A Practical Application of ‘human-hazop’ for Critical Procedures

INTRODUCTION The accidents at Texas City and Buncefield remind us of the importance of human factors in preventing major accident hazards in the Process Industry. Much of the advice focuses on organisational factors required to ensure a motivated and competent workforce working within a good safety culture. Another key area that is often overlooked is the design of plants, processes and procedures to minimise the potential for human failures. This paper, written jointly by ABB and Chemtura, describes a Human Reliability Assessment carried out on the Chemtura site at Trafford Park. The COMAH Safety Report describes a number of potential major accidents and their associated prevention, control and mitigation measures. Whilst many of these events are controlled by engineered protective systems, there are a few examples where actions or omissions by operating staff are critical. A structured and qualitative risk assessment methodology was developed for these critical procedures based on guidance from HSE. The method is similar to the well proven HAZOP study for assessing new process design, but focussing on the sequence of actions carried out during a critical procedure. The key steps in the activity are identified with an experienced operator followed by a team based study to identify potential human failures at each key step, using appropriate guidewords. For credible failures the team assesses the consequences, potential to recover and other risk reduction measures. If the risk of human failure is high the team recommends improvements to minimise the likelihood for error. This paper describes the results of the study and the key learning points for future studies. The authors believe that the ‘Human-HAZOP’ method developed is of wider interest for those seeking to demonstrate that the risks associated with failures of critical procedures have been reduced to ‘as low as reasonably practicable’. The method could be applied retrospectively to existing operations or be used during the design stage of new processes linked to the normal HAZOP studies.