Is a medical gas outlet the same as a terminal unit?

The international standard, ISO 9170-1:2017, is titled Terminal units for medical gas pipeline systems, Part 1: Terminal units for use with compressed medical gases and vacuum. HTM 02-01 Part B (2026), the NHS England guidance, writes "terminal units (gas outlets)" in its list of what record drawings should show, and the WHO-UNICEF Technical specifications and guidance for oxygen therapy devices (2019) write "terminal unit (i.e. medical gas outlet)". The glossary entry is terminal unit.

What the ISO term covers

ISO 9170-1:2017 applies to more than the wall or ceiling outlets of a pipeline built to ISO 7396-1. It also covers terminal units used as pressure outlets on regulators (ISO 10524-1) and on regulators integrated with cylinder valves (VIPR, ISO 10524-3), terminal units for vacuum systems, and terminal units for both the supply and the disposal of nitrogen and air for driving surgical tools. Terminal units for anaesthetic gas scavenging are specified in a separate part, ISO 9170-2.

The standard is intended to ensure gas-specific assembly, mechanical resistance, flow, leakage and pressure drop, and to prevent terminal units being interchanged between gases and services. It does not specify the dimensions of probes or gas-specific connection points: it notes that regional or national standards specify them, and that other connection systems in national use may be acceptable. See which countries use which outlet standard.

The US term

The NFPA 99 text of the 2021 edition, as reproduced in a 2021 NFPA committee input report, speaks of station outlet/inlet assemblies, of gas outlets and vacuum inlets, and of operational pressure tests at each station outlet or terminal where the user makes connections and disconnections. NFPA now lists the 2027 edition of NFPA 99 as current.

The same tests, whatever the name

HTM 02-01 (2026) records the tests of each terminal unit on form B24: it should be gas-specific, resist rotational movement, securely retain the appropriate probe and be correctly labelled, with identification to BS EN ISO 9170-1. In Canada, a 2025 British Columbia training textbook on CSA Z7396.1 testing also uses the term terminal unit and says each one shall be tested for flow resistance. See the flow test on an outlet.

Ultra Controlo supplies medical gas wall outlets with a probe-operated anti-cross-connection design, including a version available in "Schraeder", NIST, DISS and DIN configurations for oxygen, compressed air, vacuum, nitrous oxide and anaesthetic gas evacuation.