Chromium has been used commercially in the U.S. for more than 100 years. Chromium occurs mainly in three forms, described by its valence state. Metallic chromium (Cr[0]) is a steel-gray solid with a high melting point that is used to make steel and other alloys. Chromium metal does not occur naturally but is produced from chrome ore. Trivalent chromium (Cr[III]) occurs naturally in rocks, soil, plants, animals, and volcanic emissions. Cr(III) is used industrially as brick lining for high-temperature industrial furnaces and to make metals, metal alloys, and chemical compounds. Cr(III) is also believed to be an essential nutrient but in only trace amounts. Most diets tend to be deficient in Cr(III). Hexavalent chromium (Cr[VI]) occurs through the oxidation of chromium compounds with lower valence states. Cr(VI) is considered the greatest occupational and environmental health concern, as it is the most toxic. Other valence states are unstable so they are less common. They will most likely be quickly converted to either
Cr(III) or Cr(VI).
This article summarizes common welding processes, relative fume generates, and the primary Cr(VI) exposure factors from welding operations.
