Fire presents many challenges, not least due to the variables that determine which suppression medium is acceptable for a given hearth scenario. Our goal in this two-part article is to supply guidance based on a hazard-specific approach and assist you to make an knowledgeable determination on applicable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or flamable materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires usually related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting monitors, we specialise primarily within the Class B class: flammable liquids.
Foam is taken into account to be the best 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 where water only might not penetrate the fire load effectively.
Fire courses.
How will we make foam?
Finished foam solution contains a easy recipe of foam concentrate, water and air. Foam focus is typically 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’ll cover proportioning later on this article and discharge methods in Part 2. At this level air is entrained through the use of gadgets designed to naturally aspirate the solution. The quantity of aspiration and the type of concentrate determines the enlargement ratio. This is typically split between low, medium and excessive growth. Low enlargement is up to 20:1, medium is 200:1 and excessive enlargement is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to increase the foam adequately, though naturally aspirated turbines are also used. The decision to choose a particular expansion ratio is set by the hazard underneath review.
Put simply, water and oil do not mix. Applying only water to Class B products 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 want a medium that enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to be successful. Whatever technique is chosen to produce that blanket or movie, the objective is identical.
Steps of foam era Images provided by Author / Contributor
A little of the history of froth improvement
We can date the event 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 disadvantage was as a result of restricted gas tolerance, which meant it was prone 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 gasoline tolerance in addition to forming a vapour-sealing film across the surface of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s improvement did not utterly substitute using protein-based foam. Fluoroprotein, or FP, meant that protein foam could both combat gasoline pick-up (mixing) and offer a good resistance to warmth, defined by the industry as ‘burn-back resistance’.
Further improvement in the Nineteen Eighties took FP to the next stage with film-forming fluoroprotein or FFFP. We now had one of the best of both worlds: a film-forming foam that additionally had good burn-back resistance.
The Eighties further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had always presented an extra 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 similar know-how also turned out there with the new generation of AFFF-ARs.
In current years fluorine, one of the cornerstone components to all foams, has turn out to be an environmental problem, because of persistence in groundwater. The business has been introduced with a significant challenge to get rid of the ‘fluoro’ element of all of the different foam concentrate varieties. We have witnessed an period of manufacturers’ claims and counter claims relating to the efficacy of a complete range of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn into the new normal and first alternative for operators altering current stock or reviewing new projects. As a foam proportioner manufacturer we must study the bodily properties of froth rigorously (especially viscosity) as they influence choices on the overall proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more essential 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 combat the small degree of water miscibility of the gasoline.
All foam focus producers will naturally promote their product as being extremely efficient. The greatest means of comparing their claims is to familiarise your self 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 within the check protocols. This additionally covers fresh and seawater in addition to light and forceful application of the foam. 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 most effective foam in your wants.
Whilst EN 1568 is an excellent benchmark normal, awareness of the consequences on foam efficiency from components exterior the usual checks must be noted. For example, significantly aggressive solvents can problem the firefighting effectiveness of certain foams. This could be exacerbated by different ambient air temperatures, the application method, gas depth and so on. Our advice can be to know the small print of the checks and attempt to match them to the foam’s appropriateness on your particular person hazards. We would all the time suggest consulting particular person foam manufacturers as they can often present specific in-house fire-performance data towards a few of the extra unusual fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned nonetheless stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the growth ratio Images equipped by Author / Contributor
Critical components for achievement: the time and utility rate matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary components: time and the rate at which finished foam is applied. Both are decided by empirically based mostly standards published by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue means that for a given measurement of fireplace area it’s necessary to apply the foam for lengthy enough to realize extinction and to prevent re-ignition. This is especially critical in guide intervention as firefighter’s will be in danger during post-fire operations. When it comes to mounted safety for hydrocarbon and polar solvent tanks, the applying time could be as lengthy as 60 minutes for the largest tank diameters.
