Use of foam for firefighting in tank farms of the oil and petrochemical industry – Part 2

Part One of this article described the standard incident eventualities at tank farm fires and presented foam as the most suitable extinguishing agent along with the firefighting gear most commonly used. In Part Two we have a look at foam concentrate proportioning technologies, cell extinguishing methods and conclude with classes learned.
NFPA eleven describes various kinds of foam concentrate proportioning gear. In the following, three techniques are checked out which are commonest. Tight limits for the proportioning of foam concentrate apply to all of them.
The proportioning price should not be less than the permitted values – i.e. 3% for a 3% foam focus or 6% for a 6% foam focus.
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 price is allowed to be an absolute most 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 guarantee right proportioning, the proportioner, including the proportioning price have to be tested a minimum of annually and its right functioning have to be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a proven and cost-effective know-how. The bladder tank is a pressurized vessel with a bladder inside which is crammed with foam focus. 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 using the venturi principle. When the hearth pumps are activated, pressure is generated by the pump, inflicting supply of foam focus to the proportioner. The extinguishing water flows through the venturi proportioner. The ensuing vacuum induces the froth focus into the extinguishing water flow.
The advantages of this system are its simple design with out shifting elements and its straightforward operation. No external power is required, and the system is relatively inexpensive.
Unconventional is that the system is a pressurized vessel subject to corresponding regulations 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 focus. At a given proportioning price, the system is suitable only for low variations in the extinguishing water move stress and quantity. Adding or altering individual foam discharge gadgets is feasible only to a very limited 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 on the venturi proportioner throughout the extinguishing water line. The right proportioning rate have to be measured in the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam concentrate in the bladder tank needs to be changed.
Fig. 2: Driven proportioning pump with circulate meter.
Driven proportioning pump with move meter
The system consists of an atmospheric tank for the froth focus, an electrical or diesel-powered foam concentrate pump with an electronically controlled valve and a circulate meter within the extinguishing water flow line. When the fireplace pumps are activated, the foam concentrate pump drive and electronic management system must be activated. The extinguishing water circulate fee is measured by the flow meter and the management system adjusts the correct foam focus amount through the management valve. The foam concentrate is injected into the extinguishing water flow by the froth focus pump. If there’s a change in the move rate, the amount of injected foam focus is regulated by the control valve.
The system’s advantage lies within the precise proportioning of the foam concentrate, unbiased of the extinguishing water stress or circulate rate. Foam focus may be topped up in the course of the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the aim of annual testing, the system must be activated; nevertheless, the delivered foam focus may be measured through a return line. The proportioning fee is calculated from the extinguishing water/foam concentrate move price. No premix is produced; and as a result of the foam concentrate is handed again into the tank, no foam concentrate must be refilled.
Disadvantages are the requirement for an external interruption-free vitality provide for the froth focus pump and the management system, in addition to the necessity for a complicated management system and the comparatively higher buying prices. 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 high quality may be compromised when continually changing working situations as foam discharge devices are turned on or off or modified.
Water motor with proportioning pump
The system consists of an atmospheric tank for the froth focus, a water motor installed within the extinguishing water move line and a foam concentrate pump which is linked on to the water motor. Water motor and pump form one compact unit. Upon activation of the fireplace pumps, rotation within the water motor begins. The direct coupling to the foam-concentrate pump provides instant foam-concentrate injection into the extinguishing water. If the flow price adjustments, the quantity of foam concentrate is adapted instantly.
The benefit of the system is its independence from external energy sources in addition to a exact and immediate foam-concentrate proportioning regardless of the extinguishing water pressure or circulate fee. If a piston or plunger pump is used, adjustment or calibration after set up just isn’t necessary since the water motor and the pump are volumetric units firmly linked to one another. Foam focus refilling throughout operation is feasible. The system can be capable of proportioning highly viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam focus can be measured via a return line. The proportioning price is calculated from the extinguishing water/foam concentrate flow rate. No premix is generated; and if the foam focus is handed back into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively greater buying costs are an obstacle of the system.
With any system, consideration should be taken into account for the annual testing prices, which can be appreciable in phrases of replacement foam concentrate, disposal of premix and labour prices.
Mobile extinguishing methods
As the stationary foam discharge gear can be broken in in depth fires within the tank or within the dyke area and thus lose effectiveness, mobile hearth monitors and foam pipes could also be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they have solely restricted extinguishing agent flow rates and reaches.
Firefighting displays
Firefighting displays are discharge devices mounted on automobiles or trailers and available in plenty of sizes. The extinguishing agent circulate rate may be up to 60,000 litres/min and the attain may be as a lot as 180m if the strain of the fireplace pumps is sufficient. They are suitable 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 so as to prevent it reaching the important 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 avoid an overflow of the dyke.
Mobile hearth displays can be equipped both by the extinguishing water of the stationary fireplace pumps or by cellular pumps. The injection of the foam focus usually takes place through cell proportioners. This clearly points in the direction of the benefit of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular models out there as back-ups is shown by the following example for the placement of monitors 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 leads to several alternatives for the screens. Generally, foam-concentrate proportioners for a minimum of 32,000 litres/min are required, which ought to be able to deal with various circulate charges to ensure flexibility during extinguishing operations. Depending on the local situations, the screens will need to maintain a minimum distance to the burning tank or might not be able to be positioned near to the tanks because of debris. In addition, it won’t always be attainable to place several displays across the tank. It must be ensured the monitor has enough throwing height in relation to the tank height, to deliver foam into the inside of the tank.
The dimensioning of the entire firefighting system is made following legal regulations as nicely as recommendations by associations like NFPA and is not looked at more carefully within the current article.
Fig. four: 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 text, plainly many authorities and corporations haven’t learned the required classes from disastrous fireplace incidents of past years. Tank farm fires within the oil and petrochemical business don’t occur frequently. When they do, they often have devastating consequences. Let us keep 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 defective valve for 30 minutes and caught hearth 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 didn’t have fastened extinguishing methods installed. All 15 tanks were surrounded by one single dyke. The proprietor had relied on the native hearth service, which was on the spot in a short time but could not take control over the fireplace with the tools available, partially as a result of flammable substance was continuously leaking from the tank. Thirty-six hours after the hearth had broken out, a contract was made with an external firefighting firm to do the extinguishing work. Mobilization of equipment and foam concentrate in addition to the preparation of a plan of action took roughly 13 hours. The fire was finally extinguished after 14 hours of firefighting, sixty three hours after it initially broke out. Extinguishing attempts have been revamped three days, with foam focus and water shortages occurring within the meantime. In complete, over 500,000 litres of froth concentrate have been used. Instead of a fire in the dyke area, 11 of the 15 tanks burnt down.
It is very possible that the fireplace would have been extinguished shortly if the warning systems and valves had labored and a fixed fire extinguishing system had existed. It is also probable that the fire would have been extinguished quickly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both circumstances would have resulted in notably less injury.
Summing up, the next factors should be learned as a minimum. As far as they have not yet been implemented, or just partly, they should function a basis for discussions about one’s own fire-protection idea:
Have an acceptable fire-protection concept together with alternative eventualities which adapt to the given state of affairs frequently.
Always have a enough number of mobile extinguishing techniques as a backup to fastened extinguishing systems.
Stock an appropriate foam focus.
Ensure adequate foam focus supply.
Ensure adequate water supply.
Keep well-maintained, rapidly and well-accessible, strategically positioned and functioning extinguishing tools available in a enough quantity.
Have trained personnel out there in a enough quantity.
Ensure a quick implementation of an appropriate plan of motion.
For extra info, go to www.firedos.com
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