Industrial hygienists, people who study how to protect ourselves from airborne chemicals and infectious agents. they determined based on the cdc s data that an infectious dose can occur in 15 minutes, meaning enough virus in a room for me to breathe in, just like if it were sig rate smoke, where i d get infected. they did the work along with data from nye ash who showed if you wear a face covering, you get five additional extra protection, surgical mask is ten minutes, if you wear an n95 respirator, 2.5 hours, and one tightly face fitted may get up to 25 hours of protection. you tell me how you want to parse that out? if you were driving an old car and it only had an old seatbelt, wear it. if you have one with a body harness, air bags, had shard