On Board Trains Occupational Health and Safety Regulations

7.7 Every ventilation system used to control the concentration of an airborne hazardous substance shall be so designed, constructed and installed that

• (a) the concentration of the airborne hazardous substance does not exceed the values and percentages referred to in sections 7.20 and 7.21; and

• (b) if there is no value or percentage set out in respect of the airborne hazardous substance, its concentration is not hazardous to the health or safety of employees.