In 3 to 5 hours the same concentration can lead to unconsciousness and death. Physical exertion, with an accompanying increase in respiration rate, shortens the time to critical levels by 2 or 3 fold. Respiratory capacity decreases and the risk of heart attack increases at levels well below 50 ppm. The EPA level of 9 ppm appears to be a reasonable limit in homes. Flu-like symptoms decrease while away from the house.
Illness is present when gas appliances are in use.
Excess moisture on the interior of windows. They should immediately be moved into fresh air and medical authorities consulted. Treatment depends on the amount of carbon monoxide in the bloodstream and assessment of the patient. Often oxygen is administered. In severe cases, patients are treated in a hyperbaric chamber.