Part One of this text described the standard incident situations at tank farm fires and presented foam as essentially the most suitable extinguishing agent along with the firefighting gear most commonly used. In Part Two we have a glance at foam concentrate proportioning applied sciences, cell extinguishing systems and conclude with lessons realized.
NFPA eleven describes numerous types of foam focus proportioning tools. In the following, three methods are checked out which are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning price should not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
The proportioning rate must not exceed 30% above the permitted worth 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 focus or 7% for a 6% foam focus (the smaller value must be used respectively).
To guarantee correct proportioning, the proportioner, including the proportioning fee should be examined a minimal of once a year and its appropriate functioning have to be checked.
เกจวัดแรงดันpressuregauge 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 filled with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the froth concentrate 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, inflicting delivery of foam focus to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the foam concentrate into the extinguishing water circulate.
The advantages of this technique are its simple design with out transferring elements and its easy operation. No exterior energy is required, and the system is relatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system should be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam focus. At a given proportioning price, the system is appropriate only for low variations within the extinguishing water move pressure and quantity. Adding or altering individual foam discharge devices is feasible solely to a really limited extent. The system can additionally be unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system should be activated and premix generated at the venturi proportioner within the extinguishing water line. The appropriate proportioning fee have to 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 circulate meter.
Driven proportioning pump with move 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 flow line. When the hearth pumps are activated, the froth concentrate pump drive and digital control system have to be activated. The extinguishing water circulate rate is measured by the circulate meter and the control system adjusts the right foam focus quantity by way of the control valve. The foam focus is injected into the extinguishing water circulate by the froth concentrate pump. If there is a change within the flow fee, the quantity of injected foam focus is regulated by the control valve.
The system’s advantage lies within the exact proportioning of the foam focus, impartial of the extinguishing water pressure or move price. Foam concentrate may be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nonetheless, the delivered foam concentrate could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate rate. No premix is produced; and as 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 supply for the froth concentrate pump and the control system, in addition to the necessity for a classy control system and the comparatively greater purchasing prices. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water circulate fee and the newly adjusted foam concentrate amount. The foam quality may be compromised when continuously altering working situations 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 focus, a water motor put in within the extinguishing water circulate line and a foam concentrate pump which is related directly to the water motor. Water motor and pump kind one compact unit. Upon activation of the hearth pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the move rate modifications, the amount of froth concentrate is customized instantly.
The advantage of the system is its independence from exterior energy sources in addition to a exact and immediate foam-concentrate proportioning regardless of the extinguishing water stress or move price. If a piston or plunger pump is used, adjustment or calibration after installation is not needed since the water motor and the pump are volumetric units firmly linked to each other. Foam concentrate refilling during operation is possible. The system can additionally be capable of proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam concentrate could be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate price. No premix is generated; and if the froth focus is handed again into the tank, no foam focus must be topped up.
The bigger design and the comparatively higher buying costs are an obstacle of the system.
With any system, consideration should be taken into consideration for the annual testing prices, which could be appreciable when it comes to replacement foam focus, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge tools could be damaged in intensive fires within the tank or in the dyke area and thus lose effectiveness, cell fireplace screens and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve solely limited extinguishing agent circulate charges and reaches.
Firefighting screens
Firefighting screens are discharge devices mounted on autos or trailers and out there in lots of sizes. The extinguishing agent flow fee could be up to 60,000 litres/min and the reach could be up to 180m if the strain of the fire pumps is adequate. They are suitable to discharge foam, e.g., to extinguish a surface fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank so as to prevent it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke area should always be noticed to avoid an overflow of the dyke.
Mobile fire displays could be provided both by the extinguishing water of the stationary fireplace pumps or by mobile pumps. The injection of the froth focus often takes place by way of cellular proportioners. This clearly factors in direction of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell units available as back-ups is shown by the following example for the placement of monitors for fireplace extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This leads to several alternate options for the displays. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which should be ready to deal with varying move rates to guarantee flexibility during extinguishing operations. Depending on the local circumstances, the monitors will want to keep a minimum distance to the burning tank or may not be succesful of be positioned near to the tanks as a end result of particles. In addition, it won’t always be possible to place several monitors around the tank. It should be ensured the monitor has enough throwing peak in relation to the tank top, to ship foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following legal regulations as properly as recommendations by associations like NFPA and isn’t looked at more closely in 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 necessary classes from disastrous hearth incidents of past years. Tank farm fires in the oil and petrochemical trade do not occur frequently. When they do, they often have devastating consequences. Let us keep in mind the tank farm hearth at Deer Park, Texas in March 2019 talked about in the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fire for but unknown reasons. The plant had no gasoline warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have mounted extinguishing methods installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the local hearth service, which was on the spot very quickly however could not take management over the fire with the tools available, partially because flammable substance was constantly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of equipment and foam focus in addition to the preparation of a plan of action took roughly thirteen hours. The hearth was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts have been revamped three days, with foam concentrate and water shortages occurring within the meantime. In whole, 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 methods and valves had labored and a fixed hearth extinguishing system had existed. It can also be possible that the fire would have been extinguished rapidly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably less injury.
Summing up, the next factors must be discovered at the least. As far as they haven’t yet been applied, or just partly, they should serve as a foundation for discussions about one’s own fire-protection concept:
Have an appropriate fire-protection concept together with alternative eventualities which adapt to the given scenario frequently.
Always have a enough number of mobile extinguishing systems as a backup to fastened extinguishing systems.
Stock an acceptable foam concentrate.
Ensure sufficient foam concentrate supply.
Ensure adequate water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing equipment obtainable in a enough number.
Have educated personnel obtainable in a adequate number.
Ensure a quick implementation of a suitable plan of motion.
For extra data, go to www.firedos.com
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