HAZOP and SIL (Risk Graph Method) for CNG

Abstract

Process Safety Management (PSM) Program describes the management system for protecting people, property, and the environment from catastrophic releases of highly hazardous chemicals in the workplace. PSM is accomplished by systematically evaluating the process (or processes) using approaches to assess the effectiveness of the process design, technology, operations, maintenance, non-routine activities, procedures, emergency preparedness, training, and other process elements. The OSHA Process Safety Management (PSM) standard (29 CFR 1910.119) program describes how employees are involved in the programs, how process hazard analyses are conducted, and preparation of operating procedures and practices, training, contractors, pre-startup safety, mechanical integrity, managing change, incident investigation, emergency preparedness, and compliance audits. The hazard question is a complicated one as it involves the degree of hazard, precautionary steps taken to prevent the initiation of the hazard and adequacy of the protection of personnel as well as facilities. This thesis report is focusing the Pressure Reduction Skid (PRS) for compressed natural gas (CNG) safety. However, looking to numerous scenarios of natural gas (NG) fire & explosions we preferred PRS as a focus area for HAZOP and SIL (by Risk Graph Method). Also, Ethyl Mercaptan (EM) is used as an odorant in NG; and several hazards are associated for Environment & human. Hazard and operability (HAZOP) methodology is a Process Hazard Analysis (PHA) technique used worldwide for studying not only the hazards of a system, but also its operability problems, by exploring the effects of any deviations from design conditions by using guidewords under multi-disciplinary technical team. It is the most commonly-used PHA method in the world today. Our focal area is to minimize the risk As Low as Reasonably Practicable (ALARP). For that we did SIL study by Risk Graph Method. Once HAZOP study is completed, then SIL study will carried out based on the High potential consequence. To ensure that failure of the instrumentation does not take place due to its mechanical integrity, its Functional Safety has to be established. Allocation of safety functions to specific protection layers for the purpose of prevention, control, or mitigation of hazards from the accelerator and its associated equipment is necessary to maintain safety integrity. Safety integrity level (SIL) is a discrete level (one out of a possible four) for specifying the safety integrity requirements of the safety functions to be allocated to the Electrical/ electronic/ programmable electronic system (E/E/PE) as for safety-related systems, where SIL 4 has the highest level of safety integrity and SIL 1 the lowest. Safety Integrity Level (SIL) is a criterion that judges the reliability of the safe-guards. It specifies or assigns the required safety integrity level to the scenario to identify the level of risk involved in the scenario. International Electro technical Commission (IEC) 61511 has published different methods for the determination of SIL in chemical process industries.