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

Part One of this text described the standard incident eventualities at tank farm fires and introduced foam as the most suitable extinguishing agent together with the firefighting gear mostly used. In Part Two we look at foam focus proportioning applied sciences, cellular extinguishing systems and conclude with classes realized.
NFPA eleven describes numerous kinds of foam focus proportioning tools. In the following, three methods are checked out which are most common. Tight limits for the proportioning of froth focus 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 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 focus 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 minimum of annually and its appropriate 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 know-how. The bladder tank is a pressurized vessel with a bladder inside which is filled 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 linked to a proportioner which operates utilizing the venturi principle. When the fire pumps are activated, stress is generated by the pump, inflicting delivery of froth focus to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water flow.
The advantages of this technique are its simple design without transferring parts and its easy operation. No exterior vitality is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic 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 focus. At a given proportioning price, the system is suitable only for low variations in the extinguishing water move pressure and quantity. Adding or changing individual foam discharge gadgets is feasible only to a very limited extent. The system can additionally be 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 throughout the extinguishing water line. The right proportioning rate 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 must be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter within the extinguishing water move line. When the hearth pumps are activated, the froth concentrate pump drive and digital control system should be activated. The extinguishing water flow price is measured by the move meter and the management system adjusts the right foam focus quantity via the control valve. The foam focus is injected into the extinguishing water move by the froth concentrate pump. If there is a change in the circulate rate, the quantity of injected foam concentrate is regulated by the control valve.
หลักการทำงานของเกจ์วัดแก๊ส ’s benefit lies in the exact proportioning of the foam focus, impartial of the extinguishing water stress or flow price. Foam concentrate could be topped up through the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system should be activated; however, the delivered foam concentrate could be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate move fee. No premix is produced; and because the foam focus is handed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free power supply for the foam focus pump and the control system, in addition to the need for a complicated management system and the comparatively higher buying prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water move fee and the newly adjusted foam concentrate 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 foam concentrate, a water motor installed in the extinguishing water flow line and a foam focus pump which is connected on to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the move fee changes, the quantity of froth focus is adapted instantly.
The benefit of the system is its independence from external power sources as properly as a exact and immediate foam-concentrate proportioning whatever the extinguishing water stress or move fee. If a piston or plunger pump is used, adjustment or calibration after installation isn’t necessary because the water motor and the pump are volumetric units firmly related to every other. Foam focus refilling during operation is feasible. The system can additionally be able to proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus can be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus move price. No premix is generated; and if the foam concentrate is passed again into the tank, no foam concentrate must be topped up.
The larger design and the comparatively greater buying prices are a drawback of the system.
With any system, consideration should be taken into consideration for the annual testing prices, which can be appreciable in terms of substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge gear can be broken in extensive fires within the tank or within the dyke area and thus lose effectiveness, mobile hearth monitors 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 flow rates and reaches.
Firefighting displays
Firefighting monitors are discharge gadgets mounted on autos or trailers and available in many sizes. The extinguishing agent flow price can be up to 60,000 litres/min and the reach could be up to 180m if the pressure of the fireplace pumps is sufficient. They are suitable 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 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 area should at all times be observed to keep away from an overflow of the dyke.
Mobile fireplace screens may be provided either by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the froth focus normally takes place through cell proportioners. This clearly points in the direction of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of mobile items out there as back-ups is proven by the following example for the location of monitors 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 results in a quantity of alternate options for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should be capable of handle various circulate charges to ensure flexibility throughout extinguishing operations. Depending on the local circumstances, the displays will need to maintain a minimal distance to the burning tank or may not be in a position to be positioned near to the tanks because of particles. In addition, it will not at all times be possible to position a number of monitors around the tank. It have to be ensured the monitor has sufficient throwing top in relation to the tank peak, to ship foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following legal laws in addition to recommendations by associations like NFPA and isn’t checked out more closely within the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons realized
As talked about within the introduction to Part One of this text, plainly many authorities and firms have not realized the required classes from disastrous fire incidents of previous years. Tank farm fires within the oil and petrochemical industry do not occur incessantly. When they do, they often have devastating penalties. Let us remember the tank farm fire at Deer Park, Texas in March 2019 mentioned in 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 fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fastened extinguishing systems installed. All 15 tanks had been surrounded by one single dyke. The owner had relied on the native fire service, which was on the spot in a brief time but could not take control over the fireplace with the equipment out there, partially as a end result of flammable substance was continuously leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of kit 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 makes an attempt were made over three days, with foam concentrate and water shortages occurring in the meantime. In complete, over 500,000 litres of foam concentrate had been used. Instead of a fire within the dyke space, 11 of the 15 tanks burnt down.
It is very possible that the fire would have been extinguished shortly if the warning systems and valves had labored and a exhausting and fast hearth extinguishing system had existed. It can be possible that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been began earlier. Both cases would have resulted in notably less harm.
Summing up, the following factors must be learned at least. As far as they haven’t but been implemented, or just partly, they need to serve as a foundation for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection idea including different situations which adapt to the given state of affairs frequently.
Always have a enough number of cell extinguishing systems as a backup to mounted extinguishing techniques.
Stock a suitable foam focus.
Ensure sufficient foam concentrate provide.
Ensure sufficient water supply.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing equipment out there in a adequate number.
Have skilled personnel available in a enough quantity.
Ensure a quick implementation of an acceptable plan of action.
For extra info, go to www.firedos.com
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