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Part One of this article described the standard incident situations at tank farm fires and presented foam as the most suitable extinguishing agent together with the firefighting tools mostly used. In Part Two we have a glance at foam focus proportioning applied sciences, cell extinguishing techniques and conclude with classes realized.
NFPA 11 describes numerous forms of foam focus proportioning equipment. In the following, three techniques are checked out that are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning price must not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
The proportioning price should not exceed 30% above the permitted value i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam focus; respectively, the proportioning price is allowed to be an absolute maximum of 1% above the permitted value – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller worth have to be used respectively).
To assure right proportioning, the proportioner, including the proportioning price must be examined no much less than annually and its appropriate functioning should be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a confirmed and cost-effective know-how. The bladder tank is a pressurized vessel with a bladder inside which is crammed with foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the froth focus from the bladder as required. The bladder is connected to a proportioner which operates using the venturi precept. When the hearth pumps are activated, stress is generated by the pump, causing supply of foam focus to the proportioner. The extinguishing water flows by way of the venturi proportioner. The ensuing vacuum induces the froth focus into the extinguishing water circulate.
The advantages of this technique are its easy design with out transferring parts and its straightforward operation. No exterior power is required, and the system is relatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic to corresponding regulations corresponding to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system must be shut down and drained. The rubber bladder is delicate; when damaged, water will contaminate the froth concentrate. At a given proportioning fee, the system is appropriate only for low variations in the extinguishing water circulate strain and volume. Adding or altering particular person foam discharge gadgets is feasible only to a very restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct เกจ์วัดความดัน required annual testing, the system must be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The correct proportioning fee must be measured within the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam focus within the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the foam focus, an electrical or diesel-powered foam concentrate pump with an electronically managed valve and a move meter in the extinguishing water move line. When the fire pumps are activated, the foam concentrate pump drive and digital management system should be activated. The extinguishing water circulate fee is measured by the circulate meter and the management system adjusts the proper foam concentrate quantity via the management valve. The foam concentrate is injected into the extinguishing water move by the froth focus pump. If there’s a change in the circulate rate, the quantity of injected foam concentrate is regulated by the management valve.
The system’s benefit lies in the exact proportioning of the foam focus, independent of the extinguishing water strain or circulate rate. Foam focus can be topped up in the course of the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the purpose of annual testing, the system should be activated; nonetheless, the delivered foam concentrate may be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move price. No premix is produced; and as a result of the foam focus is handed again into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an exterior interruption-free power provide for the foam focus pump and the control system, in addition to the need for a complicated management system and the comparatively greater buying prices. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water circulate price and the newly adjusted foam concentrate amount. The foam high quality may be compromised when continually altering operating situations as foam discharge devices are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam focus, a water motor installed in the extinguishing water flow line and a foam concentrate pump which is related on to the water motor. Water motor and pump form one compact unit. Upon activation of the hearth pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the flow rate changes, the quantity of froth concentrate is tailored instantly.
The advantage of the system is its independence from external energy sources as properly as a exact and immediate foam-concentrate proportioning whatever the extinguishing water strain or circulate rate. If a piston or plunger pump is used, adjustment or calibration after set up is not needed for the reason that water motor and the pump are volumetric units firmly linked to one another. Foam concentrate refilling during operation is possible. The system can additionally be able to proportioning highly viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam focus may be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate rate. No premix is generated; and if the foam concentrate is handed again into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively higher purchasing prices are a disadvantage of the system.
With any system, consideration should be taken into account for the annual testing costs, which could be appreciable by way of replacement foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge tools could be damaged in intensive fires within the tank or in the dyke space and thus lose effectiveness, cellular fire displays and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they have only limited extinguishing agent flow charges and reaches.
Firefighting displays
Firefighting monitors are discharge devices mounted on autos or trailers and available in many sizes. The extinguishing agent circulate rate can be up to 60,000 litres/min and the reach could be up to 180m if the strain of the hearth pumps is sufficient. They are appropriate to discharge foam, e.g., to extinguish a surface fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank in order to forestall it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke area ought to at all times be noticed to keep away from an overflow of the dyke.
Mobile fire displays can be provided either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the foam concentrate normally takes place through cellular proportioners. This clearly points towards the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell units out there as back-ups is proven by the following example for the location of displays for hearth extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This results in a quantity of alternatives for the monitors. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which should be ready to handle varying move rates to guarantee flexibility throughout extinguishing operations. Depending on the native circumstances, the displays will want to maintain a minimum distance to the burning tank or might not be ready to be positioned close to to the tanks because of debris. In addition, it is not going to all the time be attainable to position a number of monitors around the tank. It have to be ensured the monitor has enough throwing peak in relation to the tank height, to deliver foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal rules as well as suggestions by associations like NFPA and isn’t checked out more carefully within the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As talked about within the introduction to Part One of this article, it appears that evidently many authorities and companies haven’t discovered the required classes from disastrous fireplace incidents of past years. Tank farm fires in the oil and petrochemical industry don’t occur frequently. When they do, they often have devastating penalties. Let us remember the tank farm hearth at Deer Park, Texas in March 2019 talked about within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fire for yet unknown causes. The plant had no gasoline warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have mounted extinguishing techniques installed. All 15 tanks had been surrounded by one single dyke. The owner had relied on the local fire service, which was on the spot in a quick time however could not take management over the fireplace with the tools obtainable, partially as a result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of equipment and foam focus in addition to the preparation of a plan of motion took approximately thirteen hours. The fireplace was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt were remodeled three days, with foam concentrate and water shortages occurring within the meantime. In total, over 500,000 litres of foam focus were used. Instead of a fire in the dyke space, 11 of the 15 tanks burnt down.
It could be very probable that the fireplace would have been extinguished shortly if the warning techniques and valves had labored and a fixed fire extinguishing system had existed. It can be probable that the fireplace would have been extinguished rapidly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably much less injury.
Summing up, the following points should be discovered at the least. As far as they haven’t yet been carried out, or just partly, they need to function a foundation for discussions about one’s personal fire-protection idea:
Have an acceptable fire-protection concept including different situations which adapt to the given situation frequently.
Always have a enough variety of cellular extinguishing methods as a backup to fastened extinguishing techniques.
Stock an acceptable foam focus.
Ensure adequate foam concentrate supply.
Ensure sufficient water provide.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing tools obtainable in a enough quantity.
Have skilled personnel obtainable in a adequate number.
Ensure a quick implementation of a suitable plan of motion.
For extra information, go to www.firedos.com
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