# How is a medical gas pipeline pressure tested for leaks?

**How is a new medical gas pipeline pressure tested for leaks?**

Under HTM 02-01, the NHS England guidance, a new medical gas pipeline is pressure tested in two stages, first the bare pipework filled with nitrogen and then the complete system with outlets fitted, checking with a precise electronic gauge that the pressure holds for at least two hours.

ISO 7396-1, the international standard for medical gas pipeline systems, includes requirements for testing and commissioning. The procedure below is from HTM 02-01 Part A, the guidance published by NHS England in August 2026; other standards set their own pressures and durations.

## Stage 1: carcass test

- Only the first-fix pipework is tested: terminal units, pressure switches, pressure safety valves and other ancillary equipment are excluded, and the zone and line valves are open.
- Each system is tested on its own, with a physical break from adjoining systems. Combining several systems in one test should not be permitted, as it introduces a risk of cross-contamination.
- HTM 02-01 says the tests should be performed with nitrogen, so that a leak or cross-connection can be remedied immediately.
- Test pressures: 1000 kPa for 400 kPa oxygen, nitrous oxide, oxygen/nitrous oxide and medical air systems, and 1800 kPa for 700 kPa surgical air.
- Over at least two hours after filling and settling, the pressure loss should be less than 0.2 kPa for 400 kPa systems and vacuum, and less than 0.5 kPa for 700 kPa systems, measured with electronic equipment resolving 0.01 kPa in 10,000 kPa.
- No allowance is made for temperature over two hours. If the accuracy of the instrument is in doubt, the test is extended to 24 hours, and on such a test the gas laws may be used to correct for large temperature changes.

## Stage 2: pipeline test

Once all valves are open and the terminal units and other second-fix components are installed, the whole system is tested again for leaks at about the normal working pressure, with the same pass criterion over at least two hours. Every terminal unit carries a 'Do not use' plug until the Quality Controller (MGPS) signs the system off for patient use.

Vacuum pipelines have a separate leakage test, in which there should be no loss of vacuum over at least two hours.

## Other procedures

Not every document uses these values. A 2024 Global Fund and Build Health International commissioning overview for PSA oxygen plants asks for a 24-hour pressure test of the piping at 20% above operating pressure, with a fall of no more than 10%, and for leak tests from the compressor to the bedside outlet. After a pipe repair, HTM 02-01 Part B describes purging with the working gas to remove residual nitrogen, followed by a pressure test at the normal working pressure using the working gas.

### Why is nitrogen used for the test?

HTM 02-01 specifies nitrogen so that, if a leak or cross-connection is found, remedial action can be taken immediately.

### How long does the pressure test last?

At least two hours in HTM 02-01, extended to 24 hours if the accuracy of the pressure-measuring equipment is in doubt.

## Sources

- [NHS England, HTM 02-01 (2026) Part A, paragraphs 19.63, 19.99 to 19.105, 19.110, 19.119, 19.121, 19.197, 19.200 to 19.203, 19.219 and Table 30](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 (2026) Part B, paragraph 7.20](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)
- [ISO 7396-1:2016 Medical gas pipeline systems, Part 1 (iso.org summary)](https://www.iso.org/standard/60061.html)
- [Global Fund / Build Health International, Overview: PSA Oxygen Plant Commissioning Guidelines (28 August 2024), piping checks](https://resources.theglobalfund.org/media/qp3h1vxo/cr_c19rm-psa-oxygen-plant-commissioning_overview_en.pdf)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/what-is-a-pipeline-pressure-test/