A fire needs fuel, heat and comburent. The water mist systems act on the first two elements. They are able to generate a very fine mist of water, with drops of tens or hundreds of mm in diameter. By absorbing heat in proportion to the contact surface, the drops, expanding by heating, remove energy from the fire, hinder the contribution of comburent and absorb radiant heat. The water mists have been used in fire-fighting since the 1880s but it was only a hundred years later that water mist technology became established and was used in fixed extinguishing systems. Perfectly eco-compatible, it is a technology that economises on the use of extinguishing agents (using flow rates from one tenth to one hundredth less than sprinklers) and, in proportion to the nebulisation rate, minimises wetting (and related damage). This means that water mist systems are suitable for situations in which the available water reserves are limited (for example on the top floors of very tall buildings) or where, for reasons of weight and compatibility, the distribution system must have a minimal impact (pipes of just 15 -20 millimetres make the system particularly suitable for ships and areas of artistic interest). Terrestrially, the main uses are the protection of engine rooms, ordinary risk residential areas and data centres.