Industrial gases are usually classified as Class 2 compressed gas and liquefied gas in the national standard "Classification and Marking of Commonly Used Hazardous Chemicals" (GB13690-1992). This category of chemicals refers to gases that are compressed, liquefied, or dissolved under pressure. After the gas is pressurized or lowered in temperature, the distance between the gas molecules can be greatly reduced and be pressed into the cylinder. This gas is called compressed gas (also known as permanent gas, such as oxygen, nitrogen, argon, hydrogen, etc.). Continue to pressurize the compressed gas and cool down appropriately, and the compressed gas will become liquid, which is called liquefied gas (such as liquid chlorine, liquid ammonia, liquid carbon dioxide, etc.). In addition, there is a very unstable gas that needs to be dissolved in a solvent and stored in a cylinder after pressurization. This gas is called a dissolved gas (such as dissolved acetylene, etc.).

Industrial gases can be divided into 4 categories according to their chemical properties: (1) Highly toxic gases, which are extremely toxic, and can cause poisoning or even death when invading the human body. Such as chlorine, ammonia, etc. ⑵ Flammable gas, with flammability, chemical explosion hazard, and certain toxicity. Such as hydrogen, acetylene, etc. (3) Combustion-supporting gas, which has the ability to support combustion, but does not burn by itself, and has the risk of expanding fire, such as oxygen. ⑷ Non-combustible gas, suffocating to humans, stable in nature, non-combustible, such as nitrogen, carbon dioxide and argon. In the national standard GB13690-1992, the above-mentioned 4 kinds of gases are divided into 3 sub-categories, namely the 2.1-type flammable gas, the 2.2-type non-combustible gas (including the combustion-supporting gas), and the 2.3-type toxic gas

Industrial gases can be divided into single-type industrial pure gases and binary or multi-element industrial mixed gases according to their components. In the national standard "Classification of Bottled Compressed Gases" (GB16163-1996), industrial pure gases are classified according to their physical state and critical temperature in cylinders, and are grouped according to their chemical properties, flammability, toxicity, and corrosivity. The first category is permanent gas, its critical temperature is less than -10℃. It is gaseous during filling and storage and transportation and use at the allowable working temperature. It is divided into two groups: a and b: group a is non-flammable and non-toxic And non-combustible toxic gases (including oxygen, nitrogen, argon, etc.), group b is combustible non-toxic and combustible toxic gases (including hydrogen, etc.). The second category is liquefied gas, its critical temperature is ≥-10℃, including high-pressure liquefied gas and low-pressure liquefied gas. Among them, the critical temperature of high-pressure liquefied gas is ≥-10℃ and ≤70℃. It is liquid when filled, but will evaporate into gas when the temperature rises to the critical temperature during storage, transportation and use at the allowable working temperature. , Divided into three groups: a, b, and c: group a is non-combustible, non-toxic and non-combustible toxic gas (including carbon dioxide); group b is combustible non-toxic and spontaneously combustible toxic gas; group c is combustible gas that is easy to decompose or polymerize. The critical temperature of low-pressure liquefied gas is> 70℃. It is liquid during filling and storage and transportation at the allowable working temperature. It is also divided into three groups: a, b, and c: group a is non-combustible, non-toxic and non-combustible and toxic And acidic corrosive gases (including chlorine); group b is combustible non-toxic and combustible toxic and alkaline corrosive gases (including ammonia); group c is combustible gas that is easy to decompose or polymerize. The third category is the gas that dissolves acetylene and dissolves in the solvent in the cylinder under pressure. There is only a group: combustible gas (including acetylene) that is easy to decompose or polymerize. This classification is the basis of mixed gas preparation.

Industrial mixed gas is a new variety that has appeared in the past two decades and has a wide range of uses, but there is no uniform standard for its classification. Industrial mixed gas includes two types: natural synthesis and pure product preparation. According to its state, it is divided into gaseous mixture, liquid mixture and gas-liquid mixture. According to the main dangerous components contained in it, it can generally be divided into flammable gas mixture, spontaneous combustion gas mixture, highly toxic gas mixture and corrosive gas mixture, etc. When the newly-appearing new gas-liquid mixture is applied to cutting, compared with other gas mixtures, the stability, mixing degree, safety and use effect all highlight great advantages.

The common physical properties of industrial gases can be summarized as: compressibility and expandability. When the temperature of a certain amount of gas remains basically unchanged, the greater the pressure applied, the smaller its volume will become. If the pressure is continued, the gas will be compressed into a liquid, which is the compressibility of the gas. Industrial gases are usually stored in cylinders in a compressed or liquefied state. After the gas is illuminated or heated, the temperature rises, the thermal movement between molecules is intensified, and the volume increases. If the gas is heated in a certain container, the higher the temperature of the gas, the greater the pressure formed after expansion. This is the thermal expansion of the gas Sex. Compressed gas and liquefied gas are contained in the container. If exposed to high temperature and sunlight, the gas can easily expand and generate a lot of pressure. When the pressure exceeds the pressure strength of the container, it will cause an explosion. Therefore, industrial gases have a great explosion hazard.