Speaking more softly reduces transmission

TOKYO: More quiet zones in highrisk indoor spaces, such as hospitals and restaurants, could help to cut coronavirus contagion risks, researchers have said, after a study showed that lowering speaking volume can reduce the spread of the disease.

In efforts to rein in transmission, a reduction of 6 decibels (dB) in average speech levels can have the same effect as doubling a room’s ventilation, scientists said on Wednesday, in an advance copy of a paper detailing their study.

‘‘The results suggest that public health authorities should consider implementing ‘quiet zones’ in highrisk indoor environments, such as hospital waiting rooms or dining facilities,’’ wrote the six researchers from the University of California, Davis.

The World Health Organisation changed its guidance in July to acknowledge the possibility of aerosol transmission, such as during choir practice, or when in restaurants or fitness classes.

Microscopic droplets ejected while speaking evaporate to leave behind aerosol particles big enough to carry viable virus, the paper showed. An increase of about 35dB in loudness, or the difference between whispering and shouting, boosts the particle emission rate by 50 times.

Normal conversation is above the 10dB range, while ambient noise in restaurants is about 70dB.

‘‘Not all indoor environments are equal in terms of aerosol transmission risk,’’ lead researcher William Ristenpart said.

‘‘A crowded but quiet classroom is much less dangerous than an uncrowded karaoke bar where patrons are socially distanced but talking and singing over loud music.’’

The global death toll from the virus passed 900,000 on Tuesday, as worldwide cases topped 27.7 million.

An average of more than 5600 people die each day, according to Reuters calculations. — Reuters