3. Construction of the various devices

Gas detectors are classified into three main types: fixed detectors, transportable detectors and portable detectors. They can be designed to detect a single type of gas (a single-function device such as an explosimeter, for example), or several types of gas (a multi-function device such as a portable multi-gas detector, where several gases may be detected: for example a flammable gas (CH ₄ or another gas), oxygen(O ₂ ), carbon monoxide (CO) and hydrogen sulfide (H ₂ S).

They operate by diffusion or can be fitted with a pump, which brings the gas to be detected inside the device. The detection head is either integrated into the device, or remote from the electronics, the latter also comprising a part in the remote head, and a part...