Assessing Mitigation Strategies to Reduce Potential Exposures to Indoor Particle Release Events

Airborne transmission is a major concern for many infectious pathogens, including the novel coronavirus. Ventilation is the principal engineering method used to control airborne health hazards in buildings. Understanding potential air pollution hazards are a particular concern for highly populated indoor environments, such as workplaces and classrooms. This study discusses the results of ventilation testing in a university classroom which contains two fan coil units as the primary HVAC system. A particle nebulizer was used to release aerosol particles into the air, and multiple particulate measuring devices were placed strategically around the room to measure the particle concentration over time. An exponential particle decay rate is determined from the data and converted to a particle concentration half-life, which ranged from over 60 minutes down to under 10 minutes. We then assess how quickly the particles were removed by ventilation systems with varying conditions, including the addition of both high-and low-cost portable mitigation devices into the classroom. Our results indicate that a low-cost unit, made of a simple box fan with a MERV13 filter taped to it, may perform as well at removing particles from a room as a high-cost HEPA filter unit, owing to a tradeoff between filtration efficiency and the number of air changes per hour. As is observed in numerous other studies, the particle concentration half-life in each classroom setup decreases as the mechanical air changes per hour increases from about 1.3 to 9.3. These results are used to evaluate the potential personal exposure risk associated with various classroom ventilation setups. Our results indicate that, when compared to running the fan coil units on low fan speed, operating on a high fan speed reduces potential exposure by 22% and using a portable HEPA filter in the room reduces potential exposure by 66%.