Tolerable risk guidelines

Safety instrumented systems (SIS) should be designed to reduce the amount of risk in a process to a tolerable level. Expressing the tolerable level of risk is one of the most difficult tasks facing organizations trying to comply with the standards that govern SIS use. Organizations are basing their risk decision-making criteria on a variety of benchmarks including industry standards, local and foreign government regulations, practices of industry partners, and a qualitative assessment of what is fair and reasonable. This paper explores the ways that industry and government have made decisions on what risks are tolerable. The paper begins by reviewing qualitative criteria that are evaluated to determine what amount of risk can reasonably be tolerated. The paper also reviews some methods that have been used in government and industry to include financial aspects into the decision-making process. It then proceeds to review some of the quantitative ways that risk is represented. After discussing risk presentation, the paper reviews and compares tolerable risk guidelines that have been set by government and industry. The paper concludes by comparing the amount of risk reduction that can be justified by sociopolitical tolerability guidelines and that which can be justified by cost-benefit analysis.