Oxygen and PSA
Derating (altitude and site conditions)
Open Critical Care, in an answer by Assist International, says PSA oxygen plants are rated at 1,000 ft above sea level or lower and that, because much of sub-Saharan Africa is above this, plants there have to be derated significantly; AIGA 113/20 notes that compressor throughput depends on altitude.
AIGA 113/20 (EIGA Doc 195) adds that allowances should be made for variations in barometric pressure. Open Critical Care also says that the manufacturer needs to know where the plant will be installed in order to design it for the altitude above sea level and the usual temperature range.
Two documents stated the site conditions in which a PSA plant should be capable of supplying the specified oxygen concentration continuously:
| Document | Ambient temperature | Relative humidity | Elevation |
|---|---|---|---|
| WHO interim technical specifications for PSA plants (2020, superseded by WHO's technical specifications of 31 December 2024) | 10 to 40 °C | 15 to 95% (preferably simultaneously) | 0 to 1,000 m, minimum |
| PATH and CHAI (July 2021) | 10 °C to 40 °C | 15% to 95% | 0 to at least 2,000 m |
For medical air plant, NHS England guidance, HTM 02-01 (2026), says manufacturers should be consulted over the range of operating temperatures the supply system is designed for, and that in extreme cases refrigerator cooling may be required between the compressors and the dryer and filter set. WHO’s Foundations of medical oxygen systems (2023) says VSA operation is less affected by altitude above sea level.
Sources
- Open Critical Care, Oxygen FAQ (Assist International): converting a PSA plant’s production into cylinders filled, and derating
- AIGA 113/20 (EIGA Doc 195), Safe design and operation of on site generation of oxygen 93% for medicinal use, section 4.4
- WHO, Technical specifications for PSA oxygen plants, interim guidance (8 June 2020)
- PATH and CHAI, Oxygen Generation and Storage: Pressure/Vacuum Swing Adsorption Plant (July 2021)
- HTM 02-01 (2026) Part A, paragraph 7.17 (NHS England)
- WHO, Foundations of medical oxygen systems (17 February 2023), section 2.1
- WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), note on the oxygen generator plant specification (supersedes the 2020 interim PSA specifications)
Ultra Controlo figures come from its technical datasheets. Third-party facts were read at the source on the date shown.