A information to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least due to the variables that decide which suppression medium is appropriate for a given hearth scenario. Our objective in this two-part article is to supply steerage based on a hazard-specific strategy and assist you to make an informed decision on applicable 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 similar to magnesium
Class F – fires usually related to cooking such as vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting monitors, we specialise primarily within the Class B category: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only could not penetrate the hearth load effectively.
Fire classes.
How will we make foam?
Finished foam resolution contains a easy recipe of foam concentrate, water and air. Foam concentrate is typically combined within 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 device – we’ll cover proportioning later on this article and discharge strategies in Part 2. At this point air is entrained through the use of devices designed to naturally aspirate the answer. The amount of aspiration and the kind of concentrate determines the enlargement ratio. This is often cut up between low, medium and excessive enlargement. Low growth is as much as 20:1, medium is 200:1 and excessive enlargement is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the froth adequately, though naturally aspirated mills are additionally used. The determination to determine on a specific growth ratio is determined by the hazard beneath evaluate.
Put merely, water and oil do not mix. Applying only water to Class B products will not suppress the burning vapours. This is a vital level 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 film to achieve success. Whatever methodology is chosen to supply that blanket or film, the objective is the same.
Steps of froth technology Images provided by Author / Contributor
A little of the history of froth development
We can date the development of modern foam concentrates from the Sixties onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the base component). The major drawback was as a end result of limited fuel tolerance, which meant it was vulnerable to gasoline pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a higher gas tolerance in addition to forming a vapour-sealing film across the surface of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth didn’t utterly substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam might both fight gas pick-up (mixing) and provide a good resistance to warmth, outlined by the industry as ‘burn-back resistance’.
Further development within the Eighties took FP to the subsequent degree with film-forming fluoroprotein or FFFP. We now had the best of each worlds: a film-forming foam that additionally 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 a further problem as they had been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar technology additionally became out there with the new technology of AFFF-ARs.
In recent years fluorine, one of many cornerstone elements to all foams, has turn out to be an environmental problem, as a end result of persistence in groundwater. The industry has been presented with a major problem to get rid of the ‘fluoro’ element of all the different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims regarding 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 model new normal and first choice for operators altering existing stock or reviewing new tasks. As a foam proportioner producer we must study the bodily properties of foam carefully (especially viscosity) as they influence decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more necessary in 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 important to combat the small degree of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being highly effective. The finest means of comparing their claims is to familiarise yourself with the empirically based commonplace EN 1568 or UL162. The tests cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are each included in the test protocols. This additionally covers recent and seawater in addition to light and forceful software of the foam. Each foam is given a ranking with IA being one of the best, IIID the worst. This means that you could problem foam suppliers in order to make an informed determination on the most effective foam for your needs.
Whilst EN 1568 is an excellent benchmark standard, consciousness of the consequences on foam efficiency from elements outside the usual tests must be famous. For instance, notably aggressive solvents can challenge the firefighting effectiveness of certain foams. This could be exacerbated by different ambient air temperatures, the application technique, gasoline depth etc. Our advice would be to know the details of the checks and try to match them to the foam’s appropriateness in your particular person hazards. We would always suggest consulting individual foam manufacturers as they’ll typically present specific in-house fire-performance information in opposition to a variety of the more uncommon fuels.
However, despite the foam manufacturers’ generally conflicting claims on performance, the earlier fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams based on the growth ratio Images equipped by Author / Contributor
Critical components for fulfillment: the time and software fee matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary components: time and the rate at which finished foam is utilized. Both are determined by empirically based mostly standards published by bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor means that for a given measurement of fire space it’s essential to use the foam for lengthy sufficient to realize extinction and to prevent re-ignition. This is very important in handbook intervention as firefighter’s might be at risk during post-fire operations. When it comes to fixed protection for hydrocarbon and polar solvent tanks, the application time may be so long as 60 minutes for the biggest tank diameters.
