(122c) Ram Modelling and Operations Performance Standards

In Europe and the Asia Pacific region the Safety Case methodology is increasing in popularity as a comprehensive technique for managing safety risk on operating facilities. Operators using the Safety Case methodology are realising production and financial benefits as well as safety improvements at their facilities. A unique outcome of the Safety Case methodology is the identification of Safety Critical Items. Development of Operations Performance Standards and Written Schemes of Examination provide the necessary assurance that these Safety Critical Items are managing risks effectively.

Safety Critical Items are structures, equipment, instrumentation, process control, etc, that are critical to minimising the likelihood or consequence of a Major Accident Event in an operating plant. Historically RAM (Reliability, Maintainability and Availability) modelling has been used to optimise production critical items but there has been a shift to using this tool to optimise Safety Critical Items. Where Safety Critical Items are part of the operating plant, RAM modelling can be used to identify optimum maintenance plans. The results of the RAM modelling can be used to support the Operations Performance Standards and Written Schemes of Examination for Safety Critical Items. The result is that Safety Critical Items are operable and reliable to the level required in order to maintain a safe operating plant.

The process used is based on the internationally accepted guidance from UKOOA (United Kingdom Offshore Operators Association) for identifying and maintaining Safety Critical Items. The main elements of the process involve the following:

?

Identification of the Safety Critical Items that are required to manage the Major Accident Events. This includes a Hazard Identification review of technical drawings and charts such as process flow diagrams, piping and instrumentation diagrams and cause and effects charts;

?

Development of Bow-tie Diagrams for each Major Accident Event to ascertain the relationships between the hazards, threats, barriers (preventative and mitigative), Major Accident Events and Safety Critical Items;

?

The development of the Safety Case and supporting safety studies (eg Hazard Identification, Hazard Analysis and Quantitative Risk Assessment) to demonstrate the Major Accident Events for the facility are managed effectively;

?

RAM modelling of the Safety Critical Items and their related facility systems to determine whether safe operating objectives are practical and achievable. The output of such modelling would provide optimum availability targets for individual components and for the whole system. Therefore the output of such analyses would be the performance target for the asset, a system or sub-system and the identification or high downtime contributors;

?

Development of the Operations Performance Standards to include Safety Critical Item functionality, reliability, availability, survivability and interdependencies; and

?

The development of Written Schemes of Examination prescribing how the Operations Performance Standard will be achieved and maintained. The Operations Performance Standards and Written Schemes of Examination can also include contingency actions for when systems fail to meet their performance requirements.

The Operations Performance Standards are a practical tool that can be used as an input into the facility Maintenance Management System. This is a quantitative approach to developing management processes for process plant safety that also provides financial returns through increased production and decreased downtime. The focus of this paper will be the process for developing these Operations Performance Standards for Safety Critical Items utilising RAM modelling and the benefits that can be attained for a facility using this approach.