What is the definition of compressed gas and liquefied gas?

(1) The compressed or liquefied gas whose critical temperature is lower than 50 ° C, or whose vapor pressure is greater than 294kPa at 50 ° C;

(2) Compressed gas with an absolute pressure greater than 275kPa at a temperature of 21.1 ° C, or with an absolute pressure greater than 715kPa at 54.4 ° C; Or at 37.8 ° C, red vapor pressure greater than 275kPa of liquefied gas or pressurized dissolved gas.

In order to facilitate storage, transportation and use, the gas is often compressed or liquefied by cooling and pressurizing method and stored in cylinders. Due to the different properties of various gases, some gases at room temperature, no matter how much pressure is added to it will not become liquid, but must be pressurized at the same time to reduce the temperature to a certain value to make it liquefied (the temperature is called the critical temperature), at the critical temperature, the minimum pressure necessary for gas liquefaction is called the critical pressure. Some gases are easy to liquify and can be made liquid by simple pressure at room temperature, such as chlorine, ammonia and carbon dioxide. Some gases are more difficult to liquefy, such as helium, hydrogen, nitrogen, and oxygen. Therefore, some gases are easy to pressurize into liquid, some are still gaseous, in the cylinder in the gas state is called compressed gas, in the liquid state is called liquefied gas. In addition, this class includes gases dissolved under pressure, such as acetylene.

What are the dangerous characteristics of compressed and liquefied gases?

(1) More than half of compressed and liquefied gases are flammable and explosive. Once flammable gas is ignited, it can be completely burned out in a very short time, which makes the explosion danger very great and the fire fighting difficulty very great.

(2) Strong flow dispersion. Compressed and liquefied gases can spontaneously fill any container and diffuse very easily. For example, most flammable gases are heavier than air, and can spread quite far. They drift on the surface, ditches, tunnels, dead corners of factories and other places, and gather for a long time. In case of fire source combustion or explosion, it is easy to cause fire expansion.

(3) Expansion by heat and increase of air pressure. Compressed and liquefied gases stored in cylinders usually have high air pressure. Excessive heat will lead to a sharp rise in air pressure, once the air pressure exceeds the pressure strength of the container, it will cause the container to rupture and physical explosion, resulting in fire or poisoning and other accidents.

(4) Easy to generate or accumulate static electricity. When compressed gas and liquefied gas are spewing out at high speed from the orifice or breakage, static electricity will be generated due to strong friction.

(5) Corrosive and toxic. In addition to oxygen and compressed air, compressed and liquefied gases are mostly toxic and corrosive.

(6) Choking. Compressed gas and liquefied gas have a certain degree of suffocation, once leakage occurs, if the corresponding ventilation measures are not taken, people can be suffocated to death.

(7) Oxidizing property. There are two kinds of hazards of compressed gas and liquefied gas: one is combustion-supporting gas, such as oxygen; The second is toxic gas, itself non-combustible, but very oxidizing, and combustible gas mixed can occur combustion or explosion, such as chlorine and acetylene.