Part One of this article described the standard incident eventualities 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 have a look at foam focus proportioning applied sciences, cellular extinguishing systems and conclude with lessons discovered.
NFPA eleven describes varied kinds of foam concentrate proportioning equipment. In the following, three techniques are checked out which are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning rate must not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning price must not exceed 30% above the permitted worth i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning rate is allowed to be an absolute most of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller worth must be used respectively).
To assure appropriate proportioning, the proportioner, including the proportioning rate have to be examined a minimal of every year and its right functioning should 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 concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is linked to a proportioner which operates using the venturi principle. When the fire pumps are activated, strain is generated by the pump, causing supply of froth focus to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water circulate.
The benefits of this method are its easy design with out shifting components and its straightforward operation. No exterior energy is required, and the system is comparatively inexpensive.
A drawback is that the system is a pressurized vessel subject to corresponding regulations corresponding to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system have to be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the froth concentrate. At a given proportioning fee, the system is appropriate only for low variations in the extinguishing water flow strain and quantity. Adding or altering individual foam discharge devices is feasible solely to a very restricted extent. The system can also be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system have to be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The right proportioning fee should be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus in the bladder tank needs to be replaced.
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 electrical or diesel-powered foam focus pump with an electronically controlled valve and a move meter in the extinguishing water flow line. When the hearth pumps are activated, the froth focus pump drive and electronic management system have to be activated. The extinguishing water circulate fee is measured by the move meter and the management system adjusts the right foam focus quantity by way of the control valve. The foam focus is injected into the extinguishing water move by the froth focus pump. If there is a change within the move rate, the amount of injected foam focus is regulated by the management valve.
The system’s benefit lies within the exact proportioning of the froth focus, impartial of the extinguishing water pressure or circulate fee. Foam focus may be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system should be activated; nevertheless, the delivered foam concentrate could be measured through a return line. The proportioning price is calculated from the extinguishing water/foam concentrate flow price. No premix is produced; and as a outcome 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 energy supply for the froth focus pump and the management system, as well as the necessity for a sophisticated management system and the comparatively larger buying costs. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water circulate fee and the newly adjusted foam focus quantity. The foam high quality could also be compromised when continuously changing operating situations 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 in the extinguishing water move line and a foam concentrate pump which is connected 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 quick foam-concentrate injection into the extinguishing water. If the flow price modifications, the quantity of foam concentrate is adapted instantly.
The advantage of the system is its independence from external power sources in addition to a exact and quick foam-concentrate proportioning regardless of the extinguishing water stress or circulate price. 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 gadgets firmly related to every other. Foam focus refilling during operation is feasible. The system is also capable of proportioning extremely viscous foam concentrates. The system have to be activated for annual testing; nonetheless, the delivered foam focus may be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus circulate price. No premix is generated; and if the froth concentrate is handed back into the tank, no foam focus must be topped up.
The larger design and the comparatively higher buying costs are an obstacle of the system.
With any system, consideration should be taken into account for the annual testing costs, which can be appreciable in phrases of substitute foam concentrate, disposal of premix and labour costs.
Mobile extinguishing methods
As the stationary foam discharge tools can be damaged in extensive fires in the tank or in 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 flexible. Yet they’ve only limited extinguishing agent circulate rates and reaches.
Firefighting displays
Firefighting screens are discharge units mounted on vehicles or trailers and obtainable in plenty of sizes. The extinguishing agent circulate rate could be up to 60,000 litres/min and the reach can be up to 180m if the strain of the hearth pumps is enough. They are suitable to discharge foam, e.g., to extinguish a floor hearth in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank so as to stop it reaching the crucial temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke space ought to at all times be observed to keep away from an overflow of the dyke.
Mobile hearth screens may be provided both by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the foam focus often takes place through cellular proportioners. This clearly points towards the benefit of power independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of mobile items available as back-ups is proven by the following example for the placement of displays for hearth extinguishing at tanks which are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several alternatives for the monitors. Generally, foam-concentrate proportioners for a minimum of 32,000 litres/min are required, which should have the power to deal with varying move rates to ensure flexibility during extinguishing operations. Depending on the native situations, the screens might want to maintain a minimal distance to the burning tank or may not have the power to be positioned close to to the tanks due to debris. In addition, it won’t at all times be potential to place several screens around the tank. It have to be ensured the monitor has sufficient throwing top in relation to the tank height, to deliver foam into the inside of the tank.
The dimensioning of the whole firefighting system is made following authorized regulations in addition to suggestions by associations like NFPA and isn’t checked out more closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned
As talked about in the introduction to Part One of this article, it appears that evidently many authorities and firms haven’t learned the mandatory classes from disastrous fireplace incidents of past years. ราคาเกจวัดแรงดันน้ำ in the oil and petrochemical trade don’t happen frequently. When they do, they normally have devastating penalties. Let us bear in mind the tank farm fireplace at Deer Park, Texas in March 2019 mentioned in the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught hearth for yet unknown reasons. The plant had no gasoline warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have mounted extinguishing systems put in. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native fireplace service, which was on the spot very quickly but couldn’t take control over the hearth with the tools obtainable, partially as a result of flammable substance was continuously leaking from the tank. Thirty-six hours after the hearth had damaged out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of kit and foam concentrate as nicely as the preparation of a plan of motion took roughly 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 remodeled three days, with foam focus and water shortages occurring in the meantime. In total, over 500,000 litres of foam focus have 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 methods and valves had worked and a set fire 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 harm.
Summing up, the following factors ought to be learned at least. As far as they haven’t but been carried out, or just partly, they should serve as a foundation for discussions about one’s own fire-protection idea:
Have an appropriate fire-protection idea together with various scenarios which adapt to the given scenario regularly.
Always have a sufficient variety of cellular extinguishing systems as a backup to fixed extinguishing techniques.
Stock an appropriate foam concentrate.
Ensure enough foam focus supply.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing gear obtainable in a enough quantity.
Have educated personnel out there in a sufficient quantity.
Ensure a fast implementation of an acceptable plan of motion.
For extra information, go to www.firedos.com
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