Inactivation of Pathogens in Air Using Ultraviolet Direct Irradiation Below Exposure Limits.

Area of Science:

• Microbiology and Virology
• Environmental Health Engineering
• Photochemistry and Photobiology

Background:

• Airborne pathogens, such as SARS-CoV-2, pose significant public health risks.
• Conventional methods like ventilation and filtration have limitations in achieving high disinfection rates.
• Ultraviolet (UV) radiation is a known germicide, but safety concerns limit its application in occupied spaces.

Purpose of the Study:

• To introduce and evaluate a novel method called direct irradiation below exposure limits (DIBEL) for inactivating airborne pathogens.
• To demonstrate the efficacy of low-intensity UV radiation in achieving high equivalent air changes per hour (ACHeq) in occupied spaces.
• To assess the potential of DIBEL as a complementary or alternative strategy to conventional air disinfection technologies.

Main Methods:

• Utilizing UV-C light-emitting diodes (LEDs) with a peak wavelength of 275 nm for direct irradiation.
• Exposing occupied spaces to UV radiation doses below the accepted actinic exposure limit (EL).
• Measuring and calculating the equivalent air changes per hour (ACHeq) achieved by the DIBEL method.

Main Results:

• DIBEL achieved an ACHeq of 4 h⁻¹ for SARS-CoV-2 over an 8-hour period using UV-C LEDs at 275 nm.
• The method continuously inactivates existing and newly introduced pathogens, reaching 99% and 99.9% cumulative inactivation.
• Current UV-C DIBEL offers ACHeq values of 1-10 h⁻¹, comparable to or exceeding conventional methods, with future projections exceeding 100 h⁻¹.

Conclusions:

• Low-intensity UV radiation delivered below exposure limits (DIBEL) is an effective strategy for inactivating airborne pathogens.
• DIBEL provides high ACHeq values, offering a valuable addition to layered disinfection strategies, including upper-room UV germicidal irradiation and filtration.
• The method's simplicity, low cost, and unobtrusive nature make it a practical solution for enhancing indoor air quality and safety.