Bread-Bakers v106.n020.7

Put a large plastic bag around the bread & pan, and blow some air 
into it to inflate it so the plastic is well away from the rising 
dough, and seal it with a loose knot, bag clip, or twist tie.  It 
should be sealed loosely enough that some gas can escape without 
causing the bag to burst.

And the yeast is working anaerobically--without air--inside the 
dough. It does not need fresh air as it is fermenting.