How are colorimetric gas detector tubes used to assess gas concentrations?

• A. Air is drawn through the tube and a chemical color change indicates concentration.
• B. Tubes are read by electronic sensors.
• C. Tubes are used to measure volume of gas directly.
• D. Tubes automatically calibrate themselves.

Answer: (A)

Colorimetric gas detector tubes work by drawing an air sample through a tube that contains a reagent which reacts with the target gas to produce a color change. A hand pump pulls a known volume of air through the tube, and as the gas passes the reactive zone, the color develops along the length of the tube. The length of the colored portion corresponds to a concentration on a printed scale specific to that tube and gas, giving a quick, semi-quantitative measurement without electronics. This reading is best when the user selects the correct tube for the gas and concentration range and reads it within the tube’s calibration limits, keeping in mind that factors like temperature and humidity can affect results. Tubes are generally single-use and not self-calibrating, and the measurement is based on the extent of color change, not an electronic sensor or a direct measurement of gas volume.