ISO 20486:2017 — Non-destructive testing. Leak testing. Calibration of reference leaks for gases is one of the most frequently cited and least understood standards in leak testing.
It is worth being precise about what it covers, because it is often described loosely as “the air leak testing standard”, which it is not. ISO 20486 does not tell you how to test a part. It tells you how the reference leaks used to calibrate your leak detectors are themselves calibrated — and that makes it the foundation everything else rests on.
Where ISO 20486 Sits in the Family
Leak testing standards divide into vocabulary, method and calibration. Knowing which is which saves a lot of confusion:
| Standard | What it covers |
|---|---|
| ISO 20484 | Vocabulary — the agreed terminology for leak testing |
| ISO 20485 | Tracer gas method — how to carry out tracer gas leak testing (superseded EN 1779) |
| ISO 20486 | Calibration of reference leaks for gases — how the calibrated leak artefacts themselves are established |
In the UK these are implemented as BS EN ISO versions; ISO 20486 supersedes the earlier BS EN 13192.
What a Reference Leak Actually Is
A reference leak — also called a calibrated leak, test leak or leak standard — is a precision-engineered artefact that emits a known gas flow at a stated rate, temperature and pressure. It is the physical embodiment of “this is what a leak of X mbar·l/s looks like”.
Without one, a leak detector produces a number with nothing to anchor it to. With one, you can demonstrate that your instrument detected a known leak on a known day — which is the difference between a reading and evidence.
How ISO 20486 Says They Are Calibrated
The standard sets out the recognised approaches, along with requirements for data handling, uncertainty, labelling and reporting:
- Comparison method — the routine leak is compared against a reference leak of known rate. This is the preferred approach for helium mass spectrometer detectors.
- Direct or volumetric calibration — the leak rate is calculated or measured directly across a known volume over time.
- Uncertainty and reporting — procedures for analysing and stating measurement uncertainty, and for labelling and documenting the leak.
It also recognises different physical leak constructions — including capillary, orifice and permeation types — each with its own characteristics and drift behaviour.
Why This Matters on Your Production Line
Three practical consequences follow:
- Reference leaks drift and expire. Permeation leaks in particular deplete over time. A leak standard with an out-of-date certificate is not a standard.
- Temperature matters. Leak rate is stated at a specific temperature. Using a reference leak well outside its stated conditions introduces error before you have even tested a part.
- Traceability is what auditors ask for. The certificate must trace back through an unbroken chain to national standards. For UK manufacturers that usually means UKAS accreditation — see our guide to UKAS traceable leak standards.
Applying It in Practice
A defensible leak testing regime generally involves three layers:
- Shift or daily verification — run a calibrated reference leak through the full test cycle to confirm the system still detects a known reject.
- Periodic instrument calibration — formal calibration of the detector with traceable certification, typically annually.
- Fixture verification — leak-check the fixture and seals separately, so fixture leaks are never attributed to parts.
Related Reading
For the methods these standards govern, see air leak testing, pressure decay leak testing and our helium leak testing service. For traceable calibration using certified leak standards, see our calibration services.
