Part One of this text described the everyday incident scenarios at tank farm fires and offered foam as the most suitable extinguishing agent along with the firefighting equipment mostly used. In Part Two we look at foam concentrate proportioning technologies, mobile extinguishing systems and conclude with lessons learned.
NFPA 11 describes various forms of foam focus proportioning equipment. In the next, three systems are checked out which are most common. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price 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. three.9% for a 3% foam concentrate or 7.8% for a 6% foam focus; respectively, the proportioning rate is allowed to be an absolute most of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller value must be used respectively).
To guarantee right proportioning, the proportioner, together with the proportioning price must be examined no less than every year and its correct functioning have to 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 crammed 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 connected to a proportioner which operates using the venturi principle. When the fire pumps are activated, pressure is generated by the pump, causing supply of froth focus to the proportioner. The extinguishing water flows via the venturi proportioner. The ensuing vacuum induces the foam concentrate into the extinguishing water circulate.
The advantages of this system are its easy design without shifting components and its easy operation. No exterior energy is required, and the system is relatively inexpensive.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws such as ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, 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 only for low variations within 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 be unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system should be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The appropriate proportioning rate should be measured in the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus within the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam focus pump with an electronically managed valve and a flow meter in the extinguishing water flow line. When the hearth pumps are activated, the foam concentrate pump drive and digital management system should be activated. The extinguishing water flow rate is measured by the flow meter and the management system adjusts the right foam concentrate quantity by way of the management valve. The foam concentrate is injected into the extinguishing water circulate by the froth concentrate pump. If there’s a change in the move fee, the quantity of injected foam concentrate is regulated by the management valve.
The system’s advantage lies in the precise proportioning of the foam focus, unbiased of the extinguishing water stress or move fee. Foam focus may be topped up through the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the aim of annual testing, the system should be activated; nonetheless, the delivered foam concentrate can be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus move rate. No premix is produced; and as the foam focus is handed again into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an external interruption-free energy supply for the froth concentrate pump and the control system, as nicely as the necessity for a sophisticated management system and the comparatively higher purchasing prices. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water circulate price and the newly adjusted foam concentrate quantity. The foam quality could also be compromised when continuously altering working conditions as foam discharge gadgets are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the froth focus, a water motor put in within the extinguishing water circulate line and a foam concentrate pump which is connected on to the water motor. Water motor and pump kind one compact unit. Upon activation of the hearth pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the flow rate modifications, the quantity of foam concentrate is tailored immediately.
The advantage of the system is its independence from external energy sources as well as a exact and quick foam-concentrate proportioning regardless of the extinguishing water pressure or move price. If a piston or plunger pump is used, adjustment or calibration after set up is not essential for the rationale that water motor and the pump are volumetric units firmly related to one another. Foam focus refilling throughout operation is possible. The system can additionally be capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus may be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate flow rate. No premix is generated; and if the foam focus is passed back into the tank, no foam concentrate needs to be topped up.
The bigger design and the comparatively higher purchasing prices are an obstacle of the system.
With any system, consideration ought to be taken under consideration for the annual testing prices, which can be appreciable in phrases of alternative foam concentrate, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge tools can be damaged in extensive fires within the tank or in the dyke area and thus lose effectiveness, cell hearth screens and foam pipes could also be used.
Foam pipes are normally held by firefighters, making them very versatile. Yet they’ve solely limited extinguishing agent flow charges and reaches.
Firefighting monitors are discharge units mounted on vehicles or trailers and available in many sizes. The extinguishing agent move fee can be as much as 60,000 litres/min and the attain could be up to 180m if the stress of the fireplace pumps is enough. They are suitable to discharge foam, e.g., to extinguish a surface hearth in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank to be able to prevent it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space ought to at all times be noticed to avoid an overflow of the dyke.
Mobile fireplace monitors may be supplied either by the extinguishing water of the stationary fire pumps or by cellular pumps. The injection of the froth focus normally takes place by way of mobile 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 cellular items out there as back-ups is proven by the following instance for the location of monitors for fire extinguishing at tanks which are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This results in several options for the displays. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which ought to have the flexibility to deal with varying circulate charges to ensure flexibility during extinguishing operations. Depending on the native circumstances, the displays will want to hold a minimum distance to the burning tank or might not have the flexibility to be positioned near to the tanks due to particles. In addition, it won’t at all times be attainable to position several monitors around the tank. It should be ensured the monitor has sufficient throwing peak in relation to the tank peak, to deliver foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following legal laws as nicely as suggestions by associations like NFPA and is not looked at extra closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
As mentioned within the introduction to Part One of this article, it appears that many authorities and firms haven’t realized the necessary classes from disastrous fireplace incidents of previous years. Tank farm fires within the oil and petrochemical trade do not occur regularly. When they do, they normally have devastating penalties. Let us bear in mind the tank farm hearth 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 gas warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fixed extinguishing systems installed. All 15 tanks had been surrounded by one single dyke. เกจ์วัดความดัน had relied on the local fire service, which was on the spot in a quick time however couldn’t take management over the fireplace with the gear obtainable, partially because flammable substance was repeatedly leaking from the tank. Thirty-six hours after the hearth had damaged out, a contract was made with an external firefighting firm 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 finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt have been revamped three days, with foam focus and water shortages occurring in the meantime. In total, over 500,000 litres of foam concentrate were used. Instead of a fireplace within the dyke area, 11 of the 15 tanks burnt down.
It could be very probable that the fireplace would have been extinguished quickly if the warning techniques and valves had worked and a hard and fast hearth extinguishing system had existed. It can also be possible that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded ultimately, had been started earlier. Both instances would have resulted in notably less injury.
Summing up, the next factors ought to be discovered at least. As far as they have not yet been carried out, or just partly, they should serve as a foundation for discussions about one’s own fire-protection idea:
Have an appropriate fire-protection concept including alternative situations which adapt to the given scenario often.
Always have a adequate variety of cell extinguishing systems as a backup to fixed extinguishing techniques.
Stock an appropriate foam focus.
Ensure adequate foam concentrate provide.
Ensure adequate water supply.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing gear out there in a enough number.
Have skilled personnel out there in a adequate number.
Ensure a quick implementation of a suitable plan of action.
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