# Gas-specific probe

A gas-specific probe is the plug-in connector on a hose or medical device that fits only the terminal units of one medical gas or vacuum service, so that equipment cannot be connected to the wrong gas.

ISO 9170-1 requires [terminal units](https://library.ultracontrolo.com/glossary/terminal-unit/) to be gas-specific and to prevent interchange between gases and services, but it does not specify the dimensions of probes. Those come from national standards: the British BS 5682 sets the dimensions of probes and terminal units, the German DIN 13260-2 the dimensions and allocation of probes and gas-specific connection points, and the French NF S90-116 the sockets and related probes. The World Health Organization notes that each connector style uses key-like indexing so that the fittings of each gas service connect only with their own type.

Each gas has its own probe, and gas-specific connections are also identified by symbol and colour. The 2025 edition of DIN 13260-2 adds a gas-specific probe for oxygen 93.

HTM 02-01 (2026), the NHS England guidance, checks probe fit at commissioning and in service. Form B24 verifies that each terminal unit is gas-specific and securely retains the appropriate probe, and all terminal units should be tested quarterly by inserting a blank probe to check gas-specificity, mechanical function and leaks.

## Sources

- [ISO 9170-1:2017, Terminal units for medical gas pipeline systems (ISO summary)](https://www.iso.org/standard/67451.html)
- [HTM 02-01 (2026) Part A, form B24 and references (BS 5682:2015) (NHS England)](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)
- [HTM 02-01 (2026) Part B: Operational management, terminal unit maintenance (NHS England)](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)
- [DIN Media, DIN 13260-2:2025-06](https://www.dinmedia.de/en/standard/din-13260-2/389570410)
- [AFNOR, NF S90-116 (October 2020), store page](https://www.boutique.afnor.org/en-gb/standard/nf-s90116/medical-gas-pipeline-distribution-systems-sockets-and-related-probes-for-me/fa191757/260496)
- [WHO, Foundations of medical oxygen systems (2023), outlet connector styles](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/glossary/gas-specific-probe/