i havent thought of air exchange. our basement is pretty big, but if one makes a small protected enclosure inside the basement i reckon an air exchange system would be helpful, id like to hear what you work out.
we have the 3 windows above the ground level and a door that is at ground level with a walk way leading outside, im thinking the walkway can be tarped to protect the entryway from fallout dust. the windows will need to be sandbagged or something adn the door needs to be covered and maybe move the freezer in front of it for some shielding.
in the center of our basement are 3 small rooms, laundry, small hallway and furnace room, so im thinking of that as a temp location for best protection aided with some extra protection built up or stacked around for further shielding. overhead is still the weak point im thinking.
if i could convince dh, id start filling sandbags and stack them outside on the half of the walls exposed above ground (its all under a big porch anyway), then berm with some earth and even lay some sod over it so the sandbags wont be exposed. but im not getting far in him letting me do it. but id sure hate to have to do it at the last minute, i dont like leaving too much to be done at the last minute for anything.
like alot of other folks, we dont have funds to make the place a real fallout shelter, we gotta use what we got--- in the time allowed after some nuke goes off.