Ventilation Assessment by Carbon Dioxide Levels in Dental Treatment Rooms

Abstract

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.

Keywords: COVID-19; air filter; baking soda; dentistry; indoor air quality; pathogen transmission.

Figure 1.

Carbon dioxide (CO₂) levels during dental treatment procedures in operatories with low and high mechanical ventilation. (A) Significant CO₂ accumulation occurred in a room with low ventilation (air change per hour [ACH] = 3.9) and multiple persons in the room during clinical teaching activities for dental implant surgery. CO₂ level is associated with ventilation rate in rooms with the same number of persons. Peak CO₂ level reached 1,100 ppm in the room with 3.9 ACH (B) but stayed under 700 ppm in the rooms with 35 ACH (C).

Figure 2.

The 24-h continuous measurements of carbon dioxide (CO₂) levels in 10 dental treatment rooms with various ventilation rates. CO₂ accumulation occurred in rooms with lower ventilation rates (air change per hour [ACH] ≤6). CO₂ levels stayed under 800 ppm in rooms with a higher ventilation rate and lower number of persons. CO₂ level in nonworking hours is close to that of outdoors at 400 ppm in all rooms.

Figure 3.

Correlations between ventilation rate and carbon dioxide (CO₂) clearance in dental treatment rooms. (A) CO₂ decay constants by dry ice and (B) CO₂ decay constants by baking soda and vinegar. (C, D) Correlations between mechanical ventilation rates measure by airflow (ACH_VENT) and ventilation rates measured by CO₂ decay using dry ice (ACH_DI) and baking soda and vinegar (ACH_BV) in dental treatment rooms. Rooms with high mechanical ventilation rates showed a rapid decrease of CO₂ concentrations over time (A, B). Both ACH_DI and ACH_BV are linearly correlated with ACH_VENT (C, D). (E, F) Correlations between ventilation rate by airflow (ACH_VENT) and ventilation rates by time needed to reach 63% removal of excess CO₂ generated using (E) dry ice (ACH_DI63) and (F) baking soda and vinegar (ACH_BV63).