Fire presents many challenges, not least due to the variables that determine which suppression medium is suitable for a given fire situation. Our goal in this two-part article is to supply steering primarily based on a hazard-specific method and allow you to make an knowledgeable choice on applicable fire-suppression measures, particularly 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 such as magnesium
Class F – fires generally associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a manufacturer of foam proportioners and firefighting monitors, we specialise mainly in 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, sure forms of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only could not penetrate the fireplace load effectively.
Fire classes.
How will we make foam?
Finished foam resolution includes a easy recipe of foam concentrate, water and air. Foam concentrate is usually combined in the ratio of 1% or 3% to both 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 strategies in Part 2. At this level air is entrained through the use of units designed to naturally aspirate the solution. The quantity of aspiration and the kind of focus determines the growth ratio. This is often cut up between low, medium and excessive expansion. Low growth is up to 20:1, medium is 200:1 and high expansion is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the froth adequately, though naturally aspirated mills are additionally used. The determination to decide on a specific growth ratio is determined by the hazard underneath evaluate.
Put simply, water and oil do not combine. Applying solely water to Class B products won’t suppress the burning vapours. This is an important point to make as it’s the vapours, not the liquid itself, that burns. We want a medium that allows for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to achieve success. Whatever methodology is chosen to produce that blanket or film, the objective is identical.
Steps of foam technology Images provided by Author / Contributor
A little of the history of froth growth
We can date the event 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 base component). The main drawback was due to limited fuel 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 utilizing protein as the bottom product, synthetic detergents gave foam a larger fuel tolerance as nicely as forming a vapour-sealing movie across the floor of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating devices are fitted.
Nevertheless, AFFF’s improvement didn’t utterly substitute the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might each fight gas pick-up (mixing) and supply a good resistance to warmth, defined by the business as ‘burn-back resistance’.
Further growth within the Nineteen Eighties took FP to the following level with film-forming fluoroprotein or FFFP. เกจ์วัดแรงดันแก๊ส had the most effective of each worlds: a film-forming foam that additionally had good burn-back resistance.
The 1980s additional added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times introduced a further challenge as they have been water soluble and foam destructive. 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 new era of AFFF-ARs.
In latest years fluorine, one of the cornerstone ingredients to all foams, has turn into an environmental problem, due to persistence in groundwater. The trade has been presented with a significant challenge to eliminate the ‘fluoro’ component of all of the completely different foam concentrate types. We have witnessed an period of manufacturers’ claims and counter claims regarding the efficacy of an entire 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 new normal and first alternative for operators altering present stock or reviewing new projects. As a foam proportioner producer we must study the bodily properties of froth rigorously (especially viscosity) as they affect selections on the overall proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant sorts are increasingly essential within the fuel-storage enviornment. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, implies that the alcohol-resistant quality of SFFF/F3 is necessary to combat the small diploma of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being highly efficient. The greatest means of comparing their claims is to familiarise yourself with the empirically based mostly 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 more demanding polar solvents are each included within the take a look at protocols. This additionally covers fresh and seawater as nicely as mild and forceful utility of the froth. Each foam is given a ranking 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 in your wants.
Whilst EN 1568 is a wonderful benchmark standard, consciousness of the effects on foam efficiency from elements outside the usual checks ought to be famous. For example, notably aggressive solvents can problem the firefighting effectiveness of sure foams. This could be exacerbated by completely different ambient air temperatures, the appliance technique, gasoline depth and so forth. Our recommendation could be to know the details of the exams and attempt to match them to the foam’s appropriateness for your individual hazards. We would all the time recommend consulting individual foam producers as they’ll usually provide particular in-house fire-performance data in opposition to a few of the more uncommon fuels.
However, regardless of the froth manufacturers’ sometimes conflicting claims on efficiency, the earlier fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the enlargement ratio Images supplied by Author / Contributor
Critical factors for fulfillment: the time and utility rate matrix
Successful extinction of flammable liquid fires is dependent upon two converging and complementary elements: time and the speed at which finished foam is applied. Both are decided by empirically primarily based requirements printed by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ issue means that for a given measurement of fireside area it’s essential to use the froth for long sufficient to achieve extinction and to prevent re-ignition. This is very critical 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 so long as 60 minutes for the biggest tank diameters.
