Foam systems

foam systems

Proportional response

Water-driven positive pressure foam proportioning systems are growing in popularity. David Owen from Hawkes Fire explains the practical, environmental, and financial benefits of a proportional response to foam attack.

Foam proportioners from Firedos are made up of two main elements: the water-powered motor and the mixer pump. No other power source is required other than the water supply.

It is often said that the fire suppression industry operates on an ‘evolution not revolution’ approach. Game-changing new developments rarely come out of nowhere to shake up the industry. Instead, technology is refined and redesigned to keep pace with modern materials and techniques and changes in operational practices.

David Owen from Hawkes Fire believes that the increased use of wind-turbine proportioning for fixed extinguishing systems and mobile fire service units is an example of this evolution. Hawkes Fire is a distributor of Firedos, one of the manufacturers of such systems. Owen explains the Firedos targets those areas of fire suppression it believes can be improved on, and focuses on two main product areas: foam proportioning and water/foam monitors.

Foam proportioners from Firedos are made up of two main elements: the water-powered motor and the mixer pump. No other power source is required other than the water supply. There is a proportional relationship between volumetric flow rate and the rev speed of the motor. Changes in the volumetric flow rate have a direct effect on the speed of rotation of the motor drive shaft, and the water-powered motor drives the mixing pump.

‘One of the key benefits of these systems is the flexibility to deal with different flow rates,’ Owen explains. ‘Units can accommodate flow rates from as low as 100lpm up to 22,000lpm and each unit has a turndown ratio of 10:1, providing a range of options in each size. The systems also offer flexibility on the fireground because they can be mounted at various

points in the supply chain.’ Owen explains that the units can usually be mounted far enough away from the fire that it won’t pose an unacceptable risk to firefighters. 'The run-out of hose or fixed pipework is only limited by the pressure and flow available to mount the foam attack. In addition, because the piston pump is a positivedisplacement pump, it has none of the problems associated with inductors. Nor does it require specialised discharge devices other than those in common use by both municipal and industrial fire and rescue services.'

Owen also argues that the flexibility in flow rates means that not all hazards need to be dealt with using large volume firefighting techniques. ‘These techniques certainly have their place, but it is also important to remember that numerous hazards can be dealt with using mid-range flow rates. This kind of situation can be accommodated by using Firedos units of typically around 6,000lpm in conjunction with monitors or fixed pourers.’

Foam proportioning can also be beneficial for environmental reasons as these systems can provide more accurate and less wasteful foam proportioning alongside testing that doesn’t discharge to ground.

‘Accurate mixing can minimise both wasteful rich mixtures and make the best use of modern 1% concentrates,’ Owen explains. ‘With a directly proportional system, stepless variable adjustment is possible so that injection can range from 0.1% to 1%, 0.3% to 3% and 0.6% to 6% and is not subject to the back pressures that affect inductors.’

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foam systems

AUTOMATIC EXTINGUISHMENT FOR STORAGE TANK FIRES

Fires at industrial facilities for flammable liquids are among the most dangerous conflagrations that firefighters can attend. Potential hazards include explosions, toxic fumes, and liquid jet fires, and it can take hours if not days to bring a blaze under control.

Many such sites rely on the services of local fire brigades, but there are built-in systems that can deliver foam to a fire automatically within minutes of a fire breaking out. Swiss Fire Protection R&D is one manufacturer of such systems, and the company claims that its Pressurised Instant (Pi) Foam System can put out any storage-tank blaze in three minutes or less.

The system is constructed around a pressurised vessel in which foam is stored well in advance of any fire event. When a storage tank ignites, sensors send a signal that opens the vessel’s valves, unleashing large quantities of foam that inundate the tank surface. It smothers the flames within three minutes without needing to put a single firefighter’s life at risk.

The system is suitable for any facility that relies on foam to extinguish fires and doesn’t require any external energy source. A system of pipes guides the foam around the facility and applies it inside the tanks through apertures in the pipework. It doesn’t use pumps, foam chambers, foam generators, or proportioning systems.

The vessel is pressurised by the introduction of a gas mixture that dissolves inside the premix foam solution. This gas mixture will vary according to the features of the stored product and local environmental factors such as temperature, which will affect the pressure requirements. And, as the volume of foam in the system is pre-calculated, there is no possibility of the foam overflowing the tank or of foam being lost during application.

Swiss Fire Protection R&D has tested the performance of a number of commercial, off-the-shelf foams with Pressurised Instant Foam System and has also developed a fluorine-free alternative. This is currently undergoing various approvals.

The relatively high viscosity of many 1% foams isn’t a problem for a water-driven positive-displacement piston pump. ‘Wetted parts are either ceramic or highly resistant plastics so aggressive foam concentrates don’t affect the mechanism. If the unit will be used with seawater or in harsh environments, alternative materials such as titanium are available.’

When compared with traditional bladder tanks, a foam proportioner also significantly reduces wastage in testing. Where bladder tanks require a certain amount of foam solution to be run through the discharge device in order to test the foam proportioning rate via a refractometer, a Firedos proportioner, for example, returns foam concentrate to the atmospheric

storage tank and flow meters are used to check water throughput.

Firedos also makes proportioning units for fire appliances or trailers, which are so compact they can fit in a locker. Owen says that these are particularly useful for when foam or a wetting agent is used on Class A fires to reduce the surface tension of the water. ‘The aim is to improve adhesion, penetration and retention time of the agent on the burning material, transferring more energy and improving the cooling effect of the firefighting media. The ability to accurately proportion these products saves money, especially as they are used in very low concentrations, from 1% down to 0.1%.’

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