Ventilation rate assessment by carbon dioxide levels in dental treatment rooms

Abstract

Objectives: The purpose of the present study was to monitor and evaluate CO2 levels in dental operatories using a consumer-grade CO2 sensor and determine the utility and accuracy of various methods using CO2 levels to assess ventilation rate in dental clinics. We aim to find a practical tool for dental practitioners to conveniently and accurately monitor CO2 levels and assess the ventilation rates in their office in order to devise a pragmatic and effective strategy for ventilation improvement in their work environment. Methods: Mechanical ventilation rate in air change per hour (ACHVENT) of 10 dental operatories was first measured with an air velocity sensor and air flow balancing hood. CO2 levels were measured in these rooms to analyze the effects of ventilation rate and number of persons in the room on 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 ACHVENT and ventilation rates estimated by steady states CO2 model with low (0.3 L/min, ACHSS30) or high (0.46 L/min, ACHSS46) CO2 generation rates, by CO2 decay constants using dry ice (ACHDI) or baking soda (ACHBV), and by time needed to remove 63% of excess CO2 generated by dry ice (ACHDI63%) or baking soda (ACHBV63%). Results: ACHVENT varied from 3.9 to 35.0 with a mean of 13.2 ({+/-}10.6) in the 10 dental operatories. CO2 accumulation occurred in rooms with low ventilation (ACHVENT [≤]6) and more persons (n>3) but not in those with higher ventilation and less persons. ACHSS30 and ACHSS46 correlated well with ACHVENT (r=0.83, p=0.003), but ACHSS30 was more accurate for rooms with low ACHVENT. Ventilation rates could be reliably estimated using CO2 released from dry ice or baking soda. ACHVENT was highly correlated with ACHDI (r=0.99), ACHBV(r=0.98), ACHDI63%(r=0.98), and ACHBV63% (r=0.98). There were no statistically significant differences between ACHVENT and ACHDI63% or ACHBV63%. Conclusions: Dental operatories with low ventilation rates and overcrowding facilitate CO2 accumulations. Ventilation rates could be reliably calculated by observing the changes in CO2 levels after a simple mixing of household baking soda and vinegar in dental settings. Time needed to remove 63% of excess CO2 generated by baking soda could be used to accurately assess the ventilation rates using a consumer-grade CO2 sensor and a basic calculator.