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

Part One of this article described the everyday incident scenarios at tank farm fires and offered foam as the most suitable extinguishing agent together with the firefighting tools most commonly used. In Part Two we have a glance at foam concentrate proportioning technologies, mobile extinguishing techniques and conclude with lessons realized.
NFPA eleven describes various kinds of foam focus proportioning tools. In the next, three techniques are looked at which are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning fee must not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning fee should not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning price is allowed to be an absolute most of 1% above the permitted worth – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller worth have to be used respectively).
To assure appropriate proportioning, the proportioner, together with the proportioning fee have to be tested at least annually 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 proven and cost-effective know-how. The bladder tank is a pressurized vessel with a bladder inside which is filled with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam focus from the bladder as required. The bladder is linked to a proportioner which operates utilizing the venturi principle. When the fire pumps are activated, stress is generated by the pump, causing supply of foam concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water move.
The benefits of this technique are its simple design with out transferring parts and its easy operation. No external energy is required, and the system is comparatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding regulations similar 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 damaged, water will contaminate the froth focus. At a given proportioning rate, the system is suitable just for low variations in the extinguishing water flow stress and quantity. Adding or altering individual foam discharge devices is feasible only to a very restricted extent. The system can 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 throughout the extinguishing water line. The appropriate proportioning rate must be measured within 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 changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with move meter

The system consists of an atmospheric tank for the froth focus, an electrical or diesel-powered foam focus pump with an electronically controlled valve and a circulate meter within the extinguishing water circulate line. When the fire pumps are activated, the froth focus pump drive and electronic management system should be activated. The extinguishing water flow price is measured by the flow meter and the control system adjusts the correct foam concentrate quantity by way of the management valve. The foam focus is injected into the extinguishing water circulate by the foam focus pump. If there’s a change in the move fee, the quantity of injected foam focus is regulated by the management valve.
The system’s advantage lies within the exact proportioning of the froth concentrate, unbiased of the extinguishing water strain or flow rate. Foam focus may be topped up in the course of the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the aim of annual testing, the system must be activated; nonetheless, the delivered foam focus may be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate circulate rate. No premix is produced; and as a result of the foam focus is handed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an external interruption-free power supply for the foam focus pump and the control system, in addition to the need for a sophisticated management system and the comparatively greater purchasing prices. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water move price and the newly adjusted foam concentrate quantity. The foam high quality may be compromised when constantly changing working circumstances 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 foam focus, a water motor put in in the extinguishing water circulate line and a foam concentrate pump which is linked on to the water motor. Water motor and pump kind one compact unit. Upon activation of the fire pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the circulate fee changes, the quantity of foam concentrate is adapted immediately.
The advantage of the system is its independence from exterior vitality sources as nicely as a precise and quick foam-concentrate proportioning whatever the extinguishing water stress or flow price. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t essential since the water motor and the pump are volumetric units firmly connected to each other. Foam concentrate refilling throughout operation is feasible. The system can be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nonetheless, the delivered foam focus may be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus flow price. No premix is generated; and if the foam focus is passed again into the tank, no foam focus needs to be topped up.
The larger design and the comparatively higher buying prices are a drawback of the system.
With any system, consideration should be taken under consideration for the annual testing prices, which can be appreciable when it comes to replacement foam concentrate, disposal of premix and labour costs.
Mobile extinguishing techniques

As the stationary foam discharge gear could be broken in extensive fires within the tank or within the dyke area and thus lose effectiveness, mobile fire screens and foam pipes may be used.
Foam pipes

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

Firefighting displays are discharge devices mounted on vehicles or trailers and obtainable in plenty of sizes. The extinguishing agent flow fee could be up to 60,000 litres/min and the reach may be up to 180m if the pressure of the hearth pumps is sufficient. They are suitable to discharge foam, e.g., to extinguish a floor hearth in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank so as to stop it reaching the crucial temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space ought to always be observed to keep away from an overflow of the dyke.
Mobile fire displays could be provided either by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the foam focus usually takes place by way of cellular proportioners. This clearly factors in direction of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell models available as back-ups is shown by the next example for the position of displays 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 ends in a quantity of alternate options for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be able to deal with varying flow charges to ensure flexibility throughout extinguishing operations. Depending on the local circumstances, the screens might want to keep a minimum distance to the burning tank or may not have the ability to be positioned near to the tanks as a outcome of particles. In addition, it is not going to at all times be possible to position several monitors around the tank. It must be ensured the monitor has enough throwing peak in relation to the tank height, to deliver foam into the within of the tank.
The dimensioning of the complete firefighting system is made following legal rules as properly as recommendations by associations like NFPA and is not checked out more carefully within the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons learned

As mentioned within the introduction to Part One of this text, it appears that many authorities and companies have not realized the required classes from disastrous fireplace incidents of past years. Tank farm fires within the oil and petrochemical industry do not happen frequently. When they do, they often have devastating penalties. Let เกจวัดแรงดันลมดิจิตอล remember the tank farm fireplace 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 faulty valve for half-hour and caught hearth for yet unknown causes. The plant had no fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have fixed extinguishing systems put in. All 15 tanks were surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot very quickly but couldn’t take control over the fire with the equipment out there, partially as a end result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire 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 action took approximately thirteen 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 remodeled three days, with foam concentrate and water shortages occurring in the meantime. In whole, over 500,000 litres of froth focus were used. Instead of a fireplace within the dyke area, eleven of the 15 tanks burnt down.
It may be very probable that the fireplace would have been extinguished rapidly if the warning systems and valves had labored and a fixed fire extinguishing system had existed. It is also probable that the fireplace would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been began earlier. Both circumstances would have resulted in notably much less harm.
Summing up, the following points should be realized at the least. As far as they haven’t yet been carried out, or just partly, they should function a foundation for discussions about one’s personal fire-protection concept:
Have a suitable fire-protection idea together with various scenarios which adapt to the given state of affairs often.
Always have a adequate number of mobile extinguishing methods as a backup to fixed extinguishing methods.
Stock an appropriate foam focus.
Ensure enough foam concentrate provide.
Ensure enough water supply.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing gear obtainable in a adequate quantity.
Have educated personnel obtainable in a enough number.
Ensure a fast implementation of a suitable plan of action.
For more data, go to www.firedos.com

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