Bogus source?

Dear Editor:

RE: Mask ‘discrimination’, July 16.

I would appreciate learning the scientific source of the claim, “It is a proven fact that when face coverings are worn, oxygen levels drop well below what is required by the OSHA and by oxygen depletion warning meters.”

Not sure how the “oxygen depletion warning meters” require anything, but anyway. What is the source of this “proven fact”?

Also curious why the newspaper article includes the above statement while the online version excludes this paragraph.

Jim Baxter, Guelph