The Assessment of Independent Layers of Protection in Gas Sweetening Towers of Two Gas Refineries

Backgrounds and Process industries are required to provide and maintain the working places safe for their workers، neighbors and environment. Safety may be provided through inherent safety design، providing several safeguards including instrumentation، applying proper procedures and training. Layer of protection analysis (LOPA) is a semi- quantitative technique. This technique has been used to analyze the protecting layers independently. This study was carried out to assess the independent layers of protection analysis in controlling the likely risks in sweetening gas units of two different gas purification plants. In the risk assessment process، hazards were identified by HAZOP technique at four nodes in each gas refinery and the incident scenarios were determined then. By using LOPA technique based on cause & effect، the level of risk for each scenario was determined considering the protective layers. Finally، the collected data was analyzed using the LOPA standard method and PHA-Pro6 software. Despite the fact that the independent protection layers (IPLs) were different in each re-finery sweetening towers، risk levels at different scenarios were similar. The application of Independent protection layers may decrease the likelihood of scenarios. The safety integrity level of control equipment was SIL-4 but total probability of failure on demand (TPFD) was higher in second gas refinery. The results suggested that safety integrity level (SIL) were the same in both gas re-finery sweetening towers while the protection layers were different. Results of research indicated that LOPA method can be used for controlling hazards based on layers of protection. Adding layers of protection to equipment are recommended to reduce the hazards to acceptable levels