What ISO 8573-1 class corresponds to medical air?

ISO 8573-1:2010 is an industrial standard for compressed air purity. It specifies purity classes with respect to particles, water and oil, and ISO lists it as due for revision. Medical air is defined by a different kind of document: the European Pharmacopoeia treats it as a medicine (monograph 1238), and HTM 02-01, the NHS England guidance, says the British Pharmacopoeia monographs are the baseline minimum standard for medical gas quality. HTM 02-01 does not use ISO 8573-1 classes for medical air, so a compressed air class number cannot be read as medical air compliance.

What medical air is tested for

The acceptance criteria that HTM 02-01 (2026) applies to medical air show the gap. Several parameters have no ISO 8573-1 purity class at all:

A compressor's ISO 8573-1 class says nothing about these gases. Carbon monoxide, for example, is strongly affected by where the compressor draws its air: HTM 02-01 notes that the position of the air intake has a considerable effect on delivered air quality, particularly on carbon monoxide levels. HTM 02-01 tests medical air against pharmacopoeial criteria, and lists detector tubes as one way to test for oil, carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen oxides and water vapour.

Where ISO 8573-1 does apply in a hospital

ISO 8573-1 is used for technical air, which is a separate system. In Portugal, ACSS ET 08/2010 sets ISO 8573-1:2010 class [2:4:2] as the minimum quality for centrally produced technical compressed air, while medical gases are covered by ACSS ET 03/2006. The WHO technical specifications for PSA oxygen plants (interim, 2020; superseded by WHO's technical specifications of 31 December 2024) also listed ISO 8573-1 among product performance standards.

Components can still carry ISO 8573-1 ratings: the ULTRAK activated carbon tower datasheet gives an ISO 8573-1 oil class of 0/1. Ultra Controlo medical air plants are specified to the Pharmacopoeia parameters instead; the ULTRAAR SC datasheet states CO below 5 ppm, SO2 below 1 ppm, NOx below 2 ppm and a working dew point of −46 °C.