The relative impact of control reliability on machinery risk

Control of risks related to machinery is central to current product and occupational health and safety legislation in North America and the European Union. Understanding these risks requires risk assessment, and this process is represented in all leading standards in these jurisdictions. Standards provide machine designers with a hierarchy of controls that can effectively control these risks when appropriately applied, including the application of engineering controls as the second stage in the hierarchy. In the second stage, safeguarding systems that involve the control system of the machinery to alter the characteristics of the hazard or the probability of exposure to the hazard have become central in the large majority of machinery designs. Reliability of these control systems is one critical element in the application of these systems. This paper explores the impact of control reliability on overall risk control for machinery, and shows the cost of analysis and design of safety-related control systems may be greater than the benefits of the risk reduction achieved.