parameter stringlengths 5 27 | unit stringclasses 6
values | acceptable_range stringlengths 12 62 | warning_threshold stringlengths 40 75 | evacuate_threshold stringlengths 14 89 | osha_reference stringlengths 17 95 | hse_uk_reference stringlengths 38 90 | iogp_reference stringclasses 9
values | notes stringlengths 89 194 |
|---|---|---|---|---|---|---|---|---|
Oxygen (O2) | % v/v | 19.5 to 23.5 | 19.5 or 23.5 (at limit — assess immediately) | <19.5 or >23.5 | OSHA 1910.146 — atmosphere-supplied respirator below 19.5% O2 | HSE UK INDG258 — deficient <19.5% enriched >23.5% | IOGP Report 415 section 5.3 | O2 readings are affected by temperature and altitude; calibrate monitors at site conditions; above 23.5% fire and explosion risk increases dramatically |
Flammable gas / LEL | % of lower explosive limit (LEL) | 0 to <10% LEL acceptable for entry | 10% to <20% LEL — increased monitoring and review, ventilate | >=25% LEL — do not enter or evacuate immediately (many operators use 10% LEL as evacuate) | OSHA 1910.146 — flammable atmosphere defined as >=10% LEL | HSE UK SCR97 — 10% LEL as action level | IOGP Report 415 — <25% LEL entry; <10% LEL preferred | Methane LEL = 5% v/v so 10% LEL = 0.5% CH4; H2 LEL = 4% v/v; sensor type must match target gas; catalytic bead sensor suppressed in O2 < 10% |
Hydrogen sulfide (H2S) | ppm | 0 to <1 ppm acceptable (some protocols 0-5 ppm short-term) | 1 to 10 ppm — odour detectable; skin/eye irritation; investigate source | >=10 ppm action / >100 ppm IDLH — evacuate immediately | OSHA PEL 20 ppm ceiling / IDLH 100 ppm (1910.146 defines IDLH as evacuation trigger) | HSE UK WEL 1 ppm TWA / 5 ppm STEL (EH40 WEL Table) | IOGP Report 415 — IDLH standard; many offshore sites use 10 ppm as evacuation trigger | H2S is heavier than air — accumulates at low points; olfactory fatigue above 100 ppm (cannot smell at IDLH); 15 min escape to 50 ft in undetected H2S at 1000 ppm = unconscious |
Carbon monoxide (CO) | ppm | 0 to <25 ppm acceptable (short stay); 0 to <50 ppm is OSHA PEL | 25 to 50 ppm — increase ventilation and monitoring; limit exposure | >=50 ppm action level (OSHA PEL) / >200 ppm NIOSH ceiling / >1200 ppm IDLH — evacuate | OSHA PEL 50 ppm TWA 29 CFR 1910.1000 / IDLH 1200 ppm | HSE UK WEL 20 ppm TWA / 100 ppm STEL (EH40) | IOGP Report 415 and confined space entry standard | CO is odourless and colourless; sources include internal combustion engines diesel exhaust; never run engine inside or near CS entry; CO poisoning may occur before O2 drops |
Sulfur dioxide (SO2) | ppm | 0 to <0.25 ppm acceptable | 0.25 to 2 ppm — irritant odour; increase ventilation | >=2 ppm (OSHA PEL) / >100 ppm IDLH — evacuate | OSHA PEL 5 ppm TWA (1910.1000) — NB NIOSH REL 0.5 ppm / ACGIH TLV 0.25 ppm more protective | HSE UK WEL 0.5 ppm TWA / 1 ppm STEL (EH40) | IOGP Report 415 references IDLH trigger | Found near acid tanks / sulphur processing / sewers with organic matter; heavier than air |
Nitrogen dioxide (NO2) | ppm | 0 to <0.2 ppm acceptable | 0.2 to 1 ppm — investigate and ventilate | >=1 ppm (OSHA PEL) / >20 ppm IDLH — evacuate | OSHA PEL 5 ppm ceiling (1910.1000); NIOSH REL 1 ppm STEL | HSE UK WEL 0.5 ppm TWA / 1 ppm STEL (EH40) | IOGP Report 415 | NO2 from combustion engines and confined silo / silo work; delayed pulmonary oedema up to 24 hours after exposure — may feel fine initially |
Ammonia (NH3) | ppm | 0 to <25 ppm acceptable (short stay) | 25 to 50 ppm — strong odour; irritant; increase ventilation | >=50 ppm OSHA PEL / >300 ppm IDLH — evacuate | OSHA PEL 50 ppm TWA (1910.1000) / IDLH 300 ppm | HSE UK WEL 20 ppm TWA / 35 ppm STEL (EH40) | IOGP Report 415 | Ammonia in refrigeration plants / fertiliser / chemical storage; lighter than air — rises to roof space; distinctive pungent odour |
Methane (CH4 / natural gas) | % v/v and % LEL | < 1% CH4 (= <20% LEL) acceptable for entry | 1% to 1.25% CH4 (20-25% LEL) — alert; ventilate before entry | >=1.25% CH4 (>=25% LEL) — do not enter | See LEL row above | HSE UK — flammable atmosphere = >=10% LEL for entry ban | IOGP Report 415 — >=25% LEL prohibits entry | Methane LEL = 5% v/v; UEL = 15% v/v; asphyxiant at high concentrations; CH4 sensor calibrated with CH4 standard gas |