The application rate refers to the quantity of completed foam applied per square metre. This varies according to the gas and the foam sort but is currently at least 4.zero litres per minute per sq. metre. One of the ongoing developments in foam efficiency is the chance that this shall be lowered, but standards usually take time to recognise product improvement. Anything lower than the minimal software fee means that fireplace management is unlikely to be achieved. This means that firefighting assets, notably in a guide fire attack, must be assembled before firefighting commences and this takes time. The benefit in becoming fastened methods is that the resources are already designed and constructed into the system for immediate application.
Principle of foam extinguishment Images equipped 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 particular hearth challenges, the next is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically related to hearth service deployment and restricted mounted methods purposes. This uses the venturi principle to create a strain drop in a small aluminium or seawater material appropriate device with built-in focus pick-up tube. The stress drop created by the venturi draws the foam concentrate from a container where it mixes with water to create foam solution. Both the pick-up tube and physique of the inductor are compact enough to be easily carried on a hearth equipment or fitted right into a pipework system.
However, while it is thought-about to be the only method, it has extreme drawbacks: (i) items are manufacturing facility calibrated so any modifications to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device 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 adjustments will adversely affect proportioning accuracy and probably stop any proportioning; (iii) changes in focus viscosity will undermine the flexibility of the venturi to attract focus into the downstream traces; (iv) stress loss is high, as a lot as 35%, so obligation pump pressures must be high sufficient to allow for it, probably including additional price into the system; (v) foam supply devices need to be sized in order not to prohibit design flows; (vi) testing cannot be achieved without creating premix and discharging finished foam. This will add to entire lifetime prices on account of foam focus utilization, which needs to be replaced, and the disposal of premix or foam.
Types of froth agentsImages provided by Author / Contributor
Balanced pressure proportioners:
These use an electrical or a mixture of electric and diesel pumps to provide foam focus into a proportioner at the next pressure 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, where disadvantages embrace: (i) further costs in hardware and design time; (ii) the foam pump is often restricted to a much tighter working vary, although the proportioner itself can accommodate wide ranges in flows; (iii) the foam pump needs a further power source, aside from water, so isn’t as reliably safe as a system with a potential single level of failure, similar to a completely water-driven system; (iv) usually, these methods are very advanced and cause 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 froth concentrate and entrain air, which in flip can undermine accurate 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 just like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the froth filled bladder so that foam focus can be proportioned with water utilizing the identical provide. The venturi precept is once more brought into play as it creates a stress drop on the point of injection for the foam concentrate. Testing can’t be achieved with out creating premix and discharging completed foam. This will add to complete lifetime prices as a end result of foam focus utilization, which needs to be changed, 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 isn’t simple to work throughout the metal pressure vessel ought to problems happen, especially if and when a substitute bladder may be required: all of it provides to the issue and price.
Compressed air foam (CAFS):
This just isn’t a proportioning method within the conventional sense as the foam is already proportioned using one of many previous strategies. However, pressurised air is then added forcefully somewhat than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the foam answer at the level of discharge. The consensus view is that CAFS enhances the completed foam’s capability to cling to vertical surfaces permitting better penetration and cooling. This can also be a benefit in wildfire conditions by coating susceptible constructions to mitigate hearth growth. The limited water supplies associated with remote wildfire areas means that the useful resource can be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an additional point of failure is feasible because of the additional CAFS equipment.
Water pushed or turbine foam proportioners:
FireDos have turn out to be synonymous with their unique water-driven foam proportioner. Now in its third generation, the product is only mechanical and highly dependable. A water-driven rotor supplies the driving force to drive a directly coupled positive-displacement plunger or piston pump. This is provided with foam focus through an atmospheric foam tank adjacent to the FireDos unit. The proportioning pump is manufacturing facility set to the required proportioning fee and will proportion the foam focus precisely throughout a wide operating range. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, fully with out using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images supplied by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embrace:
Reduced prices: proportioning fee is tested with out using foam or creating premix or foam – price effective and eco-friendly.
Improved performance: fixed proportioning rate across a wide working vary.
Optimised delivery of high-viscosity foam concentrates with improved suction capacity.
25% discount in stress loss, in comparability with older generations, via hydraulic optimisation.
Improved cylinder cut-off for easy and quick adjustment to a different proportioning rate.
FM permitted FireDos Gen III proportioners are to date the one FM approved water motor coupled variable proportioners utilizing FM permitted circulate meters. Using the check return line this provides the chance to examine the proportioning price throughout commissioning in addition to for annual checks, without creating any premix, which is a really huge benefit for the user and relieves the environment.
In the second part of this function we will explore the effects of viscosity on foam proportioning and typical foam utility areas and beneficial discharge gadgets.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share