Human speech creates long-lasting droplets

Study did not involve Covid-19 or any virus

Ordinary speech can emit small respiratory droplets that linger in the air for at least eight minutes and potentially much longer, according to a study published yesterday that could help explain why infections of the coronavirus so often cluster in nursing homes, households, conferences, cruise ships and other confined spaces with limited air circulation.

The report, from researchers at the National Institute of Diabetes and Digestive and Kidney Diseases and the University of Pennsylvania, was published in the Proceedings of the National Academy of Sciences. It is based on an experiment that used laser light to study the number of small respiratory droplets emitted through human speech. The answer: a lot.

“Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second,” the report states.

Previous research has shown large outbreaks of coronavirus infections in a call Centre in South Korea where workers were in proximity and in a crowded restaurant in China, and such events have led some experts to suspect that the highly contagious virus can spread through small aerosol droplets.

This new study did not involve the coronavirus or any other virus, but instead looked at how people generate respiratory droplets when they speak. The experiment focused on small droplets that can linger in the air much longer. These droplets still could potentially contain enough virus particles to represent an infectious dose, the authors said.