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Part One of this article described the everyday incident situations at tank farm fires and offered foam as essentially the most appropriate extinguishing agent along with the firefighting equipment most commonly used. In Part Two we have a look at foam focus proportioning technologies, cellular extinguishing methods and conclude with lessons learned.
NFPA eleven describes varied types of foam concentrate proportioning gear. 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 price should not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
The proportioning price must not exceed 30% above the permitted value i.e. 3.9% for a 3% foam concentrate 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 focus or 7% for a 6% foam concentrate (the smaller value should be used respectively).
To guarantee correct proportioning, the proportioner, including the proportioning rate should be tested at least once a year and its appropriate 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 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 focus from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi precept. When the fireplace pumps are activated, strain is generated by the pump, inflicting delivery of froth concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the foam focus into the extinguishing water flow.
The benefits of this technique are its easy design without moving elements and its simple operation. No external energy is required, and the system is relatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic to corresponding regulations corresponding to 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 froth concentrate. At a given proportioning rate, the system is appropriate only for low variations within the extinguishing water flow pressure and volume. Adding or altering particular person foam discharge gadgets is possible only to a really restricted extent. The system can also be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system should be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The appropriate proportioning rate should be measured within the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam focus within the bladder tank must be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the foam concentrate, an electrical or diesel-powered foam concentrate pump with an electronically managed valve and a circulate meter within the extinguishing water move line. When the fire pumps are activated, the foam focus pump drive and electronic management system have to be activated. The extinguishing water flow price is measured by the flow meter and the control system adjusts the right foam concentrate amount through the control valve. The foam concentrate is injected into the extinguishing water circulate by the foam focus pump. If there is a change within the circulate rate, the quantity of injected foam focus is regulated by the management valve.
The system’s benefit lies within the precise proportioning of the froth focus, independent of the extinguishing water strain or move fee. Foam focus could be topped up in the course of 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; nonetheless, the delivered foam focus could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus move rate. No premix is produced; and as a result of the foam concentrate is handed again into the tank, no foam focus must be refilled.
Disadvantages are the requirement for an exterior interruption-free energy provide for the foam concentrate pump and the management system, in addition to the need for a complicated control system and the comparatively larger buying costs. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water circulate price and the newly adjusted foam concentrate amount. The foam quality could also be compromised when continuously changing working circumstances 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 foam concentrate, a water motor put in in the extinguishing water circulate line and a foam focus pump which is connected on to the water motor. Water motor and pump form 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 price modifications, the quantity of foam focus is adapted instantly.
The advantage of the system is its independence from external power sources as nicely as a exact and instant foam-concentrate proportioning whatever the extinguishing water stress or flow rate. If a piston or plunger pump is used, adjustment or calibration after set up isn’t necessary since the water motor and the pump are volumetric units firmly related to every other. Foam focus refilling throughout operation is feasible. The system can be able to proportioning extremely viscous foam concentrates. The system should be activated for annual testing; however, the delivered foam focus could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam focus move fee. No premix is generated; and if the foam concentrate is handed back into the tank, no foam focus must be topped up.
The bigger design and the comparatively greater purchasing costs are a drawback of the system.
With any system, consideration ought to be taken under consideration for the annual testing costs, which may be appreciable by means of replacement foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge gear may be damaged in extensive fires in the tank or within the dyke area and thus lose effectiveness, cell fireplace screens and foam pipes could additionally be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very versatile. Yet they have solely limited extinguishing agent move charges and reaches.
Firefighting monitors
Firefighting screens are discharge units mounted on vehicles or trailers and available in many sizes. The extinguishing agent move rate may be up to 60,000 litres/min and the reach can be up to 180m if the pressure of the hearth pumps is enough. They are suitable to discharge foam, e.g., to extinguish a surface fireplace in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank in order to stop it reaching the critical 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 keep away from an overflow of the dyke.
Mobile fireplace screens may be supplied both by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the foam concentrate usually takes place by way of cellular proportioners. This clearly points in the direction of the benefit of energy independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell items available as back-ups is shown by the following instance for the placement of displays for hearth extinguishing at tanks that are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This leads to several alternate options for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be capable of deal with varying flow charges to ensure flexibility throughout extinguishing operations. Depending on the local situations, the screens will need to maintain a minimum distance to the burning tank or might not be succesful of be positioned near to the tanks because of particles. In addition, it will not at all times be potential to place several screens around the tank. It should be ensured the monitor has enough throwing peak in relation to the tank peak, to deliver foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following legal laws in addition to suggestions by associations like NFPA and isn’t checked out more intently within the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As talked about within the introduction to Part One of this text, plainly many authorities and firms have not discovered the mandatory classes 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 keep in mind the tank farm fireplace 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 30 minutes 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 เกจ์วัดแรงดันน้ำ , 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 native fireplace service, which was on the spot very quickly but couldn’t take management over the fire with the tools obtainable, partially as a end result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the hearth had damaged out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of kit and foam concentrate in addition to the preparation of a plan of motion took approximately thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts were revamped three days, with foam concentrate and water shortages occurring in the meantime. In complete, over 500,000 litres of froth concentrate have been used. Instead of a fireplace in the dyke area, eleven of the 15 tanks burnt down.
It is very probable that the fireplace would have been extinguished rapidly if the warning methods and valves had labored and a fixed fireplace extinguishing system had existed. It is also probable that the fire would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been began earlier. Both circumstances would have resulted in notably less injury.
Summing up, the following factors should be discovered at least. As far as they have not yet been applied, or simply partly, they should function a basis for discussions about one’s personal fire-protection idea:
Have an appropriate fire-protection concept including alternative situations which adapt to the given situation often.
Always have a sufficient variety of cell extinguishing systems as a backup to fixed extinguishing methods.
Stock a suitable foam focus.
Ensure enough foam focus provide.
Ensure enough water supply.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing gear out there in a sufficient number.
Have trained personnel out there 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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