![]() ![]() The electrode wire has a central core containing fluxing agents and additional shielding gas may be supplied externally. The consumable electrode is continuously fed from a spool and an electric arc flows between the electrode and base metal. This welding process has similarities to both SMAW and GMAW. However, due to the intense current levels, GMAW produces significant levels of ozone, nitrogen oxide, and nitrogen dioxide gases.įluxed-Cored Arc Welding (FCAW) is commonly used for mild steel, low alloy steel, and stainless steel welding. Although GMAW requires a higher electrical current than SMAW, GMAW produces fewer fumes since the electrode has no fluxing agents. Shielding gas is supplied externally, and the electrode has no flux coating or core. This process involves the flow of an electric arc between the base metal and a continuously spool-fed solid-core consumable electrode. GMAW is typically used for most types of metal and is faster than SMAW. Gas Metal Arc Welding (GMAW) is also known as metal inert gas (MIG) welding. SMAW can produce high levels of metal fume and fluoride exposure however, SMAW is considered to have little potential for generating ozone, nitric oxide and nitrogen dioxide gases. The electrode is consumed in the process, and the filler metal contributes to the weld. The electrode is covered with a flux material, which provides a shielding gas for the weld to help minimize impurities. In SMAW, the electrode is held manually, and the electric arc flows between the electrode and the base metal. Shielded Metal Arc Welding (SMAW, “stick welding”) is commonly used for mild steel, low alloy steel, and stainless steel welding. ![]() An overview of common welding processes and their relative fume generation rates is provided below: Having a basic understanding of the welding processes and their relative fume generation rates is important in order to assess the risk of exposures to welding fumes and gases. Common Welding Processesĭifferent welding processes have different fume generation rates (FGR). ![]() However, in most mild steel welding, the exposure limits for fume constituents other than Cr(VI) (such as manganese) will be exceeded before the PEL for Cr(VI) is reached (Fiore, 2006). Chromium is typically not intentionally added to mild steels or mild steel consumables but due to the use of scrap steel in the steel production process, some low levels of chromium metal may be present. Fumes from stainless steel and some low-alloy steel welding also typically contain chromium and nickel. Oxides of manganese are also typically present. The predominant metal fume generated from mild, low alloy, and stainless steel welding is iron oxide. Fumes from some processes may also include fluorides. Welding fume is a complex mixture of metal oxides. Pure CrO3 is extremely unstable however, other metal oxides, especially alkali metals, tend to stabilize Cr(VI) compounds (Fiore, 2006). Some of the metal oxides in its hexavalent form are also in the form of CrO3. The majority of the chromium found in welding fume is typically in the form of Cr2O3 and complex compounds of Cr(III). But rather, the high temperatures created by welding oxidize chromium in steel to the hexavalent state. Therefore, welders do not ordinarily work with materials containing Cr(VI). The chromium that is present in electrodes, welding wires, and base materials is in the form of Cr(0). Hexavalent Chromium in Welding FumesĬhromium metal is found in stainless steel and many low-alloy materials, electrodes, and filler materials. This article summarizes common welding processes, relative fume generates, and the primary Cr(VI) exposure factors from welding operations. They will most likely be quickly converted to either Cr(III) or Cr(VI). Other valence states are unstable so they are less common. Cr(VI) is considered the greatest occupational and environmental health concern, as it is the most toxic. Hexavalent chromium (Cr) occurs through the oxidation of chromium compounds with lower valence states. Most diets tend to be deficient in Cr(III). Cr(III) is also believed to be an essential nutrient but in only trace amounts. Cr(III) is used industrially as brick lining for high-temperature industrial furnaces and to make metals, metal alloys, and chemical compounds. Trivalent chromium (Cr) occurs naturally in rocks, soil, plants, animals, and volcanic emissions. Chromium metal does not occur naturally but is produced from chrome ore. Metallic chromium (Cr) is a steel-gray solid with a high melting point that is used to make steel and other alloys. Chromium occurs mainly in three forms, described by its valence state. Chromium has been used commercially in the U.S. ![]()
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