Atmospheric testing (confined space)
Atmospheric testing is the pre-entry confined-space gas test under AS/NZS 2865: oxygen 19.5-23.5%, flammables under 5% LEL, before anyone enters.
Ask Chalkline about this →Atmospheric testing is the discrete, pre-entry measurement of a confined space’s atmosphere to confirm it is safe before anyone goes in. It is the gas test done before entry, and it is distinct from atmospheric monitoring, which is the continuous measurement during the entry. Both are required under AS/NZS 2865:2009, in different roles, and the same multi-gas detector usually does both jobs.
What a test has to confirm
A pre-entry test checks the same multi-gas parameters against acceptance limits before entry is permitted:
| Parameter | Safe for entry | Why |
|---|---|---|
| Oxygen (O₂) | 19.5% to 23.5% | Below: asphyxiation. Above: combustibility |
| Flammable gas (LEL) | Under 5% LEL | Conservative pre-entry limit; ignition risk |
| Toxic contaminants (CO, H₂S, etc.) | Below the exposure standard | Poisoning risk |
If any parameter is outside these limits, the space fails the test and entry is not permitted. You ventilate (or purge), then re-test, and only enter once a clean result is recorded.
The 5% vs 10% LEL point
The pre-entry testing limit for flammable gas is the conservative 5% LEL. This is stricter than the 10% LEL action level allowed during continuous atmospheric monitoring (verified 2026-05-25). The reason: pre-entry you are deciding whether it is safe to go in at all, so the bar is lower; once inside with a continuous detector running and alarms set, the action level shifts. Do not apply the 10% monitoring level to a pre-entry test.
How and when to test
- From outside the space, never by leaning in. Use the detector’s probe and sample line.
- Test the full depth. Gases stratify: flammables and light gases collect high, heavy gases (CO₂, H₂S) pool low. Test top, middle, and bottom, and any remote pockets.
- Let the reading stabilise at each level before accepting it.
- Re-test before each entry, after any break in occupancy, after re-opening the space, and after ventilation.
The results set the confined space entry permit conditions: a permit cannot be issued on an untested or failed atmosphere.
For a builder
- No permit without a clean test. The entry permit depends on a recorded, passing pre-entry test. No test, no entry.
- Testing is not monitoring. A clean pre-entry test does not mean the air stays safe; most construction entries also need continuous monitoring throughout.
- Use a calibrated, bump-tested detector. Zero it in clean air, bump-test it before use; a test with an unverified detector is worthless.
- It is a competency. Pre-entry testing is done by a trained, competent person, not handed to whoever is nearest.
Also known as: pre-entry gas test, pre-entry atmospheric test, confined space gas testing.
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See also
Last updated: 2026-05-25. Verified: 2026-05-25. Quarterly review for currency.