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

Part One of this article described the everyday incident eventualities at tank farm fires and presented foam as probably the most appropriate extinguishing agent together with the firefighting equipment most commonly used. In Part Two we take a look at foam focus proportioning applied sciences, cell extinguishing systems and conclude with lessons discovered.
NFPA 11 describes varied types of foam concentrate proportioning gear. In the following, three techniques are looked at which are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price should not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
pressure gauge 10 bar 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 worth must be used respectively).
To guarantee appropriate proportioning, the proportioner, including the proportioning price have to be tested at least every year and its correct 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 filled with foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the froth focus from the bladder as required. The bladder is connected to a proportioner which operates using the venturi precept. When the fireplace pumps are activated, stress is generated by the pump, causing supply of foam concentrate to the proportioner. The extinguishing water flows through the venturi proportioner. The resulting vacuum induces the foam concentrate into the extinguishing water move.
The benefits of this method are its easy design with out moving elements and its simple operation. digital pressure gauge is required, and the system is relatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding laws such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system have to be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the froth focus. At a given proportioning rate, the system is appropriate just for low variations within the extinguishing water circulate strain and quantity. Adding or altering individual foam discharge units is feasible solely to a really limited extent. The system can also be unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated on the venturi proportioner within the extinguishing water line. The correct proportioning price should be measured in the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam focus within the bladder tank must 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 focus, an electrical or diesel-powered foam concentrate pump with an electronically controlled valve and a flow meter in the extinguishing water flow line. When the fireplace pumps are activated, the foam focus pump drive and electronic management system have to be activated. The extinguishing water circulate price is measured by the flow meter and the control system adjusts the proper foam focus quantity by way of the control valve. The foam concentrate is injected into the extinguishing water circulate by the froth focus pump. If there is a change within the circulate rate, the amount of injected foam concentrate is regulated by the control valve.
The system’s advantage lies within the exact proportioning of the froth focus, independent of the extinguishing water stress or circulate fee. Foam focus can be topped up in the course of the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the purpose of annual testing, the system should be activated; nonetheless, the delivered foam concentrate could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate circulate price. No premix is produced; and as the foam concentrate is handed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free power supply for the foam concentrate pump and the management system, in addition to the necessity for a classy management system and the comparatively higher purchasing costs. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water circulate price and the newly adjusted foam focus amount. The foam high quality may be compromised when continually changing operating situations 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 froth concentrate, 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 form one compact unit. Upon activation of the fire pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the move rate changes, the quantity of froth focus is tailored instantly.
The advantage of the system is its independence from exterior vitality sources in addition to a precise and quick foam-concentrate proportioning whatever the extinguishing water strain or move rate. 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 units firmly linked to one another. Foam concentrate refilling during 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 focus can be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow fee. No premix is generated; and if the froth focus is handed back into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively higher purchasing prices are an obstacle of the system.
With any system, consideration should be taken into account for the annual testing costs, which could be appreciable by means of substitute foam focus, disposal of premix and labour prices.
Mobile extinguishing systems

As the stationary foam discharge gear could be damaged in in depth fires within the tank or within the dyke area and thus lose effectiveness, mobile fire 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 limited extinguishing agent move rates and reaches.
Firefighting screens

Firefighting monitors are discharge gadgets mounted on automobiles or trailers and obtainable in many sizes. The extinguishing agent circulate rate may be as a lot as 60,000 litres/min and the reach can be as much as 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 chill down a neighboring tank or the tank wall of a burning tank to be able to stop it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area should at all times be noticed to avoid an overflow of the dyke.
Mobile fireplace screens may be equipped both by the extinguishing water of the stationary hearth pumps or by cellular pumps. The injection of the foam concentrate usually takes place by way of cellular proportioners. This clearly points in the path of the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular units out there as back-ups is proven by the following example for the placement 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 alternatives for the monitors. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which should be capable of handle various move rates to guarantee flexibility throughout extinguishing operations. Depending on the native conditions, the displays will want to maintain a minimal distance to the burning tank or might not have the ability to be positioned close to to the tanks because of particles. In addition, it is not going to all the time be attainable to place a number of screens across the tank. It have to be ensured the monitor has enough throwing top in relation to the tank top, to ship foam into the within of the tank.
The dimensioning of the complete firefighting system is made following legal regulations as well as suggestions by associations like NFPA and is not checked out more closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons discovered

As mentioned within the introduction to Part One of this article, it appears that many authorities and corporations have not learned the required lessons from disastrous hearth incidents of past years. Tank farm fires in the oil and petrochemical trade do not occur frequently. 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 in the introduction.
The fire developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for half-hour and caught hearth for but unknown causes. The plant had no fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have mounted extinguishing systems put in. All 15 tanks had been surrounded by one single dyke. The proprietor had relied on the local fireplace service, which was on the spot in a quick time however could not take management over the hearth with the tools obtainable, partially because flammable substance was constantly leaking from the tank. Thirty-six hours after the fireplace had damaged out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of kit and foam focus as properly as the preparation of a plan of motion took approximately 13 hours. The hearth was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt have been revamped three days, with foam concentrate and water shortages occurring in the meantime. In total, over 500,000 litres of froth focus had been used. Instead of a hearth in the dyke area, eleven of the 15 tanks burnt down.
It may be very possible that the hearth would have been extinguished quickly if the warning methods and valves had worked and a fixed fire extinguishing system had existed. It can additionally be possible that the fireplace would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been began earlier. Both cases would have resulted in notably less harm.
Summing up, the following factors ought to be realized as a minimum. As far as they have not but been implemented, or just partly, they want to function a foundation for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection concept together with alternative situations which adapt to the given situation often.
Always have a enough number of mobile extinguishing systems as a backup to fixed extinguishing systems.
Stock an acceptable foam focus.
Ensure sufficient foam concentrate provide.
Ensure pressure gauge octa provide.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing equipment available in a sufficient quantity.
Have trained personnel out there in a adequate number.
Ensure a quick implementation of an acceptable plan of action.
For extra info, go to www.firedos.com

Share

Scroll to Top