The OSHA PEL is the maximum legal limit for worker exposure to a chemical substance or physical agent in the workplace. PELs are enforceable standards set by OSHA and are typically specified in 29 CFR 1910.1000 Tables Z-1, Z-2, and Z-3 for various substances. PELs are most often expressed as an 8-hour time-weighted average (TWA), but for some chemicals, OSHA also specifies short-term exposure limits (STELs) or ceiling values.