[Q&A] Series 01 – Can flammable and toxic gas alarm controllers be integrated with DCS?

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**From June 29 to July 11, 2017, a supervision team from the State Administration of Work Safety conducted inspections on the safe production of hazardous chemicals in 5 cities in Shandong Province, identifying a number of safety hazards. It involves 28 enterprises in 5 cities of Shandong Province, with a total of 513 safety hazards identified; many of these enterprises suffer from issues such as unreasonable staffing arrangements, the absence of dual responsibilities for each position, the lack of appropriate emergency plans, and conflicting regulations. Today, let’s talk about combustible gas detection and alarm devices. Regarding this issue, in Document No. 168 issued by the State Administration of Work Safety, it was found that 3 companies had problems with the integrated design of their GDS and DCS control systems. Problem 1: At Shandong Chengtai Chemical Co., Ltd., the combustible gas detection alarms are installed together with the DCS control system, which does not comply with the requirements of the \"Design Code for Detection and Alarm of Combustible and Toxic Gases in Petrochemical Industries\". 2. When designing the combustible and toxic gas alarm system for Han Kun Energy Development Co., Ltd., it was integrated with the process control system, with no separate alarm monitoring setup. The combustible and toxic gas analyzers of Sanfeng Chemical Co., Ltd. were designed in conjunction with the DCS system, without separate input/output cards, which does not meet the requirements of the \"Design Code for Detection and Alarm of Combustible and Toxic Gases in Petrochemical Industries\". In the document titled \"Guiding Opinions of the State Administration of Work Safety on Strengthening the Management of Chemical Process Safety Instrumented Systems\", Document No. An Jian Zong Guan San [2014] 116, a chemical process safety instrumented system (SIS) includes safety interlock systems, emergency shutdown systems, as well as detection and protection systems for toxic and harmful gases, flammable gases, and fires. The safety instrumented system is independent of the process control systems (such as distributed control systems, etc.). Toxic, hazardous, and flammable gas detection and protection systems are designed and implemented in strict accordance with relevant standards; to ensure their reliable operation, such systems should be independent of the basic process control systems. The regulatory document states that combustible gas and fire detection and protection systems, when integrated into the SIS system, should be independent of the BPCS. http://mmbiz.qpic.cn/mmbiz_gif/7ibdJEiardymO6zcmMeI06QIIAqpxtUMCy6FrPK9RQ1oVMOjU0kGwsxYl1Y8teY799AibVb4hP8Jy3D447EC4Wo5Q/0?wx_fmt=gif According to GB50493-2009 \"Code for Design of Detection and Alarm Systems for Flammable and Toxic Gases in Petrochemical Industries\": 3.0.9 Detection and alarm systems for flammable and toxic gases should be installed separately. 5.3.2 Depending on the scale and characteristics of the plant (facility), the alarm devices can be installed in the following ways: 1 The combustible gas and toxic gas detection and alarm systems can be integrated with the fire detection and alarm systems ； 2 It indicates that the alarm devices should use separate industrial program controllers, programmable controllers, etc ； 3 Indicate that the alarm equipment uses conventional analog instruments ； 4 When the combustible gas and toxic gas detection and alarm system is designed in conjunction with the production process control system, the input/output cards should be installed separately. The relevant standard specifies that gas detection and alarm systems for flammable and toxic gases should be independent, and a scheme for their separate installation is provided at http://mmbiz.qpic.cn/mmbiz_gif/7ibdJEiardymO6zcmMeI06QIIAqpxtUMCy6FrPK9RQ1oVMOjU0kGwsxYl1Y8teY799AibVb4hP8Jy3D447EC4Wo5Q/0?wx_fmt=gif. According to GB50116-2013, the Code for Design of Automatic Fire Alarm Systems, it is required that 8.1.2 The flammable gas detection and alarm system shall be designed as an independent unit; flammable gas detectors should not be connected to the detector circuits of the fire alarm controller. When it is necessary to integrate the alarm signals from flammable gas detectors into the automatic fire alarm system, these signals should be connected through a dedicated flammable gas alarm controller. 8.1.3 For combustible gas detectors used in process control within the petrochemical industry, they can be installed in accordance with the relevant provisions of the current standard **\"Design Code for Detection and Alarm of Combustible and Toxic Gases in Petrochemical Industries\" GB50493; however, their alarm signals must be fed into the fire control room. The standard specifies that combustible gas detection and alarm systems should be independently constructed. http://mmbiz.qpic.cn/mmbiz_gif/7ibdJEiardymO6zcmMeI06QIIAqpxtUMCy6FrPK9RQ1oVMOjU0kGwsxYl1Y8teY799AibVb4hP8Jy3D447EC4Wo5Q/0?wx_fmt=gif In the explanatory section of GB 50770-2013 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\": 1.0.2 This code applies to the engineering design of safety instrumented systems in petrochemical plants or facilities. This specification does not apply to fire and gas alarm systems, compressor control systems, boiler control and protection systems, etc., in petrochemical plants or units. This standard specifies that GB 50770-2013 is not applicable to fire and gas alarm systems. http://mmbiz.qpic.cn/mmbiz_gif/7ibdJEiardymO6zcmMeI06QIIAqpxtUMCy6FrPK9RQ1oVMOjU0kGwsxYl1Y8teY799AibVb4hP8Jy3D447EC4Wo5Q/0?wx_fmt=gif To view the LOPA diagram: This diagram shows that FGS and SIS operate at different protection levels; FGS operates at the mitigation level, while SIS operates at the prevention level – they represent entirely different approaches to risk reduction. SIS is used to prevent incidents by carrying out safety functions, while FGS is used to mitigate the consequences after an incident occurs by implementing functions such as sprinkling water or using gas extinguishers. The main difference between FGS and SIS: SIS features a fail-safe design, remains powered under normal conditions, and operates in the event of a power loss. FGS is exactly the opposite: it operates in a normal, uncharged state with line monitoring, and is designed to activate when voltage is applied. FGS composition: As can be seen from the figure, FGS contains more elements than GDS. (Overseas FGS projects are designed in accordance with the NFPA 72 standard.) http://mmbiz.qpic.cn/mmbiz_gif/7ibdJEiardymO6zcmMeI06QIIAqpxtUMCy6FrPK9RQ1oVMOjU0kGwsxYl1Y8teY799AibVb4hP8Jy3D447EC4Wo5Q/0?wx_fmt=gif Past project experience: (1) For small and medium-sized projects, it is advisable to design them in compliance with the domestic design standard GB50493; it is also appropriate to integrate them with the BPCS, using separate I/O units ； (2) When there is a large quantity of flammable and toxic gases, or as required by the local fire department, an independent GDS should be used for alarm control. (3) When flammable and toxic gases are used in SIF, they are incorporated into the SIS based on the results of safety analysis. Statement: The Q&A series is original content; please indicate \"Self-Controlled Cat\" when reproducing it. It is strictly prohibited to compile these Q&As into a book. 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