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Relation of hydrogen cyanide concentrations in air and symptoms in humans
| HCN concentration, ppm | Symptoms |
| 0.2–5.0 | Threshold of odor |
| 10 | Maximum safe exposure |
| 18–36 | Slight symptoms (headache) |
| 45–54 | Tolerated for ½–1 h |
| 100 | Fatal – 1h |
| 110–135 | Fatal in ½–1 h |
| 180 | Fatal in > 10 min |
| 280 | Immediately fatal |
