Part One of this text described the typical incident eventualities at tank farm fires and offered foam as the most appropriate extinguishing agent along with the firefighting equipment mostly used. In Part Two we take a look at foam focus proportioning technologies, mobile extinguishing techniques and conclude with lessons realized.
NFPA 11 describes varied forms of foam focus proportioning equipment. In the following, three methods are looked at that are most common. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning fee 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 fee should not exceed 30% above the permitted value i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam focus; respectively, the proportioning price is allowed to be an absolute maximum of 1% above the permitted worth – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller value must be used respectively).
To assure right proportioning, the proportioner, together with the proportioning rate have to be tested a minimum of once a year and its appropriate functioning have to 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 crammed with foam concentrate. The tank is pressurized with water from the fire-extinguishing line and discharges the foam concentrate from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi precept. When the hearth pumps are activated, strain is generated by the pump, causing supply of froth concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The ensuing vacuum induces the froth focus into the extinguishing water circulate.
The benefits of this system are its simple design without shifting parts and its simple operation. No external energy is required, and the system is comparatively inexpensive.
A drawback is that the system is a pressurized vessel topic to corresponding rules similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system have to be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam concentrate. At a given proportioning price, the system is appropriate only for low variations in the extinguishing water circulate strain and quantity. Adding or changing individual foam discharge devices is possible solely to a very limited extent. The system can also 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 within the extinguishing water line. The appropriate proportioning fee must be measured in the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam concentrate within 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 froth concentrate, an electrical or diesel-powered foam focus pump with an electronically controlled valve and a circulate meter in the extinguishing water flow line. When the fireplace pumps are activated, the foam concentrate pump drive and digital management system should be activated. The extinguishing water circulate price is measured by the flow meter and the management system adjusts the right foam concentrate amount via the control valve. The foam concentrate is injected into the extinguishing water move by the foam focus pump. If there is a change within the move rate, the quantity of injected foam focus is regulated by the management valve.
The system’s benefit lies in the exact proportioning of the foam concentrate, impartial of the extinguishing water pressure or flow rate. เกจปรับแรงดันแก๊ส can be topped up during the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system have to be activated; however, the delivered foam focus may be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate move price. No premix is produced; and as the foam focus is handed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an exterior interruption-free vitality supply for the froth focus pump and the management system, in addition to the need for a classy control system and the comparatively greater buying prices. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water circulate price and the newly adjusted foam focus quantity. The foam quality may be compromised when constantly altering operating situations 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 froth concentrate, a water motor installed within the extinguishing water move line and a foam focus pump which is linked directly to the water motor. Water motor and pump form 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 move rate modifications, the amount of foam focus is customized immediately.
The advantage of the system is its independence from exterior energy sources as properly as a exact and immediate foam-concentrate proportioning whatever the extinguishing water pressure or move fee. If a piston or plunger pump is used, adjustment or calibration after installation isn’t essential because the water motor and the pump are volumetric gadgets firmly connected to every other. Foam concentrate refilling throughout operation is feasible. The system is also capable of proportioning extremely 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 price is calculated from the extinguishing water/foam concentrate move rate. No premix is generated; and if the foam focus is handed back into the tank, no foam focus must be topped up.
The larger design and the comparatively larger purchasing costs are a drawback of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which could be appreciable by method of alternative foam concentrate, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge tools can be broken in in depth fires within the tank or within the dyke area and thus lose effectiveness, cellular fire monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they’ve only limited extinguishing agent flow rates and reaches.
Firefighting monitors
Firefighting screens are discharge devices mounted on autos or trailers and obtainable in many sizes. The extinguishing agent circulate price may be as much as 60,000 litres/min and the reach could be as much as 180m if the strain 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 have the ability to stop it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke space ought to all the time be noticed to keep away from an overflow of the dyke.
Mobile fire monitors may be supplied either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the foam concentrate usually takes place through mobile proportioners. This clearly factors towards the benefit of power independence for water-motor-driven proportioning pumps.
The strategic decision for the sizes of cellular units out there as back-ups is proven by the next instance for the placement 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 a quantity of alternate options for the monitors. Generally, foam-concentrate proportioners for a minimum of 32,000 litres/min are required, which ought to be succesful of handle various flow charges to ensure flexibility throughout extinguishing operations. Depending on the native situations, the displays will want to keep a minimum distance to the burning tank or may not be in a position to be positioned near to the tanks because of particles. In addition, it will not at all times be attainable to place several screens across the tank. It must be ensured the monitor has enough throwing peak in relation to the tank height, to ship foam into the within of the tank.
The dimensioning of the complete firefighting system is made following legal laws as nicely as suggestions by associations like NFPA and is not looked at extra carefully in the present article.
Fig. four: 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 companies have not learned the required classes from disastrous hearth incidents of previous years. Tank farm fires within the oil and petrochemical trade don’t happen regularly. When they do, they usually have devastating consequences. Let us bear in mind the tank farm fire at Deer Park, Texas in March 2019 talked about in 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 fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have fastened extinguishing methods put in. All 15 tanks were surrounded by one single dyke. The owner had relied on the native hearth service, which was on the spot very quickly however could not take management over the fireplace with the tools available, partially as a outcome of flammable substance was continuously leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an exterior firefighting firm to do the extinguishing work. Mobilization of apparatus and foam concentrate as well 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 an attempt were made over three days, with foam focus and water shortages occurring in the meantime. In whole, over 500,000 litres of froth concentrate were used. Instead of a fireplace in the dyke space, eleven of the 15 tanks burnt down.
It is very possible that the hearth would have been extinguished shortly if the warning techniques and valves had labored and a onerous and fast fire extinguishing system had existed. It can be possible that the fireplace would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been began earlier. Both instances would have resulted in notably less injury.
Summing up, the next points must be realized at the least. As far as they have not but been implemented, or just partly, they need to serve as a basis for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection idea together with various scenarios which adapt to the given state of affairs often.
Always have a enough number of mobile extinguishing systems as a backup to mounted extinguishing techniques.
Stock an appropriate foam focus.
Ensure sufficient foam concentrate provide.
Ensure sufficient water provide.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing equipment available in a enough number.
Have educated personnel available in a adequate quantity.
Ensure a quick implementation of a suitable plan of action.
For more info, go to www.firedos.com
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