Laboratory Evaluation of Carbon Monoxide Exposure in CO 2 Arc Welding

During metal active gas (MAG) welding process, several chemical and physical emissions such as welding fumes, ozone, nitrogen compounds, and ultraviolet radiation are generated. Carbon monoxide (CO) produced from the shield gas by the action of heat upon the welding flux and slag is one of the hazardous contaminants in CO 2 arc welding (also known as MAG welding). CO is a lethal poison and can overcome the exposed person without warning because it is colorless, tasteless, odorless, and non-irritating. Although CO poisoning of a welder is not as serious as pneumoconiosis due to welding fumes, it is still a common occurrence in Japanese production weld shops. It is generally known that contaminant concentrations in stationary measurement tend to be appreciably less than those in the breathing zone. This is especially remarkable in the case of welding where the workers are close to the arc points (contaminant sources). Therefore, the exposure of a welder is better evaluated by a personal sampling method rather than by the area sampling method which is prescribed as “A-sampling” in the Japanese Working Environment Measurement Law. According to former studies, lower concentrations of welding fumes, ozone, nitric oxide and nitric dioxide inside the welding face shield have been found . Alpaugh et al. suggested that the partially confined space between the welding face shield and a welder’s head is a reservoir of relatively pure air, and continues to be an effective barrier to airborne contaminants during arc is struck. Hence, exposure will be overestimated if the sampler is mounted on the lapel or on the shoulder of a welder rather than in the actual breathing zone, inside the face shield. Since little data have been published regarding the true CO exposure level during CO 2 arc welding, the author attempted to compare CO concentrations inside and outside the welding face shield and to determine the extent of CO reduction afforded by the shield.