A number of major process industry accidents have involved SIMOPS. Company conducted construction (modifications) activities inside its own plant during the period from November 2017 to May 2018. The Group Risk Acceptability Criteria Guidelines have been defined by Company for the purpose of providing Senior Management with quantitative information about the risk profile during SIMOPS activities and to help them in taking informed decision about the execution strategy to ensure safe operations.

A DNV-GL Phast based model of the plant has been used to assess the risk level. Using Group Risk guidelines for On-site personnel based on the FN (Frequency – Number of Fatalities) Curve, Company evaluated and compared several SIMOPS options prior to the actual works to identify the optimal manning level and schedule to ensure the overall Group Risk laid in the ALARP region.

The quantitative risk assessment served as a tool to derive the optimal manning levels and shutdown schedule during the SIMOPS activities. The manning levels were controlled through additional administrative measures to ensure its implementation.

Moreover, the overall SIMOPS Risk (FN Curve) for the current activity was compared with the risk undertaken during similar previous activities conducted in 2015 and 2016. After the successful completion of the activities, the Risk Assessment was updated to take into consideration the actual manning and schedule inputs for the Pre-Shutdown and Partial Shutdown phases. The actual overall Group Risk (including Pre and Partial Shutdown) was within the Company Group Risk Acceptability Criteria.

Additionally, valuable Lessons Learned were identified such as purging (with inert gas), rather than just the depressurization of the equipment in the units during Shutdown, can contribute to a significant risk reduction.

This paper presents a novel approach to evaluate SIMOPS risk on personnel using a Group Risk criteria based on FN Curve. This provides an additional re-assurance to stakeholders involved in the activity to take informed decisions based on a quantitative risk analysis rather than a qualitative assessment.

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