Regarding gas detection in confined spaces [Daily Question 20090410]

The detection of harmful gases in confined spaces requires the detector to enter the area first for testing. Remote detection of the components of harmful gases in confined spaces should be carried out before anyone enters. Testing is carried out in the following order: (1) Verification of oxygen, to measure the current oxygen concentration level ； (2) Identification of flammable gases, monitoring changes in flammable gas levels ； (3) Detection of toxic gases to determine whether their concentrations are below the Permissible Exposure Limit (PEL) specified by OSHA. The common toxic gases in enclosed spaces are hydrogen sulfide and carbon monoxide; other toxic compounds are not included. The detectors offered by RAE Company can detect single gases as well as mixed toxic gases. It is very important to take samples from the top, middle, and bottom of a confined space in order to measure the concentrations of various gases or vapors. Some gases are lighter than air (such as methane and flammable gases), and they can be collected at the upper part of enclosed spaces ； Some gases are denser than air (such as hydrogen sulfide), and they can be found at the bottom of enclosed spaces ； There are other gases whose density is almost the same as that of air (such as carbon monoxide), and they can be detected in the middle of enclosed spaces.

Our unit currently follows the following practices: 1. Sampling and analysis should be conducted before entering confined spaces for work. Sampling for analysis should be representative and comprehensive. When the volume of the confined space is large, samples should be taken from the upper, middle, and lower sections for analysis, to ensure that the concentration of flammable gases and the oxygen level in all areas within the confined space are within acceptable limits (when the lower explosive limit of the flammable gas is greater than 4%, a concentration of no more than 0.5% is considered acceptable) ； When the lower explosion limit is less than 4%, a test concentration of no more than 0.2% is considered acceptable ； The oxygen content should be between 19.5% and 23.5% to be considered acceptable; toxic and harmful substances must not exceed the specified \"maximum allowable concentrations of toxic substances in workshop air\" (the maximum allowable concentration of H2S shall not exceed 10 ppm). After the analysis results are obtained, the sample must be retained for at least 4 hours. The temperature in confined spaces should be around normal room temperature; it must be measured again at least every 4 hours during operations. If any parameter fails to meet the requirements, work must be stopped immediately. 2. The equipment, containers, and process systems have been effectively isolated; there are no jackets, fillers, linings, seals, etc. inside, and no toxic, harmful, or flammable gases will be released. Once the initial sampling analysis shows satisfactory results, the analysis data will remain valid for an extended period of time ； When equipment or containers have jackets, packing, linings, seals, etc. that may release toxic, harmful, or flammable gases, and work is to be carried out more than 1 hour after the sampling analysis shows satisfactory results, re-testing and analysis must be conducted to obtain satisfactory results before work can resume.

Our company currently requires an oxygen level analysis before entering confined spaces for work; if welding is to be carried out, a welding analysis is also necessary； Conduct fire analysis for hot work in Class A areas ； However, there are deficiencies regarding hot work in the pipe galleries, as they are enclosed pipelines (classified as Zone 2); hot work analysis is not conducted when such work is carried out frequently. What are everyone’s thoughts on this issue?

For reference: Sampling point settings: GBZ 159-2004 – Specifications for sampling of hazardous substances in workplace air; GBZT 206-2007 – Specifications for gas detection using direct-reading instruments in confined spaces. Acceptance criteria: GBZ T205-2007 – Specifications for protecting workers from occupational hazards in confined spaces; GBZ 2.1-2007 – Occupational exposure limits for hazardous factors in the workplace, Part 1: Chemical hazardous factors

1. Sampling and analysis should be conducted before entering a confined space for work. Sampling for analysis should be representative and comprehensive. When the volume of the confined space is large, samples should be taken from the upper, middle, and lower sections for analysis, to ensure that the concentration of flammable gases and the oxygen level in all areas within the confined space are within acceptable limits (when the lower explosive limit of the flammable gas is greater than 4%, a concentration of no more than 0.5% is considered acceptable) ； When the lower explosion limit is less than 4%, a test concentration of no more than 0.2% is considered acceptable ； The oxygen content should be between 19.5% and 23.5% to be considered acceptable; toxic and harmful substances must not exceed the specified \"maximum allowable concentrations of toxic substances in workshop air\" (the maximum allowable concentration of H2S shall not exceed 10 ppm). After the analysis results are obtained, the sample must be retained for at least 4 hours. The temperature in confined spaces should be around normal room temperature; it must be measured again at least every 4 hours during operations. If any parameter fails to meet the requirements, work must be stopped immediately. 2. The equipment, containers, and process systems have been effectively isolated; there are no jackets, fillers, linings, seals, etc. inside, and no toxic, harmful, or flammable gases will be released. Once the initial sampling analysis shows satisfactory results, the analysis data will remain valid for an extended period of time ； When equipment or containers have jackets, packing, linings, seals, etc. that may release toxic, harmful, or flammable gases, and work is to be carried out more than 1 hour after the sampling analysis shows satisfactory results, re-testing and analysis must be conducted to obtain satisfactory results before work can resume.

