Do Masks Make It Impossible to Breathe in Enough Oxygen?

In a viral video on Facebook, Jeff Neff, a candidate for Pennsylvania State Senate, measured the oxygen levels behind various masks and concluded that “No matter what you choose—head sock, neoprene-type fancy mask, cheap mask, N-95, the best available—none of them allow you to breathe in the required oxygen level.”

In the video, Neff used an MSA ALTAIR 5X Multigas Detector, a device produced by MSA Safety Inc., to measure oxygen levels behind different types of masks as he wears them. A typical atmospheric oxygen concentration level is about 21...