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Worker Protection WorWkoerkrerPProotetcetiocn tion Welding Safe ty Assessing and controlling exposure to hexavalent chromium By Jerome E. Spear PURSUANT TO A COURT ORDER, OSHA issued a ing fumes, common welding processes and fume final rule on Feb. 28, 2006, that addresses occupa - generation rates (FGR), factors for Cr(VI) exposure tional exposure to hexavalent chromium [Cr(VI)]. from welding, exposure monitoring strategies and POSHA determined that the rule was necessary to considerations for feasible engineering controls. reduce significant health risks due to Cr(VI) expo - sure. Certain Cr(VI) compounds have been found to Major Provisions of OSHA’s Cr(VI) Standards cause lung cancer and nasal cancer in humans. OSHA issued separate but similar standards for Inhaling relatively high concentrations of Cr(VI) can general industry, construction and shipyard sectors. also cause a wide range of other health effects (e.g., Major provisions are summarized in Table 1 (p. 24). runny nose, sneezing, itching, nosebleeds, ulcers, holes in the nasal septum). Ingestion of very high Cr(VI) in Welding Fumes doses of Cr(VI) can cause kidney and liver damage, Chromium has been used commercially in the nausea, irritation of the gastrointestinal tract, stom - U.S. for more than 100 years. It occurs mainly in ach ulcers, convulsions and death. Dermal expo - three forms, described by its valence state. Metallic sures may cause skin ulcers or allergic reactions. chromium [Cr(0)] is a steel-gray solid with a high Activities with the potential for Cr(VI) exposure melting point that is used to make steel and other include: alloys. Chromium metal does not occur naturally •production and use of chromium but is produced from chrome ore. Jerome E. Spear, M.B.A., CSP, CIH, metal and chromium metal alloys; Trivalent chromium [Cr(III)] occurs naturally in is president of J.E. Spear Consulting LP •chromium electroplating; rocks, soil, plants, animals and volcanic emissions. in Magnolia, TX. He has 20 years’ •welding of metals containing Cr(III) is used industrially as brick lining for high- experience helping organizations chromium such as stainless steel or temperature industrial furnaces and to make metals, control losses and prevent injuries and other high chromium steels, or chromi - metal alloys and chemical compounds. illnesses. Spear holds a B.S. in um coatings; Cr(VI) occurs through the oxidation of chromium Industrial Engineering with a •production and use of Cr(VI)-con - compounds with lower valence states. It is consid - specialization in Safety Engineering taining compounds [such as Cr(VI) pig - ered the greatest occupational and environmental from Texas A&M University and an ments, Cr(VI) catalysts and chromic health concern as it is the most toxic. Other valence M.B.A. from Sam Houston State acid]; states are unstable so they are less common. They University. In his career, he has been •production of chromium-contain - will most likely be quickly converted to either Cr(III) corporate industrial hygiene manager ing pesticides; or Cr(VI) (OSHA, 2006). for Chicago Bridge and Iron Co. and •painting activities involving the Chromium metal is found in stainless steel and technical services manager for XL application of strontium chromate coat - many low-alloy materials, electrodes and filler mate - Specialty Risk Consulting. Spear ings to aerospace parts; rials. The chromium present in electrodes, welding regularly helps steel fabricators and •removal of lead chromate. wires and base materials is in the form of Cr(0). construction companies assess and According to OSHA, a total of Therefore, welders do not ordinarily work with control welding fume and gas 380,000 workers are exposed to Cr(VI). materials containing Cr(VI). However, the high tem - exposures, and also advises the Steel However, welders represent nearly half peratures created by welding oxidize chromium in Tank Institute and Steel Plate of the workers covered by OSHA’s steel to the hexavalent state. The majority of the Fabricators Association on regulatory standard. This article summarizes chromium found in welding fume is typically in the issues related to welding and major provisions of OSHA’s Cr(VI) form of Cr 2O3 and complex compounds of Cr(III). hexavalent chromium. standards, the nature of Cr(VI) in weld - Some metal oxides in hexavalent form are also in the 22 PROFESSIONAL SAFETY SEPTEMBER 2010 www.asse.org form of CrO 3. Pure CrO 3 is extremely unstable; how - requires a higher electrical current than SMAW, it ever, other metal oxides, especially alkali metals, produces fewer fumes since the electrode has no flux - tend to stabilize Cr(VI) compounds (Fiore, 2006). ing agents. However, due to the intense current lev - Welding fume is a complex mixture of metal els, GMAW produces significant levels of ozone, oxides. Fumes from some processes may also include nitrogen oxide and nitrogen dioxide gases. fluorides. The predominant metal fume generated •Flux-cored arc welding (FCAW) is commonly from mild, low-alloy and stainless