Part One of this article described the standard incident scenarios at tank farm fires and offered foam as probably the most appropriate extinguishing agent together with the firefighting gear mostly used. In Part Two we look at foam concentrate proportioning applied sciences, cell extinguishing methods and conclude with lessons discovered.
NFPA 11 describes various forms of foam concentrate proportioning equipment. In the following, three techniques are checked out that are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price must not be lower 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 concentrate or 7.8% for a 6% foam focus; respectively, the proportioning fee is allowed to be an absolute most of 1% above the permitted value – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller worth must be used respectively).
To guarantee appropriate proportioning, the proportioner, including the proportioning rate should be examined a minimal of once a 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 crammed with foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the froth concentrate from the bladder as required. The bladder is connected to a proportioner which operates using the venturi precept. When the fire pumps are activated, strain is generated by the pump, causing supply of foam concentrate to the proportioner. The extinguishing water flows via the venturi proportioner. The resulting vacuum induces the foam focus into the extinguishing water move.
The advantages of this system are its simple design without shifting components and its straightforward operation. No external power is required, and the system is relatively cheap.
A disadvantage is that the system is a pressurized vessel subject to corresponding rules corresponding 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 foam focus. At a given proportioning rate, the system is suitable only for low variations in the extinguishing water move stress and volume. Adding or altering individual foam discharge gadgets is possible only to a really limited 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 within the extinguishing water line. The correct proportioning rate have to be measured within the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam concentrate within the bladder tank needs to be replaced.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with flow meter
The system consists of an atmospheric tank for the foam concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a move meter within the extinguishing water move line. When the fireplace pumps are activated, the froth concentrate pump drive and digital control system must be activated. The extinguishing water move fee is measured by the move meter and the management system adjusts the correct foam focus quantity by way of the control valve. The foam focus is injected into the extinguishing water circulate by the foam concentrate pump. If there’s a change within the circulate fee, the quantity of injected foam concentrate is regulated by the control valve.
The system’s benefit lies in the exact proportioning of the froth concentrate, unbiased of the extinguishing water stress or circulate price. Foam focus may be topped up through 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 focus could be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus move rate. No premix is produced; and because the foam concentrate is handed back into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an external interruption-free power provide for the froth focus pump and the management system, as nicely as the necessity for a complicated management system and the comparatively larger buying prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water flow price and the newly adjusted foam focus quantity. The foam quality may be compromised when continually altering working conditions 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 focus, a water motor installed in the extinguishing water flow line and a foam concentrate pump which is connected on to the water motor. Water motor and pump type one compact unit. Upon activation of the fire pumps, rotation in the water motor begins. The direct coupling to the foam-concentrate pump offers immediate foam-concentrate injection into the extinguishing water. If the circulate rate changes, the quantity of foam concentrate is tailored immediately.
The advantage of the system is its independence from exterior power sources as well as a precise and quick foam-concentrate proportioning regardless of the extinguishing water strain or move fee. If a piston or plunger pump is used, adjustment or calibration after set up isn’t essential because the water motor and the pump are volumetric gadgets firmly related to one another. Foam focus refilling during operation is possible. The system can be capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nevertheless, the delivered foam focus may be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam focus circulate rate. 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 prices are an obstacle of the system.
With any system, consideration must be taken under consideration for the annual testing costs, which could be appreciable in phrases of alternative foam concentrate, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge gear may be broken in intensive fires within the tank or in the dyke area and thus lose effectiveness, cellular fire displays and foam pipes could also be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve only restricted extinguishing agent circulate rates and reaches.
Firefighting displays
Firefighting monitors are discharge gadgets mounted on vehicles or trailers and out there in lots of sizes. The extinguishing agent move fee could be up to 60,000 litres/min and the attain can be up to 180m if the strain of the fire pumps is sufficient. They are appropriate to discharge foam, e.g., to extinguish a surface hearth in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank in order to forestall it reaching the important temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke area should always be observed to avoid an overflow of the dyke.
Mobile fireplace monitors may be equipped either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the froth focus often takes place through cellular proportioners. This clearly factors in direction of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile models obtainable as back-ups is shown by the following example for the position of monitors for fireplace 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 a number of alternatives for the screens. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which should have the flexibility to handle various circulate rates to ensure flexibility during extinguishing operations. Depending on the local conditions, the monitors will need to maintain a minimal distance to the burning tank or could not have the flexibility to be positioned near to the tanks as a result of particles. In addition, it is not going to always be possible to position a number of screens across the tank. It have to be ensured the monitor has enough throwing peak in relation to the tank peak, to ship foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal rules in addition to suggestions by associations like NFPA and isn’t checked out extra carefully within the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons realized
As mentioned in the introduction to Part One of this text, it seems that evidently many authorities and companies haven’t learned the necessary lessons from disastrous hearth incidents of past years. Tank farm fires in the oil and petrochemical industry do not happen incessantly. When they do, they usually have devastating consequences. Let us bear in mind the tank farm fire at Deer Park, Texas in March 2019 mentioned 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 fireplace for but unknown causes. The plant had no gas warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fastened extinguishing techniques installed. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native hearth service, which was on the spot in a quick time but could not take control over the hearth with the equipment available, partially as a outcome of flammable substance was constantly leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an external firefighting firm to do the extinguishing work. ขนาดpressuregauge of apparatus and foam concentrate as nicely as the preparation of a plan of action took approximately thirteen hours. The fireplace was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt were made over 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 space, 11 of the 15 tanks burnt down.
It is very probable that the fireplace would have been extinguished quickly if the warning systems and valves had labored and a onerous and fast hearth extinguishing system had existed. It can be possible that the hearth would have been extinguished quickly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both instances would have resulted in notably less damage.
Summing up, the next points ought to be learned at least. As far as they haven’t but been implemented, or just partly, they want to serve as a foundation for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection idea together with various eventualities which adapt to the given situation regularly.
Always have a sufficient variety of cellular extinguishing systems as a backup to fixed extinguishing systems.
Stock a suitable foam focus.
Ensure enough foam concentrate supply.
Ensure sufficient water supply.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing equipment out there in a adequate quantity.
Have educated personnel available in a adequate number.
Ensure a fast implementation of a suitable plan of action.
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