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

Part One of this article described the everyday incident eventualities at tank farm fires and presented foam as the most suitable extinguishing agent along with the firefighting gear most commonly used. In Part Two we look at foam concentrate proportioning applied sciences, cellular extinguishing methods and conclude with lessons learned.
NFPA 11 describes numerous types of foam focus proportioning equipment. In the following, three techniques are checked out which are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price 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 price must not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam focus; respectively, the proportioning fee is allowed to be an absolute maximum of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller value should be used respectively).
To guarantee right proportioning, the proportioner, including the proportioning price should be tested at least once a year 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 technology. The bladder tank is a pressurized vessel with a bladder inside which is crammed with foam focus. เกจวัดแรงดันน้ำ4หุน is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is connected to a proportioner which operates using the venturi precept. When the fireplace pumps are activated, strain is generated by the pump, inflicting delivery of foam concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the foam focus into the extinguishing water flow.
The advantages of this system are its easy design without shifting elements and its straightforward operation. No exterior power is required, and the system is comparatively cheap.
A drawback is that the system is a pressurized vessel topic to corresponding laws corresponding 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 foam concentrate. At a given proportioning fee, the system is appropriate only for low variations within the extinguishing water move stress and quantity. Adding or altering individual foam discharge units is feasible only to a really limited extent. The system can be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated at the venturi proportioner within the extinguishing water line. The correct proportioning rate have to be measured within 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 circulate meter
The system consists of an atmospheric tank for the froth focus, an electrical or diesel-powered foam concentrate pump with an electronically managed valve and a flow meter in the extinguishing water circulate line. When the fire pumps are activated, the froth concentrate pump drive and electronic control system should be activated. The extinguishing water move rate is measured by the circulate meter and the control system adjusts the proper foam focus quantity via the control valve. The foam concentrate is injected into the extinguishing water circulate by the foam focus pump. If there’s a change within the circulate price, the amount of injected foam focus is regulated by the management valve.
The system’s advantage lies within the precise proportioning of the foam concentrate, unbiased of the extinguishing water strain or flow price. Foam focus may 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 have to be activated; nonetheless, the delivered foam focus could be measured through a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate price. No premix is produced; and as the foam focus is passed back into the tank, no foam focus needs to 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 necessity for a complicated management system and the comparatively larger purchasing costs. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water flow price and the newly adjusted foam concentrate quantity. 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 move line and a foam concentrate pump which is linked directly to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the flow fee adjustments, the amount of foam focus is customized instantly.
The advantage of the system is its independence from exterior power sources in addition to a precise and quick 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 because the water motor and the pump are volumetric devices firmly related to one another. Foam concentrate refilling during operation is feasible. The system can be able to proportioning highly viscous foam concentrates. The system must be activated for annual testing; nonetheless, the delivered foam concentrate could be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam focus flow price. No premix is generated; and if the froth focus is handed back into the tank, no foam focus must be topped up.
The larger design and the comparatively higher purchasing prices are an obstacle of the system.
With any system, consideration must be taken into consideration for the annual testing costs, which may be considerable by means of substitute foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge equipment can be broken in extensive fires within the tank or in the dyke space and thus lose effectiveness, cellular fireplace 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 circulate rates and reaches.
Firefighting displays
Firefighting screens are discharge units mounted on automobiles or trailers and obtainable in plenty of sizes. The extinguishing agent circulate price may be up to 60,000 litres/min and the reach could be as much 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 chill down a neighboring tank or the tank wall of a burning tank in order to stop 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 noticed to avoid an overflow of the dyke.
Mobile fireplace displays may be equipped both by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the froth concentrate often takes place by way of cellular proportioners. This clearly factors in the direction of the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular items available as back-ups is shown by the following example for the position of screens for fireplace 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 several alternate options for the monitors. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which should be ready to handle varying move charges to guarantee flexibility during extinguishing operations. Depending on the local circumstances, the displays might want to hold a minimal distance to the burning tank or may not be ready to be positioned near to the tanks due to debris. In addition, it is not going to all the time be potential to place several screens around the tank. It should be ensured the monitor has enough throwing top in relation to the tank top, to ship foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal laws as nicely as recommendations by associations like NFPA and isn’t checked out extra intently in the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons learned
As talked about within the introduction to Part One of this text, it seems that many authorities and companies haven’t learned the mandatory classes from disastrous fire incidents of past years. Tank farm fires in the oil and petrochemical industry do not occur regularly. When they do, they normally have devastating consequences. 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 defective valve for half-hour and caught fire for but unknown reasons. The plant had no gasoline warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have mounted 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 brief time however could not take control over the fire with the gear out there, partially as a end result of flammable substance was constantly leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of kit and foam concentrate as properly as the preparation of a plan of motion took roughly 13 hours. The fireplace was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt were remodeled three days, with foam focus and water shortages occurring in the meantime. In whole, over 500,000 litres of froth focus have been used. Instead of a fireplace within the dyke space, 11 of the 15 tanks burnt down.
It is very possible that the fire would have been extinguished rapidly if the warning techniques and valves had worked and a set hearth extinguishing system had existed. It is also probable that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded finally, had been started earlier. Both cases would have resulted in notably much less harm.
Summing up, the next factors ought to be realized as a minimum. As far as they have not yet been carried out, or simply partly, they need to function a basis for discussions about one’s own fire-protection concept:
Have a suitable fire-protection idea together with various situations which adapt to the given scenario frequently.
Always have a enough variety of mobile extinguishing methods as a backup to fixed extinguishing methods.
Stock an appropriate foam focus.
Ensure sufficient foam concentrate provide.
Ensure adequate water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing equipment obtainable in a adequate number.
Have skilled personnel obtainable in a adequate number.
Ensure a fast implementation of an acceptable plan of motion.
For extra information, go to www.firedos.com
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