steel welding is used for mild steel, low-alloy steel and stainless steel iron oxide. Oxides of manganese are also typically welding. This process has similarities to present. Fumes from stainless steel and some low- both SMAW and GMAW. The consumable alloy steel welding also typically contain chromium electrode is continuously fed from a spool and nickel. Chromium is usually not intentionally and an electric arc flows between the elec - added to mild steels or mild steel consumables, yet trode and base metal. The electrode wire due to the use of scrap steel in the steel production has a central core containing fluxing process, some low levels of chromium metal may be agents and additional shielding gas may present. However, in most mild steel welding, the be supplied externally. This process gener - exposure limits for fume constituents other than ates a substantial amount of fumes due to Cr(VI) (such as manganese) will be exceeded before the high electrical currents and the flux- Photo 3: Flux-cored arc welding, the PEL for Cr(VI) is reached (Fiore, 2006). cored electrode. However, FCAW gener - down-flat welding position. ates little ozone, nitric oxide and nitrogen Common Welding Processes dioxide gases. & Fume Generation Rates •Gas tungsten arc welding (GTAW) is also known as tungsten inert gas (TIG) weld - Different welding processes have different FGR. ing. GTAW is used on metals such as alu - One must have a basic understanding of these minum, magnesium, mild steel, stainless processes and their relative FGR in order to assess steel, brass, silver and copper-nickel the risk of exposures to welding fumes and gases. alloys. This technique uses a nonconsum - Following is an overview of common welding able tungsten electrode. The filler metal is processes and their relative FGR (Spear, 2004). fed manually and the shielding gas is sup - •Shielded metal plied externally. High electrical currents arc welding (SMAW are used, which causes this process to pro - or “stick welding”) duce significant levels of ozone, nitric is commonly used Photo 4: Gas tungsten arc welding. oxide and nitrogen dioxide gases. How- for mild steel, low- ever, GTAW produces very few fumes. alloy steel and stain - •Submerged arc welding (SAW) is a less steel welding. In common welding process used to weld SMAW, the electrode thick plates of mild steel and low-alloy is held manually, steels. In this process, the electric arc flows Photo 1: Shielded metal arc and the electric arc between the base metal and a consumable welding, down-flat welding flows between the wire electrode; however, the arc is not vis - position. electrode and the ible since it is submerged under flux mate - base metal. The elec - rial. This flux material keeps the fumes trode is covered with a flux material, which provides low since the arc is not visible. Little a shielding gas for the weld to help minimize impuri - ozone, nitric oxide and nitrogen dioxide ties. The electrode is consumed in the process, and Photo 5: Submerged arc welding. gases are generated. The major potential the filler metal contributes to the weld. SMAW can airborne hazard with SAW is the fluoride com - produce high levels of metal fume and fluoride expo - pounds generated from the flux material. sure; however, SMAW is considered to have little Abstract: This article potential for generating ozone, nitric oxide and nitro - Fume Generation Rates summarizes major gen dioxide gases. The primary sources of information when deter - provisions of OSHA’s •Gas metal arc mining the components likely to be in the fume is Cr(VI) standards, the welding (GMAW) is the MSDS and/or the manufacturer’s technical data nature of Cr(VI) in also known as metal sheet of the consumable electrode/wire. About 90% welding fumes, com - inert gas (MIG) to 95% of the fumes are generated from the filler mon welding process - welding. GMAW is metal and flux coating/core of consumable elec - es and fume typically used for trodes (Lyttle, 2004). generation rates, fac - most types of metal Since the base metal weld pool is much cooler tors for Cr(VI) expo - and is faster than than the electrode tip, the base metal contributes sure from welding, SMAW. This process only a minor amount of the total fumes. However, exposure monitoring Photo 2: Gas metal arc welding. involves the flow of the base metal may be a significant factor of the strategies and consid - an electric arc between the base metal and a continu - fume exposure if the metal or surface residue con - erations for feasible ously spool-fed solid-core consumable electrode. tains a highly toxic substance (e.g., chromate-con - engineering controls. Shielding gas is supplied externally, and the elec - taining coatings, lead-based paint). trode has no flux coating or core. Although GMAW In addition to the welding process, studies have www.asse.org SEPTEMBER 2010 PROFESSIONAL SAFETY 23 TaTabblee1 1 Summary of Major Provisions of OSHA’s Final Rule for Hexavalent Chromium shown that FGR is influenced by the following fac - •Arc voltage.
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