Process Safety Management in Petrochemical Industries and use of SIL concept to improve Functional Safety

Abstract

Hazardous scenario takes place when it has ample amount of risk factors for it to occur. So, a hazard can be prevented if the risk is mitigated. Risk being a function of probability and consequence, it is aimed to reduce the frequency of occurrence and also the resulting consequence. With this regard, various Qualitative as well as Quantitative methods are applied to reduce risk and prevent the hazards. This paper consists of two different approaches: Qualitative approach (PSM) and Semi-Quantitative approach (SIL Determination and verification) to reduce risk.

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. Process safety is a blend of engineering and management skills focused on preventing catastrophic accidents, particularly explosions, fires, toxic releases associated with the use of chemicals and petroleum products. The OSHA Process Safety Management (PSM) standard (29 CFR 1910.119) was published in the Federal Register on Monday, February 24, 1992. This 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 major objective of this Process Safety Management (PSM) program is to prevent unwanted releases of hazardous chemicals into locations which could expose employees and others to serious hazards including those in the surrounding community.

The PSM 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.

All the elements have their own importance to be accomplished. An on-going mechanical integrity program is used to ensure safe process operation. This includes the check for the instrumentation components in the entire plant. 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 i.e. probability of a safety-related system satisfactorily performing the required safety functions under all the stated conditions within a stated period of time. 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. SIL Verification involves conducting hardware probability of failure calculations to ensure that the probability of failure of each overall Safety Instrumented Function (SIF) loop achieves the minimum requirements, as defined by the target SIL. In order to maintain safe conditions in the environment, the safety management programs must be appropriately followed according to the management rules and regulations.

There are various methods to determine SIL according to IEC 61511. More consistently used methods are LOPA (Layers of Protection Analysis) method and Risk Graph method which are discussed. Further, modified HAZOP method and Calibrated Risk Graph method can be used to determine SIL. Use of method to determine SIL depends on the data available and the extent to which compliance can take place.

The case studies aim to demand for the need of industrial safety studies and accomplishment of the same to maintain safe conditions in the Chemical Industries and the Environment as well.