A information to foam and foam proportioning gear – Part 1

Fire presents many challenges, not least because of the variables that determine which suppression medium is acceptable for a given hearth scenario. Our objective in this two-part article is to provide guidance based mostly on a hazard-specific method and allow you to make an informed determination on acceptable fire-suppression measures, particularly with regard to the processing and storage of flammable liquids.
Fire hazards are classified 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 corresponding to vegetable oils
Class E – electrical hazards.
As a producer of foam proportioners and firefighting screens, we specialise primarily within the Class B category: flammable liquids.
Foam is considered to be the best fire-extinguishing medium for both 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 could not penetrate the fireplace load effectively.
Fire lessons.
How can we make foam?
Finished foam solution comprises a simple recipe of froth focus, water and air. Foam concentrate is often mixed in the ratio of 1% or 3% to both 99% or 97% water.
Once pressure gauge trerice ราคา (premix) is created, it is pumped to the chosen discharge device – we are going to cover proportioning later on 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 sort of focus determines the enlargement ratio. This is typically cut up between low, medium and excessive growth. Low enlargement is as much as 20:1, medium is 200:1 and high growth is more than 200:1. Only high-expansion foam may have the addition of a water-driven generator fan to expand the foam adequately, though naturally aspirated generators are also used. The choice to determine on a selected growth ratio is determined by the hazard under review.
Put simply, water and oil don’t mix. Applying only water to Class B merchandise won’t suppress the burning vapours. This is an important 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 methodology is chosen to provide that blanket or film, the objective is the same.
Steps of froth era Images equipped by Author / Contributor
A little of the history of froth growth
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 bottom component). The primary downside was because of limited gas tolerance, which meant it was prone 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 gas tolerance as properly as forming a vapour-sealing film 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 development did not completely exchange the use of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both combat gasoline pick-up (mixing) and provide an excellent resistance to heat, defined by the business as ‘burn-back resistance’.
Further development within the Nineteen Eighties took FP to the subsequent stage with film-forming fluoroprotein or FFFP. We now had one of the best of each 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 all the time introduced an extra 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 similar technology also became available with the new generation of AFFF-ARs.
In latest years fluorine, one of the cornerstone elements to all foams, has turn out to be an environmental problem, because of persistence in groundwater. The industry has been introduced with a significant problem to eliminate the ‘fluoro’ component of all the totally different foam focus sorts. We have witnessed an era of manufacturers’ claims and counter claims regarding 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 turn into the new regular and first choice for operators changing present stock or reviewing new tasks. As a foam proportioner manufacturer we must study the physical properties of foam carefully (especially viscosity) as they affect choices on the general proportioning answer. More of this later.
Multi-purpose foams such because the F3 alcohol-resistant types are more and more important within 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 necessary to fight the small degree of water miscibility of the gasoline.
All foam concentrate producers will naturally promote their product as being highly effective. The best method of evaluating their claims is to familiarise yourself with the empirically primarily based commonplace EN 1568 or UL162. The exams cowl extinction time, foam stability (via drainage time tests) and post-fire safety (burn-back test). Hydrocarbons and the extra demanding polar solvents are each included in the test protocols. This also covers contemporary and seawater in addition to light and forceful application of the froth. Each foam is given a ranking with IA being one of the best, IIID the worst. This means that you can problem foam suppliers in order to make an informed determination on the most effective foam on your needs.
Whilst EN 1568 is a superb benchmark normal, consciousness of the consequences on foam efficiency from components exterior the usual checks should be famous. For example, particularly aggressive solvents can challenge the firefighting effectiveness of certain foams. This may be exacerbated by completely different ambient air temperatures, the application method, gas depth etc. Our recommendation could be to know the details of the tests and attempt to match them to the foam’s appropriateness in your individual hazards. We would always suggest consulting particular person foam producers as they can typically present particular in-house fire-performance knowledge in opposition to a variety of the more uncommon fuels.
However, regardless of the froth manufacturers’ generally conflicting claims on performance, the sooner fundamentals of how foam is proportioned still remain: 1% & 3% concentrates are the norm for producing a finished foam.
Foams in accordance with the expansion ratio Images equipped by Author / Contributor
Critical elements for achievement: the time and software 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 determined by empirically based standards revealed by bodies such because the National Fire Protection Association (NFPA) in the United States and in Europe by the EN standards.
The ‘time’ factor implies that for a given measurement of fireplace space it is necessary to use the froth for long sufficient to achieve extinction and to forestall re-ignition. This is especially crucial in handbook intervention as firefighter’s will be in danger throughout post-fire operations. When it involves fixed protection for hydrocarbon and polar solvent tanks, the application time can be so long as 60 minutes for the largest tank diameters.
