Is 4 bar the same as 400 kPa?

Yes. 400 kPa equals 4 bar, the nominal pressure HTM 02-01 (2026) gives for oxygen, nitrous oxide and medical air.

Why is surgical air at a higher pressure than medical air?

HTM 02-01 (2026) notes that air-powered surgical tools need 600 to 700 kPa and flows of 200 to 350 L/min, while medical air at 400 kPa drives ventilators and other respiratory equipment.

What pressures do medical gas pipelines run at?

Q: At what pressures do oxygen, medical air, surgical air, nitrous oxide and vacuum pipelines run?

Medical gas pipeline pressures are set nationally: NHS England's HTM 02-01 (2026) uses 400 kPa nominal for oxygen, nitrous oxide and medical air and 700 kPa for surgical air, WHO (2023), citing the 2021 edition of NFPA 99, gives 345 to 380 kPa at the wall outlets, and vacuum runs below atmospheric pressure.

At what pressures do oxygen, medical air, surgical air, nitrous oxide and vacuum pipelines run?

Distribution pressures in two national specifications

Service	NHS England, HTM 02-01 (2026)	Portugal, ACSS ET 03/2006 v.2024 (secondary network)
Oxygen	400 kPa nominal	480 kPa (+100 kPa)
Nitrous oxide	400 kPa nominal	420 kPa (+100 kPa)
Oxygen/nitrous oxide 50%/50%	400 kPa nominal	Not listed
Medical air	400 kPa nominal (MA4)	450 kPa (±100 kPa)
Surgical air (tools)	700 kPa, at least 700 kPa at the terminal unit at 350 L/min or 100 L/min	800 kPa (+200/-100 kPa) in specific cases
Dental air	600 kPa	Not listed
Carbon dioxide	Not listed here	400 kPa (+100 kPa)
Medical vacuum	At least 315.5 mmHg vacuum at the front of each terminal unit at 40 L/min	Minimum 53 kPa below atmospheric in the pipe, 60 kPa in the receiver
Anaesthetic gas scavenging	Not listed here	Maximum 20 kPa below atmospheric in the pipe

WHO's Foundations of medical oxygen systems (2023) reports that NFPA 99, which it cites in the 2021 edition, recommends a working pressure of 345 to 380 kPa (50 to 55 psi) at the wall outlets; NFPA now lists the 2027 edition as current. Portugal's ACSS also quotes ISO 7396-1 for surgical instrument air at 8 bar (+2/-1), and for neonatal units it sets medical air at 480 kPa above oxygen at 450 kPa.

Why the gases sit at different pressures

The ACSS specification recommends that in secondary networks oxygen runs above medical air and medical air above nitrous oxide, ideally 0.3 bar apart, citing the French FD S90-155, to prevent backflow of one gas into another. In neonatal units it reverses the order for oxygen and air, to protect newborns from an air and oxygen mix if a check valve fails.

Two-stage distribution and pressure losses

Gas may also be distributed at a higher pressure and reduced near the departments. ACSS uses a primary network at 800 kPa (±100) for oxygen and nitrous oxide and 900 kPa (±100) for medical air, with at least two second-stage pressure-reducing sets per department in bypass. HTM 02-01 says the maximum working pressure of such systems should not exceed 1100 kPa, with a pressure-reducing station that should not be simplex (15.165 to 15.168), and asks for pipe sizes that keep the pressure loss from the source to the terminal unit below 5% of the nominal pipeline pressure.

At the source

WHO's 2020 interim technical specifications for PSA oxygen plants (superseded by WHO's technical specifications of 31 December 2024) asked for a continuous output pressure of 300 to 600 kPa, and its 2023 Foundations document gives the same range for the gas output pressure from the source. ULTRAOX SC and ULTRAOX ST plants deliver oxygen at 6 bar in every model of their datasheet tables (p. 5). Components are rated above these values: EN 13348 copper tube for operating pressures up to 2 000 kPa and ISO 5359 hose assemblies up to 1 400 kPa.