Our client contracted Clean Air Sciences, Inc. to monitor the work space where an employee worked at this desk for a full day and over several months during the winter. A portable gas heater was used to heat the space and the occupant complained of discomfort in the room after a short period of time had and concerns of carbon monoxide (CO) exposure. Monitoring over several hours found that the heater was not generating high carbon monoxide levels, but rather high carbon dioxide (CO2) levels, indicating very clean and complete combustion. If the levels had been reversed, a high risk of CO poisoning would have been present. Always ensure proper fresh replacement air is available to any space when using this type of combustion heater. June 2017 project.