Fire presents many challenges, not least because of the variables that decide which suppression medium is appropriate for a given fireplace state of affairs. Our objective in this two-part article is to supply guidance based on a hazard-specific strategy and help you make an informed 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 flamable supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires generally related to cooking corresponding to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting screens, we specialise primarily within the Class B class: flammable liquids.
Foam is taken into account to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain 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 will we make foam?
Finished foam resolution comprises a simple recipe of froth concentrate, water and air. Foam concentrate is typically blended 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 system – we’ll cowl proportioning later in this article and discharge strategies in Part 2. At this level 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 expansion ratio. This is typically split between low, medium and excessive enlargement. Low expansion 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 expand the foam adequately, though naturally aspirated turbines are also used. The choice to determine on a selected enlargement ratio is decided by the hazard underneath review.
Put merely, water and oil don’t combine. Applying solely water to Class B products won’t suppress the burning vapours. This is an important level to make as it’s 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 method is chosen to supply that blanket or film, the target is the same.
Steps of froth era Images equipped by Author / Contributor
A little of the historical past of foam improvement
We can date the development of contemporary foam concentrates from the Nineteen Sixties onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The main disadvantage was because 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 bottom product, synthetic detergents gave foam a larger gasoline tolerance in addition to 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 devices are fitted.
Nevertheless, AFFF’s improvement didn’t utterly replace the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam could both fight gas pick-up (mixing) and supply a good resistance to warmth, outlined by the trade as ‘burn-back resistance’.
Further improvement within the Eighties took FP to the following 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 record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented an additional problem as they have been water soluble and foam damaging. เกรดวัดแรงดัน -AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The similar expertise additionally grew to become obtainable with the model new technology of AFFF-ARs.
In latest years fluorine, one of the cornerstone components to all foams, has turn out to be an environmental problem, as a outcome of persistence in groundwater. The trade has been presented with a significant challenge to get rid of the ‘fluoro’ component of all of the totally different foam focus types. We have witnessed an period of manufacturers’ claims and counter claims concerning 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 model new regular and first selection for operators changing existing stock or reviewing new projects. As a foam proportioner producer we should study the physical properties of foam rigorously (especially viscosity) as they affect choices on the overall proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are increasingly important in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant high quality of SFFF/F3 is necessary to fight the small degree of water miscibility of the gasoline.
All foam focus manufacturers will naturally promote their product as being extremely effective. The greatest way of comparing their claims is to familiarise yourself with the empirically primarily based standard EN 1568 or UL162. The tests cover 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 fresh and seawater in addition to gentle and forceful software of the froth. Each foam is given a rating with IA being the best, IIID the worst. This means that you can challenge foam suppliers in order to make an knowledgeable choice on the best foam in your wants.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the consequences on foam efficiency from elements outdoors the usual checks must be noted. For instance, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This could be exacerbated by different ambient air temperatures, the appliance technique, fuel depth etc. Our advice could be to understand the small print of the checks and attempt to match them to the foam’s appropriateness on your individual hazards. We would all the time recommend consulting particular person foam manufacturers as they’ll typically provide specific in-house fire-performance information towards some of the extra unusual fuels.
However, despite the froth manufacturers’ typically conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the growth ratio Images provided by Author / Contributor
Critical components for fulfillment: the time and utility fee matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary elements: time and the rate at which finished foam is applied. Both are determined by empirically based standards printed by bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ issue signifies that for a given size of fireplace area it is needed to apply the froth for lengthy enough to realize extinction and to prevent re-ignition. This is particularly important in guide intervention as firefighter’s will be at risk during post-fire operations. When it comes to fixed safety for hydrocarbon and polar solvent tanks, the applying time can be so long as 60 minutes for the biggest tank diameters.
The software price refers back to the quantity of finished foam utilized per sq. metre. This varies according to the fuel and the froth type however is presently no much less than 4.zero litres per minute per sq. metre. One of the continued developments in foam efficiency is the likelihood that this might be lowered, but requirements usually take time to recognise product improvement. Anything lower than the minimal software price implies that hearth management is unlikely to be achieved. This signifies that firefighting resources, notably in a guide hearth assault, need to be assembled before firefighting commences and this takes time. The benefit in becoming fixed systems is that the sources are already designed and built into the system for immediate software.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an informed choice on how best to tackle their explicit hearth challenges, the following is an outline of the various foam proportioning methods.
Foam inductors:
Typically related to hearth service deployment and limited fixed techniques applications. This uses the venturi precept to create a strain drop in a small aluminium or seawater material appropriate 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 resolution. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a hearth appliance or fitted right into a pipework system.
However, whilst it is considered to be the only methodology, it has severe drawbacks: (i) items 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 altering quantity of discharge devices) will likely require a system re-design; (ii) system design and sign-off are crucial as deviations brought on by pipe diameter changes will adversely have an effect on proportioning accuracy and doubtlessly stop any proportioning; (iii) adjustments in concentrate viscosity will undermine the ability of the venturi to attract concentrate into the downstream lines; (iv) stress loss is high, as much as 35%, so responsibility pump pressures have to be excessive sufficient to permit for it, potentially including further cost into the system; (v) foam delivery devices must 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 complete lifetime prices as a end result of foam focus usage, which must be changed, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced strain proportioners:
These use an electrical or a combination of electrical and diesel pumps to provide foam focus into a proportioner at the next strain than the incoming water-line stress. The proportioner is put in into the water line and regulates the blending.
They are now associated with older systems, where disadvantages embrace: (i) further prices in hardware and design time; (ii) the foam pump is often restricted to a much tighter working range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an additional energy source, apart from water, so isn’t as reliably safe as a system with a possible single point of failure, such as a wholly water-driven system; (iv) usually, these techniques are very advanced and trigger high 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 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 the ones fitted to balanced stress proportioners. The incoming pressurised water compresses the foam stuffed bladder so that foam focus could be proportioned with water utilizing the identical provide. The venturi precept is again brought into play because it creates a stress drop on the point of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to complete lifetime prices because of foam concentrate usage, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because nice care is needed to keep away from a broken bladder when commissioning a model new set up. It is never easy to work inside the metal strain vessel should problems happen, particularly if and when a substitute bladder may be required: all of it provides to the issue and price.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology in the standard sense as the foam is already proportioned using one of many earlier 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 resolution on the point of discharge. The consensus view is that CAFS enhances the finished foam’s capacity to cling to vertical surfaces allowing higher penetration and cooling. This can be a benefit in wildfire situations by coating susceptible constructions to mitigate fire progress. The restricted water provides related to remote wildfire areas implies that the useful resource may be absolutely optimised. However, as with balanced strain proportioner foam pumps, a further point of failure is feasible as a outcome of additional CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is only mechanical and extremely dependable. A water-driven rotor supplies the motive force to drive a instantly 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 concentrate precisely across a large working vary. 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 permitted foam proportioners embody:
Reduced prices: proportioning price is examined without using foam or creating premix or foam – price effective and eco-friendly.
Improved performance: constant proportioning rate across a wide operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, in comparison with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning rate.
FM approved FireDos Gen III proportioners are so far the one FM accredited water motor coupled variable proportioners using FM permitted flow meters. Using the test return line this provides the possibility to check the proportioning rate throughout commissioning as well as for annual checks, with out creating any premix, which is a very massive benefit for the user and relieves the surroundings.
In the second part of this characteristic we’ll explore the consequences of viscosity on foam proportioning and typical foam software areas and really helpful discharge gadgets.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share