(Compiled) Fire hazards in silicon trichloride production and countermeasures

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Fire hazards and countermeasures in the production of trichlorosilane. Trichlorosilane is also known as trichlorosilane or silicochloroform; its English names are trichlorosilane or silicochloroform, and its molecular formula is SiHCl3. It is used in the synthesis of organosilanes as well as chlorosilanes containing alkyl, aryl, and organic functional groups. It represents the most fundamental monomer among organosilane couplings agents, and it is also a raw material for the production of semiconductor silicon and single-crystal silicon. With the development of the industry related to organosilane couplings agents, there has been a growing demand for this substance, leading to an increase in its production volume. I. Physical and chemical properties of trichlorosilane and its production principle Trichlorosilane is produced by reacting silicon powder with hydrogen chloride gas in a fluidized bed reactor. It is a colorless liquid that is volatile and hygroscopic; it reacts with air to produce white smoke, decomposes when in contact with water, and is soluble in organic solvents such as benzene and ether. It belongs to the category of materials that are highly flammable when exposed to moisture; it is both flammable and explosive, and reacts with water to produce hydrogen chloride gas ； It reacts violently with oxidizers, and can catch fire or explode in the presence of open flames or high temperatures. 　 Its physical properties are as follows: Specific gravity: 1.35 ； Relative gas density: 4.7 ； Boiling point: 31.8℃ ； Saturated vapor pressure (14.5°C): 53.33 Kpa ； Flash point: –13.9°C (open cup) ； Auto-ignition temperature: 175℃ ； Lower explosion limit: 6.9% ； Maximum explosion level: 70% ； Solubility: Soluble in organic solvents such as benzene and ether ； It has acute toxicity. II. Analysis of fire hazards in the production of trichlorosilane The raw materials used in the production of trichlorosilane are non-flammable substances, but the products generated during this process are mostly flammable and explosive substances, such as hydrogen, trichlorosilane, chlorine, etc. 　 1. Fire hazard of electrolyzing saltwater (1) A strong electric current flows during electrolysis, and poor electrical insulation can easily lead to the generation of electric sparks. Hydrogen gas often leaks in electrolysis workshops, and it can catch fire or explode when exposed to electric sparks or other open flames. (2) If hydrogen and chlorine are mixed and reach the explosive range, an explosion can also occur upon exposure to light. 　 2. Fire hazards associated with the synthesis of trichlorosilane: The synthesis of SiHCl3 takes place at temperatures between 280°C and 300°C, which is above the auto-ignition temperature of SiHCl3, which is 175°C. If SiHCl3 leaks during the synthesis process, or if air enters the reactor, it can easily lead to fires, explosions, or poisoning incidents. Furthermore, SiHCl3 is toxic and burns when it comes into contact with water, posing certain difficulties in fire fighting. 　 3. Fire hazard of silicon trichlorohydride storage tanks: If a leak occurs in a tank storing SiHCl3, the hazard is much greater than that resulting from leaks in process pipelines, due to the large volume stored. Once a leak occurs and is not sealed up promptly, the impact will continue to grow. The storage tank area often contains water due to the need for cooling water. Leaked SiHCl3 reacts with this water, producing toxic HCl that spreads throughout the area, thereby complicating emergency response efforts. III. Fire and explosion prevention measures 　　 In all stages of silicon trichloride production, to prevent fires and poisoning, it is necessary to strictly enforce various fire safety regulations, closely control process parameters, and adhere to strict operating procedures. Strengthen the maintenance of equipment and pipelines to strictly prevent leaks. The specific preventive measures are as follows: 1. Fire source management. Tools used for maintenance during production should be those that do not generate sparks; it is strictly prohibited to strike equipment or pipes with iron tools, and workers should wear cotton work clothes. Open flames are prohibited in the production and storage areas; when working with fire during production, relevant safety management procedures must be strictly followed. 　 2. Prevent leakage, spills, and drips. Most substances produced during the manufacturing process are flammable, explosive, and toxic; leaks in production equipment, process pipelines, and storage tanks can easily lead to fires, explosions, and poisoning incidents. Therefore, it is necessary to conduct safety inspections in daily work to ensure no areas are overlooked; equipment should be regularly maintained, and corrective actions should be taken promptly once issues are detected, in order to repair any parts that are leaking or showing signs of wear. 　 3. Equip emergency tools and fire-fighting facilities. A certain number of gas masks, self-contained breathing apparatus, gloves, and leak-sealing tools should be available. Members of the emergency response team should conduct regular drills to master the methods for sealing leaks and the appropriate measures to take in various situations. The amount of dry sand kept on hand in the storage tank area should ideally be at least equal to the capacity of one storage tank, and a certain amount of cement is stored in the factory’s warehouses for emergency use. Equipped with a certain number of portable carbon dioxide and dry powder fire extinguishers. 　 4. Fire and leakage prevention measures in the production process. (1) Synthesis, dust removal, and distillation sections for trichlorosilane. A check valve should be installed between the HCl gas buffer tank and the synthesis furnace to prevent SiHCl3 from the synthesis furnace from returning to the buffer tank. The flow rate of HCl gas should be controlled, as well as the temperature inside the synthesis furnace. The equipment and pipelines should be regularly maintained to prevent the leakage of trichlorosilane. During production, it is necessary to keep the entire system sealed and protected with 99.99% nitrogen. (2) Storage of trichlorosilane. Silicon trichlorohydride has a low boiling point and must be stored at low temperatures; its storage tanks are equipped with low-temperature protection devices and cooling measures. Due to the potential fire and explosion hazards associated with trichlorosilane, its storage tanks should be kept at a certain fire distance from the production facilities, and fire dikes should be installed. Gate valves should be placed on the pipelines for discharging cooling water at those locations where they pass beneath the fire dikes. The storage tank shall be equipped with an electrostatic grounding device and a lightning protection device. The gas phase inside the storage tank must be connected to a nitrogen system for protection. The balance pipe (vent pipe) that connects the gas phase of the storage tank to the outside world should be linked to the exhaust gas recovery system; it cannot be vented directly, and check valves and flame arresters must be installed. A spare tank should be installed in the storage tank area; in emergency situations, the material from the leaking tank should be transferred to this spare tank to prevent large-scale leaks. IV. Leak Handling and Fire Fighting In the event of a leak of trichlorosilane during production or storage, a safety perimeter should be established based on the amount of leakage; unauthorized personnel and vehicles are prohibited from entering this area. All sources of fire within the perimeter must be extinguished, and people in the contaminated area should be quickly evacuated to safe locations. If a storage tank leaks and the leak cannot be resolved promptly, silicon trichloride from the leaking tank should be forced into a spare tank using nitrogen pressure. If there is a leak in the equipment or pipelines during production, production must be stopped immediately, and the relevant valves should be closed swiftly to cut off the flow of materials. When there is a water source in the area of leakage, a barrier made of dry sand should be used to isolate the leaked trichlorosilane from water. Emergency responders entering hazardous areas should wear self-contained breathing apparatus or gas masks. The leakage condition at the leaking location should be determined first. Since the containers used for storing trichlorosilane are at atmospheric pressure, different sealing measures should be taken depending on the location of the leak in order to stop the source of leakage, and sand or cement should be used to absorb any residual liquid. In the event of a fire resulting from a trichlorosilane leak, dry sand, carbon dioxide, dry powder, or cement should be used to extinguish the fire; direct use of water or foam is prohibited.