Knowledge sharing on security levels

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Safety Integrity Level: The safety integrity levels are divided into SIL1, SIL2, SIL3, and SIL4. The higher the safety integrity level, the greater the ability of the safety instrumented system to perform its safety functions. The safety integrity level of petrochemical plants or units is at most SIL3. In the low-demand operation mode, the safety integrity level of the safety instrument function should be evaluated using the average failure probability. The low-demand operation mode refers to a situation where the safety instrument function is executed no more than once per year. Typically, the safety instrument systems in petrochemical plants and units operate in a low-demand mode. In high-demand operation modes, the safety integrity level of the safety instrumented function should be measured by the hourly hazardous failure probability. The high-demand operation mode refers to a situation where the activation frequency of the safety instrument function is more than once per year. For safety instrument functions with continuous operation or frequent actions, it belongs to a high-demand operation mode.