Occupant UV exposure measurements for upper-room ultraviolet germicidal irradiation

• An 80° field of view tube should be used on flat UV-C sensors for safety measurements
• The FOV tube reduced lower room irradiance readings by 18–34%.
• Lower readings allow more UV-C radiation without compromising occupant safety.
• Recommendations are made to standardize lower room irradiance measurement techniques.

The threshold limit value (TLV) guideline for ultraviolet (UV) radiation specifies that irradiance measurements to ensure occupant safety be taken over an angle of 80° at the sensor. The purpose of this study was to evaluate the effect of an 80° field of view (FOV) tube on lower room UV-C irradiation measurements.Measurements were made in an experimental chamber at a height of 1.73 m with and without an FOV tube. The FOV tube reduced the lower room irradiance readings by 18–34%, a statistically significant reduction compared to the bare sensor.An 80° FOV tube should be used for lower room irradiance measurements to comply with the TLV guideline. The resulting lower readings would allow more UV-C radiation in the upper room without compromising occupant safety. More UV-C radiation in the upper room could increase efficacy of UVGI systems for reducing transmission of airborne infectious diseases.In addition, recommendations are made to standardize lower room irradiance measurement techniques.