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I was about 10 feet away from an unmasked stranger who had a coughing fit yesterday, This was indoors and my back was turned most of the 4 minutes when I was at this proximity. I never got closer than 8 feet and was double masked. Am I correct in assuming this would be considered low risk?
Unfortunately, the unmasked person who potentially was effectively generating large quantities of infectious particles presents a significant theoretical risk for exposure. This highlights that the masking procedure is intended for the wearer of the mask to prevent wide-spread dissemination of infectious particles into the air space surrounding the wearer of the mask. Wearing the mask is not as effective to prevent exposures from persons around you; in this instance you will need to both wear a mask and wear a face shield or eye protection (the exposed eyes are an important portal for infection). [wearing masks blocks the person from infecting others but does not prevent exposure to infections] The fact that this event occurred indoors (a poorly ventilated space) indicates that those infectious particles could have remained in the air for longer periods of time. The fact that you were at a distance larger than 6 feet or that the time of exposure was relatively short may not have significantly reduced the chances of exposure to infectious particles.
Let’s illustrate this concept another way. Imagine that you are in an indoor corridor lined up in single file with spacing of 10 feet between persons in this long corridor. As everybody is lined up facing forward, there is an air current that is pushing air in one direction from your front facing direction toward the back of the line. In this scenario imagine a person in the middle of the line is unknowingly infected and is unmasked. You are in this line for one hour. Due to the air current (which can be a very gentle air current), all persons in the lineup behind (downwind) of this infected person, during this one hour of exposure and for at least 100 feet or more (because there is no UV light to inactivate the virus) behind this infected person, may be exposed to the infectious particles disseminated from exhaled breath and carried for long distances in the air current. On the other hand, the people who are in the first half of the line (up wind) are spared from exposure from the infected person in line, because of the direction of flow of air current. In this scenario it is not about distance, it is about infected particles carried along in the air current. This is why outdoors is better than indoors where it is typically stagnant air and also because there is natural UV light outdoors which can inactivate the virus quickly. When indoors, we encourage good air exchanges (good ventilation); when possible opening windows, using fans to move air, using air filters (like HEPA filters), and UV light (to decontaminate viruses).
