Mask tip
by rob1 on Wed May 27, 2020 5:21 pm

Since a mask traps a significant amount of exhaled virus, and the risk you present to others is proportional to both the degree and duration of their exposure, there may be runs when it seems worth wearing a mask for quite a while.

But after a half hour or so, water vapor trapped in the mask makes it hard to inhale, since a flexible mask pulls itself up against your mouth and allows air through only a small portion of the mask. There's no problem exhaling because the mask puffs out and air passes out through its whole area.

A foam mesh sleeve, as used to protect fruit such as Asian pears, placed inside the mask holds it away from your mouth and ensures that most of the mask area is available all the time. The foam used for fruit seems to be closed cell polyethylene, it doesn't absorb water and can be washed with the mask. It tends to stay in place if the mask is pulled down when not needed, but could be stitched to the mask. ;)


Runners need much more space than 6 Feet
by wmac-admin on Sat May 09, 2020 10:43 pm

Ken is right! While running with others, the six foot rule is a poor guideline. The breath of a person ahead is entrained into that person's slipstream and persists well beyond six feet. In absence of a strong wind or at least a mild crosswind, the person behind runs into the breath of the person ahead, like railroad cars behind Thomas the Tank Engine. We need to learn to be as aware of the wind as is a deer.

The basic conclusion of the paper is that if you are running in the slipstream of another runner you should be 10 meters or more back. You can get the idea by looking at Fig. 12 in the preprint, "Towards aerodynamically equivalent COVID-19 1.5 m social distancing for walking and running", by B. Blocken, F. Malizia, T. van Druenen, T. Marchal:

Fig. 12 of Blocken preprint

Bert Blocken, the aerodynamics guy who wrote the paper, is in a group at Eindhoven University of Technology (in the Netherlands) that does some cool stuff ( about aerodynamics of bicyclists, as well as air flow in buildings.

For those technically inclined, here's a non-specialist overview of how droplets behave in air, as they diffuse, fall, and evaporate to smaller size: (just in case you were wondering...)

Be aware of the wind direction, visualize slipstreams, and keep 10 meters apart if not running into clean air! ;)

Runners need much more space than 6 Feet
by Ken S on Thu Apr 16, 2020 8:21 pm

read article! ... nough.html