Part One of this article described the typical incident eventualities at tank farm fires and offered foam as essentially the most suitable extinguishing agent along with the firefighting gear most commonly used. In Part Two we take a look at foam concentrate proportioning technologies, cell extinguishing systems and conclude with classes realized.
NFPA eleven describes numerous types of foam focus proportioning equipment. In the following, three techniques are checked out which are most common. Tight limits for the proportioning of foam focus 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 concentrate.
The proportioning price must not exceed 30% above the permitted worth i.e. 3.9% for a 3% foam concentrate or 7.8% for a 6% foam focus; 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 concentrate (the smaller value should be used respectively).
To assure appropriate proportioning, the proportioner, including the proportioning fee should be examined at least annually and its right functioning should 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 filled with foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the foam 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, inflicting supply of foam focus to the proportioner. The extinguishing water flows by way of the venturi proportioner. The ensuing vacuum induces the froth focus into the extinguishing water flow.
The advantages of this system are its easy design without moving parts and its straightforward operation. No external energy is required, and the system is comparatively inexpensive.
A drawback is that the system is a pressurized vessel subject to corresponding laws 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 delicate; when damaged, water will contaminate the froth concentrate. At a given proportioning rate, the system is appropriate only for low variations within the extinguishing water circulate strain and quantity. Adding or altering individual foam discharge units is feasible only to a very limited extent. The system can additionally be unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system should be activated and premix generated at the venturi proportioner inside the extinguishing water line. The right proportioning price have to be measured in the premix by laboratory evaluation. The generated premix must then be disposed of, and the consumed foam concentrate in the bladder tank must 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 flow meter within the extinguishing water move line. When the fire pumps are activated, the froth focus pump drive and electronic management system must be activated. The extinguishing water circulate price is measured by the flow meter and the control system adjusts the correct foam concentrate quantity via the management valve. The foam focus is injected into the extinguishing water flow by the foam focus pump. If there’s a change within the move price, the quantity of injected foam concentrate is regulated by the management valve.
The system’s benefit lies within the exact proportioning of the foam concentrate, impartial of the extinguishing water stress or circulate rate. Foam concentrate can be topped up during the extinguishing operation. The system is able to proportioning highly viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nonetheless, the delivered foam focus could be measured by way of a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate flow rate. Ridiculous is produced; and because the foam focus is handed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free power provide for the foam focus pump and the control system, as well as the necessity for a sophisticated control system and the comparatively greater purchasing costs. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water flow rate and the newly adjusted foam concentrate amount. The foam high quality could also be compromised when continuously changing working circumstances 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 concentrate, a water motor put in in the extinguishing water circulate line and a foam concentrate pump which is related on to the water motor. Water motor and pump form one compact unit. Upon activation of the hearth pumps, rotation within the water motor starts. The direct coupling to the foam-concentrate pump offers instant foam-concentrate injection into the extinguishing water. If the flow fee modifications, the quantity of foam concentrate is customized immediately.
The advantage of the system is its independence from exterior power sources as nicely as a exact and quick foam-concentrate proportioning whatever the extinguishing water pressure or move price. If a piston or plunger pump is used, adjustment or calibration after set up is not necessary for the rationale that water motor and the pump are volumetric devices firmly related to one another. Foam concentrate refilling throughout operation is feasible. The system can also be able to proportioning extremely viscous foam concentrates. The system should 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 move rate. No premix is generated; and if the foam concentrate is handed again into the tank, no foam focus must be topped up.
The larger design and the comparatively greater purchasing costs are a disadvantage of the system.
With any system, consideration must be taken into consideration for the annual testing prices, which can be appreciable by means of replacement foam concentrate, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge gear may be damaged in intensive fires in the tank or in the dyke area and thus lose effectiveness, cellular fire displays and foam pipes may be used.
Foam pipes
Foam pipes are normally held by firefighters, making them very versatile. Yet they have only restricted extinguishing agent flow charges and reaches.
Firefighting screens
Firefighting screens are discharge devices mounted on vehicles or trailers and available in lots of sizes. The extinguishing agent circulate fee may be as a lot as 60,000 litres/min and the attain can be as much as 180m if the stress of the fireplace pumps is sufficient. They are appropriate to discharge foam, e.g., to extinguish a surface fireplace 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 inside the dyke area ought to at all times be noticed to avoid an overflow of the dyke.
Mobile fire 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 factors in course of the advantage of power independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of cellular models available as back-ups is proven by the next example for the position of monitors 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 ends in several alternatives for the monitors. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which should have the flexibility to handle varying flow rates to guarantee flexibility throughout extinguishing operations. Depending on the local conditions, the monitors will want to maintain a minimal distance to the burning tank or could not have the ability to be positioned near to the tanks as a outcome of debris. In addition, it is not going to at all times be possible to place several monitors around the tank. It must be ensured the monitor has adequate 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 isn’t checked out more closely in the current article.
Fig. 4: 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 text, plainly many authorities and firms haven’t realized the mandatory classes from disastrous hearth incidents of previous years. Tank farm fires within the oil and petrochemical business do not occur incessantly. When they do, they usually have devastating penalties. Let us remember the tank farm fireplace at Deer Park, Texas in March 2019 mentioned within the introduction.
The hearth developed after over 30,000 litres butane-enriched naphtha had been leaking from a defective valve for 30 minutes and caught fireplace for yet unknown reasons. The plant had no fuel warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas did not have fastened extinguishing techniques installed. All 15 tanks have been surrounded by one single dyke. The owner had relied on the native fire service, which was on the spot very quickly however could not take control over the fireplace with the tools out there, partially as a end result of flammable substance was constantly leaking from the tank. Thirty-six hours after the fireplace had broken out, a contract was made with an exterior 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 13 hours. The fireplace was finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts have been remodeled three days, with foam focus and water shortages occurring in the meantime. In complete, over 500,000 litres of froth focus have been used. Instead of a fireplace in the dyke space, eleven of the 15 tanks burnt down.
It may be very probable that the fireplace would have been extinguished rapidly if the warning techniques and valves had worked and a fixed hearth extinguishing system had existed. It is also probable that the hearth would have been extinguished rapidly if the extinguishing operation, which succeeded ultimately, had been started earlier. Both circumstances would have resulted in notably less harm.
Summing up, the next points must be learned at the least. As far as they have not but 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 including alternative scenarios which adapt to the given scenario frequently.
Always have a enough number of mobile extinguishing systems as a backup to fastened extinguishing systems.
Stock an appropriate foam focus.
Ensure enough foam focus provide.
Ensure enough water provide.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing tools available in a sufficient number.
Have trained personnel out there in a adequate number.
Ensure a fast implementation of an appropriate plan of action.
For extra data, go to www.firedos.com
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