Part One of this article described the everyday incident scenarios at tank farm fires and offered foam as the most suitable extinguishing agent together with the firefighting equipment mostly used. In Part Two we take a glance at foam focus proportioning technologies, mobile extinguishing techniques and conclude with classes realized.
NFPA eleven describes varied forms of foam focus proportioning tools. In the next, three systems are checked out which are commonest. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning rate must not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
The proportioning rate must not exceed 30% above the permitted worth i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning price 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 should be used respectively).
To assure appropriate proportioning, the proportioner, together with the proportioning fee must be examined a minimum of 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 proven and cost-effective technology. 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 foam focus from the bladder as required. The bladder is related to a proportioner which operates using the venturi principle. When the fireplace pumps are activated, strain is generated by the pump, causing delivery of froth focus to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the foam focus into the extinguishing water move.
The benefits of this method are its simple design with out moving components and its easy operation. No exterior vitality is required, and the system is relatively inexpensive.
A disadvantage 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 should be shut down and drained. The rubber bladder is delicate; when damaged, water will contaminate the froth focus. At a given proportioning fee, the system is appropriate just for low variations within the extinguishing water move pressure and quantity. Adding or changing individual foam discharge gadgets is feasible only to a very limited extent. The system can additionally 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 throughout the extinguishing water line. The right proportioning rate should be measured within the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam focus within the bladder tank needs to be replaced.
เกจวัดแรงดันลมราคา : Driven proportioning pump with move meter.
Driven proportioning pump with flow 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 flow meter in the extinguishing water flow line. When the fire pumps are activated, the foam concentrate pump drive and digital management system have to be activated. The extinguishing water flow price is measured by the flow meter and the control system adjusts the right foam concentrate quantity via the control valve. The foam focus is injected into the extinguishing water circulate by the foam focus pump. If there’s a change in the flow rate, the amount of injected foam focus is regulated by the management valve.
The system’s advantage lies in the exact proportioning of the foam focus, impartial of the extinguishing water pressure or flow price. Foam concentrate may be topped up through the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system must be activated; however, the delivered foam focus may be measured by way of a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate flow fee. No premix is produced; and as a end result of the foam concentrate is handed back into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an external interruption-free vitality provide for the foam focus pump and the management system, as properly as the necessity for a sophisticated control system and the comparatively larger buying prices. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water flow fee and the newly adjusted foam focus amount. The foam quality could additionally be compromised when continuously changing operating circumstances 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 focus, a water motor installed within the extinguishing water move 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 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 move rate modifications, the amount of foam focus is tailored instantly.
The benefit of the system is its independence from external energy sources as properly as a exact and immediate foam-concentrate proportioning regardless of the extinguishing water stress or move rate. 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 connected to one another. Foam focus refilling during operation is feasible. The system can also be capable of proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nonetheless, the delivered foam focus could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow rate. No premix is generated; and if the froth focus is handed back into the tank, no foam focus needs to be topped up.
The larger design and the comparatively greater buying prices are a disadvantage of the system.
With any system, consideration should be taken under consideration for the annual testing prices, which could be appreciable in phrases of substitute foam concentrate, disposal of premix and labour costs.
Mobile extinguishing techniques
As the stationary foam discharge tools may be broken in intensive fires in the tank or within the dyke space and thus lose effectiveness, cell fireplace displays and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they have solely restricted extinguishing agent circulate charges and reaches.
Firefighting monitors
Firefighting displays are discharge gadgets mounted on automobiles or trailers and obtainable in many sizes. The extinguishing agent move price can be up to 60,000 litres/min and the attain could be as much as 180m if the stress of the hearth pumps is adequate. They are suitable 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 to have the ability to forestall it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke space should at all times be noticed to keep away from an overflow of the dyke.
Mobile hearth displays can be equipped both by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the foam concentrate normally takes place through cellular proportioners. This clearly points towards the advantage of power independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular units obtainable as back-ups is proven by the next instance for the location of displays for hearth extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This results in a quantity of alternate options for the screens. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which should be succesful of handle various move rates to guarantee flexibility during extinguishing operations. Depending on the native circumstances, the displays might need to maintain a minimum distance to the burning tank or might not have the power to be positioned close to to the tanks because of particles. In addition, it will not all the time be attainable to place several monitors around the tank. It have to be ensured the monitor has adequate throwing top in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal laws in addition to recommendations by associations like NFPA and is not checked out extra closely in the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As talked about in the introduction to Part One of this article, plainly many authorities and corporations have not discovered the necessary lessons from disastrous fire incidents of past years. Tank farm fires within the oil and petrochemical trade do not occur regularly. When they do, they usually have devastating penalties. Let us remember the tank farm fireplace at Deer Park, Texas in March 2019 talked about in the introduction.
The fire 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 fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fixed extinguishing methods installed. All 15 tanks had been surrounded by one single dyke. The proprietor had relied on the local fireplace service, which was on the spot in a short time but could not take management over the fire with the gear available, partially as a outcome of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the hearth had damaged out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of equipment and foam concentrate in addition to the preparation of a plan of action took approximately thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts have been remodeled three days, with foam focus and water shortages occurring within the meantime. In total, over 500,000 litres of foam focus had been used. Instead of a fireplace within the dyke area, eleven of the 15 tanks burnt down.
It is very possible that the fireplace would have been extinguished rapidly if the warning systems and valves had worked and a fixed hearth extinguishing system had existed. It can also be possible 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 learned at least. As far as they haven’t but been carried out, or simply partly, they should serve as a basis for discussions about one’s own fire-protection concept:
Have an appropriate fire-protection idea including different situations which adapt to the given state of affairs regularly.
Always have a sufficient number of mobile extinguishing systems as a backup to fixed extinguishing systems.
Stock an appropriate foam focus.
Ensure sufficient foam concentrate supply.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing equipment available in a adequate quantity.
Have educated personnel out there in a enough quantity.
Ensure a quick implementation of a suitable plan of action.
For more data, go to www.firedos.com
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