On hazard analysis in chemical manufacturing enterprises [Daily Question 090421]

The products and raw materials used in chemical enterprises are often hazardous chemicals that are flammable and explosive; some of them are also toxic. Many of the production processes involve high temperatures and pressures

1. The materials being processed (including raw materials, intermediate products, and finished products) are mostly flammable, explosive, toxic, or corrosive in nature； 2. The manufacturing process is complex, with stringent process conditions, involving high temperatures and pressures on a frequent basis ； 3. Diverse working conditions ； 4. Larger scale, continuity, and automation of production facilities.

The topic is too broad; it should be classified according to products and processes.

Chemical enterprises face the following risks: First, they have a large quantity of hazardous materials, resulting in a high risk of fires; accidents in such cases can easily lead to severe casualties and significant property damage. 　　Since the chemical raw materials and products manufactured, processed, and stored by chemical enterprises are highly flammable, explosive, and toxic, fire or leakage incidents lead to complex situations. Explosions, re-ignitions, and secondary explosions occur, with the spread occurring over large areas at high speeds, which easily results in fires that affect multiple locations on a large scale. It not only leads to production halts, equipment damage, inability to produce products, and accumulation of raw materials, thereby disrupting the social production chain and reducing social productivity, but it also causes severe casualties and property losses, and may even result in immeasurable damages and irreversible impacts on society. 　　II. Enterprises use a large amount of hazardous materials, and accidents can easily lead to environmental pollution and fires. 　　In chemical production, it is inevitable to use large quantities of products, intermediates, by-products, as well as impurities contained within them, along with various waste emissions generated during the production process. All of these are considered industrial toxins, possessing toxicity, corrosiveness, and fire hazards. Once released into the atmosphere or discharged into rivers, substances such as chlorine, hydrogen sulfide, and phosphorus-containing wastewater can cause heavy casualties as well as air and water pollution. After leaks of certain highly toxic chemical raw materials occur, they cause severe damage to the atmosphere and water, have a lasting impact, and are difficult to address. Such as cyanides, nitriles, organophosphates, etc. These items generally have a low ignition point, are easy to ignite and can catch fire on their own; they are flammable and explosive in the presence of acids or oxidizing agents. They are highly toxic either in their original form or as combustion products, often leading to unexpected fires and explosions. 　　III. There are many hazardous materials, fire situations are complex, extinguishing fires and carrying out rescue operations is difficult, which increases the risk for rescuers. 　　After a fire breaks out in a chemical plant, the situation is generally very complex, often accompanied by explosions, flash fires, secondary explosions, or explosions that occur after burning, as well as alternating periods of burning and exploding. Explosions can be physical or chemical, or explosions of both types may occur one after the other. Furthermore, chemical products have a high calorific value, and the thermal radiation generated upon combustion can rapidly heat the surrounding containers and equipment, causing the chemical products in the adjacent containers and pipes to experience a rapid increase in pressure, volatilize, and decompose, thereby creating additional risks that contribute to the spread of the fire. 　　Furthermore, chemical fires often change very rapidly, with various dangerous situations arising continuously; toxic gases pose a serious threat to the safety of firefighters and rescue personnel ； Corrosive substances can burn the skin of rescuers and damage firefighting equipment ； The collapse of buildings can lead to serious consequences such as casualties among rescue workers. All these have posed significant difficulties to firefighting and rescue operations. (Excerpt from Fire Safety)

The main hazards and risks in chemical manufacturing enterprises include fires, explosions, poisoning, asphyxiation, electrical injuries, mechanical injuries, falls from heights and object strikes, burns, corrosion, lifting injuries, noise and vibration, dust, vehicle-related injuries, drowning, and collapses.

The risks are too great; generally, chemical enterprises face issues such as flammability and explosiveness, high temperatures and pressures, as well as complex production processes. What’s important is to find ways to prevent the dangers arising from these factors, and this should be approached from three aspects: first, human factors related to safety. II. Unsafe condition of the object. III. Management deficiencies.

