Dosimeter Tubes

A Different Question From a Spot Reading

A colorimetric tube tells you the concentration at the moment you draw the sample. A dosimeter tube tells you what someone was exposed to across a shift, which is the figure workplace exposure standards are written against.

It works without a pump. Gas moves into the tube by natural diffusion at a constant, known rate, so there’s nothing to carry, nothing to charge and nothing to calibrate. Clip the tube into a holder on a collar to measure a person, or place it in a work area to measure a location.

The result is read straight off the printed scale. Divide by the actual sampling time, and you have the time weighted average. There’s no chart, no laboratory and no waiting.

Sampling runs from 30 minutes to 48 hours, depending on the tube. The short end captures a peak during a specific task. The long end allows low concentration measurement, where a single shift wouldn’t build up a readable stain.

What It Replaces

Conventional personal exposure monitoring means a calibrated sampling pump on a worker, a flow check before and after, sample media sent to a laboratory, and a wait of days or weeks.

A dosimeter tube removes the pump, the laboratory and the wait. The trade off is precision and scope, since a laboratory method resolves lower concentrations and covers substances no tube exists for. Where a tube exists and the concentration sits in its range, it gives a usable answer straight away, at a fraction of the cost.

That changes what’s possible, not just what it costs. Monitoring ten workers monthly is impractical with pumps and laboratory analysis, and entirely practical with tubes.

Available Dosimeter Tubes

Keep the table, replaced with the corrected version in section 3 below.

Three Things the Table Tells You

Check the tube reaches the exposure limit. This is the most important comparison on the page, and it’s easy to miss. Look at hydrazine: the exposure limit is 0.01 ppm, and the tube reads from 1.6 ppm upwards, so it can’t measure anywhere near the limit. Benzene is similar, with a limit of 0.02 ppm and a tube starting at 2.4 ppm. Those tubes are useful for detecting a significant release, but they can’t show compliance with the limit. The 9DL nitrogen dioxide tube, by contrast, reads from 0.01 ppm, well below its 0.2 ppm limit. Compare the range and limit columns before ordering.

One tube can cover several substances, and that cuts both ways. The 3D Ammonia tube also reads dimethylamine, dimethylethylamine, hydrazine and triethylamine. The 122DL Toluene tube reads benzene, cumene, ethyl benzene, styrene and xylene. That’s convenient for stock holding, since a handful of tube types cover the whole table. But it also means those substances interfere with each other. If you’re measuring toluene and xylene is present, the reading covers both, and the tube can’t tell you which. Where a mixture is likely, that needs allowing for.

Range and shelf life vary between tubes for the same gas. Ammonia comes as the 3D, reading 2.5 to 1,000 ppm, or the 3DL, reading 0.1 to 10 ppm. Carbon monoxide, nitrogen dioxide and sulphur dioxide also have a high and a low option. Pick the range against the concentration you expect, not just the gas.

Corrections and Storage

Many tubes in the table need a temperature correction, and some need a humidity correction as well. The instruction sheet supplied with each box sets out both. Skipping them is a common source of error.

Tubes marked with an asterisk need refrigerated storage. In most of Australia, that means a dedicated fridge rather than a store room. Shelf life runs from 12 to 36 months, with the expiry date printed on the box. Don’t use expired tubes, because the reagent degrades in a way you can’t see.

One Practical Point on Carbon Dioxide

Exhaled breath contains around 4% carbon dioxide, so a CO2 tube worn close to the mouth can measure the wearer’s breathing rather than the workplace. Check the 2D tube’s instruction sheet for where to position it on a person.

You Need the Holder

A dosimeter tube is worn in the Gastec No. 710 tube holder, which clips to a collar or lapel. It’s reusable and ordered separately.

Where It’s Used

Personal exposure monitoring against workplace exposure standards. Occupational hygiene surveys. Solvent exposure in workshops, paint shops and fabrication. Formaldehyde in laboratories and healthcare. Carbon monoxide around vehicles and plant. Hydrogen sulphide in wastewater and around organic decomposition. Ammonia in refrigeration and processing. Area monitoring over a full day to locate a source. Baseline assessment before a control is installed, and checking it afterwards.

Selecting a tube needs three things: the substance, the concentration range you expect, and the exposure standard you’re assessing against. Send us those and we’ll confirm the tube, or talk to our Technical Consultants if the atmosphere is a mixture.

Available Dosimeter Tubes