Part One of this text described the standard incident situations at tank farm fires and introduced foam as the most appropriate extinguishing agent together with the firefighting gear mostly used. In Part Two we look at foam focus proportioning technologies, cell extinguishing methods and conclude with classes discovered.
NFPA eleven describes various types of foam concentrate proportioning gear. In the following, three techniques are checked out which are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning fee should not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning price must not exceed 30% above the permitted value 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 maximum of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller value have to be used respectively).
To guarantee right proportioning, the proportioner, together with the proportioning price have to be examined a minimum of once a 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 crammed with 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 related to a proportioner which operates utilizing the venturi precept. When the fire pumps are activated, strain is generated by the pump, causing supply of foam concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The ensuing vacuum induces the froth focus into the extinguishing water flow.
The advantages of this technique are its easy design without moving elements and its simple operation. No external energy is required, and the system is comparatively inexpensive.
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 have to be shut down and drained. The rubber bladder is delicate; when damaged, water will contaminate the foam focus. At a given proportioning price, the system is suitable just for low variations within the extinguishing water move pressure and quantity. Adding or changing individual foam discharge devices is possible solely to a really limited 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 within the extinguishing water line. The right proportioning fee should be measured within the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam concentrate within the bladder tank must be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with flow 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 circulate meter in the extinguishing water circulate line. When the fire pumps are activated, the foam focus pump drive and digital control system have to be activated. The extinguishing water flow rate is measured by the circulate meter and the control system adjusts the proper foam focus amount by way of the control valve. The foam concentrate is injected into the extinguishing water move by the foam concentrate pump. If there is a change within the circulate price, the quantity of injected foam concentrate is regulated by the management valve.
The system’s benefit lies within the precise proportioning of the foam focus, impartial of the extinguishing water stress or move fee. Foam concentrate could be topped up in the course of the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the aim of annual testing, the system have to be activated; nevertheless, the delivered foam concentrate could be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate circulate rate. No premix is produced; and as the foam concentrate is passed back into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an exterior interruption-free power supply for the froth focus pump and the management system, as properly as the need for a complicated management system and the comparatively higher buying costs. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water move fee and the newly adjusted foam focus amount. The foam quality may be compromised when continuously changing operating conditions as foam discharge devices 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 installed within the extinguishing water circulate 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 hearth pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump provides immediate foam-concentrate injection into the extinguishing water. If the flow fee modifications, the amount of froth focus is customized instantly.
The benefit of the system is its independence from external power sources as properly as a exact and immediate foam-concentrate proportioning regardless of the extinguishing water strain or move fee. If a piston or plunger pump is used, adjustment or calibration after set up is not essential because the water motor and the pump are volumetric devices firmly related to one another. Foam concentrate refilling during operation is possible. The system is also able to proportioning extremely viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam focus could be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam focus flow fee. No premix is generated; and if the froth concentrate is handed again into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively greater buying prices are a disadvantage of the system.
With any system, consideration ought to be taken into consideration for the annual testing costs, which could be appreciable when it comes to replacement foam concentrate, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge tools can be damaged in extensive fires in the tank or within the dyke space and thus lose effectiveness, cellular hearth displays 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 circulate charges and reaches.
Firefighting displays
Firefighting displays are discharge devices mounted on autos or trailers and out there in lots of sizes. The extinguishing agent move fee can be as much as 60,000 litres/min and the attain can be up to 180m if the pressure of the fireplace 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 so as to forestall it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space should always be noticed to keep away from an overflow of the dyke.
Mobile hearth monitors may be supplied either by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the froth focus normally takes place through cell proportioners. This clearly points in path of the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular models available as back-ups is proven by the following example for the location of displays for fireplace extinguishing at tanks which are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This leads to several options for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be succesful of deal with various move charges to ensure flexibility throughout extinguishing operations. Depending on the native conditions, the screens might need to keep a minimal distance to the burning tank or could not be succesful of be positioned close to to the tanks due to particles. In addition, it won’t always be attainable to place several displays around the tank. It must be ensured the monitor has adequate throwing height in relation to the tank height, to ship foam into the within of the tank.
The dimensioning of the complete firefighting system is made following authorized rules in addition to suggestions by associations like NFPA and is not looked at more closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons learned
As talked about in the introduction to Part One of this text, plainly many authorities and corporations haven’t learned the mandatory classes from disastrous fireplace incidents of previous years. Tank farm fires in the oil and petrochemical trade do not happen frequently. When they do, they normally have devastating penalties. Let us remember the tank farm fireplace at Deer Park, Texas in March 2019 mentioned in the introduction.
The hearth 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 reasons. 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 methods installed. All 15 tanks had been surrounded by one single dyke. The proprietor had relied on the local hearth service, which was on the spot very quickly but couldn’t take control over the fire 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 external firefighting company to do the extinguishing work. เครื่องวัดแรงดันเกจที่นิยมใช้ of equipment and foam concentrate as properly as the preparation of a plan of action took roughly thirteen hours. The hearth was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt have been revamped three days, with foam concentrate and water shortages occurring in the meantime. In total, over 500,000 litres of foam focus have been used. Instead of a fireplace in the dyke area, eleven of the 15 tanks burnt down.
It could be very possible that the fire would have been extinguished quickly if the warning techniques and valves had worked and a onerous and fast hearth extinguishing system had existed. It can be probable that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been started earlier. Both instances would have resulted in notably much less damage.
Summing up, the following factors ought to be realized at least. As far as they haven’t yet been carried out, or just partly, they should serve as a basis for discussions about one’s personal fire-protection idea:
Have an acceptable fire-protection concept including alternative eventualities which adapt to the given state of affairs frequently.
Always have a sufficient number of cell extinguishing systems as a backup to fastened extinguishing techniques.
Stock an acceptable foam concentrate.
Ensure sufficient foam concentrate provide.
Ensure adequate water provide.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing gear obtainable in a sufficient number.
Have trained personnel available in a enough quantity.
Ensure a quick implementation of an acceptable plan of motion.
For extra information, go to www.firedos.com
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