Gas is a mixture of many gases, and its composition is very complicated. It contains methane (CH4), carbon dioxide, nitrogen and a small amount of inert gases, such as helium and argon, but the main component is methane (CH4).

In the standard state (temperature is 0℃, atmospheric pressure is 10 1.3kPa), the gas density is 0.7 16kg/m3 (air density is 1.29kg/m3). Because the gas is light, it often accumulates at the top of roadway and the change of section. Gas has a special smell because it contains other gases.

Harm of gas

It is easy to cause suffocation. Although methane (CH4) itself is non-toxic, when the concentration of methane (CH4) in the air is high, the oxygen concentration in the air will be relatively reduced. When the oxygen concentration drops to 17%, people will feel difficult to breathe. If the oxygen concentration drops below 12%, people will suffocate. Therefore, all areas with poor ventilation in the tunnel must be closed or fenced in time, and warning signs of "No Entry" should be hung to prevent personnel from entering.

Burning and explosion. When the mixture of gas and air reaches a certain concentration, it will burn or explode when it meets a high temperature fire source. Once the disaster accident is formed, it will cause a large number of casualties and seriously affect the safe production of the tunnel.

Explosion condition

The conditions of gas explosion are: a certain concentration of gas, the existence of high-temperature fire source and sufficient oxygen, all of which are indispensable.

Gas concentration. Gas explosion has a certain concentration range, and the concentration range that can cause explosion after gas meets fire in the air is called gas explosion boundary. The gas explosion limit is 5% to 16%, 5% is the lower explosion limit and 16% is the upper explosion limit.

When the gas concentration is lower than 5%, it will not explode in case of fire, but it can form a combustion layer around the flame. When the gas concentration is 9.5%, its explosive power is the largest (oxygen and gas react completely); When the gas concentration is above 16%, it loses its explosiveness, but it will still burn in the air.

High temperature fire source. The ignition temperature of gas is the lowest temperature for igniting gas. It is generally considered to be 650 degrees Celsius to 750 degrees Celsius, but it will change due to factors such as gas concentration, nature of fire source and pressure of mixed gas.

When the gas comes into contact with a high-temperature fire source, it will not burn or explode immediately, but will go through a short time interval, which is called ignition delay period and induction period.

The induction period of gas explosion is of great significance to safety production. For example, when blasting with qualified explosives, the initial temperature is about 2000 degrees Celsius, but the high temperature only exists for a few thousandths of a second. The induction period of Bibas explosion is short, so it will not cause gas explosion. If the quality of explosives is not up to standard, the stemming is not dense or the blasting is not standardized (such as blasting and paste blasting, etc.). ), it will prolong the existence time of high temperature and cause gas explosion accidents.

Plenty of oxygen. Practice has proved that when the oxygen concentration in the air decreases, the gas explosion boundary decreases, and when the oxygen concentration decreases below 12%, the mixed gas loses its explosiveness. Therefore, when a large amount of gas is accumulated in the tunnel and there is a fire source, if the oxygen concentration is too low, there will be no explosion. If fresh air enters and the oxygen concentration reaches more than 12%, an explosion may occur.

Related case

● 2065438+February 24, 2005

A gas explosion occurred in Wu Luo Road 1 Tunnel in Luodai Town, Longquanyi District, Chengdu, Sichuan Province, which was built by the 15th Engineering Bureau Co., Ltd. of China Hydropower Construction Group, causing 7 deaths and 19 injuries.

● February 2009 16

A sudden gas explosion occurred in a tunnel under construction in Jianshi County, Enshi Prefecture, Hubei Province, causing 6 injuries and 1 death.

● 65438+February 22, 2005

A gas explosion occurred in Dongjiashan Tunnel of Dujiangyan-Wenchuan Expressway in Sichuan, killing 44 people and injuring 1 1.

Emergency treatment of gas explosion

General methods for handling explosion accidents:

1. First, rescue people in distress and send them to the hospital.

2. The explosion caused a fire. When there are people in distress in the disaster area, the direct fire extinguishing method must be adopted.

3. In the case that all personnel in the air inlet direction have been evacuated, windproof measures can be considered.

4. When it is confirmed that there is no danger of secondary explosion, the disaster area can be ventilated to discharge toxic and harmful gases.

Safety precautions:

1. Before carrying out the task, the rescue team must understand the nature of the accident and formulate safety measures.

2. After entering the disaster area, it is necessary to check the concentration of gas and other gases at any time, grasp the changes of various gas concentrations, and take measures to prevent the continuous explosion of gas.

3. Before the rescue team enters the disaster area, the power supply should be cut off.

4. Don't change the ventilation system easily, so as not to change the airflow and cause accidents.

Safety measures in tunnel construction

★ Do a good job in tunnel gas advance forecast.

In order to ensure the safety of tunnel construction, comprehensive advanced geological prediction should be made according to geological structure and gas emission characteristics. In order to ensure the accuracy of geological prediction, it is necessary to verify each other through various advanced detection means to ensure the accuracy. Then according to the geological forecast results, the corresponding gas control scheme is formulated to ensure the safety of tunnel construction.

★ Strengthen gas detection.

From the past cases of tunnel gas explosion accidents, it can be seen that the main causes of tunnel gas explosion accidents are the omission, omission and improper handling of gas information during construction. Therefore, in order to ensure the safety of tunnel construction, gas detection must be carried out timely and accurately in the construction process. It is necessary to detect the gas concentration in the tunnel in real time and check the operation of the fan to ensure the safety of personnel in the tunnel.

★ Ensure a reliable ventilation system.

Strengthening the ventilation management in the tunnel to ensure uninterrupted ventilation during the tunnel construction is the fundamental measure to ensure that the Nevas concentration in the tunnel does not exceed the standard, and it is also the main means of gas dilution and smoke extraction and dust removal. Ventilation must be carried out according to the design and specification requirements. According to the requirements of gas prevention and control, tunnel ventilation must be equipped with standby fan and standby power supply. At the same time, it is necessary to ensure that the standby fan and the standby power supply are automatically switched and maintain 24-hour continuous ventilation. In addition, the ventilator should also be equipped with special transformers, special lines and special switches.

★ Explosion-proof construction equipment.

In order to prevent gas explosion and other disasters in the tunnel, the electrical equipment and working machinery in the high gas working area and gas outburst working area must be explosion-proof. In the process of tunnel construction, the working machinery should be properly explosion-proof. Therefore, before the tunnel construction, the general electromechanical equipment should be transformed into explosion-proof electromechanical equipment.

★ Establish a perfect safety management system.

Perfect safety management system is the basic guarantee of safety production, so before tunnel construction, perfect safety management system must be established, such as tunnel welding system, tunnel ventilation system, gas detection system and so on. Before entering the tunnel, the construction personnel must be inspected by the personnel on duty. It is forbidden to bring tobacco, ignition materials or wear chemical fiber clothes to enter. Incandescent lamps, electric furnaces and other items that are easy to generate sparks are strictly prohibited in the tunnel. Choose a diesel vehicle or install an exhaust gas purifier to ballast the vehicle to prevent the exhaust gas from becoming a dangerous source.

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