Fire presents many challenges, not least because of the variables that decide which suppression medium is appropriate for a given hearth scenario. Our objective on this two-part article is to provide guidance based on a hazard-specific approach and allow you to make an informed determination on appropriate fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or combustible materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals corresponding to magnesium
Class F – fires typically related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise mainly in the Class B class: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure types of foam (known as wetting agents) are particularly for deep-seated Class A fires where water only may not penetrate the fireplace load successfully.
Fire classes.
How can we make foam?
Finished foam resolution includes a simple recipe of froth concentrate, water and air. Foam focus is often mixed within the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it is pumped to the chosen discharge device – we are going to cowl proportioning later in this article and discharge strategies in Part 2. At this point air is entrained by using devices designed to naturally aspirate the answer. The amount of aspiration and the type of concentrate determines the growth ratio. This is often cut up between low, medium and excessive expansion. Low expansion is as a lot as 20:1, medium is 200:1 and high growth is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to increase the foam adequately, though naturally aspirated mills are also used. The determination to determine on a specific enlargement ratio is determined by the hazard under evaluate.
Put merely, water and oil do not mix. Applying solely water to Class B products is not going to suppress the burning vapours. This is a crucial 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 achieve success. Whatever methodology is chosen to supply that blanket or movie, the target is identical.
Steps of froth generation Images provided by Author / Contributor
A little of the historical past of froth development
We can date the development of modern foam concentrates from the Nineteen Sixties onwards. Up to that point foam concentrates were comprised of animal-based protein (typically ground hoof and horn is the bottom component). The major downside was because of restricted gasoline 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 utilizing protein as the base product, artificial detergents gave foam a greater gas tolerance as properly as forming a vapour-sealing movie across the surface of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement did not utterly replace the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat gas pick-up (mixing) and supply an excellent resistance to warmth, outlined by the trade as ‘burn-back resistance’.
Further improvement in the 1980s took FP to the next stage 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 1980s further added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced a further problem as they have been water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The identical expertise also became available with the new technology of AFFF-ARs.
In latest years fluorine, one of many cornerstone ingredients to all foams, has turn out to be an environmental issue, due to persistence in groundwater. The business has been presented with a serious challenge to remove the ‘fluoro’ component of all the different foam focus varieties. We have witnessed an period of manufacturers’ claims and counter claims concerning 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 outline these foams, which have turn into the new normal and first selection for operators changing existing stock or reviewing new tasks. As a foam proportioner manufacturer we should examine the bodily properties of foam fastidiously (especially viscosity) as they influence choices on the overall proportioning answer. เกจวัดแรงดันสูง of this later.
Multi-purpose foams such because the F3 alcohol-resistant varieties are increasingly important in the fuel-storage enviornment. 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 fight the small diploma of water miscibility of the fuel.
All foam focus producers will naturally promote their product as being extremely efficient. The finest method of comparing their claims is to familiarise your self with the empirically based mostly normal 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 both included in the test protocols. This additionally covers fresh and seawater as well as light and forceful application of the froth. Each foam is given a score with IA being the most effective, IIID the worst. This means that you could challenge foam suppliers to find a way to make an informed decision on the most effective foam in your needs.
Whilst EN 1568 is a wonderful benchmark normal, awareness of the results on foam performance from factors outdoors the standard exams should be famous. For instance, particularly aggressive solvents can challenge the firefighting effectiveness of certain foams. This could be exacerbated by completely different ambient air temperatures, the application methodology, fuel depth etc. Our advice would be to know the primary points of the checks and try to match them to the foam’s appropriateness for your individual hazards. We would at all times recommend consulting individual foam manufacturers as they can typically present specific in-house fire-performance knowledge in opposition to a variety of the more uncommon fuels.
However, despite the froth manufacturers’ generally conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the expansion ratio Images provided by Author / Contributor
Critical components for achievement: the time and utility price matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary components: time and the rate at which finished foam is utilized. Both are decided by empirically based requirements printed by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ factor signifies that for a given size of fireplace space it’s essential to apply the foam for lengthy enough to achieve extinction and to forestall re-ignition. This is especially critical in guide intervention as firefighter’s might be in danger during post-fire operations. When it comes to mounted protection for hydrocarbon and polar solvent tanks, the appliance time could be so lengthy as 60 minutes for the biggest tank diameters.
