Classification & Working Mechanisms for Toxic Gas Detectors
According to hazards, hazardous gases can be divided into two major categories: combustible gases and toxic gases. Due to differences in their properties and hazards, corresponding detection methods vary. Toxic gas detectors are professional testing instruments for this purpose.
Combustible gases are common hazardous gases in industrial sites such as petrochemical plants, mainly including organic gases like alkanes and certain inorganic gases such as carbon monoxide. Explosions of combustible gases require three essential conditions: combustible gas at a specific concentration, a certain amount of oxygen, and an ignition source with sufficient heat. These are the three elements of explosion, and none can be omitted. A fire or explosion will not occur if any condition is missing. When combustible gas vapor, dust mix with oxygen and reach a certain concentration, explosion will be triggered once exposed to an ignition source of adequate temperature.
The concentration range at which combustible gas explodes upon encountering an ignition source is defined as the explosion concentration limit, or explosion limit for short, generally expressed in %. In fact, explosion only occurs within a specific concentration range instead of all mixing ratios. No explosion will take place when the combustible gas concentration is below the Lower Explosive Limit (LEL, insufficient combustible gas) or above the Upper Explosive Limit (UEL, insufficient oxygen). The LEL and UEL values differ for various combustible gases (refer to Issue 8), which requires special attention during instrument calibration. For safety purposes, alarms are usually triggered when the combustible gas concentration reaches 10% LEL and 20% LEL. 10% LEL is the warning alarm threshold, while 20% LEL is the danger alarm threshold. This explains why combustible gas detectors are also known as LEL detectors.
