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The raw materials, intermediates, and products used in chemical manufacturing are mostly flammable and explosive. The processing equipment is highly centralized and operates continuously; production takes place under conditions such as high or low temperatures, chemical corrosion, and involves complex chemical reactions. After a fire breaks out, given its rapid burning rate, high explosive power, large affected area, severe damage to production facilities, and the simultaneous combustion of various chemical substances, investigating chemical plant fires is a complex task. Therefore, identifying the causes of chemical plant fires in a timely manner and properly drawing lessons from them is an important measure to guide production and ensure safety in the chemical industry. This article attempts to provide a brief overview of how to determine the causes of chemical plant fires, focusing on aspects such as chemical materials, chemical equipment, reaction conditions, electricity, static electricity, and operational procedures. I. Analysis of chemical raw materials Chemical materials are the foundation of chemical production. Most chemical materials possess hazardous properties such as flammability, explosiveness, toxicity, and corrosivity, which are the fundamental causes of fire and explosion accidents. Therefore, starting with the analysis of the materials is the first step in investigating the cause. The analysis is mainly carried out from the following four aspects: 1. Material purity. The purity of materials not only affects the quality of products but is also related to the occurrence of fires and explosions. If the phosphorus content in calcium carbide is too high, accidents are likely to occur during the production of acetylene. In the chlor-alkali industry, too high a hydrogen content in chlorine gas or too high a chlorine content in hydrogen gas can lead to fires and explosions. Therefore, when analyzing the causes of chemical plant fires, examining the purity of the relevant materials is an essential step. Analysis methods: (1) The unburned materials or those remaining at the fire scene are promptly extracted for analysis and testing, to check for any impurities and to assess the impact of the fire ； (2) Locate the automatic control instruments and original records used to manage production in order to verify the relationship between the materials and the fire prior to its occurrence. 2. Material formula. The formula is determined through prior scientific experiments, and an incorrect formula can also pose a fire hazard in many chemical manufacturing processes. In cases such as the reaction between flammable liquids and oxidizers, it is necessary to strictly control the composition and amount of the oxidizer; otherwise, an excessive amount of oxidizer can lead to intense oxidation, thereby causing fires and explosions. Analysis method: (1) Promptly inquire with the operators on site about the formula ratios used for control prior to the fire ； (2) Check chemical equipment and valves for any abnormalities caused by mixing, which may lead to imbalances in the formula proportions ； (3) Extract the residual material in containers and pipes for testing to analyze whether there is a formulation error. 3. The amount and speed of material feeding. The amount of material and the feeding rate during production are essential control conditions for obtaining qualified products. In some chemical production processes, large quantities of material fed in too quickly can lead to intense reactions, resulting in overflow that may cause fires and explosions. For example, on June 22, 1984, in the central laboratory of a chemical plant, workers added toluene and sodium into the reaction vessel too quickly; furthermore, they left their posts without cooling the mixture in a timely manner, which caused a violent reaction and an overflow of material. This led to a fire when it came into contact with an electric furnace. Analysis method: (1) Extract the unburned and remaining materials from the fire scene to determine whether a certain substance is present in excess amounts ； (2) Check the records of the automatic instruments that control the yield to see if the product curve is normal ； (3) Check whether the explosion-proof membrane (plate) of the reactor is damaged, and look for signs of material intrusion or combustion ； (4) Check whether the cooling valve of the reactor is open ； (5) Check whether there are any abnormalities in the operator’s procedures, and analyze to determine the possibility of excessive feeding or too fast speed. 4. Material feeding sequence. Generally, in chemical production, materials are added in a strict sequence determined by scientifically validated reaction mechanisms; if the addition of materials is not carried out in this order, it can also lead to fires. For example, in the synthesis of hydrogen chloride, hydrogen should be added first followed by chlorine; other chemical production processes also have strict operating procedures. Such fires and explosions often originate first within the reactor; therefore, analyzing the sequence of material addition, carefully examining the conditions of combustion and explosion inside the reactor, and asking workers about their specific procedures are all essential methods for determining whether a fire or explosion was caused by an incorrect sequence of operations. II. Analysis of production equipment Chemical production equipment is the main facility through which materials are transformed into products via reactions. Due to the hazardous properties of materials such as flammability, corrosivity, and explosiveness, as well as the operational conditions such as specific temperature and pressure required for reaction processes, chemical production equipment must have excellent airtightness and high reliability. Leakage of materials in chemical processing equipment is a major hazard that can lead to fires and explosions. Therefore, in fire investigations, it is necessary to check the integrity of the chemical equipment at the point of origin of the fire to determine what defects existed there previously ； Inspect the equipment, containers, and pipelines after a fire to check for holes or cracks, and determine whether any leakage of materials preceded the fire. III. Analysis of reaction conditions in production Chemical production relies on chemical reactions, which take place under certain conditions such as specific temperatures, pressures, or the presence of catalysts. Therefore, improper operation is also an important factor causing fires and explosions. 1. The effect of temperature. Temperature is an important parameter in chemical production operations. If the temperature is not well controlled, the reactants may decompose due to overheating, posing a risk of explosion. In chemical production involving thermochemical reactions, inadequate cooling can lead to the leakage of materials, which may cause fires and explosions. Sometimes, a drop in temperature causes the materials to solidify, blocking pipes and even leading to the rupture of equipment and pipes; the leaked flammable materials can then catch fire. Analysis method: (1) Carefully examine the automatic instrument records and instruments in the control room to determine the control temperature prior to the fire ； (2) Check the chemical plant’s piping system for signs of material blockages ； (3) Find out the specific temperature at which the workers are operating, and analyze the impact of temperature on the occurrence of fires. 