Oil burning furnaces are safe appliances when properly maintained. However, burning waste oil poses an additional hazard of producing dangerous or deadly airborne chemicals depending on the origin and composition of the oil involved.
Burning waste oils has the potential to produce a number of toxic airborne chemicals according to the Allegheny County Health Department, including arsenic, cadmium, chromium and lead. In addition, any oil burning device runs the risk of producing carbon monoxide gas, as reported by the Chimney Safety Institute of America. The potential dangers involved are magnified if the waste oil burner in question is used in a poorly ventilated environment.