Engine-driven welders are generally used when electric power is not available for arc welding. Usually these are outdoor applications. However, engine-drive welders are also used for indoor applications when it is not convenient to supply power to electric "plug-in" arc welders. 

These indoor situations include everything from minor repair jobs to major plant shutdowns. When operating engine-driven welders indoors, vent the exhaust outside if at all possible, or use in large spaces with good ventilation.

LPG is much less common, but becomes an important alternative choice when diesel and gasoline exhaust emissions are not permitted for indoor applications.