Part One of this text described the standard incident situations at tank farm fires and presented foam as essentially the most suitable extinguishing agent together with the firefighting gear most commonly used. In Part Two we look at foam focus proportioning applied sciences, cell extinguishing systems and conclude with lessons realized.
NFPA 11 describes various kinds of foam concentrate proportioning gear. In the following, three methods are looked at that are most typical. Tight limits for the proportioning of foam focus apply to all of them.
The proportioning rate must not be lower than the permitted values – i.e. 3% for a 3% foam concentrate or 6% for a 6% foam focus.
The proportioning fee should 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 rate is allowed to be an absolute maximum of 1% above the permitted value – i.e. 4% for a 3% foam focus or 7% for a 6% foam concentrate (the smaller worth must be used respectively).
To assure right proportioning, the proportioner, together with the proportioning fee must be tested at least once a year and its appropriate functioning have to be checked.
Fig. 1 Bladder tank with proportioner.
Bladder tank with proportioner
The bladder tank with a proportioner is a confirmed and cost-effective expertise. 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 foam focus from the bladder as required. The bladder is related to a proportioner which operates utilizing the venturi principle. When the hearth pumps are activated, stress is generated by the pump, inflicting supply of foam focus to the proportioner. The extinguishing water flows via the venturi proportioner. digital pressure gauge ensuing vacuum induces the froth focus into the extinguishing water move.
The benefits of this system are its simple design with out moving components and its straightforward operation. No external power is required, and the system is comparatively inexpensive.
A drawback 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 should be shut down and drained. The rubber bladder is sensitive; when broken, water will contaminate the foam concentrate. At a given proportioning fee, the system is appropriate just for low variations in the extinguishing water flow stress and volume. Adding or changing particular person foam discharge devices is feasible only to a very restricted extent. The system is also unsuitable for proportioning highly viscous foam concentrates.
To conduct any necessary required annual testing, the system have to be activated and premix generated at the venturi proportioner inside the extinguishing water line. The correct proportioning rate should be measured in the premix by laboratory analysis. The generated premix should then be disposed of, and the consumed foam focus within the bladder tank needs to 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 controlled valve and a circulate meter in the extinguishing water flow line. When the fire pumps are activated, the froth concentrate pump drive and electronic management system have to be activated. The extinguishing water circulate fee is measured by the move meter and the management system adjusts the correct foam focus quantity via the control valve. The foam concentrate is injected into the extinguishing water circulate by the froth concentrate pump. If there is a change in the circulate rate, the amount of injected foam concentrate is regulated by the management valve.
The system’s benefit lies in the precise proportioning of the froth concentrate, unbiased of the extinguishing water pressure or circulate fee. Foam concentrate may be topped up during the extinguishing operation. The system is capable of proportioning highly viscous foam concentrates. For the purpose of annual testing, the system have to be activated; nonetheless, the delivered foam concentrate may be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus move fee. No premix is produced; and as a result of the foam concentrate is passed again into the tank, no foam focus needs to be refilled.
Disadvantages are the requirement for an external interruption-free power supply for the froth concentrate pump and the management system, as nicely as the need for a classy control system and the comparatively greater buying prices. Furthermore, it should be accepted that a delay occurs between the change of the extinguishing water circulate fee and the newly adjusted foam concentrate amount. The foam high quality may be compromised when continually changing working conditions as foam discharge units 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 installed in the extinguishing water move line and a foam concentrate pump which is related directly to the water motor. Water motor and pump form one compact unit. Upon activation of the fire 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 circulate rate modifications, the amount of foam concentrate is adapted instantly.
The advantage of the system is its independence from external power sources in addition to a precise and instant foam-concentrate proportioning whatever the extinguishing water strain or flow rate. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t essential because the water motor and the pump are volumetric gadgets firmly linked to each other. Foam concentrate refilling during operation is possible. The system can also be capable of proportioning highly viscous foam concentrates. The system should be activated for annual testing; nonetheless, the delivered foam focus could be measured by way of a return line. The proportioning price is calculated from the extinguishing water/foam concentrate flow fee. No premix is generated; and if the froth concentrate is handed again into the tank, no foam focus needs to be topped up.
