Part One of this text described the everyday incident situations at tank farm fires and presented foam as the most suitable extinguishing agent together with the firefighting gear most commonly used. In Part Two we look at foam focus proportioning technologies, cell extinguishing methods and conclude with lessons realized.
NFPA 11 describes varied types of foam focus proportioning equipment. 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 price must not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
The proportioning fee should not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning rate is allowed to be an absolute maximum of 1% above the permitted worth – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller value should be used respectively).
To assure right proportioning, the proportioner, together with the proportioning fee should be tested 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 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 froth focus from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi precept. When the hearth pumps are activated, pressure is generated by the pump, inflicting delivery of foam concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water flow.
The benefits of this technique are its simple design without moving elements and its simple operation. No external vitality is required, and the system is relatively cheap.
A drawback is that the system is a pressurized vessel topic 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 delicate; when damaged, water will contaminate the foam concentrate. At a given proportioning fee, the system is appropriate only for low variations in the extinguishing water flow pressure and quantity. Adding or changing particular person foam discharge gadgets is feasible only to a really restricted extent. The system can also be unsuitable for proportioning extremely 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 appropriate proportioning fee should be measured within the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam focus within the bladder tank must be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the foam concentrate, an electrical or diesel-powered foam concentrate pump with an electronically controlled valve and a move meter in the extinguishing water circulate line. When the fire pumps are activated, the foam concentrate pump drive and electronic control system should be activated. The extinguishing water move price is measured by the move meter and the control system adjusts the correct foam focus quantity by way of the management valve. The foam concentrate is injected into the extinguishing water flow by the froth concentrate pump. If there is a change within the move fee, the amount of injected foam focus is regulated by the management valve.
The system’s advantage lies in the exact proportioning of the froth focus, impartial of the extinguishing water stress or circulate rate. Foam concentrate could be topped up through the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nevertheless, the delivered foam focus could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus flow fee. No premix is produced; and as a result of the foam concentrate is passed again into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an external interruption-free power provide for the froth focus pump and the management system, as well as the need for a complicated management system and the comparatively greater purchasing prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water flow fee and the newly adjusted foam concentrate quantity. The foam quality could also be compromised when continually changing working 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 froth focus, a water motor put in within the extinguishing water move line and a foam focus pump which is linked on to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If เกจแรงดัน , the quantity of foam concentrate is customized instantly.
The advantage of the system is its independence from external power sources as nicely as a exact and quick foam-concentrate proportioning whatever the extinguishing water pressure or flow rate. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t needed for the explanation that water motor and the pump are volumetric units firmly linked to every other. Foam concentrate refilling throughout operation is feasible. The system is also capable of proportioning highly viscous foam concentrates. เกจวัดแรงดัน have to be activated for annual testing; however, the delivered foam focus can be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow fee. No premix is generated; and if the froth concentrate is passed back into the tank, no foam concentrate needs to be topped up.
The bigger design and the comparatively greater buying prices are a drawback of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which could be appreciable when it comes to replacement foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge equipment can be broken in intensive fires in the tank or within the dyke area and thus lose effectiveness, cellular fire monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they’ve only restricted extinguishing agent flow rates and reaches.
Firefighting screens
Firefighting monitors are discharge devices mounted on automobiles or trailers and available in many sizes. The extinguishing agent circulate price can be up to 60,000 litres/min and the reach can be up to 180m if the pressure of the hearth pumps is enough. They are appropriate 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 forestall it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke space ought to always be observed to keep away from an overflow of the dyke.
Mobile hearth monitors could be equipped either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the froth concentrate usually takes place via cell proportioners. This clearly points in direction of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile units out there as back-ups is shown by the following example for the placement of monitors for fire 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 several alternatives for the displays. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should have the flexibility to handle various circulate rates to ensure flexibility during extinguishing operations. Depending on the local situations, the displays will want to hold a minimal distance to the burning tank or may not be in a position to be positioned near to the tanks as a end result of particles. In addition, it won’t all the time be potential to place a quantity of screens around the tank. It must be ensured the monitor has adequate throwing top in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal rules in addition to suggestions by associations like NFPA and is not looked at more closely within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons realized
As mentioned within the introduction to Part One of this text, plainly many authorities and firms haven’t discovered the mandatory classes from disastrous hearth incidents of previous years. Tank farm fires within the oil and petrochemical industry don’t happen frequently. When they do, they usually have devastating consequences. Let us bear in mind the tank farm fire at Deer Park, Texas in March 2019 mentioned within 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 yet unknown causes. The plant had no gasoline warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have mounted extinguishing techniques installed. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native hearth service, which was on the spot in a brief time but could not take management over the fireplace with the equipment out there, partially because flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire had damaged out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of kit and foam focus as nicely as the preparation of a plan of motion 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 remodeled three days, with foam concentrate and water shortages occurring in the meantime. In complete, over 500,000 litres of froth 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 fire would have been extinguished shortly if the warning systems and valves had worked and a fixed fireplace extinguishing system had existed. It can additionally be probable that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded finally, had been started earlier. Both instances would have resulted in notably less injury.
Summing up, the following points must be discovered as a minimum. As far as they have not yet been carried out, or just partly, they need to serve as a basis for discussions about one’s personal fire-protection idea:
Have an acceptable fire-protection concept including different situations which adapt to the given state of affairs often.
Always have a sufficient number of cellular extinguishing techniques as a backup to mounted extinguishing systems.
Stock an acceptable foam concentrate.
Ensure enough foam concentrate provide.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment out there in a adequate quantity.
Have educated personnel available in a sufficient quantity.
Ensure a quick implementation of an appropriate plan of action.
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