Welding is a method of fusing metals in which an electric arc is formed between a metal electrode and the material to be welded. During the process the electrode melts and forms a bond. The electrode is made of the same metal as that being welded. The commonly used electrode is steel, which, on heating, gives off fumes containing particles of iron oxide measuring 0.5 millimicron in diameter. The electrodes usually are coated, and the coating, on heating, forms a gaseous cone that prevents the molten metal from evaporating too readily. The composition of the coating varies, but fluorides, silicates, borates, aluminum, cadmium, and chromium are found in different products. Of these, fluorides and cadmium are the most irritating, and there is reason to believe chromium may be carcinogenic.
The fumes of welding, particularly those arising from fluorides, cadmium, and chromium, are irritating to the mucosa of the respiratory tract.