AbstractThe exhaust detritiation system (EDS) is one of the key safety related systems, which allows operation of the Joint European Torus (JET) machine. Its role is to detritiate the exhaust gases in case of an accident and to minimise the tritium release to the environment. EDS has also been used on JET during the last 3 years for maintenance purposes. During the main phase of the deuterium–tritium experiment (DTE1), the EDS was the final stage for detritiation of gases coming from the Torus vessel. There is a regulatory requirement to prepare an ‘Engineering Substantation’ of key safety related systems. Although this requirement applies to EDS when dealing with accidental tritium releases, it has been possible to investigate the efficiency of the system by analysing the experimental data obtained during maintenance. In 2000, during the shutdown, campaign measurements on EDS have been performed to determine its efficiency on a daily basis. Detritiation factors (DF) range between 20 and 80 000. Results are presented and discussed in relation to the requirements of the JET safety case and the factors, which cause apparent low DFs. An enhancement of the system for tritium control tracking is proposed.