The TLV of a chemical is the level that a worker can be exposed day after day for a working lifetime without adverse effects. The American Conference of Governmental Industrial Hygienists (ACGH), a private, creates them not for profit, non-governmental scientific organization, made up of industrial hygienists and other occupational safety professionals. Among its duties, is the creation of the TLVs that can be used to help evaluate worker exposure to chemicals. Industrial hygienists regard them as the best available benchmarks.
Unlike the Permissible Exposure Limits (PEL) created by OSHA, they are not consensus standards, which are based upon health effects, as well as technical, economic, and feasibility considerations. The TLVs are health-based values that are created by committees that look at published and peer reviewed epidemiologic, toxicological, and other scientific studies.