The risks associated with hydrogen use cannot be ignored in hydrogen peroxide systems

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To thoroughly learn from the serious explosion and fire accident that occurred at Luxi Chemical on May 1, the First Department for Hazardous Chemicals under the Ministry of Emergency Management issued the \"Guidelines for Identifying Safety Risks and Hazards in Hydrogen Peroxide Production Enterprises,\" to encourage such enterprises to carry out self-inspections and make necessary improvements. Emergency management departments at all levels have also actively organized experts to conduct special inspections of hydrogen peroxide production enterprises, in order to strengthen the control of safety risks in such enterprises. During the inspection, the author found that most enterprises have made significant improvements in their understanding of the risks associated with hydrogen peroxide as well as in the control measures taken to address these risks; however, the risk management related to the use of hydrogen gas during the production of hydrogen peroxide is inadequate. The explosive limit of hydrogen in air is 4.0%–74.8%, and its flash point is -253°C; it is highly prone to explosion in the event of a leak. Historically, there have been several accidents in hydrogen peroxide production facilities caused by inadequate control of hydrogen-related risks. Typical Cases Case 1: In March 2015, an explosion occurred in the hydrogenation tower of a hydrogen peroxide production facility at a chemical company in Shandong, resulting in 4 deaths and 2 injuries, with direct economic losses amounting to 4.882 million yuan. The cause of the accident was that, in order to address the issues of flow imbalance in the fixed bed of the lower section of the hydrogenation tower and uneven distribution of the working fluid, the company sent personnel into that section of the tower to conduct measurements ahead of technical upgrades. During the measurement process, due to the lack of effective isolation and replacement measures, there was internal leakage in the ball valve of the bottom condensate discharge line and the globe valve of the pure hydrogen inlet line; hydrogen entered the tower, and an explosion occurred when it came into contact with a source of ignition. Case 2: In August 2011, a flash explosion occurred in the double-water workshop of a company in Hebei while filling alumina into an alumina bed, resulting in 1 death and 4 injuries. The direct cause of the accident was a flash explosion resulting from the mixing of hydrogen and air. Upon inspection, it was found that there were internal leaks in the isolation valve between Bed 1 and Bed 2, the valve connecting the adsorbent bed to the regenerated steam condenser, and the series valve connecting the regenerated steam condenser to the hydrogenation exhaust gas condenser. Hydrogenation exhaust gas leaked into the adsorbent bed, where it mixed with air to form explosive gases. When alumina was poured into the adsorbent bed, friction between the alumina and the packaging bags (plastic woven bags) generated static electricity sparks, which caused a flash explosion. The root cause of the accident was: no risk analysis was conducted prior to the operation, no work permit was issued, energy isolation measures were inadequate, and valves were used instead of blind flanges for isolation. Case 3: In August 2010, an explosion and fire occurred in the hydrogen peroxide production unit of a chemical plant in Ningxia. The direct cause of the accident was: accumulation of material in the extraction tower, interruption of the working fluid circulation, low liquid level in the hydrogenation fluid gas-liquid separator, which allowed hydrogen to enter the hydrogenation fluid storage tank; there it mixed with air and exploded, triggering the combustion of the working fluid. Of these 3 accidents, 2 were caused by hydrogen leaking into the tower due to valve leaks during operations, leading to explosions, while one was caused by a loss of the liquid seal, resulting in high pressure escaping to low pressure. There have been many accidents caused by hydrogen throughout history as well. For example, during the initial startup of a hydrogen peroxide production plant in Hunan, hydrogen was introduced into the hydrogenation tower without first purging the system with nitrogen, which caused the sight glass in the tower to explode. When the production system of a factory was in circulation mode, the oxygen generated by the decomposition of hydrogen peroxide present in the working fluid accumulated at the top of the hydrogenation tower. Since nitrogen purging was not carried out before introducing hydrogen into the system, hydrogen mixed with oxygen caused an explosion; as a result, the head of the hydrogenation tower was blown off and the floor above the top of the tower was damaged. In addition, in hydrogen-related facilities, there are also issues such as the use of explosion-proof electrical equipment that does not meet the requirements, and the absence of combustible gas alarms. Problems exist: In recent inspections, the author has identified that many companies still have numerous similar issues regarding the management of hydrogen-related risks. Question 1: Inadequate management of special operations. For example, in a company in Guangxi, during the catalyst replacement operation in a hydrogenation tower, no sampling and analysis