The size of the drops varies depending on how and where they are produced within the airways. While cough generates the most drops, research has shown that just two to three minutes of talking can produce as many drops as a cough.
Droplets that are smaller than 5 microns can remain suspended in the air for many minutes to hours because the effect of air drag relative to gravity is great. In addition, the water content of the virus-carrying droplets evaporates while in the air, decreasing their size. Even if most of the liquid evaporates from a virus-laden droplet, the droplet does not disappear; it just gets smaller, and the smaller the drop, the longer it will remain suspended in midair. Because smaller diameter drops are more efficient at penetrating deep into the lung system, they also have a much higher risk of infection.
WHO guidelines suggest that RNA from the virus found in tiny droplets was not viable in most circumstances. However, early research on the SARS-COV-2 virus has shown that it is viable as an aerosol for up to three hours.
Do the masks protect from the transmission of aerosols?
Facial coatings and masks are absolutely necessary for protection against the transmission of aerosols. They serve a dual purpose.
First, they filter the air expelled by an individual, capture respiratory droplets, and therefore reduce the risk of exposure to others. This is particularly important since they are more effective in capturing larger drops that are more likely to have large amounts of virus encapsulated within them. This prevents larger drops from directly affecting someone or evaporating to a smaller size and circulating in the air.
They also reduce the speed of the air puff produced by sneezing, coughing, or talking. Decreasing the speed of the expelled air reduces the distance that the drops are initially transported to the person’s surroundings.
However, it is important to realize that the protection provided by face masks and coatings varies depending on the material they are made of and how well they fit. However, wearing face covers to decrease the risk of airborne exposure is critical.
Is keeping your distance safe enough?
The recommendation to maintain a two-meter separation is based on a study by WF Wells in 1934, which showed that an expelled drop of water falls to the ground or evaporates, at a distance of approximately 2 meters. However, the study did not take into account the fact that after evaporation of the water into a virus-laden droplet, the nucleus of the droplet remains, thus still posing a risk of infection in the air.
Consequently, while staying away from others reduces exposure, it may not be sufficient in all situations, such as in closed, poorly ventilated rooms.
How can I protect myself from indoor sprays?
Strategies to mitigate airborne exposure are similar to strategies to stay dry when it rains. The longer you stay in the rain, and the more it rains, the wetter you will be. Similarly, the more drops you are exposed to and the longer you stay in that environment, the greater the risk of exposure. Therefore, the mitigation risk is based on decreasing levels of aerosol concentration and exposure time.
Aerosol concentrations can be reduced with increased ventilation, although recirculation of the same air should be avoided unless the air can be effectively filtered prior to reuse. When possible, open doors and windows to increase the flow of fresh air.
Decreasing the number of emission sources (people) within a space and ensuring that facial covering is used at all times can further decrease concentration levels.
Methods can also be used to deactivate the virus, such as germicidal ultraviolet light.
Finally, reducing the amount of time you spend in poorly ventilated and crowded areas is a good way to reduce the risk of airborne exposure.