Assessment of Technologies for Measuring Exposure to NO2 during Welding on Aluminum Alloys

Thomas Neil Mcmanus,Assed Haddad

doi:10.5539/enrr.v9n2p75

Abstract

Arc welding is a complex process that results in many air contaminants of health significance to humans. As a result, regulators worldwide require employers to determine exposure of welders and other workers to these contaminants. The very small Exposure Limit for NO2 limits the technology available for assessing exposure. Bias caused by ozone, a known interferent in the measurement of NO2, is a major concern. This investigation involved side-by-side comparison of results provided by handheld instruments containing electrochemical sensors for NO2 to those produced by an air pollution analyzer specific to NO2 using bag samples of plumes collected during production welding (Gas Shielded Metal Arc Welding [GMAW] commonly known as Metal Inert Gas [MIG welding]) on aluminum alloys. The shield gas was argon. Monitoring to confirm utility of the method was performed on welders. Results from all instruments were similar despite differences in measurement technology and instrument and sensor manufacturer. Levels experienced during confirmatory testing on welders to determine exposures of short duration and long intermittency as occur during real-world activity were comparable to the Threshold Limit Value for NO2 of 0.2ppm (parts per million) expressed as a Time-Weighted Average over 8 hours, and were less than the Ceiling Limit of 1ppm used by some jurisdictions. Hand-held instruments containing electrochemical sensors for NO2 and datalogging capability are suitable for use in this application. The ability to draw the sample to the instrument by a pump is an important consideration in providing welder safety and protecting the instrument.

Highlights

1.1 Arc Welding and Workplace Regulatory RequirementsGas-shielded arc welding is a major process for joining aluminum alloys in shipbuilding operations (Althouse et al, 1988)
Results provided by instruments containing the two types of electrochemical sensing technology were approximately the same and slightly less than the concentration measured by the bench-top analyzer
At the levels of NO2 measured here, these differences do not appear to be significant deterrents to use of the hand-held instruments in this application

Summary

Introduction

1.1 Arc Welding and Workplace Regulatory RequirementsGas-shielded arc welding is a major process for joining aluminum alloys in shipbuilding operations (Althouse et al, 1988). GMAW (MIG) was used for production welding and GTAW for touch-up work in this operation. Both types rely on a gaseous shield that forms a hemispherical atmosphere surrounding the arc. The gas shield intentionally excludes atmospheric oxygen in order to prevent rapid oxidation of the metal due to the heat and molten state. Gaseous emissions include the shield gases (argon, helium, carbon dioxide, and nitric oxide present in some mixtures) and gases resulting from chemical reactions occurring inside and outside the shield because of the heat (Moyer, 2002; NIOSH, 1988). Nitrogen dioxide (NO2) results from subsequent reaction between NO and atmospheric oxygen or ozone (O3). Ozone results from the interaction between Ultra-Violet (UV) energy emitted by the arc and oxygen in the air (McKinlay, 1992)

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