The use of programmable electronic systems (PES) in industry has grown considerably with the availability of microcomputers. These systems offer many benefits to the designer and user in providing more comprehensive control of industrial processes, enviroments, machine tools and in robot installations. As confidence grows with the application of PES, users and manufacturers are considering incorporating safety functions within the requirements and functions of the PES. This book represents the proceedings of the Programmable Electronic Systems Safety Symposium (PES-3) held in Guernsey, Channel Islands, May 28th - 30th 1986, which presented the guidance available to users, designers and safety assessors of programmable electronic systems. This guidance is applicable for many real and potential risk and safety situations in a wide variety of industries ranging from nuclear power plants and industrial robotics, to machine tools and chemical process controllers. The original impetus to hold the Symposium came from a two year collaborative project partially funded by the Commission of the European Communities under the 1979-83 Informatics Initiative. The sponsors of the Symposium studied the assessment, architecture and performance of industrial programmable electronic systems, with particular reference to robotics. The group of papers in the first session give the first public report of the results of this project. The session was Chaired by H Fangmeyer from the Commission's Joint Research Centre at Ispra, Italy, who was the Commission's Project Manager throughout the collaboration.