Part One of this article described the typical incident scenarios at tank farm fires and presented foam as probably the most suitable extinguishing agent together with the firefighting tools most commonly used. In Part Two we take a look at foam concentrate proportioning applied sciences, cellular extinguishing methods and conclude with lessons learned.
NFPA eleven describes numerous forms of foam focus proportioning equipment. In the next, three techniques are looked at that are most common. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning price must 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 should 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 concentrate or 7% for a 6% foam focus (the smaller worth must be used respectively).
To assure appropriate proportioning, the proportioner, including the proportioning rate must be tested at least once a year and its correct functioning must be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a proven and cost-effective technology. 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 foam focus from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi principle. When the fire pumps are activated, stress is generated by the pump, inflicting supply of froth concentrate to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the foam focus into the extinguishing water circulate.
The advantages of this system are its easy design with out shifting elements and its easy operation. No exterior vitality is required, and the system is comparatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding laws similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system have to be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the froth concentrate. At a given proportioning price, the system is suitable only for low variations within the extinguishing water move strain and quantity. Adding or altering particular person foam discharge gadgets is possible solely to a very restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated on the venturi proportioner inside the extinguishing water line. The appropriate proportioning fee should be measured within the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam concentrate within the bladder tank needs to be replaced.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the froth concentrate, an electrical or diesel-powered foam focus pump with an electronically controlled valve and a circulate meter within the extinguishing water circulate line. When the fireplace pumps are activated, the froth concentrate pump drive and digital management system must be activated. The extinguishing water circulate price is measured by the move meter and the control system adjusts the correct foam concentrate amount through the control valve. The foam focus is injected into the extinguishing water move by the foam concentrate pump. If there is a change in the circulate fee, the quantity of injected foam focus is regulated by the management valve.
The system’s advantage lies in the precise proportioning of the froth focus, independent of the extinguishing water pressure or move rate. Foam focus can be topped up in the course of the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nevertheless, the delivered foam focus may be measured via a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate fee. No premix is produced; and as a result of 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 energy supply for the froth focus pump and the control system, in addition to the need for a classy control system and the comparatively higher purchasing prices. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water flow fee and the newly adjusted foam focus quantity. The foam high quality could also be compromised when continuously altering operating circumstances as foam discharge units are turned on or off or modified.
เกจวัดแรงดัน with proportioning pump
The system consists of an atmospheric tank for the froth focus, a water motor installed within the extinguishing water move line and a foam concentrate pump which is connected directly to the water motor. Water motor and pump form one compact unit. Upon activation of the fireplace pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump offers immediate foam-concentrate injection into the extinguishing water. If the flow rate modifications, the quantity of foam focus is customized instantly.
The advantage of the system is its independence from exterior vitality sources in addition to a precise and immediate foam-concentrate proportioning regardless of the extinguishing water pressure or circulate price. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t necessary for the explanation that water motor and the pump are volumetric devices firmly linked to every other. Foam focus refilling during operation is possible. The system is also able to proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus move rate. No premix is generated; and if the foam focus is handed again into the tank, no foam concentrate needs to be topped up.
The bigger design and the comparatively larger buying costs are a drawback of the system.
With any system, consideration ought to be taken into consideration for the annual testing costs, which can be considerable when it comes to alternative foam focus, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge gear may be damaged in extensive fires in the tank or within the dyke space and thus lose effectiveness, mobile fireplace screens and foam pipes could also be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve solely limited extinguishing agent circulate rates and reaches.
Firefighting screens
Firefighting displays are discharge units mounted on vehicles or trailers and out there in plenty of sizes. The extinguishing agent flow rate could be up to 60,000 litres/min and the reach could be as much as 180m if the pressure of the fireplace pumps is enough. They are appropriate 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 important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area should at all times be noticed to keep away from an overflow of the dyke.
Mobile fireplace displays can be supplied either by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the foam focus often takes place via cell proportioners. This clearly points in the direction of the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular models obtainable as back-ups is proven by the next example for the location 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 leads to several alternatives for the monitors. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which ought to have the flexibility to deal with various flow rates to guarantee flexibility during extinguishing operations. Depending on the local conditions, the screens will want to keep a minimal distance to the burning tank or may not be able to be positioned close to to the tanks as a result of debris. In addition, it won’t always be possible to position a quantity of monitors across the tank. It have to be ensured the monitor has sufficient throwing height in relation to the tank height, to ship foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following legal rules in addition to suggestions by associations like NFPA and isn’t checked out extra carefully in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons realized
As mentioned in the introduction to Part One of this article, it seems that many authorities and companies have not realized the required lessons from disastrous fireplace incidents of previous years. Tank farm fires in the oil and petrochemical business do not occur incessantly. When they do, they usually have devastating consequences. Let us bear in mind the tank farm fire 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 faulty valve for 30 minutes and caught fireplace for yet unknown reasons. 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 installed. All 15 tanks had been surrounded by one single dyke. เพรสเชอร์เกจ had relied on the local fire service, which was on the spot very quickly but couldn’t take management over the fire with the gear available, partially because flammable substance was continuously leaking from the tank. Thirty-six hours after the fire had damaged out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of equipment and foam focus in addition to the preparation of a plan of motion took roughly 13 hours. The hearth was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts have been made over three days, with foam concentrate and water shortages occurring within the meantime. In whole, over 500,000 litres of foam concentrate were used. Instead of a fireplace within the dyke space, 11 of the 15 tanks burnt down.
It may be very possible that the hearth would have been extinguished shortly if the warning systems and valves had labored and a onerous and fast hearth extinguishing system had existed. It can be probable that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both circumstances would have resulted in notably much less harm.
Summing up, the following factors must be discovered as a minimum. As far as they haven’t but been carried out, or simply partly, they should function a basis for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection idea together with various scenarios which adapt to the given state of affairs frequently.
Always have a sufficient number of mobile extinguishing techniques as a backup to mounted extinguishing techniques.
Stock an appropriate foam concentrate.
Ensure sufficient foam focus provide.
Ensure enough water provide.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing gear obtainable in a adequate quantity.
Have skilled personnel obtainable in a sufficient quantity.
Ensure a fast implementation of a suitable plan of motion.
For extra data, go to www.firedos.com
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