A carbon monoxide level of 220 parts per million is very dangerous, according to the U.S. Consumer Product Safety Commission. At levels of 150 ppm or over, sustained exposure causes severe symptoms such as disorientation, unconsciousness and, in some cases, results in death.
For concentrations of carbon monoxide of 70 ppm or lower, most people do not experience symptoms, states the Consumer Product Safety Commission. However, patients with heart complications may begin to experience symptoms at this point. When concentrations reach levels over 70 ppm, people begin to experience symptoms such as headache, dizziness, nausea and shortness of breath. Anyone experiencing these symptoms needs to leave the house immediately and call the fire department to report the symptoms.