What toxic substance is released when welding stainless steel?

Hexavalent chromium (Cr(VI))—also called hex chrome—is one of the primary toxic substances released when welding stainless steel. While stainless steel naturally contains chromium in a less harmful form called trivalent chromium (Cr(III)), the intense heat of welding can oxidize it into highly toxic hexavalent chromium fumes. These fumes may create serious health risks when inhaled and are a major concern for welders and employers.