The utility rate refers to the quantity of completed foam utilized per sq. metre. This varies according to the gas and the foam type but is at present a minimum of four.zero litres per minute per sq. metre. One of the continuing developments in foam efficiency is the probability that this will be decreased, but standards often take time to recognise product improvement. Anything lower than the minimum software price implies that hearth control is unlikely to be achieved. This implies that firefighting resources, notably in a handbook fireplace attack, must be assembled earlier than firefighting commences and this takes time. The advantage in fitting mounted methods is that the assets are already designed and built into the system for quick application.
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 knowledgeable determination on how finest to tackle their specific fireplace challenges, the next is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted mounted systems applications. This makes use of the venturi precept to create a strain drop in a small aluminium or seawater materials compatible system with built-in focus pick-up tube. The pressure drop created by the venturi draws the foam focus from a container where it mixes with water to create foam answer. Both the pick-up tube and body of the inductor are compact enough to be simply carried on a hearth appliance or fitted right into a pipework system.
However, while it is thought-about to be the only methodology, it has severe drawbacks: (i) items are manufacturing unit calibrated so any modifications 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 likely require a system re-design; (ii) system design and sign-off are crucial as deviations attributable to pipe diameter modifications will adversely have an effect on proportioning accuracy and doubtlessly forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to draw focus into the downstream lines; (iv) pressure loss is excessive, as a lot as 35%, so duty pump pressures need to be high enough to permit for it, doubtlessly including further cost into the system; (v) foam delivery units must be sized so as to not prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging completed foam. This will add to complete lifetime costs because of foam focus utilization, which has to be changed, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced stress proportioners:
These use an electric or a mixture of electrical and diesel pumps to provide foam concentrate into a proportioner at a better strain than the incoming water-line strain. The proportioner is put in into the water line and regulates the blending.
They at the second are associated with older systems, the place disadvantages embrace: (i) extra prices in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter working vary, though the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump wants an extra energy source, other than water, so is not as reliably secure as a system with a possible single point of failure, such as a wholly water-driven system; (iv) usually, these methods are very complicated and cause high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to damage the froth focus and entrain air, which in turn 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 much like those fitted to balanced stress proportioners. The incoming pressurised water compresses the froth crammed bladder in order that foam focus can be proportioned with water using the same supply. The venturi precept is again brought into play as it creates a strain drop on the point of injection for the froth focus. เกจวัดแรงดันไอน้ำ can’t be achieved without creating premix and discharging finished foam. This will add to complete lifetime prices as a result of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a end result of great care is required to avoid a damaged bladder when commissioning a new set up. It is never simple to work within the steel stress vessel ought to issues occur, particularly if and when a replacement bladder could additionally be required: all of it provides to the problem and cost.
digital pressure gauge ราคา (CAFS):
This isn’t a proportioning methodology within the conventional sense as the froth is already proportioned using one of the earlier methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam 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 can be a benefit in wildfire situations by coating vulnerable constructions to mitigate fireplace growth. The restricted water provides related to distant wildfire areas signifies that the useful resource may be totally optimised. However, as with balanced stress proportioner foam pumps, an extra point of failure is feasible due to the additional CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is solely mechanical and highly reliable. A water-driven rotor provides the motive force to drive a immediately coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning price and can proportion the foam focus precisely throughout a wide operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, completely with out utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The advantages of FireDos Gen III FM approved foam proportioners embody:
Reduced prices: proportioning price is examined with out utilizing foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: fixed proportioning price across a wide working range.
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 simple and quick adjustment to a unique proportioning price.
FM approved FireDos Gen III proportioners are thus far the one FM approved water motor coupled variable proportioners utilizing FM approved move meters. Using the take a look at return line this provides the chance to examine the proportioning fee throughout commissioning in addition to for annual tests, with out creating any premix, which is a really massive benefit for the user and relieves the environment.
In the second a half of this function we are going to explore the consequences of viscosity on foam proportioning and typical foam utility areas and really helpful discharge units.
For more information, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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