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Part One of this text described the typical incident eventualities at tank farm fires and introduced foam as probably the most suitable extinguishing agent together with the firefighting gear most commonly used. In Part Two we have a glance at foam focus proportioning applied sciences, cell extinguishing methods and conclude with lessons learned.
NFPA eleven describes varied kinds of foam concentrate proportioning equipment. In the following, three techniques are looked at which are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning fee should not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam focus.
The proportioning rate must not exceed 30% above the permitted value i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning fee is allowed to be an absolute most of 1% above the permitted worth – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam concentrate (the smaller value have to be used respectively).
To assure correct proportioning, the proportioner, including the proportioning price have to be tested at least every year 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 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 froth concentrate from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi precept. When the hearth pumps are activated, stress is generated by the pump, inflicting delivery of foam focus to the proportioner. The extinguishing water flows via the venturi proportioner. The ensuing vacuum induces the froth concentrate into the extinguishing water circulate.
The benefits of this technique are its simple design without transferring elements and its easy operation. No external power is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws corresponding 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 broken, water will contaminate the froth focus. At a given proportioning rate, the system is appropriate just for low variations within the extinguishing water circulate pressure and quantity. Adding or changing particular person foam discharge units is feasible only to a very limited extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any mandatory required annual testing, the system have to be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The correct proportioning fee should be measured in the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam concentrate within the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the froth focus, an electrical or diesel-powered foam focus pump with an electronically managed valve and a flow meter in the extinguishing water circulate line. When the fire pumps are activated, the foam concentrate pump drive and digital control system have to be activated. The extinguishing water move price is measured by the move meter and the management system adjusts the right foam focus amount through the control valve. The foam focus is injected into the extinguishing water move by the foam concentrate pump. If there’s a change within the flow rate, the quantity of injected foam concentrate is regulated by the control valve.
The system’s benefit lies within the exact proportioning of the foam focus, impartial of the extinguishing water strain or flow rate. Foam focus can 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 must be activated; nevertheless, the delivered foam concentrate may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate circulate fee. No premix is produced; and as the foam concentrate is passed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free energy supply for the foam focus pump and the control system, as well as the necessity for a complicated management system and the comparatively greater buying costs. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water circulate fee and the newly adjusted foam focus quantity. The foam quality may be compromised when constantly changing operating circumstances 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 concentrate, a water motor put in in the extinguishing water flow line and a foam focus pump which is related on to the water motor. Water motor and pump form one compact unit. Upon activation of the fire pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump offers quick foam-concentrate injection into the extinguishing water. If the flow rate adjustments, the quantity of foam focus is customized instantly.
The advantage of the system is its independence from external energy sources as properly as a precise and immediate foam-concentrate proportioning regardless of the extinguishing water stress or circulate rate. If a piston or plunger pump is used, adjustment or calibration after set up isn’t necessary since the water motor and the pump are volumetric gadgets firmly connected to one another. Foam concentrate refilling during operation is feasible. The system is also able to proportioning highly viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam concentrate can be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow rate. No premix is generated; and if the foam concentrate is passed back into the tank, no foam focus must be topped up.
The larger design and the comparatively higher buying prices are a disadvantage of the system.
With any system, consideration should be taken into consideration for the annual testing prices, which can be considerable when it comes to substitute foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge equipment may be damaged in extensive fires within the tank or in the dyke area and thus lose effectiveness, cell fire monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they have only restricted extinguishing agent flow charges and reaches.
Firefighting monitors
Firefighting monitors are discharge devices mounted on automobiles or trailers and out there in many sizes. The extinguishing agent move fee could be up to 60,000 litres/min and the attain can be as much as 180m if the stress of the fire pumps is enough. 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 in order 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 ought to all the time be observed to avoid an overflow of the dyke.
Mobile hearth screens could be equipped either by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the foam focus often takes place through cellular proportioners. This clearly points towards the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of mobile units available as back-ups is proven by the following instance for the placement of screens for fire extinguishing at tanks which are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. ร้านซ่อมเครื่องวัดความดัน ends in a number of alternatives for the monitors. Generally, foam-concentrate proportioners for a minimum of 32,000 litres/min are required, which ought to be ready to deal with various circulate rates to guarantee flexibility throughout extinguishing operations. Depending on the local conditions, the monitors will want to hold a minimum distance to the burning tank or may not be succesful of be positioned close to to the tanks due to particles. In addition, it is not going to all the time be possible to place several displays around the tank. It should be ensured the monitor has sufficient throwing peak in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the whole firefighting system is made following legal laws in addition to recommendations by associations like NFPA and is not looked at more carefully 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 text, it appears that evidently many authorities and companies have not realized the necessary classes from disastrous hearth incidents of past years. Tank farm fires within the oil and petrochemical industry don’t occur frequently. When they do, they normally have devastating penalties. Let us remember the tank farm hearth 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 fire 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 did not have fastened extinguishing systems put in. All 15 tanks had been surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot in a brief time but couldn’t take management over the fireplace with the gear out there, partially because 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 company to do the extinguishing work. Mobilization of apparatus and foam concentrate as properly as the preparation of a plan of action took approximately 13 hours. The hearth was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt have been made over three days, with foam concentrate and water shortages occurring in the meantime. In total, over 500,000 litres of froth focus were used. Instead of a fireplace in the dyke area, 11 of the 15 tanks burnt down.
It could be very possible that the hearth would have been extinguished quickly if the warning systems and valves had labored and a fixed fireplace extinguishing system had existed. It is also probable that the fireplace would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been started earlier. Both instances would have resulted in notably less harm.
Summing up, the next factors should be discovered at least. As far as they have not but been carried out, or simply partly, they should function a foundation for discussions about one’s personal fire-protection idea:
Have an acceptable fire-protection concept together with alternative eventualities which adapt to the given state of affairs often.
Always have a enough number of mobile extinguishing systems as a backup to fastened extinguishing methods.
Stock an appropriate foam focus.
Ensure sufficient foam focus provide.
Ensure enough water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing equipment obtainable in a adequate number.
Have trained personnel obtainable in a enough number.
Ensure a fast implementation of an acceptable plan of motion.
For more data, go to www.firedos.com
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