Gates Package — page 985

n's head to simulate the nasal ile will stop a large majority of the droplets that are a chief source of transmission for COVID and other coronaviruses. Whereas just about any material covering your mask will do a pretty good job of source control, protecting yourself from someone else's germs is a whole other matter. Any mask will give you some security, but the level of protection you get depends greatly on the material and the way the mask fits your face. This is because now you want to capture both the larger droplets, which are short-lived, and the smaller aerosols, which can linger longer and travel farther. (By the way, some of the experiments used to test this kind of thing are wonderfully creative. One research team27 padded the inside of mannequin's head to simulate the nasal cavities of a human skull, set it at a height of 5 feet 8 inches--near the global median height for men--and hooked it up to a smoke machine and a pump. Then they measured how far the droplets traveled when the mannequin coughed in various scenarios: with its mouth uncovered, with its mouth covered by a bandana made from a T-shirt, with a folded handkerchief, and finally with a stitched mask. Another group of researchers set two mannequins next to each other, simulated a cough from one of them, and then measured how many particles made it from the cougher to coughee.)28 As long as your mask fits snugly, then a decent rule of thumb is that the denser the material, the more filtration you get. A mask cut from a T-shirt provides substantial protection, but not as much as a surgical one, and the surgical one doesn't protect you as much as an N95. A few numbers from one study that looked at the effectiveness of different masks:29 If two people are talking to each other at a distance of six feet, and if one of them is infected with COVID, the odds that the other will be infected within a few minutes are as high as 90 percent. If they both