The supplied air/breathable gas must be of breathable quality for each wearer as well as sufficient quantity and the required pressure. The quality of the breathable gas must be checked regularly by a competent person and records kept. SA/SNZ TS ISO 16975.1 provide the following details for the minimum requirements for breathable air quality.

Low Pressure Supplied Air/Breathable Gas

When measured at normal atmospheric conditions (1 013 hPa and 20 °C), the following shall apply:

  • oxygen content with a volume fraction of 19,5 % to 23,5 %;
  • carbon monoxide ≤ 10 ml/m3;
  • carbon dioxide ≤ 1 000 ml/m3;
  • volatile organic compounds (as methane equivalent) ≤ 25 ml/m3;
  • oil, particulate and condensate ≤ 2 mg/m3;
  • odour — no significant odour or taste;
  • water content.

The dew point must be sufficiently low to prevent condensation and freezing. Where the RPD is used and stored at a known temperature, the pressure dew point shall be at least 5 °C below the likely lowest temperature.

Medium & High Pressure Supplied Air/Breathable Gas

When measured at normal atmospheric conditions (1 013 hPa and 20 °C), the following shall apply:

  • oxygen content with a volume fraction of 19,5 % to 23,5 %;
  • carbon monoxide ≤ 5 ml/m3;
  • carbon dioxide ≤ 500 ml/m3;
  • volatile organic compounds (as methane equivalent) ≤ 25 ml/m3;
  • oil, particulate and condensate ≤ 0,5 mg/m3;
  • odour — no significant odour or taste;
  • water content.

The dew point shall be sufficiently low to prevent condensation and freezing. Where the RPD is used and stored at a known temperature, the pressure dew point 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 dew point shall not exceed −11 °C to which any part of the system is exposed. The maximum water content of air measured at atmospheric pressure are given in the SA/SNZ TS ISO 16975.1 Table 12.

SA/SNZ TS ISO 16975.1 also provides the following criteria for

  • Water content of compressed air in relation to cold environment (Section 7.6.4.3 Table 13)
  • Composition of breathing oxygen (Section 7.6.4.4 Table 14)
  • Composition of oxygen and nitrogen gas mixtures (Section 7.6.5.2 Table 15)
  • Composition of oxygen and helium gas mixtures (Section 7.6.5.3 Table 16)

 

AS/NZS 1715 outlines that the air being used to supply respirators must have no have no objectionable or nauseous odour and contain not less than 19.5% and not more than 22% by volume of oxygen.

At 15°C and 100 kPa absolute, the air must

  1. contain not more than 11 mg/m3 (10 p.p.m. by volume) of carbon monoxide;
  2. contain not more than 1400 mg/m3 (800 p.p.m. by volume) of carbon dioxide;
  3.  contain not more than 1 mg/m3 of oil; and
  4. for cylinders, contain not more than 100 mg/m3 of water when sampled from a cylinder initially filled to pressure of at least 12 MPa.

Regular testing of the air at the respirator must also be undertaken to verify the quality of the air and records are kept. The air being supplied should also be at a comfortable breathing temperature within the range of 15°C to 25°C.

Reference/s for further information and detail:

AS/NZS 1715:2009 – Selection, use and maintenance – Appendix A
SA/SNZ TS ISO 16975.1:2023 – Selection, use and maintenance – 7.6.4