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Carbon Monoxide (CO) is a colorless and odorless toxic gas that is a product of incomplete combustion. When CO is introduced into the bloodstream, through the lungs, it is accepted in place of oxygen at a rate of 300:1 and literally suffocates its victim. Since CO is an accumulative and direct reacting toxin, it can be dangerous even at low levels over periods of time. The harmful effect of CO inhalation depend on the following factors:
The following chart shows the maximum allowable exposure limits and symptoms devoloped for CO inhalation.
| Concentration of CO in the air | Inhalation time and symptoms |
| 9 ppm (parts per million) | The maximum allowable concentration for short term exposure in a living area according to ASHRAE. |
| 35 ppm | The maximaum allowable concentration for continuous exposure in any 8-hour period, according to Federal Law. |
| 200 ppm NOTE: Exposure to this concentration or higher, the effects can vary depending on the size, age and health. | Maximum concentration allowable at any time according to OSHA. Slight headache, fatigue, dizziness, nausea after 2-3 hours. |
| 400 ppm | Frontal headaches within 1-2 hours, life-threatening after 3 hours. Maximum allowable limit in flue gas according to EPA and AGA. |
| 800 ppm | Dizziness, nausea and convulsions within 45 minutes. Unconsciousness within 2 hours. Death within 2-3 hours. |
| 1600 ppm | Headache, dizziness and nausea within 20 minutes. Death within one hour. |
| 3200 ppm | Headache, dizziness and nausea within 5-10 minutes. Death within 30 minutes. |
| 6400 ppm | Headache, dizziness and nausea within 1-2 minutes. Death within 10-15 minutes. |
| 12,800 ppm | Death within 1-3 minutes. |
Have a look at the EPA's Dos and Don'ts for Carbon Monoxide.