The COSHH Regulations are concerned with the health of employees in relation to their exposure to harmful substances, particularly airborne contaminants. COSHH places a great deal of emphasis on the control of substances to reduce exposure. Featuring prominently under control is ventilation, whether it be dilution ventilation or localised extract. The Building Services Engineer has and important and prominent role to playunder COSHH in relation to ventilation and control measures, in particular in defining performance criteria and establishing examination and testing procedures.