Ventilation Assessment by Carbon Dioxide Levels in Dental Treatment Rooms

It is important for dental care professionals to reliably assess carbon dioxide (CO2) levels and ventilation rates in their offices in the era of frequent infectious disease pandemics. This study was to evaluate CO2 levels in dental operatories and determine the accuracy of using CO2 levels to assess ventilation rate in dental clinics. Mechanical ventilation rate in air change per hour (ACH(VENT)) was measured with an air velocity sensor and airflow balancing hood. CO2 levels were measured in these rooms to analyze factors that contributed to CO2 accumulation. Ventilation rates were estimated using natural steady-state CO2 levels during dental treatments and experimental CO2 concentration decays by dry ice or mixing baking soda and vinegar. We compared the differences and assessed the correlations between ACH(VENT) and ventilation rates estimated by the steady-state CO2 model with low (0.3 L/min, ACH(SS30)) or high (0.46 L/min, ACH(SS46)) CO2 generation rates, by CO2 decay constants using dry ice (ACH(DI)) or baking soda (ACH(BV)), and by time needed to remove 63% of excess CO2 generated by dry ice (ACH(DI63%)) or baking soda (ACH(BV63%)). We found that ACH(VENT) varied from 3.9 to 35.0 in dental operatories. CO2 accumulation occurred in rooms with low ventilation (ACH(VENT) <= 6) and overcrowding but not in those with higher ventilation. ACH(SS30) and ACH(SS46) correlated well with ACH(VENT) (r = 0.83, P = 0.003), but ACH(SS30) was more accurate for rooms with low ACH(VENT). Ventilation rates could be reliably estimated using CO2 released from dry ice or baking soda. ACH(VENT) was highly correlated with ACH(DI) (r = 0.99), ACH(BV) (r = 0.98), ACH(DI63%) (r = 0.98), and ACH(BV63%) (r = 0.98). There were no statistically significant differences between ACH(VENT) and ACH(DI63%) or ACH(BV63%). We conclude that ventilation rates could be conveniently and accurately assessed by observing the changes in CO2 levels after a simple mixing of household baking soda and vinegar in dental settings.