Page 227 - IGC BOOK

Neither device can estimate the concentration of the dust cloud but may indicate that air monitoring
is required.

Tyndall Beam Apparatus.

A quantitative indication of a gas or vapour can be achieved using a stain tube detector (grab
sampler). A sample of air is drawn over crystals in a calibrated tube via a hand pump. The
gas or vapour needs to be identified before this method is used as the specific tube for the
substance should be obtained.

The presence of a hazardous substance causes the crystals to change colour. The tube is
calibrated so that the extent of the crystal colour change along the tube indicates the
concentration in parts per million (ppm) of the hazardous substance in the air sample.

There are over 200 tubes available, e.g. oxygen, carbon monoxide, sulphur dioxide, H2S,
acetone, etc.

An extension tube is available to permit sampling in a confined space without the tester
having to enter the space.

Stain Detector Tube.

ENSIGN| Unit IG2 – Element 7 – Chemical and Biological 22
Agents