The first study was conducted by two mathematicians from Loughborough University in the UK. They simulated the flight of droplets (“expiratory clouds”) when sneezing, taking into account various possible conditions.
In most simulations carried out by mathematicians, the droplet’s horizontal flight range exceeded two meters. The World Health Organization recommends keeping a distance of 1 meter from other people, the US Centers for Disease Control and Prevention – 2 meters.
Scientists have found that the cloud of moisture that comes out of the mouth when sneezing is sprayed like a toroidal vortex. There is a turbulent swirling of the cloud, then it circulates in the form of a torus (ring, donut). A similar phenomenon is observed in a nuclear explosion – the well-known “mushroom”.
Sneezing droplets can quickly rise to a height of more than four meters (the smallest droplets are higher). Scientists point out that at this altitude, ventilation can affect their further spread: the infected cloud can move unexpectedly far.
How the droplets spread is strongly influenced by the primary direction of the sneeze. If the head is tilted down, then, most likely, fewer drops will fly upward, the risk of spreading the infection will be reduced. In this regard, the authors of the study offer a new recommendation: when sneezing, you should tilt your head down.
In another study, which was published in the same journal, Japanese scientists showed why using a face shield without other protective equipment does not protect against COVID-19.
The reason for the ineffectiveness of the shields may be the phenomenon described above: clouds of droplets that form during sneezing form toroidal vortices (“nuclear mushrooms”). Such “bagels” can simply bend around the protective shield. Scientists have demonstrated this in a video that simulates a similar situation.