The “classic” way of gas concentration measurements in containers, still used by most of the companies, consists in the use of a combination of portable handheld devices. They each have their strong and their weak points.
PID : Photo ionization detection
The PID detects volatile hydrocarbons (VOC, volatile organic components). This method is indicative, but not selective. It provides a quick indication of most of the hydrocarbons present, but cannot determine which components. A positive reading on the PID should be followed by an additional measurement with gas detection tubes.
EC : electrochemical cells
Some – mostly – smaller molecules can be measured with specific electrochemical cells. In most cases a combination of EC’s is built in the PID handheld.
Some examples of molecules are oxygen, carbon monoxide, carbon dioxide, ammonia, phosphine and the Lower Explosion Limit.
Gas detection tubes
The oldest and most classic way to measure gas concentrations in air. An air sample is sucked by an hand pump trough a glass tube. The tube is filled with chemicals that will react with a specific gas in the air sample. By means of a scale on the tube the coloration can be translated in a gas concentration.
Gas detection tubes are specific, but there is a lot of cross sensitivity. Due to external factors deviations in the results can go up to 30 %.