Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given fireplace situation. Our objective in this two-part article is to supply steerage based on a hazard-specific method and help you make an knowledgeable choice on acceptable 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 typically related to cooking similar to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise mainly within the Class B category: flammable liquids.
Foam is taken into account to be the most effective 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 fireplace load successfully.
How will we make foam?
Finished foam answer comprises a simple recipe of froth focus, water and air. Foam focus is often mixed in the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge gadget – we will cowl proportioning later on this article and discharge methods in Part 2. At this point air is entrained by using gadgets designed to naturally aspirate the answer. The quantity of aspiration and the type of focus determines the expansion ratio. This is usually break up between low, medium and high expansion. Low enlargement is as a lot as 20:1, medium is 200:1 and excessive enlargement is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the froth adequately, though naturally aspirated generators are also used. The choice to choose a selected expansion ratio is set by the hazard under review.
Put simply, water and oil do not combine. Applying only water to Class B products won’t suppress the burning vapours. This is a vital 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 achieve success. Whatever technique is chosen to provide that blanket or film, the target is the same.
Steps of froth era Images equipped by Author / Contributor
A little of the history of foam growth
We can date the event of contemporary 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 main disadvantage was because of restricted gasoline tolerance, which meant it was vulnerable to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, synthetic detergents gave foam a larger fuel tolerance as well as forming a vapour-sealing movie across the surface of the gasoline. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s development didn’t utterly exchange using protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight gasoline pick-up (mixing) and supply a great resistance to heat, defined by the industry as ‘burn-back resistance’.
Further growth within the 1980s took FP to the following degree with film-forming fluoroprotein or FFFP. We now had the most effective of each worlds: a film-forming foam that additionally had good burn-back resistance.
The Nineteen Eighties further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time introduced a further problem as they had been water soluble and foam destructive. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. pressure gauge -how additionally grew to become available with the model new era of AFFF-ARs.
In recent years fluorine, one of the cornerstone elements to all foams, has turn out to be an environmental concern, due to persistence in groundwater. The business has been presented with a major challenge to eliminate the ‘fluoro’ factor of all of the different foam concentrate varieties. We have witnessed an period of manufacturers’ claims and counter claims concerning the efficacy of a complete vary 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 out to be the brand new normal and first choice for operators changing current stock or reviewing new projects. As a foam proportioner producer we should study the physical properties of foam fastidiously (especially viscosity) as they influence choices on the general proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are more and more necessary in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant high quality of SFFF/F3 is critical to fight the small diploma of water miscibility of the gasoline.
All foam concentrate manufacturers will naturally promote their product as being extremely efficient. The finest means of comparing their claims is to familiarise your self with the empirically primarily based commonplace EN 1568 or UL162. The exams cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included in the take a look at protocols. This also covers contemporary and seawater as nicely as light and forceful software of the foam. Each foam is given a ranking with IA being the best, IIID the worst. This means that you could problem foam suppliers to have the ability to make an informed decision on the most effective foam for your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the consequences on foam performance from elements exterior the standard exams must be famous. For example, particularly aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the applying technique, gasoline depth and so on. Our advice would be to grasp the major points of the checks and try to match them to the foam’s appropriateness on your individual hazards. We would all the time recommend consulting individual foam manufacturers as they’ll often provide specific in-house fire-performance data in opposition to some of the more unusual fuels.
However, regardless of 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 finished foam.
Foams according to the growth ratio Images equipped by Author / Contributor
Critical elements for fulfillment: the time and utility price matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the speed at which finished foam is utilized. Both are decided by empirically based standards revealed by our 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 fireside area it is essential to use the froth for lengthy enough to realize extinction and to stop re-ignition. This is very critical in handbook intervention as firefighter’s shall be in danger throughout post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the appliance time could be as lengthy as 60 minutes for the most important tank diameters.
