Gas detection of toxic gas detectors
Both toxic and suffocating gases can cause harm to the human body when they invade the body, so they are collectively referred to as harmful gases. However, when detecting gases, we often refer to them as toxic gases, such as carbon monoxide (CO), hydrogen sulfide (H2S), ammonia (NH3), methanol (CH3OH), etc. They are a significant risk factor for workers, including not only immediate short-term injuries such as physical discomfort, illness, death, etc., but also long-term hazards to the human body such as disability, cancer, etc.
The degree of harm of harmful gases to the human body is related to the type and quantity of harm. In order to ensure that workers do not experience acute and chronic occupational hazards during production and labor, China adopts the maximum allowable mass concentration (MAC, mg/m3) as the hygiene standard. We often see TLV as the standard in the gas detection instrument manual. TLV, also known as Threshold Limit Values, is a US standard developed by the American Association of Governmental Industrial Hygiene (ACGIH) and is divided into three types:
① TWA (8-hour statistical weight average), mg/m3;
② STEL (15 minute short-term exposure level), mg/m3;
③ IDLH (immediate lethal dose), 10-6.
For portable detection and alarm devices for toxic gases, they can usually display the peak concentration, TWA value, and STEL value data of toxic gases to provide specific guidance for workers' health and safety. The true value of toxic gas concentration is often represented by 10-6, which is the volume fraction of the gas in 1 million parts of the total volume of the gas. The maximum allowable mass concentration in China's health standards is in mg/m3, and the conversion relationship between these two units is:
Maximum allowable concentration=true value of toxic gas mass concentration × In the formula M/24.25, M is the relative molecular weight of the toxic gas, 24.25 is a constant, and is the molar volume of the toxic gas at 25 ℃ and 101.33kPa.
Due to the fact that the detection of toxic gases does not have the same "universal" detector as the detection of combustible gases, corresponding gas sensors are required for each type of gas. For toxic gases, the commonly used and comprehensive method with good indicators is the constant potential electrolysis method, which belongs to electrochemistry. When selecting a detector, it is necessary to first indicate which gas to detect and whether there may be other toxic gases around it, Different gas detectors should be selected based on the on-site situation. For petrochemical enterprises, toxic gas detectors such as CO, H2S, NH3, CH3OH, etc. should generally be equipped. For the alarm values set by the instrument, the warning and danger alarms for each toxic gas are different.
