This guide is intended to serve as a source of general industrial hygiene information for workers, employers, and occupational health professionals. Key information and data are presented in abbreviated tabular form for 398 chemicals or substance groupings that are found in the work environment and that have existing Occupational Safety and Health Administration (OSHA) regulations. The industrial hygiene information found in the Guide should help users recognize and control occupational chemical hazards. The Guide lists chemical names and structural formulas, Chemical Abstracts Service (CAS) and the NIOSH Registry of Toxic Effects of Chemical Substances (RTECS) numbers and Department of Transportation (DOT) identification and guide numbers. Exposure limits, physical descriptions, chemical and physical properties are listed for the compounds along with an indication of the concentration at which the compound is immediately dangerous to life or health (IDLH). Additional information includes recommendations for respirator selection, symptoms of exposure, and first aid data.