# Cross-connection

A cross-connection is a fault in a medical gas pipeline where one gas or vacuum service is joined to the pipework or outlets of another, so that a patient or a device can receive the wrong gas.

Preventing cross-connection is a basic aim of the pipeline standards. ISO 7396-1 sets requirements for non-interchangeability between the components of different gas and vacuum systems, ISO 9170-1 requires terminal units that are gas-specific and cannot be interchanged between gases and services, and ISO 7396-2 requires anaesthetic gas scavenging disposal systems to avoid cross connections with medical gas and vacuum pipelines.

HTM 02-01 (2026) states that it is essential to rule out any possibility of a cross-connection between parts of the medical gas pipeline system, and that every part users can connect to is gas-specific. Its validation and verification include a cross-connection test in two stages: from the plant to the departmental area valve service units (AVSUs), then from the AVSUs to the [terminal units](https://library.ultracontrolo.com/glossary/terminal-unit/). In the first stage, each gas supply system is opened in turn and gas flow is checked at the departmental AVSUs; the results go on form B21.

The pipeline equipment Ultra Controlo supplies, from manifolds and valves to alarms and outlets, is built to EN ISO 7396-1.

## Sources

- [ISO 7396-1:2016, Medical gas pipeline systems, Part 1 (ISO summary)](https://www.iso.org/standard/60061.html)
- [ISO 9170-1:2017, Terminal units for medical gas pipeline systems (ISO summary)](https://www.iso.org/standard/67451.html)
- [ISO 7396-2:2007, Anaesthetic gas scavenging disposal systems (ISO summary)](https://www.iso.org/standard/41945.html)
- [HTM 02-01 (2026) Part A, paragraphs 2.5 and 19.226 to 19.228 (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)
- [Ultra Controlo, Medical gas answers: MGPS equipment built to EN ISO 7396-1](https://www.ultracontrolo.com/medical-gas-answers)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/glossary/cross-connection/