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 offered foam as probably the most appropriate extinguishing agent along with the firefighting tools mostly used. In Part Two we have a glance at foam concentrate proportioning applied sciences, cell extinguishing techniques and conclude with classes discovered.
NFPA eleven describes numerous types of foam focus proportioning equipment. In the following, three systems are looked at that are most typical. Tight limits for the proportioning of froth focus apply to all of them.
The proportioning rate must not be less 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 focus or 7.8% for a 6% foam concentrate; respectively, the proportioning price 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 worth must be used respectively).
To assure right proportioning, the proportioner, together with the proportioning rate should be examined a minimum of annually and its appropriate functioning should 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 full of foam focus. The tank is pressurized with water from the fire-extinguishing line and discharges the froth focus from the bladder as required. The bladder is connected to a proportioner which operates utilizing the venturi precept. When the hearth pumps are activated, pressure is generated by the pump, causing supply of froth concentrate to the proportioner. The extinguishing water flows by way of the venturi proportioner. The resulting vacuum induces the froth focus into the extinguishing water move.
The advantages of this system are its simple design with out transferring parts and its straightforward operation. No external energy is required, and the system is comparatively cheap.
A drawback is that the system is a pressurized vessel topic to corresponding regulations corresponding 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 focus. At a given proportioning rate, the system is suitable only for low variations within the extinguishing water move strain and volume. Adding or changing particular person foam discharge gadgets is feasible solely to a very restricted extent. The system can additionally be 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 within the extinguishing water line. The right proportioning fee have to be measured in the premix by laboratory analysis. The generated premix must then be disposed of, and the consumed foam focus 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 managed valve and a flow meter within the extinguishing water move line. When the fireplace pumps are activated, the foam focus pump drive and digital control system have to be activated. The extinguishing water move price is measured by the flow meter and the management system adjusts the proper foam focus amount by way of the management valve. The foam concentrate is injected into the extinguishing water circulate by the froth focus pump. If there is a change within the flow fee, the amount of injected foam concentrate is regulated by the control valve.
The system’s advantage lies in the exact proportioning of the froth concentrate, impartial of the extinguishing water pressure or flow fee. Foam focus could be topped up during the extinguishing operation. The system is capable of proportioning extremely viscous foam concentrates. For the purpose of annual testing, the system must be activated; nevertheless, the delivered foam concentrate can be measured through a return line. The proportioning rate is calculated from the extinguishing water/foam concentrate circulate fee. No premix is produced; and as the foam concentrate is passed back into the tank, no foam concentrate needs to be refilled.
Disadvantages are the requirement for an exterior interruption-free energy supply for the froth concentrate pump and the management system, in addition to the need for a classy control system and the comparatively higher purchasing costs. Furthermore, it must be accepted that a delay happens between the change of the extinguishing water move rate and the newly adjusted foam focus amount. The foam quality could additionally be compromised when continuously altering 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 put in 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 starts. The direct coupling to the foam-concentrate pump gives quick foam-concentrate injection into the extinguishing water. If the move price adjustments, the quantity of foam focus is customized instantly.
The benefit of the system is its independence from external vitality sources as well as a exact and quick foam-concentrate proportioning whatever the extinguishing water stress or move fee. If a piston or plunger pump is used, adjustment or calibration after installation just isn’t necessary for the explanation that water motor and the pump are volumetric units firmly related to one another. Foam focus refilling throughout operation is possible. The system is also capable of proportioning extremely viscous foam concentrates. The system have to be activated for annual testing; nevertheless, the delivered foam concentrate can be measured through a return line. The proportioning price is calculated from the extinguishing water/foam focus flow fee. No premix is generated; and if the foam focus is handed back into the tank, no foam concentrate must be topped up.
The bigger 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 could be considerable in phrases of replacement foam focus, disposal of premix and labour prices.
Mobile extinguishing methods

As the stationary foam discharge gear may be damaged in extensive fires within the tank or within the dyke area and thus lose effectiveness, cell fire screens and foam pipes may be used.
Foam pipes

