Fire presents many challenges, not least because of the variables that decide which suppression medium is appropriate for a given hearth scenario. Our goal on this two-part article is to provide steering primarily based on a hazard-specific method and allow you to make an knowledgeable choice on applicable fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are classified 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 generally related to cooking such as vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting screens, we specialise primarily in the Class B class: flammable liquids.
Foam is considered to be the most effective fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, sure forms of foam (known as wetting agents) are particularly for deep-seated Class A fires the place water only may not penetrate the fireplace load effectively.
Fire courses.
How will we make foam?
Finished foam resolution comprises a easy recipe of froth concentrate, water and air. Foam focus is often combined within the ratio of 1% or 3% to both 99% or 97% water.
Once the solution (premix) is created, it’s pumped to the chosen discharge device – we will cover proportioning later in this article and discharge strategies in Part 2. At this level air is entrained by utilizing gadgets designed to naturally aspirate the answer. The quantity of aspiration and the kind of concentrate determines the enlargement ratio. This is often break up between low, medium and excessive expansion. Low enlargement is up to 20:1, medium is 200:1 and excessive growth is greater than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the foam adequately, though naturally aspirated generators are additionally used. The decision to choose a particular growth ratio is set by the hazard beneath evaluation.
Put simply, water and oil don’t mix. Applying solely water to Class B merchandise 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 want a medium that enables for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to obtain success. Whatever technique is chosen to produce that blanket or film, the objective is similar.
Steps of foam generation Images supplied by Author / Contributor
A little of the historical past of froth development
We can date the development of modern foam concentrates from the 1960s onwards. Up to that point foam concentrates have been comprised of animal-based protein (typically ground hoof and horn is the base component). The main downside was due to limited gasoline tolerance, which meant it was vulnerable to gasoline pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, artificial detergents gave foam a greater gas tolerance as nicely as forming a vapour-sealing film throughout the floor of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s development didn’t fully exchange the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam may both fight fuel pick-up (mixing) and provide an excellent resistance to heat, outlined by the business as ‘burn-back resistance’.
Further growth within the 1980s took FP to the following stage with film-forming fluoroprotein or FFFP. We now had the best of both 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 offered a further problem as they had been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the froth blanket from early destruction. The same expertise additionally grew to become available with the model new generation of AFFF-ARs.
In recent years fluorine, one of many cornerstone elements to all foams, has turn into an environmental problem, due to persistence in groundwater. The industry has been offered with a major challenge to eliminate the ‘fluoro’ component of all of the totally different foam concentrate sorts. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a whole 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 out to be the new regular and first choice for operators changing present inventory or reviewing new tasks. As a foam proportioner manufacturer we must examine the bodily properties of foam carefully (especially viscosity) as they influence decisions on the general proportioning resolution. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are increasingly necessary in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small diploma of water miscibility of the gasoline.
All foam concentrate producers will naturally promote their product as being extremely efficient. The greatest way of evaluating their claims is to familiarise your self with the empirically primarily based normal EN 1568 or UL162. The tests cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are each included in the take a look at protocols. This also covers contemporary and seawater as nicely as gentle and forceful application of the foam. Each foam is given a rating with IA being one of the best, IIID the worst. This means that you can challenge foam suppliers so as to make an informed choice on one of the best foam on your wants.
Whilst EN 1568 is a wonderful benchmark commonplace, awareness of the results on foam efficiency from elements exterior the standard exams ought to be noted. For example, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by totally different ambient air temperatures, the application methodology, gas depth and so forth. Our advice could be to grasp the details of the exams and attempt to match them to the foam’s appropriateness for your particular person hazards. We would at all times suggest consulting individual foam manufacturers as they’ll typically provide particular in-house fire-performance knowledge against a variety of the extra uncommon fuels.
However, regardless of the foam manufacturers’ typically conflicting claims on performance, 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 enlargement ratio Images provided by Author / Contributor
Critical components for fulfillment: the time and utility fee matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the rate at which finished foam is applied. Both are determined by empirically based mostly standards revealed by bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN standards.
The ‘time’ factor means that for a given measurement of fireside area it’s needed to use the foam for long enough to achieve extinction and to stop re-ignition. This is particularly important in handbook intervention as firefighter’s will be at risk during post-fire operations. When it comes to fastened protection for hydrocarbon and polar solvent tanks, the application time may be as lengthy as 60 minutes for the biggest tank diameters.
