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

Part One of this article described the everyday incident situations at tank farm fires and introduced foam as the most suitable extinguishing agent along with the firefighting equipment most commonly used. In Part Two we have a look at foam focus proportioning applied sciences, mobile extinguishing techniques and conclude with lessons discovered.
NFPA eleven describes numerous kinds of foam concentrate proportioning tools. In the next, three systems are looked at which are most common. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning rate must not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning fee should 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 price 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 concentrate (the smaller worth should be used respectively).
To assure appropriate proportioning, the proportioner, together with the proportioning price should be tested at least once a year and its correct 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 filled with foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the foam focus from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi principle. When the hearth pumps are activated, strain is generated by the pump, causing supply of froth concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth concentrate into the extinguishing water move.
The benefits of this system are its simple design with out transferring elements and its straightforward operation. No external energy is required, and the system is comparatively cheap.
A drawback 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. เกจวัดแก๊ส is sensitive; when damaged, water will contaminate the froth concentrate. At a given proportioning price, the system is suitable just for low variations within the extinguishing water move strain and quantity. Adding or altering individual foam discharge gadgets is possible solely to a really restricted extent. The system can additionally be unsuitable for proportioning highly viscous foam concentrates.
To conduct any mandatory required annual testing, the system must be activated and premix generated on the venturi proportioner within the extinguishing water line. The appropriate proportioning price should 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 circulate meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the foam focus, an electric or diesel-powered foam focus pump with an electronically controlled valve and a circulate meter within the extinguishing water circulate line. When the fireplace pumps are activated, the foam concentrate pump drive and digital control system have to be activated. The extinguishing water move price is measured by the move meter and the control system adjusts the correct foam concentrate quantity through the management valve. The foam concentrate is injected into the extinguishing water circulate by the froth focus pump. If there’s a change in the circulate fee, the quantity of injected foam concentrate is regulated by the management valve.
The system’s advantage lies within the precise proportioning of the froth concentrate, impartial of the extinguishing water stress or move price. Foam focus could 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; nevertheless, the delivered foam focus can be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam focus circulate rate. No premix is produced; and as a end result of the foam concentrate is handed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free power supply for the foam focus pump and the management system, in addition to the need for a classy management system and the comparatively greater purchasing prices. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water circulate rate and the newly adjusted foam concentrate quantity. The foam high quality may be compromised when continuously altering operating circumstances as foam discharge devices 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 within 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 fireplace pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump offers quick foam-concentrate injection into the extinguishing water. If the flow fee adjustments, the amount of froth focus is tailored immediately.
The advantage of the system is its independence from exterior power sources as well as a exact and quick foam-concentrate proportioning whatever the extinguishing water stress or move rate. If a piston or plunger pump is used, adjustment or calibration after set up isn’t necessary because the water motor and the pump are volumetric units firmly connected to every other. Foam focus refilling throughout operation is feasible. The system can be able to proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam focus may be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate circulate price. No premix is generated; and if the foam focus is handed again into the tank, no foam concentrate needs to be topped up.
The bigger design and the comparatively greater buying costs are a drawback of the system.
With any system, consideration ought to be taken under consideration for the annual testing costs, which can be appreciable in terms of replacement foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge gear can be damaged in in depth fires in the tank or within the dyke space and thus lose effectiveness, cellular fireplace monitors and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they have solely restricted extinguishing agent move rates and reaches.
Firefighting displays
Firefighting monitors are discharge gadgets mounted on automobiles or trailers and obtainable in plenty of sizes. The extinguishing agent circulate rate could be up to 60,000 litres/min and the reach can be as a lot as 180m if the pressure of the fire 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 in order to stop it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke space should always be observed to avoid an overflow of the dyke.
Mobile fire displays can be provided either by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the froth concentrate usually takes place by way of mobile proportioners. This clearly points in path of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of mobile items available as back-ups is proven by the next instance for the location 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 alternate options for the screens. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which ought to be succesful of handle varying circulate charges to guarantee flexibility during extinguishing operations. Depending on the local conditions, the monitors will need to hold a minimum distance to the burning tank or may not be capable of be positioned close to to the tanks as a end result of debris. In addition, it is not going to at all times be possible to place a number of screens around the tank. It should be ensured the monitor has enough throwing top in relation to the tank peak, to ship foam into the within of the tank.
The dimensioning of the whole firefighting system is made following legal rules as nicely as suggestions by associations like NFPA and is not checked out more carefully within the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons discovered
As mentioned within the introduction to Part One of this text, it appears that evidently many authorities and firms have not learned the required lessons from disastrous fireplace incidents of previous years. Tank farm fires within the oil and petrochemical business do not happen incessantly. When they do, they often have devastating penalties. Let us bear in mind 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 fireplace for but unknown reasons. The plant had no fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have fixed extinguishing systems installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native fire service, which was on the spot very quickly however couldn’t take management over the hearth with the equipment out there, partially as a outcome 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 company to do the extinguishing work. Mobilization of kit and foam focus in addition to the preparation of a plan of action took roughly 13 hours. The fireplace was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been made over three days, with foam focus and water shortages occurring in the meantime. In whole, over 500,000 litres of foam concentrate were used. Instead of a hearth within the dyke space, 11 of the 15 tanks burnt down.
It could be very probable that the hearth would have been extinguished shortly if the warning methods and valves had labored and a set fire extinguishing system had existed. It is also possible that the fireplace would have been extinguished rapidly if the extinguishing operation, which succeeded eventually, had been started earlier. Both circumstances would have resulted in notably less harm.
Summing up, the next factors should be realized at least. As far as they haven’t but been carried out, or just partly, they need to function a basis for discussions about one’s own fire-protection concept:
Have an acceptable fire-protection concept together with different situations which adapt to the given state of affairs frequently.
Always have a adequate variety of mobile extinguishing systems as a backup to fixed extinguishing techniques.
Stock an appropriate foam focus.
Ensure enough foam focus supply.
Ensure enough water supply.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing equipment out there in a adequate quantity.
Have educated personnel available in a sufficient number.
Ensure a quick implementation of an acceptable plan of action.
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