Academic buildings are the main gathering places in universities and colleges. The crowd flow could cause a change in environmental parameters of buildings. In other words, the change in environmental parameters in buildings can be somewhat reflective of the crowd flow. Therefore, field measurements of the crowd flow and environmental parameters in an academic building at a university were conducted in this study. During the periods of 7:30–8:00 and 13:20–13:50, the average speed of the crowd was the highest, which was about 1.2 m/s; the CO2 concentration was low, which was about 750 ppm. In the periods of 9:20–9:50 and 15:10–15:40, the average speed of people walking in the opposite directions was the lowest, which is 0.42 m/s; however, the CO2 concentration could reach 1800 ppm. Test results showed that the variations of CO2 concentrations were inversely related to the average speed of the crowd in the evacuation passage, except for the periods of 7:30–8:00 and 13:20–13:50. Spatial separation and physical separation could be used in the management of personnel flow in the academic building. The results may provide reference for the management of the crowd flow in similar academic buildings of other universities.

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People ubiquitously produce CO2. The quantitative relationship between the CO2 concentration and pedestrian flow needs to be determined if the CO2 concentration is to be used to reflect pedestrian flow. Therefore, a field test was carried out to measure the CO2 concentration and pedestrian flow in an evacuation passageway of a densely populated building. The results show that the variation in the CO2 concentration always lags behind the variation in the pedestrian parameters. When pedestrians enter a building evacuation passageway over a long time span with high randomness, the quantitative relationships between the pedestrian density and CO2 concentration and between the pedestrian flow rate and CO2 concentration are not clear. When all the people in the building are required to leave at the same time, the relationships between the pedestrian density and CO2 concentration and between the pedestrian flow rate and CO2 concentration can be described quantitatively. The CO2 concentration can be taken as an early warning index to manage pedestrians in evacuation passageways of densely populated buildings. Two possible methods are provided to help provide early warnings in pedestrian management. These results are expected to provide new ideas for pedestrian statistics and pedestrian flow management in densely populated buildings.