Purpose Algeria occupies an important place in all of the oil-producing countries. However, in recent years, industrial facilities have experienced a rapid increase in the number of major industrial accidents and calamities, where fires and explosions have caused impacts and severe effects on people, property and the environment. Therefore, this paper aims to analyze the risks involved and assess the performance of the technical barriers at the thermo-hydraulic level of facilities at the level of the refinery of Skikda. Design/methodology/approach The most effective methods in this field of activity are the systematic analyses of deviations or failures. As working tools, hazard and operability (HAZOP) method and fault tree analysis (FTA) were used to identify the various possible risks that could lead to undesirable phenomena, with the Topping unit. Using this type of analysis, it is possible to understand what the most risky process steps are and, where appropriate, to propose appropriate corrective and preventive measures. HAZOP is dedicated to the analysis of the risks of thermo-hydraulic systems and to control drift parameters such as pressure, temperature and flow. Unfortunately, with its limitations to the detection of leaks, the authors completed the study by FTA, working with a predetermined set of process parameters associated with system operation (compression, temperature, flow, etc.). Each of these parameters are combined with a series of possible potential deviations (too much, little, inverse, etc). For each analyzed equipment, the relevant parameters are selected and combined with the relevant deviations. For each parameter of the deviant process, the causes and consequences are determined. Findings The combination of these two methods has allowed to highlight the various possible risks that could lead to undesirable phenomena, to respond to industrial expectations or even to manage the operation process safely. Thus, it enabled the authors to detect the weaknesses of the process. This allowed the authors to reinforce the technical safety barriers of the functional links of the process and propose appropriate, corrective and preventive measures. Originality/value The work intends to reflect the real situation in which companies face risks. The originality of the work is represented by the combination of two methods: HAZOP and the FTA. This association allowed the authors to identify areas of weakness to set priorities for action by the company, through organizational, technical and human solutions, while engaging in a process of continuous improvement.