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Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment. Guide to the Draeger Gas Pump
How to Select & Use Gas Detector Tubes for Draeger, Gastec, Komyo Gas Detection

  • Dräger GAS DETECTORS - CONTENTS: Recommendations for gas measurement instruments, gas detector tubes, Draeger & Gastec, Komyo. How gas detection tubes work. How to select & use gas detection tubes. Guide to Use of a Drager pump or Sensidyne pump and colorimetric gas detection tubes
  • POST a QUESTION or READ FAQs about how to use gas sampling pumps to test for and measure the level of toxic or other gas contaminants in buildings
  • REFERENCES
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Gas detection indoors: how to use sampling pumps: This document discusses the Draeger or Drager gas testing pump and gas detection tubes as tools and methods used to test for the level of toxic and other gases in buildings and in outdoors.

We give additional references and explanation regarding toxicity of several of the most common indoor gases, based on literature search and obtained from the U.S. government and expert sources.



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An Example of Use of a Draeger pump and Dräger Colorimetric Gas Detection Tube (to measure the level of CO2)

Draeger gas tube detector pump unit schematic (C) InspectApediaShown at the top of this page is is our Draeger bellows-type gas sampling pump. This instrument accepts a remarkably wide range of colorimetric gas detection tubes offered by Drager, and includes a counter to count pump strokes.

As we explained at the beginning of this article, there is a variety of gas detection pumps available for use with gas detection tubes such as we describe just below, including easy to use, accurate, and quality instruments from Gastec, Sensidyne, as well as Drager and other manufacturers.

The photo below shows a Drager colorimetric gas detection tube (also called a "color detector tube") used to test levels of a very wide range of specific gases in air. In an indoor air test (in our laboratory) this particular detector was not being used to measure oxygen, but rather carbon dioxide.

As the blue-stained portion of the tube shows, this tube detected that the CO2 level was about 600ppm which is typical of indoor air and is an acceptable and safe level.

Colorimetric gas detection tubes and how they work

Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.

Colorimetric gas detection tubes such as those sold by Drager (or Draeger), Gastec, (two that we use predominantly) and by Kitagawa, and pumps from Drager, Gastec, Komyo Rikagaku Kitagawa, and RAE all work on a similar principle:

a measured volume of gas (or air) is drawn through a tube which contains chemicals which change in color in response to the presence of a specific target gas (or range of gases) present in the sample.

By knowing the volume of gas or air sampled, the amount of color change read on a linear scale on the colorimetric gas detection tube can be translated into a very accurate measurement of level of gas present, described in percentage of the total air or in parts per million (PPM).

Well it's almost that simple but as we mention in more detail below, you may need to make adjustments for temperature and you may need to watch out for the presence of other gases or chemicals which can interfere with gas detector tube operation.

Watch out: This text may assist readers in understanding these topics. However it should by no means be considered exhaustive. Seek prompt advice from your doctor or health/safety experts if you have any reason to be concerned about exposure to toxic gases.

How a Colorimetric gas detector tube is used

Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.Colorimetric gas detection tubes are sold and distributed in the U.S., Latin America, Asia, and Europe primarily by

To select the appropriate gas detection tube you need to know what gas or gases is/are to be detected, and at what probable concentrations the gas may be present, or at what level of exposure the test is to be conducted.

NIOSH and other agencies publish specific test parameters that industrial hygienists use for industrial testing for the presence of gases in buildings or outdoors.

Check with the gas tube supplier: A building inspector, IAQ inspector, hygienist, building authority, or fire department who have the appropriate training and experience to perform these tests but who are uncertain about which detector tube to purchase should take advantage of the expert chemists and hygienists employed by the gas detector tube companies by calling for advice.

Using a color-changing gas detector tube (colorimetric) is simple: the tube and the instruction sheet are removed from the package.

Read the gas sampling tube instructions: The gas sampling tube instruction sheet may give various numbers of pump strokes or test air volume to be sampled depending on the level of detection needed. (More pump strokes = more air = a more sensitive test.) The ends of the glass tube are broken off using a special cutter provided by the manufacturer of the tube.

Connect the gas sampling tube to the gas pump: The "outlet" end of the detector tube is inserted into the gas collecting pump. The "inlet" end of the tube is exposed to the air to be tested, and the pump is operated for the required number of strokes before looking for a color change on the tube's gas concentration scale.

