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

Part One of this text described the everyday incident eventualities at tank farm fires and offered foam as the most appropriate extinguishing agent along with the firefighting equipment mostly used. In Part Two we have a look at foam focus proportioning technologies, mobile extinguishing methods and conclude with lessons learned.
NFPA 11 describes various types of foam concentrate proportioning tools. In the following, three systems are looked at that are most common. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning fee must not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
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 rate is allowed to be an absolute maximum of 1% above the permitted worth – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller value should be used respectively).
To guarantee correct proportioning, the proportioner, including the proportioning price have to be examined no less than annually and its correct functioning have to 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 full of foam concentrate. 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 using the venturi principle. When the hearth pumps are activated, strain is generated by the pump, inflicting supply of foam focus to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the froth focus into the extinguishing water circulate.
The advantages of this method are its simple design with out moving components and its easy operation. No external power is required, and the system is relatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding regulations 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 broken, water will contaminate the froth concentrate. At a given proportioning price, the system is suitable only for low variations in the extinguishing water flow pressure and volume. Adding or altering individual foam discharge gadgets is possible only 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 should be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The appropriate proportioning rate have to be measured in the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam focus in the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a move meter within the extinguishing water circulate line. When the fireplace pumps are activated, the froth concentrate pump drive and electronic management system should be activated. The extinguishing water move price is measured by the circulate meter and the control system adjusts the correct foam focus amount by way of the control valve. The foam concentrate is injected into the extinguishing water circulate by the froth focus pump. If there is a change within the circulate price, the quantity of injected foam concentrate is regulated by the management valve.
The system’s advantage lies within the exact proportioning of the froth concentrate, unbiased of the extinguishing water pressure or flow fee. Foam focus may be topped up through the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system must 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 fee. No premix is produced; and as the foam focus is passed again into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an external interruption-free vitality supply for the froth focus pump and the control system, in addition to the necessity for a classy management system and the comparatively greater buying prices. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water move price and the newly adjusted foam concentrate amount. The foam high quality could also be compromised when constantly changing operating situations as foam discharge devices are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam concentrate, a water motor installed within the extinguishing water flow line and a foam concentrate pump which is connected directly to the water motor. Water motor and pump kind one compact unit. Upon activation of the hearth pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the circulate fee changes, the quantity of foam concentrate is customized immediately.
The benefit of the system is its independence from external vitality sources in addition to a exact and quick foam-concentrate proportioning regardless of the extinguishing water strain or circulate price. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t needed since the water motor and the pump are volumetric devices firmly related to every other. Foam concentrate refilling during operation is possible. The system can be capable of proportioning extremely viscous foam concentrates. The system must 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 flow rate. No premix is generated; and if the froth concentrate is passed again into the tank, no foam concentrate needs to be topped up.
The bigger design and the comparatively higher purchasing costs are a disadvantage of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which may be appreciable by method of replacement foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge gear may be broken in extensive fires within the tank or within the dyke area and thus lose effectiveness, cell hearth screens and foam pipes could additionally be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they’ve solely restricted extinguishing agent move charges and reaches.
Firefighting screens
Firefighting displays are discharge units mounted on vehicles or trailers and out there in many sizes. The extinguishing agent circulate price can be as a lot as 60,000 litres/min and the attain could be as a lot as 180m if the pressure of the fireplace 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 in order to prevent it reaching the critical temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke space should at all times be noticed to keep away from an overflow of the dyke.
Mobile fireplace monitors can be supplied either by the extinguishing water of the stationary fireplace pumps or by mobile pumps. The injection of the foam focus normally takes place via mobile proportioners. This clearly factors towards the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of mobile items available as back-ups is shown by the next instance for the placement 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 results in several options for the displays. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which ought to be in a position to deal with various flow charges to guarantee flexibility during extinguishing operations. Depending on the native conditions, the displays might need to hold a minimum distance to the burning tank or might not have the flexibility to be positioned near to the tanks because of debris. In addition, it won’t all the time be potential to position several screens across the tank. It have to be ensured the monitor has enough throwing top in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the complete firefighting system is made following legal regulations in addition to suggestions by associations like NFPA and isn’t checked out extra intently within 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 article, it seems that evidently many authorities and companies haven’t learned the mandatory lessons from disastrous fireplace incidents of past years. Tank farm fires in the oil and petrochemical trade don’t happen incessantly. When they do, they normally have devastating penalties. Let us remember the tank farm hearth at Deer Park, Texas in March 2019 mentioned in the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for half-hour and caught fireplace for but unknown reasons. The plant had no gas warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fastened extinguishing techniques put in. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the local fireplace service, which was on the spot in a brief time but could not take management over the fireplace with the gear obtainable, partially because flammable substance was continuously leaking from the tank. Thirty-six hours after the fireplace had damaged 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 roughly thirteen hours. The fire was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts had been made over three days, with foam focus and water shortages occurring in the meantime. In total, over 500,000 litres of froth focus were used. Instead of a hearth within the dyke area, eleven of the 15 tanks burnt down.
It may be very probable that the fireplace would have been extinguished quickly if the warning techniques and valves had labored and a fixed hearth extinguishing system had existed. It can also be possible that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been started earlier. Both cases would have resulted in notably much less harm.
Summing up, the next factors must be realized at least. As far as they haven’t but been applied, or just partly, they need to function a foundation for discussions about one’s own fire-protection concept:
Have an appropriate fire-protection concept together with different scenarios which adapt to the given situation frequently.
Always have a sufficient number of cell extinguishing systems as a backup to fastened extinguishing techniques.
Stock a suitable foam focus.
Ensure เกจวัดความดันแก๊ส concentrate supply.
Ensure adequate water supply.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing gear out there in a adequate number.
Have trained personnel out there in a enough number.
Ensure a fast implementation of an acceptable plan of motion.
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