Part One of this text described the everyday incident scenarios at tank farm fires and offered foam as essentially the most suitable extinguishing agent together with the firefighting tools mostly used. In Part Two we look at foam focus proportioning technologies, cellular extinguishing methods and conclude with classes discovered.
NFPA 11 describes varied kinds of foam concentrate proportioning gear. In the following, three methods are checked out which are most common. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning price must not be lower than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning rate should not exceed 30% above the permitted worth i.e. three.9% for a 3% foam focus or 7.8% for a 6% foam concentrate; respectively, the proportioning fee is allowed to be an absolute most of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam focus (the smaller worth must be used respectively).
To guarantee correct proportioning, the proportioner, together with the proportioning rate have to 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 proven and cost-effective technology. 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 concentrate from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi principle. When the fireplace pumps are activated, stress is generated by the pump, causing supply of foam focus 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 technique are its easy design with out moving components and its straightforward operation. No exterior energy is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel subject to corresponding laws corresponding to ASME Boiler & Pressure Vessel Codes. In order to refill foam focus, the system have to be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the foam focus. At a given proportioning price, the system is suitable only for low variations in the extinguishing water circulate stress and volume. Adding or changing individual foam discharge units is possible solely to a really restricted extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any necessary required annual testing, the system must be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The right proportioning price should be measured within the premix by laboratory evaluation. The generated premix should then be disposed of, and the consumed foam concentrate within the bladder tank needs to be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with flow 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 flow meter in the extinguishing water flow line. When the hearth pumps are activated, the froth focus pump drive and electronic control system should be activated. The extinguishing water flow fee is measured by the move meter and the management system adjusts the proper foam focus quantity via the management valve. The foam focus is injected into the extinguishing water flow by the froth concentrate pump. If there is a change in the circulate rate, the quantity of injected foam concentrate is regulated by the management valve.
The system’s benefit lies in the precise proportioning of the froth concentrate, independent of the extinguishing water pressure or flow price. Foam concentrate could 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; nevertheless, the delivered foam concentrate can be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam focus circulate rate. No premix is produced; and because the foam concentrate is handed again into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an external interruption-free energy provide for the froth focus 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 occurs between the change of the extinguishing water circulate price and the newly adjusted foam focus amount. The foam quality could additionally be compromised when continually altering working situations as foam discharge gadgets 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 in the extinguishing water circulate line and a foam focus pump which is connected on to the water motor. Water motor and pump kind one compact unit. Upon activation of the hearth pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump gives immediate foam-concentrate injection into the extinguishing water. If the circulate fee adjustments, the quantity of froth focus is adapted instantly.
The advantage of the system is its independence from exterior power sources in addition to a exact and instant foam-concentrate proportioning whatever the extinguishing water strain or flow rate. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t necessary because the water motor and the pump are volumetric devices firmly related to every other. Foam concentrate refilling throughout operation is possible. The system can be able to proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nonetheless, the delivered foam focus could be measured through a return line. The proportioning price is calculated from the extinguishing water/foam concentrate circulate rate. No premix is generated; and if the froth concentrate is handed back into the tank, no foam focus must be topped up.
The larger design and the comparatively higher purchasing costs are an obstacle of the system.
With any system, consideration ought to be taken into consideration for the annual testing costs, which could be appreciable when it comes to substitute foam focus, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge tools may be damaged in extensive fires within the tank or within the dyke space and thus lose effectiveness, cellular hearth monitors and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they’ve solely restricted extinguishing agent circulate rates and reaches.
Firefighting displays
Firefighting displays are discharge gadgets mounted on automobiles or trailers and obtainable in plenty of sizes. The extinguishing agent flow rate could be up to 60,000 litres/min and the attain may 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 fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank so as to forestall it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke space ought to always be observed to keep away from an overflow of the dyke.
Mobile fireplace screens can be equipped either by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the froth concentrate usually takes place via mobile proportioners. This clearly factors in the path of the advantage of vitality independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular items obtainable as back-ups is proven by the next instance for the placement of displays for fireplace extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several alternate options for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should be capable of deal with various move rates to guarantee flexibility throughout extinguishing operations. Depending on the local circumstances, the monitors might want to maintain a minimum distance to the burning tank or could not have the power to be positioned close to to the tanks because of particles. In เกจวัดแรงดันลมคือ , it will not always be potential to position a number of screens around the tank. It should be ensured the monitor has sufficient throwing peak in relation to the tank peak, to ship foam into the within of the tank.
The dimensioning of the whole firefighting system is made following authorized laws as well as suggestions by associations like NFPA and is not checked out more carefully in the current article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons realized
As talked about within the introduction to Part One of this article, it seems that many authorities and companies haven’t realized the mandatory lessons from disastrous fireplace incidents of past years. Tank farm fires within the oil and petrochemical business don’t occur frequently. When they do, they usually have devastating consequences. Let us bear in mind the tank farm hearth 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 30 minutes and caught fire for but unknown causes. 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 had been surrounded by one single dyke. The proprietor had relied on the native hearth service, which was on the spot very quickly however couldn’t take management over the fireplace with the gear available, partially as a outcome of flammable substance was constantly leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of apparatus and foam focus in addition to the preparation of a plan of action took approximately thirteen hours. The fireplace was lastly extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts were made over three days, with foam focus and water shortages occurring in the meantime. In complete, over 500,000 litres of foam concentrate were used. Instead of a fire within the dyke space, 11 of the 15 tanks burnt down.
It may be very possible that the fire would have been extinguished shortly if the warning techniques and valves had labored and a exhausting and fast fire extinguishing system had existed. It is also probable that the fireplace would have been extinguished quickly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both instances would have resulted in notably less damage.
Summing up, the next factors must be realized at the least. As far as they haven’t but been implemented, or simply partly, they want to function a basis for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection concept together with alternative scenarios which adapt to the given state of affairs regularly.
Always have a sufficient variety of cellular extinguishing techniques as a backup to fixed extinguishing techniques.
Stock an appropriate foam focus.
Ensure sufficient foam concentrate supply.
Ensure enough water supply.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing equipment available in a adequate quantity.
Have trained personnel available in a sufficient quantity.
Ensure a fast implementation of an appropriate plan of motion.
For more info, go to www.firedos.com
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