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Dräger sampling tubes and systems - 20351 A

2.5 Evaluation of Dräger-Tubes

The evaluation of the indication on the Dräger-Tube is another important factor to be taken into consideration. The following are guidelines for interpreting the indication: -continuously observe the tube during the measurement-evaluate the indication immediately following the measurement according to the instructions for use-use sufficient lighting -light background -compare with an unused tube Observing the tube during the measurement is particularly important to make sure that acomplete discoloration of the tube has not happened without being realised. This completediscoloration can sometimes occur abruptly with high concentrations even during the courseof the first stroke.A sufficient lighting source is necessary. However, direct sunlight should be avoided becausethe UV-radiation of the sun may cause a change in the discoloration. Since such a changecan sometimes occur even after a longer period of time. The reading of the tube must be done immediately following the measurement. Also, keeping the used tube as proof is not useful in most cases, because even tubes whichhave been sealed with rubber caps will show a change in the indication over time.A light background (white paper) is very helpful, in improving the readability of the discoloration. When there is no source of ambient lighting the reflector of a switched-onflashlight will suffice.The comparison of a used tube with an unused one is yet another way to more accuratelyevaluate the discoloration.In all cases the entire length of the discoloration must be read. This means the sum of allcolors (e. g. carbon monoxide tubes produce light brownish green discolorations).It must also be pointed out that an individual's perception of a particular color or intensityof a color is somewhat subjective. It is possible, for example, that one person calls a colorlight brown whereas another person calls the same color brown. These deviations in theindividual perception of color or sense of color should not be overemphasised unless color blindness is an issue.