Working principle and technical performance of carbon dioxide fire truck
Carbon dioxide fire engines are mainly used in the environment that is not suitable for setting water-based fire extinguishing systems and other fire extinguishing systems. They are suitable for fires in confined spaces and small-area flammable and combustible liquid fires, such as computer rooms, important libraries and archives, mobile communication base stations, valuable instruments, important cultural relics, electrical equipment (except high-voltage electrical equipment), etc.
8.4.1 working principle of carbon dioxide fire truck
The carbon dioxide fire truck is equipped with carbon dioxide fire extinguishing system, including carbon dioxide cylinder group, high-pressure distribution pipeline, hose reel and spray barrel hose, as shown in Figure 8-5.

Carbon dioxide injection takes carbon dioxide gas as the driving force, drives the saturated liquefied gas out of the bottle mouth, enters the reel hose through the control of the volume pipe, and ejects from the spray barrel to achieve the fire extinguishing effect.
Carbon dioxide is a compound composed of one carbon atom and two oxygen atoms. Its chemical formula is Co. According to different temperatures and pressures, carbon dioxide can coexist in three states: solid, liquid and gas, or exist in a single state. Under normal atmospheric pressure, carbon dioxide is a colorless and tasteless gas, which is 1.5 times heavier than air. Carbon dioxide does not burn or support combustion. It can be used to block oxygen and extinguish fire. When carbon dioxide is in a container with appropriate pressure, it can exist in any form of solid, liquid and gas according to its temperature and pressure. The temperature and pressure of the three state coexistence equilibrium point are 56.6 ℃ and 130.8 MPa respectively. At this time, there are three states of carbon dioxide at the same time. This equilibrium point is called the three-phase point. When the temperature and pressure are lower than the three-phase point, carbon dioxide has both solid and gas. The critical points of carbon dioxide are 31.1 ℃ and 7.38 MPa. When the temperature and pressure exceed this value, carbon dioxide cannot exist in liquid state. At this time, carbon dioxide can only exist in a supercritical fluid state. When the temperature and pressure exceed the three-phase point and are lower than the critical point, the carbon dioxide liquid with gas on the upper layer can be stored in a sealed container in equilibrium. Due to this property of carbon dioxide, a large amount of carbon dioxide liquid can be loaded into narrow and thin-walled pressure vessels, that is, carbon dioxide can be stored in low-pressure bulk containers ◇ "low pressure" is used in industry, which often means that carbon dioxide should be stored at a low temperature below the ambient temperature, usually at a temperature of 17.8 ℃). When carbon dioxide is released under reduced pressure, it can be instantly gasified into high-pressure gas from the liquid to extinguish the fire.
8.4.2 technical performance of carbon dioxide fire truck
GA 39-2016 fire fighting requirements and test methods for fire engines requires that the total water volume of the steel cylinder and tank of gas fire extinguishing agent shall not be less than 1500L. At least one set of injectors and connecting hoses shall be set on both sides of the vehicle, and the vehicle shall be equipped with fire gloves and noise reduction earplugs or earmuffs twice the number of members. Shockproof pressure gauges shall be installed at the outlet of the cylinder and before and after decompression, with an accuracy grade of no less than 2.5. The range of the pressure gauge shall be suitable for the working pressure and easy to observe. See table 8-4 for the performance of carbon dioxide injection system.