The carbon monoxide fire extinguishing system must be filled according to the standard of 0.6 kg / L. The bottled gas belongs to high-pressure liquefied gas, and its critical temperature is 31 ℃. When the temperature is lower than 31 ℃, it can be liquefied under pressure. When the temperature is equal to or higher than 31 ℃, the liquid carbon dioxide in the bottle will be transformed into gaseous carbon dioxide. When filling carbon dioxide according to the standard of 0.6 kg / L, when the temperature is close to 31 ℃, the pressure in the bottle is in the state of gas-liquid coexistence, and the saturated vapor pressure on the liquid interface is 7.39 MPa. When the temperature reaches or exceeds 31 ℃, the phase transition from liquid to gas occurs. The pressure in the bottle is no longer the extension of the saturated vapor pressure of carbon dioxide, but the sudden rise of the pressure caused by the large amount of gasification of liquid carbon dioxide. At this time, the pressure condition in the bottle is essentially the same as that of permanent gas. When the temperature continues to rise to 54 ℃, the pressure in the cylinder will increase to about 15 MPa, which is equivalent to the nominal working pressure of the cylinder. Because the carbon dioxide in the cylinder has these characteristics, in order to ensure the safety of the cylinder during filling, storage, transportation and use, it should be filled in strict accordance with the specified filling coefficient. The gas cylinder is an independent thin-walled closed container without insulating layer. The pressure of carbon dioxide in the cylinder is related not only to the temperature, but also to the filling volume. The nominal working pressure of the gas cylinder refers to the limited filling pressure of the gas filled at 20 ℃ for permanent gas cylinders, and the filling volume is measured by pressure; For cylinders containing high-pressure liquefied gases such as carbon dioxide, it refers to the limited value of gas pressure in the cylinder when the temperature is 60 ℃, and the filling volume is measured by weight. If the bottle is not filled according to the standard of 0.6 kg / L, but over filled, the gas phase space in the bottle will be reduced accordingly. With the increase of temperature, the volume of liquid carbon dioxide will expand accordingly, and the gas phase space will continue to decrease, resulting in the disappearance of "full liquid" and gas phase space in the bottle. The bottle is full of liquid, and its pressure is no longer the saturated vapor pressure, but the expansion force of the volume expansion of liquid carbon dioxide. This expansion force is much greater than the saturated vapor pressure. The liquid carbon dioxide and volume expansion system is relatively large. In the range of - 5 ~ 35 degrees, the pressure in the cylinder will rise by 0.314 ~ 0.834mpa for each temperature rise. Therefore, overpressure explosion of the cylinder is easy to occur due to overpressure.

Precautions for application of carbon dioxide fire truck
① Prevent the use temperature of carbon dioxide fire truck from being too high. The steel cylinder shall be stored in a cool, dry place away from heat sources (such as sunlight, heating and furnace fire) and shall not exceed 31 degrees, so as to avoid the volume expansion caused by the rise of liquid carbon dioxide temperature and the formation of high-pressure gas, resulting in explosion hazard.
② The opening and closing of the valve shall be carried out slowly to prevent too fast and too fierce. When discharging, the liquid phase shall be discharged first, and then the phase shall be discharged (except for emergency pressure relief) to prevent dry ice in the storage tank.
③ Carbon dioxide can't be misplaced. Otherwise, when the decompression is opened, the rushed carbon dioxide liquid will vaporize rapidly, which is easy to burst the airway and leak a large amount of carbon dioxide, resulting in accidents. ④ The stop, joint and pressure gauge device shall be connected correctly, without leakage, damage and in good condition.
⑤ Carbon dioxide shall not be overfilled. The volume of liquefied carbon dioxide in tropical climate shall not exceed 66.7%, and the filling volume of carbon dioxide in temperate climate shall not exceed 66.7%.
⑥ During pressure relief and discharge, pay attention to whether there are basements and sewers around to prevent carbon dioxide from accumulating in low-lying places and endangering personal safety.
⑦ Carbon dioxide fire engines are subject to regular safety inspection. If the service life of carbon dioxide fire truck exceeds the safety specification, it can only be used after passing the pressure test.