Safety issues that the chemical industry should be aware of
The substances produced by chemical production are often characterized by flammable, explosive, corrosive and toxic substances, and the production equipment tends to be large. Once an accident occurs, the impact is large, and it is safe for the national economy and the people in the area. Bringing unpredictable losses and disasters. Therefore, the significance of chemical safety is very important, and it is an important part of chemical production management.
The basic contents of chemical safety technology mainly include:
◆1 Technology to prevent occupational hazards.
For example, dust control, anti-virus, heating and ventilation, lighting, vibration and noise control and treatment, high temperature, high frequency, radioactive and other hazard protection, as well as various health monitoring techniques for workers' working environment.
◆2 Technology to prevent various types of accidents.
For example, fire protection, explosion-proof in the chemical production process, safe storage and transportation of chemical dangerous goods, safe use, maintenance, overhaul of pressure vessels and equipment, personal protection, mathematical statistics analysis of accidents, and safety system engineering.
◆3 Develop and continuously improve the standards, procedures and specifications of various chemical safety technologies.
There are about 2,000 types of dangerous goods for the classification and storage of dangerous goods. According to the main characteristics, there are 10 categories, namely explosives, compressed and liquefied gases, pyrophoric articles, water-burning articles, flammable liquids, and flammable materials. Solids, oxidants, drugs and poisons, corrosives, and radioisotopes. In addition to the special requirements of corrosive and radioactive materials, the storage of other general chemical dangerous goods also has its requirements.
Fireproof and explosion-proof technology is one of the main contents of chemical safety technology.
To prevent the work, we must first eliminate or control the factors that cause combustion and explosion during the production process.
Basic concepts of fire and explosion The concepts that are important for handling flammable and explosive materials are explosion limits, combustion hazards and explosion hazards.
When a combustible gas, flammable vapor or a mixture of dust and air is exposed to an open flame or other source of ignition within a certain concentration range, an explosion will occur. This concentration range is the explosive limit of a substance. The lowest concentration (usually expressed as a percentage by volume) of a combustible gas, flammable vapor or dust that forms an explosive mixture in air is called the lower explosion limit, and the highest concentration is called the upper explosion limit. The explosion limit of flammable gases, flammable vapors and dust is the original value for preventing explosions and is an important data in explosion-proof technology.
The explosion limit is not a fixed value and varies with various factors such as temperature, pressure, inert gas, and container conditions. The higher the original temperature of the explosive mixture, the greater the explosion limit, ie the lower explosion limit is lowered and the upper explosion limit is increased.
The original pressure of the explosive mixture has a major impact on the explosion limit:
When the pressure is reduced, the explosion limit is reduced; when the pressure drops to a certain value, the lower limit coincides with the upper limit, and the pressure at this time is called the critical pressure of the explosion; if the pressure is below the critical pressure of the explosion, the system will not explode. The content of the inert gas in the mixture increases, and the explosion limit is reduced; the concentration of the inert gas is increased to a certain value, so that the mixture does not explode. The smaller the diameter of the tube filling the container, the smaller the explosion limit range. When the pipe diameter (or flame passage) is small enough, the flame cannot pass. Other energy such as sparks, the area of the heated surface, the contact time of the fire source with the mixture, and the illumination of the light all have an effect on the explosion limit.
Classify flammable solids and flammable liquids from the perspective of fire prevention. Flammable solids generally use their ignition point as a grading basis for the risk of burning. Flammable liquids are classified into four grades according to their flash point (the lowest temperature at which the liquid vapor flashes) (Table 2 Liquid Combustion Hazard Classification Standard), the first and second grades are called flammable liquids, and the third and fourth grades It is called a flammable liquid.
The explosive concentration of flammable gas, flammable vapors and dust is calculated by the following formula: The greater the value of the explosion hazard (the explosion hazard of typical flammable gases in Table 3), the greater the hazard, and vice versa. Less sexual.
Fire hazard classification A comprehensive analysis of the fire hazard in a chemical production process to determine the type of fire hazard in production or storage, so that it is a key consideration from the start of the design.
