AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Evaporation and Transport of Bodily Fluid Aerosol Droplets
JONATHAN THORNBURG, Quentin Malloy, James Hanley, Jerome Gilberry, Howard Walls, RTI International
Abstract Number: 88 Working Group: Environmental Fate of Infectious Aerosols
Abstract Researchers have determined the typical aerosol generated by a coughing person, such as an Ebola infected patient, has a size distribution spanning 1 to 500 micrometers with a mass median diameter of approximately 100 micrometers. The apparently large size of the expelled droplets leads to the assumption that rapid gravitational settling to surfaces will occur. However, spaces with the proper environmental and ventilation conditions may cause aerosol droplets to evaporate and their airborne residence time increases substantially. The aerosol droplet evaporation rate as a function of particle and environmental conditions is important for designing the proper safety procedures.
We used published aerosol equations to calculate droplet evaporation and transport. The equations accounted for impurities in the aerosol droplets, and aerosol dynamics in the Stokes and non-Stokes regimes. Expected values for temperature, RH, and air velocity within an isolation system were used as inputs. We modeled cough events at 1 or 1.5 meters above the floor. Horizontal air velocities in the direction of airflow of 250 cm/s and 13 cm/s were selected.
Modeling results identified the drop sizes that will evaporate to minimum diameter before depositing on a surface. At 250 cm/s and 1 meter height, the maximum drop size that will evaporate to a cluster of biological agent before traversing a horizontal distance of 3 meters is 26 micrometers. Cough droplets between 26 to 155 micrometers will completely traverse 3 meters before traveling 1 meter vertically and depositing. Cough droplets larger than 155 micrometers will vertically travel 1 meter and deposit on the floor before traversing 3 meters. As the air velocity decreases, the maximum drop size that will evaporate increases before gravitational deposition occurs. Our modeling showed expelled bodily fluid droplets may travel a significant distance before depositing onto a surface or remain an aerosol because of evaporation.