Oxygen and PSA
PSA, cylinders or liquid oxygen: what is the difference?
Short answer
Under AIGA 113/20, oxygen 93 produced by PSA can be manufactured on site within the healthcare facility, while medicinal oxygen supplied in cylinders or as a cryogenic liquid is required to be manufactured by an approved supplier with a manufacturer’s licence.
Three ways to supply hospital oxygen
| On-site PSA plant | Cylinders from a gas supplier | Liquid oxygen (bulk tank) | |
|---|---|---|---|
| Where it is made | On site, from ambient air (WHO interim guidance, April 2020; International Pharmacopoeia, 2025) | Manufactured by an approved supplier with a manufacturer’s licence, which AIGA 113/20 says is required | Always off site, by cryogenic distillation of ambient air (WHO interim guidance, April 2020; International Pharmacopoeia, 2025) |
| Who answers for its quality | Qualified personnel of the healthcare facility, normally the head pharmacist (AIGA 113/20) | The medical gas supplier (AIGA 113/20) | The medical gas supplier (AIGA 113/20) |
| Grade | Oxygen 93: 90.0% to 96.0% oxygen, the rest mainly argon and nitrogen (International Pharmacopoeia, 2025) | Above 99% oxygen (HTM 02-01, 2026) | At least 99.5% oxygen (Ph. Eur. 0417; International Pharmacopoeia, Oxygen 99.5%) |
| Form at the hospital | Gas, which can be piped directly to bedside terminal units (WHO interim guidance, April 2020) | Gas at high pressure: the rated working pressure typically ranges from 137 to 150 bar, depending on the manufacturer (WHO, Foundations of medical oxygen systems, 2023) | Liquid stored at down to −183 °C in a VIE (vacuum-insulated evaporator) and vaporised to gas for the pipeline (HTM 02-01, 2026) |
| Electricity at the hospital | Needed: HTM 02-01 (2026) says all components of the PSA supply system should be connected to the essential electrical supply | Not needed: cylinders require no electricity to be functional (PATH and CHAI, 2021) | Not needed: the tank feeds the pipeline by self-vaporisation (WHO interim guidance, April 2020) |
| Checks and monitoring | Daily checklist, with oxygen purity recorded on the PLC and with a handheld analyser (Global Fund / BHI checklist, 2025) | Periodic inspection and pressure testing at intervals set by national or international transport rules (see how often cylinders are retested) | Telemetry should be installed so that the hospital and the gas supplier can monitor vessel levels and pressures continuously (HTM 02-01, 2026) |
Sources
- European Pharmacopoeia (EDQM)
- WHO, Oxygen sources and distribution for COVID-19 treatment centres, interim guidance (4 April 2020)
- WHO, Foundations of medical oxygen systems (17 February 2023)
- The International Pharmacopoeia, 13th edition (2025), Medicinal oxygen
- AIGA 113/20 (adopted from EIGA Doc 195), On site generation of oxygen 93% for medicinal use, section 1
- NHS England, HTM 02-01 Part A (2026), paragraphs 6.35 to 6.37, 6.48, 6.112 and 6.126
- PATH and CHAI, Oxygen Generation and Storage: Oxygen Cylinders (July 2021)
- Global Fund / Build Health International, PSA plant Daily Maintenance Checklist (2025)
Ultra Controlo figures come from its technical datasheets. Third-party facts were read at the source on the date shown.
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