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

Part One of this text described the everyday incident situations at tank farm fires and offered foam as essentially the most appropriate extinguishing agent together with the firefighting gear mostly used. In Part Two we look at foam concentrate proportioning technologies, cellular extinguishing systems and conclude with lessons discovered.
NFPA 11 describes various types of foam concentrate proportioning tools. In the next, three methods are checked out that are most common. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price should not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam focus.
The proportioning fee should not exceed 30% above the permitted value i.e. three.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 concentrate or 7% for a 6% foam concentrate (the smaller value have to be used respectively).
To guarantee appropriate proportioning, the proportioner, including the proportioning rate should be examined at least annually 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 full of foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam focus from the bladder as required. The bladder is connected to a proportioner which operates using the venturi principle. When the fireplace pumps are activated, strain is generated by the pump, inflicting delivery of foam focus to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the foam focus into the extinguishing water move.
The advantages of this system are its simple design without moving components 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 topic to corresponding laws such as 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 appropriate just for low variations in the extinguishing water circulate pressure and quantity. Adding or changing individual foam discharge units is feasible only to a very limited extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory 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 analysis. The generated premix must then be disposed of, and the consumed foam concentrate 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 froth focus, an electrical or diesel-powered foam concentrate pump with an electronically managed valve and a move meter within the extinguishing water move line. When the fire pumps are activated, the froth focus pump drive and electronic control system must be activated. The extinguishing water move price is measured by the flow meter and the management system adjusts the proper foam focus quantity by way of the control valve. The foam concentrate is injected into the extinguishing water move by the foam focus pump. If there is a change in the move price, the amount of injected foam focus is regulated by the control valve.
The system’s advantage lies in the exact proportioning of the foam concentrate, independent of the extinguishing water stress or circulate fee. Foam focus can 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; however, the delivered foam focus may be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow rate. No premix is produced; and as the foam concentrate is handed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free power provide for the froth concentrate pump and the control system, in addition to the necessity for a classy management system and the comparatively higher buying prices. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water flow price and the newly adjusted foam concentrate amount. The foam quality could additionally be compromised when constantly 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 froth concentrate, a water motor installed within the extinguishing water flow line and a foam focus pump which is related directly to the water motor. Water motor and pump type one compact unit. Upon activation of the fireplace pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the circulate price adjustments, the amount of froth concentrate is customized instantly.
เกจวัดแรงดัน4นิ้วราคา of the system is its independence from external energy sources as well as a precise and instant foam-concentrate proportioning regardless of the extinguishing water stress or circulate rate. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t essential for the reason that water motor and the pump are volumetric devices firmly connected to one another. Foam focus refilling throughout operation is feasible. The system can additionally be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam focus 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 concentrate is handed back into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively higher purchasing costs are an obstacle of the system.
With any system, consideration ought to be taken under consideration for the annual testing costs, which may be appreciable by method of replacement foam concentrate, disposal of premix and labour costs.
Mobile extinguishing techniques
As the stationary foam discharge equipment may be broken in intensive fires within the tank or in the dyke space and thus lose effectiveness, cell fire monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have solely limited extinguishing agent move rates and reaches.
Firefighting screens
Firefighting displays are discharge gadgets mounted on vehicles or trailers and out there in lots of sizes. The extinguishing agent move rate could be up to 60,000 litres/min and the attain could be up to 180m if the stress 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 prevent it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space ought to all the time be noticed to keep away from an overflow of the dyke.
Mobile hearth monitors could be equipped either by the extinguishing water of the stationary fireplace pumps or by cell pumps. The injection of the froth focus usually takes place via cell proportioners. This clearly points in the direction of the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell units available as back-ups is shown by the next example for the position of monitors for fire 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 quantity of alternatives for the displays. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be able to handle varying circulate rates to ensure flexibility throughout extinguishing operations. Depending on the native circumstances, the monitors will need to keep a minimum distance to the burning tank or could not have the power to be positioned near to the tanks due to debris. In addition, it will not at all times be potential to place a quantity of screens around the tank. It must be ensured the monitor has enough throwing peak in relation to the tank peak, to ship 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 isn’t looked at 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 talked about in the introduction to Part One of this article, it appears that evidently many authorities and companies have not realized the necessary lessons from disastrous hearth incidents of past years. Tank farm fires in the oil and petrochemical industry do not happen regularly. When they do, they often have devastating consequences. Let us keep in mind the tank farm fireplace at Deer Park, Texas in March 2019 talked about within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for 30 minutes 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 didn’t have fastened extinguishing systems installed. All 15 tanks had been surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot very quickly but couldn’t take control over the hearth with the gear out there, partially as a outcome of flammable substance was continuously leaking from the tank. Thirty-six hours after the hearth had damaged out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of kit and foam focus in addition to the preparation of a plan of motion took approximately 13 hours. The hearth was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts have been revamped three days, with foam focus and water shortages occurring within the meantime. In total, over 500,000 litres of froth focus have been used. Instead of a fire in the dyke space, 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 hearth extinguishing system had existed. It can also be probable that the fireplace would have been extinguished rapidly if the extinguishing operation, which succeeded finally, had been began earlier. Both circumstances would have resulted in notably less damage.
Summing up, the next points must be learned at least. As far as they have not but been applied, or just partly, they need to function a foundation for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection concept including various eventualities which adapt to the given situation often.
Always have a enough number of cell extinguishing techniques as a backup to fastened extinguishing systems.
Stock an acceptable foam concentrate.
Ensure adequate foam focus supply.
Ensure enough water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing gear obtainable in a sufficient quantity.
Have skilled personnel available in a adequate number.
Ensure a fast implementation of an appropriate plan of action.
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