Chlorine (Cl2) | ppm | 0 to <0.5 ppm | 0.5 to 1 ppm — distinctive bleach odour; irritant | >=1 ppm OSHA PEL ceiling / >10 ppm IDLH — evacuate | OSHA PEL 1 ppm ceiling (1910.1000) / IDLH 10 ppm | HSE UK WEL 0.5 ppm TWA / 1 ppm STEL (EH40) | IOGP Report 415 | Water treatment plants / chlorination vessels; heavier than air; greenish-yellow gas; reacts with moisture forming HCl and HOCl on eyes and airways |
Hydrogen cyanide (HCN) | ppm | 0 to <4.7 ppm (NIOSH REL ceiling) | 4.7 to 10 ppm — investigate source immediately | >=10 ppm OSHA PEL / >50 ppm IDLH — evacuate | OSHA PEL 10 ppm skin / IDLH 50 ppm (1910.1000) | HSE UK WEL 0.9 ppm TWA / 4.5 ppm STEL (EH40) | IOGP Report 415 | Fumigation / electroplating / nitrile rubber combustion; very rapid onset; bitter almond odour not detectable by 40-50% of population; antidote kits required in rescue kit for HCN confined space |
Benzene | ppm | 0 to <0.5 ppm (OSHA action level) | 0.5 to 1 ppm — OSHA action level reached; medical surveillance | >=1 ppm OSHA PEL / >500 ppm IDLH — evacuate | OSHA PEL 1 ppm TWA (1910.1028) / STEL 5 ppm / action level 0.5 ppm | HSE UK WEL 1 ppm TWA / 3 ppm STEL (EH40) | IOGP Report 415 | Petroleum / chemical industry; Group 1 IARC carcinogen; continuous exposure monitoring required above action level; confined space entry near hydrocarbon products or tank cleaning |
Temperature | degrees Celsius | 18 to 30 degrees C acceptable for typical work | 30 to 35 degrees C — assess work rate and rest breaks (WBGT considerations) | >=35 degrees C — heat illness risk high; restrict work duration | OSHA 29 CFR 1910 General Industry — heat illness NPRM (proposed 2024); WBGT-based action levels | HSE UK — thermal comfort guidance and HSG194 working in hot conditions | IOGP Report 415 Section 5.4 | Internal temperature in enclosed vessels can exceed ambient by 10-15 degrees C; forced ventilation required; consider wet bulb globe temperature (WBGT) for heat index calculations |
Noise | dB(A) | < 85 dB(A) 8-hour TWA — no additional controls | 85 to 90 dB(A) — hearing protection required (OSHA action level) | >=90 dB(A) OSHA PEL — engineering controls required; >140 dB(C) peak immediately harmful | OSHA 1910.95 — action level 85 dB(A) TWA / PEL 90 dB(A) TWA | HSE UK COSHH Noise Regulations 2005 — first action value 80 dB(A) / second action 85 dB(A) | IOGP 415 references occupational noise inside CS | High noise in confined spaces from equipment; reverberation increases effective noise level; impact noise common from percussive work on metal vessels |
Canonical landing page: https://www.smartqhse.com/datasets/confined-space-atmospheric-action-levels-2026
Confined Space Atmospheric Action Levels 2026 — Multi-Jurisdiction
Confined space atmospheric monitoring thresholds across OSHA 1910.146 (US), HSE UK (INDG258 / EH40 WELs / SCR97), and IOGP Report 415. ~13 parameters: O2 (19.5-23.5%), LEL (<10% acceptable), H2S (IDLH 100 ppm), CO (PEL 50 ppm OSHA), SO2, NO2, NH3, methane, chlorine, HCN, benzene, temperature, noise. Per row: acceptable range, warning threshold, evacuation threshold, all three jurisdiction references, and practical notes.
Dataset details
- Publisher: SmartQHSE Ltd (https://www.smartqhse.com)
- License: CC BY 4.0 -- please cite with link to https://www.smartqhse.com
- Format: CSV (UTF-8)
- Schema: see data.csv first row (header)
- DOI: 10.5281/zenodo.20171693 -- permanent Zenodo citation
- Update cadence: annual or on regulatory change
- Canonical home: https://www.smartqhse.com/datasets
Suggested citation
SmartQHSE Ltd (2026). Confined Space Atmospheric Action Levels 2026 — Multi-Jurisdiction [dataset]. Zenodo. https://doi.org/10.5281/zenodo.20171693
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Disclaimer
This dataset is published for reference, training, and research. Regulatory text and action levels are summarised; consult the authoritative source listed before basing operational or compliance decisions on this dataset. SmartQHSE Ltd accepts no liability for errors or omissions.
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