Carbon dioxide is normally a constituent of
exhaled breath, it is also a common combustion byproduct. It is comparably
nontoxic and it is a good cross sensitive gas for odor and a reliable indirect
measure of inadequate ventilation.
The typical outdoor CO2 is 300 – 400ppm. It
is usually greater indoor. As a guideline, according to ASRAE standard 62-1989,
it is recommended that indoor CO2 concentration should not exceed 1000 ppm. At
1000ppm usually indicate inadequate ventilation or other contaminants in the
building, and occupants usually complain of eye irritation, fatigue, headaches
and throat irritation.