Welder Exposure to NO and NO2 during Argon-Shielded Arc Welding on Aluminum Alloys

Abstract

This work was performed to assess welder exposure to NO and NO2 and to assess the importance of these gases in the hierarchy of contaminants produced during welding (GMAW [MIG welding], GTAW [TIG welding], plasma cutting) on aluminum alloys. Personal air samples in the breathing zone were collected on welders using a small, person-portable, direct-reading, datalogging instrument containing an electrochemical sensor rated for NO2 and colorimetric detector tubes rated for NO to assess exposure during welding. Exceedance of the Threshold Limit Value -Time-Weighted Average (TLV-TWA) of 0.2 ppm (parts per million) averaged over 8 hours for NO2 and the Ceiling Limit of 1 ppm used by some jurisdictions was likely during GTAW (TIG welding) in poorly ventilated conditions. Exceedance of these limits was unlikely during plasma arc cutting and GMAW (MIG welding). Exceedance of the TLV-TWA of 25 ppm for NO was unlikely to occur. Exceedance of the TLV-TWA of 0.2 ppm and the Ceiling Limit of 1 ppm mandated in some jurisdictions for exposure to NO2 during argon-shielded GTAW on aluminium alloys is likely to occur in the shipyard environment examined during this study. Exceedance of Exposure Limits for NO2 during GMAW or plasma arc cutting is unlikely to occur. The critical substance at the top of the exposure hierarchy involving a complex mixture could be a gas. As well, this substance could be process-specific (GTAW versus GMAW). This situation illustrates the importance of monitoring worker exposure in consideration about the likelihood of exceedance of Exposure Limits and identification of critical substance(s) in the hierarchy of contaminants produced during a process.