The utility fee refers to the quantity of completed foam utilized per square metre. This varies according to the gas and the froth kind however is at present no much less than four.0 litres per minute per square metre. One of the ongoing developments in foam performance is the likelihood that this will be lowered, however requirements often take time to recognise product development. Anything less than the minimum utility fee implies that hearth control is unlikely to be achieved. This means that firefighting assets, notably in a guide fire assault, must be assembled earlier than firefighting commences and this takes time. The advantage in becoming mounted techniques is that the sources are already designed and constructed into the system for instant utility.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to permit readers to make an informed choice on how finest to tackle their particular hearth challenges, the next is an overview of the varied foam proportioning methods.
Typically associated with fireplace service deployment and limited mounted systems applications. This makes use of the venturi principle to create a pressure drop in a small aluminium or seawater material suitable device with built-in concentrate pick-up tube. The strain drop created by the venturi draws the foam focus from a container where it mixes with water to create foam resolution. Both the pick-up tube and body of the inductor are compact sufficient to be easily carried on a hearth appliance or fitted right into a pipework system.
However, while it’s considered to be the only technique, it has severe drawbacks: (i) units are manufacturing facility calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a altering amount 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 result on proportioning accuracy and probably prevent any proportioning; (iii) modifications in focus viscosity will undermine the flexibility of the venturi to draw focus into the downstream strains; (iv) stress loss is excessive, as much as 35%, so obligation pump pressures must be high sufficient to permit for it, doubtlessly including additional value into the system; (v) foam supply devices have to be sized so as to not restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs because of foam concentrate utilization, which has to be changed, and the disposal of premix or foam.
Types of froth agentsImages supplied by Author / Contributor
Balanced strain proportioners:
These use an electric or a mix of electrical and diesel pumps to provide foam focus right into a proportioner at the next pressure than the incoming water-line pressure. The proportioner is put in into the water line and regulates the blending.
They at the second are associated with older methods, the place disadvantages embrace: (i) additional costs in hardware and design time; (ii) the froth pump is normally restricted to a much tighter working vary, although the proportioner itself can accommodate broad ranges in flows; (iii) the foam pump needs an extra energy source, aside 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 techniques are very complex and cause excessive 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 focus and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Comprised of a metal stress vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner much like those fitted to balanced stress proportioners. The incoming pressurised water compresses the froth filled bladder in order that foam focus may be proportioned with water using the identical supply. The venturi principle is again brought into play because it creates a pressure drop at the level of injection for the froth concentrate. Testing can’t be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs on account of foam focus usage, which must be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a outcome of great care is needed to avoid a broken bladder when commissioning a brand new installation. It is rarely straightforward to work inside the steel strain vessel ought to problems happen, particularly if and when a substitute bladder may be required: all of it provides to the problem and price.
Compressed air foam (CAFS):
This isn’t a proportioning technique in the conventional sense as the foam is already proportioned utilizing one of many previous strategies. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth resolution at the point of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces permitting better penetration and cooling. This can be a profit in wildfire conditions by coating weak constructions to mitigate fireplace growth. The restricted water provides related to remote wildfire areas means that the resource could be absolutely optimised. However, as with balanced pressure proportioner foam pumps, a further point of failure is feasible due to the extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is only mechanical and extremely reliable. A water-driven rotor provides the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning price and will proportion the foam focus accurately across a large working range. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, completely with out 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 permitted foam proportioners embody:
Reduced prices: proportioning price is tested with out using foam or creating premix or foam – price effective and eco-friendly.
Improved efficiency: fixed proportioning fee across a wide working range.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in strain loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a special proportioning fee.
FM approved FireDos Gen III proportioners are thus far the only FM accredited water motor coupled variable proportioners using FM permitted move meters. Using the test return line this provides the possibility to check the proportioning rate during commissioning in addition to for annual exams, without creating any premix, which is a very big profit for the consumer and relieves the environment.
In the second a half of this function we are going to discover the results of viscosity on foam proportioning and typical foam software areas and recommended discharge units.
For extra data, go to www.firedos.com