The Control of Substances Hazardous to Health Regulations (COSHH) require that Local Exhaust Ventilation Plant is examined by a competent person and an examination should be completed at intervals dependent on the trade/business and the application of equipment.
COSHH - Regulation 9 (2)
Where engineering controls are provided to meet the requirements of regulation 7, the employer shall ensure that thorough examination and testing of those controls is carried out -
(a) in the case of local exhaust ventilation plant, at least once every 14 months, or for local exhaust ventilation plant used in conjunction with a process specified in Column 1 of Schedule 4, at no more than the interval specified in the corresponding entry in Column 2 of that Schedule; or
(b) in any other case, at suitable intervals.