# How should medical gas outlets be specified in a tender?

**How should a tender specify medical gas outlets: standard, connector style, double closure, mounting and testing?**

ISO 9170-1:2017 covers the gas-specific assembly, flow, leakage and pressure drop of medical gas outlets but leaves probe dimensions to regional or national standards, so a tender cannot rely on it alone; NHS England's HTM 02-01 (2026) also asks for BS 5682 and adds mounting, labelling, anti-swivel, "Do not use" plug and test requirements.

ISO 9170-1:2017 is the international standard for terminal units on medical gas and vacuum pipelines. Its purpose is gas-specific assembly, mechanical resistance, flow, leakage and pressure drop, and preventing a terminal unit from being interchanged between gases, but it does not specify probe dimensions. The ISO summary points to regional or national standards for probe dimensions (see [outlet types](https://library.ultracontrolo.com/answers/what-medical-gas-outlet-types-exist/)). HTM 02-01 (2026 edition), the NHS England guidance, asks for terminal units to conform to both BS 5682 and BS EN ISO 9170-1.

## What to write into the specification

- Standard and connector style: ISO 9170-1 plus the regional or national connector standard in use (HTM 02-01 asks for BS 5682). In Portugal, the ACSS specification ET 03/2006 (revised 2024) asks for double-closure outlets that are not interchangeable between gases.
- Performance: pressure losses across terminal units in accordance with ISO 9170-1, as HTM 02-01 asks, and the flows each outlet should pass (see [outlet flow test](https://library.ultracontrolo.com/answers/what-flow-test-is-done-on-a-medical-gas-outlet/)). For vacuum, HTM 02-01 asks for at least 315.5 mmHg at the front of each terminal unit at a design flow of 40 L/min.
- Gases and sequence: the services per room and the order of the array, which for a horizontal array in HTM 02-01 runs from left to right as oxygen, nitrous oxide, oxygen/nitrous oxide mixture, medical air, surgical air, vacuum, AGS and carbon dioxide; carbon dioxide uses a NIST connection, not a probe connection.
- Mounting (HTM 02-01): wall terminal units between 900 mm and 1600 mm above finished floor level, centres 135 ± 2.5 mm apart for three or more units or 150 ± 2.5 mm for two; floor-mounted terminal units are not permitted.
- Anti-swivel (HTM 02-01): terminal units for directly connected equipment, such as flowmeters, should include an anti-swivel device; units for hose connection only do not need one.
- Units in medical supply units (HTM 02-01): a male NIST connector and nut brazed to the rear of the terminal unit.
- Identification (HTM 02-01): dual-circuit terminal units should carry a colour-coded circular label around the outlet, with the gas at the top and the circuit below; in critical care areas the circuit numbers should match the area valve service units.
- "Do not use" plugs (HTM 02-01): single-piece plugs that interlock with the probe-retaining mechanism, left in every second-fix outlet until it has been tested; stickers should not be used instead.

## Testing after handover

HTM 02-01 Part B asks for all terminal units other than AGSS units to be tested quarterly, starting with a blank probe to check gas specificity, mechanical function and leaks (see [how often outlets are tested](https://library.ultracontrolo.com/answers/how-often-should-medical-gas-outlets-be-tested/)).

## Ultra Controlo

The ULTRAOX SC datasheet lists medical gas outlets, second stage regulators and valves among the Ultra Controlo accessories for medical gas pipeline systems.

### Is ISO 9170-1 enough on its own?

No. ISO 9170-1 does not specify probe dimensions and points to regional or national standards for them; HTM 02-01, for example, asks for terminal units to conform to both BS 5682 and BS EN ISO 9170-1.

### Can medical gas outlets be mounted in the floor?

Not under HTM 02-01, which does not permit floor-mounted terminal units.

## Sources

- [ISO 9170-1:2017 Terminal units for medical gas pipeline systems, Part 1 (iso.org summary)](https://www.iso.org/standard/67451.html)
- [NHS England, HTM 02-01 Medical gas pipeline systems, Part A (2026), paras 3.9 to 3.34, 3.43, 4.46, 15.159 and chapter 18](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [NHS England, HTM 02-01 Medical gas pipeline systems, Part B (2026), para 11.213](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-b-operational-management-aug-26.pdf)
- [ACSS, ET 03/2006 v.2024 Gases medicinais e aspiração em edifícios hospitalares, section 7.4](https://www.acss.min-saude.pt/wp-content/uploads/2016/10/ET-03_2006_v2024-Gases-medicinais_VF.pdf)
- [ULTRAOX SC datasheet, p. 4](https://www.ultracontrolo.com/products/ultraox)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-should-medical-gas-outlets-be-specified-in-a-tender/