam delivery gadgets must be sized in order not to prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices because of foam focus usage, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electrical or a combination of electric and diesel pumps to produce foam focus into a proportioner at a better strain than the incoming water-line stress. The proportioner is installed into the water line and regulates the mixing.
They are actually related to older techniques, where disadvantages include: (i) further prices in hardware and design time; (ii) the froth pump is generally restricted to a much tighter working vary, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants an extra power source, other than water, so is not as reliably secure as a system with a possible single point of failure, corresponding to a wholly water-driven system; (iv) typically, these techniques are very advanced and cause excessive efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to wreck the foam focus and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel strain vessel containing a flexible 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 stuffed bladder so that foam concentrate may be proportioned with water utilizing the identical provide. The venturi precept is once more brought into play because it creates a stress drop on the level of injection for the froth concentrate. Testing can’t be achieved with out creating premix and discharging finished foam. This will add to whole lifetime costs because of foam focus utilization, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is required to keep away from a damaged bladder when commissioning a brand new installation. It is never straightforward to work inside the metal pressure vessel ought to problems occur, especially if and when a substitute bladder could also be required: all of it adds to the difficulty and value.
Compressed air foam (CAFS):
This is not a proportioning method in the typical sense as the froth is already proportioned utilizing one of many previous strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam solution on the level 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 can additionally be a profit in wildfire situations by coating susceptible buildings to mitigate fire progress. The limited water supplies associated with remote wildfire areas implies that the resource could be fully optimised. However, as with balanced stress proportioner foam pumps, a further level of failure is possible because of the further CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is only mechanical and extremely dependable. A water-driven rotor supplies the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning price and will proportion the froth focus accurately across a wide operating vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, fully without 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 permitted foam proportioners include:
Reduced prices: proportioning price is tested with out utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: fixed proportioning price throughout a large working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in stress loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a different proportioning fee.
FM permitted FireDos Gen III proportioners are to date the one FM accredited water motor coupled variable proportioners utilizing FM approved circulate meters. Using the check return line this offers the likelihood to check the proportioning price during commissioning as nicely as for annual tests, with out creating any premix, which is a really massive benefit for the consumer and relieves the surroundings.
In the second a part of this function we are going to explore the results of viscosity on foam proportioning and typical foam utility areas and really helpful discharge units.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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