Due to the fact that chemical enterprises possess numerous flammable, explosive, and drug-making substances, along with their inherent tendency to undergo chemical reactions, the main types of accidents that occur are fires, explosions, and poisoning. To prevent hazards from turning into accidents, we can start by considering the five key elements: people, machinery, materials, methods, and the environment. 1. People: Every activity in a company relies on people as a crucial element; they are the foundation for ensuring safety. The vast majority of accidents are human-caused accidents. It is necessary to improve the safety skills and awareness of all employees, so that they are motivated to prioritize safety and know how to ensure it, which can fundamentally prevent accidents from occurring ； 2. The good condition of machinery and equipment is a guarantee for safe production. This is a guarantee to prevent fires, explosions, poisoning, and mechanical injury accidents; it is necessary to strictly control the quality of materials purchased, as well as proper daily maintenance and use ； 3. Materials are integral to the entire production process, and this is also an important aspect of safe production. Including processes such as procurement, storage, dispatch, turnover, and use ； 4. It is essential to continuously formulate and improve various rules and regulations, and to ensure their strict implementation, in order to guarantee the safety of employees while pushing safety efforts to a higher level ； 5. A favorable working environment and a positive safety culture will play a positive role in ensuring effective safety practices. This post was last edited by glf_js on 2009-4-21 11:21]

Flammable and explosive, toxic and harmful, high temperature and high pressure, low temperature and low pressure, and so on； If classified into 20 categories, almost all types of hazards exist, except for those associated with coal mines.

The chemical industry is a technology-intensive and high-risk sector that involves high temperatures, high pressures, and continuous production. Especially in the case of the production of hazardous chemicals, the technical requirements are even higher, the risks are greater, and there are more specific standards as well as stricter demands regarding the qualifications of those who work in this field. In recent years, with the restructuring of enterprises and changes in employment practices, many chemical companies, especially small and medium-sized ones, have made extensive use of temporary workers who have not received proper professional education or thorough training to work in hazardous chemical-related positions. Due to their low educational level and lack of basic knowledge and operational skills in the chemical industry, improper operations and reckless behavior are widespread, which easily leads to accidents. Severe chemical production accidents caused by operators’ illegal operations and reckless behavior account for 75% of the total number of such accidents. The low quality of workers, especially those in positions involving hazardous tasks who lack basic chemical engineering knowledge, has become one of the major safety hazards in chemical enterprises today.

