Action levels are used by OSHA and NIOSH to express a health or physical hazard. They indicate the level of a harmful or toxic substance/activity which requires medical surveillance, increased industrial hygiene monitoring, or biological monitoring. Action levels are generally set at one half of the permissible exposure limit (PEL), but the actual level may vary from standard to standard. The intent is to identify a level at which the vast majority of randomly sampled exposures will be below the PEL. MSDS Relevance: Action levels are not defined for all compounds. There are OSHA standards for a variety of chemical substances such as asbestos, benzene and lead. There are even OSHA action levels for noise exposure! If you are dealing with a substance which has a PEL and you exceed 50% of the PEL, you need to take appropriate action to monitor the levels and/or employee health on a regular basis. Consult your industrial hygienist, safety officer or local OSHA compliance (not enforcement) office for assistance (See below for contact information). See: EPCRA, Heavy Metal, PEL, PPE, SARA, Ventilation