Average outdoor carbon dioxide levels are typically 300 to 500 ppm. (6) Use colormetric detector tubes or other direct-reading instruments calibrated and operated according to the manufacturer's instructions for measuring carbon dioxide concentrations.
(Average outdoor carbon dioxide levels; are typically; 300 to 500 ppm) (other direct-reading instruments; calibrated; )
Average outdoor carbon dioxide levels other direct-reading instruments
are typically calibrated
300 to 500 ppm