Gents! Many thanks to all of you for your input. I would not have
thought of approaching the problem from the point of view of either
replacing the nails with screws or bracketing the popped nails with
screws on either side.

Think I may go ahead with putting some flooring up there anyway just
to make it a bit easier for servicemen to get around...and reduce the
possibility of one of them putting his foot through my ceiling!

So...planks and not particleboard???

bob