| CO concentration (parts per million) | Symptoms |
| 50 | No adverse effects with 8 hours of exposure |
| 200 | Mild headache after 2-3 hours of exposure |
| 400 | Headache and nausea after 1-2 hours of exposure |
| 800 | Headache, nausea, and dizziness after 45 minutes; collapse and unconsciousness after 1 hour of exposure |
| 1,000 | Loss of consciousness after 1 hour of exposure |
| 1,600 | Headache, nausea, and dizziness after 20 minutes of exposure. |
| 3,200 | Headache, nausea, and dizziness after 5-10 minutes; collapse and unconsciousness after 30 minutes of exposure |
| 6,400 | Headache and dizziness after 1-2 minutes; unconsciousness and danger of death after 10-15 minutes of exposure |
| 12,800 | Immediate physiological effects, unconsciousness and danger of death after 1-3 minutes of exposure |
![]() National Fire Protection Association |
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| Last Updated: |
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