Recently, FireDos published an article focused on the ‘Use of foam for fire fighting in tank farms of the oil- and petrochemical industry’. In that publication the focus was put on common tank farm configurations, laws and regulations, typical incidents, foam as an extinguishing agent, extinguishing systems including foam concentrate proportioning and firefighting monitors, and lessons learnt from disastrous fire incidents of past years. For access please follow the following link: www.firedos.com/en/news-overview/news/use-of-foam-for-fire-fighting-in-tank-farms
Here the focus will be on mobile extinguishing solutions and technology. In some cases, these technologies are used as the main means of extinguishing; in other cases they may be available as a backup in case the fixed systems are not sufficient for the fire scenario or because the fixed systems may have been damaged by or in the course of the fire.
In any case the following categories of technology are necessary:
Water supply
Generally, for big incidents, the water supply can come from one of two sources. Where available the supply will come from the fire water ring main. This will generally be fed through fixed installed water pumps delivering the required water flow and pressure. Otherwise, the water will come from water reservoirs in the vicinity of the fire and will be pumped to the emergency site using mobile equipment. The systems will generally consist of one or more hydraulic-driven portable submersible floating pumps that are linked to diesel-powered hydraulic powerpacks. For firefighting purposes, the submersible pumps will often be coupled to booster pumps that will increase the pressure of the water flow. Depending on the requirements, these systems are available in various sizes ranging from 8,000 lpm at 10 bar (2,100 gpm at 145 psi) to 45,000 lpm at 12 bar (12,000 gpm at 175 psi).
Foam supply
The foam concentrate for mobile systems will most likely be supplied through foam tender or tank trucks. Their capacities will depend on the max allowable loads for the roads they must drive on. Sizes range from several thousand litres (under 1,000 gallon) to 20,000 litres (5,250 gallon).
Notice should be taken that the minimum foam concentrate quantity available should always be sufficient to allow extinguishing of the largest protected object, or of the objects to be protected simultaneously. When protecting big objects, where high water flows are to be expected, the foam concentrate for refilling the tanker trucks should not be stocked in IBC containers. At water flows of e.g. 18,000 lpm (4,750 gpm) and a foam concentrate proportioning rate of 3% the foam concentrate will be depleted at a rate of approx. 540 lpm (143 gpm). This means that an IBC must be emptied within 2 minutes. This will be a challenge with Newtonian fluids and may be next to impossible with high viscous, pseudoplastic fluids. Here good advance planning and training is essential.
Water transfer
For mobile systems the water transfer must be done using hoses. These hoses may have to be laid over distances of several thousand metres. When having to use large volumes of water, hoses of larger diameters are essential. The larger the diameter, the fewer hoses must be laid and the smaller the pressure loss. Standard big-volume hoses are available in 152mm (6in), 204mm (8in), 254mm (10in) and 308mm (12in). Compared to one 12in hose you must use 4 x 6in or 3 x 10in or 2 x 8in hoses to transport the same volume of water. Beside the additional workload in laying the hoses and the space necessary, the pressure drop will be significantly higher when using smaller hoses. As with the bigger pressure drop in smaller hoses, the pressure drop also decreases when reducing the water flow rate. As can be seen in Picture 1, the pressure drop when using 2 x 12in hoses is approximately 5.8 bar per 1,000m (84psi per 3,300ft), whereas it is only about 1.8 bar per 1,000m (26psi per 3,300ft) when using 4 x 12in hoses.
Especially when dealing with large-diameter hoses it is advantageous to use hose handling equipment. The most common are hose boxes for mechanized laying of the hoses and hose recovery units for the retrieval. In Pictures 2 and 3 you can see an example of a hose deployment unit and a hose recovery unit.
If the pressure drop in the hoses, due to too high distances, is too big, booster pumps can be introduced to the system. The unit consists of a water pump, direct driven by a powerful diesel engine. Capacity of these units can be up 45,000 lpm (12,000gpm) @ 12 bar (175psi). The systems are programmed to automatically maintain the preset outlet pressure within specified flows. Picture 1 shows the use in Option 1.
Foam proportioning
Foam proportioning for mobile units can generally be done in several ways. The most basic is the use of self-inducting fire monitors. The disadvantage would be the requirement to have the foam supply directly at the fire monitor, as suction is not possible over long distances. In addition, when using highly viscous pseudoplastic foam concentrates, the usage may be very limited.
