Looking back it becomes clear that the idea behind water mist technology is not new. In 1880 the US-American company F.E. Myers developed a back pack system with a lance. Ten years later Grinnell launched its ‘pepper pot’ nozzle.
Both system fought fires using small water droplets. Only a few decades later several companies were involved in the application of water mist, among those the German company Lechler which had designed a multiple orifice nozzle which at the time was called “water dust nozzle”. And Factory Mutuals’s engineering division started to carry out their first tests comprising small droplet nozzles in the 1940s.
However, the interest in water mist remained small for quite some time. In Europe and the USA scientists were busy with research. But commercially speaking water mist made no real impact at the time. It simply did not meet the requirements for fixed installations and was therefore mainly used to fight fires manually.
It was only in the 1990s that water mist started to push forward. This was mainly due to two incidents.
Two incidents paved the way
In the late 1980s the Montreal Protocol on “substances that deplete the ozone layer” was executed. On the morning 7th April 1990 a fire on a passenger ferry 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 which has in consequence become a crucial field of study, research and development.
In fire protection it often takes severe incidents to bring about changes. The fire on the “Scandinavian Star” eventually led to a reform of the International Maritime Organisation’s (IMO) fire safety requirements and installation guidelines and fire test procedures for alternative sprinkler systems were developed.
In Sweden there had already been a great deal of deployment on high-pressure water mist between the years 1975 and 1990. The main topics had been systems to protect hotels and passenger cabins as well as research into flammable liquid hazards. In consequence the fire on the “Scandinavian Star” gave those who had carried out this work the chance to present their results in June 1990 – only two months after the disaster.
This marked the establishment of the Swedish company Ultra Fog. Only six months later Marioff from Finland started to develop high-pressure water mist fire fighting systems.
On 4th April 1998 the International Water Mist Association (IWMA) was founded. The intention was and is to be a platform for companies, institutes, research bodies, authorities having jurisdiction, insurance companies and individuals involved in water mist technology.
Every year the IWMA hosts several seminars as well as an international conference. The objective is to collect and distribute knowledge but also to provide events for networking. Apart from this the association supports scientific research and is involved in standardization work.
How does it work?
There are basically four questions that people ask when it comes to water mist: How does it work? How effective is it? How much does it cost? And: How about standards?
A fire triangle consists of: a combustible material, heat and oxygen. Water mist removes two of these elements: heat and oxygen. (traditional sprinkler systems only remove the heat) It does so by jetting water at low, medium or high pressure through nozzles which are specially designed for this purpose. The size of the droplets decreases as the system pressure increases.
This results in 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. Thus, energy is removed from the fire. Water mist also prevents re-ignition due to its cooling effect.
Low pressure systems work with less than 12.5 bar (175 psi). The span of medium pressure lies between 12.5 and 35 bar (490 psi). High pressure systems can reach a pressure of up to 120 bar (1680 psi). Each of these systems has its eligibility, low pressure being suited for different purposes than medium or high pressure and vice versa.
The water mist technology can be a cost effective way of fire protection as it needs a fairly small amount of water only. Apart from that it is reliable and environmentally friendly, it does not contribute to global warming, it does not cause massive water damage, it does not cause ozone depletion and 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 – the “NFPA 750 Standard for Water Mist Fire Protection Systems”. After that other standards and guidelines have been developed by FM (FM 5560), the European Committee for Standardization (CEN TS 14972) and others. As mentioned before, the IWMA and its members are very much involved in this.
Nowadays water mist fire-fighting systems are well established. They 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.
Main Image from WMFE