Quantifying Residual Risk as part of the HAZOP Process

Presented at AGM & Technical Meeting, 23 November 2017 at Hilton London Paddington HOtel, London by Zaffer Khan and Ian HItchin, Rowan House
Process safety is a blend of engineering and management skills focused on preventing accidents and near misses. Plant operators/owners are solely responsible for ensuring the health and safety of employees, and of the general public. It is therefore a requirement that hazard and risk assessments are completed at each stage of the project lifecycle: from design, installation and commissioning, through to operation. At the design stage, risk assessments such as HAZOP must be carried out to assess the possibility and consequence of potential hazards, with appropriate precautions incorporated into the design to minimise risk. The risk can be quantified to determine if these precautions offer adequate protection, and to ensure that ALARP (as low as reasonably practical) is being achieved. Tolerable risk reduction levels can be set and the evaluation of residual risk against tolerable risk can be determined through the HAZOP process. This is the first part of determining if any Safety Integrity Levels (SIL), a measurement for quantifying risk reduction, are required. Additional study, such as LOPA (Layer of Protection Analysis) maybe used to determine if additional protection is required against a risk, or if a SIL rated safety instrumented function is needed. The presentation will discuss the requirement of a HAZOP study, setting acceptable tolerable risk levels and quantifying risk as part of the HAZOP process.