An initial test of an LEV system to check it is effective at protecting workers. It is done in four stages by a competent person, usually after an LEV system has been installed or modified
Health and Safety Executive (HSE), Glossary of Terms: Local Exhaust Ventilation, HSE, Merseyside, England, UK 2012. www.hse.gov.uk/lev/glossary.htm, (Hlth and Sfty - Brit) {704}