Optimization of safety barriers by staged LOPA

Accidents occurring in offshore installations may have severe consequences in terms of economic drawbacks, life losses and environmental damages. In fact, hazards due to process and substances handled are increased by specific features of the offshore structures (space limitations, congestion, work-over operations, etc.). Current paper focuses on design strategies to limit hazards and improve the efficiency of the safety barriers which are adopted to reduce risks to acceptable levels. A systematic method for analysis and optimization of the safety performance of the system is proposed. The method developed allows the identification of the safety barrier configurations that maximize the application of inherently safer approaches. The method is based on a staged Layer Of Protection Analysis (LOPA), where the barriers are assessed progressively according to the level in the hierarchy of risk reduction strategies. Cost allocation among barriers is taken into account as well, during each stage, with the final goal of a more reliable and more economical realization of the barriers. Critical components in the barrier system are identified by appropriate inherent safety indicators. This provides the basic support for design choices aimed at the improvement of the safety barriers at each strategy level. The methodology is demonstrated by the application to a case study in an up-stream off-shore installation.