Attention, hazardous chemicals enterprises! Checklist for Major Risks in Fine Chemicals and Relevant Precautions

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With the rapid development of human economies and societies, countries around the world have made precision work a **key industry for development**. The rapid development of industries such as new materials, functional materials, pharmaceuticals, pesticides, and intermediates for pharmaceuticals and pesticides has effectively improved the standard and quality of people’s lives. However, due to insufficient awareness of the safety risks associated with fine chemicals, production safety accidents in such enterprises have occurred from time to time in recent years. https://p8.itc.cn/images01/20210226/1773bd21424d46b9adb0c20453255cb5.jpeg Case review: Case 1 – An explosion at a fine chemical manufacturing plant in Lianyungang, Jiangsu, resulted in 10 deaths. Immediate cause: Nitrogen oxides from the exhaust gas treatment system (containing sulfuric acid) entered the insulated tank, where they reacted chemically with the materials inside the tank, generating heat continuously and causing the temperature to rise, ultimately leading to an explosion. Case 2: An explosion at a pharmaceutical intermediate company in Linhai, Zhejiang, resulted in 3 deaths. Immediate cause: During the process of concentrating the reaction mixture by vacuum distillation, the operator opened the jacket steam bypass valve, which caused the high-temperature interlock system to lose its protective function. The temperature inside the reactor exceeded the decomposition temperature of the reaction products, leading to rapid decomposition of these products and the release of heat. As a result, the pressure and temperature in the system rose sharply, ultimately causing physical explosion of the reactor due to overpressure. Case 3: An explosion at a fine chemical company in Shaoxing, Zhejiang, resulted in 3 deaths. Immediate cause: The experiment was conducted on a scale 10,000 times larger than that of the 500 ml pilot test. During the concentration of the intermediate oxadiazabicycloheptane at the later stage of the desolventization process, issues such as improper heating methods and temperature measurement equipment that were unable to accurately detect the actual temperature of the liquid in the reactor led to the temperature of the oxadiazabicycloheptane rising too high, resulting in intense thermal decomposition. This caused a sudden increase in pressure inside the equipment, leading to an explosion. Case 4: An explosion at a pharmaceutical company in Linhai, Zhejiang, resulted in 1 death. Immediate cause: The centrifuge was started by opening the discharge valve without applying nitrogen protection as required by the operating procedures. As the toluene solution containing piperazine entered the rapidly rotating centrifuge, static electricity sparks were generated, which ignited the toluene mixture and caused the centrifuge to explode. https://p6.itc.cn/images01/20210226/964eeb9924aa452fb2587d2bbd87ac43.jpeg The painful lessons from accident after accident have served as a warning to fine chemical companies regarding safety. Currently, fine chemical production is primarily carried out using batch and semi-batch processes. It involves a large variety of hazardous chemicals, complex processes that are difficult to control, low levels of automation, and uneven skill levels among personnel, all of which can lead to fires, explosions, and poisoning incidents. This article summarizes the accident risks in the field of fine chemicals from five aspects: facility defects, static electricity hazards, reaction and material hazards, dust explosions, and improper storage of solid waste, providing a guide for enterprises to identify hazard sources, detect potential risks, and take appropriate measures. 1. Facility defects 1.1 Systems SIS are not installed in units involving hazardous chemical processes that are under strict supervision ； 1.2 The hazardous chemical storage areas that constitute level 1 and level 2 major hazard sources do not have an emergency shutdown function ； 1.3 Chemical storage areas that are classified as major hazard sources of level 1 or 2 and involve toxic gases, liquefied gases, or highly toxic liquids do not have an independent safety instrumented system ； 1.4 Facilities involving leaks of flammable and toxic hazardous gases are not equipped with detection and alarm devices in accordance with **standards ； 1.5 Explosion-hazardous areas fail to install and use explosion-proof electrical equipment in accordance with **standards ； 1.6 Flammable and toxic liquid materials are not transported using leak-proof pumps (magnetic pumps, shielded pumps, diaphragm pumps). 2. Static electricity hazards 2.1 Kettles or containers with enamel linings or polytetrafluoroethylene linings that do not have nitrogen sealing systems in place, nor do they have adequate facilities for dissipating static electricity ； 2.2 For the reaction vessels, high-level tanks, and intermediate tanks used for flammable materials, when feeding from the top, no nitrogen seal is installed ； 2.3 Transferring flammable liquids using non-conductive hoses ； 2.4 The materials containing flammable solvents were dried using a bench centrifuge; there was no nitrogen seal, and no interlock protection linking oxygen level to the start of the centrifuge was in place ； 2.5 Using ordinary plastic barrels of over 5 liters to hold flammable liquids ； 2.6 Transporting flammable gases in non-conductive plastic pipes or fiberglass-reinforced plastic pipes ； 2.7 The scrubbing/absorption tower is made of anti-static materials, and the exhaust gas consists of flammable vapors or gases ； 2.8 Solid powder was not added to the reactor containing the organic solvent via a sealed feeder ； 2.9 Use of non-conductive belt drives for combustible gas compressors, pumps for flammable liquids of categories A and B, and centrifuges ； 2.10 The floors in flammable and explosive areas are non-conductive, and personnel are not wearing anti-static work shoes ； 2.11 For vacuum units pumping flammable gases or vapors, there is no interlock in place to close the unit’s inlet valve after shutdown. 