Dräger diffusion tubes - Time weighted average exposure TWA measurement

Dräger diffusion tubes, dosimeter tubes

Passive reagent tubes - also called dosimeter tubes - are intended for controlling and monitoring the total daily concentrations of gas present in the air. Dräger passive tubes measure the total amount of gas breathed in during the working day (usually 8 hours). It is a simple and economical way to control the TWA (time weighted average value).

This measurement system is said to be “passive” and is based on the diffusion of contaminant molecules in the air, it does not require a pump unlike conventional colorimetric reagent tubes.

Dräger diffusion tubes measuring principle

According to Fick's first law, the contaminant molecules move by themselves inside the tube or the badge. The driving force behind this molecular flux is the difference in concentration between ambient air loaded with harmful substances and the inside of the tube. As Dräger diffusion tubes do not require a pump, they are particularly suitable for individual monitoring measurements.

The graduated scale printed on the tube represents the product of the concentration and the exposure time (for example ppm x h). To establish the average contaminant concentration, divide the scale reading by the exposure time (or sampling time).

It is a simple and economical method of measuring the time weighted average exposure value (TWAEV), requiring no special technical skill, no analysis costs in a specialized laboratory, nor waiting time.