This discussion document was produced by the HSC's Advisory Committee on Toxic Substances. It considered ways to improve the contribution occupational exposure limits (OELs) make to the protection of workers' health. Under health and safety law, OELs are standards that determine the amount of a substance allowable in the workplace air. Under the current system in the UK there are two types of OEL, the Occupational Exposure Standard (OES) and the Maximum Exposure Limit (MEL). This document explains the difficulties with the current system, sets out objectives for a revised system and examines the merits of three options. It sought your views on all these issues.