Part One of this text described the standard incident situations at tank farm fires and offered foam as the most suitable extinguishing agent together with the firefighting gear mostly used. In Part Two we have a glance at foam focus proportioning applied sciences, cellular extinguishing techniques and conclude with lessons realized.
NFPA eleven describes varied types of foam focus proportioning tools. In the next, three systems are looked at which are most common. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning rate must not be lower 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 value i.e. three.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; respectively, the proportioning rate 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 worth should be used respectively).
To assure appropriate proportioning, the proportioner, together with the proportioning rate should be examined at least every 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 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 related 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 through the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water move.
The advantages of this technique are its easy design with out shifting elements and its straightforward operation. No external vitality is required, and the system is relatively cheap.
A disadvantage is that the system is a pressurized vessel topic to corresponding laws such as ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system should be shut down and drained. The rubber bladder is delicate; when damaged, water will contaminate the foam concentrate. At a given proportioning price, the system is suitable just for low variations in the extinguishing water flow strain and volume. Adding or altering individual foam discharge gadgets is feasible solely to a very restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated on the venturi proportioner inside the extinguishing water line. The correct proportioning fee should be measured in 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 replaced.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the froth focus, an electric or diesel-powered foam focus pump with an electronically managed valve and a flow meter in the extinguishing water move line. When the fireplace pumps are activated, the froth focus pump drive and electronic control system should be activated. The extinguishing water circulate fee is measured by the flow meter and the control system adjusts the right foam concentrate amount by way of the control valve. The foam concentrate is injected into the extinguishing water flow by the froth focus pump. If there is a change in the flow rate, the quantity of injected foam concentrate is regulated by the control valve.
The system’s advantage lies within the exact proportioning of the foam concentrate, independent of the extinguishing water strain or circulate price. Foam concentrate may be topped up through the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system have to be activated; however, the delivered foam concentrate can be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move price. No premix is produced; and as a end result of the foam focus is passed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an external interruption-free power provide for the froth focus pump and the control system, in addition to the necessity for a classy control system and the comparatively greater purchasing prices. Furthermore, it should be accepted that a delay happens between the change of the extinguishing water circulate rate and the newly adjusted foam focus amount. The foam quality could additionally be compromised when constantly changing working situations as foam discharge devices 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 installed within the extinguishing water flow line and a foam focus pump which is related directly to the water motor. Water motor and pump type one compact unit. Upon activation of the fireplace pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump gives quick foam-concentrate injection into the extinguishing water. If the move rate modifications, the quantity of foam focus is adapted immediately.
The benefit of the system is its independence from external power sources in addition to a exact and instant foam-concentrate proportioning regardless of the extinguishing water stress or flow rate. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t necessary for the reason that water motor and the pump are volumetric gadgets firmly linked to each other. Foam concentrate refilling throughout operation is possible. The system is also able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam focus could be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate move rate. No premix is generated; and if the foam focus is passed again into the tank, no foam concentrate needs to be topped up.
The larger design and the comparatively higher buying prices are a drawback of the system.
With any system, consideration must be taken into consideration for the annual testing costs, which may be appreciable in phrases of alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing techniques
As the stationary foam discharge equipment could be broken in intensive fires in the tank or within the dyke area and thus lose effectiveness, cell fireplace monitors and foam pipes may be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they have solely restricted extinguishing agent flow charges and reaches.
Firefighting monitors
Firefighting displays are discharge units mounted on autos or trailers and out there in many sizes. The extinguishing agent circulate fee can be as much as 60,000 litres/min and the attain can be as a lot as 180m if the strain of the fire pumps is enough. They are appropriate to discharge foam, e.g., to extinguish a floor fire in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank so as to prevent it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke space ought to always be observed to avoid an overflow of the dyke.
Mobile hearth displays may be supplied both by the extinguishing water of the stationary fireplace pumps or by mobile pumps. The injection of the foam concentrate normally takes place through cell proportioners. This clearly points towards the advantage of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of mobile items obtainable as back-ups is proven by the next example for the location of screens for fire extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This results in several alternatives for the displays. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should be able to deal with various move charges to ensure flexibility during extinguishing operations. Depending on the local circumstances, the screens will need to maintain a minimal distance to the burning tank or could not be ready to be positioned near to the tanks because of particles. In addition, it will not always be possible to place a number of monitors around the tank. It have to be ensured the monitor has adequate 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 rules as properly as recommendations by associations like NFPA and is not looked at more intently in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons learned
As talked about in the introduction to Part One of this text, plainly many authorities and firms have not discovered the mandatory lessons from disastrous fireplace incidents of past years. Tank farm fires in the oil and petrochemical business do not happen regularly. When they do, they usually have devastating consequences. Let us remember 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 defective valve for 30 minutes and caught fireplace for yet unknown reasons. The plant had no gas warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fixed extinguishing systems put in. All 15 tanks have been surrounded by one single dyke. The owner had relied on the local hearth service, which was on the spot very quickly but couldn’t take control over the fire with the equipment out there, partially because flammable substance was constantly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of apparatus and foam concentrate as properly as the preparation of a plan of action took roughly 13 hours. The fireplace was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt have been revamped three days, with foam focus and water shortages occurring in the meantime. In total, over 500,000 litres of foam focus have been used. Instead of a fireplace within the dyke area, 11 of the 15 tanks burnt down.
It is very possible that the fire would have been extinguished quickly if the warning methods and valves had labored and a hard and fast fire extinguishing system had existed. It can be possible that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been started earlier. Both circumstances would have resulted in notably less injury.
Summing up, the next points ought to be learned at the least. As far as ตัววัดแรงดันน้ำ haven’t yet been applied, or simply partly, they want to serve as a basis for discussions about one’s personal fire-protection concept:
Have an acceptable fire-protection concept including various situations which adapt to the given situation often.
Always have a sufficient number of cell extinguishing systems as a backup to mounted extinguishing methods.
Stock an acceptable foam concentrate.
Ensure adequate foam concentrate supply.
Ensure sufficient water supply.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing gear out there in a sufficient quantity.
Have skilled personnel out there in a adequate quantity.
Ensure a quick implementation of an appropriate plan of motion.
For more information, go to www.firedos.com
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