Fire presents many challenges, not least because of the variables that decide which suppression medium is appropriate for a given fire state of affairs. Our goal on this two-part article is to provide steerage based on a hazard-specific approach and help you make an informed decision on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires typically associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting monitors, we specialise mainly in the Class B class: flammable liquids.
Foam is considered to be the most effective 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 the place water only may not penetrate the fireplace load effectively.
Fire lessons.
How will we make foam?
Finished foam solution comprises a easy recipe of foam focus, water and air. Foam focus is typically combined 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 gadget – we’ll cover proportioning later on this article and discharge methods in Part 2. At this level air is entrained by utilizing gadgets designed to naturally aspirate the answer. The quantity of aspiration and the sort of focus determines the growth ratio. This is usually break up between low, medium and excessive enlargement. Low enlargement is as much as 20:1, medium is 200:1 and high enlargement is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the foam adequately, though naturally aspirated generators are also used. The choice to choose a selected growth ratio is set by the hazard beneath evaluation.
Put simply, water and oil don’t mix. 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 want a medium that allows 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 film, the target is identical.
Steps of froth generation Images equipped by Author / Contributor
A little of the historical past of foam development
We can date the event of recent foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically floor hoof and horn is the bottom component). The major disadvantage was due to limited gasoline tolerance, which meant it was prone to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a higher 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 improvement did not fully replace using protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat gasoline pick-up (mixing) and offer an excellent resistance to warmth, defined by the business as ‘burn-back resistance’.
Further development in the Eighties took FP to the next level 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 Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. differential pressure gauge ราคา or polar solvents had always offered an additional challenge as they had been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar technology additionally turned available with the new generation of AFFF-ARs.
In recent years fluorine, one of many cornerstone components to all foams, has become an environmental concern, as a end result of persistence in groundwater. The business has been introduced with a serious challenge to eliminate the ‘fluoro’ factor of all of the totally different foam concentrate sorts. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of a complete range of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn into the brand new regular and first alternative for operators changing current inventory or reviewing new initiatives. As a foam proportioner producer we must look at the bodily properties of froth carefully (especially viscosity) as they influence choices on the overall proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are more and more necessary within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant quality of SFFF/F3 is critical to fight the small degree of water miscibility of the gasoline.
All foam focus manufacturers will naturally promote their product as being highly effective. The greatest means of evaluating their claims is to familiarise yourself with the empirically primarily based normal EN 1568 or UL162. The checks cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included in the check protocols. This additionally covers recent and seawater in addition to light and forceful utility of the foam. Each foam is given a rating with IA being the most effective, IIID the worst. This means that you could problem foam suppliers so as to make an informed decision on the best foam on your needs.
Whilst EN 1568 is a superb benchmark standard, awareness of the consequences on foam performance from factors outdoors the usual tests should be famous. For instance, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This can be exacerbated by totally different ambient air temperatures, the application method, fuel depth etc. Our recommendation can be to understand the details of the exams and try to match them to the foam’s appropriateness on your individual hazards. We would all the time suggest consulting particular person foam producers as they will often provide particular in-house fire-performance data against a number of the more uncommon fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned still 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 factors for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary components: time and the speed at which finished foam is utilized. Both are determined by empirically based mostly requirements revealed by bodies such because 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 size of fireplace area it’s essential to apply the froth for lengthy sufficient to attain extinction and to stop re-ignition. This is particularly important in handbook intervention as firefighter’s will be in danger throughout post-fire operations. When it involves mounted protection for hydrocarbon and polar solvent tanks, the applying time can be so lengthy as 60 minutes for the biggest tank diameters.
The utility price refers back to the quantity of finished foam utilized per sq. metre. This varies based on the gas and the foam kind but is presently a minimum of four.zero litres per minute per sq. metre. One of the continued developments in foam performance is the likelihood that this might be lowered, however standards typically take time to recognise product development. Anything less than the minimal application rate means that fire control is unlikely to be achieved. This means that firefighting assets, particularly in a handbook hearth attack, have to be assembled before firefighting commences and this takes time. The benefit in fitting fixed systems is that the assets are already designed and constructed into the system for immediate application.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to allow readers to make an informed determination on how finest to sort out their explicit hearth challenges, the next is an overview of the assorted foam proportioning methods.
Foam inductors:
Typically associated with fire service deployment and restricted mounted techniques functions. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater materials appropriate system with built-in focus pick-up tube. The strain drop created by the venturi attracts the foam focus from a container the place it mixes with water to create foam answer. Both the pick-up tube and body of the inductor are compact enough to be easily carried on a hearth equipment or fitted into a pipework system.
However, while it’s thought-about to be the best technique, 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 gadget or a changing amount of discharge devices) will likely require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter adjustments will adversely have an result on proportioning accuracy and potentially prevent any proportioning; (iii) modifications in focus viscosity will undermine the ability of the venturi to draw focus into the downstream strains; (iv) pressure loss is high, as a lot as 35%, so responsibility pump pressures have to be high enough to allow for it, potentially adding extra value into the system; (v) foam supply units have to be sized in order not to prohibit design flows; (vi) testing can’t be achieved without creating premix and discharging finished foam. This will add to whole lifetime prices on account of foam focus usage, which has to be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mixture of electrical and diesel pumps to produce foam concentrate right into a proportioner at a higher pressure than the incoming water-line strain. The proportioner is installed into the water line and regulates the blending.
They are now related to older methods, where disadvantages include: (i) extra costs in hardware and design time; (ii) the foam pump is generally restricted to a a lot tighter working range, though the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump wants an additional power supply, aside from water, so is not as reliably secure as a system with a potential single level of failure, such as an entirely water-driven system; (iv) sometimes, these techniques are very advanced and cause high efforts on 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 concentrate and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel stress vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam concentrate may be proportioned with water using the identical provide. The venturi precept is again introduced into play as it creates a strain drop on the point of injection for the froth focus. Testing cannot be achieved with out creating premix and discharging completed 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.
However, the bladder itself is seen as a weak point as a outcome of nice care is needed to avoid a damaged bladder when commissioning a model new set up. It isn’t easy to work throughout the steel stress vessel should problems occur, particularly if and when a alternative bladder may be required: all of it adds to the difficulty and price.
Compressed air foam (CAFS):
This is not a proportioning technique within the standard sense as the froth is already proportioned using one of the 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 froth answer on the point 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 is also a benefit in wildfire conditions by coating weak buildings to mitigate fireplace development. The restricted water provides associated with distant wildfire areas implies that the resource can be totally optimised. However, as with balanced pressure proportioner foam pumps, a further level of failure is feasible as a result of 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 solely mechanical and extremely dependable. A water-driven rotor provides the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and will proportion the froth concentrate precisely throughout a large working vary. The purely mechanical system supplies cost-efficient and eco-friendly proportioning rate testing, fully with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners include:
Reduced costs: proportioning fee is tested without using foam or creating premix or foam – value effective and eco-friendly.
Improved performance: constant proportioning rate throughout a wide working range.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in pressure loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a unique proportioning rate.
FM approved FireDos Gen III proportioners are so far the one FM permitted water motor coupled variable proportioners using FM permitted move meters. Using the take a look at return line this provides the likelihood to examine the proportioning rate during commissioning as nicely as for annual exams, without creating any premix, which is a very big profit for the person and relieves the environment.
In the second a part of this characteristic we will discover the results of viscosity on foam proportioning and typical foam software areas and beneficial discharge gadgets.
For more data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share