Part One of this article described the everyday incident eventualities at tank farm fires and offered foam as essentially the most appropriate extinguishing agent along with the firefighting equipment most commonly used. In Part Two we look at foam concentrate proportioning applied sciences, cell extinguishing techniques and conclude with lessons learned.
NFPA eleven describes numerous forms of foam focus proportioning equipment. In the following, three techniques are looked at that are most typical. Tight limits for the proportioning of froth concentrate apply to all of them.
The proportioning fee must not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam concentrate.
The proportioning rate should not exceed 30% above the permitted value i.e. three.9% for a 3% foam concentrate 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 focus or 7% for a 6% foam concentrate (the smaller worth should be used respectively).
To assure correct proportioning, the proportioner, including the proportioning price should be examined at least every year and its correct 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 concentrate from the bladder as required. The bladder is linked to a proportioner which operates using the venturi principle. When the fireplace pumps are activated, strain is generated by the pump, inflicting delivery of froth 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 shifting parts and its simple operation. No exterior vitality is required, and the system is comparatively inexpensive.
A disadvantage is that the system is a pressurized vessel topic to corresponding regulations similar to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system should be shut down and drained. The rubber bladder is sensitive; when damaged, water will contaminate the foam focus. At a given proportioning fee, the system is suitable only for low variations within the extinguishing water circulate stress and volume. Adding or changing individual foam discharge devices is possible solely to a very limited extent. The system is also unsuitable for proportioning extremely viscous foam concentrates.
To conduct any obligatory required annual testing, the system have to be activated and premix generated on the venturi proportioner throughout the extinguishing water line. The appropriate proportioning rate must be measured within the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam focus in the bladder tank must 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 focus, an electrical or diesel-powered foam focus pump with an electronically controlled valve and a circulate meter in the extinguishing water move line. When the hearth pumps are activated, the froth 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 right foam focus quantity through the management valve. The foam focus is injected into the extinguishing water flow by the froth focus pump. If there’s a change in the circulate price, the amount of injected foam focus is regulated by the management valve.
The system’s benefit lies in the exact proportioning of the froth focus, unbiased of the extinguishing water pressure or flow fee. Foam focus can be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the aim of annual testing, the system have to be activated; however, the delivered foam focus may be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate circulate fee. No premix is produced; and as the foam focus is handed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an external interruption-free energy supply for the foam focus pump and the control system, in addition to the need for a sophisticated control 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 fee and the newly adjusted foam focus amount. The foam quality could additionally be compromised when constantly changing operating circumstances as foam discharge gadgets are turned on or off or modified.
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 focus pump which is related on to the water motor. Water motor and pump type 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 circulate fee modifications, the amount of foam focus is tailored instantly.
The advantage of the system is its independence from external energy sources as properly as a exact and quick foam-concentrate proportioning regardless of the extinguishing water strain or flow price. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t necessary for the rationale that water motor and the pump are volumetric devices firmly related to each other. Foam concentrate refilling during operation is possible. The system can also be able to proportioning highly viscous foam concentrates. The system must be activated for annual testing; nevertheless, the delivered foam concentrate may be measured via a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move fee. No premix is generated; and if the froth concentrate is passed again into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively higher buying costs are a drawback of the system.
With any system, consideration should be taken under consideration for the annual testing costs, which can be appreciable in phrases of replacement foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge tools may be broken in intensive fires in the tank or in the dyke area and thus lose effectiveness, mobile fireplace screens and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very flexible. Yet they have solely limited extinguishing agent move charges and reaches.
Firefighting displays
Firefighting displays are discharge devices mounted on autos or trailers and obtainable in many sizes. The extinguishing agent move price could be up to 60,000 litres/min and the reach may be up to 180m if the stress of the fire pumps is sufficient. They are appropriate to discharge foam, e.g., to extinguish a floor fireplace in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to find a way to prevent it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water inside the dyke area ought to always be noticed to keep away from an overflow of the dyke.
Mobile fireplace displays may be supplied both by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the froth focus usually takes place through mobile proportioners. This clearly factors towards the advantage of energy independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular units out there as back-ups is proven by the following example for the location of screens 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 alternate options for the screens. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which ought to be able to deal with various move rates to guarantee flexibility during extinguishing operations. Depending on the native circumstances, the monitors will want to maintain a minimal distance to the burning tank or could not be succesful of be positioned near to the tanks due to particles. In addition, it will not all the time be potential to place a number of screens around the tank. It have to be ensured the monitor has sufficient throwing top 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 authorized regulations in addition to suggestions by associations like NFPA and isn’t checked out extra intently within the current article.
Fig. four: 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 seems that many authorities and firms haven’t learned the required lessons from disastrous hearth incidents of previous years. Tank farm fires in the oil and petrochemical industry do not happen frequently. When they do, they often have devastating consequences. Let us bear in mind the tank farm hearth at Deer Park, Texas in March 2019 mentioned within the introduction.
pressure gauge หน้าปัด 4 นิ้ว developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught hearth for but unknown reasons. The plant had no fuel warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas didn’t have mounted extinguishing systems put in. All 15 tanks were surrounded by one single dyke. The owner had relied on the native fireplace service, which was on the spot very quickly but could not take management over the hearth with the tools obtainable, partially as a result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fire had damaged out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of kit and foam concentrate in addition to the preparation of a plan of motion took approximately thirteen hours. The fireplace was finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing makes an attempt were remodeled three days, with foam focus and water shortages occurring within the meantime. In complete, over 500,000 litres of foam concentrate had been used. Instead of a fire within the dyke space, eleven of the 15 tanks burnt down.
It may be very possible that the fireplace would have been extinguished rapidly if the warning systems and valves had worked and a fixed fire extinguishing system had existed. It can be probable that the hearth would have been extinguished shortly if the extinguishing operation, which succeeded eventually, had been began earlier. Both cases would have resulted in notably much less damage.
Summing up, the next points must be learned at least. As far as they have not but been applied, or just partly, they should serve as a basis for discussions about one’s own fire-protection concept:
Have a suitable fire-protection concept including alternative eventualities which adapt to the given situation often.
Always have a enough variety of mobile extinguishing systems as a backup to fixed extinguishing methods.
Stock an acceptable foam focus.
Ensure enough foam focus supply.
Ensure adequate water provide.
Keep well-maintained, quickly and well-accessible, strategically placed and functioning extinguishing equipment out there in a enough number.
Have educated personnel out there in a sufficient quantity.
Ensure a fast implementation of an acceptable plan of action.
For extra data, go to www.firedos.com
Share