From 1974, he worked as a TUM guest researcher at SIN, the Swiss Institute for Nuclear Research in Villigen and subsequently joined the SIN Laboratory for High Energy Physics at ETH Zurich as senior researcher for Professor J. P. Blaser.
In 1978 he joined HSK (the predecessor to ENSI) and worked on issues relating to the radiological protection of staff and the environment. From 1990 – 2000 he was Director of the School of Radiological Protection at the Paul Scherrer Institute (PSI) in Würenlingen. In January 2000 he was appointed Head of the Department of Radiation Protection, Emergency Preparedness and Organisation (SANO) at HSK and in 2002 became 1st Deputy to the Director.
Between 2000 and 2007, he represented Switzerland on RASSC, the Radiation Safety Standards Committee of the IAEA in Vienna. He was a member of the governing body of the German/Swiss Radiological Protection Association and a member of the Federal Commission for NBC Protection (ComNBC).
Hans Pfeiffer retired on 1 December 2007 and on 1 January 2008 became a member of the ENSI Board.
