Carbon Monoxide Concentrations: What Do They Mean? (AEN-171)

ISU Extension Pub # AEN-171
Author: Thomas H. Greiner, Extension Agricultural Engineer
Department of Agricultural and Biosystems Engineering, Iowa State University.
August 1997

Carbon Monoxide Concentrations: What Do They Mean?

Carbon monoxide poisoning results from impaired oxygen delivery and utilization. The brain and heart are particularly susceptible. When CO is inhaled, it replaces oxygen on the hemoglobin molecule. Hemoglobin “prefers” carbon monoxide over oxygen by a factor of over 200 fold, so breathing even a small concentration of carbon monoxide greatly increases carbon monoxide in the blood. The more carbon monoxide in the blood, the less hemoglobin available to deliver oxygen to the body. Persons at health risk (the unborn, the sick, and the elderly) are at increased risk.

The amount of carbon monoxide in the blood is measured in terms of percent carboxyhemoglobin (carbon monoxide and hemoglobin). In the following table the percent hemoglobin is abbreviated HbCO.

The amount of carbon monoxide in the air is measured in terms of parts per million (ppm). Only a few ounces of carbon monoxide are required to raise CO concentrations in an entire house to dangerous concentrations.

When exposed to a given concentration of carbon monoxide in the air, the amount in the body depends primarily on the following:

* Concentration in the air. The higher the concentration, the greater the risk and the more quickly it will increase in the body to toxic levels.

* Duration of exposure. At low concentrations, it might take several hours for enough CO to be breathed into the body to be a health risk. At high concentrations, the levels in the body can be life-threatening in less than one minute.

* Respiration rate. Faster breathing increases the rate CO moves into (and out of) the body.

* Individual difference. Persons who smoke will already have carbon monoxide in their body and will be affected sooner. Persons who normally breath faster will typically reach higher levels of carbon monoxide in their blood more quickly.

Breathing fresh air removes carbon monoxide. Typically five and one-half hours of breathing fresh air cuts the carbon monoxide concentration in the blood by one-half. Breathing faster, breathing pure oxygen, or breathing pure oxygen under pressure, will significantly speed the removal of carbon monoxide from the blood. Faster removal can reduce health problems caused by carbon monoxide.

Concentrations that are not immediately life-threatening, and do not raise the carboxyhemoglobin levels significantly in a short-term exposure can have significant health effects during long-term exposures. Anyone exposed to carbon monoxide and experiencing health problems should immediately seek medical advice.

AEN-172, Carbon Monoxide Poisoning – Carbon Monoxide Concentrations Table, contains additional information about CO concentrations

Note: Residential carbon monoxide detectors are NOT designed to provide protection against low-level chronic carbon monoxide exposures for persons at risk.