of flammable gases inside the tower was carried out, nor were the relevant work permits for blind plate installation and removal provided ； A company in Ganzhou City, Jiangxi Province, failed to obtain a permit for working in a confined space when replacing activated alumina in an alumina bed, nor did it obtain a permit for performing plug-and-unplug operations on the blind flanges of that bed. Question 2: The explosion protection of electrical equipment in hydrogen-related facilities does not meet the required standards. For example, the lighting fixtures added next to the hydrogen buffer tank at a hydrogen pressure station of a chemical company in Shandong are of a dust explosion protection rating (ExtDA21), which does not satisfy the requirements for environments involving hydrogen ； The explosion-proof rating of the external explosion-proof wiring box for the hydrogen online monitoring cabinet in the PSA process of the hydrogen peroxide production unit at a company in Yunnan does not meet the required standards. Question 3: The leak prevention measures are inadequate; for example, in the hydrogen water seal on the second floor of a hydrogen purification unit at a chemical company in Guangxi, as well as in the area where control valves are located, no hydrogen detectors have been installed ； In the hydrogen sampling process of the hydrogen peroxide production unit at a chemical company in Anhui, a closed-loop sampling system was not used; moreover, the combustible gas detectors installed at the hydrogen buffer tank did not cover the sampling points ； In the hydrogen sampling process on the second floor of the hydrogen peroxide production facility at a chemical company in Hubei, a closed-loop sampling system was not used. Risk management recommendations 1 Image Image: Pay close attention to risk management in hydrogen-related environments and hydrogenation processes, and fully recognize the risks associated with hydrogen’s wide explosive range in air and low flash point; especially in confined spaces such as hydrogenation towers, alumina beds, and hydrogen storage tanks, where hydrogen can accumulate more easily, leading to explosions. 2 Images: Images to strengthen risk prevention and control in hydrogenation towers. The oxygen content in hydrogen must be strictly controlled, with the oxygen content in the exhaust gases not exceeding 2.0% (vol%). Before starting up the hydrogenation system, nitrogen should be used to purge the pipelines and equipment that come into contact with hydrogen, until the oxygen concentration in these pipelines and equipment is below 2.0% (vol%), thereby preventing the accumulation of oxygen at the top of the tower and the formation of explosive mixtures. 3 Images. It is necessary to strengthen the risk management of the hydrogenation liquid gas-liquid separator; level low alarms and interlocks that shut down the emergency shutdown valve for discharge must be installed in accordance with the requirements. The tank holding the hydrogenation liquid should be equipped with alarms for high pressure as well as high and low liquid levels, in order to prevent high pressure from leaking into the lower pressure area. 4 Images Images Strengthen the management of special operations such as work in confined spaces and hot work. In particular, when replacing catalysts in hydrogenation towers or alumina in clay beds, risk analyses must be conducted strictly in accordance with requirements. Energy isolation measures should be taken based on the results of these analyses; it is prohibited to use valve closure as a substitute for blind flange isolation. In response to the identified issues and the lack of safety knowledge among operators, targeted training was organized for technical personnel. This included studies of standards such as the \"Safety Regulations for Special Operations in Hazardous Chemical Enterprises\" (GB 30871-2022) and the \"Guidelines for Safety Management in Chemical Processes\" (AQ/T 3034-2022), thereby improving their awareness and capabilities in identifying risks associated with special operations, handling approval procedures, and implementing risk control measures, so as to ensure effective management of operational risks. 5 Images: A thorough inspection is carried out regarding the use of non-explosion-proof electrical equipment in areas prone to explosions, as well as situations where the explosion-proof rating of such equipment does not meet the required standards. Special attention is given to equipment that has been added or modified, as well as exhaust treatment systems, fire protection facilities, and lighting and monitoring equipment, with inspections conducted to identify similar issues. It is recommended that relevant technical personnel and managers study carefully standards such as the \"Code for Design of Electrical Installations in Explosive Hazardous Environments\" (GB 50058-2014), in order to enhance their understanding of explosive hazard areas, improve their ability to conduct thorough inspections, and eliminate potential explosion risks associated with electrical equipment. 6 Strengthen leak prevention management. The control of risk points such as hydrogen pipelines, valves, sampling ports, and discharge ports should involve the use of sealed samplers as required, as well as the installation of gas detectors and safety devices such as flame arresters at the vent ports, in order to effectively manage the risk of hydrogen leaks.