This is a relatively comprehensive document: Zhejiang Province Regulations on Safety Management for Work in Confined Spaces (Trial). 1 Scope of Application: These regulations specify the safety requirements for work in confined spaces, emergency measures, and the management of the \"Permit for Work in Confined Spaces\". These procedures apply to work in confined spaces in chemical enterprises. It can be used as a reference for work in confined spaces in enterprises such as municipal services, storage and transportation, and metallurgy. 2 Referenced Standards The provisions of the following standards become provisions of this regulation through reference in it; the versions indicated are all valid at the time of issuance. Subsequently, for any modifications to the following standards, all parties using these procedures should consider adopting the latest versions of those standards. · GB Z1-2002 Hygienic Standards for the Design of Industrial Enterprises · GB Z2-2002 Occupational Exposure Limits for Hazardous Factors in the Workplace · GB8958－2006 Safety Regulations for Operations Involving Oxygen Deficiency · GB 12331-90 Classification of Toxic Operations · GBZ159-2004 Sampling Specifications for Monitoring Hazardous Substances in Workplace Air · GB1251.1-89 Warning Signals in the Workplace – Auditory Warning Signals · GB/T19670－2005 Mechanical Safety – Prevention of Unintended Starting · GB 3883.1-91 Safety of Handheld Electric Tools (Part 1: General Requirements) · GB 16556—1996 Self-Contained Breathing Apparatus · GB 3836.1-2000 Electrical Equipment for Explosive Gas Environments – Part 1: General Requirements · GB 3836.2-2000 Electrical Equipment for Explosive Gas Environments – Part 2: Explosion-Proof Type “d” · GB/T 3805-1993 Extremely Low Voltage (ELV) Limits · GB 11651-1989 Rules for Selecting Personal Protective Equipment · HG23011-1999 Safety Regulations for Welding Operations in Factories · HG23013-1999 Safety Regulations for Plugging and Unplugging Blind Flanges in Factories · HG23018–1999 Safety Regulations for Equipment Maintenance Operations in Factories · HG23012–1999 Safety Regulations for Operations Inside Factory Equipment 3 Definitions The following definitions are used in these regulations. 3.1 Chemical confined spaces refer to areas within chemical enterprises where the following potential dangers and hazards exist, including: 3.1.1 the interiors of various enclosed, narrow, and poorly ventilated equipment, towers, pipelines, containers, reactors, furnaces, etc., with restricted access ； 3.1.2 Enclosed or open spaces with a depth of more than 1.2 meters, spaces that are not designed for prolonged use ； 3.1.3 Confined areas underground or in underground structures with poor ventilation. 3.2 Chemical confined space operations: Operations carried out inside chemical confined spaces. 4 Preparations before work 4.1 Identification of hazardous and harmful factors. Identification should be carried out by personnel with the appropriate professional qualifications, through an analysis of the following (but not limited to) hazardous factors: 4.1.1 Whether the structure within the confined space is complex or narrow, whether there are partitions, slopes, or other complex structures that may restrict operations, and whether there is a risk of mechanical injuries ； 4.1.2 Whether there are mechanical kinetic energy devices in the space, and whether they can be effectively locked or interlocked ； 4.1.3 Presence of acids, alkalis, corrosive chemicals, or their vapors inside the space ； 4.1.4 Presence of flammable chemicals, toxic chemicals, or their vapors ； 4.1.5 Whether the space is effectively isolated from external materials ； 4.1.6 Whether the working lighting conditions meet the requirements ； 4.1.7 Are there high temperatures and high humidity that cause fatigue among workers? ； 4.1.8 Whether there is hypoxia or hyperoxia, and whether ventilation is inadequate ； 4.1.9 Whether cross-operation may occur 4.1.10 Other hazardous factors 4.2 Verifying or determining the presence of hazardous factors 4.2.1 For the hazardous factors that have been identified, it is necessary to assess their severity based on the process, the structure of the equipment, and the chemicals present ； When necessary, qualitative and quantitative analyses should be employed to determine the types and quantities of chemicals present in the confined space, and hazard analysis and risk assessment should be carried out in conjunction with relevant technical personnel. 4.2.2 Gas sampling and analysis should be conducted in all confined spaces, and the results of such analysis serve as an important basis for issuing work permits ； 4.3 Conduct a comprehensive analysis of various hazardous factors to establish procedures for working in confined spaces as well as corresponding safety and technical protective measures. 