Gases and vapours

Examples of gases in the work environment are ammonia, carbon monoxide, chlorine and nitrogen oxides. Vapours are the gaseous phase of a chemical that is liquid at room temperature. They result from evaporation of liquid into the gaseous phase. Examples of vapours are organic solvents such as acetone, benzene and gasoline, as well as metal vapour such as mercury.

There are different methods for how to measure gases and vapours in workplace air, such as:

Color indicator tubes

The indicator tubes are connected to a hand-held pump. The number of pump strokes is specific to each type of tube. The indicator tubes contain a reagent that, when reacting with the gas, causes a color change in the tube. The length of the color zone is read directly on the tube. Results are just an instant measurement.

Colour indicator tube connected to a pump. ^{© M. Bråtveit}

Active Sampling

Uses a sampling train, similar to aerosol air sampling. However, for vapour sampling the air is drawn through an adsorbent tube (e.g., charcoal) instead of a filter. The sorbent tube is submitted to the lab for analysis after the sampling period.

Sampling train for active sampling of vapour on a charcoal tube connected to a pump. ^{© M. Bråtveit}

Passive Sampling

Vapours diffuse into a a badge-type sorbent material, usually worn on the lapel of the workers. After a specified period of exposure, the badge is sealed, and shipped to a lab for analysis.

Dosimeter attached in the breathing zone. ^{© M. Bråtveit}

Direct Reading Instruments

Battery powered instruments, most with real-time data logging capabilities, many of them suitable for personal air measurements. Many direct reading devices can measure specific contaminants (e.g., carbon monoxide or hydrogen sulphide), some can monitor simultaneously multiple gases and vapours. Others are not able to differentiate between the different gases and vapours that may be present and instead report a “composite” single result that may require careful interpretation, for instance for a combination of organic solvents.

Direct-reading instrument for measurement of volatile organic hydrocarbons (VOC). ^{© M. Bråtveit}