Part One of this text described the everyday incident scenarios at tank farm fires and presented foam as the most suitable extinguishing agent together with the firefighting tools mostly used. In Part Two we take a glance at foam concentrate proportioning technologies, mobile extinguishing methods and conclude with classes realized.
NFPA 11 describes various kinds of foam focus proportioning equipment. In the following, three systems are looked at which are most typical. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price must not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam concentrate.
The proportioning fee should not exceed 30% above the permitted worth i.e. three.9% for a 3% foam concentrate or 7.8% for a 6% foam focus; respectively, the proportioning fee 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 concentrate (the smaller worth have to be used respectively).
To assure appropriate proportioning, the proportioner, together with the proportioning rate must be examined 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 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 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, strain is generated by the pump, causing delivery of foam concentrate to the proportioner. The extinguishing water flows through the venturi proportioner. The resulting vacuum induces the foam focus into the extinguishing water circulate.
The benefits of this method are its simple design without moving elements and its straightforward operation. No external power is required, and the system is relatively inexpensive.
A disadvantage 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 have to be shut down and drained. The rubber bladder is delicate; when damaged, water will contaminate the foam focus. At a given proportioning price, the system is suitable only for low variations within the extinguishing water circulate strain and volume. Adding or altering individual foam discharge units is feasible only to a really limited extent. The system can be unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated at the venturi proportioner throughout the extinguishing water line. The right proportioning rate must 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 must be replaced.
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 flow meter in the extinguishing water circulate line. When the fireplace pumps are activated, the froth focus pump drive and digital management system have to be activated. The extinguishing water flow price is measured by the circulate meter and the control system adjusts the right foam focus amount by way of the control valve. The foam concentrate is injected into the extinguishing water move by the foam concentrate pump. If there’s a change in the circulate rate, the quantity of injected foam focus is regulated by the control valve.
The system’s benefit lies within the precise proportioning of the foam concentrate, independent of the extinguishing water strain or move rate. Foam concentrate could be topped up through 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 focus could be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move rate. เกจวัดแรงอัดกระบอกสูบ is produced; and as a result of the foam focus is passed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an external interruption-free vitality provide for the foam focus pump and the management system, as nicely as the need for a classy management system and the comparatively greater buying prices. Furthermore, it must be accepted that a delay occurs between the change of the extinguishing water flow rate and the newly adjusted foam focus amount. The foam high quality may be compromised when continuously altering operating conditions 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 foam focus, a water motor put in within the extinguishing water flow line and a foam concentrate pump which is connected on to the water motor. Water motor and pump kind one compact unit. Upon activation of the fireplace pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump gives instant foam-concentrate injection into the extinguishing water. If the flow rate adjustments, the amount of froth concentrate is customized instantly.
The benefit of the system is its independence from external vitality sources as nicely as a precise and immediate foam-concentrate proportioning regardless of the extinguishing water stress or flow fee. If a piston or plunger pump is used, adjustment or calibration after set up isn’t needed since the water motor and the pump are volumetric gadgets firmly related to one another. Foam focus refilling throughout operation is possible. The system is also able to proportioning extremely viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam concentrate may be measured by way of a return line. The proportioning fee is calculated from the extinguishing water/foam focus flow price. No premix is generated; and if the foam focus is passed back into the tank, no foam focus must be topped up.
The larger design and the comparatively higher purchasing costs are a drawback of the system.
With any system, consideration ought to be taken into account for the annual testing prices, which could be appreciable when it comes to substitute foam concentrate, disposal of premix and labour costs.
Mobile extinguishing techniques
As the stationary foam discharge tools could be damaged in intensive fires in the tank or within the dyke area and thus lose effectiveness, cellular hearth screens and foam pipes could also be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have solely limited extinguishing agent flow charges and reaches.
Firefighting monitors
Firefighting displays are discharge units mounted on vehicles or trailers and out there in lots of sizes. The extinguishing agent move fee could be up to 60,000 litres/min and the attain could be up to 180m if the stress of the hearth pumps is sufficient. They are suitable 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 in order to stop it reaching the critical temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke area ought to always be noticed to keep away from an overflow of the dyke.
Mobile hearth displays may be equipped either by the extinguishing water of the stationary hearth pumps or by cell pumps. The injection of the froth concentrate usually takes place by way of cell proportioners. This clearly factors towards the benefit of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile items obtainable as back-ups is proven by the following example for the location of displays 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 number of alternatives for the monitors. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which ought to be in a position to handle various flow 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 may not be capable of be positioned close to to the tanks as a result of debris. In addition, it will not always be attainable to position several screens around the tank. It should be ensured the monitor has sufficient throwing height in relation to the tank peak, to ship foam into the within of the tank.
The dimensioning of the complete firefighting system is made following legal rules as well as recommendations by associations like NFPA and is not checked out more closely in the present article.
Fig. 4: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam concentrate tank.
Lessons discovered
As talked about in the introduction to Part One of this article, plainly many authorities and corporations have not realized the necessary lessons from disastrous fire incidents of past years. Tank farm fires in the oil and petrochemical industry don’t happen frequently. When they do, they often have devastating penalties. Let us bear in mind the tank farm fire at Deer Park, Texas in March 2019 talked about in the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for half-hour and caught hearth for yet unknown reasons. The plant had no gasoline warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fixed extinguishing techniques installed. 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 could not take control over the fireplace with the tools available, 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 exterior firefighting company to do the extinguishing work. Mobilization of apparatus and foam focus in addition to the preparation of a plan of action took roughly 13 hours. The fireplace was lastly extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing makes an attempt had been made over three days, with foam focus and water shortages occurring within 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 fireplace would have been extinguished quickly if the warning methods and valves had labored and a set fire extinguishing system had existed. It is also possible that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been started earlier. Both cases would have resulted in notably less harm.
Summing up, the following points should be discovered at least. As far as they haven’t yet been implemented, or simply partly, they should function a foundation for discussions about one’s personal fire-protection concept:
Have an appropriate fire-protection idea together with various situations which adapt to the given scenario frequently.
Always have a sufficient variety of cellular extinguishing methods as a backup to fastened extinguishing systems.
Stock an appropriate foam concentrate.
Ensure sufficient foam focus provide.
Ensure enough water supply.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing equipment obtainable in a sufficient number.
Have trained personnel available in a enough quantity.
Ensure a quick implementation of an appropriate plan of action.
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