Collective responses to issues related to the implementation of GB/T50493-2019

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The article provides answers to various questions related to the implementation of GB/T50493-2019, including the installation of toxic gas detectors, the placement of area alarms, the principles for identifying source areas, the installation of oxygen detectors, detector certificates, and multi-component toxic gas detection. These answers aim to help people understand and apply GB/T50493-2019, the \"Design Standard for Detection and Alarm Systems of Flammable and Toxic Gases in Petrochemical Industries\", more accurately. Digital display instruments: yunrun.com.cn/product/. Issues related to the setup of toxic gas detectors: Question: When setting up toxic gas detectors, is it necessary to configure them for all 56 types of toxic gases listed in GBZ/T223-2009 \"Specifications for the Installation of Toxic Gas Detection and Alarm Devices in Workplaces\", as well as the 339 chemical hazardous gases listed in GBZ2.1-2019 \"Occupational Exposure Limits for Hazardous Factors in Workplaces – Part 1: Chemical Hazardous Factors\"? Answer: GBZ/T223-2009 \"Specifications for the Installation of Toxic Gas Detection and Alarm Devices in Workplaces\" is a standard related to occupational health and safety. The types of toxic gases listed are provided as appendices for reference only, and it is not mandatory to follow the guidelines outlined in it when designing GDS systems ； GBZ2.1-2019 \"Occupational Exposure Limits for Hazardous Factors in the Workplace – Part 1: Chemical Hazardous Factors\" is also a standard related to occupational health and safety; it deals primarily with the OEL values for toxic gases in the working environment. The types of chemical hazardous gases listed are part of the requirements for occupational health monitoring, and their consideration is not necessary in GDS design. GB/T50493-2019 is a safety standard; it lists the common toxic gases used in the petrochemical industry. The basis for this listing comes from: ① the 54 gases or vapors specified in the \"Catalogue of Highly Toxic Substances\" issued under Document No. Wei Fa Jian Fa 142 ； ②According to the standard GB 30000.18—2018, \"Specifications for the classification and labeling of chemicals – Part 18: Acute toxicity\", acute toxic gases classified as Category 1 and Category 2 in terms of acute toxicity hazards. The toxic gases listed in GBZ/T223-2009 and GBZ2.1-2019 cannot be used as a basis for determining toxic gases according to GB/T50493-2019, but they can be used as a basis for setting the alarm thresholds for toxic gases. Issues regarding the installation of zone alarms: According to the explanatory notes in Article 5.3.1 of GB/T50493-2019, when the number of detectors in a given alarm zone is less than 10, the noise level at the site is below 85 dBA, and the detectors are equipped with integrated acoustic and optical alarms, it is not necessary to install zone alarms ； When the noise level at the site is above 85 dBA, a local alarm must be installed there. There are three conditions in the provision notes: ① The number of detectors in the alarm zone is less than 10 ； ②The noise level at the site is below 85 dBA ； ③The on-site detector is equipped with an integrated acoustic and optical alarm. Explanation of Clause 3.0.4 of GB/T50493-2019: To alert on-site workers, on-site area alarms are typically installed at the main entrances and exits of the production site as well as in areas with high noise levels (noise exceeding 85 dB(A)). In relatively enclosed areas such as compressor rooms, pump houses, silos (storage tanks), analysis booths, and laboratory rooms where inspections are carried out and where the accumulation of flammable or toxic gases may occur, audible and visual alarms are installed in prominent locations at the entrances and exits, with the aim of alerting the inspectors to be cautious when entering these areas. Question: Is it only when all three conditions in 5.3.1 are met that there is no need to set up area alarms? Is it necessary to install a zone alarm when any one of the three conditions is not met? In other words: if the number of detectors in an alarm zone is greater than 10, an area alarm still needs to be installed, even if the noise level is below 85 dBA and the detectors on site are equipped with integrated audio and visual alarms ； If the noise level at the site is above 85 dBA, it is still necessary to install a zone alarm, even if the number of detectors in the alarm zone is less than 10 and the detectors at the site are equipped with integrated acoustic and optical alarms ； If the on-site detectors do not come equipped with integrated sound and light alarms, then regional alarms still need to be installed, even if the number of detectors in the alarm zone is less than 10 and the noise level is below 85 dBA. Answer: The GDS should divide the devices or units into alarm zones according to the warning ranges of the combustible gas and toxic gas detection and alarm systems, and then install on-site area alarms in accordance with these alarm zones. When the number of detectors in the alarm zone is less than 10, the ambient noise level is below 85 dBA, and the detectors on site are equipped with integrated acoustic and optical alarms, then it is not necessary to install a zone alarm at that location. On-site area alarms are installed at the main entrances and exits of the production site as well as in areas with high noise levels (noise exceeding 85 dB(A)), in order to alert inspection personnel to be cautious when entering such places. For example, in relatively enclosed areas such as compressor rooms, pump rooms, silos (storage tanks), analysis booths, and laboratory facilities where people enter for inspection work and where there is a risk of the accumulation of flammable or toxic gases, audible and visual alarms should be installed in prominent locations at the entrances and exits. Even if the number of detectors in such enclosed areas is less than 10, the noise level there is below 85 dBA, and the detectors are equipped with integrated audible and visual alarms, it is still necessary to install audible and visual