Fire presents many challenges, not least because of the variables that determine which suppression medium is acceptable for a given hearth scenario. Our goal in this two-part article is to provide guidance based on a hazard-specific strategy and assist you to make an knowledgeable determination on appropriate fire-suppression measures, especially 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 typically associated with cooking corresponding to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting monitors, we specialise primarily within the Class B category: flammable liquids.
Foam is considered to be the most effective fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water solely could not penetrate the fire load successfully.
Fire lessons.
How will we make foam?
Finished foam resolution contains a simple recipe of foam focus, water and air. Foam concentrate is often blended in 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 gadget – we will cover proportioning later on this article and discharge strategies in Part 2. At this point air is entrained by using units designed to naturally aspirate the answer. The amount of aspiration and the sort of focus determines the enlargement ratio. This is usually split between low, medium and high expansion. Low growth is as a lot as 20:1, medium is 200:1 and excessive expansion is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to expand the foam adequately, although naturally aspirated mills are also used. The determination to choose on a selected enlargement ratio is set by the hazard under evaluate.
Put merely, water and oil do not combine. Applying solely water to Class B products is not going to suppress the burning vapours. This is a crucial level to make as it’s the vapours, not the liquid itself, that burns. We need a medium that permits 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 the same.
Steps of froth technology Images provided by Author / Contributor
A little of the history of froth growth
We can date the development of recent foam concentrates from the 1960s onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The primary 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 base product, synthetic detergents gave foam a greater gasoline tolerance as well as forming a vapour-sealing film throughout the surface of the gasoline. Performance is additional enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth didn’t utterly exchange the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat fuel pick-up (mixing) and offer a good resistance to heat, defined by the trade as ‘burn-back resistance’.
Further development within the Eighties took FP to the subsequent degree with film-forming fluoroprotein or FFFP. We now had one of the best of both worlds: a film-forming foam that also had good burn-back resistance.
The 1980s further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time presented a further challenge as they were 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 turned out there with the brand new generation of AFFF-ARs.
In latest years fluorine, one of the cornerstone elements to all foams, has become an environmental issue, as a result of persistence in groundwater. The industry has been presented with a major challenge to get rid of the ‘fluoro’ element of all of the totally different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of a complete vary of newly formulated fluorine-free foam. The term ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to outline these foams, which have turn out to be the brand new normal and first selection for operators changing existing inventory or reviewing new tasks. As a foam proportioner manufacturer we must look at the physical properties of foam fastidiously (especially viscosity) as they affect selections on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are more and more important in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, means that the alcohol-resistant quality of SFFF/F3 is important to combat the small degree of water miscibility of the gas.
All foam concentrate manufacturers will naturally promote their product as being extremely efficient. The greatest means of evaluating their claims is to familiarise your self with the empirically primarily based commonplace 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 within the check protocols. This additionally covers recent and seawater as well as mild and forceful software of the froth. Each foam is given a ranking with IA being the most effective, IIID the worst. This means you could challenge foam suppliers in order to make an informed determination on the best foam in your needs.
Whilst EN 1568 is a wonderful benchmark normal, consciousness of the effects on foam efficiency from factors outdoors the standard exams must be famous. For example, significantly aggressive solvents can problem the firefighting effectiveness of sure foams. This can be exacerbated by different ambient air temperatures, the appliance technique, gasoline depth etc. Our recommendation can be to know the main points of the checks and try to match them to the foam’s appropriateness in your particular person hazards. We would at all times recommend consulting particular person foam producers as they’ll often provide particular in-house fire-performance knowledge in opposition to a few of the more uncommon fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on performance, the sooner fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a completed foam.
Foams according to the expansion ratio Images equipped by Author / Contributor
Critical elements for success: 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 mostly standards published by our bodies such as the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ issue implies that for a given dimension of fireside area it is needed to use the foam for long sufficient to attain extinction and to forestall re-ignition. This is especially crucial in guide intervention as firefighter’s might be at risk during post-fire operations. When it involves mounted safety for hydrocarbon and polar solvent tanks, the appliance time may be so long as 60 minutes for the largest tank diameters.
