The poisonous and harmful gases in the tunnel are always the main hazard in the construction, if the construction is not proper, it is easy to cause serious safety accidents. The harmful gases in the tunnel mainly include methane, carbon monoxide, carbon dioxide, hydrogen sulfide, nitrogen, heavy hydrocarbons and trace rare gases.
According to the chemical properties, these toxic and harmful gases are divided into two categories: combustible gas and toxic gas.
The main components of the flammable gas in the tunnel are methane (CH4, gas) and some volatile organic compounds (VOC), and the main hazard is the explosion caused by gas combustion, which causes harm to property and human life. But flammable gas explosion must have certain conditions. A certain amount of combustible gas, sufficient oxygen and ignition source. All three conditions are indispensable. The gas concentration at which a combustible gas explodes is usually referred to as the minimum explosion limit, generally expressed by LEL. Different combustible gases have different LEL. Therefore, the detection of combustible gas generally detects its LEL.
The toxic gases in the tunnel are divided into irritating gases, asphyxiating gases and acute toxic organic gases (VOC) according to their different mechanisms of action on the human body.
The first type: irritating gases include [chlorine, phosgene, biphosgene, sulfur dioxide, nitrogen oxides, formaldehyde, ammonia, ozone] and other gases. The irritating gas has a strong stimulating effect on the skin and mucosa, some of which have a strong corrosion effect at the same time.
The second category: asphyxiating gases include [carbon monoxide, hydrogen sulfide, hydrocyanic acid, carbon dioxide, nitrogen, methane, ethane, ethylene, nitrobenzene vapor, hydrogen cyanide] and other gases. When these compounds enter the body, they cause hypoxia in tissue cells. It is worth mentioning that methane (CH4) can also be an asphyxiating gas, which itself has no obvious toxicity to the body, and the hypoxia caused by it is actually the anoxic asphyxia caused by the reduction of oxygen concentration in the inhaled gas. Acute toxic organic solvents include hexane, dichloromethane and so on.
The third category: acute toxic organic gases (VOC) three categories, the above organic volatile compounds with the above inorganic toxic gases, will also cause harm to the human respiratory system and nervous system, and some carcinogenic, such as benzene. Since most organic compounds are combustible substances, the detection of organic compounds used to detect their explosiveness, but the minimum explosion limit of organic compounds is far greater than its MAC (maximum allowable concentration in space) value. In other words, it is necessary and necessary to test the toxicity of organic compounds. Such as n-hexane, dichloromethane, etc. However, it is usually the value when the lower explosive limit (LEL) concentration of the gas is not reached. Its toxicity has already caused harm to the human body, so for the detection of organic compounds (VOC), we must first test the poison and then test the explosion.
At present, when we choose all kinds of gas detectors, there are still many problems, which are manifested in:
A) The detection of combustible gases is more important than that of toxic gases.
B) The detection of gases that may cause acute poisoning is more important than that of gases that may cause chronic poisoning.
For all kinds of different production occasions and testing requirements, the selection of the right gas detector is every person engaged in safety and production work must pay great attention.
If methane and other less toxic alkanes are mostly, choosing a combustible gas detector is undoubtedly the best choice. This is not only because the combustible gas detector principle is simple and widely used, but also has the characteristics of convenient maintenance and calibration. If there are toxic gases such as carbon monoxide (CO) and hydrogen sulfide (H2S), a specific gas detector should be preferred to ensure the safety of the staff. If it is more organic toxic and harmful gases, taking into account the low concentration that may cause human poisoning, such as aromatic hydrocarbons, halogenated hydrocarbons, ammonia (amine), ethers, alcohols, esters, etc., it should choose the photoionization detector (PID), and absolutely do not use the combustible gas detector to deal with it, because it may lead to casualties. If the gas types cover the above several types of gases, choosing a compound gas detector may achieve twice the result with half the effort.
Fixed multi gas detector is widely used in tunnel field, welcome inquiry.