Passive dositubes for time-weighted measurements
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Passive dositubes are used to measure time-waited average (TWA) gas concentrations over longer periods. Dositubes use the principle of the natural diffusion of gas.
A dositube is a glass tube of a specific inner diameter that is filled with a diffuser and chemical reagent in parallel that enable gas to disperse at a constant rate resulting in a longer discolouration and better demarcation. The passive dositube can then be positioned in the worker's breathing zone where it can be attached with a holder and collar clip (separately available: Art.No.710) and the amount of individual exposure can be measured. Stationary use is also possible for TWA measurements of concentration distribution or change within a fixed environment over longer periods, such as the course of a whole day. Features
- Compact, lightweight, and versatile
(can be used anywhere) - Easy direct measuring and reading - No sampling pump necessary  
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  Dositube holder No. 710
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Passive dositube list
| 1. | Clicking on the above Passive dositube list button will display a list of tubes arranged according to gases/vapours to be measured. If you do not find your desired gas, it may be listed under a slightly different spelling or abbreviation. Try searching (control/command F on most computers) using the chemical formula. You may also contact your GASTEC representative for assistance. |
| 2. |
Click on the tube no. or name for detailed information. Information on the individual detector tubes |
| Example of a Passive dositube chart |
| Gas or Vapour to be Measured Chemical Formula |
Gastec Tube No. & Name |
Measuring Range (ppm) |
Measuring Time (hours) |
Shelf Life (year) |
Note | TLV-TWA,C (ACGIH) (ppm) |
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| Acetaldehyde CH3CHO |
91D | Formaldehyde | 0.1-20 | 1-10 | 1* | - | C 25 |
| 151D | Acetone | 4-1200 | 1-10 | 2* | T | ||
| 152D | Methyl ethyl ketone | 1.2-360 | 1-10 | 2* | T | ||
| Acetic acid CH3CO2H |
81D | Acid gases | 0.5-100 | 1-10 | 3 | T | 10 |
| Acetic anhydride (CH3CO)2O |
81D | Acetic acid | 0.45-90 | 1-10 | 3 | T | 5 |
