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John Z. Zhai

As the global pandemic developed, keeping adequate personal distance and using effective ventilation systems were emphasized to control the spread of COVID-19 – especially in confined spaces.

That is because social distancing avoids direct contact among people and reduces transmission of virus-carrying droplets from human respiration, while improved ventilation dilutes virus concentration in enclosed spaces.

Because of those dynamics in human activities and air movements, Professor John Zhai and his team wanted specific answers to questions like “what is the safest social distance” and “what is sufficient ventilation indoors?”

It was published online in July and in the journal in Novemeber 2020.  

Zhai, of the Department of Civil, Environmental and Architectural Engineering, said the paper considers the distributed particle sizes and associated virus output from typical human conversation, as well as the ventilation system effectiveness on the infection risk.

“The study indicated that 5.2 to 9.8 feet is a safe social distance when considering aerosol transmission of exhaled large droplets from talking, while this distance can be up to 26 feet if you are taking into account droplets of all sizes under a calm air environment,” Zhai said. “Our improved formula can help predict the probability of infection risk and determine appropriate ventilation air need for different indoor spaces such as classrooms or airplanes.”

Since publication, the work is among the most downloaded on the journal’s website. Zhai said his team is now developing a more detailed model that can predict spatial and temporal distribution of contaminant/virus in any built environment. The model will help estimate the infection risk and assess and improve new mitigating measures.

Indoor air quality is one of the primary research areas for the Zhai Lab. His team have conducted both experimental and modeling studies for a variety of applications in this field for decades. Other recent studies related to the pandemic include evaluating infection risks in various commercial buildings and developing proper mitigation strategies in public spaces, such as restaurants, by using portable air purifiers.