WHO Foundations of medical oxygen systems (2023)

What it covers

WHO compiled the document to capture definitions, technical requirements, tools and resources related to medical oxygen systems, for national authorities, policy-makers, donors, implementing partners, practitioners and biomedical engineers. It has five main sections:

• Oxygen history, ecosystem and related systems.
• Health facility oxygen systems: onsite production (PSA, VSA and VPSA), technical requirements and sizing of PSA plants, cylinder filling, changeover systems, high-pressure cylinders, medical gas pipeline systems and onsite liquid oxygen.
• Operationalization of oxygen systems, including estimation of oxygen demand.
• Offsite oxygen production.
• Tools and resources.

Its five web annexes are: A, technical considerations for the procurement of oxygen generator plants; B, site evaluation; C, site readiness; D, commissioning report; and E, oxygen supplier's mapping.

Key technical statements

• The purity of concentrated oxygen from generator plants should be 93% ±3%.
• PSA plants use a compressor to push air through the sieve beds; VSA plants use a vacuum system to draw air in, and their lower output pressure generally adds the need for an oil-free booster compressor. WHO puts VSA capital cost about 15% above PSA because of that booster, a margin that drops off when units generate more than 100 Nm³/h.
• WHO names ISO 7396-1, HTM 02-01 and NFPA 99 as the three reference standards widely used for pipeline design.
• For high-pressure cylinders, it states that the entity responsible for refilling must oversee maintenance every 5 years, with at least a hydrostatic test, a weight loss test (> 5%) and a corrosion test, and it names the EU TPED, which requires a Pi mark on the cylinder shoulder.

Status and type

WHO lists the document under COVID-19 clinical care, with reference WHO/2019-nCoV/Clinical/Oxygen/2023.1, dated 17 February 2023 and with corrigenda of 3 November 2023. It is a compilation; WHO's technical specifications for health facility medical oxygen systems (31 December 2024) give the product specifications and point back to the Foundations for an overview of system design. In UNDP procurement, REQ-OXY-001 (in force since 1 January 2025) lists web annex A among its references.

Points to watch

• Its HTM 02-01 reference is the 2006 edition; NHS England published a new edition of HTM 02-01 on 19 August 2026.
• It cites the 10th edition (2020) of The International Pharmacopoeia; the current edition is the 13th, published in 2025 (medicinal oxygen monograph).
• It refers to WHO's 2020 PSA plant specifications, which WHO's 2024 technical specifications state they supersede.