This paper focuses on the development of an integrated risk assessment system to increase the safety of gas refinery plants. This integration is important in managing the design and the operation of chemical plants and it requires significant time, effort and specialized expertise. We propose a systematic procedure to apply quantitative and qualitative hazard identification methods before constructing the refinery plants. Advantages of this assessment procedure are 1) systematic method in identifying most of the important hazards, 2) complete and rigorous analysis, and 3) reducing budget and time. The qualitative and quantitative assessment method consists of two and three steps, respectively. After these five steps, the risk of the same plant was calculated and analyzed. This method can identify risk and potential hazards from local gas refinery plants effectively and systematically. We applied the integrated qualitative and quantitative risk assessment method to remove the risk of a local gas refinery plant with 160 P&ID sheets. The result of this work confirmed that no residential population existed within the bounds of the 1×10^(-6) per annum risk contour. Therefore, the risk to the public from the gas refinery plants should be considered acceptable.