Fire presents many challenges, not least because of the variables that determine which suppression medium is acceptable for a given fire situation. pressure gauge 4 นิ้ว ราคา on this two-part article is to supply guidance primarily based on a hazard-specific method and help you 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 flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires generally associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting screens, we specialise primarily in the Class B class: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only might not penetrate the hearth load effectively.
Fire lessons.
How can we make foam?
Finished foam answer includes a simple recipe of foam focus, water and air. Foam concentrate is often blended in the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge system – we are going to cowl proportioning later on this article and discharge strategies in Part 2. At this level air is entrained through the use of units designed to naturally aspirate the answer. The quantity of aspiration and the type of focus determines the growth ratio. This is usually break up between low, medium and excessive expansion. 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 foam adequately, though naturally aspirated turbines are additionally used. The decision to choose a selected enlargement ratio is decided by the hazard under evaluation.
Put merely, water and oil do not combine. Applying solely water to Class B merchandise is not going to suppress the burning vapours. This is a crucial point to make as it is 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 be successful. Whatever method is chosen to produce that blanket or film, the target is similar.
Steps of foam technology Images provided by Author / Contributor
A little of the history of foam improvement
We can date the event of modern foam concentrates from the Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the base component). The main drawback was as a end result of limited gas 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, artificial detergents gave foam a larger fuel tolerance as properly as forming a vapour-sealing film throughout the floor 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 utterly substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight fuel pick-up (mixing) and supply an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further improvement within the Eighties took FP to the following level with film-forming fluoroprotein or FFFP. We now had the best of both worlds: a film-forming foam that also had good burn-back resistance.
The 1980s additional added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented a further problem as they have been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The same technology also grew to become available with the new technology of AFFF-ARs.
In recent years fluorine, one of the cornerstone components to all foams, has turn into an environmental issue, due to persistence in groundwater. The business has been presented with a significant challenge to eliminate the ‘fluoro’ factor of all the different foam focus sorts. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a whole vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have become the new normal and first choice for operators altering current stock or reviewing new initiatives. As a foam proportioner producer we should look at the bodily properties of foam carefully (especially viscosity) as they influence choices on the overall proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly essential within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant high quality of SFFF/F3 is important to combat the small diploma of water miscibility of the fuel.
All foam focus manufacturers will naturally promote their product as being extremely efficient. The finest way of evaluating their claims is to familiarise your self with the empirically primarily based standard EN 1568 or UL162. The checks cover 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 take a look at protocols. This also covers recent and seawater in addition to gentle and forceful application of the froth. Each foam is given a ranking with IA being the most effective, IIID the worst. This means that you could challenge foam suppliers so as to make an knowledgeable determination on the most effective foam for your wants.
Whilst EN 1568 is a wonderful benchmark standard, consciousness of the results on foam efficiency from components outside the usual checks must be noted. For example, significantly aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by different ambient air temperatures, the application method, gas depth and so on. Our recommendation could be to understand the small print of the checks and attempt to match them to the foam’s appropriateness in your individual hazards. We would always recommend consulting individual foam producers as they will typically provide specific in-house fire-performance information towards a few of the extra uncommon fuels.
However, regardless of the foam manufacturers’ typically conflicting claims on performance, the earlier fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the enlargement ratio Images provided by Author / Contributor
Critical factors for success: the time and utility price matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary components: time and the speed at which finished foam is utilized. Both are determined by empirically based requirements printed by our bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor signifies that for a given dimension of fire space it’s essential to apply the foam for lengthy sufficient to realize extinction and to forestall re-ignition. This is particularly crucial in guide intervention as firefighter’s will be in danger during post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the appliance time could be as long as 60 minutes for the largest tank diameters.
The application rate refers back to the amount of finished foam utilized per sq. metre. This varies according to the gas and the foam sort however is presently a minimal of 4.0 litres per minute per sq. metre. One of the continuing developments in foam efficiency is the chance that this will be lowered, however requirements typically take time to recognise product growth. Anything less than the minimum application fee means that fire control is unlikely to be achieved. This signifies that firefighting sources, significantly in a handbook fire assault, need to be assembled before firefighting commences and this takes time. The advantage in fitting mounted techniques is that the sources are already designed and constructed into the system for quick software.
Principle of froth extinguishment Images provided 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 tackle their particular fire challenges, the next is an outline of the various foam proportioning methods.
Foam inductors:
Typically associated with hearth service deployment and restricted fastened techniques purposes. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater material appropriate gadget with built-in focus pick-up tube. The pressure drop created by the venturi draws the froth 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 sufficient to be simply carried on a hearth appliance or fitted into a pipework system.
However, while it’s thought-about to be the simplest method, it has extreme drawbacks: (i) units are manufacturing facility calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge gadget or a altering 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 changes will adversely have an result on proportioning accuracy and probably prevent any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to attract concentrate into the downstream lines; (iv) strain loss is excessive, as a lot as 35%, so duty pump pressures have to be high sufficient to allow for it, potentially including further value into the system; (v) foam delivery gadgets need to be sized in order to not restrict design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices because of foam concentrate utilization, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electric or a combination of electrical and diesel pumps to produce foam focus right into a proportioner at a better pressure than the incoming water-line pressure. The proportioner is installed into the water line and regulates the blending.
They are now related to older systems, the place disadvantages embrace: (i) additional costs in hardware and design time; (ii) the foam pump is normally restricted to a much tighter operating range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs a further energy supply, other than water, so just isn’t as reliably safe as a system with a possible single point of failure, corresponding to a completely water-driven system; (iv) usually, these systems are very advanced and trigger high 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 break the foam concentrate and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal stress 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 crammed bladder in order that foam concentrate can be proportioned with water using the same supply. The venturi precept is once more brought into play because it creates a stress drop at the point of injection for the froth concentrate. Testing can’t be achieved without creating premix and discharging finished foam. This will add to whole 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 great care is needed to avoid a broken bladder when commissioning a new set up. It isn’t straightforward to work within the metal stress vessel should issues occur, especially if and when a alternative bladder could additionally be required: all of it provides to the problem and cost.
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 quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth resolution at the level of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces permitting higher penetration and cooling. This can be a profit in wildfire conditions by coating susceptible constructions to mitigate fire development. The limited water supplies related to distant wildfire areas signifies that the resource may be absolutely optimised. However, as with balanced strain proportioner foam pumps, a further point of failure is feasible as a end result of further CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have turn into synonymous with their unique water-driven foam proportioner. Now in its third technology, the product is purely mechanical and highly 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 via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning fee and will proportion the foam focus precisely throughout a wide operating range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning price testing, utterly with out using 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 embrace:
Reduced prices: proportioning price is examined with out utilizing foam or creating premix or foam – price efficient and eco-friendly.
Improved performance: fixed proportioning fee across a large operating vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% discount in strain loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a different proportioning price.
FM permitted FireDos Gen III proportioners are to date the one FM approved water motor coupled variable proportioners using FM approved move meters. Using the check return line this provides the chance to examine the proportioning fee throughout commissioning as nicely as for annual tests, without creating any premix, which is a very massive profit for the user and relieves the surroundings.
In the second a half of this function we are going to discover the consequences of viscosity on foam proportioning and typical foam software areas and recommended discharge units.
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Written by
David Owen
Andreas Hulinsky