Confined Space Atmospheric Action Levels 2026 — Multi-Jurisdiction (OSHA / HSE UK / IOGP)

Machine-readable reference of confined-space atmospheric monitoring action levels and evacuation thresholds across three major jurisdictions and frameworks: US OSHA (29 CFR 1910.146 permit-required confined spaces) UK HSE (INDG258 / Safe Working in Confined Spaces, EH40 WELs, SCR97) IOGP (Report 415 — Life-Saving Rule 2: Confined Space; industry standard for upstream oil and gas) ~13 parameters including: oxygen (O2 acceptable 19.5–23.5%), LEL flammable gas (action at 10%, evacuate at 25%), hydrogen sulfide (H2S — IDLH 100 ppm), carbon monoxide (CO — PEL 50 ppm OSHA / WEL 20 ppm UK), sulfur dioxide, nitrogen dioxide, ammonia, methane, chlorine, hydrogen cyanide, benzene, temperature, and noise. Per row: parameter, unit, acceptable range, warning threshold, evacuation threshold, OSHA reference, HSE UK reference, IOGP reference, and practical notes (monitoring gotchas, heavier/lighter-than-air, derating factors, physiological effects). Useful for: confined space entry permit preparation, gas monitor calibration specification, HSE training, ARIA AI assistant grounding for confined space queries, contractor competency assessment. Sources: OSHA 1910.146, EH40 WEL table (UK HSE), HSE UK INDG258, IOGP Report 415, NIOSH IDLH values, ACGIH TLV documentation (2024). Published as part of the SmartQHSE Open HSE Data collection.