Range of common toxic gases and setting of alarm values

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Range settings and alarm values for common toxic gases: With the implementation of GB/T 50493-2019, the \"Design Standard for Detection and Alarm Systems of Flammable and Toxic Gases in the Petrochemical Industry,\" the long-standing issue of determining the range settings and alarm values for common flammable and toxic gases has once again become a topic of interest. This article shares the standards underlying these settings as well as experimental data from relevant manufacturers, in the hope of helping everyone resolve such issues more quickly. In accordance with **standard and regulatory requirements, relevant enterprises install gas detection devices in workplaces where acute occupational poisoning may occur, depending on the technical level of the automatic alarm systems available. When the concentration of toxic gases in the area where the alarm device is installed reaches the set alarm threshold, the alarm unit immediately emits sound and light alerts that are sent to the control room in that area, allowing the enterprise to quickly activate emergency plans and measures to prevent poisoning incidents and thus ensure the health and safety of the workers. How to set the alarm device and alarm values? ☟Requirements for setting up alarm devices: These should be determined based on the physical and chemical properties of the gas, the characteristics of the source of release, the layout of the production site, geographical conditions, environmental climate, and the routes used for operations and inspections, in order to ensure real-time and effective alerts. Installed in work areas where highly toxic or extremely toxic gases may be released: generally located at the seals of gas compressors and liquid pumps ； Liquid sampling port and gas sampling port ； Liquid discharge (water) port and vent port ； Flanges and gate assemblies for equipment and pipelines, etc. When the conditions for installing a fixed alarm are not available, a portable toxic gas alarm should be equipped. Requirements for setting alarm values: The setting of alarm values should adhere to the principles of safety, science, and feasibility, so as to ensure that workers on site can respond promptly, take emergency rescue measures, and eliminate abnormal conditions. The alarm values can be set at three levels: forecast, alarm, and high alarm. Employers should, based on the toxicity of the toxic gases, the site conditions, and the selection of alarm devices, establish at least an alarm value and a high-alarm value, or a pre-alarm value and an alarm value. The forecast values and alarm values can be set in accordance with the following standards (additional information is welcome): GB/T 50493-2019 \"Design Standards for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Industries\", GBZ/T 223-2009 \"Specifications for the Installation of Detection and Alarm Devices for Toxic Gases in Workplaces\", GBZ 2.1—2019 \"Occupational Exposure Limits for Hazardous Factors in Workplaces – Part 1: Chemical Hazardous Factors\", GBZ/T 300.1-2017 \"Determination of Toxic Substances in Workplace Air\", GBZ/T 192.1-2007 \"Determination of Dust in Workplace Air\", GBZ/T 295—2017 \"General Principles for Biological Monitoring of Occupational Populations\", GBZ/T 224—2010 \"Terminology in Occupational Health\", GBZ/T 229.2-2010 \"Classification of Jobs with Occupational Disease Hazards in Workplaces\", GBZ/T 225-2010 \"Guidelines for Employers on the Prevention and Control of Occupational Diseases\". GB/T 50493-2019 specifies the detection ranges and alarm values for flammable gases as well as toxic and hazardous gases, as detailed below: 5.5.1 The measurement range shall comply with the following requirements: 1 The measurement range for flammable gases shall be 0~100% LEL. 2 The measurement range for toxic gases should be 0~300% OEL ； When the measurement range of existing detectors cannot meet the above requirements, the measurement range for toxic gases can be 0~30% IDLH ； The measurement range for ambient oxygen can be 0~25% VOL. 3 The linear combustible gas measurement range is 0~5LEL·m. 5.5.2 The setting of alarm values shall comply with the following provisions: 1 The first-level alarm setting for combustible gases shall be less than or equal to 25% LEL. 2 The secondary alarm setpoint for combustible gases should be less than or equal to 50% LEL. 3 The first-level alarm setting for toxic gases should be less than or equal to 100% OEL, while the second-level alarm setting for toxic gases should be less than or equal to 200% OEL. When the measurement range of existing detectors is insufficient to meet the measurement requirements, the first-level alarm setpoint for toxic gases shall not exceed 5% IDLH, and the second-level alarm setpoint for toxic gases shall not exceed 10% IDLH. 4 The preset value for the oxygen peroxide alarm in the environment should be 23.5% VOL, while the preset value for the oxygen deficiency alarm in the environment should be 19.5% VOL. 5 For linear combustible gas measurement, the set value for the first-level alarm should be 1 LEL·m ； The set value for the secondary alarm should be 2LEL·m. Unit explanation: LEL: The lowest concentration of a mixture of flammable vapors, gases, or dust with air at which an explosion can occur upon exposure to a flame source; it is also known as the lower explosive limit. OEL: Occupational Exposure Limit (for toxic and harmful gases; the detection range must be selected based on the specific gas. Different gases have different occupational exposure limits, as well as different detection ranges and alarm values. ) IDLH: Concentration that poses an immediate threat to life and health; toxic and harmful gases are generally expressed in ppm. VOL: %Vol refers to the volume percentage. The overreported value can be determined by the enterprise after taking into comprehensive account various on-site factors, such as toxic gases and their toxicity, personnel conditions, accident consequences, processes and equipment, as well as meteorological conditions. The alarm indicates that a large amount of toxic gas has been released in this facility, reaching a dangerous level; it is necessary to promptly activate the emergency response plan, ensure the protection of staff, and evacuate those people in the area. Ranges of common toxic gases and set values for alarms☟ Data source: Wuxi Shihhe Safety Equipment Co., Ltd. Based on GB50493-2019 \"Design Code for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Enterprises\", these values have been determined through experimental data; Wuxi Shihhe Safety Equipment Co., Ltd. retains the right to interpret them. This text is