Notes

Use of foam for firefighting in tank farms of the oil and petrochemical business – Part 2
Part One of this article described the typical incident scenarios at tank farm fires and offered foam as essentially the most appropriate extinguishing agent along with the firefighting tools most commonly used. In Part Two we look at foam focus proportioning applied sciences, mobile extinguishing methods and conclude with lessons discovered.
NFPA eleven describes various forms of foam focus proportioning tools. In the following, three systems are looked at which are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning rate should not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning fee must 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 focus or 7% for a 6% foam focus (the smaller worth should be used respectively).
To assure right proportioning, the proportioner, including the proportioning fee should be examined no 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 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 concentrate 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, inflicting supply of foam concentrate 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 method are its simple design without transferring elements and its easy operation. No exterior vitality is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel subject to corresponding rules corresponding 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 broken, water will contaminate the foam concentrate. At a given proportioning price, the system is appropriate just for low variations in the extinguishing water circulate pressure and quantity. Adding or changing particular person foam discharge devices is feasible only to a really restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated at the venturi proportioner within the extinguishing water line. The right proportioning rate must be measured in the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam focus within the bladder tank needs to be replaced.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with circulate meter

The system consists of an atmospheric tank for the foam concentrate, an electrical or diesel-powered foam focus pump with an electronically managed valve and a move meter within the extinguishing water circulate line. When the fire pumps are activated, the froth focus pump drive and electronic management system have to be activated. The extinguishing water flow fee is measured by the flow meter and the control system adjusts the proper foam concentrate quantity by way of the management valve. The foam focus is injected into the extinguishing water flow by the foam concentrate pump. If there is a change within the move price, the quantity of injected foam concentrate is regulated by the control valve.
The system’s benefit lies within the exact proportioning of the foam concentrate, unbiased of the extinguishing water stress or flow rate. Foam focus could be topped up through the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For pressure gauge ไฮ ด รอ ลิ ค of annual testing, the system must be activated; nonetheless, the delivered foam concentrate could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate price. No premix is produced; and as the foam concentrate is passed again into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free power supply for the froth concentrate pump and the management system, in addition to the need for a sophisticated management system and the comparatively higher purchasing costs. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water move rate and the newly adjusted foam concentrate quantity. The foam high quality may be compromised when continually changing operating situations 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 installed within the extinguishing water flow line and a foam concentrate pump which is related on to the water motor. Water motor and pump kind one compact unit. Upon activation of the fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump offers quick foam-concentrate injection into the extinguishing water. If the circulate rate changes, the quantity of foam focus is tailored instantly.
The benefit of the system is its independence from exterior vitality sources as well as a exact and immediate foam-concentrate proportioning regardless of the extinguishing water stress or move price. If a piston or plunger pump is used, adjustment or calibration after installation just isn't necessary because the water motor and the pump are volumetric devices firmly connected to each other. Foam concentrate 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; however, the delivered foam focus can be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move rate. No premix is generated; and if the froth focus is handed again into the tank, no foam focus must be topped up.
The larger design and the comparatively higher buying prices are a disadvantage of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which can be considerable by method of substitute foam focus, disposal of premix and labour prices.
Mobile extinguishing techniques

As the stationary foam discharge equipment can be damaged in extensive fires in the tank or in the dyke space and thus lose effectiveness, mobile fireplace displays and foam pipes could additionally be used.
Foam pipes

Foam pipes are normally held by firefighters, making them very flexible. Yet they have only restricted extinguishing agent circulate rates and reaches.
Firefighting screens

Firefighting displays are discharge units mounted on automobiles or trailers and obtainable in many sizes. The extinguishing agent flow fee could be as much as 60,000 litres/min and the attain may be up to 180m if the strain of the hearth pumps is enough. They are suitable to discharge foam, e.g., to extinguish a floor fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank so as to prevent it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke area should at all times be observed to keep away from an overflow of the dyke.
Mobile fireplace monitors can be equipped either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the froth focus normally takes place by way of cell proportioners. This clearly factors in path of the advantage of vitality independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of mobile items available as back-ups is shown by the next example for the location of screens for fireplace extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several options for the displays. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which ought to be capable of handle various flow rates to ensure flexibility during extinguishing operations. Depending on the native situations, the monitors will need to keep a minimum distance to the burning tank or might not have the power to be positioned near to the tanks due to debris. In addition, it will not all the time be potential to position a number of monitors 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 inside of the tank.
The dimensioning of the whole firefighting system is made following legal regulations as nicely as suggestions by associations like NFPA and isn't looked at extra carefully in the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned

As mentioned within the introduction to Part One of this article, it appears that many authorities and corporations have not discovered the required classes from disastrous hearth incidents of past years. Tank farm fires within the oil and petrochemical industry don't happen frequently. When they do, they usually have devastating penalties. 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 defective valve for half-hour and caught fireplace for yet unknown causes. The plant had no gasoline warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn't have fastened extinguishing methods put in. All 15 tanks have been surrounded by one single dyke. The proprietor had relied on the local fire service, which was on the spot in a brief time but couldn't take control over the fireplace with the equipment 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 equipment and foam focus as properly as the preparation of a plan of motion took approximately 13 hours. The fire was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt were made over three days, with foam focus and water shortages occurring within the meantime. In complete, over 500,000 litres of froth concentrate have been used. Instead of a fireplace in the dyke space, eleven of the 15 tanks burnt down.
It may be very possible that the hearth would have been extinguished shortly if the warning methods and valves had worked and a onerous and fast fireplace extinguishing system had existed. It can also be possible that the fire would have been extinguished rapidly if the extinguishing operation, which succeeded eventually, had been started earlier. Both cases would have resulted in notably less damage.
Summing up, the next factors should be realized at the least. As far as they have not but been carried out, or just partly, they want to function a basis for discussions about one’s own fire-protection idea:
Have a suitable fire-protection idea together with various scenarios which adapt to the given scenario frequently.
Always have a enough number of mobile extinguishing methods as a backup to fastened extinguishing techniques.
Stock an acceptable foam focus.
Ensure enough foam concentrate supply.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically placed and functioning extinguishing equipment out there in a sufficient number.
Have skilled personnel obtainable in a adequate quantity.
Ensure a fast implementation of an appropriate plan of action.
For extra data, go to www.firedos.com

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