Regarding SIS and ESD
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(II) Automated control systems for chemical production facilities and equipment involving major hazard sources that meet safety production requirements； For Class 1 or Class 2 major hazard sources, an emergency shutdown system is required ； (III) Install emergency shutoff devices for key facilities such as toxic gases, highly toxic liquids, and flammable gases among the major hazard sources ； For facilities handling toxic gases, emergency devices for dealing with leaks must be installed. Major hazard sources of grade 1 or 2 involving toxic gases, liquefied gases, or highly toxic liquids are equipped with an independent Safety Instrumented System (SIS) ； -------Excerpt from **Order No. 40 of the State Administration of Work Safety**: For key hazard sources of level 1 and 2 that do not involve toxic gases, liquefied gases, or highly toxic liquids, is it not necessary to install a SIS? Is it sufficient to install only an ESD? What are the differences between SIS and ESD in terms of the system architecture as well as the field actuators?
SIS includes ESD; the selection of SIS and ESD components varies depending on the system as well as the field actuators. SIS is required to meet SIL certification standards, ensuring a high level of safety.
SIS stands for Safety Instrumented System, a system designed for continuous safe production. ESD is the emergency shutdown system, which is designed to safely stop production in case of danger. Reliability was emphasized earlier; for instruments, options such as two-out-of-two or three-out-of-two are required, with control of each component being based on the principle of reliability. The latter focuses on the ability to automatically stop production, and there are requirements regarding process operations; this implies that the control system design must incorporate elements that ensure operational efficiency. This includes a series of interconnections, as well as detailed components such as actuator blocks and pneumatic units designed to increase the speed at which valves close