Fire presents many challenges, not least due to the variables that determine which suppression medium is acceptable 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 assist you to make an knowledgeable decision on applicable 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 supplies
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 displays, we specialise mainly 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 kinds of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water solely could not penetrate the hearth load effectively.
Fire courses.
How will we make foam?
Finished foam answer contains a easy recipe of foam focus, water and air. Foam focus is typically combined within the ratio of 1% or 3% to both 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge device – we are going to cover proportioning later in this article and discharge methods in Part 2. At this level air is entrained by using gadgets designed to naturally aspirate the answer. The amount of aspiration and the kind of focus determines the expansion ratio. This is typically break up between low, medium and excessive growth. Low enlargement is as a lot as 20:1, medium is 200:1 and high enlargement is more than 200:1. Only high-expansion foam might have the addition of a water-driven generator fan to expand the froth adequately, although naturally aspirated generators are additionally used. The decision to decide on a particular growth ratio is decided by the hazard underneath evaluation.
Put simply, water and oil do not mix. Applying only water to Class B products won’t suppress the burning vapours. This is a vital level to make as it is the vapours, not the liquid itself, that burns. We need a medium that allows 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 film, the target is identical.
Steps of foam generation Images equipped by Author / Contributor
A little of the history of froth improvement
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 floor hoof and horn is the base component). The major drawback was because of restricted gasoline tolerance, which meant it was prone to gas pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, artificial detergents gave foam a larger fuel tolerance as nicely as forming a vapour-sealing movie across the floor of the gas. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s growth did not fully substitute the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam may both combat fuel pick-up (mixing) and supply a great resistance to warmth, defined by the trade as ‘burn-back resistance’.
Further improvement in the Eighties took FP to the subsequent degree with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that also had good burn-back resistance.
The 1980s additional added to our listing of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had all the time introduced an extra challenge as they have been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The similar know-how also became available with the new technology of AFFF-ARs.
In current years fluorine, one of many cornerstone ingredients to all foams, has turn out to be an environmental problem, as a outcome of persistence in groundwater. The industry has been presented with a serious problem to remove the ‘fluoro’ factor of all of the totally different foam focus types. We have witnessed an era of manufacturers’ claims and counter claims concerning 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 into the new regular and first alternative for operators altering existing inventory or reviewing new initiatives. As a foam proportioner producer we must look at the physical properties of foam carefully (especially viscosity) as they influence selections on the general proportioning resolution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are more and more necessary in the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, means that the alcohol-resistant quality of SFFF/F3 is critical to fight the small degree of water miscibility of the gasoline.
All foam concentrate manufacturers will naturally promote their product as being highly effective. The best means of evaluating their claims is to familiarise your self with the empirically based mostly normal EN 1568 or UL162. The exams cover extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are both included in the check protocols. This also covers fresh and seawater in addition to mild and forceful utility of the foam. Each foam is given a ranking with IA being one of the best, IIID the worst. This means that you could challenge foam suppliers to find a way to make an knowledgeable decision on one of the best foam for your needs.
Whilst EN 1568 is a superb benchmark standard, awareness of the results on foam efficiency from elements outside the standard exams must be famous. For instance, particularly aggressive solvents can problem the firefighting effectiveness of certain foams. This can be exacerbated by totally different ambient air temperatures, the applying technique, gasoline depth and so forth. Our recommendation could be to know the major points of the tests and attempt to match them to the foam’s appropriateness on your particular person hazards. We would always suggest consulting particular person foam manufacturers as they will typically present particular in-house fire-performance information against a variety of the extra uncommon fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on efficiency, the sooner fundamentals of how foam is proportioned nonetheless 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 success: the time and application rate matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary factors: time and the speed at which completed foam is applied. Both are decided by empirically based requirements revealed by bodies such as the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given size of fireside area it is necessary to use the foam for lengthy enough to attain extinction and to forestall re-ignition. This is particularly crucial in guide intervention as firefighter’s will be at risk throughout post-fire operations. When it involves fixed protection for hydrocarbon and polar solvent tanks, the appliance time can be so lengthy as 60 minutes for the most important tank diameters.
