Use of froth for firefighting in tank farms of the oil and petrochemical business – Part 2

Part One of this article described the standard incident eventualities at tank farm fires and presented foam as the most suitable extinguishing agent together with the firefighting equipment mostly used. In Part Two we look at foam concentrate proportioning applied sciences, mobile extinguishing techniques and conclude with lessons realized.
NFPA eleven describes various types of foam focus proportioning tools. In the following, three methods are looked at that are most typical. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning fee must not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning rate should not exceed 30% above the permitted value i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; respectively, the proportioning price is allowed to be an absolute most of 1% above the permitted worth – 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, together with the proportioning price should be tested no less than every year and its correct functioning should 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 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 principle. When the fireplace pumps are activated, strain is generated by the pump, inflicting supply of froth focus to the proportioner. The extinguishing water flows via the venturi proportioner. เกจวัดแรงลม ensuing vacuum induces the foam concentrate into the extinguishing water move.
The benefits of this method are its simple design without moving parts and its simple operation. No exterior power is required, and the system is relatively cheap.
A drawback is that the system is a pressurized vessel subject 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 sensitive; when broken, water will contaminate the froth focus. At a given proportioning fee, the system is appropriate only for low variations in the extinguishing water circulate pressure and quantity. Adding or changing individual foam discharge gadgets is possible only to a very limited extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system should be activated and premix generated at the venturi proportioner within the extinguishing water line. The correct proportioning fee should be measured in the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam concentrate within the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the foam focus, an electrical or diesel-powered foam focus pump with an electronically managed valve and a flow meter within the extinguishing water flow line. When the hearth pumps are activated, the froth focus pump drive and digital control system should be activated. The extinguishing water circulate rate is measured by the circulate meter and the control system adjusts the right foam focus amount through the management valve. The foam concentrate is injected into the extinguishing water move by the froth focus pump. If there’s a change within the flow fee, the amount of injected foam focus is regulated by the control valve.
The system’s benefit lies in the exact proportioning of the foam focus, impartial of the extinguishing water stress or flow rate. Foam focus could be topped up in the course of the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nonetheless, the delivered foam focus could be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate move fee. No premix is produced; and as the foam focus is handed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an external interruption-free vitality supply for the foam concentrate pump and the control system, in addition to the necessity for a sophisticated control system and the comparatively higher purchasing costs. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water move price and the newly adjusted foam concentrate quantity. The foam quality could additionally be compromised when continuously altering operating conditions as foam discharge units are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the froth focus, a water motor put in within the extinguishing water flow line and a foam concentrate pump which is linked directly to the water motor. Water motor and pump kind one compact unit. Upon activation of the fireplace pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the circulate fee modifications, the quantity of foam concentrate is adapted immediately.
The benefit of the system is its independence from exterior power sources in addition to a exact and immediate foam-concentrate proportioning regardless of the extinguishing water pressure or move price. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t necessary because the water motor and the pump are volumetric gadgets firmly connected to every other. Foam focus refilling during operation is possible. The system can be able to proportioning highly viscous foam concentrates. The system must be activated for annual testing; however, the delivered foam concentrate could 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 foam focus is passed again into the tank, no foam focus must be topped up.
The larger design and the comparatively greater purchasing prices are a disadvantage of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which could be appreciable when it comes to replacement foam focus, disposal of premix and labour costs.
Mobile extinguishing techniques
As the stationary foam discharge gear may be damaged in intensive fires within the tank or in the dyke area and thus lose effectiveness, cellular hearth screens and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve only limited extinguishing agent move rates and reaches.
Firefighting monitors
Firefighting monitors are discharge gadgets mounted on automobiles or trailers and available in many sizes. The extinguishing agent circulate price may be up to 60,000 litres/min and the attain may be up to 180m if the strain of the fireplace pumps is sufficient. They are appropriate to discharge foam, e.g., to extinguish a floor fireplace in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank so as to forestall it reaching the crucial temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke space should all the time be observed to keep away from an overflow of the dyke.
Mobile fire displays may be provided both by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the froth concentrate usually takes place via cellular proportioners. This clearly factors in course of the advantage of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular models available as back-ups is proven by the next instance for the position of monitors for fireplace extinguishing at tanks which are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in a quantity of options for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be capable of handle varying circulate charges to ensure flexibility during extinguishing operations. Depending on the local circumstances, the monitors will need to maintain a minimal distance to the burning tank or might not be succesful of be positioned close to to the tanks as a outcome of debris. In addition, it won’t always be attainable to place several screens across the tank. It must be ensured the monitor has enough throwing top in relation to the tank height, to ship foam into the inside of the tank.
The dimensioning of the whole firefighting system is made following legal laws in addition to suggestions by associations like NFPA and isn’t looked at extra carefully in the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons discovered
As talked about in the introduction to Part One of this text, it seems that evidently many authorities and corporations haven’t realized the required lessons from disastrous fire incidents of previous years. Tank farm fires in the oil and petrochemical business don’t happen frequently. When they do, they usually have devastating consequences. Let us keep in mind the tank farm fireplace at Deer Park, Texas in March 2019 talked about in the introduction.
The fire developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for half-hour and caught hearth for but unknown reasons. The plant had no gas warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have fixed extinguishing techniques installed. All 15 tanks were surrounded by one single dyke. The owner had relied on the local hearth service, which was on the spot in a quick time but couldn’t take control over the fire with the equipment obtainable, partially because flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire had damaged out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of kit and foam focus as properly as the preparation of a plan of action took roughly thirteen hours. The fire was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes เกจวัดน้ำยาแอร์refco were made over three days, with foam concentrate and water shortages occurring within the meantime. In whole, over 500,000 litres of froth concentrate were used. Instead of a fire in the dyke space, 11 of the 15 tanks burnt down.
It could be very possible that the fire would have been extinguished rapidly if the warning methods and valves had worked and a set hearth extinguishing system had existed. It can be probable that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded eventually, had been started earlier. Both circumstances would have resulted in notably less harm.
Summing up, the next factors should be realized at least. As far as they haven’t but been implemented, or just partly, they should serve as a basis for discussions about one’s own fire-protection concept:
Have a suitable fire-protection concept together with various scenarios which adapt to the given scenario often.
Always have a sufficient number of cell extinguishing methods as a backup to mounted extinguishing systems.
Stock a suitable foam focus.
Ensure sufficient foam concentrate provide.
Ensure enough water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing tools obtainable in a sufficient number.
Have skilled personnel available in a enough quantity.
Ensure a quick implementation of an appropriate plan of motion.
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