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

Part One of this text described the everyday incident scenarios at tank farm fires and introduced foam as the most appropriate extinguishing agent along with the firefighting equipment mostly used. In Part Two we take a look at foam focus proportioning technologies, mobile extinguishing systems and conclude with classes realized.
NFPA 11 describes varied forms of foam concentrate proportioning gear. 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 price must not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning fee should 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 price 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 focus (the smaller value must be used respectively).
To guarantee correct proportioning, the proportioner, together with the proportioning rate should be tested at least annually and its appropriate functioning have to be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner

The bladder tank with a proportioner is a proven and cost-effective expertise. ไดอะแฟรม ซีล 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 froth focus from the bladder as required. The bladder is related to a proportioner which operates using the venturi principle. When the fireplace pumps are activated, stress is generated by the pump, causing supply of froth 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 advantages of this method are its simple design without shifting elements and its simple operation. No external energy is required, and the system is relatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding rules such as ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system must be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam focus. At a given proportioning fee, the system is suitable only for low variations within the extinguishing water circulate strain and quantity. Adding or changing individual foam discharge units is feasible only to a really restricted extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system should be activated and premix generated at the venturi proportioner inside the extinguishing water line. The appropriate proportioning rate have to be measured in the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam focus in the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with flow meter

The system consists of an atmospheric tank for the froth focus, an electric or diesel-powered foam focus pump with an electronically controlled valve and a flow meter within the extinguishing water flow line. When the fireplace pumps are activated, the foam focus pump drive and digital control system have to be activated. The extinguishing water move rate is measured by the circulate meter and the management system adjusts the proper foam concentrate quantity via the management valve. The foam focus is injected into the extinguishing water flow by the foam focus pump. If there is a change in the circulate rate, the quantity of injected foam focus is regulated by the management valve.
The system’s benefit lies in the precise proportioning of the froth concentrate, independent of the extinguishing water pressure or move rate. Foam concentrate could 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 could be measured via a return line. The proportioning price is calculated from the extinguishing water/foam focus circulate rate. No premix is produced; and as a outcome of the foam concentrate is handed 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, as properly as the need for a classy control system and the comparatively higher buying prices. Furthermore, it should be accepted that a delay happens between the change of the extinguishing water flow price and the newly adjusted foam focus amount. The foam quality may be compromised when continuously changing operating situations as foam discharge units are turned on or off or modified.
Water motor with proportioning pump

The system consists of an atmospheric tank for the froth concentrate, a water motor put in within the extinguishing water flow line and a foam concentrate pump which is linked directly to the water motor. Water motor and pump form one compact unit. Upon activation of the fireplace 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 flow rate changes, the quantity of foam concentrate is tailored instantly.
The benefit of the system is its independence from external power sources as nicely as a precise and quick foam-concentrate proportioning regardless of the extinguishing water stress or flow fee. If a piston or plunger pump is used, adjustment or calibration after installation isn’t needed because the water motor and the pump are volumetric gadgets firmly connected to one another. Foam focus refilling during operation is feasible. The system is also able to proportioning extremely viscous foam concentrates. The system have to be activated for annual testing; however, the delivered foam concentrate can be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate price. No premix is generated; and if the foam concentrate is passed again into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively larger buying costs are a drawback of the system.
With any system, consideration must be taken under consideration for the annual testing costs, which could be appreciable by means 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 in the tank or in the dyke space and thus lose effectiveness, cell fire monitors and foam pipes could additionally be used.
Foam pipes

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

Firefighting monitors are discharge units mounted on automobiles or trailers and available in many sizes. The extinguishing agent flow price may be up to 60,000 litres/min and the attain may be up to 180m if the strain of the fire 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 to have the ability to forestall it reaching the important temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke space ought to always be noticed to keep away from an overflow of the dyke.
Mobile fireplace displays could be equipped both by the extinguishing water of the stationary fire pumps or by mobile pumps. The injection of the foam focus normally takes place via mobile proportioners. This clearly factors towards the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular items available as back-ups is shown by the following instance for the location of displays for hearth 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 monitors. Generally, foam-concentrate proportioners for a minimum of 32,000 litres/min are required, which should have the power to handle varying circulate rates to guarantee flexibility during extinguishing operations. Depending on the local conditions, the displays will want to hold a minimal distance to the burning tank or could not be in a position to be positioned close to to the tanks because of particles. In addition, it is not going to at all times be potential to place a number of screens across the tank. It have to be ensured the monitor has enough throwing peak in relation to the tank top, to deliver foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following legal regulations in addition to recommendations by associations like NFPA and is not looked at more closely within the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons realized

As talked about within the introduction to Part One of this article, plainly many authorities and companies haven’t learned the necessary classes from disastrous fire incidents of past years. Tank farm fires in the oil and petrochemical business don’t occur regularly. When they do, they normally have devastating consequences. Let us bear in mind the tank farm fire at Deer Park, Texas in March 2019 mentioned 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 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 methods put in. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native fireplace service, which was on the spot very quickly however could not take control over the hearth with the gear obtainable, partially as a result of flammable substance was constantly leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of equipment and foam focus as properly as the preparation of a plan of motion took approximately thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts had been remodeled three days, with foam focus and water shortages occurring in the meantime. In whole, over 500,000 litres of froth focus have been used. Instead of a hearth within the dyke space, eleven of the 15 tanks burnt down.
It could be very probable that the hearth would have been extinguished quickly if the warning systems and valves had worked and a fixed fire extinguishing system had existed. It can be probable that the fireplace would have been extinguished rapidly if the extinguishing operation, which succeeded finally, had been began earlier. Both cases would have resulted in notably much less injury.
Summing up, the next factors ought to be learned at least. As far as they have not yet been implemented, or just partly, they should function a foundation for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection idea together with alternative situations which adapt to the given state of affairs regularly.
Always have a adequate variety of cellular extinguishing techniques as a backup to fixed extinguishing methods.
Stock an appropriate foam concentrate.
Ensure adequate foam concentrate supply.
Ensure adequate water supply.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing equipment available in a sufficient quantity.
Have educated personnel out there in a enough quantity.
Ensure a quick implementation of an appropriate plan of motion.
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