It’s difficult to detect most gases that can be present in diving cylinders because they are colourless, odourless and tasteless. Gas mixtures generally need to be analysed either in-process, or after blending for safety and quality control. This is particularly important for breathing gas mixtures, where any errors could affect the health and safety of the user.
Electronic sensors exist for some gases, such as oxygen analysers, helium analysers, carbon monoxide detectors and carbon dioxide detectors. Oxygen analysers are commonly found underwater in rebreathers. Oxygen and helium analysers are often used on the surface during gas blending, to determine the percentage of oxygen or helium in a breathing gas mix.
Chemical and other types of gas detection methods are not often used in recreational diving. Generally, they are used for periodical quality testing of compressed breathing air from diving air compressors.