3. Reactions and Material Hazards 3.1 Organic solvents are recovered from the mother liquor containing the material by distillation, or the reaction mixture is concentrated; however, the thermal stability of the mother liquor has not been tested ； 3.2 For reactors in which the maximum reaction temperature (MTSR) under adiabatic temperature rise is higher than the technical maximum temperature (MTT), there is no high-temperature interlock to shut off the addition of reactants, or the reaction is not carried out via a dropwise addition method; for reactions that involve the batch addition of solid reactants, no appropriate engineering measures are in place for such batch feeding ； 3.3 The temperature of the heat source in the reactor jacket exceeds the decomposition temperature of the reaction materials or products (including intermediates), and the decomposition heat is greater than 400 J/g; yet no mechanism is in place to cut off the heat source at such high temperatures ； 3.4 The maximum temperature of the reaction under adiabatic temperature rise (MTSR) is higher than the decomposition temperature of the reaction materials or products, and the decomposition heat exceeds 400 J/g; therefore, no high-temperature cut-off for the addition of reactants is implemented ； 3.5 Reactors that decompose when exposed to water and produce large amounts of gas, without regular inspection to check for damage to the enamel on these reactors ； 3.6 The materials that react with each other share a single exhaust gas main, and the enterprise did not conduct any compatibility analysis on the exhaust gases flowing through the exhaust pipes in the workshop ； 3.7 In the oxidation reactors fed with air or oxygen into reactors containing flammable materials, there is no online oxygen analyzer at the exhaust gas outlet connected to an interlock system for the incoming air, nor are any burst discs installed ； 3.8 Hydrogen gas that has been depressurized using high-pressure cylinders or tube trailers is used as the hydrogen source for the hydrogenation reactor; the set value of the safety valve located after the pressure regulator is higher than the design pressure of the reactor ； 3.9 For highly exothermic reactions, or when the raw materials are prone to decomposition and are stored in barrels, no measures are in place to prevent human error that could result in both types of materials being poured into the high-level tank or the reactor ； 3.10 Open-system operations are used for handling self-igniting substances such as palladium on carbon, Raney nickel, and n-butyl lithium ； 3.11 Errors in feeding raw materials within the same operating area can lead to serious process safety issues, as there is no separate design for this purpose ； 3.12 For venting reactions (such as hydrogenation, oxidation, chlorination, etc.), there is no interlock to cut off the high-pressure gas supply ； 3.13 For reactions that produce gas, there is no high-pressure cut-off mechanism for the liquid to be added, nor is there a sealed feeder ； 3.14 For reactions in which the slow reaction rate at low temperatures leads to an accumulation of reactants, when the reaction proceeds rapidly at high temperatures with significant heat release or gas generation, no low-temperature interlock is provided to stop the addition of liquid or solid feedstocks ； 3.15 Materials containing high-energy groups (such as nitro and azido groups) have not had their storage critical size, critical temperature, and critical time evaluated to determine the risk of spontaneous combustion or explosion of such materials. https://p2.itc.cn/images01/20210226/b26a7c887d1544a089c51eae57320f39.jpeg4. Dust explosions 4.1 For solid intermediates or products prone to dust explosions, if N2 inerting is not carried out during the powdering process, this can trigger a dust explosion hazard ； 4.2 The temperature of hot mechanical surfaces exceeds the MIT of solid dust, causing the dust to self-ignite. https://p0.itc.cn/images01/20210226/2a066b57439547fd97945c4902784940.jpeg5. Disordered storage of solid waste 5.1 The areas where solid waste is stored are not organized into separate zones, posing a risk of reactions between different types of waste ； 5.2 Decomposable substances or substances that can self-ignite upon exposure to air remain in the solid waste; no inactivation treatment is carried out when transferring the waste to the solid waste landfill ； 5.3 For waste materials that are prone to self-decomposition, if they are piled up too high and have poor ventilation, the heat generated by self-decomposition cannot be released, leading to spontaneous combustion or even explosion. To encourage fine chemical enterprises to strengthen their capabilities in risk research, risk assessment, and risk control, further improve their inherent safety levels, and promote the safe development of the industry, all hazardous chemicals manufacturers need to enhance their risk identification efforts, eliminate potential safety hazards, and ensure safe production. This article is reproduced from Chemical Industry Help.