Use of froth for firefighting in tank farms of the oil and petrochemical trade – Part 2

Part One of this text described the standard incident situations at tank farm fires and offered foam as the most appropriate extinguishing agent along with the firefighting tools most commonly used. In Part Two we have a look at foam focus proportioning technologies, mobile extinguishing techniques and conclude with lessons realized.
NFPA eleven describes varied types of foam concentrate proportioning equipment. In the following, three systems are checked out which are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning rate must not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning rate should not exceed 30% above the permitted worth i.e. three.9% for a 3% foam concentrate or 7.8% for a 6% foam focus; respectively, the proportioning price is allowed to be an absolute maximum of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller worth must be used respectively).
To guarantee appropriate proportioning, the proportioner, including the proportioning rate should be tested a minimum of annually and its appropriate functioning have to 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 crammed with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the froth focus from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi precept. When the hearth pumps are activated, stress is generated by the pump, causing supply of froth focus to the proportioner. The extinguishing water flows via the venturi proportioner. The ensuing vacuum induces the foam focus into the extinguishing water circulate.
The advantages of this technique are its simple design without shifting parts and its straightforward operation. No external 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 focus, the system must be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the foam focus. At a given proportioning rate, the system is appropriate just for low variations within the extinguishing water flow stress and volume. Adding or altering particular person foam discharge units is feasible only to a really limited extent. pressure gauge trerice ราคา is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The right proportioning price should be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam concentrate in the bladder tank needs to 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 froth focus, an electrical or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter within the extinguishing water move line. When the hearth pumps are activated, the foam concentrate pump drive and electronic control system have to be activated. The extinguishing water flow price is measured by the move meter and the management system adjusts the correct foam concentrate quantity via the management valve. The foam concentrate is injected into the extinguishing water circulate by the foam concentrate pump. If there’s a change in the move price, the amount of injected foam focus is regulated by the control valve.
The system’s benefit lies in the exact proportioning of the foam focus, unbiased of the extinguishing water stress or circulate price. Foam focus can be topped up through the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system must be activated; nonetheless, the delivered foam focus may be measured through a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate rate. No premix is produced; and as the foam focus is passed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free vitality supply for the foam concentrate pump and the control system, in addition to the necessity for a classy control system and the comparatively larger purchasing prices. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water move rate and the newly adjusted foam focus quantity. The foam quality could also be compromised when continually changing operating conditions 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 foam concentrate, a water motor installed in the extinguishing water circulate line and a foam concentrate pump which is linked on to the water motor. Water motor and pump form one compact unit. Upon activation of the fireplace pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump provides instant foam-concentrate injection into the extinguishing water. If the flow fee modifications, the amount of froth concentrate is customized immediately.
The benefit 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 flow price. If a piston or plunger pump is used, adjustment or calibration after installation isn’t essential because the water motor and the pump are volumetric devices firmly related to every other. Foam focus refilling during operation is possible. The system can be able to proportioning extremely viscous foam concentrates. The system must be activated for annual testing; however, the delivered foam concentrate can be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus move fee. No premix is generated; and if the foam focus is handed back into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively larger purchasing prices are a disadvantage of the system.
With any system, consideration should be taken into consideration for the annual testing costs, which could be considerable when it comes to alternative foam focus, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge gear can be damaged in extensive fires within the tank or in the dyke area and thus lose effectiveness, cellular fireplace screens and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they have solely restricted extinguishing agent circulate rates and reaches.
Firefighting screens
Firefighting monitors are discharge devices mounted on autos or trailers and available in lots of sizes. The extinguishing agent circulate rate could be as much as 60,000 litres/min and the reach could be as much as 180m if the pressure of the hearth pumps is sufficient. 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 prevent it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke area ought to always be observed to avoid an overflow of the dyke.
Mobile fire monitors could be provided both by the extinguishing water of the stationary fireplace pumps or by mobile pumps. เพรสเชอร์เกจnuovafima of the foam concentrate normally takes place by way of mobile proportioners. This clearly points in path of the advantage of vitality independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell items available as back-ups is shown by the next example for the position of monitors 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 ends in a number of alternatives for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should be in a position to deal with various move charges to guarantee flexibility throughout extinguishing operations. Depending on the native circumstances, the screens will want to maintain a minimal distance to the burning tank or might not have the flexibility to be positioned near to the tanks because of particles. In addition, it won’t at all times be potential to position a number of screens across the tank. It have to be ensured the monitor has adequate throwing height in relation to the tank top, to deliver foam into the within of the tank.
The dimensioning of the whole firefighting system is made following legal rules as nicely as suggestions by associations like NFPA and is not looked at more closely in the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons learned
As talked about within the introduction to Part One of this article, it appears that evidently many authorities and corporations haven’t discovered the necessary lessons from disastrous hearth incidents of previous years. Tank farm fires in the oil and petrochemical trade do not occur regularly. When they do, they normally have devastating consequences. Let us keep in mind 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. The plant had no fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have mounted extinguishing methods 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 but couldn’t take control over the hearth with the tools out there, partially because flammable substance was constantly leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of equipment and foam concentrate in addition to the preparation of a plan of motion took roughly thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt have been remodeled three days, with foam focus and water shortages occurring within the meantime. In whole, over 500,000 litres of foam focus were used. Instead of a fire within the dyke space, eleven of the 15 tanks burnt down.
It may be very probable that the hearth would have been extinguished rapidly if the warning techniques and valves had labored and a set fireplace extinguishing system had existed. It is also possible that the fire would have been extinguished rapidly if the extinguishing operation, which succeeded finally, had been started earlier. Both instances would have resulted in notably much less harm.
Summing up, the following factors must be learned at least. As far as they have not yet been carried out, or simply partly, they should function a basis for discussions about one’s own fire-protection concept:
Have an acceptable fire-protection concept together with different scenarios which adapt to the given scenario regularly.
Always have a adequate variety of cell extinguishing techniques as a backup to fixed extinguishing techniques.
Stock a suitable foam focus.
Ensure adequate foam focus provide.
Ensure enough water supply.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment available in a sufficient quantity.
Have educated personnel obtainable in a sufficient number.
Ensure a fast implementation of an acceptable plan of motion.
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