Part One of this article described the everyday incident eventualities at tank farm fires and introduced foam as probably the most appropriate extinguishing agent along with the firefighting tools most commonly used. In Part Two we take a glance at foam concentrate proportioning technologies, mobile extinguishing systems and conclude with classes learned.
NFPA 11 describes various types of foam focus proportioning equipment. In the next, three methods are looked at that are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning price should not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
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 value – i.e. 4% for a 3% foam focus or 7% for a 6% foam focus (the smaller value should be used respectively).
To assure correct proportioning, the proportioner, together with the proportioning price have to be examined at least once a year 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 confirmed and cost-effective expertise. The bladder tank is a pressurized vessel with a bladder inside which is full of 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 precept. When the fireplace pumps are activated, pressure is generated by the pump, causing supply of froth 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 method are its simple design without shifting elements and its straightforward 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 regulations corresponding to 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 broken, water will contaminate the foam concentrate. At a given proportioning price, the system is suitable only for low variations in the extinguishing water flow pressure and volume. Adding or altering individual foam discharge units is possible solely to a very restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system should be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The right proportioning rate must 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 flow meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam concentrate pump with an electronically managed valve and a flow meter in the extinguishing water flow line. When the fireplace pumps are activated, the foam concentrate pump drive and electronic control system should be activated. The extinguishing water circulate rate is measured by the flow meter and the management system adjusts the right foam focus quantity through the control valve. The foam focus is injected into the extinguishing water move by the froth concentrate pump. If there is a change in the flow price, the quantity of injected foam focus is regulated by the management valve.
The system’s benefit lies within the precise proportioning of the foam concentrate, impartial of the extinguishing water strain or move price. Foam concentrate may be topped up in the course of the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system should be activated; however, the delivered foam focus may be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate flow rate. No premix is produced; and as the foam concentrate is passed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free power supply for the foam focus pump and the management system, in addition to 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 rate and the newly adjusted foam focus amount. The foam high quality may be compromised when continually changing operating circumstances 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 flow line and a foam concentrate pump which is connected on to the water motor. Water motor and pump type one compact unit. Upon activation of the hearth pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the circulate rate modifications, the amount of foam focus is adapted immediately.
The advantage of the system is its independence from exterior vitality sources as well as a precise and instant 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 isn’t necessary since the water motor and the pump are volumetric devices firmly linked to one another. Foam concentrate refilling throughout operation is feasible. The system can also be capable of proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam concentrate can be measured by way of a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate move rate. No premix is generated; and if the foam concentrate is handed back into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively larger buying prices are a drawback of the system.
With any system, consideration ought to be taken into consideration for the annual testing prices, which may be appreciable in phrases of substitute foam focus, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge gear may be damaged in intensive fires within the tank or within the dyke space and thus lose effectiveness, cellular fire screens and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have only restricted extinguishing agent flow rates and reaches.
Firefighting monitors
Firefighting monitors are discharge devices mounted on vehicles or trailers and available in plenty of sizes. The extinguishing agent circulate rate may be up to 60,000 litres/min and the attain can be up to 180m if the stress of the hearth pumps is adequate. They are appropriate 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 to find a way to stop 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 all the time be observed to avoid an overflow of the dyke.
Mobile fireplace monitors could be supplied either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the foam concentrate often takes place via cell proportioners. This clearly points in path of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile models available as back-ups is proven by the following example for the placement of monitors for fireplace extinguishing at tanks which are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This leads to a number of alternate options for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be in a position to deal with varying move charges to ensure flexibility during extinguishing operations. Depending on the native circumstances, the monitors will want to hold a minimum distance to the burning tank or might not have the ability to be positioned close to to the tanks as a result of debris. In addition, it won’t all the time be potential to position a quantity of monitors across the tank. It should 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 entire firefighting system is made following legal regulations as well as suggestions by associations like NFPA and is not checked out more closely within the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons realized
As mentioned in the introduction to Part One of this text, it seems that many authorities and corporations haven’t learned the mandatory lessons from disastrous fire incidents of previous years. Tank farm fires within the oil and petrochemical business do not occur frequently. When they do, they normally have devastating penalties. Let us keep in mind the tank farm hearth at Deer Park, Texas in March 2019 talked about 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 fire for but unknown reasons. The plant had no fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have mounted extinguishing systems put in. All 15 tanks have been surrounded by one single dyke. The proprietor had relied on the local fireplace service, which was on the spot in a quick time however could not take control over the fireplace with the gear available, partially because flammable substance was constantly leaking from the tank. เกจวัดแรงดันลม -six hours after the fire had damaged out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of apparatus and foam focus in addition to the preparation of a plan of action took approximately 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 concentrate had been used. Instead of a hearth in the dyke area, eleven of the 15 tanks burnt down.
It may be very probable that the fire would have been extinguished quickly if the warning systems and valves had worked and a fixed fire extinguishing system had existed. It can additionally be probable that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been began earlier. Both cases would have resulted in notably much less harm.
Summing up, the next factors must be learned at the least. As far as they have not but been implemented, or simply partly, they need to function a basis for discussions about one’s personal fire-protection concept:
Have an appropriate fire-protection idea together with alternative eventualities which adapt to the given scenario often.
Always have a sufficient number of cellular extinguishing techniques as a backup to mounted extinguishing systems.
Stock an acceptable foam focus.
Ensure enough foam concentrate provide.
Ensure sufficient water supply.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing tools out there in a sufficient number.
Have skilled personnel out there in a sufficient quantity.
Ensure a quick implementation of an acceptable plan of motion.
For more information, go to www.firedos.com
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