In our continuing effort to document the terrifying threat of manhole explosions, a new entry: The Post says that a 30-ft. geyser of white hot steam erupted out of a manhole near the Newseum at about 5:30 p.m. on Sunday. Thirty feet! That’s big. No one appears to have been injured. The steam looks to have been the result of a failure of a bypass hose being used while repairs were being made to an…