Fire presents many challenges, not least because of the variables that decide which suppression medium is suitable for a given hearth scenario. Our goal on this two-part article is to provide guidance based on a hazard-specific strategy and help you make an knowledgeable decision on acceptable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorized as follows:
Class A – carbonaceous or combustible supplies
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires typically associated with cooking such as vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise primarily in the Class B category: flammable liquids.
Foam is taken into account to be the best fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only could not penetrate the fireplace load successfully.
Fire classes.
How do we make foam?
Finished foam solution comprises a simple recipe of froth focus, water and air. Foam concentrate is usually combined within the ratio of 1% or 3% to either 99% or 97% water.
Once the answer (premix) is created, it’s pumped to the chosen discharge gadget – we are going to cover proportioning later in this article and discharge methods in Part 2. At this point air is entrained by using units designed to naturally aspirate the answer. The quantity of aspiration and the type of focus determines the enlargement ratio. This is usually split between low, medium and excessive enlargement. Low growth is up to 20:1, medium is 200:1 and high enlargement is greater than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to broaden the froth adequately, although naturally aspirated mills are additionally used. The decision to determine on a particular growth ratio is set by the hazard under review.
Put simply, water and oil do not combine. Applying only water to Class B merchandise won’t suppress the burning vapours. This is a vital point 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 film to obtain success. Whatever method is chosen to provide that blanket or movie, the objective is similar.
Steps of froth generation Images supplied by Author / Contributor
A little of the historical past of froth growth
We can date the development of contemporary foam concentrates from the Sixties onwards. Up to that time foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the bottom component). The main disadvantage was due to limited gas tolerance, which meant it was prone to fuel pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of utilizing protein as the bottom product, artificial detergents gave foam a larger gas tolerance in addition to forming a vapour-sealing film across the floor of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s growth didn’t fully exchange using protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight fuel pick-up (mixing) and offer a good resistance to heat, outlined by the trade as ‘burn-back resistance’.
เกจวัดแรงดันน้ำ10บาร์ in the Eighties took FP to the following 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 Nineteen Eighties further added to our record 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 damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same expertise also became out there with the brand new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone ingredients to all foams, has become an environmental issue, as a result of persistence in groundwater. The industry has been introduced with a major challenge to eliminate the ‘fluoro’ element of all of the completely different foam concentrate 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 time period ‘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 altering existing inventory or reviewing new tasks. As a foam proportioner producer we should study the bodily properties of froth carefully (especially viscosity) as they influence choices on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant types are more and more important within the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant high quality of SFFF/F3 is necessary to fight the small diploma of water miscibility of the gasoline.
All foam concentrate producers will naturally promote their product as being extremely efficient. The best means of evaluating their claims is to familiarise yourself with the empirically based mostly standard 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 additionally covers recent 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 can problem foam suppliers so as to make an knowledgeable choice on one of the best foam on your needs.
Whilst EN 1568 is a superb benchmark standard, consciousness of the effects on foam efficiency from components outdoors the standard exams should be noted. For example, notably aggressive solvents can problem the firefighting effectiveness of certain foams. This may be exacerbated by totally different ambient air temperatures, the application method, fuel depth and so on. Our advice can be to know the small print of the checks and try to match them to the foam’s appropriateness in your individual hazards. We would all the time suggest consulting individual foam producers as they can usually present particular in-house fire-performance data in opposition to some of the more unusual fuels.
However, despite the froth manufacturers’ sometimes conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned nonetheless remain: 1% & 3% concentrates are the norm for producing a completed foam.
Foams in accordance with the enlargement ratio Images provided by Author / Contributor
Critical factors for fulfillment: the time and application fee matrix
Successful extinction of flammable liquid fires is determined by two converging and complementary factors: time and the speed 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 requirements.
The ‘time’ factor means that for a given dimension of fireside space it’s necessary to apply the froth for lengthy enough to realize extinction and to stop re-ignition. This is especially crucial 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 could be so long as 60 minutes for the most important tank diameters.
