Accident risk and safety protection in automated production

Abstract: This thesis treats automation accidents in manufacturing industry. An automation accident is defined as an accident whereby a person is injured by an energy which was controlled, or should have been controlled, by an automated item of equipment. The thesis comprises five papers. The first three are based on data from mandatory Swedish occupational-injury reports. Their aim is to show frequencies, kind of injuries and context for automation accidents. The two final papers describe the sequence of events involved in automation accidents on the basis of tailored investigations. The aim of these papers is to develop concepts and theories. The one concentrates on technical faults, the other on safeguards. The findings do not provide grounds for designating any particular kind of automated equipment as the most dangerous. However, the parts of the equipment where injuries most often incurred are those for the automated conveying and handling of work pieces. The majority of persons injured in automation accidents are machine operators, who also show a higher frequency of automation accidents per person. Automation accidents give rise to comparatively long periods of sick leave. Most of the injuries were to the hands and fingers. Aspects of the genesis of automation accidents are described. In a vast majority of automation accidents an injury is incurred when contact is made between a person and a moving part of an automated machine. Necessary conditions for this injury event are a) that a person is in the machine-movement zone, b) that a machine movement is taking place, and c) that there is no safety device preventing either of these two conditions being met. How these three conditions can arise is described, and advice is provided on measures that might reduce automation-specific accident risks. While analyzing the genesis of automation accidents, it became evident that the development of a new accident model was motivated. The systemic accident model (SAM) consists of three elements: system evolution, situational conditions, and accident sequence. One of the key measures for promoting personal safety at automated installations is to eliminate machine failures. First, efforts can be made to avoid loss of system equilibrium. Second, future losses of equilibrium should be planned for. Third, persons operating automated equipment should be given resources to cope with unforeseen loss of system equilibrium. Various safety ideals are discussed. A conclusion is that future safety may lie in the use of safety devices which, as far as possible, do not hamper the performance of work, combined with organizational and social barriers to unsafe work.