More common is the use of hydraulic-driven foam dosage pumps. These units are available as stand-alone systems with their own diesel engine to drive the foam pump and generate power for the flow meters used. The water flow rate is measured by a flow meter and the control system calculates and adjusts the correct foam concentrate quantity via a control valve. The foam concentrate is injected into the extinguishing water flow by the foam concentrate pump. If there is a change in the flow rate of the firefighting water, the amount of injected foam concentrate is regulated by the control valve. The system’s advantage lies in the precise proportioning of the foam concentrate, independent of the extinguishing water pressure or flow rate, and a very low pressure drop. Depending on which system is used, the lag between the change in water flow and adjusting the foam concentrate flow may be several seconds up to 20 seconds. If the extinguishing scenario requires a constant change in water flow, e.g. due to pulsating outlet devices or the switching on and off of outlet devices, the proportioning rate may not be correct if the foam concentrate adjustment time is long.
A very effective alternative is the use of a water motor installed in the extinguishing water flow line and a foam concentrate pump which is connected directly to the water motor, as offered by FireDos in its GEN III proportioning systems. Water motor and pump form one compact unit. Upon activation of the fire pumps, rotation in the water motor starts. The direct coupling to the foam-concentrate pump enables immediate foam concentrate injection into the extinguishing water. If the flow rate changes, the amount of foam concentrate is adapted immediately. The advantage of the system is its independence from external energy sources as well as a precise and immediate foam concentrate proportioning regardless of the extinguishing water flow rate or pressure. If a piston or plunger pump is used, adjustment or calibration is not necessary since the water motor and the pump are volumetric devices firmly connected to each other. The correct proportioning rate is 100% tested by FireDos in its in-house test facility and certified over the wide water-flow range the system offers. The system is also ideally suited to proportion high-viscosity foam concentrates.
The power independency, direct injection of the foam concentrate and wide flow range clearly points towards the advantage of using trailer-mounted water-motor-driven proportioning pumps.
Outlet devices
Usually, only fire monitors or hand lines with foam pipes are used as outlet or discharge devices in mobile firefighting scenarios.
Foam pipes are normally held by firefighters, making them very flexible. Yet they have only limited water or foam agent flow rates and reaches. Their advantage on the other hand is the flexibility in use in regard to the possibility of rapidly being able to change the set-up location.
Firefighting monitors are discharge devices designed for bigger flow rates. For smaller flow rates up to 2,000 lpm (500gpm) they can be hand carried for placement on the ground. At 8 bar (120psi) they will have a throwing range of 40–50m (130ft to 150ft).
Fire monitors with larger flows will be mounted on vehicles or trailers and are available in many sizes. For the FireDos line of fire monitors the extinguishing water flow rate can be up to 60,000 lpm (16,000gpm) with a reach of 130m (420ft) at an inlet pressure at the monitor flange of 8 bar (120psi) and, if the pressure of the fire pumps is sufficient, the reach can be up to 160m (520ft) at 12 bar (175psi). They are suitable to discharge foam, e.g. to extinguish a surface fire in a tank or bund, or water, to cool down a neighbouring tank or the tank wall of a burning tank to prevent it reaching the critical temperature for a boil over. In special applications the additional use of powder is possible.
Combined units
While the above has introduced individual components of the mobile firefighting system, combined units are also available.
Picture 4 shows a FireDos trailer with a proportioning system FD20000/1.5/1.5 (max flow 20,000 lpm (5,300gpm) with two proportioning pumps of 1.5% each) and a M9 fire monitor. Picture 5 shows a FireDos trailer with a proportioning system FD8000/0.5 (max flow 8,000 lpm (2,100gpm) with a 0.5% proportioning pump), a fire monitor M4 and foam agent tanks. With a 0.5% foam agent, the max extinguishing time of the trailer, without refilling foam concentrate and at max flow rate of 8,000 lpm, is approx. 25 minutes.
As an alternative to trailer-mounted units, it is also possible to combine different components on A-frames that can be handled by forklifts or equipped with hook arms to allow easy on and offloading. Picture 6 shows a frame-mounted system with hook arm housing a FD15000/3/3(1) (max flow 15,000 lpm or 4,000gpm) with an adjustable 1%, 3% or 6% proportioning pump), a M7 fire monitor and six IBC foam concentrate containers.
For more information on FireDos, water-motor-driven proportioners, fire monitors and trailers, go to www.firedos.com.
About the Author
Frank Preiss is Managing Director of FireDos GmbH. FireDos are experts in foam concentrate proportioners and monitors for firefighting, focusing on their in-house-developed leading technology and customer service.