Foam pipes are usually held by firefighters, making them very flexible. Yet they’ve solely restricted extinguishing agent flow charges and reaches.
Firefighting screens

Firefighting screens are discharge gadgets mounted on autos or trailers and out there in many sizes. The extinguishing agent move fee can be up to 60,000 litres/min and the attain may be as a lot as 180m if the strain of the fire pumps is adequate. They are appropriate to discharge foam, e.g., to extinguish a floor hearth in a tank, or water, to chill down a neighboring tank or the tank wall of a burning tank to have the ability to forestall it reaching the important temperature for a boilover, or to keep the flames from spreading. The accumulation of water contained in the dyke area should all the time be noticed to keep away from an overflow of the dyke.
Mobile fire displays could be supplied both by the extinguishing water of the stationary fire pumps or by cellular pumps. The injection of the froth concentrate usually takes place by way of mobile proportioners. This clearly factors towards the benefit of vitality independence for water-motor-driven proportioning pumps.
The strategic choice for the sizes of mobile units out there as back-ups is shown by the next example for the location of displays for hearth extinguishing at tanks which are 45m in diameter and 15m high.
According to NFPA, 32,000 litres of premix per minute are required. This ends in several alternate options for the screens. Generally, foam-concentrate proportioners for at least 32,000 litres/min are required, which should have the power to deal with various move charges to ensure flexibility throughout extinguishing operations. Depending on the native situations, the displays will need to hold a minimum distance to the burning tank or might not be able to be positioned close to to the tanks due to particles. In addition, it is not going to all the time be possible to position several monitors across the tank. It should be ensured the monitor has adequate throwing height in relation to the tank top, to deliver foam into the within of the tank.
The dimensioning of the complete firefighting system is made following authorized laws in addition to suggestions by associations like NFPA and isn’t checked out extra carefully within the present article.
Fig. four: Trailer with monitor M4, water motor with proportioning pump FD8000 and foam focus tank.
Lessons realized

As talked about in the introduction to Part One of this text, plainly many authorities and corporations haven’t realized the mandatory lessons from disastrous fireplace incidents of previous years. Tank farm fires within the oil and petrochemical trade don’t happen incessantly. When they do, they usually have devastating consequences. Let us bear in mind the tank farm hearth 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 fireplace for yet unknown causes. The plant had no gas warning system and no remote-controlled valves to close off the leaking fluid. In addition, some areas didn’t have fastened extinguishing techniques installed. ตัววัดแรงดันน้ำ were surrounded by one single dyke. The owner had relied on the local hearth service, which was on the spot in a short time however couldn’t take control over the fire with the equipment obtainable, partially because flammable substance was repeatedly leaking from the tank. Thirty-six hours after the hearth had damaged out, a contract was made with an exterior firefighting company to do the extinguishing work. Mobilization of equipment and foam concentrate as properly as 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 makes an attempt were remodeled three days, with foam concentrate and water shortages occurring in the meantime. In complete, over 500,000 litres of foam concentrate had been used. Instead of a hearth in the dyke space, eleven of the 15 tanks burnt down.
It is very possible that the hearth would have been extinguished quickly if the warning systems and valves had worked and a onerous and fast hearth extinguishing system had existed. It is also probable that the fireplace would have been extinguished quickly if the extinguishing operation, which succeeded eventually, had been began earlier. Both circumstances would have resulted in notably less damage.
Summing up, the next points should be discovered as a minimum. As far as they have not but been implemented, or simply partly, they want to function a foundation for discussions about one’s own fire-protection concept:
Have an acceptable fire-protection concept together with alternative scenarios which adapt to the given scenario frequently.
Always have a sufficient variety of cellular extinguishing systems as a backup to fastened extinguishing systems.
Stock an appropriate foam focus.
Ensure adequate foam focus supply.
Ensure enough water provide.
Keep well-maintained, shortly and well-accessible, strategically placed and functioning extinguishing equipment obtainable in a enough number.
Have educated personnel out there in a sufficient quantity.
Ensure a quick implementation of an appropriate plan of action.
For extra info, go to


Leave a Comment