Poor ventilation can spread COVID indoors

April 7, 2021-Insufficient ventilation could have caused COVID-19 to be infected in the air at a restaurant in Guangzhou, China, affecting 10 people in three families. New research Was announced in Building and environment..

To prevent the spread of the coronavirus, researchers write that indoor spaces need to prevent overcrowding, open windows and doors, and ensure proper air distribution.

“First-class health authorities have recognized the importance of airborne transmission in special environments since October 2020,” they write. “But the effective minimum ventilation to avoid airborne propagation remains unknown.”

The research team analyzed outbreaks in Guangzhou related to three unrelated families. Local health officials learned that the family had lunch at the same restaurant during the Chinese New Year on January 24, 2020. A family of three was sitting at a table adjacent to a crowded section of the restaurant, and the person at the middle table began to experience symptoms later that day in Index COVID-19 cases. During the next two weeks, the other nine members of the three families were positive.

The family of three had never met before and had no close contact except sitting close to each other in a restaurant during a meal, some sitting back to back. None of the restaurant workers at the other 15 tables and the other 68 patrons were infected with the virus.

The research team obtained video recordings and seating arrangements from the restaurant and investigated the restaurant’s air conditioning system across the facility’s five zones. Using the original table settings, they tested the dispersion of warm tracer gas, which acts like an exhaled virus droplet, to simulate the spread of droplets in a restaurant. They found that the measured ventilation rate was 0.9 L / s per person, which was lower than the recommended standard.

It turned out that the seating area where the family of three was sitting was covered with one air conditioner. Simulations showed that droplets exhaled by indexers rose into the air and were carried by air conditioning to other tables. The droplets also reached other nearby tables, but were dispersed by the other four air conditioners in the room. The researchers write that the three affected tables were in a recirculation zone, a bubble, with a high concentration of droplets.

Researchers write that patrons are at increased risk of becoming infected with COVID-19 if they are exposed to higher concentrations of droplets and longer exposures. The three families shared the same space for 53-75 minutes. While the infected were present, restaurant workers had shorter exposure times in the recirculation zone. The authors write that this can explain why none of them tested positive. In addition, patrons at other tables nearby had less overlap time with infected individuals.

Ultimately, researchers concluded that the polluted recirculation bubble did more than just explain the outbreak. Poor ventilation, lack of outside air, and close proximity between the tables seemed to contribute to the droplet dispersal of the infected. The restaurant was crowded due to Chinese New Year and tables were added to accommodate more customers.

“Our results do not indicate that long-range aerial propagation of SARS-CoV-2 can occur in any indoor space, but that it can occur in a congested, poorly ventilated space. It is important to note that. “

“A sufficiently high ventilation flow reduces the contribution of airborne propagation to very low levels, but a low ventilation flow leads to a relatively high contribution of the aerosol to permeation,” they added.