| Carbon monoxide content of inhaled air (%) | Physiological effects |
|---|---|
| 0.020 | Possible mild frontal headache after two to three hours |
| 0.040 | Frontal headache and nausea after one to two hours; occipital (rear of head) headache after 2.5 to 3.5 hours. |
| 0.080 | Headache, dizziness, and nausea in 45 min; collapse and possible unconsciousness in two hours. |
| 0.160 | Headache, dizziness, and nausea in 20 min; collapse, unconsciousness and possible death in two hours. |
| 0.320 | Headache and dizziness in 5 to 10 min; unconsciousness and danger of death in 30 min. |
| 0.640 | Headache and dizziness in 1 to 2 min; unconsciousness and danger of death in 10 to 15 min. |
| 1.280 | Immediate physiological effect; unconsciousness and danger of death in 1 to 3 min. |