The risk analysis is performed of carbon monoxide formation during manual arc welding of metal products using electrodes. The system of protection is considered of the person against carbon monoxide in the room of manufacturing which consists of means of collective and individual protection. The reasons are analysed for failures of the workplace safety system. A failure tree was constructed of the welder's protection system against carbon monoxide using a protective mask, which is not equipped with a gas detector, and when working in a mask which is equipped with a gas detector. The mathematical models of welding processes are obtained as a result of research and analysis of the results. Mathematical expressions are given for calculating the reliability of the protection system. The risk assessment take the place for carbon monoxide poisoning during welding works with the system of ensuring the safety of the employee, i.e. the notification system for the presence of carbon monoxide in the work area (individual alarm) and without it.

This paper reports a study of the air medium where welding processes take place, with special attention paid to the evolution of carbon monoxide (CO) in the working medium in the process of gas welding. Plots were constructed and polynomial dependences were obtained to show a change in the concentration of carbon monoxide in the air of the working area during gas welding. It was confirmed experimentally that the concentration of carbon monoxide exceeds the permissible sanitary and hygienic indicators MPC (20 mg/m3) during gas welding. As a result of the experiment, the effectiveness of the use of an additional device was proven, namely an umbrella gas concentrator, in order to capture welding gases that are formed during gas welding. It was established that the MPC is exceeded under certain working conditions and welding wire. The carbon monoxide formation during gas welding was analyzed; these processes were compared with electric arc welding. The mathematical dependences derived make it possible to assess the risks of the welders’ work and conclude that the electric arc welding is characterized by a much higher rate of CO evolution from the beginning of the welding process (8.5 mg/s), that speed then decreases over 20 s by 2 times (to 4.5 mg/s). In 90 s, the speed becomes constant, to 2 mg/s. In comparison, gas welding has almost the same rate of CO formation, namely 0.3–0.9 mg/s. By changing the types of welding wires used in gas welding and taking into consideration the type of material that needs to be welded (including the period of its use), it is possible to influence the volume of CO emissions entering the working area and an employee’s respiratory area