The importance of gas detectors in industry
At present, electrochemical sensors that can detect specific gases include: carbon monoxide, hydrogen sulfide, sulfur dioxide, nitrogen monoxide, nitrogen dioxide, ammonia, chlorine, hydrogen cyanide, ethylene oxide, hydrogen chloride, etc. The photoionization detector introduced in the previous chapter can be used to detect VOC detectors. Oxygen is also a factor that requires great attention in industrial environments, especially in closed environments. Generally, we call the oxygen content exceeding 23.5% oxygen excess (oxygen-enriched), at which time the danger of explosion is likely to occur; and the oxygen content below 19.5% is oxygen deficiency (hypoxia), at which time workers are prone to suffocation and coma to the risk of death. The normal oxygen content should be around 20.9%. Oxygen detector is also a kind of electrochemical sensor.
At present, there are many problems in the selection of toxic and harmful gas detectors: In our country, due to historical and cognitive reasons, there are still many problems in the selection of various detectors, which are specifically reflected in:
1) The detection of combustible gases is more important than the detection of toxic gases.
2) The detection of gases that may cause acute poisoning is more important than the detection of gases that may cause chronic poisoning.
Due to the bloody lessons of explosion accidents caused by the leakage of many combustible gases, people attach great importance to the detection of combustible gases. It can be said that in any petrochemical and chemical plant, most of the dangerous gas detectors are LEL detectors. But only equipped with LEL detectors is far from enough to truly protect the safety and health of workers. It is undeniable that most of the volatile hazardous gases are combustible gases, but the catalytic combustion combustible gas detector (LEL) is not the best choice for all combustible gas detection. It is designed specifically for the detection of methane, and its detection performance for other substances is relatively poor. Therefore, the lower limit concentration of combustible gases other than methane that they can detect is much higher than their allowable concentration.
For example: For dangerous and toxic gases such as benzene and ammonia, it is a very dangerous practice to simply use a combustible gas detector. For example, the lower explosion limit of benzene is 1.2%, and its correction coefficient on the LEL detector is 2.51, that is to say, the concentration of benzene displayed on a LEL detector calibrated with methane is only 40% of its actual concentration! ! In this way, the lowest alarm concentration of benzene that can be detected by LEL is 10%LEL=10%*1.2%*2.51=3.0*10-3, which is nearly higher than the allowable concentration of benzene 5*10-6 600 times!!. Similarly, the alarm concentration of 1.5*10-2 obtained by ammonia on the LEL detector is about 600 times higher than the allowable concentration of 2.5*10-5. Therefore, depending on the detected gas, it is more accurate and reliable to choose a specific toxic gas detector than to simply choose an LEL detector.
In addition, at present, we pay more attention to the detection of gases that can cause acute poisoning, such as hydrogen sulfide and hydrogen cyanide, but not enough attention to the detection of gases that can cause chronic poisoning, such as aromatic hydrocarbons and alcohols. The health and safety hazards of workers are no less harmful than the gas that can cause acute poisoning! They can cause cancer and other invisible diseases, affecting the lifespan and health of workers. The appearance of this phenomenon, in addition to the cognitive reasons, is also an important reason for the lack of suitable organic gas detectors that can detect lower concentrations in the market. With the development of science and technology and the improvement of people's health awareness, people are no longer satisfied with "going to work happily and going home safely", but are pursuing higher quality of life and living conditions. People are not only concerned about today's work, but also about tomorrow - life after retirement.
Therefore, in the work of industrial hygiene and industrial safety, it is necessary to constantly introduce new concepts and new ideas, so as not only to avoid immediate dangers, but also to avoid future tragedies. All of these require the formulation of laws and regulations and the improvement of people's quality be continuously improved and enhanced. We will discuss how to select and maintain various types of toxic and harmful gas sensors in the next section.
