Compressed air gets used across a range of industries to provide respiratory protection. It’s used in applications where the risk of breathing ambient air is too high to mitigate using half or full-face respirators.

But it is not safe to breathe the compressed air directly following compression. It needs to get filtered by a multistage breathing air filter.


In Europe, the required quality of breathing air is stated in BS EN 12021:2014, ‘Respiratory equipment. Compressed gases for breathing apparatus’. This provides information on the safe limits of potential contaminants, such as Carbon Dioxide, Water Vapour and Residual Oil and to ensure that oxygen is of an adequate level.

European breathing air standards:
OdourThe gas must be free from unsatisfactory odour or taste
Oxygen(21 ± 1)%
Carbon Dioxide≤ 500 PPM
Carbon Monoxide≤ 5 PPM
Oil≤ 0.5 mg/m3

There are many factors which can affect the safety and quality of the breathing air, for example:

  • Malfunctioning compressors can produce unsafe levels of carbon monoxide and carbon dioxide.
  • Breathing air filtration can fail causing contamination to be present in the air.
  • The compressor air intake can get polluted by airborne contamination. This can come from nearby processes and vehicle exhaust fumes. This does not get removed by standard breathing air filtration.
  • Insufficient air flow or pressure to the respiratory protective equipment (RPE) reduces the protection factor and can expose the user to external contaminants.

All employers have a duty of care to ensure that the breathing air they supply to their employees is safe to breathe. The only way to check that the air supply is fit breathing is by regular testing.

How often should breathing air quality get tested?

Breathing air quality needs to get tested routinely to make sure control measures get put in place to maintain the quality required.

In the HSE guideline document Respiratory Equipment at Work (HSG53) it states the frequency of such tests should be based on a risk assessment. It should happen at least every three months, and more often when the quality of air cannot be assured to these levels.

It is different for high pressure systems as the lifespan of filter elements tend to be shorter.

Yet the final decision on test frequency is down to the employer. Breathing air quality tests should be included with risk assessments, considering the task and regularity of use.

What is in a breathing air quality test?

In the UK, COSHH specifies the following information should be included in a breathing air quality test:

  • Name and address of the employer
  • Details of the equipment and of the distinguishing number or mark, together with a description to identify it, and the name of the maker
  • Date of the examination
  • Name and signature of person carrying out the examination and test
  • The condition of the equipment and details of any defect found
  • For self-contained compressed air/gas breathing apparatus, the pressure of air/gas in the supply cylinder
  • For powered/power-assisted respirators and breathing apparatus, the volume flow rate to ensure that they can deliver at least the manufacturer’s minimum recommended flow rate

What to do with breathing air test results?

Records should be kept for at least 5 years and be accessible at any reasonable time for examination by safety inspectors.

From paint spray booths to fire stations, you don’t have to be health and safety personnel to be responsible for clean, safe breathing air.

Does your compressed air system meet these standards for breathing air? If you cannot confidently answer yes, you should speak to a compressed air specialist immediately.