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How Much CO is Too Much?
The level of CO concentration is measured using a system called Parts Per Million (PPM). For example, 100 PPM CO means that for every 999,900 molecules of air, there are 100 molecules of CO. CO effects people differently depending on the concentration. In addition to measuring the current level of CO concentration, another measurement used is the Time-Weighted Average (TWA). This measures your average exposure to CO over time, and is also measured in PPM. For example, if you were exposed to a large dose of CO in the begining of the day, but none afterwards, your TWA for the day would be low, since for most of the day you had no exposure. If, however, you are continually exposed to 20 PPM CO throughout the day, your TWA for the day will be 20 PPM.
The table below summarizes some health effects due to prolonged exposure to various concentrations of CO, as well as some government recommended limits, and Pocket CO alarm levels. It has been compiled from various sources, including the NFPA:
| Level of CO | Health Effects, and Other Information |
| 0 PPM | Normal, fresh air. |
| 9 PPM | Maximum recommended indoor CO level (ASHRAE). |
| 10-24 PPM | Possible health effects with long-term exposure. |
| 25 PPM |
Max TWA Exposure for 8 hour work-day (ACGIH). Pocket CO TWA warning sounds each hour. |
| 50 PPM |
Maximum permissible exposure in workplace (OSHA). First Pocket CO ALARM starts (optional, every 20 seconds). |
| 100 PPM | Slight headache after 1-2 hours. |
| 125 PPM | Second Pocket CO ALARM starts (every 10 seconds). |
| 200 PPM | Dizziness, naseau, fagitue, headache after 2-3 hours of exposure. |
| 400 PPM |
Headache and nausea after 1-2 hours of exposure. Life threatening in 3 hours. Third Pocket CO ALARM starts (every 5 seconds). |
| 800 PPM |
Headache, nausea, and dizziness after 45 minutes; collapse and unconsciousness after 1 hour of exposure. Death within 2-3 hours. |
| 1000 PPM | Loss of consciousness after 1 hour of exposure. |
| 1600 PPM |
Headache, nausea, and dizziness after 20 minutes of exposure. Death within 1-2 hours. |
| 3200 PPM |
Headache, nausea, and dizziness after 5-10 minutes; collapse and unconsciousness after 30 minutes of exposure. Death within 1 hour. |
| 6400 PPM | Death within 30 minutes. |
| 12,800 PPM |
Immediate physiological effects, unconsciousness. Death within 1-3 minutes of exposure. |
