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

Part One of this text described the standard incident scenarios at tank farm fires and offered foam as essentially the most suitable extinguishing agent along with the firefighting tools mostly used. In เกจวัดแรงดันดิจิตอลราคา take a look at foam concentrate proportioning applied sciences, cell extinguishing methods and conclude with classes discovered.
NFPA eleven describes numerous kinds of foam focus proportioning equipment. In the next, three systems are looked at which are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price must 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 must not exceed 30% above the permitted value i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning fee is allowed to be an absolute maximum of 1% above the permitted value – i.e. 4% for a 3% foam focus or 7% for a 6% foam focus (the smaller value must be used respectively).
To assure appropriate proportioning, the proportioner, including the proportioning rate must be examined at least once a year and its appropriate functioning should 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 filled with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is related to a proportioner which operates using the venturi principle. When the hearth pumps are activated, pressure is generated by the pump, causing supply of froth concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water circulate.
The benefits of this system are its easy design without moving parts and its straightforward operation. No external power is required, and the system is relatively cheap.
A disadvantage is that the system is a pressurized vessel topic to corresponding laws such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system have to be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam focus. 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 devices is possible only to a very limited extent. The system can additionally 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 inside the extinguishing water line. The correct proportioning price must be measured in the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam concentrate within the bladder tank must be changed.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the foam focus, an electrical or diesel-powered foam concentrate pump with an electronically managed valve and a circulate meter within the extinguishing water flow line. When the fire pumps are activated, the foam concentrate pump drive and electronic management system should be activated. The extinguishing water move rate is measured by the circulate meter and the control system adjusts the proper foam concentrate amount via the management valve. The foam focus is injected into the extinguishing water move by the foam concentrate pump. If there’s a change within the circulate rate, the quantity of injected foam concentrate is regulated by the management valve.
The system’s benefit lies within the exact proportioning of the foam concentrate, independent of the extinguishing water pressure or flow rate. Foam concentrate can be topped up through the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system have to be activated; nonetheless, the delivered foam focus could be measured via a return line. The proportioning price is calculated from the extinguishing water/foam concentrate move rate. No premix is produced; and as the foam focus is handed back into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an external interruption-free power provide for the froth concentrate pump and the management system, in addition to the necessity for a sophisticated control system and the comparatively higher buying costs. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water flow fee and the newly adjusted foam concentrate amount. The foam high quality may be compromised when constantly changing operating situations as foam discharge gadgets 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 linked on to the water motor. Water motor and pump type one compact unit. Upon activation of the fire 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 flow rate modifications, the amount of foam focus is adapted immediately.
The benefit of the system is its independence from external vitality sources as properly as a precise and quick foam-concentrate proportioning whatever the extinguishing water stress or flow fee. If a piston or plunger pump is used, adjustment or calibration after installation is not essential for the rationale that water motor and the pump are volumetric units firmly linked to every other. Foam focus refilling during operation is feasible. The system is also capable of proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam focus could be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam focus circulate fee. No premix is generated; and if the froth focus is handed again into the tank, no foam focus needs to be topped up.
The larger design and the comparatively larger buying costs are an obstacle of the system.
With any system, consideration must be taken under consideration for the annual testing costs, which can be appreciable when it comes to substitute foam focus, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge tools could be damaged in extensive fires in the tank or within the dyke space and thus lose effectiveness, cellular fire screens and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve solely restricted extinguishing agent move rates and reaches.
Firefighting monitors
Firefighting monitors are discharge gadgets mounted on automobiles or trailers and out there in plenty of sizes. The extinguishing agent move rate could be up to 60,000 litres/min and the reach could be as a lot as 180m if the strain of the fireplace pumps is enough. They are appropriate to discharge foam, e.g., to extinguish a surface fireplace in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank so as to stop it reaching the critical temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area should always be observed to keep away from an overflow of the dyke.
Mobile fireplace screens could be provided both by the extinguishing water of the stationary fireplace pumps or by mobile pumps. The injection of the froth focus often takes place by way of mobile proportioners. This clearly points towards the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of mobile models out there as back-ups is proven by the next example for the placement of displays for hearth extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This ends in a quantity of alternatives for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be capable of deal with varying move charges to ensure flexibility during extinguishing operations. Depending on the local conditions, the monitors might want to maintain a minimum distance to the burning tank or may not be in a position to be positioned near to the tanks due to debris. In addition, it is not going to always be potential to place a quantity of monitors around the tank. It have to be ensured the monitor has adequate throwing top in relation to the tank top, to deliver foam into the inside of the tank.
The dimensioning of the whole firefighting system is made following authorized rules in addition to suggestions by associations like NFPA and isn’t checked out more closely in the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons learned
As mentioned in the introduction to Part One of this text, it seems that evidently many authorities and companies haven’t realized the required classes from disastrous fire incidents of previous years. Tank farm fires within the oil and petrochemical business don’t happen incessantly. When they do, they normally have devastating penalties. Let us remember the tank farm fire at Deer Park, Texas in March 2019 mentioned within 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 fireplace 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 fastened extinguishing systems installed. All 15 tanks had been surrounded by one single dyke. The owner had relied on the local fire service, which was on the spot very quickly however couldn’t take management over the fire with the tools available, partially because 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 firm to do the extinguishing work. Mobilization of apparatus and foam focus in addition to the preparation of a plan of action took approximately thirteen hours. The hearth was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been remodeled three days, with foam focus and water shortages occurring within the meantime. In complete, over 500,000 litres of foam concentrate have been used. Instead of a hearth in the dyke space, 11 of the 15 tanks burnt down.
It could be very probable that the hearth would have been extinguished rapidly if the warning techniques and valves had labored and a set fireplace extinguishing system had existed. It can also be possible that the fireplace would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been started earlier. Both instances would have resulted in notably less harm.
Summing up, the following points ought to be learned as a minimum. As far as they haven’t yet been applied, or just partly, they need to function a basis for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection idea together with different situations which adapt to the given scenario regularly.
Always have a enough variety of mobile extinguishing methods as a backup to fixed extinguishing techniques.
Stock an appropriate foam concentrate.
Ensure enough foam concentrate provide.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment out there in a enough quantity.
Have educated personnel available in a adequate number.
Ensure a fast implementation of a suitable plan of motion.
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