A welding smoke eater can help remove toxic gas, dust, fumes, vapors and smoke that results from welding with certain materials. Many materials that are commonly welded are toxic to breathe and should therefore be used with a welding smoke eater. Common metals that are used in welding that are toxic to work with are as common as galvanized metal, lead, and cadmium; all of which can cause a serious lack of oxygen to the welder and also release toxic fumes. Even the most forgiving codes require at least 2000 cfm ventilation when welding materials that are not considered hazardous. However, many materials are considered very hazardous and should be welded only in adequately ventilated areas to prevent the build up of toxic materials or to ensure there is no lack of oxygen not only to the operator but to others working close by.

http://www.smokeeaters.org/welding/