Exposure Determination and Respirator Selection under the OSHA Hexavalent Chromium Standards
- By Paul Puncochar, CIH
- Oct 01, 2006
Compliance will facilitate the selection process for operations in which respiratory protection is used to control exposures.
The following summarizes key provisions of the Hexavalent Chromium (CrVI) standards potentially affecting the selection and use of respiratory protection for CrVI exposures in the workplace. Where applicable, guidelines assisting employers to comply with OSHA requirements are offered. This summary was prepared by the 3M Occupational Health and Environmental Safety Division and does not represent an official, legal, or complete interpretation of the regulation. If specific questions arise, the regulation itself should be reviewed and relied on, rather than this summary. A copy of the final regulation can be viewed on the OSHA Web site at www.osha.gov.
On Feb. 28, 2006, the Occupational Safety and Health Administration published the final Hexavalent Chromium (CrVI) Standard. Three separate standards covering occupational exposures to CrVI were published, including general industry (1910.1026), shipyards (1915.1026), and construction (1926.1126). A Permissible Exposure Limit (PEL) of 5 ug/m3 was established in all three versions.
OSHA estimates there are approximately 558,000 workers exposed to CrVI, of which 352,000 are exposed above the Action Level of 2.5 ug/m3 and 68,000 above the PEL. According to OSHA, potential adverse health effects associated with CrVI exposures include lung cancer, asthma, and damage to the nasal epithelia and skin. (U.S. Department of Labor, Occupational Safety and Health Administration. Occupational Exposure to Hexavalent Chromium--Fed. Reg. 71:10099-10385.)
Employers covered under the standards must determine the eight-hour TWA exposure for each employee exposed to CrVI, using either the scheduled-monitoring option or the performance-oriented option. Respirator selection for CrVI requires information on specific conditions of use, including air concentrations. Compliance with exposure determination requirements of the CrVI standards will assist employers in the selection process for work operations where respirators are used to control CrVI exposures.
Sources of CrVI Exposure
Chromium is a metal that exists in several oxidation or valence states, ranging from Cr-2 to Cr+6 (hexavalent chromium). Chromium compounds of the trivalent state (Cr+3) are the most common and occur naturally in ores such as ferrochromite, or chromite ore. Hexavalent chromium or chromate is the second most stable state; however, it rarely occurs naturally. Chromium compounds in higher valence states (CrVI) are able to undergo reduction to lower valence states in the presence of oxidizable organic matter or the presence of inorganic chemicals such as iron. Likewise, lower valence state chromium compounds are able to undergo oxidation to higher valence states.
Major users of chromium are in the metallurgical, refractory, and chemical industries. Chromium is used to produce stainless steel, alloy steel, and nonferrous alloys. CrVI is used in the chemical industry in pigments, metal plating, and chemical synthesis as ingredients and catalysts. There are about 30 major industries and processes where CrVI is used. These include producers of chromates and related chemicals from chromite ore, electroplating, welding, painting, chromate pigment production and use, steel mills, and iron and steel foundries. CrVI compounds have a lemon yellow, orange, or dark red appearance and are typically crystalline, granular, or powder. Their color characteristics and chemical properties make them suitable for use as high-quality pigments in textile dyes, paints, inks, and plastics.
Welding operations affected by the CrVI standards are those performed on stainless steel and high-chrome content carbon steel, as well as carbon steel welding in confined and enclosed spaces. Fume generated from the welding of stainless steel may contain both trivalent chromium and hexavalent chromium compounds. Fume composition and the rate of generation will depend on the welding process used and filler material used, if any. The International Chromium Development Association indicates the rate of fume generation during welding of stainless steel depends on a number of factors, including welding current (current density), arc voltage (arc length), type of metal transfer (type of filler material and/or welding process), and the shielding gas or welding atmosphere ("Chromium in Stainless Steel Welding Fumes," The Chromium File, Issue No. 9, April 2002. International Chromium Development Association, Paris, France).
The welding processes expected to generate the highest CrVI exposures are shielded-metal arc welding (SMAW) and gas-metal arc welding (GMAW). It's estimated that CrVI accounts for approximately 4 percent of the of the total chromium content in GMAW fume and up to 50 percent of chromium content in SMAW fume. Other types of welding, such as tungsten-arc welding (TIG) and submerged-arc welding (SAW), may also present exposure concerns. However, these processes generally present lower fume volumes compared to SMAW and GMAW.
This article originally appeared in the October 2006 issue of Occupational Health & Safety.