title: Influence of Bioaerosol Source Location and Ceiling Fan Direction on Eggcrate Upper-room Ultraviolet Germicidal Irradiation.
abstract: BACKGROUND
  Eggcrate upper-room ultraviolet germicidal irradiation (UVGI), an engineering control method for reducing the airborne transmission of infectious diseases, was recently developed as an alternative to conventional upper-room UVGI using conventional louvered fixtures. A UV screen, which is composed of open-cell eggcrate panels supported in a frame designed for a conventional suspended ceiling, was used to minimize UV radiation in the lower room. A ceiling fan, which was blowing upward directly above the microbiological source, provided vertical air exchange between the upper and lower room. This system has been shown to be significantly more effective than conventional upper-room UVGI.
  
  
  METHODS
  In the present study, the microbiological source location and the airflow direction due to the ceiling fan were varied in order to evaluate their impact on germicidal efficacy.
  
  
  RESULTS
  The test results clearly showed that placing an aerosol source directly underneath an upward blowing ceiling fan produces the maximum efficacy.
  
  
  CONCLUSIONS
  The likely explanation for this outcome is that the fan sucks the microorganisms emitted by the source into the UV beam before being mixed with the air in the room. This is somewhat analogous to local exhaust ventilation in which the contaminant is removed prior to being mixed with the air in the room. Thus, when possible, the ceiling fan should be blowing upward and directly above the source. However, for experimental testing, the source location should be varied in order to access the range of germicidal efficacies that can be expected.
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA.
authors.forename: Sumayah F
authors.initials: SF
authors.lastname: Rahman
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA.
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Rudnick
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA.
authors.forename: Sonya P
authors.initials: SP
authors.lastname: Milonova
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: McDevitt
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA ; Department of Medicine, Division of Global Health Equity, Brigham and Women's Hospital, Boston, MA, USA ; Department of Global Health and Social Medicine Harvard Medical School, Boston, MA, USA.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Nardell
keywords: Airborne disease transmission; air disinfection; air mixing; bioaerosol; eggcrate; infection; upper-room ultraviolet germicidal irradiation; whole ceiling ultraviolet germicidal irradiation system