Part One of this article described the everyday incident eventualities at tank farm fires and presented foam as the most appropriate extinguishing agent together with the firefighting gear mostly used. In Part Two we look at foam focus proportioning applied sciences, mobile extinguishing methods and conclude with classes realized.
NFPA 11 describes numerous kinds of foam focus proportioning gear. In the next, three techniques are looked at which are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price should not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning rate must not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning fee is allowed to be an absolute maximum of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam focus (the smaller value should be used respectively).
To guarantee เพรสเชอร์เกจน้ำ , the proportioner, including the proportioning price must be examined at least annually and its right 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 expertise. 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, causing supply of foam concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The ensuing vacuum induces the foam focus into the extinguishing water move.
The advantages of this system are its simple design with out shifting components and its easy operation. No external vitality is required, and the system is relatively inexpensive.
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 have to be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the foam concentrate. At a given proportioning price, the system is appropriate just for low variations in the extinguishing water flow pressure and quantity. Adding or changing particular person foam discharge gadgets is possible only to a very limited extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system must be activated and premix generated on the venturi proportioner within the extinguishing water line. The right proportioning fee must be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus within the bladder tank needs to be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with circulate 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 in 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 flow price is measured by the flow meter and the control system adjusts the correct foam focus amount through the control valve. The foam concentrate is injected into the extinguishing water flow by the froth focus pump. If there’s a change in the move price, the amount of injected foam concentrate is regulated by the control valve.
The system’s advantage lies in the exact proportioning of the froth concentrate, independent of the extinguishing water pressure or circulate price. Foam focus could be topped up in the course of the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nonetheless, the delivered foam focus may be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam focus move 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 supply for the froth concentrate pump and the control system, as well as the necessity for a classy control system and the comparatively larger purchasing costs. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water move price and the newly adjusted foam concentrate quantity. The foam quality may be compromised when continuously changing operating circumstances as foam discharge units are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam concentrate, a water motor installed in the extinguishing water flow line and a foam focus pump which is connected directly to the water motor. Water motor and pump type one compact unit. Upon activation of the hearth pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump offers immediate foam-concentrate injection into the extinguishing water. If the circulate fee modifications, the amount of froth focus is adapted instantly.
The benefit of the system is its independence from exterior energy sources as nicely as a precise 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 necessary since the water motor and the pump are volumetric devices firmly related to one another. Foam concentrate refilling throughout operation is possible. The system can additionally be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nonetheless, the delivered foam focus can be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam focus move rate. No premix is generated; and if the froth focus is handed again into the tank, no foam focus must be topped up.
The larger design and the comparatively greater buying prices are an obstacle of the system.
With any system, consideration should be taken into consideration for the annual testing prices, which could be appreciable by method of substitute foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge equipment may be damaged in in depth fires within the tank or within the dyke area and thus lose effectiveness, cellular fireplace monitors and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they have solely limited extinguishing agent move charges and reaches.
Firefighting screens
Firefighting displays are discharge devices mounted on vehicles or trailers and out there in many sizes. The extinguishing agent flow rate may be as a lot as 60,000 litres/min and the reach could be as a lot as 180m if the stress of the fireplace pumps is adequate. They are suitable to discharge foam, e.g., to extinguish a floor fireplace in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank to have the ability to stop it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area should all the time be observed to avoid an overflow of the dyke.
Mobile fire screens could be equipped either by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the foam concentrate normally takes place through mobile proportioners. This clearly points towards the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular items obtainable as back-ups is shown by the following instance for the location of screens for fire 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 a minimal of 32,000 litres/min are required, which should be succesful of handle various flow rates to guarantee flexibility during extinguishing operations. Depending on the local situations, the screens might want to maintain a minimum distance to the burning tank or could not be capable of be positioned close to to the tanks because of particles. In addition, it will not all the time be potential to position a number of displays across the tank. It should be ensured the monitor has enough throwing peak in relation to the tank peak, to deliver foam into the inside of the tank.
The dimensioning of the whole firefighting system is made following authorized rules in addition to recommendations by associations like NFPA and is not 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 text, it appears that evidently many authorities and companies haven’t discovered the required classes from disastrous fire incidents of previous years. Tank farm fires within the oil and petrochemical industry don’t happen regularly. When they do, they normally have devastating penalties. Let us remember the tank farm fireplace at Deer Park, Texas in March 2019 talked about 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 fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have mounted extinguishing systems installed. All 15 tanks had been surrounded by one single dyke. The proprietor had relied on the local hearth service, which was on the spot in a short time however couldn’t take control over the fire with the gear out there, partially as a end result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of equipment and foam concentrate as well as the preparation of a plan of motion took approximately 13 hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been made over three days, with foam concentrate and water shortages occurring in the meantime. In whole, over 500,000 litres of foam concentrate had been used. Instead of a hearth within the dyke space, eleven of the 15 tanks burnt down.
It could be very possible that the fire would have been extinguished rapidly if the warning techniques and valves had worked and a onerous and fast fireplace 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 started earlier. Both instances would have resulted in notably much less damage.
Summing up, the following points must be discovered at least. As far as they have not yet been applied, or simply partly, they should function a basis for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection idea together with various scenarios which adapt to the given situation frequently.
Always have a sufficient number of cell extinguishing techniques as a backup to fastened extinguishing methods.
Stock an appropriate foam focus.
Ensure enough foam concentrate provide.
Ensure adequate water supply.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing tools out there in a enough number.
Have skilled personnel available in a enough quantity.
Ensure a quick implementation of an acceptable plan of motion.
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