Part One of this text described the everyday incident eventualities at tank farm fires and presented foam as probably the most appropriate extinguishing agent along with the firefighting gear mostly used. In Part Two we take a glance at foam concentrate proportioning technologies, cell extinguishing systems and conclude with classes discovered.
NFPA eleven describes varied types of foam focus proportioning tools. In the next, three techniques are looked at that are most typical. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning price should not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning price should not exceed 30% above the permitted value i.e. 3.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning rate 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 have to be used respectively).
To assure appropriate proportioning, the proportioner, including the proportioning price must be examined at least once a year and its correct functioning should 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 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 precept. When the fire pumps are activated, pressure is generated by the pump, inflicting delivery of froth focus to the proportioner. The extinguishing water flows through the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water flow.
The benefits of this technique are its simple design without shifting parts and its straightforward operation. No exterior vitality is required, and the system is relatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic to corresponding laws corresponding to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system must be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the foam focus. At a given proportioning fee, the system is appropriate only for low variations within the extinguishing water flow stress and quantity. Adding or changing individual foam discharge units is feasible solely to a really restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any mandatory required annual testing, the system should be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The appropriate proportioning fee have to be measured in the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam concentrate in the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with move meter.
Driven proportioning pump with circulate meter
The system consists of an atmospheric tank for the froth concentrate, an electric or diesel-powered foam focus pump with an electronically controlled valve and a flow meter in the extinguishing water circulate line. When the fire pumps are activated, the foam concentrate pump drive and digital management system must be activated. The extinguishing water circulate price is measured by the move meter and the management system adjusts the proper foam concentrate quantity via the management valve. The foam focus is injected into the extinguishing water circulate by the froth focus pump. If there is a change in the flow fee, the amount of injected foam focus is regulated by the management valve.
The system’s advantage lies in the precise proportioning of the froth focus, unbiased of the extinguishing water strain or flow price. Foam focus could be topped up through the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the aim of annual testing, the system have to be activated; nonetheless, the delivered foam focus can be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam focus flow fee. No premix is produced; and as the foam concentrate is handed back into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free energy provide for the froth focus pump and the control system, in addition to the necessity for a complicated control system and the comparatively higher buying prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water circulate fee and the newly adjusted foam concentrate quantity. The foam quality could additionally be compromised when constantly changing operating conditions 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 focus, a water motor installed within the extinguishing water circulate line and a foam concentrate pump which is linked directly to the water motor. Water motor and pump form one compact unit. Upon เกจ์แรงดัน of the fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the move rate modifications, the amount of froth focus is tailored instantly.
The advantage of the system is its independence from external energy sources in addition to a exact and instant foam-concentrate proportioning whatever the extinguishing water strain or circulate fee. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t essential for the explanation that water motor and the pump are volumetric units firmly related to each other. Foam concentrate refilling during operation is possible. The system can also be capable of proportioning highly viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam concentrate could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate flow fee. No premix is generated; and if the froth focus is handed back into the tank, no foam focus needs to be topped up.
The larger design and the comparatively greater buying prices are an obstacle of the system.
With any system, consideration ought to be taken into consideration for the annual testing costs, which could be considerable in terms of alternative foam concentrate, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge equipment may be damaged in extensive fires within the tank or in the dyke space and thus lose effectiveness, cell fireplace displays and foam pipes could also be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have only restricted extinguishing agent flow rates and reaches.
Firefighting monitors
Firefighting screens are discharge devices mounted on autos or trailers and out there in plenty of sizes. The extinguishing agent circulate rate can be up to 60,000 litres/min and the reach could be as a lot as 180m if the pressure of the hearth pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a surface hearth 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 crucial temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke area should all the time be observed to avoid an overflow of the dyke.
Mobile fireplace screens could be provided either by the extinguishing water of the stationary fire pumps or by mobile pumps. The injection of the foam concentrate usually takes place by way of cellular proportioners. This clearly factors in direction of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cell units out there as back-ups is proven by the following example for the placement of monitors 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 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 ready to handle various flow rates to guarantee flexibility during extinguishing operations. Depending on the local conditions, the displays might want to maintain a minimal distance to the burning tank or could not be capable of be positioned close to to the tanks due to particles. In addition, it will not at all times be potential to position several displays across the tank. It must be ensured the monitor has sufficient throwing top in relation to the tank top, to deliver foam into the within of the tank.
The dimensioning of the entire firefighting system is made following legal regulations in addition to suggestions by associations like NFPA and isn’t checked out more intently within the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons discovered
As mentioned in the introduction to Part One of this text, it appears that many authorities and companies haven’t discovered the required lessons from disastrous hearth incidents of previous years. Tank farm fires in the oil and petrochemical trade do not happen incessantly. When เกจวัดแรงดัน4บาร์ do, they normally have devastating consequences. Let us remember the tank farm fireplace at Deer Park, Texas in March 2019 mentioned within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fire for yet unknown causes. The plant had no fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fixed extinguishing techniques put in. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native fire service, which was on the spot in a quick time however could not take management over the fire with the equipment obtainable, partially as a end result of flammable substance was continuously 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 apparatus and foam concentrate in addition to the preparation of a plan of motion took approximately thirteen hours. The hearth was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts were made over three days, with foam concentrate and water shortages occurring in the meantime. In complete, over 500,000 litres of foam focus were used. Instead of a fireplace within the dyke area, 11 of the 15 tanks burnt down.
It could be very probable that the fireplace would have been extinguished shortly if the warning methods and valves had worked and a fixed fire extinguishing system had existed. It is also probable that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both cases would have resulted in notably less damage.
Summing up, the following factors must be realized as a minimum. As far as they have not yet been applied, or just partly, they should function a basis for discussions about one’s personal fire-protection concept:
Have an acceptable fire-protection idea including alternative eventualities which adapt to the given situation frequently.
Always have a sufficient number of cellular extinguishing systems as a backup to fixed extinguishing systems.
Stock an appropriate foam focus.
Ensure enough foam focus supply.
Ensure enough water supply.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing tools available in a enough quantity.
Have trained personnel obtainable in a adequate number.
Ensure a fast implementation of a suitable plan of motion.
For more data, go to www.firedos.com
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