The software price refers to the amount of finished foam applied per square metre. This varies in accordance with the fuel and the foam sort but is presently at least 4.0 litres per minute per sq. metre. One of the ongoing developments in foam performance is the chance that this will be decreased, however requirements often take time to recognise product improvement. Anything lower than the minimum utility price signifies that fireplace management is unlikely to be achieved. This implies that firefighting resources, significantly in a handbook hearth assault, have to be assembled before firefighting commences and this takes time. The benefit in fitting fastened methods is that the sources are already designed and constructed into the system for quick software.
Principle of froth extinguishment Images supplied by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to allow readers to make an knowledgeable decision on how finest to deal with their specific fireplace challenges, the following is an overview of the varied foam proportioning strategies.
Foam inductors:
Typically associated with hearth service deployment and limited fastened methods purposes. This makes use of the venturi principle to create a stress drop in a small aluminium or seawater material suitable system with built-in focus pick-up tube. The pressure drop created by the venturi attracts the froth concentrate from a container where 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 fireplace equipment or fitted into a pipework system.
However, while it’s thought-about to be the only methodology, it has severe drawbacks: (i) units are factory calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are critical as deviations brought on by pipe diameter adjustments will adversely affect proportioning accuracy and probably forestall any proportioning; (iii) changes in focus viscosity will undermine the power of the venturi to draw concentrate into the downstream traces; (iv) pressure loss is excessive, as much as 35%, so obligation pump pressures have to be high enough to permit for it, probably adding additional cost into the system; (v) foam supply gadgets need to be sized in order not to prohibit design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to entire lifetime costs on account of foam concentrate usage, which needs 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 combination of electrical and diesel pumps to produce foam concentrate right into a proportioner at a better 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 embody: (i) further prices in hardware and design time; (ii) the foam pump is normally restricted to a a lot tighter working vary, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants an additional power source, aside from water, so is not as reliably secure as a system with a potential single level of failure, corresponding to an entirely water-driven system; (iv) sometimes, these methods are very complex and trigger excessive efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam focus creates pointless agitation that has the potential to break the froth focus and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel stress vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner similar to those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam crammed bladder in order that foam focus can be proportioned with water utilizing the identical provide. The venturi precept is again brought into play because it creates a strain drop on the point of injection for the foam concentrate. Testing cannot be achieved without creating premix and discharging completed foam. This will add to whole lifetime prices because of foam focus utilization, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point as a outcome of nice care is needed to keep away from a broken bladder when commissioning a brand new set up. It is never straightforward to work inside the steel strain vessel ought to problems occur, especially if and when a substitute bladder may be required: all of it adds to the problem and cost.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology in the conventional sense as the froth is already proportioned using one of the earlier strategies. However, pressurised air is then added forcefully somewhat 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 completed foam’s ability to cling to vertical surfaces allowing higher penetration and cooling. This can be a benefit in wildfire situations by coating vulnerable constructions to mitigate fireplace development. The limited water provides related to remote wildfire areas signifies that the resource can be totally optimised. However, as with balanced pressure proportioner foam pumps, a further point of failure is feasible as a end result of further 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 purely mechanical and highly dependable. A water-driven rotor provides the motive force to drive a directly coupled positive-displacement plunger or piston pump. This is equipped with foam focus 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 concentrate precisely throughout a wide working vary. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, completely without using any foam concentrate or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners embody:
Reduced prices: proportioning fee is tested without utilizing foam or creating premix or foam – price efficient and eco-friendly.
Improved performance: constant proportioning fee across a wide operating vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in pressure loss, compared to older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a unique proportioning rate.
FM permitted FireDos Gen III proportioners are thus far the only FM permitted water motor coupled variable proportioners utilizing FM approved move meters. Using the test return line this offers the chance to examine the proportioning fee during commissioning as well as for annual checks, with out creating any premix, which is a very huge benefit for the person and relieves the environment.
In the second part of this characteristic we are going to explore the consequences of viscosity on foam proportioning and typical foam software areas and beneficial discharge units.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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