Part One of this text described the standard incident situations at tank farm fires and introduced foam as essentially the most appropriate extinguishing agent together with the firefighting gear most commonly used. In Part Two we look at foam focus proportioning applied sciences, mobile extinguishing techniques and conclude with classes discovered.
NFPA 11 describes various types of foam focus proportioning gear. In the next, three systems are looked at which are most common. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning rate 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 price 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 fee 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 worth have to be used respectively).
To assure right proportioning, the proportioner, together with the proportioning fee should be examined at least every year and its appropriate functioning should be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a proven and cost-effective technology. The bladder tank is a pressurized vessel with a bladder inside which is full of 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 connected to a proportioner which operates utilizing the venturi precept. When the fireplace pumps are activated, stress is generated by the pump, causing delivery of froth focus to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the froth concentrate into the extinguishing water move.
The advantages of this method are its simple design with out moving elements and its simple operation. No exterior power 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 should be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the froth focus. At a given proportioning rate, the system is suitable just for low variations within the extinguishing water circulate stress and quantity. Adding or altering individual foam discharge units is feasible solely to a really restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any mandatory required annual testing, the system must be activated and premix generated at the venturi proportioner inside the extinguishing water line. The right 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 in the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the foam focus, an electric or diesel-powered foam focus pump with an electronically managed valve and a move meter in the extinguishing water circulate line. When the fire pumps are activated, the foam concentrate pump drive and digital management system must be activated. The extinguishing water flow fee is measured by the move meter and the management system adjusts the right foam focus amount by way of the control valve. The foam focus is injected into the extinguishing water move by the foam focus pump. If there’s a change in the circulate rate, the amount of injected foam concentrate is regulated by the control valve.
The system’s benefit lies within the precise proportioning of the foam concentrate, independent of the extinguishing water pressure or circulate rate. Foam focus could 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 have to be activated; nevertheless, the delivered foam concentrate may be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam focus circulate rate. No premix is produced; and as the foam focus is handed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free vitality provide for the froth concentrate pump and the control system, in addition to the need for a classy control system and the comparatively higher buying costs. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water flow price and the newly adjusted foam focus amount. The foam quality could also be compromised when continually changing operating conditions 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 foam focus, a water motor installed in the extinguishing water move line and a foam concentrate pump which is linked on to the water motor. Water motor and pump kind one compact unit. Upon activation of the fireplace pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the circulate price changes, the quantity of foam focus is tailored immediately.
The benefit of the system is its independence from exterior vitality sources as nicely as a exact and immediate foam-concentrate proportioning regardless of the extinguishing water pressure or circulate 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 devices firmly related to every other. Foam concentrate refilling during operation is feasible. The system is also capable of proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam focus can be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate circulate fee. No premix is generated; and if the froth focus is handed again into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively larger buying prices are an obstacle of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which may be appreciable by method of alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge gear may be broken in intensive fires in the tank or within the dyke area and thus lose effectiveness, cellular fireplace displays and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they’ve solely limited extinguishing agent circulate charges and reaches.
Firefighting displays
Firefighting displays are discharge devices mounted on vehicles or trailers and out there in many sizes. The extinguishing agent circulate rate can be up to 60,000 litres/min and the attain can be up to 180m if the stress of the fire pumps is adequate. They are suitable to discharge foam, e.g., to extinguish a surface hearth in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank in order to forestall it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke area ought to at all times be observed to avoid an overflow of the dyke.
Mobile fire displays can be supplied either by the extinguishing water of the stationary fireplace pumps or by mobile pumps. The injection of the foam focus normally takes place by way of cellular proportioners. This clearly points in direction of the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile units available as back-ups is shown by the next example for the position of monitors for fire 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 a quantity of options for the screens. Generally, foam-concentrate proportioners for a minimum of 32,000 litres/min are required, which ought to have the flexibility to deal with varying circulate charges to guarantee flexibility throughout extinguishing operations. Depending on the native conditions, the screens will want to hold a minimum distance to the burning tank or may not have the power to be positioned near to the tanks as a outcome of particles. In addition, it won’t at all times be possible to place a quantity of monitors around the tank. It should be ensured the monitor has sufficient throwing peak in relation to the tank peak, to ship foam into the within of the tank.
The dimensioning of the complete firefighting system is made following authorized rules in addition to recommendations by associations like NFPA and isn’t checked out extra carefully within the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
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 hearth incidents of previous years. Tank farm fires in the oil and petrochemical industry don’t happen frequently. When they do, they usually have devastating penalties. Let us remember the tank farm fireplace at Deer Park, Texas in March 2019 mentioned within the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught hearth for but unknown reasons. เกจวัดแรงดันไฟฟ้า had no gas warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have fixed extinguishing techniques installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the local fire service, which was on the spot very quickly however couldn’t take management over the hearth with the tools 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 exterior firefighting company to do the extinguishing work. Mobilization of apparatus and foam focus as properly as the preparation of a plan of motion took roughly 13 hours. The fire was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt were 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 space, eleven of the 15 tanks burnt down.
It could be very possible that the hearth would have been extinguished quickly if the warning methods and valves had labored and a fixed fireplace extinguishing system had existed. It can be probable that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably much less harm.
Summing up, the following points ought to be realized at the least. As far as they have not yet been implemented, or just partly, they need to function a basis for discussions about one’s personal fire-protection idea:
Have an appropriate fire-protection concept together with different scenarios which adapt to the given scenario regularly.
Always have a sufficient variety of cell extinguishing systems as a backup to mounted extinguishing methods.
Stock an acceptable foam concentrate.
Ensure sufficient foam focus supply.
Ensure enough water supply.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing tools obtainable in a sufficient quantity.
Have educated personnel available in a sufficient number.
Ensure a fast implementation of a suitable plan of action.
For more information, go to www.firedos.com
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