SpaceX Crew-1 members during spacewalk preparations

iss064e028065 (Feb. 1, 2021) — Clockwise from bottom right are, Expedition 64 Flight Engineers Soichi Noguchi, Michael Hopkins, Shannon Walker and Victor Glover during spacewalk preparations inside the U.S. Quest airlock. Hopkins and Glover are wearing masks breathing pure oxygen to purge nitrogen from their bodies before beginning their spacewalk. The pre-breathe protocol helps prevent a condition known as the “bends” that can occur when the body is exposed to different pressure environments.