Improvements in mechanisation should not be considered independently of safety and of environmental hazards. The need to keep gas contents within statutory limits may make the time needed to partially drain a gassy seam the effective control on face development times._x000D_
Dust levels may provide an effective control on coal extraction rates on any one face. The combination of gas and dust on high output longwall faces may make it necessary for each one to be treated as a separate mine in terms of ventilation, and the faceworkers may need special protection. Mechanisation and safety can be mutually beneficial when mechanisation combined with systematic safety assessment reduces accidents, and when a thorough study of how to reduce accidents and health risks indicates the best method to improve mechanisation.