Information Problems in Selecting Hazardous Gas Detectors
The use of oxygen in industrial environments, especially in enclosed environments, requires careful consideration of various factors. Generally, we refer to oxygen content exceeding 23.5% as oxygen excess (oxygen enrichment), which can easily lead to the risk of explosion; And an oxygen content below 19.5% indicates oxygen deficiency (hypoxia), which can easily lead to worker suffocation, coma, and even death. The normal oxygen content should be around 20.9%. Oxygen detector is also a type of electrochemical sensor.
In China, due to historical and cognitive reasons, there are still many problems when choosing various types of detectors, which are specifically reflected in:
1) The detection of flammable 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 lessons learned from numerous explosion accidents caused by combustible gas leaks, people attach great importance to combustible gas detection. It can be said that in any petrochemical or chemical plant, the vast majority of hazardous gas detectors are LEL detectors. However, equipping only with LEL detectors is still far from enough to truly protect the safety and health of workers.
It cannot be denied that most volatile hazardous gases are combustible gases, but catalytic combustion combustible gas detectors (LELs) are not the best choice for detecting all combustible gases. It is specifically designed for detecting methane, but its detection performance for other substances is relatively poor. So, the lower limit concentration of combustible gases other than methane that they can detect is much higher than their allowable concentration. For example, for hazardous and toxic gases such as benzene and ammonia, simply using a combustible gas detector is a very dangerous approach. For example, the lower explosive limit of benzene is 1.2%, and its correction factor on the LEL detector is 2.51. This means that the displayed concentration of benzene on a LEL detector calibrated with methane is only 40% of its actual concentration!! In this way, the minimum 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 600 times higher than the allowable concentration of benzene of 5 * 10-6!!. Similarly, the alarm concentration of 1.5 * 10-2 for ammonia obtained on the LEL detector is approximately 600 times higher than its allowable concentration of 2.5 * 10-5. Therefore, based on the different gases being detected, choosing a specific toxic gas detector is much safer and more reliable than simply choosing an LEL detector.
