This invention relates to an electric arc heater process and apparatus for the essentially complete decomposition of hazardous materials including polychlorinated biphenyls. Finely divided liquid or gaseous hazardous material is injected into a primary gas stream which has been superheated in an electric arc heater. The mixture is directed into a primary reactor for complete decomposition with dwell times in the reactor being in the order of 0.05 to 0.15 seconds. The decomposition products are neutralized with the gases being released to atmosphere and any remaining particulates being collected for ultimate disposal. Large solid hazardous material is first shredded then heated in a roaster or rotary kiln to vaporize the primary gas stream. A soaking reactor is provided where increased dwell times are required for the decomposition of thermally stable compounds which may be formed in the primary reactor. When these compounds are absent the soaking reactor can be by-passed.