Although interest in high pressure water mist systems is growing, the scale of the contribution they can make to fire suppression is not yet fully appreciated.
Andrew Shiner looks at how they work, and how they can be used to overcome some of the issues affecting conventional suppression systems.
High-pressure water mist systems convert water (at a pressure of 100bar) to a fine atomised mist. This mist evaporates very quickly creating a significant cooling effect, which is the primary fire extinguishing mechanism. As the water evaporates it expands in volume, helping to displace oxygen from the flame and further aiding fire extinguishing.
Water mist systems combine some of the characteristics of conventional deluge or sprinkler water-based fire suppression systems with those of gaseous fire suppression systems, and are very effective at reducing the impact of radiant heat, which is beneficial in reducing fire damage. They are an obvious choice from an environmental point of view as they contain nothing but pure water, so are 100 per cent safe for people, property and the environment.
Economic impacts
One of the main advantages of high pressure water mist is the minimal amount of water discharged in the event of a fire, so ensuring very little consequential damage. These factors make it an ideal solution for the protection of electronic equipment, data processing centres, offices and hotels. High pressure water mist is also suitable for the heritage sector to help protect irreplaceable archives, old manuscripts and historic artefacts. Fire tests conducted in association with Historic Scotland, for example, showed that only those documents that were actually set alight for the purpose of the test were damaged; all other documents near the seat of the fire remained unscathed or dried out naturally within 30 minutes.
Tyco Fire & Integrated Solutions’ MicroDrop system, for example, typically uses 10 per cent of the water per square metre that traditional water based systems use. The fine water mist further limits fire damage by washing smoke particles out of the contaminated air. This reduction in water use and the increased protection of a building’s contents, have the secondary benefit of helping customers secure lower insurance premiums.
Where avoiding production downtime is a key issue, high pressure water mist systems are very well suited. The time required to re-instate such a system is minimal compared to a typical gaseous fire suppression system, or any traditional system that requires cylinders to be refilled or control valves to be reset. The intelligent use of water ensures that such systems are suitable for many industrial applications including engine test cells, rolling roads, hydraulic pits, industrial ovens and paint spray booths.
Hazardous materials
Water should not be used to extinguish a fat burning fire, because water applied in volume penetrates the hot oil or fat, and the resulting rapid expansion can cause a fat ‘explosion’. The use of water mist avoids this by applying very fine droplets which do not penetrate the hot oil or fat, and this has led to its widespread adoption in the food production industry. The secondary benefit is that it lowers the temperature of the hot oil, reducing the possibility of re-ignition. Additionally, expensive clean-up operations are avoided. In a commercial environment where ‘just-in-time’ deliveries are vital, this is invaluable in reducing downtime.
Similarly, one of the key challenges in industrial areas is how to contain a fire fuelled by flammable liquids, with paint spray booths and paint drying ovens being typical examples. High pressure water mist lends itself well to this challenge, with conventional nozzles discharging water to cover the hazardous area itself, while a row of micro-nozzles mounted on a pipe create a curtain of water mist to cover any large openings to the area. This improves compartmentalisation and reduces the amount of toxic fumes and gas that can escape into the surrounding area.
There are many situations where conventional water based systems are not suitable, for example in wind farms. The very nature of their design and construction means high pressure water mist systems are an ideal solution for wind turbine protection. The very low water supply requirements of these systems, coupled with the small and lightweight pipe diameters and compact pump design, ensure that a system can be fully contained within the turbine housing. The water tank on the pump contains a heating element to make the unit frost-proof, and there is battery back-up in case of power failure.
Looking ahead
According to a report prepared in the UK in 2005 by the Building Research Establishment, there are “still a number of myths, misunderstandings and a lack of knowledge about water mist systems”. The key issues are a lack of understanding of both how water mist systems work, and the very appreciable difference between these and sprinkler systems. What is undeniable, however, is that water mist is an emerging and credible fire protection technology that is the obvious choice where little water is available, and where the effects of discharge of the fire protection system are a major consideration.
With the growing concern for the environment and an increasing desire to adopt sustainable solutions, high pressure water mist is a firefighting technology that can rightly take its place alongside the other leading solutions. With these in mind, I believe that we will see an ever increasing take-up of these systems in many public spaces, and in key industries such as food production, the automotive sector and electrical equipment manufacture.
Andrew Shiner is Director of Strategic Products (Europe, Middle East and Africa) for Tyco Fire and Integrated Solutions
