Part One of this article described the standard incident situations at tank farm fires and offered foam as essentially the most suitable extinguishing agent along with the firefighting equipment mostly used. In Part Two we look at foam concentrate proportioning applied sciences, cellular extinguishing methods and conclude with lessons discovered.
NFPA eleven describes various kinds of foam focus proportioning equipment. In the following, three systems are checked out that are most typical. 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 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 concentrate; 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 must be used respectively).
To guarantee correct proportioning, the proportioner, including the proportioning rate must be tested at least once a 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 proven and cost-effective expertise. The bladder tank is a pressurized vessel with a bladder inside which is filled with foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the froth focus from the bladder as required. The bladder is linked to a proportioner which operates utilizing the venturi precept. When the hearth 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 resulting vacuum induces the foam concentrate into the extinguishing water flow.
The advantages of this technique are its simple design with out shifting components and its straightforward operation. No external vitality is required, and the system is relatively cheap.
A disadvantage 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 should be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the foam focus. At a given proportioning fee, the system is suitable just for low variations in the extinguishing water flow stress and volume. Adding or changing individual foam discharge devices is possible solely to a very limited extent. The system can be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated at the venturi proportioner inside the extinguishing water line. The appropriate proportioning fee 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 needs to be replaced.
Fig. 2: Driven proportioning pump with circulate 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 move meter within the extinguishing water circulate line. When the fireplace pumps are activated, the foam concentrate pump drive and digital control system should be activated. The extinguishing water flow price is measured by the circulate meter and the management system adjusts the proper foam focus quantity via the management valve. The foam concentrate is injected into the extinguishing water flow by the foam concentrate pump. If there’s a change within the flow fee, the amount of injected foam focus is regulated by the control valve.
The system’s benefit lies in the exact proportioning of the froth focus, independent of the extinguishing water strain or move price. Foam concentrate can be topped up through the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the aim of annual testing, the system must be activated; however, the delivered foam focus could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow rate. No premix is produced; and as the foam concentrate is passed again into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free power provide for the foam concentrate pump and the management system, as well as the need for a sophisticated management system and the comparatively higher purchasing costs. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water move rate and the newly adjusted foam focus amount. The foam high quality may be compromised when continually altering working circumstances as foam discharge gadgets are turned on or off or modified.
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 focus pump which is linked directly 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 provides instant foam-concentrate injection into the extinguishing water. If the circulate rate modifications, the quantity of foam focus is customized instantly.
The advantage of the system is its independence from exterior power sources in addition to a exact and quick foam-concentrate proportioning regardless of the extinguishing water strain or flow 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 units firmly related to one another. Foam concentrate refilling during operation is possible. The system is also capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus may be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate circulate rate. No premix is generated; and if the foam focus is passed back into the tank, no foam focus must be topped up.
The larger design and the comparatively higher buying costs are a disadvantage of the system.
With any system, consideration must be taken under consideration for the annual testing costs, which could be appreciable in phrases of substitute foam focus, disposal of premix and labour costs.
Mobile extinguishing methods
As the stationary foam discharge tools can be damaged in extensive fires within the tank or within the dyke space and thus lose effectiveness, mobile fireplace monitors and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve only restricted extinguishing agent circulate rates and reaches.
Firefighting monitors
Firefighting monitors are discharge devices mounted on vehicles or trailers and available in plenty of sizes. The extinguishing agent move price can be as much as 60,000 litres/min and the reach can be as much as 180m if the strain of the hearth pumps is enough. They are appropriate to discharge foam, e.g., to extinguish a floor fire in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank so as to forestall 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 always be observed to avoid an overflow of the dyke.
Mobile fire monitors could be equipped both by the extinguishing water of the stationary fire pumps or by cellular pumps. The injection of the foam focus normally takes place by way of mobile proportioners. เพรสเชอร์เกจnuovafima towards the advantage of vitality independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of mobile items obtainable as back-ups is proven by the next instance for the position of monitors 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 options for the screens. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which ought to be ready to handle varying move rates to ensure flexibility throughout extinguishing operations. Depending on the native conditions, the displays will want to keep a minimum distance to the burning tank or might not have the ability to be positioned near to the tanks due to particles. In addition, it won’t all the time be potential to place several displays across the tank. It must be ensured the monitor has adequate throwing top in relation to the tank height, to ship foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following authorized rules in addition to recommendations by associations like NFPA and isn’t looked at extra intently in the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons discovered
As talked about in the introduction to Part One of this text, it seems that many authorities and companies haven’t learned the mandatory classes from disastrous fireplace incidents of previous years. Tank farm fires within the oil and petrochemical trade don’t occur incessantly. When they do, they usually have devastating consequences. Let us bear in mind the tank farm fireplace at Deer Park, Texas in March 2019 mentioned within 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 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 mounted extinguishing systems installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot in a brief time however couldn’t take management over the fireplace with the equipment out there, partially as a outcome of flammable substance was continuously leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of kit and foam focus in addition to the preparation of a plan of motion took approximately thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts had been revamped three days, with foam concentrate and water shortages occurring within the meantime. In complete, 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 may be very possible that the fireplace would have been extinguished rapidly if the warning techniques and valves had labored and a fixed hearth extinguishing system had existed. It can also be possible that the fire would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably less damage.
Summing up, the next points ought to be discovered as a minimum. As far as they haven’t yet been carried out, or simply partly, they want to serve as a foundation for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection idea including various eventualities which adapt to the given situation often.
Always have a adequate number of mobile extinguishing methods as a backup to fastened extinguishing techniques.
Stock an appropriate foam focus.
Ensure sufficient foam concentrate supply.
Ensure sufficient water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing gear available in a sufficient quantity.
Have educated personnel available in a adequate quantity.
Ensure a quick implementation of a suitable plan of motion.
For extra info, go to www.firedos.com
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