Personally I just loot the whole place as it's burning, so don't really mind being on fire since I do it with my own character or Karlach who are resistant to fire (both are Zariel Tieflings)
BUT thankfully Larian now made it so that the place is no longer on fire once all the people are saved and leave for Baldur's Gate
As for the hammer's damage, it's
1d4 Thunder damage on jump.
