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Part One of this text described the standard incident scenarios at tank farm fires and introduced foam as probably the most suitable extinguishing agent together with the firefighting equipment mostly used. In Part Two we take a look at foam concentrate proportioning applied sciences, cell extinguishing techniques and conclude with lessons discovered.
NFPA eleven describes numerous types of foam focus proportioning equipment. In the next, three systems 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 fee must not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; respectively, the proportioning rate is allowed to be an absolute most of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller worth should be used respectively).
To guarantee appropriate proportioning, the proportioner, together with the proportioning fee should be tested no less than annually 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 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 froth 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, pressure is generated by the pump, causing supply of foam concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth concentrate into the extinguishing water flow.
The advantages of this system are its easy design without moving parts and its simple operation. เกจแรงดันน้ำ is required, and the system is relatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding regulations such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system should be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the froth focus. At a given proportioning fee, the system is appropriate only for low variations within the extinguishing water move stress and volume. เกจวัดแรงดันต่ำ or altering particular person foam discharge devices is possible solely to a very restricted extent. The system can be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system should be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The appropriate proportioning rate have to be measured in the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus within the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a circulate meter within the extinguishing water circulate line. When the fire pumps are activated, the froth focus pump drive and digital management system must be activated. The extinguishing water move rate is measured by the move meter and the control system adjusts the correct foam concentrate amount by way of the management valve. The foam concentrate is injected into the extinguishing water flow by the foam concentrate pump. If there is a change within the flow fee, the amount of injected foam concentrate is regulated by the management valve.
The system’s advantage lies within the precise proportioning of the froth focus, unbiased of the extinguishing water stress or flow rate. Foam focus could be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system should be activated; nevertheless, the delivered foam focus could be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate move fee. No premix is produced; and as the foam focus is passed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free energy provide for the foam focus pump and the control system, in addition to the necessity for a sophisticated control system and the comparatively larger purchasing costs. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water circulate price and the newly adjusted foam concentrate quantity. The foam quality could also be compromised when continually changing 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 froth focus, a water motor put in within the extinguishing water circulate 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 begins. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the circulate rate adjustments, the quantity of froth focus is customized immediately.
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 stress or move rate. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t essential for the explanation that water motor and the pump are volumetric gadgets firmly related to each other. Foam focus refilling during operation is feasible. The system can be able to proportioning highly viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam concentrate could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate rate. No premix is generated; and if the froth focus is handed again into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively higher buying costs are a disadvantage of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which can be considerable by method of substitute foam focus, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge tools may be damaged in extensive fires within the tank or within the dyke area and thus lose effectiveness, cell fireplace displays 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 move rates and reaches.
Firefighting monitors
Firefighting monitors are discharge gadgets mounted on autos or trailers and obtainable in many sizes. The extinguishing agent move rate could be up to 60,000 litres/min and the attain could be as much as 180m if the strain of the fireplace pumps is sufficient. 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 so as to prevent it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area should always be noticed to avoid an overflow of the dyke.
Mobile fire screens can be provided either by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the froth concentrate normally takes place by way of cellular proportioners. This clearly points towards the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular items obtainable as back-ups is proven by the following instance for the location of monitors for hearth extinguishing at tanks which are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several options for the screens. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which should be succesful of handle various flow rates to ensure flexibility during extinguishing operations. Depending on the local conditions, the monitors might want to hold a minimum distance to the burning tank or may not be succesful of be positioned near to the tanks as a outcome of debris. In addition, it won’t always be possible to position a number of monitors across the tank. It should 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 whole firefighting system is made following authorized rules as well as suggestions by associations like NFPA and isn’t checked out more intently in the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons discovered
As mentioned within the introduction to Part One of this article, it appears that many authorities and firms haven’t realized the required lessons from disastrous fireplace incidents of past years. Tank farm fires in the oil and petrochemical industry don’t occur frequently. When they do, they normally have devastating consequences. Let us keep in mind the tank farm fire at Deer Park, Texas in March 2019 mentioned within 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 gasoline warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have fastened extinguishing methods installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the local hearth service, which was on the spot very quickly but couldn’t take control over the hearth with the tools available, partially as a end result of flammable substance was constantly leaking from the tank. Thirty-six hours after the fire had damaged out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of apparatus and foam concentrate as nicely as the preparation of a plan of motion took approximately thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts have been remodeled three days, with foam focus and water shortages occurring within the meantime. In whole, over 500,000 litres of froth concentrate have been used. Instead of a hearth in the dyke space, 11 of the 15 tanks burnt down.
It may be very probable that the fire would have been extinguished rapidly if the warning methods and valves had worked and a set fireplace extinguishing system had existed. It can be possible that the fireplace 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 damage.
Summing up, the following points ought to be discovered as a minimum. As far as they haven’t yet been implemented, or simply partly, they should serve as a basis for discussions about one’s personal fire-protection concept:
Have an acceptable fire-protection idea together with different eventualities which adapt to the given situation regularly.
Always have a enough number of mobile extinguishing techniques as a backup to fixed extinguishing techniques.
Stock an appropriate foam focus.
Ensure adequate foam focus provide.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing equipment out there in a sufficient number.
Have educated personnel out there in a adequate quantity.
Ensure a quick implementation of an appropriate plan of action.
For more data, go to www.firedos.com
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