Exposure to welding gases can cause health adverse effects. Risk assessment is a useful tool for good assessment of exposed workers. The purpose of this study was to determine the risk levels for exposed welders to welding gases. Welders (n=239) were selected from Iranian Natural Gas Transmission Pipelines Industry from four regions in Iran including Assaluyeh, Omidieh, Loshan, and Borujen. Ozone (O3) and nitrogen dioxide (NO2) samples were collected according to the OSHA ID-214 method and the

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... IOSH analytical method 6014, respectively. Direct reading instruments were used for sampling of carbon monoxide (CO) and carbon dioxide (CO2). A semi-quantitative method was used for risk assessment. Exposure to O3, NO2, CO, and CO2 ranged 0-0.0371, 0.01-0.58, 0.375-4.33, and 89.5- 1395.44 ppm, respectively. Among welders, Back weld group had the maximum exposure to O3, CO, CO2, while, the maximum exposure to NO2 was seen for Filling group and then for Back weld group. Although average exposure values were significantly lower than Threshold Limit Values-Time Weighted Average (TLV-TWA) (p<0.05), the results of risk assessment showed that, control approaches should be applied for welders specially in Full pass, Filling, Filling cap, and Back weld groups due to their medium (M) and high (H) rank of risk.