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Part One of this text described the everyday incident eventualities at tank farm fires and introduced foam as essentially the most appropriate extinguishing agent along with the firefighting tools mostly used. In Part Two we look at foam focus proportioning technologies, cell extinguishing systems and conclude with classes realized.
NFPA 11 describes varied kinds of foam concentrate proportioning tools. In the following, three systems are looked at that are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning fee should 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 should not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; 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 concentrate (the smaller value have to be used respectively).
To guarantee right proportioning, the proportioner, together with the proportioning rate have to be examined at least every year and its correct 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 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 related to a proportioner which operates using the venturi principle. When the hearth pumps are activated, stress is generated by the pump, causing delivery of froth concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the foam focus into the extinguishing water circulate.
The benefits of this system are its easy design without shifting components and its simple operation. No external power is required, and the system is relatively cheap.
spmk700 is that the system is a pressurized vessel topic to corresponding regulations such as 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 froth concentrate. At a given proportioning fee, the system is suitable only for low variations within the extinguishing water flow stress and volume. Adding or changing particular person foam discharge units is feasible only to a really restricted extent. The system can additionally be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system should be activated and premix generated at the venturi proportioner within the extinguishing water line. The correct proportioning price must be measured in the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam concentrate within 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 electric or diesel-powered foam concentrate pump with an electronically managed valve and a move meter within the extinguishing water move line. When the hearth pumps are activated, the foam concentrate pump drive and electronic management system have to be activated. The extinguishing water flow fee is measured by the circulate meter and the management system adjusts the correct foam concentrate quantity through the control valve. The foam focus is injected into the extinguishing water circulate by the foam focus pump. If there’s a change in the flow fee, the quantity of injected foam focus is regulated by the management valve.
The system’s benefit lies within the precise proportioning of the foam focus, unbiased of the extinguishing water stress or flow fee. Foam focus may be topped up in the course of the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system should be activated; however, the delivered foam concentrate can be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus flow price. No premix is produced; and as a outcome of the foam focus is handed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an external interruption-free energy provide for the foam concentrate pump and the control system, as well as the necessity for a sophisticated control system and the comparatively larger purchasing costs. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water flow rate and the newly adjusted foam concentrate quantity. The foam high quality could additionally be compromised when continuously changing operating situations as foam discharge units are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam concentrate, a water motor put in in the extinguishing water circulate line and a foam concentrate pump which is linked on to the water motor. Water motor and pump type one compact unit. Upon activation of the hearth pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump provides instant foam-concentrate injection into the extinguishing water. If the move fee modifications, the quantity of froth focus is tailored immediately.
The advantage of the system is its independence from exterior energy sources in addition to a exact and quick foam-concentrate proportioning regardless of the extinguishing water pressure or circulate price. If a piston or plunger pump is used, adjustment or calibration after installation is not necessary because the water motor and the pump are volumetric units firmly connected to one another. Foam concentrate refilling throughout operation is possible. The system can additionally be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; however, the delivered foam concentrate can be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate circulate rate. No premix is generated; and if the froth focus is handed back into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively greater buying costs are a drawback of the system.
With any system, consideration must be taken into account for the annual testing prices, which can be appreciable in terms of alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing methods
As the stationary foam discharge gear can be damaged in intensive fires in the tank or in the dyke area and thus lose effectiveness, cell fireplace screens and foam pipes could additionally be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have only restricted extinguishing agent flow rates and reaches.
Firefighting screens
Firefighting displays are discharge units mounted on autos or trailers and obtainable in many sizes. The extinguishing agent move price could be up to 60,000 litres/min and the attain can be as a lot as 180m if the stress of the fire pumps is adequate. They are suitable to discharge foam, e.g., to extinguish a surface fireplace in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to find a way to prevent it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke area should at all times be noticed to avoid an overflow of the dyke.
Mobile fire displays can be provided both by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the froth concentrate often takes place by way of cell proportioners. This clearly points in course of the advantage of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of mobile items obtainable as back-ups is shown by the following instance for the placement of monitors for hearth 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 quantity of options for the screens. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which should be succesful of handle various circulate charges to ensure flexibility during extinguishing operations. Depending on the local situations, the displays might want to keep a minimum distance to the burning tank or might not be succesful of be positioned close to to the tanks due to debris. In addition, it won’t at all times be potential to position several screens across the tank. It have to be ensured the monitor has adequate throwing peak in relation to the tank height, to deliver foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following legal laws in addition to suggestions by associations like NFPA and is not checked out extra intently within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As talked about in the introduction to Part One of this text, plainly many authorities and companies have not learned the necessary classes from disastrous fire incidents of previous years. Tank farm fires in the oil and petrochemical industry don’t happen incessantly. When they do, they normally have devastating consequences. Let us bear in mind the tank farm fireplace at Deer Park, Texas in March 2019 mentioned in 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 but unknown causes. The plant had no fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have mounted extinguishing techniques put in. All 15 tanks have been surrounded by one single dyke. The proprietor had relied on the local hearth service, which was on the spot in a short time but could not take control over the fire with the equipment obtainable, partially as a end result of flammable substance was continuously 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 as properly as the preparation of a plan of action took approximately thirteen hours. The hearth was finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt had been made over three days, with foam focus and water shortages occurring in the meantime. In total, over 500,000 litres of foam concentrate had been used. Instead of a hearth within the dyke area, 11 of the 15 tanks burnt down.
It could be very probable that the hearth would have been extinguished quickly if the warning methods and valves had labored and a hard and fast fire extinguishing system had existed. It can additionally be probable that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both cases would have resulted in notably less damage.
Summing up, the following points must be discovered as a minimum. As far as they haven’t yet been implemented, or just partly, they should function a foundation for discussions about one’s personal fire-protection concept:
Have a suitable fire-protection concept together with different scenarios which adapt to the given scenario often.
Always have a enough number of cell extinguishing systems as a backup to fixed extinguishing methods.
Stock a suitable foam concentrate.
Ensure enough foam concentrate provide.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment available in a adequate quantity.
Have trained personnel obtainable in a enough number.
Ensure a fast implementation of an acceptable plan of action.
For more information, go to www.firedos.com
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