To prevent accidents like the "3?12" explosion and fire incident in the hydrogenation unit of a petrochemical enterprise in Jiujiang, Jiangxi Province, this study proposes the application of Hazard and Operability Analysis (HAZOP) and Safety Integrity Level (SIL) classification in the basic design phase of the emergency cut?off function hazards control project for a refining and chemical enterprise. HAZOP analysis adopts a workflow based on the parameter preference method while SIL classification is based on the LOPA (Layers of Protection Analysis) method, following the ALARP (As Low As Reasonably Practical) principle. HAZOP & SIL classification was carried out for a coking steam kerosene hydrorefining unit, a hydrogenation combined diesel hydrorefining unit and an ethylbenzene unit in a refining enterprise. A total of 12 accident scenarios were identified and 6 recommended measures were put forward. The results demonstrate that HAZOP & SIL classification can effectively assist the refining and chemical enterprise in managing the risks of intermingling pressures, maintaining control over safety production, reducing intermingling pressure risks to an acceptable level, or eliminating them promptly, thereby preventing accidents caused by intermingling pressures and ensuring the inherent safety of the refining and chemical enterprise.