provided for reference only. Wuxi Shishan Safety Equipment Co., Ltd. was established in 2003. It is a company that works in partnership with the German company GFG, and specializes in the field of gas safety measurement and control. It focuses on gas safety detection, as well as automatic control of industrial processes and online monitoring of environmental pollutants and dust. Its main products include gas safety detection instruments, online analyzers for environmental pollutants, CEMS systems for continuous flue gas monitoring, VOCs online detection systems, as well as automatic control systems for fire and gas (F&GS) and gas detection/monitoring (GDS) systems. How to establish an alarm management system☟ To improve the management of combustible gas and toxic gas detection alarms (hereinafter referred to as “alarms”), and to ensure the safe operation of production facilities, it is essential to have a comprehensive alarm management system. Such a system can be developed by defining relevant responsibilities and roles, selecting and installing alarms, carrying out routine maintenance and calibration, as well as establishing procedures for inspection and evaluation. The Equipment Department is the authority in charge of alarms in the factory, and its main responsibilities include: determining the appropriate models of alarms for new installations, upgrades, and technical improvement projects in the factory, as well as conducting inspections prior to their deployment. Responsible for the updating of factory alarms and the review of major maintenance plans. Responsible for the regular inspection of factory alarms, as well as for evaluating their operational status (installation rate, usage rate, integrity rate). Responsible for the annual (quarterly) maintenance of the alarm system. Responsible for organizing the construction of adding and updating alarms. Responsible for the operation status of alarms, as well as the inspection of maintenance and repair quality. The Safety and Environment Department is involved in the review of new alarm devices added to the unit, as well as in the acceptance checks prior to their deployment. Its main responsibilities include overseeing the removal, deactivation, or temporary suspension of existing alarm devices, and keeping records of such actions ； Responsible for overseeing the design, installation, commissioning, management, and maintenance of alarms. Responsible for reviewing the installation of new equipment and the addition of new alarms in the unit. Responsible for the management of portable alarms. The Electrical and Instrumentation Workshop is responsible for the daily maintenance of alarms, and its main duties include preparing plans for the retirement, replacement, and major repairs of alarms, which are then submitted to the Equipment Department. When the workshop needs to remove or deactivate alarms, it must obtain approval from the Safety and Environment Department and file a record with the Equipment Department; the Electrical and Instrumentation Workshop is responsible for carrying out the task. Responsible for the management, daily maintenance, and calibration of alarms. Other relevant departments are primarily responsible for the following tasks: Before purchasing alarms, the supply department must obtain approval from the Equipment Department regarding the selected suppliers as well as the specifications and models. Only after confirmation by the Equipment Management Department and the Safety and Environmental Protection Department of the branch company can the purchase be carried out; otherwise, the procedures will not be processed. Operators in the production workshop must understand the principles and functions of alarms, as well as know how to operate them. Selection and Installation: The alarm selected must meet the following requirements: its functions, structure, performance, and quality must comply with **legal requirements. Obtain a license for manufacturing measuring instruments issued by the technical supervision administrative department. Imported alarms must obtain a type approval certificate for measuring instruments issued by the General Administration of Quality Supervision, Inspection and Quarantine. Obtain an explosion-proof certification issued by a **designated explosion-proof inspection agency, and meet the explosion-proof rating required at the installation site. Advanced technology, stable quality, rapid response, easy maintenance, and guaranteed supply of spare parts. It is less affected by other gases, as well as by temperature and humidity. It meets **or industry standard specifications. All newly built, expanded, or renovated production facilities and storage and transportation systems must be equipped with alarms in accordance with the \"three simultaneities\" principle. Key issues to consider when installing alarms: the properties of flammable and toxic gases that may leak ； When installing outdoors, environmental factors such as the prevailing wind direction should be taken into account ； The impact of rainwater and toxic gases on detection elements ； It is easy to maintain and verify. Daily maintenance and calibration: The electrical and instrumentation workshop is responsible for the management of alarms as well as their daily maintenance; the installation rate, utilization rate, and integrity rate of these alarms should all be 100%. The electrical and instrumentation workshop establishes comprehensive technical documentation and formulates regular calibration plans. Assign a dedicated person to be responsible for the daily maintenance of the alarms, and carry out thorough inspections of these alarms in accordance with the company’s equipment inspection procedures ； Cooperate with the technical supervision department to carry out regular inspections ； Responsible for regularly calibrating the alarms (the person performing the calibration must hold a certification as a metrology inspector) to ensure their safe and stable operation. Testing and calibration of alarms: Regular testing of alarms should be carried out in accordance with standard requirements, at least once a year. The regular calibration of alarms is carried out quarterly (except during the quarters when inspections are conducted by the technical supervision department). The standard gases used for the regular inspection and calibration of alarms, as well as the testing instruments, must meet the requirements specified in the metrological inspection regulations. Inspection and assessment methods: During inspections of equipment in the factory, alarms are included as one of the items to be checked. Check and evaluate technical indicators: the installation rate, integrity rate, and utilization rate of alarms should all be 100%.