Part One of this article described the standard incident situations at tank farm fires and introduced foam as probably the most suitable extinguishing agent along with the firefighting equipment mostly used. In Part Two we look at foam focus proportioning applied sciences, cell extinguishing techniques and conclude with lessons learned.
NFPA 11 describes varied forms of foam focus proportioning gear. In the following, three techniques are checked out that are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price 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 fee must 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 price is allowed to be an absolute maximum of 1% above the permitted value – i.e. 4% for a 3% foam concentrate or 7% for a 6% foam concentrate (the smaller value should be used respectively).
To assure right proportioning, the proportioner, together with the proportioning fee have to be examined at least once a 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 know-how. The bladder tank is a pressurized vessel with a bladder inside which is full of foam concentrate. เพรสเชอร์เกจ 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 using the venturi precept. When the hearth pumps are activated, stress is generated by the pump, causing supply of foam concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the foam focus into the extinguishing water circulate.
The advantages of this method are its easy design with out transferring elements and its simple operation. No external energy is required, and the system is comparatively cheap.
A disadvantage is that the system is a pressurized vessel topic to corresponding laws corresponding to ASME Boiler & Pressure Vessel Codes. In order to refill foam concentrate, the system must be shut down and drained. The rubber bladder is delicate; when broken, water will contaminate the foam concentrate. At a given proportioning rate, the system is appropriate only for low variations within the extinguishing water circulate strain and volume. Adding or changing particular person foam discharge gadgets is feasible solely to a very limited extent. The system can be unsuitable for proportioning highly viscous foam concentrates.
To conduct any obligatory required annual testing, the system must be activated and premix generated on the venturi proportioner inside the extinguishing water line. The appropriate proportioning price should be measured within the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam concentrate within the bladder tank must be replaced.
Fig. 2: Driven proportioning pump with flow meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the foam focus, an electric or diesel-powered foam focus pump with an electronically managed valve and a circulate meter in the extinguishing water flow line. When the hearth pumps are activated, the froth focus pump drive and electronic management system must be activated. The extinguishing water move price is measured by the move meter and the management system adjusts the correct foam concentrate amount through the control valve. The foam focus is injected into the extinguishing water circulate by the froth focus pump. If there’s a change within the circulate price, the amount of injected foam concentrate is regulated by the management valve.
The system’s benefit lies in the exact proportioning of the foam focus, impartial of the extinguishing water strain or flow rate. Foam concentrate may be topped up in the course of the extinguishing operation. The system is able to proportioning extremely viscous foam concentrates. For the aim of annual testing, the system have to be activated; nonetheless, the delivered foam focus may be measured via a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate flow price. No premix is produced; and as the foam concentrate is handed back into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free power supply for the foam concentrate pump and the control system, in addition to the necessity for a complicated management system and the comparatively greater buying prices. Furthermore, it have to be accepted that a delay occurs between the change of the extinguishing water circulate rate and the newly adjusted foam focus quantity. The foam quality may be compromised when continually changing working conditions as foam discharge units are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the froth concentrate, a water motor installed within the extinguishing water circulate 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 fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump provides instant foam-concentrate injection into the extinguishing water. If the circulate price adjustments, the amount of froth focus is adapted immediately.
The benefit of the system is its independence from external power sources as well as a exact and instant foam-concentrate proportioning regardless of the extinguishing water stress or circulate rate. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t needed because the water motor and the pump are volumetric gadgets firmly connected to every other. Foam concentrate refilling during operation is feasible. The system can be capable of proportioning highly viscous foam concentrates. The system must be activated for annual testing; nonetheless, the delivered foam focus may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move rate. No premix is generated; and if the foam focus is passed back into the tank, no foam focus needs to be topped up.
The larger design and the comparatively larger buying costs are a drawback of the system.
With any system, consideration must be taken into account for the annual testing costs, which may be considerable when it comes to replacement foam focus, disposal of premix and labour costs.
Mobile extinguishing systems
As the stationary foam discharge tools could be damaged in intensive fires in the tank or in the dyke area and thus lose effectiveness, mobile fire screens 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 gadgets mounted on autos or trailers and obtainable in many sizes. The extinguishing agent flow price may be as much as 60,000 litres/min and the attain can be as a lot as 180m if the pressure of the hearth pumps is enough. They are suitable to discharge foam, e.g., to extinguish a floor fire in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to be able to prevent it reaching the important temperature for a boilover, or to maintain the flames from spreading. The accumulation of water contained in the dyke area should always be observed to keep away from an overflow of the dyke.
Mobile fire screens can be supplied both by the extinguishing water of the stationary hearth pumps or by cellular pumps. The injection of the froth concentrate often takes place through mobile proportioners. This clearly factors in path of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic determination for the sizes of cellular models available as back-ups is shown by the following example for the location of displays for fire extinguishing at tanks that are 45m in diameter and 15m excessive.
According to NFPA, 32,000 litres of premix per minute are required. This results in a quantity of alternatives for the screens. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which should be ready to handle various flow charges to guarantee flexibility during extinguishing operations. Depending on the local situations, the screens will need to hold a minimal distance to the burning tank or might not be ready to be positioned near to the tanks due to particles. In addition, it will not all the time be possible to place a quantity of displays across the tank. It must be ensured the monitor has enough 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 authorized regulations as properly as recommendations by associations like NFPA and is not checked out more carefully in the current article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons discovered
As talked about in the introduction to Part One of this article, it seems that many authorities and firms have not realized the necessary classes from disastrous hearth incidents of past years. Tank farm fires in the oil and petrochemical industry don’t occur incessantly. When they do, they normally have devastating penalties. Let us keep in mind the tank farm hearth 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 fireplace for but unknown reasons. The plant had no gas warning system and no remote-controlled valves to shut off the leaking fluid. In addition, some areas did not have fastened extinguishing techniques installed. 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 couldn’t take control over the fire with the equipment available, partially as a result of flammable substance was repeatedly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of kit and foam focus as properly as the preparation of a plan of motion took approximately thirteen hours. The fireplace was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts were made over three days, with foam concentrate and water shortages occurring within the meantime. In complete, over 500,000 litres of foam concentrate were used. Instead of a hearth in the dyke area, eleven of the 15 tanks burnt down.
It may be very possible that the fireplace would have been extinguished quickly if the warning techniques and valves had labored and a fixed hearth extinguishing system had existed. It can also be probable that the fire would have been extinguished shortly if the extinguishing operation, which succeeded finally, had been began earlier. Both cases would have resulted in notably less injury.
Summing up, the following points must be realized at least. As far as they haven’t yet been implemented, or just partly, they should function a basis for discussions about one’s personal fire-protection idea:
Have an acceptable fire-protection concept together with alternative situations which adapt to the given situation regularly.
Always have a adequate variety of mobile extinguishing techniques as a backup to mounted extinguishing techniques.
Stock an appropriate foam focus.
Ensure enough foam focus provide.
Ensure enough water supply.
Keep well-maintained, quickly and well-accessible, strategically positioned and functioning extinguishing tools obtainable in a enough number.
Have educated pressure gauge น้ำ in a sufficient number.
Ensure a fast implementation of a suitable plan of action.
For more data, go to www.firedos.com
Share