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This post was last edited by Huahua Jianghu on 2020-3-14 at 17:11. It should be noted that my knowledge is limited; this is provided for reference only, and I welcome corrections and additions from those with more expertise. In the 1940s and 1950s, semiconductor electronics developed rapidly; their application in industrial production provided the technical foundation for process control. Combined with the theoretical advancements in cybernetics, PLCs were introduced in 1969, while DCS was introduced in 1975. The improvement in control levels provides a foundation for producing complex and larger-scale products. As production became more complex and on a larger scale, many accidents occurred in various facilities during the 1960s, which prompted engineers to seriously consider safety issues and find ways to avoid such accidents As a result, many methods for safety analysis have been developed; the most typical one is HAZOP. In terms of control, safety interlock systems other than DSC process control have also emerged, such as ESD, FGS, BMS, etc. By the year 2000, the IEC developed standards covering everything from concepts to practical operations for electronic, electrical, and programming systems used in industrial applications related to safety; this resulted in the publication of IEC61508. Of course, prior to that, various countries and organizations already had relevant standards in place. But this is international, so it carries even greater significance. In this standard, the SIS concept and a series of related concepts are introduced. From then on, all safety interlock systems were included in the SIS, such as ESD, FGS, BMS, and so on. This has led to the systematic standardization of safety functions in terms of electronics, electricity, and programming for industrial process control. This is one of them. Secondly, is the security function itself secure? This specification devotes a large amount of space to explaining this issue. In other words, we have an SIF circuit – what is its safety level? Will it meet the needs? What is that going to require? It’s safe! What is safety? It’s a risk that can be taken! What level of risk is acceptable? That needs to be analyzed! What analysis to use? Use HAZOP! HAZOP is only qualitative; it’s not enough. Then use LOPA for another quantification; of course, LOPA provides a quantification on an order-of-magnitude scale, but this level of precision is sufficient. From then on, the following specific steps were followed: 1, the PID was determined; 2, a HAZOP analysis was conducted. That’s it for now! Check whether a safety interlock is needed; if other safety measures are sufficient, then there is no need to go any further. If that is not sufficient, it is necessary to use SIS; then proceed to step 3, which involves LOPA analysis. The purpose of LOPA analysis is to assign safety functions, one of which is to specify the safety functions for the SIS system as well as the level of the SIF, that is, the SIL rating. 4. Based on the above, prepare the SRS. 5. Conduct a preliminary design of the SIFs. 6. Verify whether the SIL level of each SIF meets the requirements of the analysis. 7. Carry out detailed design. 8. Procure materials. 9. Install the systems. 10. Perform commissioning. 11. Put the systems into operation. 12. Manage the systems.