I. Hazard factors in the chemical industry The Insurance Association of America (AIA) investigated 317 fire and explosion incidents in the chemical industry, analyzed the primary and secondary causes, and classified the hazard factors in this industry into the following nine categories. 　　1. Plant location 　　(1) Prone to natural disasters such as earthquakes, floods, and storms ； 　　(2) Insufficient water supply ； 　　(3) Lack of support from public fire-fighting facilities ； 　　(4) There are climate issues such as high humidity and significant temperature fluctuations ； 　　(5) Affected by nearby industrial facilities with high risk ； 　　(6) Proximity to transportation facilities such as highways, railways, and airports ； 　　(7) It is difficult to evacuate people and vehicles to safe locations in an emergency. 　　2. Plant layout 　　(1) Process equipment and storage equipment are too densely packed ； 　　(2) The safety distance between process units with significant hazard and those without hazard is insufficient ； 　　(3) Expensive equipment is overly concentrated ； 　　(4) There is no effective protection for devices that cannot be replaced ； 　　(5) The distance between heat sources such as boilers and heaters and the combustible process equipment is too small ； 　　(6) There are topographical obstacles. 　　3. Structure 　　(1) Supports, doors, walls, etc. are not fire-resistant structures ； 　　(2) Electrical equipment lacks protective measures ； 　　(3) Insufficient explosion-proof ventilation capacity ； 　　(4) The control and management indicator devices lack protective measures ； 　　(5) The foundation of the device is weak. 　　4. Insufficient awareness of the hazards of the processed substances. 　　(1) The raw materials are mixed in the device and decompose naturally under the action of a catalyst ； 　　(2) The explosion range of the treated gases, dusts, etc., under their process conditions is unclear ； 　　(3) There is a lack of thorough understanding of the detailed conditions of materials and products when the process becomes abnormal due to operational errors or poor control. 　　5. Chemical Process Engineering 　　(1) There is insufficient kinetic data regarding chemical reactions ； 　　(2) Insufficient awareness of dangerous side effects ； 　　(3) The explosion energy has not been determined through thermodynamic studies ； 　　(4) Insufficient detection of process abnormalities. 　　6. Material transportation 　　(1) Poor control over material flow during various unit operations ； 　　(2) The product labeling is incomplete ； 　　(3) Dust explosion in the air delivery system ； 　　(4) Treatment of waste gas, wastewater, and waste residues ； 　　(5) Loading and unloading facilities within the device. 　　7. Mistakes in operation 　　(1) Ignoring training on operation and maintenance ； 　　(2) The supervisory role of management personnel has not been fully utilized ； 　　(3) Inappropriate driving and parking plans ； 　　(4) Lack of operational training for emergency shutdown ； 　　(5) A collaborative system between operators and safety personnel has not been established. 　　8. Equipment defects 　　(1) Corrosion and damage of the device caused by improper material selection ； 　　(2) Inadequate equipment, such as the lack of reliable control instruments ； 　　(3) Fatigue of materials ； 　　(4) The metal material was not subjected to adequate non-destructive testing or was not inspected and approved by experts ； 　　(5) Structural defects, such as the inability to stop the vehicle, preventing regular inspections or preventive maintenance ； 　　(6) The equipment operates under process conditions that exceed its design limits ； 　　(7) Problems existing during operation or inadequate disaster prevention measures were not improved in a timely manner ； 　　(8) There are no continuous records of temperature, pressure, start/stop conditions, and pressure changes in the intermediate tank and the pressurized tank. 　　9. Inadequate disaster prevention plans 　　(1) Lacks strong support from regulatory authorities ； 　　(2) Unclear division of responsibilities ； 　　(3) Abnormal operations or failures of the device are the responsibility of the security department alone, with only a single circuit in operation ； 　　(4) There is no plan to prevent accidents, or if one exists it is poor ； 　　(5) Failure to take effective measures in case of an emergency ； 　　(6) Regular safety inspections conducted jointly by the management and production departments were not implemented ； 　　(7) No continuing education on safe production nor necessary disaster prevention training was provided for production supervisors and technical staff.

