Introduction: Radon (Rn) is a radioactive natural gas widespread in the earth's crust. It travels towards the surface with the soil air and, if the building envelope in contact with the ground is not tight, accumulates in the basement and ground floor. Carbon dioxide (CO2) is present in the atmosphere and acts as a greenhouse gas. It is also produced during cellular respiration and therefore accumulates in closed spaces. Rn and CO2 in elevated concentrations have adverse effects on health, but on the other hand are reliable indicators of room ventilation. In this research, we measured Rn and CO2 concentrations in the air of three elderly care homes (DSO), located in three different areas, concerning the radon risk map for the presence of Rn in buildings: on low (DSO-N), moderate (DSO- Z) and high (DSO-V) risk area. Purpose: In the selected premises of the DSO, we studied the dynamics of Rn and CO2 in the air as risk factors for health; especially from the point of view of the location of the building, its construction-technical characteristics and ventilation systems, as well as the specifics of the users. By calculating the effective doses received by exposure to Rn (and its progeny, RnP) in the air, we assessed the impact on the health of employees and residents. Experimental: Rn and CO2 concentrations were measured in the cold and warm half of the year, from 2021 – 2022. First, we measured the instantaneous Rn concentrations in unventilated rooms in the morning, when the values are generally the highest. Based on the instantaneous Rn concentrations, we selected the premises for further continuous measurements of Rn and CO2 concentrations over several weeks. When visiting the buildings, we recorded their construction and technical characteristics in the evaluation sheet. We paid particular attention to the search for potential entry points of Rn to the rooms. The tightness of the building envelope was checked by calculating the rate of air infiltration through the building envelope into the building, based on the continuous measurements of CO2 concentration. From the average Rn concentrations, we calculated the annual effective doses received by employees and residents in each DSO. Results: The average Rn concentrations (Bq m–3) in the warm/cold half of the year were as follows: 54/185 in DSO-N, 91/60 in DSO-Z and 176/160 in DSO-V. The total exceedings of the Rn limit concentration of 300 Bq m–3 in the warm/cold half of the year were as follows: 5/17 in DSO-N, 1/4 in DSO-Z and 19/39 in DSO-V. Each DSO has a different ventilation scheme; they ventilate least often in DSO-N, more often in DSO-Z and most often in DSO-V. The average CO2 concentrations (ppm) reflect the occupancy of the premises and were the following in the cold half of the year: 543 in DSO-N, 619 in DSO-Z and 458 in DSO-V. The total exceedings of the CO2 limit concentration of 1000 ppm were in the cold half of the year as follows: 7 in DSO-N, 21 in DSO-Z and 0 in DSO-V. The average yearly effective doses (mSv) of employees/residents are as follows: 0.54/0.02 in DSO-N, 0.45/0.29 in DSO-Z and 1.15/0.21 in DSO-V. Discussion and conclusion: Rn concentrations reflect more room ventilation than risk areas on the radon map or building construction-technical characteristics. The CO2 concentrations further confirm the different room ventilation schemes, which is sufficient in DSO-V, but it would be necessary to increase it in DSO-N and DSO-Z. Satisfactorily low CO2 concentration and elevated Rn concentration in the air of one of the DSO-V rooms indicate a strong source of Rn entering the room from the sewage audit shaft. In this room, the concentration of Rn in the morning most often exceeds the limit value; therefore, we recommend remediation. The effective doses are higher in the cold than in the warm half of the year, but they are not worrying. The effective doses will decrease with more frequent ventilation of the premises in DSO-N and DSO-Z. If the Rn concentration in the room of the DSO-V, where the employee receives a yearly effective dose of 2.19 mSv, were reduced with appropriate remedial measures, the effective dose would decrease too.
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