Gas testing before confined-space entry

Testing the atmosphere before entering a confined space (tank, pit, silo, manhole, cargo hold, process vessel) is the first step against fatal incidents. Entry without measurement can kill through oxygen deficiency, an explosive mixture or a toxic gas. ESA Gaz Kalibrasyon summarises the field order of tests, typical limits and why a calibrated gas detector is required.

Why gas testing is required

Ventilation is weak in a confined volume. Nitrogen inerting, decay, welding fume or a leak can drop oxygen, push flammable vapour toward LEL, or accumulate H₂S or CO. A permit to work is incomplete without a written gas test. The detector itself is not “safe” on the day without a bump-test or calibration record.

Standard testing order

1. Oxygen (O₂) first — some sensors mis-read without oxygen.
2. Flammable gases (LEL) — %LEL for methane, propane, solvent vapour.
3. Toxic gases — H₂S, CO and the process gas with the correct cell.

Safe atmospheric limits

• Oxygen: a typical acceptance band is 19.5–23.5% vol (site procedure and national rules apply).
• Test at top, middle and bottom; gases stratify by density.
• Keep monitoring during the job; a single snapshot is not enough.
• Ventilate if required, then re-test.

Best practice

Calibrate the detector before entry and zero it in clean air. A bump test proves the cell responds; periodic calibration documents deviation. Do not start without a permit, attendant and rescue plan.

ESA Calibration Laboratory calibrates fixed and portable detectors in the lab or on site under TS EN ISO/IEC 17025:2017 and TURKAK AB-0319-K. Current scope is on the certificates page.

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