Fire presents many challenges, not least due to the variables that decide which suppression medium is appropriate for a given fire state of affairs. Our goal on this two-part article is to supply steering primarily based on a hazard-specific strategy and allow you to 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 materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals similar to magnesium
Class F – fires generally associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of froth proportioners and firefighting monitors, we specialise mainly within the Class B class: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for each hydrocarbons and polar solvents. In addition, certain types of foam (known as wetting agents) are specifically for deep-seated Class A fires the place water solely could not penetrate the hearth load successfully.
How do we make foam?
Finished foam resolution comprises a simple recipe of foam focus, water and air. Foam concentrate is often combined within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge device – we are going to cowl proportioning later in this article and discharge methods in Part 2. At this point air is entrained by utilizing devices designed to naturally aspirate the solution. The quantity of aspiration and the sort of focus determines the enlargement ratio. This is often split between low, medium and excessive expansion. Low expansion is as much 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 increase the froth adequately, although naturally aspirated turbines are also used. The determination to choose on a particular expansion ratio is determined by the hazard underneath evaluate.
Put simply, water and oil don’t mix. Applying solely water to Class B products is not going to 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 permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to be successful. Whatever methodology is chosen to produce that blanket or film, the target is the same.
Steps of froth technology Images supplied by Author / Contributor
A little of the history of foam growth
We can date the development of recent foam concentrates from the 1960s onwards. Up to that time foam concentrates have been comprised of animal-based protein (typically floor hoof and horn is the base component). The primary downside was because of limited gas tolerance, which meant it was susceptible to gasoline pick-up (mixing). A breakthrough came with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a higher fuel tolerance in addition to forming a vapour-sealing movie throughout the floor of the gas. Performance is additional enhanced with the formation of a foam blanket when air aspirating units are fitted.
Nevertheless, AFFF’s improvement did not completely exchange the utilization of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat fuel pick-up (mixing) and supply a good resistance to warmth, defined by the business as ‘burn-back resistance’.
Further development within the Nineteen Eighties took FP to the next degree with film-forming fluoroprotein or FFFP. We now had the best of both worlds: a film-forming foam that also had good burn-back resistance.
The 1980s additional added to our list of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented a further challenge as they were water soluble and foam damaging. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The same know-how additionally grew to become obtainable with the brand new era of AFFF-ARs.
In current years fluorine, one of many cornerstone ingredients to all foams, has turn into an environmental issue, as a result of persistence in groundwater. The industry has been presented with a major problem to get rid of the ‘fluoro’ factor of all of the totally different foam focus varieties. We have witnessed an era of manufacturers’ claims and counter claims regarding the efficacy of a complete range 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 new normal and first alternative for operators altering present inventory or reviewing new tasks. As a foam proportioner producer we should study the physical properties of froth rigorously (especially viscosity) as they influence decisions on the general proportioning solution. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are more and more important in the fuel-storage area. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content material, signifies that the alcohol-resistant quality of SFFF/F3 is necessary to fight the small diploma of water miscibility of the gas.
All foam focus manufacturers 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 standard EN 1568 or UL162. The tests cowl 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 within the test protocols. This also covers recent and seawater as nicely as gentle and forceful software of the froth. Each foam is given a rating with IA being the best, IIID the worst. This means you could problem foam suppliers in order to make an knowledgeable decision on the best foam in your needs.
Whilst EN 1568 is an excellent benchmark normal, awareness of the effects on foam performance from factors exterior the standard checks must be noted. For example, notably aggressive solvents can challenge the firefighting effectiveness of sure foams. This may be exacerbated by different ambient air temperatures, the applying methodology, gasoline depth etc. Our recommendation would be to know the major points of the checks and try to match them to the foam’s appropriateness for your particular person hazards. We would all the time recommend consulting individual foam manufacturers as they can typically provide particular in-house fire-performance information against a few of the extra uncommon fuels.
However, regardless of 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 completed foam.
Foams in accordance with the enlargement ratio Images provided by Author / Contributor
Critical elements for success: the time and application rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary factors: time and the speed at which completed foam is utilized. Both are determined by empirically based mostly requirements printed by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN requirements.
The ‘time’ factor implies that for a given dimension of fireside space it is needed to apply the froth for long enough to attain extinction and to prevent re-ignition. This is especially important in guide intervention as firefighter’s will be in danger during post-fire operations. When it involves mounted safety for hydrocarbon and polar solvent tanks, the appliance time could be so long as 60 minutes for the most important tank diameters.
