The effectiveness of an air cleaner in controlling droplet/aerosol particle dispersion emitted from a patient's mouth in the indoor environment of dental clinics

Abstract

Dental healthcare workers (DHCWs) are at high risk of occupational exposure to droplets and aerosol particles emitted from patients' mouths during treatment. We evaluated the effectiveness of an air cleaner in reducing droplet and aerosol contamination by positioning the device in four different locations in an actual dental clinic. We applied computational fluid dynamics (CFD) methods to solve the governing equations of airflow, energy and dispersion of different-sized airborne droplets/aerosol particles. In a dental clinic, we measured the supply air velocity and temperature of the ventilation system, the airflow rate and the particle removal efficiency of the air cleaner to determine the boundary conditions for the CFD simulations. Our results indicate that use of an air cleaner in a dental clinic may be an effective method for reducing DHCWs' exposure to airborne droplets and aerosol particles. Further, we found that the probability of droplet/aerosol particle removal and the direction of airflow from the cleaner are both important control measures for droplet and aerosol contamination in a dental clinic. Thus, the distance between the air cleaner and droplet/aerosol particle source as well as the relative location of the air cleaner to both the source and the DHCW are important considerations for reducing DHCWs' exposure to droplets/aerosol particles emitted from the patient's mouth during treatments.

Figure 1.

Measured data of the air cleaner's removal efficiency.

Figure 2.

Schematic of the dentist office in case 0.

Figure 3.

Comparison of average fates of droplets/aerosol particles calculated with an initial velocity of 1 m s⁻¹ (white bars) and 30 m s⁻¹ (black bars; 20 µm in case 0).

Figure 4.

Velocity distribution for each case at X = 2.2 m. (a) Case 0, (b) case 1, (c) case 2, (d) case 3 and (e) case 4. Scale bar, (a) 0.1 m s⁻¹; (b–e) 0.5 m s⁻¹.

Figure 5.

Droplet/aerosol particle dispersion near the breathing zone of the DHCW (0.3 µm). (a) Case 0, (b) case 1, (c) case 2, (d) case 3 and (e) case 4.

Figure 6.

Percentage of droplets/aerosol particles entering the breathing zone of the DHCW. White bar, 0.3 μm; light grey bar, 0.5 μm; dark grey bar, 1 μm; black bar, 2 μm; striped bar, 10 μm; checked bar, 20 μm.

Figure 7.

Percentage of droplets/aerosol particles reaching the body surface of the DHCW. White bar, 0.3 μm; light grey bar, 0.5 μm; dark grey bar, 1 μm; black bar, 2 μm; striped bar, 10 μm; checked bar, 20 μm.

Figure 8.

Percentage of droplets/aerosol particles removed by the air cleaner. White bar, 0.3 μm; light grey bar, 0.5 μm; dark grey bar, 1 μm; black bar, 2 μm; striped bar, 10 μm; checked bar, 20 μm.

Figure 9.

Percentage of droplets/aerosol particles trapped by the patient (either the body surface or the face). White bar, 0.3 μm; light grey bar, 0.5 μm; dark grey bar, 1 μm; black bar, 2 μm; striped bar, 10 μm; checked bar, 20 μm.

Figure 10.

General zoning map for guiding the position of an air cleaner in dental clinics. The grey square represents the dental operation zone. Arrows indicates the direction of airflow from the cleaner. Pentagram represents the general best position of the air cleaner in this case. Influence of the dental operation process; poor droplet/aerosol particle controlling effect; influence of the dental operation process; good droplet/aerosol particle controlling effect; do not influence the dental operation process; poor droplet/aerosol particle controlling effect; do not influence the dental operation process; good droplet/aerosol particle controlling effect; do not influence the dental operation process; good droplet/aerosol particle controlling effect.