Part One of this text described the typical incident eventualities at tank farm fires and offered foam as the most suitable extinguishing agent along with the firefighting equipment mostly used. In Part Two we have a glance at foam concentrate proportioning applied sciences, cellular extinguishing systems and conclude with lessons realized.
NFPA 11 describes varied types of foam focus proportioning gear. In the next, three methods are checked out that are most common. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning rate should not be less than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning rate must not exceed 30% above the permitted worth i.e. three.9% for a 3% foam concentrate or 7.8% for a 6% foam concentrate; 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 assure right proportioning, the proportioner, including the proportioning fee should be examined no much less than 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 confirmed and cost-effective expertise. The bladder tank is a pressurized vessel with a bladder inside which is full of foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the foam focus from the bladder as required. The bladder is linked to a proportioner which operates utilizing the venturi precept. When the fireplace pumps are activated, strain is generated by the pump, causing delivery 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 circulate.
The benefits of this system are its simple design with out transferring elements and its easy operation. No external vitality is required, and the system is relatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding regulations such as ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system must be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the froth focus. At a given proportioning rate, the system is suitable just for low variations within the extinguishing water move strain and volume. Adding or changing individual foam discharge units is possible only to a very limited extent. The system can additionally be unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated at the venturi proportioner inside the extinguishing water line. The right proportioning price have to be measured within the premix by laboratory analysis. The generated premix should 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 move meter
The system consists of an atmospheric tank for the foam concentrate, an electrical or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter in the extinguishing water move line. When the fireplace pumps are activated, the foam focus pump drive and digital control system should be activated. The extinguishing water flow price is measured by the circulate meter and the management system adjusts the correct foam concentrate quantity via the management valve. The foam focus is injected into the extinguishing water circulate by the froth focus pump. If there’s a change within the circulate rate, the amount of injected foam concentrate is regulated by the control valve.
The system’s benefit lies within the exact proportioning of the froth focus, independent of the extinguishing water strain or move price. Foam focus may be topped up during the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system must be activated; nonetheless, the delivered foam concentrate may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam focus move price. No premix is produced; and as the foam focus is passed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free energy provide for the froth concentrate pump and the control system, in addition to the necessity for a complicated management system and the comparatively larger buying costs. Furthermore, it have to be accepted that a delay happens between the change of the extinguishing water move price and the newly adjusted foam focus quantity. The foam high quality may be compromised when continually altering operating conditions as foam discharge units are turned on or off or changed.
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 focus pump which is linked directly to the water motor. Water motor and pump kind one compact unit. Upon activation of the fire pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump provides quick foam-concentrate injection into the extinguishing water. If the circulate fee changes, the amount of foam concentrate is tailored immediately.
The benefit of the system is its independence from exterior energy sources as properly as a precise and quick foam-concentrate proportioning whatever the extinguishing water pressure or circulate fee. If a piston or plunger pump is used, adjustment or calibration after installation is not essential since the water motor and the pump are volumetric devices firmly related to every other. Foam concentrate refilling throughout operation is feasible. The system can be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam focus can be measured via a return line. The proportioning price is calculated from the extinguishing water/foam focus flow price. No premix is generated; and if the foam concentrate is handed back into the tank, no foam concentrate must be topped up.
The bigger design and the comparatively higher buying costs are a disadvantage of the system.
With any system, consideration ought to be taken into consideration for the annual testing prices, which can be considerable when it comes to alternative foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge gear could be broken in in depth fires in the tank or in the dyke space and thus lose effectiveness, mobile fire displays and foam pipes could additionally be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have solely restricted extinguishing agent move rates and reaches.
Firefighting monitors
Firefighting screens are discharge units mounted on autos or trailers and obtainable in many sizes. The extinguishing agent move fee can be up to 60,000 litres/min and the reach could be as much as 180m if the pressure of the fireplace pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a floor hearth in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to find a way to forestall it reaching the critical temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke space should at all times be observed to avoid an overflow of the dyke.
Mobile hearth monitors could be provided both by the extinguishing water of the stationary fire pumps or by cell pumps. The injection of the foam focus usually takes place by way of mobile proportioners. This clearly points in direction of the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile units obtainable as back-ups is proven by the next 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 results in several options for the screens. Generally, foam-concentrate proportioners for no much less than 32,000 litres/min are required, which should be capable of deal with various flow rates to guarantee flexibility throughout extinguishing operations. Depending on the native circumstances, the monitors will want to hold a minimum distance to the burning tank or could not have the power to be positioned near to the tanks due to particles. In addition, it will not at all times be potential to position several monitors around the tank. It have to be ensured the monitor has enough throwing height in relation to the tank peak, to deliver foam into the inside of the tank.
The dimensioning of the complete firefighting system is made following legal laws as properly as recommendations by associations like NFPA and isn’t checked out extra carefully in the present article.
Fig. 4: 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 article, plainly many authorities and firms haven’t discovered the mandatory classes from disastrous fire incidents of previous years. Tank farm fires within the oil and petrochemical business do not happen incessantly. When they do, they usually have devastating penalties. Let us keep in mind the tank farm fireplace at Deer Park, Texas in March 2019 talked about within the introduction.
The fire developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for 30 minutes and caught fire for but 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 methods put in. All 15 tanks had been surrounded by one single dyke. The proprietor had relied on the local fire service, which was on the spot in a quick time however could not take management over the fireplace with the gear out there, partially because flammable substance was continuously leaking from the tank. Thirty-six hours after the hearth had damaged out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of apparatus and foam concentrate as nicely as the preparation of a plan of motion took roughly 13 hours. The hearth was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes pressure gauge were revamped three days, with foam focus and water shortages occurring in the meantime. In complete, over 500,000 litres of froth concentrate had been used. Instead of a fireplace within the dyke space, eleven of the 15 tanks burnt down.
It could be very possible that the fire would have been extinguished quickly if the warning systems and valves had labored and a fixed fireplace extinguishing system had existed. It can be probable that the fireplace would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been started earlier. Both circumstances would have resulted in notably less damage.
Summing up, the next factors should be discovered as a minimum. As far as they haven’t but been applied, or simply partly, they need to serve as a basis for discussions about one’s personal fire-protection idea:
Have a suitable fire-protection idea together with alternative situations which adapt to the given state of affairs frequently.
Always have a sufficient variety of cell extinguishing methods as a backup to fastened extinguishing techniques.
Stock an appropriate foam focus.
Ensure adequate foam focus supply.
Ensure sufficient water provide.
Keep well-maintained, rapidly and well- pressure gauge 10 bar , strategically placed and functioning extinguishing tools obtainable in a adequate quantity.
Have educated personnel available in a adequate quantity.
Ensure a fast implementation of a suitable plan of action.
For extra info, go to www.firedos.com
Share