Moderately toxic gas with no warning properties; decreases the ability of the blood to carry oxygen to the tissues.

The acute toxicity of carbon monoxide by inhalation is moderate. Carbon monoxide is a chemical asphyxiant that exerts its effects by combining preferentially with hemoglobin, the oxygen-transport pigment of the blood, thereby excluding oxygen. Symptoms of exposure to CO at 500 to 1000 ppm include headache, palpitations, dizziness, weakness, confusion, and nausea. Loss of consciousness and death may result from exposure to concentrations of 4000 ppm and higher; high concentrations may be rapidly fatal without producing significant warning symptoms. Exposure to this gas may aggravate heart and artery disease and may cause chest pain in individuals with preexisting heart disease. Pregnant women are more susceptible to the effects of carbon monoxide exposure. Since carbon monoxide is odorless, colorless, and tasteless, it has no warning properties, and unanticipated overexposure to this highly dangerous gas can readily occur.

Carbon monoxide has not been found to be carcinogenic in humans. This substance has shown developmental toxicity in animal tests. Chronic exposures to carbon monoxide at levels around 50 ppm are thought by some investigators to have a negative impact on