Part One of this text described the typical incident eventualities at tank farm fires and introduced foam as the most suitable extinguishing agent along with the firefighting gear mostly used. In Part Two we take a glance at foam focus proportioning applied sciences, mobile extinguishing systems and conclude with lessons realized.
NFPA eleven describes varied forms of foam focus proportioning tools. In the next, three methods are checked out that are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning fee must not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam focus.
The proportioning price must not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning price is allowed to be an absolute maximum of 1% above the permitted value – 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, together with the proportioning fee should be examined at least 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 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 focus from the bladder as required. The bladder is connected to a proportioner which operates using the venturi precept. When the fire pumps are activated, strain is generated by the pump, causing delivery of foam focus to the proportioner. The extinguishing water flows through the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water circulate.
The advantages of this system are its simple design with out moving parts and its straightforward operation. No exterior vitality is required, and the system is comparatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system should be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the foam focus. At เกจวัดแรงดัน given proportioning rate, the system is suitable just for low variations within the extinguishing water flow strain and quantity. Adding or altering individual foam discharge units is possible only to a really limited extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system should be activated and premix generated on the venturi proportioner within the extinguishing water line. The right proportioning fee must be measured within 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 changed.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the froth focus, an electric or diesel-powered foam focus pump with an electronically managed valve and a move meter within the extinguishing water circulate line. When the hearth pumps are activated, the foam focus pump drive and electronic control system should be activated. The extinguishing water move fee is measured by the flow 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 focus pump. If there’s a change within the circulate price, the quantity of injected foam focus is regulated by the control valve.
The system’s benefit lies in the exact proportioning of the froth concentrate, impartial of the extinguishing water pressure or circulate fee. Foam concentrate can be topped up during the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the purpose of annual testing, the system have to be activated; however, the delivered foam concentrate can be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate flow rate. No premix is produced; and as a end result of the foam concentrate is handed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an external interruption-free vitality supply for the foam concentrate pump and the control system, in addition to the need for a sophisticated management system and the comparatively higher purchasing prices. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water circulate price and the newly adjusted foam concentrate amount. The foam quality may be compromised when continually changing working conditions as foam discharge units 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 within the extinguishing water flow line and a foam concentrate pump which is connected directly to the water motor. Water motor and pump form one compact unit. Upon activation of the hearth 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 move fee adjustments, the quantity of foam focus is adapted immediately.
The advantage of the system is its independence from exterior vitality sources as well as a precise and immediate foam-concentrate proportioning regardless of the extinguishing water pressure or circulate fee. If a piston or plunger pump is used, adjustment or calibration after set up isn’t essential since the water motor and the pump are volumetric units firmly connected to one another. Foam focus refilling throughout operation is feasible. The system can additionally be able to proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nonetheless, the delivered foam concentrate may be measured via a return line. The proportioning price is calculated from the extinguishing water/foam focus move rate. No premix is generated; and if the foam concentrate is passed again into the tank, no foam focus must be topped up.
The larger design and the comparatively greater buying prices are an obstacle of the system.
With any system, consideration ought to be taken into account for the annual testing prices, which may be appreciable when it comes to substitute foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge tools can be damaged in intensive fires in the tank or within the dyke space and thus lose effectiveness, cellular fire monitors and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they’ve only restricted extinguishing agent flow charges and reaches.
Firefighting screens
Firefighting monitors are discharge gadgets mounted on vehicles or trailers and out there in lots of sizes. The extinguishing agent move price could be as much as 60,000 litres/min and the reach could be up to 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 so as to prevent it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space ought to always be observed to keep away from an overflow of the dyke.
Mobile hearth displays may be provided either by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the foam focus often takes place by way of mobile proportioners. This clearly factors towards the advantage of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular units available as back-ups is shown by the next instance for the location of displays for fireplace extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This leads to a number of options for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should be capable of handle various flow charges to ensure flexibility throughout extinguishing operations. Depending on the local conditions, the monitors might need to hold a minimum distance to the burning tank or could not be ready to be positioned near to the tanks due to particles. In addition, it will not at all times be possible to position a number of screens around the tank. It must be ensured the monitor has enough throwing peak in relation to the tank top, to ship foam into the within of the tank.
The dimensioning of the complete firefighting system is made following authorized regulations as properly as recommendations by associations like NFPA and is not looked at more closely within the current 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 text, it seems that many authorities and companies have not discovered the mandatory classes from disastrous hearth incidents of past years. Tank farm fires within the oil and petrochemical trade don’t happen 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 talked about within the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fireplace for yet unknown reasons. The plant had no fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fastened extinguishing techniques installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native fireplace service, which was on the spot in a quick time but could not take control over the fireplace with the equipment obtainable, partially as a end result of flammable substance was constantly leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of apparatus and foam concentrate in addition to the preparation of a plan of action took approximately 13 hours. The fire was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been revamped three days, with foam focus and water shortages occurring in the meantime. In complete, over 500,000 litres of foam concentrate had been used. Instead of a fireplace within the dyke space, eleven of the 15 tanks burnt down.
It is very probable that the fireplace 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 be possible that the fireplace would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably less injury.
Summing up, the following points must be realized at least. As far as they haven’t yet been applied, or just partly, they need to serve as a foundation for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection concept together with alternative eventualities which adapt to the given state of affairs regularly.
Always have a sufficient number of cellular extinguishing methods as a backup to mounted extinguishing methods.
Stock a suitable foam focus.
Ensure sufficient foam concentrate provide.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing gear out there in a enough quantity.
Have educated personnel obtainable in a enough number.
Ensure a fast implementation of an appropriate plan of motion.
For extra information, go to www.firedos.com
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