Abstract
British HSE has introduced a target safety level that should result in the incidence of work-related deaths being less than 10-6 times per year. However, the general methodology to achieve this target is not necessarily clear. This study proposes an equation that is able to estimate the probability of occurrence of accidents in a man-machine working system quantitatively based on Markov analysis. Based on this equation, the following result was obtained. 1) It will be difficult to achieve the target objective if only the machines' users take countermeasures (safety management) that depend on workers' attentiveness. It is vital to apply a wide range of duplicate and automated monitoring technology. 2) It will be possible to achieve the target objective under the following conditions - less than 10-5 hour (around 30 msec.) as the test interval for the sensor and processor-related safety function on a single control system, less than 0.05 hour (3 minutes) as a test interval on diverse duplicate control systems, less than 0.5 hour (30 minutes) as the test interval on diverse triple redundancy control systems. 3) The above-mentioned target cannot be achieved for hazardous point operations. However, when probability of occurrence of accidents that cause worker death is set at less than 10-4 times per year as a target value , this target might be able to be achieved through integration between implemented protective measures (safety of machinery) and safety management.
