Our newly developed criticality programme examines the events at Tokaimura in 1999, when Hisashi Ouchi was exposed to more radiation than any other human being in history. The session looks at the circumstances which lead up to the criticality event, and also the tragic consequences for Mr.Ouchi which followed. For anyone involved in the nuclear industry this programme is a reminder of how quickly things can change and how mindful people must remain at all times.