Unlike a lot of other portable field instruments, the detector tube is inexpensive and very easy to use with very little prep
Synergist Q&A’s are edited excerpts of conversations with representatives of companies participating in AIHA’s Professional Partner Program. This month’s Q&A features Steve Luecke, the industrial hygiene manager for Nextteq, a leading provider of industrial hygiene products and solutions in gas detection, respiratory protection, first response hazmat testing, and water and soil analysis. For more information, visit www.nextteq.com. The entire conversation is available as a podcast from http://bit.ly/synergist-podcasts. References to products or services in this article or the podcast do not constitute endorsement by AIHA® or The Synergist. Could you explain the principles of the design and functionality of detector tubes? Detector tubes are also called length-of-stain tubes or stain tubes. They’re designed to measure many types of gases and vapors with wide ranges of measurements from percent levels on the upper end to parts-per-billion on the lower end. A sealed glass tube is what you purchase as a detector tube. You break the ends of the tube (to allow air to flow through), then you immediately install the tube on an approved detector tube pump, and then you measure a short-term air sample by pulling air through the tube. The target gas is absorbed by silica gel or similar material within the tube. Imbedded with the silica are detecting reagents, which turn color in the presence of specific chemicals. The length of the stain of the color change is directly correlated to a calibrated scale. You perform a direct reading by visually reading the calibrated scale where the length of stain ends on the detector tube.
Unlike a lot of other portable field instruments, the detector tube is inexpensive and very easy to use with very little prep. There is no annual calibration. The unit doesn’t need to be sent in for service, and there are no sensors that need to be replaced or calibrated. All that needs to take place is for the user to perform a daily pump leak check of the volumetric pump and to ensure the detector tubes are not expired. What factors influence detector tube measurements? With detector tubes you are measuring gases, and these gases are subject to the ideal gas law, so temperature, humidity, and altitude can influence detector tube measurements. Some tubes need to be corrected for temperature or humidity, while others don’t. Regarding atmospheric pressure, that’s typically a function of altitude in an outdoor or indoor ambient environment since these tubes aren’t used to measure pressurized atmospheres. If you’re at 2,800 feet or less, most detector tubes don’t require any correction. For extreme elevations, it would be something to look into.
Coexisting compounds can definitely influence detector tubes. This is a situation where you have a chemical that’s so closely related to the chemical of interest that it may result in a similar color-change reaction. What types of applications are well-suited for detector tube use? Safety-and-health and industrial-hygiene applications are ideal uses for detector tubes. You can take short-term measurements for job hazard analysis or hazard recognition purposes. Some types of tubes don’t have a pump—they are dosimeter-based tubes that allow long-term passive exposure. These can be suitable for full-shift personal exposure measurements. There are specialty process applications, such as determining the amount of odorant in propane by measuring the headspace gas. For confined spaces, a standard four-gas meter can be augmented with the use of certain detector tubes. Hazmat is a great application because the detector tubes not only measure compounds but they can help you identify unknown compounds by allowing you to see what is reacting and what is not reacting on a series of tubes. Most detector tube hazmat kits will include a flowchart to help you identify unknown compounds.
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Design, Functionality, and Applications