IDLH (Immediately Dangerous to Life or Health) is an occupational exposure limit defined by NIOSH (CDC) as the maximum concentration of a hazardous substance that poses an immediate threat to life causes irreversible health effects or impairs escape. Below are key IDLH values for common industrial substances.
1. Common Industrial IDLH Values (NIOSH Standards)
| Substance | IDLH (ppm or mg/m³) | Key Risks | Industries Affected |
|---|---|---|---|
| Ammonia (NH₃) | 300 ppm | Lung damage, burns | Fertilizers, refrigeration |
| Carbon Monoxide (CO) | 1,200 ppm | Asphyxiation, poisoning | Steel, automotive, firefighting |
| Chlorine (Cl₂) | 10 ppm | Fatal pulmonary edema | Water treatment, chemical plants |
| Hydrogen Sulfide (H₂S) | 100 ppm | Respiratory paralysis, death | Oil & gas, sewage |
| Sulfur Dioxide (SO₂) | 100 ppm | Severe lung irritation | Power plants, smelting |
| Benzene (C₆H₆) | 500 ppm | Carcinogenic, CNS damage | Petrochemicals, plastics |
| Formaldehyde (CH₂O) | 20 ppm | Cancer, respiratory burns | Textiles, manufacturing |
| Hydrogen Cyanide (HCN) | 50 ppm | Rapid fatality (blocks O₂ use) | Mining, chemical synthesis |
| Nitrogen Dioxide (NO₂) | 20 ppm | Lung scarring, death | Welding, combustion engines |
| Ozone (O₃) | 5 ppm | Severe lung damage | Water treatment, electronics |
(ppm = parts per million; mg/m³ = milligrams per cubic meter)
2. IDLH vs. Other Exposure Limits
| Term | Definition | Comparison to IDLH |
|---|---|---|
| PEL (OSHA) | Permissible Exposure Limit (8-hr avg) | Much higher than IDLH |
| REL (NIOSH) | Recommended Exposure Limit (10-hr avg) | Lower than IDLH |
| STEL (ACGIH) | Short-Term Exposure Limit (15 min) | Below IDLH |
| TLV (ACGIH) | Threshold Limit Value (8-hr avg) | Below IDLH |
Key Point: IDLH is the worst-case scenario exposure above this level requires immediate evacuation and SCBA (self-contained breathing apparatus).
3. Industries with High IDLH Risks
Oil & Gas → H₂S, benzene, CO.
Chemical Manufacturing → Chlorine, ammonia, formaldehyde.
Mining & Smelting → Hydrogen cyanide, sulfur dioxide.
Wastewater Treatment → Methane, H₂S.
Firefighting → CO, hydrogen cyanide (from burning plastics).
4. Safety Measures for IDLH Environments
✔ Use SCBA or supplied-air respirators (NIOSH-approved).
✔ Continuous gas monitoring (e.g. multi-gas detectors).
✔ Emergency escape plans (must be < 30 min for IDLH conditions).
✔ Training on chemical hazards and PPE usage.
5. Regulatory Compliance
OSHA 1910.134 mandates respirator use in IDLH conditions.
NIOSH Pocket Guide provides full IDLH listings.
NFPA 704 (hazard diamond) indicates IDLH risks in facilities.
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