The hazard associated with chemical processes or technologies stems primarily from the hazards of the substances involved in those processes. Since these substances are in a dynamic state during the process, this often results in a higher level of hazard compared to when they are at rest. In addition, the hazards associated with chemical processes include the hazards inherent in the process itself, the hazards related to operating conditions, and the hazards associated with equipment. 1 Hazardity of substances in chemical processes ① Substances undergoing chemical processes are constantly subjected to various effects such as heat, mechanical forces, and chemicals, and are in a state of continuous change. And substances with potential hazards have a limited capacity to withstand these effects; accidents occur once a certain limit is exceeded. ②Hazardous substances are not only the cause of industrial accidents but also the reason for their escalation. ③The quantity of hazardous substances in the process is another key factor in the hazard level of those substances, as the nature of the accidents that occur is largely dependent on this quantity. That is, the quantity affects the system’s adiabaticity, propagability, and the transition from combustion to detonation ； The controllability, extinguishability, and destructiveness of the accident after it occurs. ④The state of the substance is also an important factor in determining its hazard, which includes the phase of existence (gas, liquid, solid) and the degree of dispersion (lumps, particles, powder). 2 Hazards in chemical processes The fundamental purpose and characteristic of chemical processes is to transform substances, and the methods used for this transformation include chemical, physical, mechanical, etc. Assessing the danger of a process means looking at the trend in its effect on increasing or decreasing the hazard of the substance ； Then there is the flow of energy from the chemical reactions involved in the process, as well as from thermal (temperature) effects, pressure, electricity, and mechanical forces. A chemical process is composed of several chemical units, which are interconnected and influence one another. The number of units, as well as their operating characteristics (batch or continuous operation, level of automation), all have an impact on safety. The main hazards in chemical processes involve the following units. 2.1 The hazards of chemical reaction processes (or reaction engineering). Reaction engineering reflects the characteristics of the chemical industry prominently; it is a type of engineering field where accidents occur frequently. Normal chemical reaction processes must take place in controlled reactors, so that the reactants, intermediates, reaction products, and the reaction process itself remain within specified safe ranges in terms of temperature, pressure, etc. However, chemical reactions are influenced by various factors. If these conditions change for some reason, causing the reaction to get out of control and leading to uncontrolled increases in temperature and pressure, it can result in material spraying, equipment damage, and even fires or explosions. This is the main hazard in reaction engineering, which will be discussed in detail later. 2.2 Hazards of transportation projects The main equipment in the transportation process includes power transmission devices, conveying machinery, and pipelines. Its function is to direct the material flow and energy flow in production to designated locations. The basic characteristic of this process is that the materials must move; as a result, friction and collisions between the materials themselves and between the materials and the equipment are inevitable. Static electricity and heat may also be generated, and these are precisely the initial energies that can lead to combustion and explosions. This requires selecting conveying methods and machinery that are compatible with the properties of the material to be transported, in order to minimize impacts and friction during transportation and to control the speed. For example, to prevent static electricity, when transporting substances with high resistivity such as petroleum products through pipelines, the flow rate should be below 1 m/s. Equipment and pipelines that generate static electricity must have proper grounding (with a ground resistance of 1–3 ohms). In pipeline transportation, there is always a pressure difference between the inside and outside of the pipeline; therefore, leakage (outflow, spraying) is the most common type of accident, which can further lead to more serious consequences such as fires and explosions. Leaks are mainly caused by defects in the pipelines or equipment themselves, such as inappropriate material, insufficient strength, excessive corrosion, poor welding, or inadequate sealing. Special safety measures are also required for high-temperature, high-pressure, low-temperature, long-distance pipes, and buried pipelines. For example: ① Corrosion prevention takes into account not only the corrosion of the materials themselves but also soil corrosion and corrosion caused by leakage current from electrified railway substations ； ②Absorption of thermal expansion ； ③Vibration prevention and resonance suppression ； ④Protection against damage caused by abnormal pressures (such as when transporting decomposable materials like peroxides). 2.3 Hazards associated with crushing and screening processes: During this process, the materials are crushed and screened as a result of intense mechanical, pneumatic, or hydraulic forces, which poses significant hazards. For self-reactive substances, they may catch fire due to mechanical impact or friction; therefore, it is necessary to consider very carefully whether such substances are suitable. Combustible materials can form explosive mixtures of dust and air due to crushing or screening ； Water-repellent substances (such as metal powder, calcium carbide, etc.) may react with water vapor, condensed water, or leaked water in the air during crushing and screening to produce flammable gases ； Oxidizers may catch fire when in contact with combustibles such as mechanical lubricants during crushing and screening. Safety measures take into account not only potential ignition sources, but also require the use of inert or dry gases for protection when necessary. 2.4 Hazards in drying processes Drying processes typically consist of main equipment, feeding and discharging systems, heating equipment, as well as ventilation and dust removal systems. Main considerations: ① Thermal stability of the material, drying temperature, and drying duration ； ②The hazard of solvents removed from the dried material ； ③Risk of overheating or local overheating ； ④Risk of electrostatic ignition ； ⑤Exhaust fumes, dust removal hazards, etc. 2.5 Hazards in distillation processes: The main considerations are: ① the thermal stability of the substance being processed, as well as the distillation temperature and duration ； ②The risk of concentrated unstable by-products and impurities ； ③Risk of residue, scaling, or overheating due to evaporation during distillation ； ④The flammable materials being distilled are at risk of coming into contact with high temperatures and air. Therefore, the safety of distillation operations is closely related to the system’s temperature, pressure, and sealing. 2.6 Hazards of mixing processes Mixing is an essential method in the preparation of compounds (through chemical reactions) and mixtures, but the mixing required in general chemical reactions is not a separate process; rather, it is part of reaction engineering. The mixing discussed here is mainly for the preparation of mixtures. In terms of state, there are dry mixing and wet mixing ； In terms of methods and equipment, there are mechanical stirring type, air-flow type, spiral type, rolling type, ball milling type, rotary mixing type, kneading type, etc. The main hazard associated with this process is the potential to create hazardous conditions for substances, such as the conditions that can lead to dust explosions during dry mixing ； Additionally, there are mechanical impacts, friction, and static electricity that can cause ignition sources. Therefore, when using dry mixing, attention must be paid to sealing and filling with an inert gas ； In wet mixing, try to avoid introducing flammable or combustible liquids, or implement strict safety measures. In hybrid engineering, special attention is also paid to the compatibility between the components being mixed, as well as the risk of impurities being introduced. 2.7 Hazards in filtration and separation processes: This process is relatively smooth and gentle, and heating is generally not used; therefore, the level of hazard is not high. However, ① when the filtrate mother liquor is or contains flammable liquids, there is a potential risk of fire and explosion ； ②Toxic mother liquors and their vapors can cause poisoning in open conditions ； ③Centrifugal separation involves significant risks of vibration, impact, and friction, especially when the separation factor is greater than 3000. Materials with a risk of combustion or explosion generally should not be subjected to centrifugal separation or have their separation factor restricted. In contrast, separation by static (slow-flow) methods involves large amounts of material and low efficiency (long processing time). For materials containing self-reactive substances with residual reactions or side reactions, there is a higher risk of uncontrolled reactions (due to the absence of stirring and cooling devices), so special attention should be paid. 2.8 Hazards associated with storage and maintenance operations: Under normal conditions, since the materials are at rest, no specific process parameters need to be applied and there is little operational activity, so the accident rate is low. However, there are also many potential dangers in abnormal situations. For example: ① Improper design or selection of the storage tanks and containers, which fail to accommodate the properties of the materials stored, leading to corrosion, damage, and leaks; as well as the lack of necessary safety devices or the failure of such devices ； ②If the material contains components that can continue to react or are prone to decomposition and polymerization, reaction and decomposition products, as well as heat generated by these reactions, will accumulate over time. Combined with the large volume of material, this can lead to material spraying, equipment damage, and fire or explosion accidents ； ③Contaminated with incompatible, unstable, or catalytic impurities ； ④Natural environmental factors, such as excessively high or low temperatures, lightning, earthquakes, etc. 2.9 Hazards of waste disposal: Waste generated in chemical processes is diverse in type, large in quantity, and complex in nature; it often goes unnoticed and is prone to reacting, releasing heat, catching fire, or producing toxic substances when in contact with one another and mixed together. 3 The hazard of equipment mainly depends on whether the equipment has complete safety functions and the reliability of their operation. (collected from the Internet)

