Background and purpose: Elevated CO2 rate in a building affect the health of occupant. This document presents results of an experimental analysis conducted in 50 offices located in 12 buildings with different layer in Cameroon (Yaounde). This study took place in 2012, during the dry and the rainy seasons. The main goal is to show the influence of the building structure, the ventilation and the number of occupants on the CO2 concentration in buildings. The areas chosen were ventilated at 60%.

Materials and Methods: A questionnaire was distributed to occupants. The different values in terms of temperature, air speed, humidity, CO2 concentration and luminosity rate were measured simultaneously during working hours and without the occupants. The measurement took place while offices were naturally ventilated. Values obtained were analyzed and integrated.

Results: Painted buildings with glasses were more pollutant than those made with soil and wood. A mechanically controlled area was more comfortable but more pollutant than a naturally ventilated area.

Conclusion: The CO2 concentration changes exponentially when the number of people in a hall increased especially when there are smokers. For temperature ranged from 20.5°C to 28.8°C and the CO2 from 350ppm to 1450ppm, the average consumption of O2 by person varied between 0.0097cfm and 0.0162 cfm.