Dr. David J. Smith is the Proprietor of Technis Consultancy. He has written numerous books on Reliability and Safety over the last 40 years. His FARADIP database has become widely used, and his other software packages are also used throughout the profession. His PhD thesis was on the subject of reliability prediction and common cause failure. He contributed to the first drafting of IEC 61508 and chairs the IGEM panel which produces SR/15 (the gas industry safety related guidance). David is past President of the Safety and Reliability Society.Kenneth G. L. Simpson is Managing Director of Engineering Safety Consultants Ltd and has been associated with safety related systems design and also with their assessment for over 40 years. He is a member of both the IEC61508 and IEC61511 drafting committees and the IGEM (SR15) panel, which writes the gas industry guidance. Following a career in aerospace, Ken has spent over 35 years in the control and safety system industry, has written a number of papers on the topic and gives frequent lectures.