| Concentration | Symptoms |
| 35 ppm | Headache and dizziness within six to eight hours of constant exposure |
| 100 ppm | Slight headache in two to three hours |
| 200 ppm | Slight headache within two to three hours; loss of judgment |
| 400 ppm | Frontal headache within one to two hours |
| 800 ppm | Dizziness, nausea, and convulsions within 45 min; insensible within 2 hours |
| 1,600 ppm | Headache, tachycardia, dizziness, and nausea within 20 min; death in less than 2 hours |
| 3,200 ppm | Headache, dizziness and nausea in five to ten minutes. Death within 30 minutes. |
| 6,400 ppm | Headache and dizziness in one to two minutes. Death in less than 20 minutes. |
| 12,800 ppm | Unconsciousness after 2-3 breaths. Death in less than three minutes. |
The extent of the harmful effects of carbon monoxide depends on the concentration of the carbon monoxide in the room and length of time of the exposure.
Although a blood test to detect increased carboxyhemoglobin levels can confirm suspected carbon monoxide poisoning, the levels can return to normal or be zero if you have been treated with oxygen before obtaining the blood test.
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Mild (or low level) exposure signs and symptoms are "non-specific" often being confused with the other illnesses such as the " flu" or a "virus"
Headache
Nausea
Vomiting
Flu-like symptoms
Dizziness
Chronic fatigue
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Moderate CO exposure signs and symptoms include increasing severity of the above but also may include:
Chest pain
Rapid heart beat
Difficulty thinking
Blurred vision
Difficulty breathing (shortness of breath) on exertion
Weakness
Unsteadiness
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Severe CO signs and symptoms include the above but may also include:
Seizures
Palpitations
Disorientation
Irregular heartbeat
Low blood pressure
Damage to the heart muscle
Coma
Death
