Breathing Air Quality

BS EN 12021 “Respiratory protective
Devices - Compressed air for breathing apparatus” specifies requirements for the quality of compressed air supplied for use with:


For breathing air devices, the quality of the air should be tested at least once every 3 months. Testing criteria listed below:

BS EN 12021 Requirements


The oxygen content shall be in the range of (21 ± 1) % by volume (dry air).


Lubricant content (droplets or mist) shall not exceed 0.5 mg/m3.

Odour and taste

The air shall be without significant odour or taste.


The carbon dioxide content shall not exceed 500 ml/m3 (500 ppm).


The carbon monoxide content shall be as low as possible but not exceed 15 ml/m3 (15 ppm).

Water Content

There shall be no free liquid water.

Air for compressed air line breathing apparatus shall have a dewpoint sufficiently low to prevent condensation and freezing. Where the apparatus is used and stored at a known temperature the pressure dewpoint shall be at least 5˚C below the likely lowest temperature. Where the conditions of usage and storage of the compressed air supply is not known the pressure dewpoint shall not exceed -11˚C.

Max water content of air at
atm pa

Nominal pressure bar

Maximum water content of air at atmospheric pressure mg/m3

40 to 200


> 200


NOTE The water content of the air supplied by the compressor for filling 200 bar or 300 bar cylinders should not exceed 25 mg/m3.