I recently got some questions regarding RAE Systems Gas Detection Tubes and I wanted to clarify their use.
First, what are they? Gas detection tubes offer a quick way to determine the presence or concentration of specific chemicals in air. This is well established technology, and has been offered by a few manufacturers for many years. The theory is that specific reagents change color as they absorb certain chemicals. This color change, or stain, is predictable and measurable. This is also how they come to be called Colorimetric Measurement Tubes.
These tubes are essentially sealed glass tubes that resemble short straws, and are filled with sorbent granules. The granules may be different colors depending on what gas the tube is supposed to be measuring. The outside of the tubes are printed with a graduated measurement scale that allows you directly read the concentration.
When ordering tubes, remembered that they are listed by the specific chemical to be measured, and in most cases, with a specific concentration range. That is, you might have a certain tube to measure 100–500ppm and another for 500-2000ppm of the same chemical. For the sake of this example, let's say you would like to measure the amount of Carbon Dioxide (CO2) in the air.
To use, break the tips off of the tube at both ends (a tip breaker is included with the pump) and place in the RAE piston hand pump. Then draw air through the pump. This pump draws a very specific amount of air (100cc) through the tubes. The granulated chemicals within the tube will react with the CO2 and will 'stain' to a given length based on the CO2 concentration. This concentration is read directly on the scale on the tube. The reading is referred to as ‘qualitative’ and is usually within +/- 20% of the actual gas content. Temperature, humidity and the ‘crispness’ of the stain all play into this inherent variability.
It is important to realize that these tubes only gather a snapshot of the air at that moment. They are also only for one time use. Once you have drawn air through the tubes you cannot use them again. The pump, however, is a sturdy piece of equipment and can be used over and over again.
It is also important to note that these are only meant to measure gas content in air. These cannot measure dissolved gas content in water or another liquid. You can use these tubes to measure the air above a tank, down a sewer, at the top of a monitoring well, or in many other locations to detect gases and vapors produced by solids and liquids.
These tubes are relatively inexpensive so they are a great tool if you don't need constant air readings. Happy measuring!