Monitoring human exposures to upper-room germicidal ultraviolet irradiation

Area of Science:

• Environmental Health Engineering
• Infectious Disease Control
• Public Health

Background:

• Resurgence of tuberculosis and bioterrorism threats have increased interest in airborne infection control.
• Upper room ultraviolet germicidal irradiation (UVGI) is a key technology for disinfecting occupied spaces.
• Current UVGI system designs may limit effectiveness by adhering to overly conservative irradiance limits.

Purpose of the Study:

• To test the hypothesis that UVGI can be safely used at higher intensities.
• To determine if occupant UV exposure remains below safe thresholds even with increased upper-room irradiance.
• To evaluate the effectiveness of UVGI for airborne pathogen control.

Main Methods:

• Subjects wore personal photometers to record actual UV dose during normal activities.
• Measured UV doses were compared to hypothetical doses calculated from maximum eye-level irradiance.
• The study focused on irradiance levels above 6.5 ft to maximize germicidal effect while minimizing lower-room exposure.

Main Results:

• Observed UV doses in occupants were significantly lower than calculated maximums.
• Measured doses were one-third to over 100 times lower than predicted by irradiance measurements.
• The findings support the hypothesis that higher UVGI intensities are safe for occupants.

Conclusions:

• Current safety limits for UVGI systems may be unnecessarily restrictive.
• Optimizing UVGI intensity, alongside air mixing, can enhance germicidal effectiveness.
• UVGI is a viable and safe technology for reducing airborne infection transmission in various settings.