China divides the fire hazard of chemical production and storage into five categories: A, B, C, D, and E.
◆Class A---Use or produce flammable liquid with flash point <28°C; flammable gas with lower explosion limit <10%; substance that can decompose at room temperature or oxidize in air, which can cause rapid spontaneous combustion or explosion; A substance that is combustible by water or air to produce a combustible gas and causes combustion or explosion; in the case of acid, heat, impact, friction, and flammable inorganic substances such as organic matter or sulfur, a strong oxidant that easily causes combustion or explosion; A substance that causes combustion or explosion when struck, rubbed, or in contact with an oxidant or organic matter; a substance that exceeds the point of spontaneous combustion in a pressure vessel.
◆Class B---flammable and flammable liquid with a flash point of 28-60 °C during use, storage or production; combustible gas with a lower explosion limit of ≥10%, combustion-supporting gas and oxidant not belonging to Class A; not classified as Class A Chemically flammable hazardous solids; flammable fibers or dust that floats in a floating state during production and use, and can form an explosive mixture with air. In the storage material, it is slowly oxidized by contact with air at normal temperature, and the accumulated heat does not disperse, causing dangerous articles of spontaneous combustion.
◆ Class C---Combustible liquid with flash point ≥60°C during use, storage or production; flammable solid.
◆Dings---Processing non-combustible materials and producing radiant heat, sparks or flames at high temperatures or in a molten state; using gases, liquids, solids as fuel, or burning gases and liquids for other purposes Various production; use or processing of difficult-to-burn materials at room temperature for production and storage.
◆ Class E - the production or processing of non-combustible materials at normal temperature.
Class A has the greatest risk and should focus on measures.
Basic measures for fire prevention and explosion protection The risk of fire and explosion depends on the type, nature and quantity of combustible materials, the size of the production equipment area and plant space, the technical status and advanced level of the production equipment, ventilation and ventilation conditions and equipment, and equipment. Is it possible to leak and operate if it is possible to make a mistake, and so on.
The basic measures usually taken are:
◆ Strictly control ignition energy.
Mainly to indicate fire (heating fire, maintenance fire, etc.), high heat and high temperature surface, electric spark, static spark, impact and friction, adiabatic compression, natural heat, chemical reaction heat, light and radiation.
◆ Strictly control the process parameters within the safe limits, preferably with automatic adjustment and control.
Improving the ability to automatically control and safety devices is an important measure to ensure safe production.
In addition, limiting the spread of fire or explosion consequences must be considered when starting the design layout, which can prevent the expansion of accidents and the ease of operation management. For example, to prevent the damaging effects of an explosion, the plant or installation should have an explosion-proof pressure relief facility, or it can be installed in isolation or open-air, as well as remote control.
China has regulations on the fire separation distance of petrochemical plants
For example, the fire separation distance between chemical plants and residential areas, neighboring factories, transportation lines, etc.: in the general layout of the factory, process production equipment, plant-wide important auxiliary production facilities, as well as machine repair, instrument and electrical repair, garage, center There are open fire or sparking places in the laboratory, flammable and flammable liquid storage tanks, etc., all have fire separation regulations; fire separation requirements between equipment, buildings and structures in the process production equipment; and chemical plant construction sites and other fire prevention There are 16 rules for spacing and so on.
The prevention of occupational hazards is mainly to prevent occupational injuries such as dust (sputum) lungs, occupational poisoning, burns, noise, radiation.
China regulates the maximum allowable concentrations of harmful gases, vapours and dusts in the air of the workshop
Prevention of burns, noise, and radiation is primarily the development of sound safety practices and the establishment of reliable preventive or protective equipment.
◆Prevent the conditions that cause dangerous substances to form a combustion explosion.
First, try to improve the process and replace it with less dangerous substances. If it is not possible, take appropriate measures, such as inert media protection, containment or ventilating to reduce the concentration of the substance or operate under negative pressure, and so on.