PRESSUREGAUGE TH LOGO.png

บทความเกจวัดแรงดัน

A guide to foam and foam proportioning equipment – Part 1

Fire presents many challenges, not least due to the variables that determine which suppression medium is appropriate for a given fire state of affairs. Our goal on this two-part article is to offer guidance primarily based on a hazard-specific approach and allow you to make an informed choice on appropriate fire-suppression measures, particularly 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 related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise primarily in 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 kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only may not penetrate the fire load successfully.
Fire courses.
How do we make foam?
Finished foam solution comprises a easy recipe of froth focus, water and air. Foam concentrate is usually mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge device – we will cowl proportioning later in this article and discharge methods in Part 2. At this point air is entrained by utilizing devices designed to naturally aspirate the solution. The amount of aspiration and the kind of concentrate determines the growth ratio. This is often break up between low, medium and excessive growth. Low expansion is as much as 20:1, medium is 200:1 and excessive growth is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated mills are additionally used. The decision to choose a particular enlargement ratio is determined by the hazard underneath review.
Put merely, water and oil don’t combine. Applying only water to Class B products will not suppress the burning vapours. This is a crucial level to make as it’s 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 obtain success. Whatever methodology is chosen to provide that blanket or film, the objective is identical.
Steps of foam era Images equipped by Author / Contributor
A little of the historical past of froth development
We can date the event of recent foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically ground hoof and horn is the bottom component). The main downside was due to restricted fuel 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 utilizing protein as the base product, synthetic detergents gave foam a greater fuel tolerance as properly as forming a vapour-sealing movie across the surface of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement did not completely exchange the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each combat fuel pick-up (mixing) and provide an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further growth within the 1980s took FP to the following level with film-forming fluoroprotein or FFFP. We now had the most effective of both worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented a further challenge as they have been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same technology additionally became available with the model new technology of AFFF-ARs.
In recent years fluorine, one of the cornerstone components to all foams, has turn out to be an environmental issue, due to persistence in groundwater. The industry has been presented with a significant problem to get rid of the ‘fluoro’ element of all the different foam concentrate sorts. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of an entire range of newly formulated fluorine-free foam. เกจวัดแรงดันลม10bar ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn out to be the brand new normal and first alternative for operators changing existing inventory or reviewing new initiatives. As a foam proportioner producer we should study the physical properties of froth rigorously (especially viscosity) as they affect decisions on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are increasingly essential in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant quality of SFFF/F3 is important to combat the small diploma of water miscibility of the gas.
All foam focus producers will naturally promote their product as being extremely efficient. The finest method of comparing their claims is to familiarise yourself with the empirically primarily based commonplace EN 1568 or UL162. The exams 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 test protocols. This also covers recent and seawater in addition to mild and forceful utility of the froth. Each foam is given a score with IA being the best, IIID the worst. This means that you can challenge foam suppliers in order to make an informed choice on the best foam for your needs.
Whilst EN 1568 is a wonderful benchmark standard, awareness of the consequences on foam performance from components outdoors the standard exams must be noted. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by completely different ambient air temperatures, the application methodology, gasoline depth and so on. Our advice would be to know the details of the tests and try to match them to the foam’s appropriateness on your individual hazards. We would at all times suggest consulting individual foam manufacturers as they can typically present particular in-house fire-performance information towards a few of the more unusual fuels.
However, despite the foam manufacturers’ sometimes conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the enlargement ratio Images equipped by Author / Contributor
Critical elements for fulfillment: the time and software fee matrix
Successful extinction of flammable liquid fires depends on two converging and complementary factors: time and the speed at which finished foam is applied. Both are decided by empirically based mostly requirements printed by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ issue implies that for a given size of fireside area it is needed to apply the foam for long sufficient to realize extinction and to stop re-ignition. This is especially crucial in manual intervention as firefighter’s might be at risk during post-fire operations. When it comes to mounted safety for hydrocarbon and polar solvent tanks, the application time may be as lengthy as 60 minutes for the most important tank diameters.
The application rate refers back to the quantity of finished foam applied per square metre. This varies in accordance with the gasoline and the froth kind but is at present no much less than four.zero litres per minute per square metre. One of the ongoing developments in foam efficiency is the chance that this will be lowered, but standards typically take time to recognise product improvement. Anything less than the minimum utility rate signifies that hearth control is unlikely to be achieved. This implies that firefighting sources, significantly in a guide hearth attack, need to be assembled earlier than firefighting commences and this takes time. The benefit in fitting fastened methods is that the assets are already designed and built into the system for instant software.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to permit readers to make an knowledgeable decision on how best to sort out their specific hearth challenges, the following is an outline of the varied foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted fastened methods functions. This uses the venturi principle to create a strain drop in a small aluminium or seawater materials compatible system with built-in focus pick-up tube. The stress drop created by the venturi attracts the foam concentrate 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 fireplace equipment or fitted into a pipework system.
However, while it is thought of to be the only methodology, it has severe drawbacks: (i) units are manufacturing facility calibrated so any modifications to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge gadget or a changing quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter modifications will adversely have an result on proportioning accuracy and probably forestall any proportioning; (iii) changes in concentrate viscosity will undermine the ability of the venturi to draw concentrate into the downstream strains; (iv) strain loss is high, as a lot as 35%, so responsibility pump pressures need to be high enough to permit for it, probably including further cost into the system; (v) foam supply units have to be sized so as not to prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime prices as a end result of foam concentrate utilization, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced strain proportioners:
These use an electric or a mix of electric and diesel pumps to provide 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 at the moment are related to older methods, where disadvantages include: (i) further prices in hardware and design time; (ii) the foam pump is generally restricted to a much tighter working range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs a further energy source, apart from water, so is not as reliably secure as a system with a possible single point of failure, similar to a wholly water-driven system; (iv) sometimes, these techniques are very complex and cause high efforts on the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates unnecessary agitation that has the potential to damage the foam concentrate and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel pressure vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner just like the ones fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth filled bladder so that foam focus could be proportioned with water using the identical provide. The venturi precept is once more brought into play because it creates a pressure drop on the level of injection for the foam focus. Testing cannot be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs as a result of foam focus usage, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness because great care is required to keep away from a broken bladder when commissioning a model new installation. It isn’t easy to work inside the metal strain vessel ought to problems happen, especially if and when a substitute bladder may be required: it all provides to the difficulty and price.
Compressed air foam (CAFS):
This isn’t a proportioning technique in the conventional 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 name suggests, CAFS injects compressed air into the foam solution on the point of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces allowing better penetration and cooling. This can be a benefit in wildfire conditions by coating vulnerable buildings to mitigate fire progress. The limited water provides associated with remote wildfire areas implies that the useful resource could be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an additional level of failure is feasible as a outcome of further CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is only mechanical and extremely reliable. A water-driven rotor supplies the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam concentrate by way of 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 focus accurately across a wide working range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning price testing, fully with out using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM approved foam proportioners include:
Reduced prices: proportioning fee is examined without using foam or creating premix or foam – cost effective and eco-friendly.
Improved performance: fixed proportioning rate throughout a wide working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a special proportioning fee.
FM accredited FireDos Gen III proportioners are so far the one FM permitted water motor coupled variable proportioners using FM accredited circulate meters. Using the check return line this presents the chance to examine the proportioning fee during commissioning in addition to for annual tests, without creating any premix, which is a really massive benefit for the person and relieves the setting.
In the second a half of this function we’ll explore the consequences of viscosity on foam proportioning and typical foam software areas and beneficial discharge devices.
For extra information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share