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

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 gear mostly used. In Part Two we look at foam focus proportioning applied sciences, cellular extinguishing systems and conclude with classes discovered.
NFPA 11 describes varied kinds of foam focus proportioning equipment. In the following, three techniques are looked at that are most common. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning rate should not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam focus.
The proportioning fee must 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 concentrate or 7% for a 6% foam focus (the smaller worth have to be used respectively).
To guarantee เกจอาร์กอน , the proportioner, together with the proportioning rate have to be tested a minimal of once a year and its right 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 full of foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the froth concentrate from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi principle. When the fireplace pumps are activated, pressure is generated by the pump, causing delivery of foam concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth concentrate into the extinguishing water flow.
The advantages of this system are its simple design with out shifting elements and its straightforward operation. No exterior power is required, and the system is comparatively 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 focus, 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 move stress and quantity. Adding or altering individual foam discharge units is possible only to a really limited extent. The system can be 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 inside the extinguishing water line. The appropriate proportioning rate must be measured in the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus within the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter within the extinguishing water flow line. When the fire pumps are activated, the froth focus pump drive and digital control system have to be activated. The extinguishing water move price is measured by the circulate meter and the management system adjusts the proper foam concentrate quantity via the management valve. The foam focus is injected into the extinguishing water circulate by the foam focus pump. If there’s a change in the move rate, the amount of injected foam focus is regulated by the control valve.
The system’s advantage lies in the precise proportioning of the foam concentrate, unbiased of the extinguishing water pressure or circulate rate. Foam concentrate can be topped up during the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the aim of annual testing, the system should be activated; nevertheless, the delivered foam concentrate may be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate circulate price. No premix is produced; and as a outcome of the foam concentrate is handed back into the tank, no foam focus 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 need for a sophisticated management system and the comparatively higher purchasing prices. Furthermore, it should be accepted that a delay happens between the change of the extinguishing water flow rate and the newly adjusted foam focus amount. The foam high quality may be compromised when continuously changing working situations 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 concentrate, a water motor put in in the extinguishing water circulate line and a foam focus pump which is connected directly to the water motor. Water motor and pump form one compact unit. Upon activation of the fireplace pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the flow fee adjustments, the amount of foam focus is customized immediately.
The advantage of the system is its independence from exterior vitality sources as well as a exact and immediate foam-concentrate proportioning whatever the extinguishing water strain or circulate fee. If a piston or plunger pump is used, adjustment or calibration after set up isn’t necessary because the water motor and the pump are volumetric devices firmly related to every other. Foam concentrate refilling throughout operation is possible. The system can be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam focus may be measured via a return line. The proportioning price is calculated from the extinguishing water/foam concentrate move price. No premix is generated; and if the foam focus is handed again into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively larger purchasing costs are a drawback of the system.
With any system, consideration must be taken into account for the annual testing costs, which can be considerable when it comes to replacement foam concentrate, disposal of premix and labour costs.
Mobile extinguishing methods
As the stationary foam discharge gear can be damaged in in depth fires in the tank or within the dyke space and thus lose effectiveness, cell hearth displays and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve only restricted extinguishing agent move charges and reaches.
Firefighting monitors
Firefighting monitors are discharge units mounted on automobiles or trailers and obtainable in many sizes. The extinguishing agent move rate may be as a lot as 60,000 litres/min and the attain can be as a lot as 180m if the strain of the fire pumps is enough. They are suitable to discharge foam, e.g., to extinguish a surface hearth in a tank, or water, to cool 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 keep the flames from spreading. The accumulation of water inside the dyke area should always be observed to avoid an overflow of the dyke.
Mobile fire screens can be supplied either by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the foam concentrate often takes place via cellular proportioners. This clearly points in the course of the advantage of power independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular models obtainable as back-ups is proven by the next instance for the placement of displays for fireplace extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in a number of alternate options for the screens. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which ought to have the power to handle varying move rates to ensure flexibility throughout extinguishing operations. Depending on the native situations, the monitors will need to hold a minimum distance to the burning tank or may not have the power to be positioned near to the tanks as a end result of particles. In addition, it won’t all the time be potential to position a number of displays around the tank. It have to be ensured the monitor has sufficient throwing height in relation to the tank peak, to ship foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following authorized rules in addition to suggestions by associations like NFPA and is not looked at extra intently within the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons realized
As talked about within the introduction to Part One of this text, it seems that many authorities and firms have not realized the mandatory lessons from disastrous hearth incidents of previous years. Tank farm fires in the oil and petrochemical industry do not happen frequently. 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 hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught hearth for but 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 put in. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native hearth service, which was on the spot in a quick time but could not take management over the fire with the equipment available, partially as a result of flammable substance was constantly leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of apparatus and foam concentrate as nicely as the preparation of a plan of motion took approximately thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt were made over three days, with foam concentrate and water shortages occurring in the meantime. In whole, over 500,000 litres of froth focus had been used. Instead of a fire in the dyke area, 11 of the 15 tanks burnt down.
It may be very probable that the fireplace would have been extinguished quickly if the warning systems and valves had labored and a onerous and fast fire extinguishing system had existed. It can also be probable that the fire would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been started earlier. Both instances would have resulted in notably less injury.
Summing up, the next factors ought to be realized at least. As far as they haven’t yet been applied, or simply partly, they should function a foundation for discussions about one’s own fire-protection concept:
Have a suitable fire-protection idea together with alternative eventualities which adapt to the given situation often.
Always have a enough variety of cell extinguishing techniques as a backup to mounted extinguishing methods.
Stock a suitable foam concentrate.
Ensure enough foam focus supply.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing equipment obtainable in a sufficient quantity.
Have trained personnel available in a adequate quantity.
Ensure a quick implementation of an acceptable plan of motion.
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