[origin: WO9741946A1] A regenerative thermal oxidizer (10) in which contaminated air is first passed through a hot heat exchange bed and into a communicating high temperature oxidation (combustion) chamber (3), and then through a relatively cool second heat exchange bed. The apparatus includes a number of internally insulated, ceramic filled heat recovery columns (2A, 2B) topped by an internally insulated combustion chamber (3). From the combustion chamber (3), the air flows vertically downward through another column containing heat exchange media, thereby storing heat in the media for use in a subsequent inlet cycle when the flow control valves reverse. Temperature is sensed within the bed of heat exchange media in order to monitor the temperature profile and control a bypass of hot combustion gases should the temperature exceed a predetermined level.