Abstract: The physical and chemical properties of welding arc affecting the amount and toxicity of fumes generated during manual arc welding with low carbon steel basic electrodes are investigated. A summary of the results might be given as follows:(1)The formation of welding fumes is due to the superheat evaporation of the slag and metal drops. (2)The amount of fumes generated is related to the amount of heat released from the arc spot, the condition of heat transfer, and the duration and area of fuming. (3)The amount of fumes, and their toxicity, is to a great extent influenced by the chemical reaction taken place between the coating constituent CaF₂ and the binder water glass, producing low boiling point KF and NaF which are very harmful. Taking advantage of the results obtained, the authors developed a new low-fume low-toxicity basic electrode for carbon steel.