I’m Not Making This Up, You Know

The Daily Caller reports that LA County will hand out KN95 masks to Super Bowl fans. The county’s Covid policies require people at “outdoor mega events,” must wear masks at all times. That’s at any event with 5,000 or more people., and a mask must be worn regardless of a person’s vaccination status.


Covid Unmasked

I usually work out of my home office, but yesterday, I needed to test a piece of equipment in a lab at Goddard Space Flight Center. For months, masks have been required at Goddard in all indoor spaces when two or more people are in the same room. This rule was effective whenever Prince George’s County, Maryland, where Goddard is located, was tagged as red or orange for Covid infection rate by the CDC. Since May, Goddard was one of the very few places I have gone where a mask was required.

Yesterday, PG County had been recoded as blue by the CDC. That meant that vaccinated individuals were not required to wear masks at Goddard, so for the first time this year I saw the faces of most of my fellow workers on site.

The Physics of Filtering

When I was small child, our family lived in house without air-conditioning. We had screens on all the windows and an attic fan to cool the house. The gaps in the screens were small enough to prevent flies and mosquitos from entering the house. It would have been foolish to replace the screens with chain link fencing and expect that the bugs would still be kept out. A housefly has a wing span around 1/2 lnch, and the wires in chain link fencing are a couple of inches apart. The gap is about four times the size of a fly. A fly can easily pass through.

The gap between fibers in a typical cloth face mask is on the order of 2 to 3 micrometers. The coronavirus is on the oder of 0.3 micrometers.

The mathematics of the filtering is left to the Gentle Reader as an exercise.