Toxic gases in tunnels are classified into three categories according to their different mechanisms of action on the human body, namely, irritant gas, asphyxiant gas, and acute poisoning of organic gases (VOC).

Class I: irritant gas

Chlorine, phosgene, phosgene, sulfur dioxide, nitrogen oxides, formaldehyde, ammonia, ozone, and other gases. The action of irritating gases on the body is characterized by strong stimulation to the skin and mucosa, some of which are strongly corrosive at the same time. For these gas detection, we need to use a chlorine gas detector, sulfur dioxide detector, ozone detection alarm, and other single gas detectors.

Class II: asphyxiating gas

Carbon monoxide, hydrogen sulfide, cyanuric acid, carbon dioxide, nitrogen, methane, ethane, ethylene, nitrobenzene vapor, hydrogen cyanide, and other gases. These compounds enter the body, resulting in hypoxia of tissue cells. It is worth mentioning that methane (CH4) can also be asphyxiated gas. It has no obvious toxicity to organisms, and its tissue cell hypoxia is actually caused by hypoxic asphyxia caused by the decrease of oxygen concentration in inhaled gas. Organic solvents in acute poisoning include hexane, dichloromethane, and so on. For these gases, a carbon monoxide detector, hydrogen sulfide detector, nitrogen detector, and methane detector are required.

Class Ⅲ: acute toxic organic gas (VOC)

The above three kinds of organic volatile compounds, like the above inorganic toxic gases, can also cause harm to the respiratory system and nervous system of the human body, and some carcinogens, such as benzene. Because organic compounds are mostly flammable substances, the detonation of organic compounds is mostly detonation before, but the minimum explosive limit of organic compounds is far greater than that of their MAC (maximum allowable concentration of space). That is to say, it is necessary and necessary to detect the toxicity of organic compounds. Such as n-hexane, dichloromethane, and so on. However, it is usually lower than the LEL concentration. Its toxicity has already caused harm to the human body. Therefore, we need to test the toxicity of organic compounds (VOC) before detonation. For VOC gas monitoring, a VOC detector can be used.

To construct the tunnel safely, it is necessary to monitor the concentration of toxic gases in the tunnel in real-time. VOC detector, formaldehyde detector, CO detector, hydrogen cyanide detector, and other gas detectors are used. Fixed gas detector, portable four in one gas detector is commonly used in the tunnel. Combustible gases, carbon monoxide, hydrogen sulfide, and oxygen are detected at the same time. Real-time monitoring and sound light vibration alarm are provided, To ensure the safety of the staff.