# Can a probe fit the wrong medical gas outlet?

**Are medical gas outlets gas-specific, and can a probe be connected to the wrong gas?**

Medical gas outlets (terminal units) are gas-specific: ISO 9170-1 requires them to prevent interchange between gases and services, so a probe for one gas should not fit another gas's outlet of the same connector style. Under HTM 02-01, outlets are still tested every quarter for gas-specificity, and new or modified pipework is tested for cross-connections.

Each gas and vacuum service has its own probe geometry, and the outlet is also identified by the gas symbol and colour. ISO 9170-1:2017 covers the gas-specific assembly, mechanical resistance, flow, leakage and pressure drop of terminal units, and their protection against interchange between gases. In England, HTM 02-01 adds that outlets built to BS 5682 and BS EN ISO 9170-1 include an automatic isolating valve, or check plate, in the assembly behind the outlet.

## Where gas-specificity ends

- Between connector styles: ISO 9170-1 does not specify probe dimensions, so BS, DIN, AFNOR and the other styles are separate systems, each with its own probe dimensions. Equipment therefore needs probes of the style installed in the hospital.
- Behind the outlet: a gas-specific outlet cannot detect a pipe that was joined to the wrong service. That is why HTM 02-01 asks for a cross-connection test on new and modified pipelines, in two stages from the plant to the area valves and from the area valves to the outlets, and for the gas at the outlets to be analysed.
- Wear and repairs: HTM 02-01 asks for every outlet to be tested quarterly with a blank probe for gas-specificity, mechanical function and leaks.

## Other gas-specific connections in the system

Hoses inside pendants and bed-head units connect with NIST (non-interchangeable screw-threaded) connectors, covered by ISO 18082 for pressures up to 1400 kPa, which keep the joint gas-specific when hoses are changed. Low-pressure hose assemblies are covered by ISO 5359. WHO stresses that a foolproof outlet supplements the other means of gas identification, including the pin-index system on cylinders, rather than replacing them.

### Is an oxygen 93 outlet different from an oxygen outlet?

It can be. In Germany the 2025 edition of DIN 13260-2 specifies a gas-specific probe for oxygen 93; elsewhere it depends on the national standard.

### How is gas-specificity checked in service?

HTM 02-01 asks for every outlet to be tested quarterly with a blank probe for gas-specificity, mechanical function and leaks.

### Do new outlets get a gas identity test?

Yes. On a new pipeline, HTM 02-01 asks the Quality Controller to test the gas at all outlets.

## 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), Context, para 3.42 and paras 19.226, 19.233 and 20.44](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), paras 7.21 and 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)
- [WHO, Foundations of medical oxygen systems (2023), section 2.9.2](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [ISO 18082:2014 NIST connectors (iso.org summary)](https://www.iso.org/standard/61329.html)
- [ISO 5359:2014 Low-pressure hose assemblies for medical gases (iso.org summary)](https://www.iso.org/standard/59953.html)
- [DIN Media, DIN 13260-2:2025-06, catalogue page](https://www.dinmedia.de/en/standard/din-13260-2/389570410)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/are-medical-gas-outlets-interchangeable/