Use of froth for firefighting in tank farms of the oil and petrochemical industry – Part 2

Part One of this text described the everyday incident scenarios at tank farm fires and introduced foam as essentially the most suitable extinguishing agent together with the firefighting tools most commonly used. In Part Two we have a look at foam concentrate proportioning applied sciences, cellular extinguishing methods and conclude with lessons realized.
NFPA eleven describes numerous forms of foam focus proportioning tools. In the next, three techniques are looked at that are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning fee should 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 should not exceed 30% above the permitted value 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 maximum of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller value should be used respectively).
To assure right proportioning, the proportioner, including the proportioning price have to be tested a minimal of every year and its appropriate functioning must be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a confirmed and cost-effective technology. The bladder tank is a pressurized vessel with a bladder inside which is full of foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi principle. When the fire pumps are activated, stress is generated by the pump, causing supply of froth concentrate to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the foam focus into the extinguishing water circulate.
The benefits of this system are its easy design with out transferring parts and its simple operation. No external vitality is required, and the system is comparatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding rules 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 damaged, water will contaminate the foam concentrate. At a given proportioning fee, the system is appropriate only for low variations in the extinguishing water flow pressure and volume. Adding or altering individual foam discharge devices is feasible solely to a really restricted extent. The system can additionally be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system must be activated and premix generated at the venturi proportioner inside the extinguishing water line. The right proportioning price should be measured in the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam concentrate in the bladder tank must be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with move 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 fire pumps are activated, the foam focus pump drive and digital management system must be activated. The extinguishing water flow rate is measured by the circulate meter and the management system adjusts the correct foam focus amount by way of the management valve. The foam concentrate is injected into the extinguishing water move by the froth concentrate pump. If there is a change within the circulate rate, the quantity of injected foam concentrate 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 price. Foam focus may be topped up during the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For pressure gauge หน้าปัด 2 นิ้ว of annual testing, the system must be activated; however, the delivered foam concentrate may be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate circulate price. No premix is produced; and as the foam concentrate is passed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free vitality supply for the froth concentrate pump and the control system, in addition to the necessity for a classy control system and the comparatively greater purchasing costs. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water flow price and the newly adjusted foam focus amount. The foam quality could also be compromised when constantly changing 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 concentrate, a water motor put in within the extinguishing water circulate line and a foam concentrate pump which is related on to the water motor. Water motor and pump kind one compact unit. Upon activation of the fire pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the circulate rate changes, the quantity of foam focus is adapted instantly.
The advantage of the system is its independence from external power sources as nicely as a exact and immediate foam-concentrate proportioning whatever the extinguishing water strain or move rate. If a piston or plunger pump is used, adjustment or calibration after installation is not essential because the water motor and the pump are volumetric units firmly connected to every other. Foam concentrate refilling during operation is possible. The system can be capable of proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus can be measured by way of a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate flow rate. No premix is generated; and if the foam focus is handed back into the tank, no foam focus must be topped up.
The bigger design and the comparatively greater purchasing prices are an obstacle of the system.
With any system, consideration must be taken into account for the annual testing costs, which could be appreciable in terms of substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge equipment can be damaged in intensive fires within the tank or within the dyke space and thus lose effectiveness, mobile fireplace screens and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they’ve only limited extinguishing agent move rates and reaches.
Firefighting screens
Firefighting screens are discharge devices mounted on autos or trailers and obtainable in lots of sizes. The extinguishing agent move fee may be as a lot as 60,000 litres/min and the attain may be up to 180m if the stress of the fireplace pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a surface fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank to have the ability to forestall it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke area ought to always be noticed to keep away from an overflow of the dyke.
Mobile fireplace monitors can be supplied either by the extinguishing water of the stationary fire pumps or by cellular pumps. The injection of the froth concentrate usually takes place by way of mobile proportioners. This clearly points towards the advantage of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile units out there as back-ups is proven by the next instance for the location of screens for fireplace extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in a number of alternate options for the monitors. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which ought to be capable of deal with varying move rates to ensure flexibility during extinguishing operations. Depending on the local situations, the displays might need to hold a minimal distance to the burning tank or could not have the flexibility to be positioned close to to the tanks as a end result of debris. In addition, it is not going to all the time be attainable to place several monitors around the tank. It should be ensured the monitor has adequate throwing top in relation to the tank top, to ship foam into the within of the tank.
The dimensioning of the entire firefighting system is made following authorized rules in addition to suggestions by associations like NFPA and is not looked at more intently in the present article.
Fig. 4: 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 article, plainly many authorities and corporations have not realized the required classes from disastrous hearth incidents of previous years. Tank farm fires within the oil and petrochemical trade don’t happen regularly. When they do, they often have devastating consequences. Let us bear in mind the tank farm fireplace at Deer Park, Texas in March 2019 mentioned within the introduction.
The fire 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 causes. The plant had no gas warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have fastened extinguishing methods put in. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native fireplace service, which was on the spot in a brief time but could not take control over the fire with the tools out there, partially because flammable substance was constantly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of apparatus and foam concentrate in addition to the preparation of a plan of action took roughly thirteen hours. The fireplace was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts were remodeled three days, with foam concentrate and water shortages occurring in the meantime. In whole, over 500,000 litres of froth focus have been used. Instead of a fireplace within the dyke area, 11 of the 15 tanks burnt down.
It could be very possible that the fireplace would have been extinguished shortly if the warning techniques and valves had labored and a set hearth extinguishing system had existed. It is also possible that the fire would have been extinguished shortly if the extinguishing operation, which succeeded ultimately, had been started earlier. Both cases would have resulted in notably much less injury.
Summing up, the next points must be realized at the least. As far as they haven’t but been applied, or just partly, they want to serve as a basis for discussions about one’s personal fire-protection concept:
Have a suitable fire-protection idea including alternative eventualities which adapt to the given situation regularly.
Always have a enough variety of cellular extinguishing techniques as a backup to mounted extinguishing techniques.
Stock an acceptable foam focus.
Ensure sufficient foam concentrate supply.
Ensure adequate water supply.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing gear obtainable in a enough number.
Have skilled personnel out there in a sufficient number.
Ensure a quick implementation of an acceptable plan of action.
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