The application price refers to the quantity of finished foam applied per square metre. This varies according to the fuel and the foam type however is at present no much less than four.zero litres per minute per sq. metre. One of the continued developments in foam efficiency is the probability that this will be reduced, but standards often take time to recognise product growth. Anything lower than the minimal software price implies that fire control is unlikely to be achieved. This implies that firefighting sources, notably in a guide hearth assault, have to be assembled before firefighting commences and this takes time. The benefit in fitting mounted techniques is that the resources are already designed and constructed into the system for quick software.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to permit readers to make an informed decision on how finest to tackle their specific fire challenges, the next is an summary of the assorted foam proportioning methods.
Foam inductors:
Typically related to fire service deployment and restricted fixed techniques applications. This makes use of the venturi principle to create a stress drop in a small aluminium or seawater material suitable gadget with built-in focus pick-up tube. The stress drop created by the venturi attracts the foam 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 enough to be simply carried on a hearth equipment or fitted into a pipework system.
However, whilst it is thought of to be the best method, it has extreme drawbacks: (i) models are factory calibrated so any adjustments to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge gadget or a altering quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are crucial as deviations caused by pipe diameter modifications will adversely have an result on proportioning accuracy and probably forestall any proportioning; (iii) modifications in focus viscosity will undermine the ability of the venturi to draw concentrate into the downstream strains; (iv) pressure loss is high, as a lot as 35%, so responsibility pump pressures need to be high enough to permit for it, potentially adding extra cost into the system; (v) foam supply units need to be sized so as to not restrict design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to complete lifetime costs as a end result of foam focus usage, which must 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 mixture of electric and diesel pumps to supply foam concentrate right into a proportioner at a better stress than the incoming water-line pressure. The proportioner is put in into the water line and regulates the blending.
They are now related to older systems, the place disadvantages embody: (i) further prices in hardware and design time; (ii) the foam pump is often restricted to a much tighter working range, although the proportioner itself can accommodate extensive ranges in flows; (iii) the foam pump wants an additional power source, apart from water, so is not as reliably safe as a system with a potential single level of failure, such as an entirely water-driven system; (iv) typically, these methods are very complicated and trigger high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to wreck the foam concentrate and entrain air, which in turn can undermine accurate foam proportioning and foam extinguishing effectiveness.
เพรสเชอร์เกจไฮดรอลิค :
Comprised of a metal pressure vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner much like those fitted to balanced strain proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam focus could be proportioned with water utilizing the same supply. The venturi precept is once more brought into play because it creates a pressure drop on the level of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging completed foam. This will add to entire lifetime prices because of foam focus usage, which has to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot because great care is required to keep away from a broken bladder when commissioning a model new installation. It is rarely easy to work throughout the metal pressure vessel should problems occur, particularly if and when a replacement bladder may be required: it all adds to the difficulty and cost.
Compressed air foam (CAFS):
This is not a proportioning method in the conventional sense as the froth is already proportioned using one of many previous methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam resolution at the level of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces allowing better penetration and cooling. This can be a profit in wildfire conditions by coating weak structures to mitigate fire growth. The limited water provides associated with remote wildfire areas means that the useful resource can be fully optimised. However, as with balanced stress proportioner foam pumps, an additional level of failure is possible as a result of extra CAFS apparatus.
Water driven or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in its third era, the product is only mechanical and highly dependable. 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 through an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning price and can proportion the froth focus accurately across a wide operating range. The purely mechanical system offers cost-efficient and eco-friendly proportioning rate testing, fully with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The advantages of FireDos Gen III FM permitted foam proportioners include:
Reduced costs: proportioning price is tested without utilizing foam or creating premix or foam – price efficient and eco-friendly.
Improved efficiency: constant proportioning fee across a wide working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capability.
25% discount in strain loss, in comparison with older generations, through hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a special proportioning price.
FM accredited FireDos Gen III proportioners are so far the one FM accredited water motor coupled variable proportioners utilizing FM permitted circulate meters. Using the take a look at return line this offers the likelihood to verify the proportioning price throughout commissioning as well as for annual exams, without creating any premix, which is a very massive benefit for the user and relieves the surroundings.
In the second a part of this characteristic we will explore the results of viscosity on foam proportioning and typical foam software areas and really helpful discharge gadgets.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share