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Part One of this article described the everyday incident eventualities at tank farm fires and presented foam as essentially the most appropriate extinguishing agent together with the firefighting gear mostly used. In Part Two we look at foam concentrate proportioning technologies, cellular extinguishing techniques and conclude with lessons discovered.
NFPA 11 describes various forms of foam focus proportioning equipment. In the following, three methods are looked at that are commonest. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning rate should not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning price should not exceed 30% above the permitted value i.e. three.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; respectively, the proportioning fee is allowed to be an absolute most of 1% above the permitted value – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller worth must be used respectively).
To guarantee correct proportioning, the proportioner, including the proportioning rate must be examined no less than annually and its appropriate functioning have to be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a proven and cost-effective expertise. The bladder tank is a pressurized vessel with a bladder inside which is filled with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam focus from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi principle. When the hearth pumps are activated, strain is generated by the pump, inflicting delivery of foam focus to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water flow.
The advantages of this method are its simple design with out shifting components and its simple operation. No external vitality is required, and the system is relatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system must be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the froth concentrate. At a given proportioning rate, the system is suitable only for low variations in the extinguishing water flow pressure and volume. Adding or changing particular person foam discharge gadgets is possible solely to a very limited extent. The system can be unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The appropriate proportioning fee should be measured within the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam concentrate 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 concentrate, an electric or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter in the extinguishing water circulate line. When the hearth pumps are activated, the foam concentrate pump drive and digital control system should be activated. The extinguishing water circulate fee is measured by the move meter and the control system adjusts the right foam concentrate quantity by way of the control valve. The foam concentrate is injected into the extinguishing water move by the foam concentrate pump. If there is a change within the move rate, the amount of injected foam concentrate is regulated by the management valve.
The system’s advantage lies in the precise proportioning of the foam focus, unbiased of the extinguishing water strain or move price. Foam concentrate may be topped up through the extinguishing operation. pressure gauge หน้าปัด 2 นิ้ว is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system must be activated; nevertheless, the delivered foam focus could be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate fee. No premix is produced; and as a result of the foam focus is handed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free energy supply for the foam focus pump and the management system, in addition to the necessity for a sophisticated control system and the comparatively higher buying prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water move rate and the newly adjusted foam concentrate quantity. The foam quality could also be compromised when continuously 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 within the extinguishing water move line and a foam concentrate pump which is related directly to the water motor. Water motor and pump form one compact unit. Upon activation of the fireplace pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump provides immediate foam-concentrate injection into the extinguishing water. If the flow price changes, the quantity of froth focus is customized instantly.
The benefit of the system is its independence from external energy sources in addition to a exact and instant foam-concentrate proportioning regardless of the extinguishing water pressure or move fee. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t needed for the reason that water motor and the pump are volumetric devices firmly connected to each other. Foam focus refilling throughout operation is feasible. The system can also be capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate fee. No premix is generated; and if the froth focus is passed back into the tank, no foam focus needs to be topped up.
The larger design and the comparatively greater purchasing prices are a drawback of the system.
With any system, consideration must be taken into consideration for the annual testing costs, which could be considerable when it comes to alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge tools could be broken in intensive fires in the tank or in the dyke space and thus lose effectiveness, mobile hearth monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they’ve solely limited extinguishing agent flow rates and reaches.
Firefighting screens
Firefighting monitors are discharge gadgets mounted on vehicles or trailers and out there in plenty of sizes. The extinguishing agent move price may be as much as 60,000 litres/min and the attain may be up to 180m if the pressure of the fire pumps is enough. They are suitable to discharge foam, e.g., to extinguish a floor fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank to be able to stop 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 always be noticed to avoid an overflow of the dyke.
Mobile hearth screens may be provided both by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the froth concentrate usually takes place through cellular proportioners. This clearly points towards the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile units available as back-ups is proven by the following instance for the placement of displays for hearth extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This results in a number of alternate options for the monitors. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which ought to be ready to deal with varying move charges to ensure flexibility throughout extinguishing operations. Depending on the local situations, the monitors might need to keep a minimum distance to the burning tank or might not be succesful of be positioned near to the tanks because of debris. In addition, it won’t always be possible to position a quantity of monitors around the tank. It have to be ensured the monitor has adequate throwing peak in relation to the tank peak, to deliver foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following authorized regulations as properly as suggestions by associations like NFPA and isn’t looked at extra closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As mentioned in the introduction to Part One of this text, it appears that evidently many authorities and corporations have not discovered the necessary lessons from disastrous fire incidents of previous years. Tank farm fires in the oil and petrochemical industry don’t happen incessantly. When they do, they normally have devastating consequences. Let us bear in mind the tank farm fireplace at Deer Park, Texas in March 2019 mentioned within the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for 30 minutes and caught hearth for but unknown reasons. The plant had no fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fixed extinguishing systems put in. All 15 tanks have been surrounded by one single dyke. The proprietor had relied on the local hearth service, which was on the spot very quickly but could not take management over the fireplace with the equipment obtainable, partially as a result of flammable substance was continuously leaking from the tank. Thirty-six hours after the fireplace had damaged out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of apparatus and foam concentrate in addition to the preparation of a plan of motion took roughly 13 hours. The hearth was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt have been remodeled three days, with foam focus and water shortages occurring in the meantime. In whole, 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 may be very probable that the fire would have been extinguished quickly if the warning methods and valves had worked and a set fireplace extinguishing system had existed. It is also probable that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both cases would have resulted in notably much less injury.
Summing up, the next factors must be learned at least. As far as they haven’t but been applied, or just partly, they should serve as a basis for discussions about one’s own fire-protection idea:
Have an appropriate fire-protection idea including various scenarios which adapt to the given scenario often.
Always have a sufficient variety of cell extinguishing systems as a backup to fastened extinguishing systems.
Stock an acceptable foam concentrate.
Ensure enough foam focus provide.
Ensure sufficient water supply.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing tools obtainable in a sufficient quantity.
Have skilled personnel obtainable in a enough quantity.
Ensure a quick implementation of a suitable plan of action.
For more info, go to www.firedos.com
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