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 in this two-part article is to supply steering based on a hazard-specific approach and assist you to make an knowledgeable determination on appropriate 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 such as magnesium
Class F – fires typically associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily within the Class B category: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only could not penetrate the fire load effectively.
Fire classes.
How will we make foam?
Finished foam answer comprises a simple recipe of froth focus, water and air. Foam concentrate is typically blended in the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge system – we’ll cowl proportioning later on this article and discharge methods in Part 2. At this level air is entrained by utilizing units designed to naturally aspirate the answer. The quantity of aspiration and the sort of focus determines the expansion ratio. This is usually break up between low, medium and excessive growth. Low enlargement is up to 20:1, medium is 200:1 and high expansion is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated generators are additionally used. The choice to choose a specific growth ratio is decided by the hazard underneath evaluation.
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 is the vapours, not the liquid itself, that burns. We want a medium that permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier movie to be successful. Whatever technique is chosen to produce that blanket or movie, the objective is similar.
Steps of froth era Images supplied by Author / Contributor
A little of the historical past of foam development
We can date the development of modern foam concentrates from the Sixties onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The primary downside was as a outcome of limited gas tolerance, which meant it was susceptible to gas pick-up (mixing). A breakthrough got here 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 properly as forming a vapour-sealing movie throughout the surface of the fuel. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth did not utterly substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam could each combat gasoline pick-up (mixing) and provide an excellent resistance to warmth, defined by the business as ‘burn-back resistance’.
Further improvement in the 1980s took FP to the subsequent stage with film-forming fluoroprotein or FFFP. pressure gauge 0 10 bar ราคา had the most effective of each worlds: a film-forming foam that additionally had good burn-back resistance.
The Eighties further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced an extra challenge as they were water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same expertise additionally turned out there with the brand new generation of AFFF-ARs.
In latest years fluorine, one of many cornerstone ingredients to all foams, has turn into an environmental problem, because of persistence in groundwater. The business has been presented with a major problem to remove the ‘fluoro’ component of all the different foam focus varieties. We have witnessed an era 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 outline these foams, which have become the new normal and first choice for operators changing current stock or reviewing new projects. As a foam proportioner manufacturer we should examine the bodily properties of foam carefully (especially viscosity) as they affect selections on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant sorts 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 diploma of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being highly efficient. The finest method of comparing their claims is to familiarise your self with the empirically based mostly commonplace EN 1568 or UL162. The tests cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included in the take a look at protocols. This additionally covers recent and seawater as nicely as gentle and forceful application of the froth. Each foam is given a rating with IA being one of the best, IIID the worst. This means that you could problem foam suppliers so as to make an informed decision on the most effective foam on your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the effects on foam performance from elements outdoors the standard tests must be noted. For instance, notably aggressive solvents can challenge the firefighting effectiveness of certain foams. This may be exacerbated by totally different ambient air temperatures, the applying method, fuel depth and so on. Our advice would be to know the details of the checks and try to match them to the foam’s appropriateness on your particular person hazards. We would at all times recommend consulting individual foam producers as they’ll typically present particular in-house fire-performance data against a few of the extra uncommon fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on efficiency, 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 expansion ratio Images provided by Author / Contributor
Critical factors for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary elements: time and the rate at which completed foam is utilized. Both are decided by empirically primarily based requirements published by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given dimension of fire area it’s necessary to use the froth for lengthy enough to attain extinction and to forestall re-ignition. This is particularly important in manual intervention as firefighter’s shall be in danger throughout post-fire operations. When it involves fastened protection for hydrocarbon and polar solvent tanks, the application time may be as lengthy as 60 minutes for the biggest tank diameters.
The application fee refers back to the quantity of completed foam utilized per square metre. This varies in accordance with the gasoline and the foam kind but is at present a minimal of four.0 litres per minute per square metre. One of the continuing developments in foam performance is the chance that this shall be lowered, but standards usually take time to recognise product growth. Anything lower than the minimal utility fee signifies that fireplace management is unlikely to be achieved. This means that firefighting resources, notably in a manual fire attack, need to be assembled before firefighting commences and this takes time. The advantage in fitting fastened methods is that the assets are already designed and constructed into the system for instant software.
Principle of foam 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 particular fireplace challenges, the following is an outline of the varied foam proportioning strategies.
Foam inductors:
Typically associated with hearth service deployment and limited fixed systems functions. This uses the venturi principle to create a stress drop in a small aluminium or seawater material appropriate device with built-in concentrate pick-up tube. The strain drop created by the venturi draws the foam concentrate from a container where it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact enough to be simply carried on a fire equipment or fitted into a pipework system.
However, whilst it is considered to be the only method, it has extreme drawbacks: (i) models are manufacturing unit calibrated so any modifications to the hydraulics (caused by length 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 critical as deviations attributable to pipe diameter changes will adversely have an effect on proportioning accuracy and potentially forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to draw concentrate into the downstream strains; (iv) strain loss is high, as much as 35%, so duty pump pressures must be high sufficient to allow for it, probably adding additional price into the system; (v) foam delivery gadgets must be sized so as not to prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices because of foam focus utilization, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced pressure proportioners:
These use an electric or a combination of electric and diesel pumps to produce foam concentrate right 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 associated with older techniques, where disadvantages include: (i) further prices 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 broad ranges in flows; (iii) the froth pump needs an extra energy supply, apart from water, so isn’t as reliably secure as a system with a possible single level of failure, similar to a completely water-driven system; (iv) usually, these methods are very complex and trigger high efforts on the buyer 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 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 similar to those fitted to balanced stress proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam focus can be proportioned with water utilizing the same supply. The venturi precept is once more brought into play because it creates a stress drop on the point of injection for the foam focus. Testing can’t 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 has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is required to avoid a broken bladder when commissioning a model new installation. It isn’t straightforward to work inside the steel pressure vessel ought to issues happen, especially if and when a replacement bladder could additionally be required: all of it adds to the issue and value.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology in the typical sense as the froth is already proportioned utilizing one of many previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth solution on the level of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces permitting higher penetration and cooling. This can be a profit in wildfire conditions by coating susceptible constructions to mitigate fireplace growth. The limited water supplies related to distant wildfire areas signifies that the useful resource can be totally optimised. However, as with balanced pressure proportioner foam pumps, an additional point of failure is feasible because of the further CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is solely 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 supplied 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 price and can proportion the foam concentrate accurately throughout a large operating 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 provided by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embrace:
Reduced costs: proportioning price is tested without utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved performance: constant proportioning price throughout a large working vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in stress loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a special proportioning price.
FM permitted FireDos Gen III proportioners are thus far the only FM permitted water motor coupled variable proportioners using FM permitted move meters. Using เครื่องมือที่ใช้วัดความดันโลหิต offers the chance to check the proportioning price during commissioning as nicely as for annual exams, without creating any premix, which is a really massive benefit for the person and relieves the environment.
In the second part of this function we are going to explore the effects of viscosity on foam proportioning and typical foam application areas and really helpful discharge gadgets.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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