Tube failure -- what would happen in worst case?

There was a spectacular demonstration at a European HIFI show last summer, the whole room burned causing several 100K$ damage. This is a sign of BAD AMP DESIGN. I am old enough to remember when everything ran on tubes; a friend who is retired from AT&T recently told me that they use to put tube amps on the sea bottom for years at a time when undersea cables used them. A well designed tube amp SHOULD be able to be left on, but I wouldn't do so either. A lot of designers run their equipment right up to [or over] the edge of their capabilities. I have seen some fairly impressive failures in SS, which is what I generally use.