【Y2025】Safety differences among pressure transmitters with different configurations at the same SIL level and engineering examples

The following replies are not part of the text and are provided for reference only: SIL (Safety Integrity Level) refers to the safety integrity grade. The SIL technical standards were first established by the International Electrotechnical Commission (IEC), with IEC/TC65 being responsible for their implementation. The standardization technical committee responsible for SIL technology is the \"National Technical Committee for Measurement, Control, and Automation in Process Industries\" (SAC/TC124), with the Secretariat located at the Comprehensive Technical and Economic Research Institute for Instruments and Meters in the machinery industry. SIL certification is divided into 4 levels in total: SIL1, SIL2, SIL3, and SIL4, covering both the product and system levels. Among them, the requirements for SIL4 are the highest.

The purpose of SIL grading is to analyze safety instrumented function (SIF) circuits in order to determine the safety integrity level (SIL) required to reduce their risks. Generally, relevant technicians and experts conduct analyses such as HAZOP/LOPA, thereby providing seamless integration with SIF identification and SIL grading services. Taking into account the industry characteristics, the properties of the process equipment, the nature of the enterprise, and management requirements, appropriate risk management and SIL classification methods are employed. Through analysis by relevant third-party experts or technicians using methods such as HAZOP/LOPA, it provides seamless integration with SIF identification and SIL classification services. Taking into account the industry characteristics, the properties of the process equipment, the nature of the enterprise, and management requirements, appropriate risk management and SIL classification methods are employed. For SIL classification, China has the standard \"Guidelines for the Application of Layer of Protection Analysis (LOPA) Method\" AQ/T 3054-2015. This standard includes a recommendation table, which is what is commonly referred to as the LOPA table.

Different industrial processes (such as production scale, types of raw materials and products, and the complexity of processes and equipment) have varying safety requirements. International standards classify it into several Safety Integrity Levels (SIL: Safety Integrity Level). Safety integrity levels can be divided into 4 grades; SIL4 is the highest level of safety integrity (with the lowest average probability), while SIL1 is the lowest level ； The higher the safety integrity level, the greater the probability that the required safety functions must be implemented. Based on the usage pattern of safety-related systems, the required frequency can be divided into a low-demand operation mode (≤1 time/year) and a high-demand or continuous operation mode (>1 time/year).

By adopting different operating mode architectures, it is possible to use several systems with lower safety integrity levels to meet the requirements of a function with a higher safety integrity level (for example, using an SIL2 system and an SIL1 system together to fulfill the requirements of a SIL3 function). Therefore, the assessment of the safety integrity level of the process is a very important task. However, at present, there are no standards or specifications in our country for assessing the safety integrity level.

Certain evaluation methods are provided in international and foreign standards, which can be referred to for implementation. If the frequency (probability) of process accidents and their degree of harm (severity) are used as indicators for risk assessment, and these frequency and severity levels are artificially quantified into several categories, a matrix table is created (see Table 3). This is used to determine the safety integrity level of the process.

The SIL level cannot be modified through configuration; it is determined through calculation. The SIL level of a system indicates the applications for which it is suitable; of course, a system with SIL3 rating can also be used in applications requiring SIL2. Whether a control loop should be rated at SIL2 or SIL3 is determined through analysis of various factors, such as the importance of that control loop within the entire production facility and its impact on safety.

Safety instrumented functions are designed for specific hazardous events, possess a certain safety integrity level (SIL), and serve as safety protection or control functions implemented using measuring instruments, logic controllers, final elements, and related software, in order to prevent or reduce the occurrence of hazardous events or maintain a safe state of the process.

The purpose of SIL grading is to analyze safety instrumented function (SIF) circuits in order to determine the safety integrity level (SIL) required to reduce their risks. Generally, relevant technicians and experts conduct analyses such as HAZOP/LOPA, thereby providing seamless integration with SIF identification and SIL grading services. Taking into account the industry characteristics, the properties of the process equipment, the nature of the enterprise, and management requirements, appropriate risk management and SIL classification methods are employed. Through analysis by relevant third-party experts or technicians using methods such as HAZOP/LOPA, it provides seamless integration with SIF identification and SIL classification services. Taking into account the industry characteristics, the properties of the process equipment, the nature of the enterprise, and management requirements, appropriate risk management and SIL classification methods are employed. For SIL classification, China has the standard \"Guidelines for the Application of Layer of Protection Analysis (LOPA) Method\" AQ/T 3054-2015. This standard includes a recommendation table, which is what is commonly referred to as the LOPA table.