The application price refers to the amount of finished foam applied per sq. metre. This varies according to the gasoline and the foam type however is presently at least 4.zero litres per minute per square metre. One of the continuing developments in foam efficiency is the probability that this will be decreased, however requirements often take time to recognise product growth. Anything lower than the minimum software rate implies that hearth management is unlikely to be achieved. This means that firefighting resources, significantly in a manual fireplace attack, need to be assembled earlier than firefighting commences and this takes time. The benefit in becoming fastened techniques is that the resources are already designed and constructed into the system for quick 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 decision on how best to deal with their explicit fireplace challenges, the following is an overview of the various foam proportioning strategies.
Foam inductors:
Typically associated with hearth service deployment and limited mounted systems functions. This makes use of the venturi precept to create a strain drop in a small aluminium or seawater materials appropriate gadget with built-in concentrate pick-up tube. The strain drop created by the venturi attracts the froth focus from a container the place it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a hearth equipment or fitted right into a pipework system.
However, whilst it’s thought of to be the only methodology, it has extreme drawbacks: (i) units are manufacturing facility calibrated so any changes 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 doubtless require a system re-design; (ii) system design and sign-off are crucial as deviations attributable to pipe diameter changes will adversely affect proportioning accuracy and probably forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the ability of the venturi to attract concentrate into the downstream traces; (iv) stress loss is high, as a lot as 35%, so obligation pump pressures must be excessive enough to allow for it, doubtlessly adding extra value into the system; (v) foam delivery devices have to be sized in order to not restrict design flows; (vi) testing cannot be achieved with out creating premix and discharging finished foam. This will add to whole lifetime prices as a outcome of foam focus usage, which has to be changed, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electric or a mix of electrical and diesel pumps to produce foam concentrate right into a proportioner at the next strain than the incoming water-line pressure. The proportioner is put in into the water line and regulates the mixing.
pressure gauge octa are actually related to older techniques, where disadvantages include: (i) extra prices in hardware and design time; (ii) the froth pump is normally restricted to a much tighter operating range, though the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump needs an extra energy source, other than water, so isn’t as reliably secure as a system with a possible single level of failure, corresponding to a completely water-driven system; (iv) typically, these systems are very complicated and trigger 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 wreck the froth concentrate and entrain air, which in flip can undermine correct 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 concentrate proportioner much like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam stuffed bladder in order that foam focus can be proportioned with water using the identical supply. The venturi precept is once more introduced into play because it creates a pressure drop at the point of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime prices on account of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot because nice care is required to keep away from a broken bladder when commissioning a new set up. It isn’t easy to work throughout the steel strain vessel should problems happen, especially if and when a substitute bladder could also be required: all of it provides to the issue and price.
Compressed air foam (CAFS):
This just isn’t a proportioning method in the standard sense as the foam is already proportioned utilizing one of the previous strategies. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth solution on 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 is also a benefit in wildfire conditions by coating weak structures to mitigate hearth progress. The limited water supplies related to distant wildfire areas implies that the resource could be absolutely optimised. However, as with balanced stress proportioner foam pumps, a further level of failure is feasible due to the further CAFS equipment.
Water driven or turbine foam proportioners:
FireDos have turn into 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 supplies the driving force to drive a immediately coupled positive-displacement plunger or piston pump. This is supplied with foam focus via an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and can proportion the froth concentrate precisely across a large operating range. The purely mechanical system offers 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 supplied by Author / Contributor
The advantages of FireDos Gen III FM approved foam proportioners embody:
Reduced prices: proportioning fee is examined without using foam or creating premix or foam – value effective and eco-friendly.
Improved performance: fixed proportioning price throughout a wide working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% reduction in stress loss, in comparability with older generations, via hydraulic optimisation.
Improved cylinder cut-off for simple and quick adjustment to a different proportioning price.
FM accredited FireDos Gen III proportioners are so far the only FM accredited water motor coupled variable proportioners using FM permitted flow meters. Using the test return line this offers the chance to verify the proportioning price during commissioning as properly as for annual checks, without creating any premix, which is a very massive benefit for the person and relieves the surroundings.
In the second part of this characteristic we’ll explore the results of viscosity on foam proportioning and typical foam application areas and really helpful discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share