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

Part One of this text described the everyday incident scenarios at tank farm fires and offered foam as the most suitable extinguishing agent together with the firefighting tools mostly used. In Part Two we look at foam focus proportioning applied sciences, mobile extinguishing systems and conclude with lessons discovered.
NFPA eleven describes varied types of foam concentrate proportioning tools. In the next, three systems are checked out which are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning fee 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 fee must not exceed 30% above the permitted value i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning fee is allowed to be an absolute most of 1% above the permitted worth – i.e. 4% for a 3% foam focus or 7% for a 6% foam focus (the smaller value must be used respectively).
To assure correct proportioning, the proportioner, including the proportioning price have to be tested a minimum of every year and its appropriate 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 know-how. 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 foam concentrate from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi principle. When the hearth pumps are activated, pressure is generated by the pump, inflicting supply of foam focus to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the froth concentrate into the extinguishing water flow.
The advantages of this method are its easy design without moving elements and its simple operation. No external energy is required, and the system is relatively inexpensive.
A drawback is that the system is a pressurized vessel subject 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 foam concentrate. At a given proportioning price, the system is appropriate only for low variations in the extinguishing water circulate strain and volume. Adding or altering individual foam discharge gadgets is feasible only to a very limited extent. The system is also 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 correct proportioning fee have to 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 replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam concentrate pump with an electronically controlled valve and a flow meter within the extinguishing water move line. When the hearth pumps are activated, the froth focus pump drive and electronic management system have to be activated. The extinguishing water flow rate is measured by the move meter and the control system adjusts the right foam concentrate quantity via the management valve. The foam focus is injected into the extinguishing water move by the froth concentrate pump. If there’s a change in the move price, the amount of injected foam concentrate is regulated by the management valve.
The system’s advantage lies within the exact proportioning of the froth concentrate, unbiased of the extinguishing water stress or flow price. Foam focus may be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system must be activated; nevertheless, the delivered foam concentrate may be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow price. No premix is produced; and as the foam concentrate is passed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free vitality provide for the foam focus pump and the management system, in addition to the need for a sophisticated management system and the comparatively larger buying costs. Furthermore, it should be accepted that a delay happens between the change of the extinguishing water flow price and the newly adjusted foam concentrate quantity. The foam high quality may be compromised when constantly altering working situations 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 installed within the extinguishing water move 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 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 fee modifications, the quantity of froth focus is adapted immediately.
The advantage of the system is its independence from external vitality sources in addition to a precise and immediate foam-concentrate proportioning whatever the extinguishing water stress or flow price. If เกจ์วัดความดัน or plunger pump is used, adjustment or calibration after installation isn’t essential for the rationale that water motor and the pump are volumetric gadgets firmly connected to each other. Foam concentrate refilling throughout operation is feasible. The system is also able to proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam focus can be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus flow price. No premix is generated; and if the froth concentrate is handed again into the tank, no foam focus must be topped up.
The bigger design and the comparatively higher buying prices are a drawback of the system.
With any system, consideration ought to be taken into account for the annual testing costs, which may be appreciable by way of alternative foam concentrate, disposal of premix and labour costs.
Mobile extinguishing methods
As the stationary foam discharge equipment may be broken in intensive fires within the tank or in the dyke area and thus lose effectiveness, mobile fireplace screens and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve only restricted extinguishing agent flow rates and reaches.
Firefighting displays
Firefighting monitors are discharge devices mounted on automobiles or trailers and out there in many sizes. The extinguishing agent flow price could be as much as 60,000 litres/min and the reach could be as a lot as 180m if the pressure of the fire pumps is sufficient. They are suitable to discharge foam, e.g., to extinguish a floor fireplace 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 keep away from an overflow of the dyke.
Mobile hearth monitors can be equipped either by the extinguishing water of the stationary fireplace pumps or by mobile pumps. The injection of the foam concentrate often takes place via cellular 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 shown by the following instance for the placement of monitors for fire extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This results in several alternate options for the monitors. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which should be ready to deal with varying flow rates to ensure flexibility throughout extinguishing operations. Depending on the local situations, the monitors will need to hold a minimal distance to the burning tank or may not have the power to be positioned near to the tanks because of particles. In addition, it won’t all the time be possible to position several monitors around the tank. It have to be ensured the monitor has enough throwing height in relation to the tank top, to ship foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following authorized laws in addition to recommendations by associations like NFPA and is not checked out extra closely within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons realized
As mentioned in the introduction to Part One of this article, it appears that evidently many authorities and companies have not realized the necessary lessons from disastrous hearth incidents of past years. Tank farm fires within the oil and petrochemical business don’t happen regularly. When they do, they normally have devastating consequences. Let us remember the tank farm hearth at Deer Park, Texas in March 2019 talked about within the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for half-hour 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 didn’t have fixed extinguishing methods installed. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native fire service, which was on the spot in a short time but couldn’t take control over the fire with the equipment available, 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 kit and foam focus in addition to the preparation of a plan of action took approximately 13 hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three 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 whole, over 500,000 litres of foam focus were used. Instead of a hearth within the dyke area, eleven of the 15 tanks burnt down.
It could be very probable that the fire would have been extinguished rapidly if the warning techniques and valves had labored and a set fire extinguishing system had existed. It is also probable that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded eventually, had been began earlier. Both instances would have resulted in notably less harm.
Summing up, the next factors should be learned at the least. As far as they haven’t but been applied, or simply partly, they need to serve as a basis for discussions about one’s own fire-protection idea:
Have a suitable fire-protection concept including different situations which adapt to the given situation frequently.
Always have a enough variety of cellular extinguishing systems as a backup to fixed extinguishing methods.
Stock an acceptable foam concentrate.
Ensure enough foam concentrate supply.
Ensure adequate water provide.
Keep well-maintained, shortly and well-accessible, strategically positioned and functioning extinguishing gear out there in a adequate quantity.
Have trained personnel obtainable in a sufficient number.
Ensure a quick implementation of an acceptable plan of motion.
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