Water is used for suppression of up to 90% of all the fires. This is the most efficient, ecologically friendly, common and cheap fire extinguishing means.
Conventional fire hoses or fixed systems serve a very effective fire suppression measure and they are very widely used. Different systems have been known for centuries. Great consumption of water (more than 0,08 L/m2s) for their application requires a great number of water bottles and tanks. Damage caused by normal water spray (droplet size – 0,4…2 mm) is often greater than that caused by the fire itself, as it takes more time to suppress a fire. Available fire fighting means such as: powder, gaseous, aerosol, and other extinguishers disregarding their high efficiency are often not suitable from a safety viewpoint or by ecological, economic or any other reason.
Atomized water application has attracted great attention over the recent years. Ecologically unfriendly halon forbidden under Montreal Agreement, great costs borne by government bodies of every level to liquidate fire consequences and, particularly, their suppression consequences, the necessity of automatic fire protection system application (AFPS) aroused a keen interest in atomized water as an extinguishing agent.
The basic advantage of 200 mcm water mist droplet size is in heat absorption velocity increase from combustible gases and the flame. The total surface of the droplet volume-to-mass of all the droplet ratio is inversely proportional to droplet radius 1/R, hence the total area and the evaporation velocity grow.
The calculations exclusively based on a heat balance do not take into account the second effect – pushing aside oxygen from a flame area. With fast evaporation the water steam drives the air away in the combustion area, which proportionally decreases the burning rate of the material and heat release intensity.
The third mechanism of fire suppression is heat emission decay. The tests showed that a heat flux in the field of 1-6 mcm wavelength from a standard fire decreases by more than 4-fold at the distance of 1,7 m from them, if the room is filled with water mist.
The most difficult issue is a desired liquid droplet size for efficient fire suppression.
With no doubt we may say that atomized water is the most promising extinguishing agent at the moment.
Fire suppession mechanisms:
a) Flame blow-off by high-velocity flow;
b) High-rate surface cooling;
c) Burning surface oxygen
access
prevention;
d) Chemical burning reaction inhibition by special additives;
e) Foam film generation on inflammable liquid surfaces;
f) Improvement of liquid spread over the surface and its pore penetration
