Carbon dioxide (CO2) is a colorless gas, odorless, approximately 1.5 times heavier than the air and may cause asphyxiation. It is one of the most common contaminants of the internal environment and because the main source of this gas is a human.
Carbon dioxide concentration is measured in ppm (parts per million) or in %. Ppm unit means one particle of a given substance for 999 999 other particles, ie one part in a million.
The so-called Pettenkofer criteria (Pettenkofer 1858), which sets the maximum level of CO2 in the interiors and residential premises where a person feels still comfortable, is 1000 ppm (0.1%). This value was also assumed by the international company ASHRAE (Professional company with more than 50 thousand members engaged in the field of building technology and building systems with the specialization on heating, air conditioning and refrigeration. It supports the technical education, it participates in the certifications and standardization, it publishes a magazine ASHRAE Journal, it publishes annotations of the research news and information about conferences.)
To determine the actual values of CO2 in the places where people spend most of the time, our company has placed an air quality sensors into two classes of a kindergarten classes, to one class of elementary school and two offices.
Values measured in the kindergarten were not as high as expected. It was the measurement in two classes of equal size 8 x 7 m, where stayed a group of 24 children an teachers. Because the area of the rooms was relatively large where children stayed, they produce lower amounts of CO2, the rooms were quite ventilated and in addition children often were outside these rooms (morning walk, lunch and sleep after lunch), the value of CO2 rarely exceeded the limit of 2000 ppm.
The measurement at the primary school in 1. grade (ie children at the age of 6-7 years) in the class of size 8.5 x 9 m). Class was thus more than in a kindergarten, there were about 26 children and only with small breaks when this class is not ventilated at an acceptable concentration of CO2. Day values thus commonly exceeded 2,000 ppm and several times reached the value of 3000 ppm. This may explain the frequent fatigue and inattention of children in the classroom.
The measured values were lowest in the office. This is due to the ventilation system, which is implemented in the company. In addition, due to the relatively large room (6 x 7,5 m) with high ceilings and low number of workers in the room (5).