MechEngr
..so you would need between 54 pounds and 144 pounds of strap tension to hold the mask on the person's face; not including the preload to keep from leaking out past the rubbery flesh of the face.
Just to try and tie up any remaining scepticism over pressure breathing and mask pressures from last night.. I've had time to check logbooks and we used to train under medical supervision for pressure breathing at 45K, using mil kit, individually fitted ( FWIW bone dome, attached mask with a rigid outer shell but no pressure jerkins or similar).
However that was then, this is now and these days I certainly wouldn't want to risk the same using a generic quick don one size "fits all" ( or doesn't
) Eros type mask as found in many flight decks..
Bottom line (for me) is that whilst you can protect yourself from a decompression quickly and reasonably adequately on the flight deck anybody in the cabin is very exposed, as Radgirl has pointed out..