4.4 Clarify the responsibilities of all personnel working in confined spaces. If necessary, detailed operating procedures should be established for commanders, operators, supervisors, and rescue personnel. 4.5 Clarify the tools, methods, and content of information communication; where feasible, secure and advanced communication tools can be utilized to assist. 4.6 Procedures for obtaining permits for work in confined spaces 4.6.1 Enterprises carrying out work in confined spaces shall implement an internal permit system. The enterprise’s safety management department is responsible for the management of work permits. 4.6.2 The department in charge of the operation shall prepare a safety operation plan, and based on this plan, fill in the brief procedures and details of the operation on the permit; the operation plan shall serve as an attachment to the permit ； 4.6.3 The safety authorities shall, based on the results of the analysis of hazardous factors, list those factors on the permit and specify the basic safety and technical protection measures ； 4.6.4 When the safety and technical protection measures specified in the operation plan involve other departments, the person in charge of those departments shall implement them in accordance with the requirements of the plan and such safety and technical protection measures, and sign to confirm on the operation permit ； 4.6.5 After the safety technical protection measures are signed and approved by the persons in charge of relevant departments, the work permit is submitted to the plant-level safety officer for approval. The approved work permit is placed under the management of the safety authority. 4.7 All personnel involved in work in confined spaces should receive relevant training. It is necessary to clarify job responsibilities during operations, and master safety operation knowledge and skills, information communication methods, emergency rescue plans, as well as the use and requirements of protective equipment ； 4.8 In accordance with safety technical protection measures, check the effectiveness and adequacy of safety protection equipment and emergency supplies (including emergency medications) ； 4.9 Safety isolation: All pipes and openings connecting the equipment to the outside world must be effectively isolated from it. The power supply connecting the device to the outside world should be effectively disconnected. 4.9.1 Pipeline safety isolation can be achieved by inserting a blind plate or removing a section of the pipeline; water seals or valves cannot be used as substitutes for blind plates or removed pipe sections. The inserted blind plates must be registered and numbered when necessary. 4.9.2 To ensure a proper disconnection of the power supply, measures such as removing the power fuse or turning off the power switch and locking it in place should be taken, along with the installation of warning signs. 4.10 Cleaning and Purging Before entering a confined space for work, it is necessary to clean and purge the space to meet the following requirements: 4.10.1 Before cleaning, the workers must be familiar with the physical and chemical properties of the substances present in the confined space, as well as the safety data sheets for those materials. 4.10.2 During cleaning, inert gases such as nitrogen should be used first to protect or displace flammable, explosive, or toxic and harmful substances ； Then, steam or hot water is used as the cleaning medium; no dead ends should remain during cleaning, and the cleaning sequence should be from top to bottom. If there are materials that are difficult to clean with steam or hot water, appropriate solvents should be used for cleaning, giving priority to non-toxic substances ； After cleaning, wash it again with steam or hot water. 4.10.3 After cleaning, air replacement should be carried out, and the levels of oxygen and other hazardous gases should be monitored at all times. 4.10.4 When using compressed air for displacement, consideration should be given to the displacement at dead ends, and the flow rate should be kept below 2 cubic meters per minute. 4.10.5 The oxygen content after permutation should be 18–21%. 4.10.6 The concentrations of toxic, harmful, and other hazardous gases in confined spaces shall comply with the requirements of GB Z2-2002. 5 Safety technical measures during operations 5.1 Ventilation Measures must be taken to ensure good air circulation in confined spaces. 5.1.1 Open all manholes, handholes, material access holes, dampers, smoke vents, etc. to enable natural ventilation. 5.1.2 When natural ventilation is limited, mechanical forced ventilation must be employed, with a frequency of no less than 3 to 5 times per hour. 5.1.3 The appropriate amount of fresh air required during operation should be 30 to 50 cubic meters per hour. Oxygen or oxygen-enriched air must not be supplied to confined spaces. 5.1.4 When using ducted air supply, it is necessary to analyze and verify the medium inside the ducts as well as the air source prior to ventilation, in order to continuously introduce air that keeps the oxygen level in the confined space within a normal range. 