Is it necessary to install a SIS for Level 4 major hazard sources, and what are the relevant standard references?

One can take a look at Document No. 116 from 2014, as well as Order No. 40 from 2011. According to **Order No. 40 issued by the State Administration of Work Safety, it is specified that emergency shutdown systems must be installed for major hazard sources of Level 1 and Level 2； For Category 1 and 2 \"AND\" situations, where toxic gases, liquefied gases, or highly toxic liquids are involved, an SIS must be installed. In other words, levels 1 and 2 only require an emergency shutdown system, but systems such as SIS are necessary for toxic substances, liquefied gases, and toxic liquids. On the other hand: In fact, a Hazop and SIL analysis should be conducted in order to configure an SIS of the appropriate level. In other words, through analysis of the aforementioned emergency shutdown system, it may be necessary to use a SIS, or a DCS might be sufficient. SIS needs to be installed for SIL1 and above. SIS: It includes field tables, cards, and systems, and refers not to just one single component.

Additional note: GB 18218-2018 provides definitions and calculations for the classification of major hazard sources

Document No. 116 of 2014 mentioned the two key aspects and one major aspect, but it did not specify how many levels of major hazard sources there are; does a major hazard source necessarily require an SIS?

Take a look at my replies on floors 2 and 3, then find the corresponding articles to check. The answer can be found

There are also **specifically listed key hazardous process units (such as hydrogenation units, nitration units, etc.) for which HAZOP analysis and SIL grading are required; based on these results, the SIS is then designed – this is the overall procedure.