The software rate refers back to the amount of finished foam applied per square metre. This varies according to the gasoline and the froth type however is currently no much less than 4.zero litres per minute per square metre. One of the continued developments in foam performance is the probability that this will be lowered, however standards often take time to recognise product improvement. Anything less than the minimum utility fee implies that fire management is unlikely to be achieved. This means that firefighting assets, notably in a manual fireplace assault, have to be assembled before firefighting commences and this takes time. The advantage in becoming mounted methods is that the sources are already designed and built into the system for immediate utility.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an informed choice on how finest to tackle their explicit fireplace challenges, the following is an summary of the assorted foam proportioning methods.
Foam inductors:
Typically related to hearth service deployment and limited fixed techniques applications. This uses the venturi principle to create a stress drop in a small aluminium or seawater materials suitable device with built-in concentrate pick-up tube. The pressure drop created by the venturi attracts the foam 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 into a pipework system.
However, whilst it’s thought-about to be the best technique, it has extreme drawbacks: (i) models are factory calibrated so any changes to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge system or a altering quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter modifications will adversely have an effect on proportioning accuracy and probably prevent any proportioning; (iii) modifications in focus viscosity will undermine the flexibility of the venturi to attract focus into the downstream lines; (iv) stress loss is high, as a lot as 35%, so duty pump pressures have to be excessive enough to permit for it, probably adding further cost into the system; (v) foam supply devices must be sized so as to not restrict design flows; (vi) testing can’t be achieved without creating premix and discharging completed foam. This will add to entire lifetime costs on account of foam concentrate usage, which has to be replaced, and the disposal of premix or foam.
Types of froth agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electric or a mixture of electric and diesel pumps to produce foam focus right into a proportioner at a better strain than the incoming water-line strain. The proportioner is installed into the water line and regulates the mixing.
They at the moment are associated with older techniques, where disadvantages embody: (i) additional costs in hardware and design time; (ii) the froth pump is normally restricted to a a lot tighter working vary, though the proportioner itself can accommodate broad ranges in flows; (iii) the froth pump needs an extra power supply, other than water, so 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 systems are very complex and cause excessive 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 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 stress vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner much like the ones fitted to balanced strain proportioners. The incoming pressurised water compresses the froth stuffed bladder so that foam focus can be proportioned with water using the same supply. The venturi principle is once more brought into play because it creates a stress drop at the point of injection for the foam focus. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs because of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
However, weksler ea14 is seen as a weak point because nice care is required to keep away from a broken bladder when commissioning a model new installation. It isn’t simple to work inside the steel stress vessel ought to problems occur, particularly if and when a substitute bladder may be required: all of it provides to the problem and cost.
Compressed air foam (CAFS):
This isn’t a proportioning method within the conventional sense as the froth is already proportioned using one of many earlier methods. However, pressurised air is then added forcefully quite than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth answer at the point of discharge. The consensus view is that CAFS enhances the completed foam’s ability to cling to vertical surfaces permitting higher penetration and cooling. This can be a profit in wildfire situations by coating susceptible structures to mitigate fire growth. The restricted water supplies associated with remote wildfire areas implies that the resource could be totally optimised. However, as with balanced pressure proportioner foam pumps, a further point of failure is possible due to the extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is purely mechanical and highly reliable. A water-driven rotor provides the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is equipped with foam focus by way of an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing unit set to the required proportioning price and can proportion the froth concentrate precisely throughout a wide operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate testing, fully without using 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 price is tested with out utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved performance: constant proportioning price across a wide operating range.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% discount in strain loss, in comparison with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a different proportioning fee.
FM permitted FireDos Gen III proportioners are to date the one FM permitted water motor coupled variable proportioners using FM permitted circulate meters. Using the check return line this provides the possibility to examine the proportioning rate during commissioning in addition to for annual tests, without creating any premix, which is a very huge profit for the consumer and relieves the environment.
In the second part of this function we’ll explore the consequences of viscosity on foam proportioning and typical foam application areas and beneficial discharge devices.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share