Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given hearth state of affairs. Our objective in this two-part article is to provide steering based mostly on a hazard-specific strategy 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 categorized as follows:
Class A – carbonaceous or combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires generally related to cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting displays, we specialise primarily within the Class B class: flammable liquids.
Foam is taken into account to be the simplest fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water solely might not penetrate the hearth load successfully.
Fire courses.
How can we make foam?
Finished foam answer includes a simple recipe of froth concentrate, water and air. Foam focus is often mixed in 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 gadget – we are going to cowl proportioning later in this article and discharge methods in Part 2. At this point air is entrained through the use of units designed to naturally aspirate the answer. The amount of aspiration and the sort of concentrate determines the expansion ratio. This is often cut up between low, medium and excessive growth. Low expansion is up to 20:1, medium is 200:1 and excessive growth is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to broaden the foam adequately, though naturally aspirated turbines are additionally used. The choice to determine on a specific expansion ratio is decided by the hazard beneath review.
Put merely, water and oil do not mix. Applying solely water to Class B merchandise will not suppress the burning vapours. This is an important level 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 obtain success. Whatever methodology is chosen to supply that blanket or movie, the target is similar.
Steps of froth generation Images equipped by Author / Contributor
A little of the history of froth growth
We can date the event of contemporary foam concentrates from the 1960s onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the base component). The primary disadvantage was as a end result of restricted gas tolerance, which meant it was vulnerable 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 higher gas tolerance as properly as forming a vapour-sealing film across the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s development didn’t utterly exchange the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam may each fight gas pick-up (mixing) and offer a great resistance to warmth, outlined by the business as ‘burn-back resistance’.
Further development 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 Eighties further added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times offered a further problem as they have been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same technology additionally grew to become obtainable with the new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone components to all foams, has turn into an environmental problem, because of persistence in groundwater. The industry has been offered with a significant problem to get rid of the ‘fluoro’ factor of all the completely different foam concentrate types. We have witnessed an period of manufacturers’ claims and counter claims regarding 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 out to be the new regular and first choice for operators changing current stock or reviewing new projects. As a foam proportioner producer we must look at the bodily properties of foam carefully (especially viscosity) as they affect decisions on the overall proportioning solution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant sorts are increasingly essential within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, implies that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small diploma of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being highly efficient. The finest method of comparing their claims is to familiarise your self with the empirically based normal 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 extra demanding polar solvents are each included within the test protocols. This additionally covers fresh and seawater as nicely as gentle and forceful software of the foam. Each foam is given a ranking with IA being the most effective, IIID the worst. This means you could problem foam suppliers in order to make an informed determination on the most effective foam in your needs.
Whilst EN 1568 is a wonderful benchmark standard, awareness of the effects on foam performance from components outdoors the usual checks must be noted. For instance, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This could be exacerbated by completely different ambient air temperatures, the applying technique, gasoline depth and so forth. Our advice could be to grasp the details of the exams and attempt to match them to the foam’s appropriateness in your particular person hazards. We would always recommend consulting particular person foam producers as they can often present particular in-house fire-performance knowledge against some of the extra uncommon fuels.
However, regardless of the foam manufacturers’ sometimes conflicting claims on performance, the earlier fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the expansion ratio Images supplied by Author / Contributor
Critical factors for success: the time and application price matrix
Successful extinction of flammable liquid fires is decided by two converging and complementary factors: time and the speed at which completed foam is utilized. Both are determined by empirically primarily based standards revealed by bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given measurement of fireplace space it’s necessary to use the foam for lengthy sufficient to realize extinction and to forestall re-ignition. This is particularly critical in manual intervention as firefighter’s will be at risk throughout post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the application time may be as lengthy as 60 minutes for the most important tank diameters.
The utility rate refers to the amount of finished foam utilized per sq. metre. This varies in accordance with the gasoline and the froth kind however is presently at least 4.zero litres per minute per square metre. One of the continuing developments in foam efficiency is the likelihood that this shall be lowered, however standards usually take time to recognise product development. Anything less than the minimal application price signifies that hearth control is unlikely to be achieved. This implies that firefighting assets, notably in a manual hearth attack, have to be assembled before firefighting commences and this takes time. The benefit in becoming mounted techniques is that the sources 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 informed decision on how greatest to sort out their specific fire challenges, the following is an summary of the assorted foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and restricted fixed methods applications. This uses the venturi precept to create a strain drop in a small aluminium or seawater materials suitable system with built-in concentrate pick-up tube. The stress drop created by the venturi draws the froth concentrate from a container the place it mixes with water to create foam solution. Both the pick-up tube and body of the inductor are compact sufficient to be simply carried on a fire appliance or fitted right into a pipework system.
However, whilst it’s thought of to be the best methodology, it has severe drawbacks: (i) models are factory calibrated so any modifications 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 doubtless require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter modifications will adversely affect proportioning accuracy and potentially prevent any proportioning; (iii) changes in focus viscosity will undermine the flexibility of the venturi to attract concentrate into the downstream strains; (iv) strain loss is high, as a lot as 35%, so obligation pump pressures must be high enough to allow for it, potentially adding additional value into the system; (v) foam supply devices need to be sized in order to not limit design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs on account of foam concentrate usage, 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 electrical or a mixture of electric and diesel pumps to supply foam focus right into a proportioner at a higher strain than the incoming water-line pressure. เพชเชอร์เกจ is installed into the water line and regulates the blending.
They at the second are related to older techniques, the place disadvantages embrace: (i) further costs in hardware and design time; (ii) the froth pump is generally restricted to a a lot tighter operating range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump needs an additional power supply, apart from water, so is not as reliably secure as a system with a possible single point of failure, such as a completely water-driven system; (iv) usually, these methods are very complex and trigger excessive 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 break the froth focus and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a metal pressure vessel containing a flexible 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 stuffed bladder so that foam focus may be proportioned with water using the same provide. The venturi principle is again brought into play as it creates a stress drop at the point of injection for the froth focus. Testing cannot be achieved without creating premix and discharging finished foam. This will add to complete lifetime costs on account of foam focus usage, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a outcome of nice care is needed to avoid a broken bladder when commissioning a new set up. It isn’t simple to work inside the metal strain vessel should issues occur, particularly if and when a alternative bladder may be required: it all adds to the issue and value.
Compressed air foam (CAFS):
This is not a proportioning method within the standard sense as the foam is already proportioned utilizing one of the previous methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the foam answer at the point of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces allowing better penetration and cooling. This can be a profit in wildfire conditions by coating susceptible constructions to mitigate hearth progress. The limited water supplies associated with distant wildfire areas signifies that the useful resource could be absolutely optimised. However, as with balanced stress proportioner foam pumps, an additional level of failure is feasible because of the extra CAFS equipment.
Water driven 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 provides the driving 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 unit set to the required proportioning fee and will proportion the froth focus accurately across a wide operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning fee testing, fully with out using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embody:
Reduced costs: proportioning rate is examined with out utilizing foam or creating premix or foam – value effective and eco-friendly.
Improved performance: constant proportioning price throughout a large working range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in pressure loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a different proportioning rate.
FM permitted FireDos Gen III proportioners are to date the one FM permitted water motor coupled variable proportioners using FM approved move meters. Using the check return line this offers the chance to verify the proportioning fee during commissioning in addition to for annual tests, with out creating any premix, which is a very huge profit for the person and relieves the surroundings.
In the second part of this function we are going to explore the consequences of viscosity on foam proportioning and typical foam application areas and really helpful discharge devices.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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