Analysis of the mandatory requirements for dual-meter setup for instrument redundancy in hazardous chemical processing units as per current standards

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The 25th National \"Safety Production Month\" in 2026: Everyone talks about safety, and everyone knows how to handle emergencies; identifying and addressing potential risks and hazards. -------------------------------------------------- In facilities for the production and storage of hazardous chemicals, pressure, temperature, and liquid level monitoring instruments constitute a crucial independent layer of protection. Single instruments are subject to risks such as failure, blockage, signal faults, and common-cause failures, and cannot meet the intrinsic safety requirements for major hazard sources and high-risk equipment. In accordance with current **standards and industry norms, high-risk locations must be equipped with a redundant configuration of dual instruments, dual level sensors, and dual measurement points. This is a mandatory requirement for compliance, as well as an essential aspect of safety instrument management and the control of major hazard sources. So, which devices and facilities require dual tables? According to clause 6.3.2 of GB 17681-2024 \"Technical Specifications for Safety Monitoring of Major Hazard Sources of Hazardous Chemicals\", atmospheric and low-pressure storage tanks shall be equipped with at least 2 sets of continuous level detection instruments, or 1 set of continuous level detection instrument together with 2 level switches. Section 6.3.3 specifies that pressure storage tanks shall be equipped with at least 2 sets of continuous level detection instruments and 1 high-high level switch, or with 3 sets of continuous level detection instruments ； The continuous level monitoring instrument shall have local indication, high and low level alarms, as well as high-high and low-low level alarms; the high-high level alarm shall trigger the interlock to close the emergency shut-off valve of the feed pipeline. Section 6.3.4 specifies that for fully refrigerated storage tanks, at least 3 sets of level detection instruments shall be installed, of which at least two sets shall be continuous detection instruments. According to 6.3.2 of SH/T 3007-2014 \"Design Code for Tank Areas in Petrochemical Storage and Transportation Systems\", a set of remote transmission instruments and local indication instruments shall be provided for liquid level measurement in pressure tanks ； 6.3.4 specifies that pressure storage tanks shall be equipped with a separate set of level measurement instruments or level switches dedicated to high liquid level alarms and to interlock the shutdown of the valves in the tank’s feed pipelines. According to clause 4.2.3 of SH/T 3184-2017 \"Design Code for Automation Systems in Petrochemical Tank Farms\", metering-grade pressure tanks shall be equipped with two sets of continuous level measurement instruments fitted with on-tank indicators at the tank top; one of these sets is used to enable the control system to issue alarms for high and low liquid levels. Requirement 4.2.4 stipulates that for the control scheme involving high liquid level alarms and interlocked shutdown of the feed valve, signals from another set of continuous liquid level measurement instruments shall be used. Paragraph 3.3 of T/CCSAS 002-2018 \"Safety Technical Specifications for Nitrocellulose Used in Industry\" stipulates that the cooking and washing tank shall be equipped with two independent sets of liquid level monitoring or observation devices (such as level gauges, sight glasses, etc.), as well as rupture discs and safety valves. The nitration reaction is a high-risk process that requires strict supervision; temperature and pressure sensors in the reactor should be installed in a redundant configuration, and key parameters must be incorporated into the SIS safety instrument system. HG/T 30033-2017 \"Safety Technical Specifications for Hydrogen Fluoride Production\" requires that hydrogen fluoride storage tanks be equipped with both a level measurement system and a weight measurement system, with the two systems providing cross-verification. Article 6.6 of AQ 3059-2023 \"Safety Management Specifications for Liquefied Hydrocarbon Storage Areas in Chemical Enterprises\" stipulates that for newly built pressurized liquefied hydrocarbon storage tanks, the level measurement instruments should be equipped with 2 sets of continuous level measuring instruments and 1 high-high level switch, or 3 sets of continuous level measuring instruments. Guidance on Strengthening the Management of Safety Instrumented Systems in the Chemical Industry, Document No. An Jian Zong Guan San [2014] 116, specifies that for key production units and storage facilities that are classified as being of high importance, as well as for critical temperature, pressure, and level parameters, a redundant voting architecture of 1oo2 or 2oo3 should be adopted based on the level of risk. Common issues in on-site management include: shared pressure tapping points for two sets of instruments, power supplies or signals entering the same circuit board, which can lead to common failure modes ； Hazardous source storage tanks are equipped with only one set of continuous level measurement, relying additionally on manual level checks, which does not comply with current standards. The core requirements for standardization can be summarized in three points: First, high-risk locations must be equipped with two sets of independent instruments ； Second, the source, power supply, circuit, and system are all separated to ensure true redundancy ； Third, instruments based on different principles are cross-verified to ensure accurate measurements and to meet the conditions for alarm and interlock actions.