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

Part One of this text described the typical incident situations at tank farm fires and introduced foam as probably the most appropriate extinguishing agent together with the firefighting gear mostly used. In Part Two we have a glance at foam concentrate proportioning applied sciences, cellular extinguishing techniques and conclude with classes discovered.
NFPA eleven describes various kinds of foam concentrate proportioning tools. In the next, three techniques are looked at which are commonest. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning fee should not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning price should not exceed 30% above the permitted value i.e. three.9% for a 3% foam concentrate 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 concentrate or 7% for a 6% foam concentrate (the smaller value have to be used respectively).
To assure right proportioning, the proportioner, together with the proportioning price should be examined no much less than every year and its correct 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 expertise. The bladder tank is a pressurized vessel with a bladder inside which is crammed with 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 principle. When the fire pumps are activated, pressure is generated by the pump, causing delivery of foam concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the foam concentrate into the extinguishing water flow.
The advantages of this technique are its easy design with out moving parts and its easy operation. No external energy is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic to corresponding laws similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system should be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam focus. At a given proportioning rate, the system is appropriate just for low variations within the extinguishing water circulate pressure and volume. Adding or changing individual foam discharge gadgets is possible only to a really limited extent. The system can also be 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 inside the extinguishing water line. The correct proportioning rate have to be measured within the premix by laboratory analysis. 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 move meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a move meter in the extinguishing water circulate line. When the hearth pumps are activated, the foam concentrate pump drive and electronic control system should be activated. The extinguishing water flow fee is measured by the circulate meter and the control system adjusts the correct foam focus amount through the management valve. The foam concentrate is injected into the extinguishing water move by the foam concentrate pump. If there’s a change within the move fee, the amount of injected foam concentrate is regulated by the control valve.
The system’s benefit lies within the exact proportioning of the froth focus, independent of the extinguishing water stress or flow price. Foam focus could be topped up through the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the aim of annual testing, the system must be activated; nonetheless, the delivered foam concentrate can 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 concentrate is passed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free energy provide for the foam concentrate pump and the management system, in addition to the necessity for a classy management system and the comparatively greater 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 concentrate amount. The foam quality could also be compromised when continually changing working conditions as foam discharge devices are turned on or off or changed.
Water motor with proportioning pump
The system consists of an atmospheric tank for the foam concentrate, a water motor put in within the extinguishing water circulate line and a foam focus pump which is connected directly 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 move fee adjustments, the amount of froth concentrate is adapted immediately.
The benefit of the system is its independence from exterior power sources as nicely as a precise and quick foam-concentrate proportioning whatever the extinguishing water strain or circulate rate. If a piston or plunger pump is used, adjustment or calibration after set up is not necessary for the reason that water motor and the pump are volumetric gadgets firmly linked to every other. Foam focus refilling during operation is feasible. The system can be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam focus could be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow rate. No premix is generated; and if the froth concentrate is passed again into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively higher purchasing costs are an obstacle of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which could be considerable when it comes to replacement foam concentrate, disposal of premix and labour prices.
Mobile extinguishing techniques
As the stationary foam discharge equipment can be damaged in extensive fires within the tank or in the dyke area and thus lose effectiveness, mobile fireplace monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have solely restricted extinguishing agent move rates and reaches.
Firefighting displays
Firefighting monitors are discharge units mounted on vehicles or trailers and available in many sizes. The extinguishing agent flow price could be as a lot as 60,000 litres/min and the reach could be as a lot as 180m if the pressure of the fire pumps is enough. They are appropriate 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 to have the ability to prevent it reaching the important temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke space should all the time be observed to avoid an overflow of the dyke.
Mobile fire displays may be supplied both by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the froth concentrate usually takes place by way of mobile proportioners. This clearly points towards the advantage of energy 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 next instance for the position of monitors for fire 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 options for the screens. Generally, foam-concentrate proportioners for a minimum of 32,000 litres/min are required, which should have the flexibility to deal with varying move rates to guarantee flexibility during extinguishing operations. Depending on the local circumstances, the screens will want to hold a minimal distance to the burning tank or could not be in a position to be positioned near to the tanks because of debris. In addition, it won’t at all times be attainable to place a quantity of displays around the tank. It should be ensured the monitor has sufficient throwing top in relation to the tank height, to ship foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following legal rules as well as suggestions by associations like NFPA and isn’t checked out more intently within the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons learned
As mentioned in the introduction to Part One of this text, it appears that evidently many authorities and firms haven’t discovered the mandatory lessons from disastrous hearth incidents of previous years. Tank farm fires in the oil and petrochemical industry don’t occur regularly. When they do, they normally have devastating penalties. Let us keep in mind the tank farm fireplace at Deer Park, Texas in March 2019 mentioned in the introduction.
The fire developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes 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 fixed extinguishing techniques installed. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native fireplace service, which was on the spot in a brief time however couldn’t take control over the fire with the tools out there, partially as a outcome of flammable substance was repeatedly 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 equipment and foam concentrate in addition to the preparation of a plan of motion took approximately 13 hours. The fireplace was finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts had been made over three days, with foam focus and water shortages occurring in the meantime. In complete, over 500,000 litres of froth focus had been used. Instead of a fireplace in the dyke space, 11 of the 15 tanks burnt down.
เกจอาร์กอน could be very probable that the fire would have been extinguished shortly if the warning methods and valves had labored and a fixed fireplace extinguishing system had existed. It can be possible that the fireplace would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been started earlier. Both cases would have resulted in notably much less damage.
Summing up, the following points should be discovered as a minimum. As far as they haven’t yet been carried out, or simply partly, they should function a basis for discussions about one’s own fire-protection idea:
Have an appropriate fire-protection concept including different scenarios which adapt to the given state of affairs frequently.
Always have a sufficient variety of cellular extinguishing methods as a backup to mounted extinguishing techniques.
Stock an appropriate foam concentrate.
Ensure adequate foam focus provide.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically placed and functioning extinguishing equipment obtainable in a adequate quantity.
Have trained personnel available in a sufficient number.
Ensure a fast implementation of an acceptable plan of motion.
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