The application fee refers back to the quantity of completed foam utilized per sq. metre. This varies according to the gas and the foam kind however is presently at least four.zero litres per minute per sq. metre. One of the ongoing developments in foam performance is the chance that this might be lowered, but standards usually take time to recognise product development. Anything lower than the minimal software fee implies that fire management is unlikely to be achieved. This implies that firefighting sources, significantly in a manual fireplace assault, have to be assembled earlier than firefighting commences and this takes time. The advantage in becoming mounted techniques is that the sources are already designed and constructed into the system for instant software.
Principle of froth extinguishment Images equipped by Author / Contributor
Foam proportioning strategies: mixing water with foam concentrate
In order to allow readers to make an knowledgeable choice on how greatest to sort out their explicit fireplace challenges, the following is an summary of the varied foam proportioning strategies.
Foam inductors:
Typically associated with fireplace service deployment and restricted fixed techniques applications. This uses the venturi principle to create a pressure drop in a small aluminium or seawater material appropriate device with built-in focus pick-up tube. The pressure drop created by the venturi draws the froth concentrate from a container the place it mixes with water to create foam solution. Both the pick-up tube and body of the inductor are compact enough to be simply carried on a fireplace equipment or fitted into a pipework system.
However, while it is considered to be the best technique, it has extreme drawbacks: (i) models are manufacturing unit calibrated so any modifications to the hydraulics (caused by length of discharge line after the inductor, the elevation of the discharge device or a changing quantity 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 affect proportioning accuracy and doubtlessly prevent any proportioning; (iii) adjustments in focus viscosity will undermine the flexibility of the venturi to attract focus into the downstream traces; (iv) strain loss is high, as a lot as 35%, so responsibility pump pressures must be excessive sufficient to permit for it, probably adding additional price into the system; (v) foam supply units have to be sized so as to not restrict design flows; (vi) testing cannot be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs because of foam concentrate usage, 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 mixture of electrical and diesel pumps to supply foam concentrate into a proportioner at a better pressure than the incoming water-line stress. The proportioner is installed into the water line and regulates the blending.
They are now related to older methods, the place disadvantages include: (i) further prices in hardware and design time; (ii) the froth pump is often restricted to a much tighter working vary, although the proportioner itself can accommodate extensive ranges in flows; (iii) the froth pump needs an extra power source, aside from water, so is not as reliably safe as a system with a possible single level of failure, corresponding to an entirely water-driven system; (iv) usually, these methods are very complex and trigger excessive 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 break the froth concentrate and entrain air, which in turn 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 crammed bladder in order that foam focus can be proportioned with water using the identical supply. The venturi precept is again introduced into play as it creates a strain drop at the point of injection for the froth concentrate. Testing can’t be achieved with out creating premix and discharging completed foam. This will add to complete lifetime prices on account of foam focus utilization, which has to be changed, and the disposal of premix or foam.
However, the bladder itself is seen as a weak point because great care is required to keep away from a damaged bladder when commissioning a model new installation. It is rarely straightforward to work throughout the steel stress vessel should problems occur, especially if and when a substitute bladder may be required: it all provides to the problem and cost.
Compressed air foam (CAFS):
This isn’t a proportioning technique in the conventional sense as the froth is already proportioned using one of many previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the name suggests, CAFS injects compressed air into the froth answer at the level of discharge. The consensus view is that CAFS enhances the completed foam’s capacity to cling to vertical surfaces permitting better penetration and cooling. This is also a profit in wildfire conditions by coating vulnerable buildings to mitigate fireplace development. The limited water provides associated with distant wildfire areas signifies that the useful resource can be absolutely optimised. However, as with balanced pressure proportioner foam pumps, an extra point of failure is feasible due to the extra CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have turn into synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is solely mechanical and extremely reliable. A water-driven rotor provides the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam focus by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and can proportion the foam focus precisely across a large working range. The purely mechanical system provides cost-efficient and eco-friendly proportioning price testing, fully without using any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images provided by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embody:
Reduced prices: proportioning price is examined without utilizing foam or creating premix or foam – value effective and eco-friendly.
Improved efficiency: constant proportioning rate throughout a large operating range.
Optimised delivery of high-viscosity foam concentrates with improved suction capability.
25% reduction in stress loss, in comparability with older generations, by way of hydraulic optimisation.
Improved cylinder cut-off for straightforward and fast adjustment to a different proportioning fee.
FM approved FireDos Gen III proportioners are to date the only FM accredited water motor coupled variable proportioners using FM permitted move meters. Using the check return line this provides the possibility to examine the proportioning fee during commissioning in addition to for annual checks, with out creating any premix, which is a really big profit for the user and relieves the environment.
In the second a half of this function we are going to discover the consequences of viscosity on foam proportioning and typical foam software areas and recommended discharge units.
For extra data, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
Share

Scroll to Top