Levitt-Safety Blog

How do colorimetric gas detection tubes work?

Heidi LevittCo-CEOFebruary 21, 2018

If you do any kind of gas detection on the job, you’ve probably heard of colorimetric tubes. They often go by different names (like stain tube detectors), or can even be referred to by their brand names (like Gastec tubes or Draeger tubes). They all do the same job, though – on the spot measurement of contaminated air.

What Exactly Are They?

Colorimetric detector tubes are graduated glass tubes filled with chemical reagents that produce a color change when exposed to the gas in question. They’re used with hand pumps that draw a sample of air into the tube.

The tubes are sealed at both ends when they come out of the package. When it’s time to sample, the end of the tube is broken off, and the tube is inserted into the pump.

Gastec Detector Tubes

How Do They Work?

As the sampled air works its way up the tube, it reacts with the reagent inside of it, producing a color change. The length of the color change is proportional to the concentration of the substance being tested. The point where the reaction stops is read off against graduated markings on the tube. The concept is similar to other colorimetric methods such as pH paper for measuring acids and bases, and bleaching of dyes to determine ozone or chlorine levels in water or air.

What Are The Benefits of Colorimetric Tubes?

For field technicians operating at a distance from a supporting facility, colorimetric tubes can provide a huge advantage.  With no need for calibration, any required supporting equipment to be able to use tubes in the field is eliminated.  Especially where only spot measurements are required, the ability to deploy and maintain a detector tube system in the field often makes it a great choice over an electronic alternative.

Colorimetric tubes can also be used to ensure that the sensors on an electronic gas detector are indeed measuring the correct gas and are giving accurate readings.  In turn, the gas detectors can then be used to provide continuous monitoring, and the user can have greater confidence that they are accurately monitoring the gas hazards.  In cases where hazards are suspected that cannot be monitored with gas detectors because there are no gas specific sensors available, colorimetric tubes can be used to expand your measuring capability.

Things to Keep In Mind

Regardless of which kind of pump is being used, it is important to note that the components are tested and certified as systems by the respective manufacturers - you cannot mix brands between the pumps and the tubes.  Colorimetric tubes also have a limited and specific shelf life based on the reagent they contain. It’s critical to check the dates to ensure that your tubes have not expired.

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