alarms in prominent locations at the entrances and exits of these enclosed areas. Whether additional area alarms are needed inside such enclosed areas depends on their size and specific conditions, as determined according to clause 5.3.1. If the number of detectors in the enclosed area is greater than 10, or if the noise level at that location is above 85 dBA, or if the detectors there do not come equipped with integrated sound and light alarms, then it is still necessary to install additional area alarms within that enclosed area; otherwise, only the area alarms installed at the main entrances and exits are sufficient). Principles for identifying release sources: Question: According to clause 4.1.3 of the standard, which defines the sources of flammable and toxic gases, how should the term \"frequently operated valve assemblies\" be understood? Do automatic valves as well as manual valves fall under this category? Answer: “Frequently disassembled and frequently operated” refers to flanges or valve assemblies that need to be disassembled or operated every shift or every day, as required by the manufacturing process. Manholes, blind flanges, etc. are flanges that are not operated frequently; manual shut-off valves and manual bypass valves located before and after isolation valves and control valves in installations or equipment also belong to valves that are not used often. Statistically, valves that are operated frequently have a much higher probability of leakage than isolation valves that only activate in an emergency situation. Therefore, the frequently used liquid and gas sampling ports, liquid (gas) discharge and vent ports, flanges that are often removed, and valve assemblies that are frequently operated require detectors. Instrument control valves are valves that operate frequently, but unlike the definition of \"frequent operation\" in section 4.1.3, instrument control valves do not need to be considered as sources of W release. Oxygen detector setup issues: Question: How should low oxygen levels be understood? What are the regulations or limits? The equipment in a certain production facility is equipped with a nitrogen sealing system; the facility is enclosed, and it has a ventilation system that operates 6 times per hour under normal conditions and 12 times per hour in case of an emergency. Is it necessary to install oxygen probes at each release source (valve) in this case? Answer: Determining whether there is a lack of oxygen should be based on the actual environment, with altitude also serving as a reference factor. The factory building is equipped with nitrogen sealing systems, and it is necessary to consider whether a nitrogen leak could create an oxygen-deficient environment in the surrounding area. If such an oxygen-deficient environment can be formed – for example, if the oxygen concentration drops by 1–2 percentage points below the normal level – then detectors should be installed. Depending on the owner’s management requirements, it is also possible to use oxygen-deficiency alarm signals to activate emergency fans. Detector certificate issue: Question: According to clause 3.0.5 of the standard, “Combustible gas detectors must possess a type approval certificate for measuring instruments issued by a **designated authority or an authorized testing unit, an explosion-proof certification, and a type inspection report for fire protection products.” Do combustible gas detectors also need to obtain a **type approval certificate for measuring instruments and CCCF certification?** Answer: ① According to Announcement No. 48 of 2019 issued by the State Administration for Market Regulation on November 04, 2019, regarding the publication of the list of measuring instruments subject to mandatory regulation, combustible gas detectors no longer require type approval as measuring instruments; **however, toxic gas detectors, where required by regulations, must undergo type approval as measuring instruments. ②In accordance with Announcement No. 11 of 2018 issued by the **State Administration for Market Regulation** and the **Certification and Accreditation Administration**, as of June 11, 2018, combustible gas detectors are no longer subject to mandatory product certification (CCCF). Enterprises may voluntarily choose designated certification bodies to carry out certification in accordance with the existing procedures, in order to obtain a type test report for fire protection products (which is required) and a fire protection product certification certificate (which is optional). Problem of detecting multi-component toxic gases: Question: The composition of the gas mixture in the gas pipeline is as follows: 1) CO: 38.64% ； 2) H2S: 3.4%; 3) NH3: 0.001% ； 4) HCN: 0.008%. According to the calculations, the concentrations of H2S, NH3, and HCN in the pipeline all exceed the allowable OEL levels. Should only CO be tested, or is it necessary to test H2S, NH3, and HCN as well? If all the tests specified in clause 3.0.1 of GB/T50493-2019 are to be carried out, several times as many detectors will be required, and from the perspective of cost and subsequent maintenance, the owner does not approve of this. If only CO is detected, are there any safety issues? It does not conform to the current standard requirements; could it fail approval during future drawing reviews or project inspections? Answer: The function of a GDS is to detect leaks, and the detector settings are based on the concentration of the substance leaking into the atmosphere, rather than on the composition of the substance within the pipeline. Gas contains various toxic gases, and the detectors should be designed primarily for detecting these toxins. If a gas leak occurs, the concentration of H2S in the atmosphere may also exceed the threshold; therefore, it is recommended to monitor both CO and H2S simultaneously, while other toxic components need not be detected. Related Reading: Interpretations by Wenke and Wu on the standards – Challenges in the design and application of GB/T50493-2019; Q&A on knowledge related to the GB/T50493-2019 standard; Pei Bing’an’s interpretation of GB/T50493-2019, the design standard for detection and alarm systems for flammable and toxic gases in the petrochemical industry