In terms of raw materials: there are many flammable, explosive, toxic, harmful, and corrosive substances； In terms of equipment: there are many high-temperature, high-pressure, or special-type devices ； In terms of the production process: it is complex to operate, and the process requirements are strict ； Also, there is relatively more pollution from the three types of waste

In the production of chemical enterprises, raw materials and products are often flammable, explosive, and subject to high temperatures and pressures. During maintenance, leaks of hazardous chemicals can occur, or these substances may remain in the equipment and pipelines. During testing, they might remain inside the equipment or mix with air, forming explosive mixtures. In the event of a fire, it tends to spread rapidly, resulting in severe losses.

Chemical enterprises use hazardous raw materials and produce hazardous products, and the processes involved are also dangerous ones such as high-temperature/high-pressure operations, polymerization, and hydrogenation. The equipment used includes pressure vessels and mechanical and electrical devices; as a result, hazards such as fires, explosions, poisoning, and mechanical injuries exist in chemical production. To better analyze the risks present in such enterprises, an assessment can be conducted from aspects such as safety management, production processes, plant layout, fire protection facilities, occupational health, and identification of major hazard sources. Additionally, enterprise employees can be encouraged to identify potential hazards in their own work areas, thereby raising everyone’s awareness of safety.

1. The vast majority of materials used in chemical production pose risks such as fire, explosion, and toxicity； 2. The production process is complex, with stringent process conditions involving high temperatures, high pressures, and strong corrosion ； 3. Large production scale, resulting in a large amount of hazardous substances accumulated ； 4. Production equipment is characterized by its large size and height.