# What is a particulate test on a medical gas outlet?

**How is a medical gas pipeline tested for particulate contamination?**

Under HTM 02-01 (NHS England), a particulate test checks that no dust or debris comes out of a medical gas outlet: gas from each terminal unit of a new system passes through a filter at a set flow for a set time, and the filter should show no visible particles.

HTM 02-01 Part A, the NHS England guidance on medical gas pipelines (2026 edition), explains that pipelines are built from chemically cleaned, capped components, with joints made under a shield gas, but can be contaminated on site by building materials, dust and inadequate purging, and that particles can affect the quality of the gas delivered. It specifies two particulate tests for a new system.

## The engineer's particulate test

The Competent Person (MGPS) tests every terminal unit of a new system, after the system pressure test and before any calibrated test equipment is connected, so that particles cannot damage it. The test may use medical air or oxygen-free nitrogen. A membrane filter is held at the outlet for 30 seconds and should be free from visible particles in good light.

| Service | Flow for 30 seconds |
|---|---|
| General rule | Not less than 150 L/min |
| Surgical air | 350 L/min |
| Nitrous oxide and carbon dioxide | 75 L/min maximum |
| Oxygen/nitrous oxide mixture | 275 L/min maximum |

## The Quality Controller's test

The Quality Controller (MGPS) repeats the test with the working gas of each pipeline during quality control testing, using a 47 mm diameter filter of 0.45 µm at every terminal unit and starting with the outlets furthest from the zone valve (AVSU). A new system should leave the filter completely clear of visible particles. Older systems may still show particulates after considerable purging; where purging will not clear them, the Authorised Person and the Quality Controller decide whether to accept the level, agree a procedure for removing the particles or, in very exceptional circumstances, condemn the system.

## Other cases and other methods

- Where the cleanliness of an existing system is in doubt, HTM 02-01 asks for particulate tests on it before a new section is connected.
- On small dental air installations, where the usual 30 seconds at 150 L/min is not practicable, purging at full flow should be enough.
- A 2024 commissioning overview for PSA oxygen plants by the Global Fund and Build Health International asks for the last outlet in every branch to be tested by blowing oxygen into a white cloth.

### Which gas is used for the particulate test?

HTM 02-01 allows the engineer's test to be done with medical air or oxygen-free nitrogen; the Quality Controller repeats it with the working gas of each pipeline.

### What if particles keep appearing?

The system is purged further. If purging cannot clear it, the Authorised Person (MGPS) decides, with the Quality Controller (MGPS), whether to accept the level, agree a procedure for removing particles or, very exceptionally, condemn the system.

## Sources

- [NHS England, HTM 02-01 (2026) Part A, paragraphs 9.10, 19.20, 19.34, 19.65, 19.74, 19.222 to 19.224 and 20.57 to 20.61](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)
- [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-particulate-test/