The documentation with each gas detection tube will describe the chemistry of the tube, its accuracy, its calibration, and the color change for which the user is to check.

Effects of temperature on gas level readings

The chemistry and thus the sensitivity and ultimate gas concentration reading shown by a colorimetric gas detection tube may be affected by temperature, it is important to read the temperature data in the gas detection tube specification sheet included with the particular gas detection tube being used.

A Gastec gas sampling pump is available which includes a "thermal ring" which can provide this important data at the time that a measurement is obtained.

Effects of other chemicals and gases on gas level readings

The gas detection tube instructions may also list other gases which, if present, can affect the accuracy of the test. The gas sampling tubes shown here were used to test for the presence of perchlorethylene and show what the tubes look like before and after the sealed end is snapped off.

The chemistry and thus the sensitivity and ultimate gas concentration reading shown by a colorimetric gas detection tube may therefore be affected by other gases or chemicals present in the location being measured.

For this reason it is also important to read the characteristics of the gas detector tube being used, and if there is risk of interference from other gases or chemicals it may be necessary to amend the test procedure, perhaps also including tests for the presence or level of these confounding gases.

However while it may be a real problem in gas measurements in industrial environments, in residential settings we have rarely encountered this issue.

Warning: About Selecting the Proper Dräger (or other brand) Gas Detection Tube

Gas Detection Tube and Gas Pump Must be Compatible: Interchanbgeability of gas detection tubes & pumps

Colorimeteric gas detection tubes produced by different manufacturers are not necessarily interchangeable among gas detection pumps. Be sure that the gas detection tube you are using is one recommended for use with your gas detection pump - check both the gas detection pump manufacturer's instructions and the gas detection tube manufacturer's specifications.

For example, as we were informed in May 2008 by Nextteq GastecTM detection tube distributor in the U.S., Gastec tubes that are currently available are not intended for use on the SensidyneTM gas detection pump.

At one point in time, Sensidyne had the contract for Gastec tubes and lost it due to rebranding.  The tubes they sell now are Kitagawa tubes, not Gastec.  We don't want to confuse anyone out there that they can use a Gastec tube with the Sensidyne pump.  The Gastec tubes are not calibrated to work with a Sensidyne pump and therefore, the reading could be incorrect and prove fatal in some cases.

Really? MiIchael Shaw (Interscan Corporation, a producer of gas detection & recording systems) disagrees with the accuracy of the above quote. Here is an excerpt [edited for clarity] from what Michael wrote to us in March 2015:

The sample size is 100 ml. Gastec and Kitagawa colorimetric gas detection tube systems are essentially identical.

Dräger system uses the same test volume, but the sampling tube contents are not as densely packed.

A bellows pump cannot pull sufficient vacuum through the Japanese-produced gas detector tubes. But then, bellows pump is [in my opinion not a great] idea, in that with Dräger design, multiple squeezes (not at all reproducible) are needed, and it is very prone to leaks. It is however a less costly sampling pump design.

Comment: I [DF] have been using precision calibrated classic hand-operated plunger type gas pumps, field-calibrated electrical pumps equipped with a flow meter, and also the Dräger bellows pump for more than a decade. My Dräger pump has not seen heavy use but in my application it still works like new. I have tested different types of gas detector pump and tube systems against one another and found the results virtually identical.

Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.The accuracy of Draeger samplers and detector tubes has also been studied for several decades and the accuracy of the bellows-pump design is well-established.

OPINION: I found that the precision of the piston pump could be deceptive. Failure to maintain the required coating of Si grease in the pump chamber, for example, produced a palpable difference in pump stroke force required and variations in the pump seal changed the time between the point at which I locked the pump pull-handle up and the time that the pump stopped drawing air. These variations left me uncertain about the true pump volume being moved. The bellows pump looks less precise but in my experience, tested by repeating measurements at the same location and time, produced very consistent, repeatable results.

While May (1988) reported good correlation between diffusive samplers and active systems, studying diesel exhaust emissions, Clark found that interference errors were significant (Clark 1982). And the effects of extremes of temperature and other environmental parameters has been shown to be significant while operating in typical building environmental temperatures and humidities is less-so. (McCammon 1982).

