A distinction is made between natural aeration (i.e. by opening windows) and artificial ventilation (i.e. by means of fans or air conditioning systems). Mechanical ventilation should be provided if natural aeration is insufficient, which can primarily be ascribed to the following causes:
- the aeration cross-sections of the room correspond to less than two per cent of the floor surface area;
- the depth of the room exceeds 10 m, with no possibility for cross ventilation;
- sufficiently good air quality cannot be attained because of a number of factors, such as, for example, excessive smoke, vapour or heat development;
- natural aeration would be associated with an intolerable noise exposure (i.e. windows opening on to highways)