The application fee refers back to the quantity of finished foam utilized per sq. metre. This varies based on the fuel and the foam sort however is currently at least four.0 litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the likelihood that this shall be reduced, however standards usually take time to recognise product development. Anything less than the minimum application rate signifies that hearth control is unlikely to be achieved. This signifies that firefighting sources, notably in a guide fireplace attack, have to be assembled earlier than firefighting commences and this takes time. The benefit in fitting fixed techniques is that the sources are already designed and built into the system for immediate application.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning strategies: mixing water with foam focus
In order to allow readers to make an knowledgeable decision on how greatest to sort out their explicit hearth challenges, the following is an summary of the various foam proportioning strategies.
Foam inductors:
Typically related to fireplace service deployment and limited mounted techniques functions. This uses the venturi principle to create a stress drop in a small aluminium or seawater materials suitable gadget with built-in concentrate pick-up tube. The strain drop created by the venturi draws the foam focus from a container where it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a fireplace appliance or fitted right into a pipework system.
However, whilst it is considered to be the simplest methodology, it has severe drawbacks: (i) items are manufacturing facility calibrated so any changes to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge system or a changing quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are important as deviations brought on by pipe diameter changes will adversely affect proportioning accuracy and doubtlessly stop any proportioning; (iii) adjustments in focus viscosity will undermine the power of the venturi to attract concentrate into the downstream lines; (iv) stress loss is high, as a lot as 35%, so responsibility pump pressures must be high enough to permit for it, doubtlessly including extra price into the system; (v) foam delivery devices have to be sized in order not to prohibit design flows; (vi) testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs on account of foam concentrate utilization, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages provided by Author / Contributor
Balanced stress proportioners:
These use an electrical or a mix of electrical and diesel pumps to produce foam focus 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.
They are now associated with older systems, where disadvantages include: (i) extra 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 broad ranges in flows; (iii) the froth pump needs a further power supply, other than water, so just isn’t as reliably secure as a system with a possible single point of failure, such as a wholly water-driven system; (iv) sometimes, these systems are very advanced and cause excessive efforts on 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 focus and entrain air, which in turn can undermine correct foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel strain vessel containing a flexible bladder (typically a butyl material) linked to a foam concentrate proportioner similar to those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam concentrate can be proportioned with water using the same provide. The venturi principle is once more introduced into play as it creates a stress drop on the level of injection for the foam focus. Testing cannot be achieved without creating premix and discharging completed foam. This will add to whole lifetime costs because of foam focus utilization, which must be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a end result of nice care is needed to avoid a broken bladder when commissioning a brand new set up. It is never straightforward to work throughout the steel strain vessel should problems happen, particularly if and when a substitute bladder may be required: it all provides to the difficulty and price.
Compressed air foam (CAFS):
This just isn’t a proportioning methodology in the typical sense as the foam is already proportioned using one of many earlier methods. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the identify suggests, CAFS injects compressed air into the froth solution on the level 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 buildings to mitigate fireplace development. The limited water supplies associated with remote wildfire areas implies that the useful resource can be totally optimised. However, as with balanced stress proportioner foam pumps, an extra point of failure is feasible because of the further CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their distinctive water-driven foam proportioner. Now in its third technology, the product is solely mechanical and highly dependable. A water-driven rotor supplies the motive force to drive a instantly coupled positive-displacement plunger or piston pump. This is equipped with foam concentrate through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is factory set to the required proportioning rate and will proportion the froth focus precisely throughout a large working range. The purely mechanical system offers cost-efficient and eco-friendly proportioning price testing, fully with out using any foam focus or creating premix or firefighting foam.
เกจวัดแรงดันออกซิเจนราคา . Images equipped by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embrace:
Reduced costs: proportioning price is examined without utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: fixed proportioning fee throughout a wide operating vary.
เกจวัดแรงดันแก๊สอาร์กอน of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, compared to older generations, through hydraulic optimisation.
Improved cylinder cut-off for simple and fast adjustment to a unique proportioning rate.
FM accredited FireDos Gen III proportioners are thus far the one FM permitted water motor coupled variable proportioners utilizing FM approved flow meters. Using the check return line this presents the possibility to check the proportioning fee throughout commissioning as well as for annual checks, without creating any premix, which is a very massive profit for the person and relieves the environment.
In the second a half of this characteristic we will discover the consequences of viscosity on foam proportioning and typical foam utility areas and beneficial discharge units.
For more info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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