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

Part One of this article described the standard incident scenarios at tank farm fires and introduced foam as the most suitable extinguishing agent along with the firefighting equipment most commonly used. In Part Two we take a look at foam concentrate proportioning applied sciences, cell extinguishing methods and conclude with classes discovered.
NFPA eleven describes varied forms of foam concentrate proportioning equipment. In the following, three systems are looked at which are commonest. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning fee must not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning rate must not exceed 30% above the permitted worth i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning rate is allowed to be an absolute most 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 fee should be examined a minimal of once a year 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 confirmed and cost-effective technology. The bladder tank is a pressurized vessel with a bladder inside which is full of foam concentrate. เกจปรับแรงดันแก๊ส is pressurized with water from the fire-extinguishing line and discharges the froth concentrate from the bladder as required. The bladder is linked to a proportioner which operates using the venturi precept. When the fire pumps are activated, stress is generated by the pump, inflicting supply of froth concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The ensuing vacuum induces the foam concentrate into the extinguishing water move.
The advantages of this system are its simple design without moving components and its simple operation. No exterior power is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system have to be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the froth concentrate. At a given proportioning rate, the system is appropriate only for low variations within the extinguishing water flow stress and volume. Adding or changing individual foam discharge gadgets is possible only to a really restricted extent. The system can be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any mandatory required annual testing, the system must be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The right proportioning fee have to be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus in the bladder tank must be changed.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam concentrate pump with an electronically managed valve and a circulate meter in the extinguishing water flow line. When the fire pumps are activated, the froth focus pump drive and digital control system have to be activated. The extinguishing water circulate rate is measured by the move meter and the control system adjusts the proper foam focus quantity by way of the control valve. The foam focus is injected into the extinguishing water circulate by the froth concentrate pump. If there’s a change within the move rate, the amount of injected foam focus is regulated by the management valve.
The system’s advantage lies within the exact proportioning of the foam focus, unbiased of the extinguishing water strain or flow price. Foam focus could be topped up through the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the aim of annual testing, the system must be activated; however, the delivered foam focus may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus move fee. No premix is produced; and as the foam focus is handed again into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an exterior interruption-free energy supply for the froth concentrate pump and the management system, in addition to the necessity for a sophisticated control system and the comparatively larger buying prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water circulate price and the newly adjusted foam focus quantity. The foam high quality may be compromised when continually changing operating 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 froth focus, a water motor installed within the extinguishing water move line and a foam focus pump which is connected on to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump gives immediate foam-concentrate injection into the extinguishing water. If the move rate modifications, the quantity of froth focus is customized instantly.
The benefit of the system is its independence from exterior energy sources as well as a precise and instant foam-concentrate proportioning whatever the extinguishing water strain or flow fee. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t essential because the water motor and the pump are volumetric units firmly related to one another. Foam concentrate refilling during operation is feasible. The system is also capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam concentrate can be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam focus move fee. No premix is generated; and if the foam focus is passed again into the tank, no foam focus must be topped up.
The bigger design and the comparatively higher buying costs are a disadvantage of the system.
With any system, consideration ought to be taken into consideration for the annual testing prices, which could be appreciable in phrases of alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge equipment could be broken in intensive fires within the tank or within the dyke area and thus lose effectiveness, cellular hearth screens and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they’ve solely restricted extinguishing agent flow charges and reaches.
Firefighting monitors
Firefighting screens are discharge devices mounted on autos or trailers and obtainable in lots of sizes. The extinguishing agent flow price can be up to 60,000 litres/min and the attain may be as a lot as 180m if the strain of the fireplace pumps is enough. They are appropriate to discharge foam, e.g., to extinguish a floor fireplace in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to be able to forestall it reaching the important temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke area ought to all the time be noticed to keep away from an overflow of the dyke.
Mobile fireplace displays can be supplied both by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the foam concentrate often takes place via mobile proportioners. This clearly points in course of the advantage of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell items available as back-ups is proven by the next example for the location of screens 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 ends in several alternate options for the monitors. Generally, foam-concentrate proportioners for no less than 32,000 litres/min are required, which ought to have the flexibility to deal with various circulate rates to guarantee flexibility throughout extinguishing operations. Depending on the local situations, the displays might want to hold a minimum distance to the burning tank or may not have the flexibility to be positioned near to the tanks as a outcome of debris. In addition, it won’t at all times be possible to position a number of monitors across the tank. It must be ensured the monitor has enough throwing peak in relation to the tank top, to deliver foam into the within of the tank.
The dimensioning of the whole firefighting system is made following legal regulations in addition to suggestions by associations like NFPA and isn’t looked at extra intently in the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons learned
As talked about in the introduction to Part One of this text, plainly many authorities and firms haven’t learned the required lessons from disastrous fireplace incidents of past years. Tank farm fires in the oil and petrochemical business don’t happen incessantly. When they do, they often have devastating consequences. Let us bear in mind the tank farm fireplace at Deer Park, Texas in March 2019 talked about within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for half-hour and caught fireplace for but unknown reasons. 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 fireplace service, which was on the spot in a brief time however couldn’t take control over the fireplace with the equipment out there, partially as a outcome of flammable substance was constantly leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of equipment and foam concentrate as properly as the preparation of a plan of action took approximately thirteen hours. The hearth 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 concentrate and water shortages occurring within the meantime. In complete, over 500,000 litres of froth concentrate had been used. Instead of a fire in the dyke space, eleven of the 15 tanks burnt down.
It may be very probable that the fireplace would have been extinguished shortly if the warning methods and valves had worked and a exhausting and fast fire extinguishing system had existed. It is also probable that the fire would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably much less injury.
Summing up, the next points should be learned at least. As far as they have not but been implemented, or simply partly, they should serve as a basis for discussions about one’s personal fire-protection idea:
Have an appropriate fire-protection concept together with various eventualities which adapt to the given scenario regularly.
Always have a sufficient variety of mobile extinguishing techniques as a backup to mounted extinguishing methods.
Stock an appropriate foam focus.
Ensure sufficient foam focus provide.
Ensure sufficient water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing gear obtainable in a adequate quantity.
Have skilled personnel out there in a adequate number.
Ensure a quick implementation of a suitable plan of action.
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