Safety integrity level assessment for safety instrumented system in oil and gas station with cyber threat

With the convergence of Information Technology and Operational Technology driven by Industry 4.0, safety and security have become increasingly interdependent, where cyberattacks pose significant risks of physical injury or environmental harm. This paper proposes a framework for assessing the integrity of cyber-physical safety barriers under both stochastic failures and cyber threats. A novel Cyber-Hazard and Operability Study (HAZOP) is developed by integrating Threat Model with HAZOP to identify cross-domain risk. The framework extends Bowtie diagrams and Layer of Protection Analysis (LOPA) to numerically characterize the coupling effects arising from logical interdependencies (e.g., conflicts, conditional dependencies, risk superposition). A case study on a crude oil storage facility demonstrates that cyber threats significantly degrade Safety Integrity Level (SIL) thresholds by one level. Compared to HAZOP-LOPA, the proposed method reduced Risk Reduction Factor (RRF) errors by 13.21-22.66 %. This error reduction is calculated by segmenting RRF differences according to SIL ranges and dividing by corresponding SIL widths, highlighting the framework’s capability to holistically evaluate interdependent cyber-physical failure behaviors in safety-critical infrastructures.