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

Part One of this article described the standard incident scenarios at tank farm fires and introduced foam as essentially the most appropriate extinguishing agent along with the firefighting equipment mostly used. In Part Two we look at foam focus proportioning applied sciences, cell extinguishing methods and conclude with lessons discovered.
NFPA 11 describes varied forms of foam concentrate proportioning gear. In the next, three systems are checked out which are commonest. 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 focus or 6% for a 6% foam focus.
The proportioning price must 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 value should be used respectively).
To guarantee right proportioning, the proportioner, together with the proportioning price must be examined a minimal of every year and its right 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 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 concentrate from the bladder as required. The bladder is linked to a proportioner which operates utilizing the venturi principle. When the hearth pumps are activated, pressure is generated by the pump, causing delivery of foam focus to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the foam focus into the extinguishing water move.
The advantages of this system are its easy design with out shifting elements and its easy operation. No exterior power is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic to corresponding regulations such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system must be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the froth concentrate. At a given proportioning fee, the system is appropriate only for low variations in the extinguishing water flow pressure and volume. Adding or changing particular person foam discharge gadgets is feasible only to a very restricted extent. The system can additionally be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system must be activated and premix generated at the venturi proportioner inside the extinguishing water line. The right proportioning fee 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 flow 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 flow meter within the extinguishing water move line. When the fireplace pumps are activated, the foam focus pump drive and electronic management system must be activated. The extinguishing water move price is measured by the move meter and the management system adjusts the proper foam concentrate quantity through the management valve. The foam focus is injected into the extinguishing water move by the froth focus pump. If there’s a change in the circulate price, the quantity of injected foam focus is regulated by the control valve.
The system’s advantage lies within the exact proportioning of the foam concentrate, unbiased of the extinguishing water strain or flow rate. Foam concentrate can be topped up in the course of the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system have to be activated; however, the delivered foam concentrate can be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam focus flow fee. No premix is produced; and as a result of the foam concentrate is handed again into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free energy supply for the froth focus pump and the management system, as nicely as the need for a classy control system and the comparatively greater purchasing prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water circulate fee and the newly adjusted foam concentrate amount. The foam quality may be compromised when continually altering 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 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 kind one compact unit. Upon activation of the fireplace pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the flow rate changes, the quantity of froth concentrate is customized instantly.
The advantage of the system is its independence from external power sources as well as a precise and quick foam-concentrate proportioning whatever the extinguishing water strain or flow fee. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t essential for the reason that water motor and the pump are volumetric gadgets firmly linked to each other. Foam concentrate refilling throughout operation is possible. The system can be able to proportioning highly viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam concentrate could be measured via a return line. The proportioning price is calculated from the extinguishing water/foam focus circulate rate. No premix is generated; and if the froth focus is handed back into the tank, no foam focus needs to be topped up.
The larger design and the comparatively greater purchasing costs are an obstacle of the system.
With เกจวัดน้ำยาแอร์refco , consideration should be taken into account for the annual testing prices, which can be considerable when it comes to substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge gear may be damaged in in depth fires in the tank or within the dyke area and thus lose effectiveness, mobile fire screens and foam pipes could also be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have only limited extinguishing agent move rates and reaches.
Firefighting monitors
Firefighting monitors are discharge gadgets mounted on vehicles or trailers and out there in plenty of sizes. The extinguishing agent move fee can be as much as 60,000 litres/min and the reach may be as much as 180m if the pressure of the fire pumps is enough. They are suitable to discharge foam, e.g., to extinguish a floor hearth in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank so as to stop it reaching the critical temperature for a boilover, or to maintain 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 fireplace displays could be supplied both by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the foam focus usually takes place through mobile proportioners. This clearly points in the path of the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular models out there as back-ups is proven by the following example for the position of displays for hearth extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This leads to a quantity of options for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to have the power to deal with various circulate rates to ensure flexibility during extinguishing operations. Depending on the local situations, the screens might need to maintain a minimal distance to the burning tank or might not have the power to be positioned close to to the tanks because of particles. In addition, it won’t always be potential to position a number of screens across the tank. It should be ensured the monitor has adequate throwing top in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the whole firefighting system is made following authorized regulations in addition to suggestions by associations like NFPA and is not looked at more intently in the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons realized
As talked about within the introduction to Part One of this article, plainly many authorities and companies haven’t learned the required lessons from disastrous hearth incidents of past years. Tank farm fires in the oil and petrochemical industry don’t occur incessantly. When they do, they often have devastating consequences. Let us remember the tank farm fire 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 30 minutes and caught hearth for yet unknown reasons. The plant 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 methods put in. All 15 tanks had been surrounded by one single dyke. The owner had relied on the native fire service, which was on the spot in a quick time however couldn’t take control over the hearth with the tools out there, partially because flammable substance was continuously leaking from the tank. Thirty-six hours after the fire had damaged out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of apparatus and foam concentrate as properly as the preparation of a plan of action took roughly thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts were revamped three days, with foam focus and water shortages occurring in the meantime. In total, over 500,000 litres of froth focus were used. Instead of a fireplace within the dyke space, 11 of the 15 tanks burnt down.
It may be very possible that the fireplace would have been extinguished rapidly if the warning techniques and valves had worked and a set fire extinguishing system had existed. It can additionally be possible that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both circumstances would have resulted in notably much less injury.
Summing up, the following points must be realized as a minimum. As far as they have not yet been applied, or simply partly, they should serve as a foundation for discussions about one’s personal fire-protection concept:
Have an appropriate fire-protection idea including different eventualities which adapt to the given state of affairs often.
Always have a sufficient variety of cell extinguishing systems as a backup to fixed extinguishing systems.
Stock an acceptable foam concentrate.
Ensure enough foam concentrate supply.
Ensure sufficient water supply.
Keep well-maintained, shortly and well-accessible, strategically placed and functioning extinguishing equipment out there in a enough quantity.
Have skilled personnel out there in a sufficient number.
Ensure a quick implementation of an appropriate plan of action.
For more info, go to www.firedos.com
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