This paper describes the engineering, construction and installation of the Exhaust Detritiation System for the JET Active Gas (Tritium) Handling Plant. Commissioning results without tritium indicated that the system has met the design requirements and operating parameters. Hydrogen and methane were fully oxidized. Dew point of −60°C was observed in the drier outlet. Tests carried out with substances potentially harmful to the performance of the recombiner catalyst indicated no significant change in hydrogen oxidation performance. However, methane oxidation was significantly reduced. Furthermore, the acidic decomposition products of these substances would damage the equipment in the system after extended exposure. Admission of these and chemically similar substances must be avoided to maintain the performance of the Exhaust Detritiation System.