The bigger design and the comparatively higher buying costs are a disadvantage of the system.
With any system, consideration must be taken into account for the annual testing prices, which may be appreciable by means of substitute foam concentrate, disposal of premix and labour prices.
Mobile extinguishing systems
As the stationary foam discharge equipment could be broken in intensive fires within the tank or within the dyke space and thus lose effectiveness, mobile fireplace screens and foam pipes could also be used.
Foam pipes
Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve only limited extinguishing agent move rates and reaches.
Firefighting monitors
Firefighting monitors are discharge devices mounted on automobiles or trailers and out there in many sizes. The extinguishing agent circulate fee could be up to 60,000 litres/min and the attain can be up to 180m if the pressure of the fire pumps is sufficient. They are suitable to discharge foam, e.g., to extinguish a surface fire in a tank, or water, to cool down a neighboring tank or the tank wall of a burning tank so as to forestall it reaching the critical temperature for a boilover, or to keep the flames from spreading. The accumulation of water inside the dyke area ought to always be noticed to avoid an overflow of the dyke.
Mobile hearth screens may be provided either by the extinguishing water of the stationary hearth pumps or by mobile pumps. The injection of the foam concentrate often takes place via mobile proportioners. This clearly factors in direction of the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile models obtainable as back-ups is shown by the next instance for the position of displays for hearth 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 options for the screens. Generally, foam-concentrate proportioners for a minimal of 32,000 litres/min are required, which should be in a position to handle varying flow charges to ensure flexibility throughout extinguishing operations. Depending on the local conditions, the screens might want to keep a minimum distance to the burning tank or may not have the flexibility to be positioned close to to the tanks as a outcome of particles. In addition, it will not all the time be potential to position a quantity of displays across the tank. It have to be ensured the monitor has sufficient throwing peak in relation to the tank peak, to deliver foam into the within of the tank.
The dimensioning of the whole firefighting system is made following authorized regulations in addition to recommendations by associations like NFPA and isn’t looked at extra closely in the current article.
Fig. 4: 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 article, it seems that many authorities and firms haven’t realized the mandatory lessons from disastrous fireplace incidents of past years. Tank farm fires within the oil and petrochemical industry don’t happen frequently. When they do, they usually have devastating penalties. Let us keep in mind the tank farm fireplace at Deer Park, Texas in March 2019 talked about within the introduction.
The fireplace developed after over 30,000 litres butane-enriched naphtha had been leaking from a faulty valve for half-hour and caught fire 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 didn’t have mounted extinguishing systems put in. All 15 tanks had been surrounded by one single dyke. The proprietor had relied on the local hearth service, which was on the spot in a brief time but couldn’t take management over the hearth with the gear obtainable, partially as a result of flammable substance was continuously leaking from the tank. Thirty-six hours after the fire had broken out, a contract was made with an external firefighting company to do the extinguishing work. Mobilization of kit and foam concentrate as properly as the preparation of a plan of action took approximately thirteen hours. The fireplace was finally extinguished after 14 hours of firefighting, 63 hours after it initially broke out. Extinguishing attempts had been made over three days, with foam focus and water shortages occurring within the meantime. In total, over 500,000 litres of froth concentrate were used. Instead of a fire in the dyke space, 11 of the 15 tanks burnt down.
It is very probable that the hearth would have been extinguished rapidly if the warning systems and valves had worked and a onerous and fast fire extinguishing system had existed. It is also probable that the fireplace would have been extinguished shortly if the extinguishing operation, which succeeded ultimately, had been began earlier. Both circumstances would have resulted in notably less harm.
Summing up, the following points should be learned at least. As far as they have not yet been carried out, or just partly, they should serve as a basis for discussions about one’s personal fire-protection idea:
Have an acceptable fire-protection idea together with various scenarios which adapt to the given situation regularly.
Always have a enough variety of cellular extinguishing systems as a backup to mounted extinguishing systems.
Stock an acceptable foam concentrate.
Ensure sufficient foam focus supply.
Ensure enough water provide.
Keep well-maintained, rapidly and well-accessible, strategically placed and functioning extinguishing gear out there in a sufficient quantity.
Have educated personnel obtainable in a enough number.
Ensure a quick implementation of a suitable plan of motion.
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