Safety assessment methods of factory automation systems

Analysis of examples of accidents that have occurred in factory automation (FA) systems in the past has clearly shown that many types of accidents cannot be expressed by probability. These include accidents caused by interlocking failures as designed due to the dead angles of obstacle sensors and those accidents caused when workers or maintenance personnel switch off the safety device or disregard the instructions and cross the safety guardrail. As reliable assessment of these accidents is difficult, an integrated method to assess system safety is required. A method is proposed here to assess the safety of FA systems for people by using a matrix of circumstances potentially encountered in the application of safety measures in order to remove hazards, render them harmless, or localize them, as well as circumstances potentially encountered when the system is handled by people. Also proposed is a method to assess each component of the matrix by integrated ranks consisting of the following six ranks: economically realizable and should be realized, 0; should be generally realized in actual conditions, +1; the other ranks, ‐2, ‐1, +2, and +3, using the above ranks as criteria. By applying this assessment method to 16 cases of accidents: nine cases during normal operation, five cases during maintenance, and two accidents involving outsiders, practical use has been confirmed. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 3, 80(3): 21–36, 1997