The utility price refers to the quantity of finished foam utilized per sq. metre. This varies in accordance with the fuel and the foam kind however is presently a minimal of litres per minute per square metre. One of the continuing developments in foam performance is the likelihood that this might be lowered, however requirements usually take time to recognise product improvement. Anything less than the minimal utility price means that fire management is unlikely to be achieved. This means that firefighting sources, significantly in a manual hearth assault, have to be assembled before firefighting commences and this takes time. The advantage in becoming fixed techniques is that the assets are already designed and constructed into the system for quick utility.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an informed determination on how greatest to sort out their particular hearth challenges, the next is an outline of the varied foam proportioning methods.
Foam inductors:
Typically associated with hearth service deployment and limited fixed systems applications. This makes use of the venturi principle to create a stress drop in a small aluminium or seawater materials suitable system with built-in concentrate pick-up tube. The stress drop created by the venturi attracts the froth 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 sufficient to be simply carried on a fire appliance or fitted into a pipework system.
However, whilst it is thought-about to be the only methodology, it has severe drawbacks: (i) units are manufacturing unit calibrated so any adjustments to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a changing quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are critical as deviations attributable to pipe diameter adjustments will adversely have an effect on proportioning accuracy and potentially stop any proportioning; (iii) modifications in focus viscosity will undermine the flexibility of the venturi to draw concentrate into the downstream lines; (iv) stress loss is excessive, as a lot as 35%, so responsibility pump pressures have to be excessive enough to permit for it, probably adding extra cost into the system; (v) foam supply gadgets have to be sized in order to not restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to whole lifetime costs as a outcome of foam focus usage, which must be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mix of electrical and diesel pumps to produce foam concentrate right into a proportioner at a higher pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the mixing.
They are now related to older techniques, the place disadvantages include: (i) extra prices 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 wants an extra energy supply, apart from water, so just isn’t as reliably safe as a system with a potential single level of failure, corresponding to a completely water-driven system; (iv) typically, these methods are very complicated and trigger high efforts at 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 concentrate and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
pressure gauge หน้าปัด 2 นิ้ว :
Comprised of a steel pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam focus proportioner much like the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the froth crammed bladder in order that foam focus could be proportioned with water utilizing the identical provide. The venturi principle is again brought into play because it creates a strain drop at the level of injection for the foam concentrate. Testing cannot be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs because of foam concentrate usage, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot because nice care is needed to avoid a damaged bladder when commissioning a new set up. It isn’t easy to work within the metal stress vessel should issues happen, especially if and when a alternative bladder may be required: it all provides to the problem and price.
Compressed air foam (CAFS):
This isn’t a proportioning method in the standard sense as the foam 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 finished foam’s capacity to cling to vertical surfaces permitting higher penetration and cooling. This can be a profit in wildfire conditions by coating vulnerable constructions to mitigate fire progress. The limited water supplies associated with distant wildfire areas implies that the resource could be fully optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is feasible because of the extra CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their unique water-driven foam proportioner. Now in เกจ์อาร์กอนsumo , the product is solely mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning price and can proportion the froth focus precisely throughout a wide working range. The purely mechanical system supplies cost-efficient and eco-friendly proportioning price testing, fully without utilizing any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The advantages of FireDos Gen III FM accredited foam proportioners embrace:
Reduced prices: proportioning fee is examined without using foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: fixed proportioning rate across a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, in comparability with older generations, through hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a different proportioning price.
FM accredited FireDos Gen III proportioners are so far the only FM approved water motor coupled variable proportioners using FM accredited move meters. Using the test return line this provides the possibility to examine the proportioning price throughout commissioning as properly as for annual exams, with out creating any premix, which is a very massive profit for the user and relieves the environment.
In the second a half of this feature we are going to explore the results of viscosity on foam proportioning and typical foam utility areas and really helpful discharge devices.
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Written by
David Owen
Andreas Hulinsky