In 1880, the American company F.E. Myers developed a backpack system with a lance using water droplets to extinguish small forest fires. Ten years later Grinnell launched its ‘pepper pot’ nozzle. A few decades later several companies were involved in the application of water mist, among those the German company Lechler. And Factory Mutual’s engineering division started to carry out first tests comprising small droplet nozzles in the 1940s.
“However, the interest in water mist remained meagre. In Europe and the USA scientists were busy with research. But commercially speaking water mist made no real impact. It simply did not meet the requirements for fixed installations and was therefore mainly used to fight fires manually”, explains IWMA General Manager Bettina McDowell.
But then, in the late 1980s the Montreal Protocol on “substances that deplete the ozone layer” was executed. And on 7th April 1990 a fire on the “Scandinavian Star” killed 158 people – nearly 50% of all passengers.
Before the Montreal protocol had been signed, halon – a bromine-based chemical fire suppression agent – had been used to extinguish fires. Its phasing out smoothed the way for water mist fire-suppression.
The fire on the “Scandinavian Star” eventually led to a reform of the International Maritime Organisation’s (IMO) fire safety requirements and installation guidelines. Fire test procedures for alternative sprinkler systems were developed.
In Sweden, there had already been some deployment on high-pressure water mist since 1975. Topics had been the protection of hotels and passenger cabins as well as research into flammable liquid hazards. Straight after the fire on the ferry the interest in water mist skyrocketed – as far as the marine sector was concerned.
In 1998, the International Water Mist Association (IWMA) was founded to be an exchange and networking platform, to supports scientific research and to get involved in standardization work.
Of course a lot of people want to know how water mist works. The answer is simple: A fire triangle consists of a combustible material, heat and oxygen. Water mist removes two of these elements: heat and oxygen. It does so by jetting water at low, medium or high pressure through specially designed nozzles. The size of the droplets decreases as the system pressure increases. The result are droplets with an altogether larger surface and water turning into steam. Consequently, the system rapidly reduces the temperature as well as the oxygen at the flame front. Energy is removed from the fire and with its cooling effect water mist prevents re-ignition.
The technology needs a fairly small amount of water. Apart from that it is reliable and environmentally friendly.It does not contribute to global warming, it does cause neither massive water damage, not does it cause ozone depletion. Plus it does not harm people. As far as standards are concerned the technology has become well established. In 1996, the National Fire Protection Association was the first body to create a standard. After that other standards and guidelines were developed by FM and UL. Now the European Standard prEN 14972 is well on its way.
Water mist fire fighting systems have been in use for over twenty years in their present stage of technology and have proven their value over a wide range of applications such as: tunnels, machinery spaces, offices, computer rooms, escalators etc. In some of these applications water mist is indeed favorable due to the way the small water droplets interact with fires. In other situations it is the limited water requirement that makes water mist systems the better choice.
For more information, go to www.iwma.net