2. The impact of stress. Just like temperature, pressure is also one of the important conditions and parameters for control in chemical production. In modern chemical production, pressure is automatically controlled and displayed through pressure instruments. The equipment, pipelines, and containers used in chemical production are specially manufactured from different materials depending on the pressure range they are designed to withstand, and they require regular inspection. In production, if the pressure is too high, it not only leads to material leakage but can also cause explosions in sealed container equipment. If a negative pressure is created within a positive-pressure system, it will draw in air that mixes with combustible materials, resulting in an explosive mixture. In a negative-pressure production system, the occurrence of positive pressure can also pose a fire hazard. Equipment and containers within different pressure systems must be protected from high-pressure systems leaking into low-pressure systems, as this could otherwise lead to fires and explosions. The analysis methods are: (1) Conducting on-site inspections to locate instrument records of pressure control and collecting physical evidence ； (2) When the equipment used in the reaction explodes, parts of the equipment are often thrown out; it is necessary to search for them promptly and investigate the possibility of overpressure explosions ； (3) Ask the workers about the actual operating pressure and analyze whether there are any factors contributing to incorrect operations. IV. Analysis of Electrical Equipment Electrical equipment is the main power facility in chemical production. Spark electricity, arcs, and the high temperatures generated by electrical equipment components are among the main sources of ignition that can cause combustion and explosions of flammable gases, vapors of flammable liquids, combustible dusts, fibers, and other flammable substances. To this end, the production and storage areas in chemical manufacturing are classified into strict explosion-proof categories and grades based on their explosion risk, and corresponding types of electrical explosion-proof equipment are installed. However, some chemical manufacturing units frequently violate regulations by failing to install explosion-proof electrical equipment, or by using models that do not meet explosion-proof safety requirements, resulting in fires and explosions. In a chemical plant, gas leaked from the water-coal gas pipes in the carbonization workshop due to pipe corrosion; when this gas came into contact with non-explosion-proof lighting fixtures inside the facility, an explosion and fire occurred, resulting in the shutdown of the entire plant. When investigating and analyzing chemical plant fires, the analysis of electrical equipment cannot be ignored. Analysis method: (1) Draw a layout diagram of the electrical installations at the fire scene to determine the locations of the main electrical equipment ； (2) Check whether the electrical equipment is of explosion-proof type, and whether the explosion-proof model meets the requirements for use in areas with explosion hazards ； (3) Check the electrical switches and motors for any signs of sparks, arcs, or overheating that could lead to ignition and explosion, as well as for any signs of melted spots resulting from wire short circuits. V. Analysis of static electricity factors Static electricity represents a major hazard in chemical production. In recent years, many chemical plants have experienced serious fire and explosion accidents caused by static electricity in their oil tanks and during production processes. Why is static electricity so commonly harmful in chemical production? This is because most chemical materials are charged. According to available information, when classified, most chemical substances possess electrical charge, with the exception of a few alcohols such as ethanol and methanol, aldehydes such as acetaldehyde, and carboxylic acids such as acetic acid. In chemical manufacturing, static electricity can be generated by large-scale friction of solid materials, the flow of flammable liquids, the dispersion of combustible dusts, and the splashing of liquefied gases. Generally speaking, three conditions must be met for electrostatic discharge to cause a fire: (1) there must be combustible materials and oxidizing agents, or an explosive mixture ； (2) Conditions for corona and spark discharge must be present ； (3) The energy of the corona or spark discharge must be equal to or greater than the minimum ignition energy of the combustible material. Therefore, understanding the hazards of static electricity in the chemical industry and the conditions under which its discharge can cause fires is essential for investigating and analyzing chemical industry fires. Analysis method: (1) First, it is necessary to determine whether the material on fire is electrically charged, and what conditions are required for discharge to cause ignition ； (2) Thoroughly inspect chemical processing equipment, containers, etc. to ensure they have proper grounding systems; the compliance with specified requirements can be verified by measuring the resistance value ； (3) Verify whether the material feeding and conveying speeds create conditions for the generation of static electricity ； (4) Conduct theoretical verification to calculate whether the energy of the electrostatic spark generated by this substance is equal to or greater than the minimum ignition energy of the combustible material. VI. Operators’ Performance The safety in chemical production is closely related to the professional skills and safety awareness of the chemical operators. In terms of the likelihood of chemical plant fires, fires and explosions caused by violations of regulations due to inadequate compliance on the part of operators still account for a significant proportion. Therefore, when analyzing the causes of fires in production, it is necessary to examine technical documents related to the chemical production processes, safety measures, and operating procedures, to understand how operators should carry out their tasks correctly, to see how the staff on duty follow the procedures and fire prevention rules, and exactly how they operate; it is also important to determine whether the fire was caused by the operators’ actions. In the event of a fire caused by improper operations or illegal use of fire, relevant physical evidence should be collected promptly. VII. Comprehensive Analysis Comprehensive analysis is the process of conducting comprehensive technical research and drawing conclusions regarding the investigation of chemical plant fires. This is the key to the entire fire accident analysis process. In the investigation of the causes of ordinary fires, it is possible to identify the cause through analysis in one of the aforementioned areas. However, in the case of complex chemical plant fires, due to the presence of many technical issues and challenges, only through comprehensive analysis involving thorough investigations, simulation experiments, theoretical deductions, and numerical calculations can correct conclusions be reached.