For the purposes of this chapter, the following definitions apply
1° Fresh air: air taken from the open air away from sources of pollution;
2° Recycled air: air taken and reintroduced into a room or group of rooms. Air taken outside pollutant collection points and reintroduced into the same room after thermal conditioning is not considered to be recycled air;
3° Non-specific pollution rooms, rooms in which pollution is linked solely to human presence, with the exception of sanitary rooms;
4° Specific pollution rooms, rooms in which dangerous or annoying substances are emitted in the form of gases, vapours, solid or liquid aerosols other than those linked solely to human presence, as well as rooms which may contain sources of potentially pathogenic micro-organisms and sanitary rooms;
5° Mechanical ventilation, ventilation provided by a mechanical installation;
6° Permanent natural ventilation: ventilation provided naturally by the wind or by the difference in temperature between the outside and inside;
7° Total dust: any solid particle whose aerodynamic diameter is no more than 100 micrometres or whose limiting speed of fall, under normal temperature conditions, is no more than 0.25 metres per second;
8° Alveolar dust, any dust likely to reach the pulmonary alveoli;
9° Aerodynamic diameter of a dust, the diameter of a sphere of density equal to unity having the same falling speed under the same conditions of temperature and relative humidity.