Hazard of dangerous/toxic substances, allowable concentration

The classification standard for hazardous chemicals is GB13690-2009 General Principles for the Classification and Labelling of Chemicals. Commonly used hazardous chemicals are classified into 8 categories based on their main hazardous properties: Category 1 – Explosives. These chemicals are those that, under external influences such as heat, pressure, or impact, can undergo violent chemical reactions, generating large amounts of gas and heat in an instant. This leads to a sudden increase in pressure and an explosion, which can cause damage to the surrounding environment. It also includes substances that do not pose a risk of explosion as a whole, but rather have risks of combustion, projection, or minor explosions. Category 2: Compressed gases and liquefied gases. These chemicals are gases that are compressed, liquefied, or dissolved under pressure, and must meet one of the following conditions: a. Gases that are compressed or liquefied with a critical temperature below 50°C, or gases for which the vapor pressure is greater than 294 kPa at 50°C ； b. Compressed gases with an absolute pressure greater than 275 kPa at a temperature of 21.1°C, or an absolute pressure greater than 715 kPa at a temperature of 54.4°C ； Or a liquefied gas or a pressurized dissolved gas with a vapor pressure of red greater than 275 kPa at 37.8°C. Category 3: Flammable liquids. The classification of flammable liquids, warning labels, and precautionary statements are specified in GB20581. Flammable liquids are those with a flash point of 63°C or lower. Category 4: Flammable solids, self-igniting substances, and substances that are flammable when exposed to moisture. Flammable solids refer to solids with a low ignition point, which are sensitive to heat, impact, and friction; they can be easily ignited by external sources of fire, burn rapidly, and may emit toxic fumes or gases. Substances that are classified as explosives are not included in this category. Spontaneously combustible materials are those with a low ignition point that readily undergo oxidation reactions in air, releasing heat and thus burning on their own. Flammable materials when exposed to moisture refer to those that undergo intense chemical reactions upon contact with water or humidity, releasing large amounts of flammable gases and heat. Some can burn or explode without the need for an open flame. Category 5: Oxidizers and organic peroxides. Oxidizers are substances that are in a high oxidation state, possess strong oxidizing properties, and are prone to decomposition, releasing oxygen and heat. This includes inorganic substances containing peroxyl groups; they may not be flammable on their own, but can cause combustible materials to burn. They can form explosive mixtures with soft, powdery combustible materials, and are sensitive to heat, vibration, or friction. Organic peroxides refer to organic compounds whose molecular structure contains peroxide groups; they are flammable and explosive, prone to decomposition, and highly sensitive to heat, vibration, or friction. Category 6: Toxic substances. These chemicals refer to those that, once they enter the body and accumulate to a certain level, can undergo biochemical or biophysical reactions with bodily fluids and organ tissues, disrupting or damaging the body’s normal physiological functions. This can lead to temporary or permanent pathological changes in certain organs and systems, and may even be life-threatening. Oral lethal dose: LD50 for solids ≤ 500 mg/kg; LD50 for liquids ≤ 2000 mg/kg; after 24 hours of skin contact, the lethal dose LD50 ≤ 1000 mg/kg; for solids or liquids in the form of dust, fumes, or vapors, the lethal concentration LC50 ≤ 10 mg/L. Category 7: Radioactive materials. Chemicals in this category refer to those with a radioactive specific activity greater than 7.4×104 Bq/kg. Category 8: Corrosives. These chemicals are solids or liquids that can burn human tissue and cause damage to metals and other materials. Solids or liquids that cause visible necrosis upon contact with skin within 4 hours, or that result in an average annual corrosion rate of more than 6.25 mm/year on the surface of grade 20 steel at a temperature of 55°C. For hazardous chemicals that are not listed in the detailed classification table, classification can be carried out by referring to those already listed that have similar chemical properties and similar levels of hazard. (Please take it; no need to thank me)