This criteria document is derived from the NIOSH evaluation of critical health effects studies of  occupational exposure to hexavalent chromium (Cr[VI]) compounds. It provides recommendations for controlling workplace exposures including a revised recommended exposure limit (REL)  derived using current quantitative risk assessment methodology on human health effects data. This  document supersedes the 1975  Criteria for a Recommended Standard: Occupational Exposure to  Chromium(VI)  and  NIOSH Testimony to OSHA on the Proposed Rule on Occupational Exposure to  Hexavalent Chromium  [NIOSH 1975a, 2005a].  Cr(VI) compounds include a large group of chemicals with varying chemical properties, uses, and  workplace exposures. Their properties include corrosion-resistance, durability, and hardness. So  -  dium dichromate is the most common chromium chemical from which other Cr(VI) compounds  may be produced. Materials containing Cr(VI) include various paint and primer pigments, graphic  art supplies, fungicides, corrosion inhibitors, and wood preservatives. Some of the industries in  which the largest numbers of workers are exposed to high concentrations of Cr(VI) compounds  include electroplating, welding, and painting. An estimated 558,000 U.S. workers are exposed to  airborne Cr(VI) compounds in the workplace.