The software rate refers back to the quantity of completed foam applied per sq. metre. This varies based on the gasoline and the froth sort however is at present a minimal of 4.0 litres per minute per square metre. One of the continuing developments in foam efficiency is the chance that this will be lowered, however standards typically take time to recognise product improvement. Anything less than the minimum application price means that fire management is unlikely to be achieved. This implies that firefighting sources, particularly in a handbook fireplace assault, need to be assembled before firefighting commences and this takes time. The benefit in becoming fastened methods is that the assets are already designed and built into the system for immediate application.
Principle of foam extinguishment Images provided by Author / Contributor
Foam proportioning methods: mixing water with foam focus
In order to allow readers to make an informed determination on how finest to tackle their specific fireplace challenges, the following is an overview of the various foam proportioning strategies.
Typically associated with fireplace service deployment and restricted fixed techniques applications. This makes use of the venturi precept to create a stress drop in a small aluminium or seawater material appropriate gadget with built-in concentrate 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 enough to be easily carried on a fire equipment or fitted into a pipework system.
However, whilst it is considered to be the simplest technique, it has severe drawbacks: (i) items are factory 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 amount of discharge devices) will doubtless require a system re-design; (ii) system design and sign-off are important as deviations attributable to pipe diameter modifications will adversely have an result on proportioning accuracy and potentially forestall any proportioning; (iii) modifications in concentrate viscosity will undermine the power of the venturi to attract concentrate into the downstream lines; (iv) strain loss is excessive, as a lot as 35%, so responsibility pump pressures need to be excessive enough to permit for it, doubtlessly including further cost into the system; (v) foam delivery devices need to be sized so as not to restrict design flows; (vi) testing cannot be achieved with out creating premix and discharging completed foam. This will add to entire lifetime costs because of foam concentrate usage, which must be replaced, and the disposal of premix or foam.
Types of foam agentsImages supplied by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a mixture of electric and diesel pumps to produce foam focus right into a proportioner at a better stress than the incoming water-line pressure. The proportioner is installed into the water line and regulates the blending.
They at the moment are related to older methods, the place disadvantages embody: (i) extra costs in hardware and design time; (ii) the froth pump is often restricted to a much tighter operating range, though the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump wants an extra power supply, other than water, so isn’t as reliably secure as a system with a possible single point of failure, such as a completely water-driven system; (iv) usually, these systems are very advanced and cause high efforts at the customer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates pointless agitation that has the potential to break the froth focus and entrain air, which in flip can undermine correct foam proportioning and foam extinguishing effectiveness.
Comprised of a metal stress vessel containing a versatile bladder (typically a butyl material) linked to a foam focus proportioner much like those fitted to balanced stress proportioners. The incoming pressurised water compresses the foam filled bladder in order that foam focus may be proportioned with water utilizing the identical supply. The venturi principle is again introduced into play as it creates a strain drop at the level of injection for the foam concentrate. Testing cannot be achieved with out creating premix and discharging finished foam. This will add to entire lifetime costs as a outcome of foam focus usage, which needs to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weakness as a outcome of nice care is required to avoid a broken bladder when commissioning a new set up. It isn’t easy to work within the metal stress vessel ought to issues happen, particularly if and when a alternative bladder could also be required: it all provides to the difficulty and price.
Compressed air foam (CAFS):
This is not a proportioning methodology in the standard sense as the froth is already proportioned using one of the earlier strategies. However, เกจวัดแรงดันไนโตรเจน is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the foam solution at the level of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces permitting higher penetration and cooling. This can be a profit in wildfire situations by coating weak constructions to mitigate fireplace progress. The restricted water provides related to remote wildfire areas signifies that the resource may be totally optimised. However, as with balanced strain proportioner foam pumps, an extra level of failure is feasible because of the additional CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third generation, the product is only 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 provided with foam concentrate via an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and can proportion the froth concentrate precisely throughout a wide operating vary. The purely mechanical system offers cost-efficient and eco-friendly proportioning fee testing, utterly with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM permitted foam proportioners embrace:
Reduced prices: proportioning fee is tested without utilizing foam or creating premix or foam – value efficient and eco-friendly.
Improved efficiency: fixed proportioning fee throughout a large working vary.
Optimised supply of high-viscosity foam concentrates with improved suction capacity.
25% reduction in pressure loss, compared to older generations, via hydraulic optimisation.
Improved cylinder cut-off for straightforward and quick adjustment to a special proportioning fee.
FM approved FireDos Gen III proportioners are to date the only FM permitted water motor coupled variable proportioners using FM accredited flow meters. Using the take a look at return line this provides the possibility to verify the proportioning fee throughout commissioning in addition to for annual exams, with out creating any premix, which is a really big benefit for the user and relieves the setting.
In the second a half of this function we are going to discover the results of viscosity on foam proportioning and typical foam application areas and really helpful discharge units.
For more info, go to www.firedos.com