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Threshold Limit Values are the exposure guidelines industrial hygienists use to estimate safe concentrations of hazardous substances in the workplace. They are published by the American Conference of Governmental Industrial Hygienists, which provides TLVs and Biological Exposure Indices to help practitioners assess risk and design controls. These guidelines are recommendations, not legally enforceable standards—regulatory limits like OSHA’s permissible exposure limits may be informed by TLVs but carry legal weight only when adopted. The other organizations listed do not publish TLVs: ANSI develops standards, NRC is a research body, and FEMA handles emergency management.