I'd use a circular saw, set the blade to the thickness of the board
so
you don't cut any pipes.
check for nails/screws first

How would he know the thickness to set the blade?


well it's likely to be 12mm or 18mm, start at 12mm maybe ?

assuming anyone is daft
enough to cut it whilst its down.


how else will he get it up if it's "nailed" down (the OP didn't say) ?
and what if he can't take the whole board up ?