National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limits (RELs): NIOSH RELs are authoritative Federal agency recommendations established according to the legislative mandate for NIOSH to recommend standards to OSHA. RELs are intended to limit exposure to hazardous substances in workplace air to protect worker health. In developing RELs and other recommendations to protect worker health, NIOSH evaluates all available medical, biological, engineering, chemical, and trade information relevant to the hazard. NIOSH transmits its recommendations to OSHA for use in developing legally enforceable standards. NIOSH also publishes its recommendations in publicly available sources such as the NIOSH Pocket Guide to Chemical Hazards, Criteria Documents, Current Intelligence Bulletins, Alerts, Special Hazard Reviews, Occupational Hazard Assessments, and Technical Guidelines. See more from topic source: https://www.osha.gov/html/a-z-index.html