I agree that if a particular gas sampling pump lacks adequate power it may not perform properly with a tightly-packed detector tube. I suspect that tube contents density varies quite a bit among different tests. One might ask if there is really a significant effect in colorimetric gas tube detector if the proper volume of air is in fact drawn through the tube but at a slower rate due to the density of the tube's contents.

The interchangeability of gas detection tubes and hand pumps has been studied by Haag (2001) who stirred a hornets' nest of marketing and technical issues, claims, counter-claims . Haag reported

Both pump flow profiles and test gas measurements demonstrate that three piston hand pumps in common use (RAE Systems LP-1200, Sensidyne/Gastec GV/100, and Matheson-Kitagawa 8014-400A) are fully interchangeable. Two bellows pumps (Draeger Accuro and MSA Kwik-Draw) also are interchangeable with each other. Mixing of bellows and piston systems is often possible, but there are enough exceptions to conclude that such practice should be discouraged because it can lead to inaccurate readings and thus potentially dangerous overexposures.

Currently the two types of systems use obviously different tube diameters; therefore, the likelihood of inadvertent mixing is low. Technical specifications rather than brand name should be used assess hand pump interchangeability. Such specifications could include total volume, initial vacuum level, and a pump flow curve. When two manufacturers' pumps meet the same standard and appropriate leak tests are performed, interchangeability is scientifically valid and poses no risk to the end user. Interchangeability allows the user greater flexibility and convenience.

Hirsh (2001) vigorously objected to Haag's report, calling it marketing propaganda, and noted that Draeger as well as various agencies do not support interchangeability of gas detection tubes.

Airborne debris indoors (C) Daniel FriedmanOxygen & carbon dioxide sampling results inside a commercial aircraft, in-flight (C) Daniel Friedman

Above, the author used a Drager bellows-pump for measuring oxygen, CO2 and other IAQ constituents during a commercial air flight as part of an ongoing private study.
See AIR QUALITY on COMMERCIAL AIRCRAFT

The accuracy of other Drager gas measuring systems such as the Drager chip system needs to be assessed and reported separately as that is a different and more recent technology. Verma (2001) found [excerpt from the article's conclusions]:

The Photovac Snapshot GC’s performance consistently meets the accuracy criteria (NIOSH-recommended criteria for detector tubes) at or below 1 ppm of benzene, even in the presence of hexane. The Drage ¨ r CMS instrument generally fails to meet the criteria at 1 ppm or less, but it is only slightly out of the acceptable range. If a less stringent accuracy criteria of ± 35 percent is considered acceptable, then all Photovac Snapshot GC results become acceptable, but four of the nine readings for the Drage ¨ r CMS still fall outside of the acceptable range.

The discrepancies observed in the measurement of accuracy of the two instruments were random error and not a systematic “bias.” The precision of the Photovac Snapshot GC is generally very good at concentrations of 1 ppm or less (i.e., CV< ± 10%) while at higher benzene concentrations it is erratic, ranging from a CV of ± 2.1 percent to ± 27 percent in random fashion. The precision of the Drage ¨ r CMS instrument is distinctly poorer than that of the Photovac Snapshot GC and typically ranges from a CV of ± 20 percent to ± 40 percent. The performance of both the Photovac GC and the Drage ¨ r CMS is better when measuring levels of up to 2 ppm benzene, which is fortunate since they are more relevant measurement ranges in industrial hygiene today.

Both the Photovac Snapshot GC and the Drage ¨ r CMS instrment appear to be good Ž field instruments for the measurement of benzene, as long as their limitations regarding accuracy and precision are taken into consideration in their use. The results of this study could provide a reasonable guide. Field studies comparing the performance of these instruments should be conducted and reported to validate the observations of the laboratory study .

Research on gas detector sampling pump accuracy & gas detector tube & pump interchangeability

Gas Detection Tube Must Be Properly Sensitive to the Anticipated Concentration of Gases Being Investigated

Be sure to select gas detection tubes designed to detect the proper gases being screened in a building, and also to select the gas detector tube which is calibrated to detect gases at the proper level of concern. The detection of many gases is supported at varying levels of sensitivity.

Selecting a gas detection tube which is not sensitive enough may result in failing to detect the presence of the target gas. Selection of a gas detection tube which is too sensitive may result in inability to accurately detect the actual level of gas which is present since the tube will become saturated before the actual gas level has been recorded.

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