Part One of this text described the everyday incident scenarios at tank farm fires and introduced foam as essentially the most appropriate extinguishing agent along with the firefighting equipment mostly used. In Part Two we take a look at foam focus proportioning technologies, mobile extinguishing techniques and conclude with lessons learned.
NFPA 11 describes various kinds of foam concentrate proportioning gear. In the next, three methods are looked at which are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price must not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning fee should not exceed 30% above the permitted value i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; 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 worth must be used respectively).
To assure appropriate proportioning, 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 know-how. The bladder tank is a pressurized vessel with a bladder inside which is crammed with foam focus. 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 using the venturi principle. When the fire pumps are activated, strain is generated by the pump, causing supply of foam focus to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the foam concentrate into the extinguishing water move.
The advantages of this system are its easy design without transferring components and its simple operation. No exterior energy is required, and the system is relatively inexpensive.
A disadvantage 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 have to be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam concentrate. At a given proportioning price, the system is appropriate just for low variations within the extinguishing water move strain and volume. Adding or changing particular person foam discharge devices is feasible solely to a really restricted extent. The system can also be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system should be activated and premix generated at the venturi proportioner within the extinguishing water line. The appropriate proportioning price must be measured within the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam focus in the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the foam focus, an electric or diesel-powered foam concentrate pump with an electronically managed valve and a circulate meter within the extinguishing water flow line. When the hearth pumps are activated, the froth concentrate pump drive and digital management system must be activated. The extinguishing water circulate fee is measured by the move meter and the management system adjusts the right foam concentrate amount via 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 circulate rate, the quantity of injected foam focus is regulated by the management valve.
The system’s advantage lies in the exact proportioning of the foam concentrate, impartial of the extinguishing water strain or circulate price. Foam focus could be topped up in the course of the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the aim of annual testing, the system have to be activated; nonetheless, 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 a outcome of 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 provide for the froth focus pump and the management system, as nicely as the need for a sophisticated management system and the comparatively larger purchasing prices. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water circulate fee and the newly adjusted foam concentrate amount. The foam quality could also be compromised when continually changing working conditions as foam discharge gadgets 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 within the extinguishing water flow line and a foam focus pump which is linked on 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 provides immediate foam-concentrate injection into the extinguishing water. If the move rate adjustments, the quantity of foam focus is customized immediately.
The benefit of the system is its independence from exterior energy sources in addition to a exact and instant foam-concentrate proportioning whatever the extinguishing water strain or circulate rate. If a piston or plunger pump is used, adjustment or calibration after set up is not needed since the water motor and the pump are volumetric devices firmly connected to every other. Foam focus refilling throughout operation is possible. The system is also capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam concentrate can be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move price. No premix is generated; and if the froth focus is passed again into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively larger purchasing prices are a disadvantage of the system.
With any system, consideration ought to be taken into account for the annual testing costs, which could be appreciable when it comes to replacement foam concentrate, disposal of premix and labour costs.
Mobile extinguishing techniques
As the stationary foam discharge tools could be damaged in in depth fires within the tank or within the dyke space and thus lose effectiveness, cell hearth monitors and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they have solely restricted extinguishing agent circulate charges and reaches.
Firefighting displays
Firefighting displays are discharge gadgets mounted on vehicles or trailers and obtainable in plenty of sizes. The extinguishing agent flow rate can be up to 60,000 litres/min and the attain may be up to 180m if the strain of the fire pumps is adequate. They are appropriate 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 in order to forestall it reaching the crucial temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area should always be noticed to keep away from an overflow of the dyke.
Mobile hearth displays could be supplied both by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the froth concentrate usually takes place through cell proportioners. This clearly factors in direction of the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cell items obtainable as back-ups is proven by the following example for the location of displays for fireplace 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 a minimum of 32,000 litres/min are required, which should be in a position to handle varying circulate charges to ensure flexibility throughout extinguishing operations. Depending on the native situations, the monitors will want to maintain a minimum distance to the burning tank or might not be succesful of be positioned near to the tanks as a result of debris. In addition, it is not going to all the time be potential to place several screens across the tank. It must be ensured the monitor has adequate throwing height in relation to the tank top, to deliver foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal regulations in addition to suggestions by associations like NFPA and isn’t checked out more intently within 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 evidently many authorities and companies have not realized the required lessons from disastrous fire incidents of previous years. Tank farm fires within the oil and petrochemical business don’t happen incessantly. When they do, they normally have devastating penalties. Let us bear 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 fire for yet unknown causes. The plant had no fuel 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 local hearth service, which was on the spot very quickly but could not take management over the fireplace with the equipment obtainable, partially as a outcome of 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 firm to do the extinguishing work. Mobilization of equipment and foam concentrate as well as the preparation of a plan of action took approximately thirteen hours. The fireplace 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 whole, over 500,000 litres of foam concentrate had been used. Instead of a hearth in the dyke space, eleven of the 15 tanks burnt down.
It could be very possible that the hearth would have been extinguished quickly if the warning methods and valves had worked and a exhausting and fast fireplace extinguishing system had existed. It can also be possible that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been started earlier. Both instances would have resulted in notably less injury.
Summing up, the following factors must be learned at least. As far as they have not yet been implemented, or just partly, they want to function a basis for discussions about one’s personal fire-protection idea:
Have an acceptable fire-protection concept together with different eventualities which adapt to the given situation frequently.
Always have a sufficient number of cellular extinguishing methods as a backup to mounted extinguishing methods.
Stock an acceptable foam concentrate.
Ensure sufficient foam focus supply.
Ensure enough water supply.
Keep well-maintained, quickly and well- pressure gauge ลม , strategically placed and functioning extinguishing tools available in a sufficient quantity.
Have educated personnel obtainable in a adequate number.
Ensure a quick implementation of an acceptable plan of motion.
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