Occupational Exposure Limit (OEL)

An upper limit on the acceptable concentration of a hazardous substance in workplace air for a particular material (e.g., gases, vapors and particles). It is typically set by competent national authorities and enforced by legislation to protect occupational safety and health.

(Sources:  Wikipedia and ILO. http://www.ilo.org/safework/info/publications/WCMS_151534/lang--en/index.htm)