5.2 Periodic Monitoring 5.2.1 Within 30 minutes before starting the operation, gas sampling and analysis must be conducted again in the confined space to verify that the analysis results meet the requirements for a safe work permit. If it does not meet the requirements, the above procedures for replacement, cleaning, or ventilation must be followed until the safety requirements for operation are satisfied. 5.2.2 The analyzed samples collected must be representative; they should be kept in the gas sampler for at least 4 hours, or even until the end of the operation. When the volume of a confined space is large, samples should be taken from the upper, middle, and lower sections for analysis, to ensure that the concentration of flammable gases and the oxygen level in all parts of the space meet the specified standards, and that levels of toxic and harmful substances do not exceed those stipulated in GB Z2-2002. 5.2.3 During the operation, regular monitoring must be strengthened; samples should be taken for reinspection at least every 4 hours. If any parameter fails to meet the requirements or any other abnormality occurs, the operation must be stopped immediately, the personnel involved must be evacuated, and the operation permit must be revoked ； After the work site has been treated and sampling analysis shows that the results meet the requirements for safe work in confined spaces, a new work permit must be issued before work can resume. 5.2.4 When entering a confined space for work, all tools and materials brought by the workers must be registered item by item ； When leaving the confined space after completing the work, it is necessary to count the tools and materials used and take them all out; none of them should be left behind in the confined space. 5.2.5 When applying coatings with volatile solvents, continuous monitoring should be carried out, and adequate ventilation measures must be implemented. 5.3 Lighting and protective measures 5.3.1 When working in confined spaces where cleaning and purging requirements cannot be met, appropriate protective measures must be taken. 5.3.1.1 In oxygen-deficient and toxic environments, a positive-pressure air respirator should be worn; where possible, a long-supply compressed air respirator can be used. 5.3.1.2 In flammable and explosive environments, explosion-proof low-voltage electrical fixtures and tools that do not generate sparks should be used, along with anti-static protective clothing. 5.3.1.3 In corrosive environments such as those with acids and bases, appropriate corrosion-resistant protective gear and anti-corrosion shoes must be worn. 5.3.2 Safe voltage and safe lighting must be used when entering confined spaces for work. The lighting voltage for working inside metal containers (furnaces, towers, kettles, tanks, etc.) and non-metallic containers that are particularly humid and have narrow working spaces shall not exceed 12V ； When electric tools are to be used or when the lighting voltage exceeds 12V, a leakage protector must be installed as required; its wiring box (board) must not be taken into the container for use. When the working environment previously contained explosive liquids, gases, or other such substances, explosion-proof flashlights or explosion-proof safety lamps with a voltage of no more than 12V should be used; the lamp transformer must not be placed inside or on the container ； Operators should wear anti-static clothing and use explosion-proof tools. 5.3.3 Handheld power tools operating at voltages above the safe level must be equipped with leakage protectors as required. 5.3.4 Temporary electrical wiring installations shall be installed and removed in accordance with regulations, ensuring good insulation of the wires. 5.3.5 In confined spaces containing unprotected rotating parts, the power supply should be cut off after shutdown, the fuses removed or grounding wires attached, and a sign reading “Work in progress – do not close switch” should be placed on the switch; if necessary, a dedicated person should be assigned to supervise the area. 5.4 Safety measures for multi-type and multi-level concurrent operations 5.4.1 Measures should be taken to avoid harm to one another. 5.4.2 A safety ladder or safety platform should be set up; if necessary, the supervisor shall use a safety rope to tie the worker in place while carrying out the work. 5.4.3 During work in confined spaces, materials, tools, and other items must not be thrown; for concurrent operations, measures must be taken to prevent objects falling from one level and injuring workers. Winches, cranes, and similar devices must not be used to transport workers. 5.4.4 Sufficient safety protection equipment, fire-fighting supplies, clean water, and other necessary emergency materials must be available outside the confined space.