Funny I thought it was CERN's job to describe what would happen. I was just having a laugh about it "burrowing" when that really means destroying all atoms and molecules in its path. I do trust them enough to expect a safety cut off switch to trigger, or that any misalignment in of itself shuts down the ion flow. My personal non-scientific expectation would be that at worst it would travel a few centimeters. Even at full strength there aren't that many ions in use in comparison to the atoms of the surrounding rock and comparable density. So even a significant time before shut off, say the emergency shut off isn't triggered and one of the scientists has to kill it manually, of 5 seconds or so maximum, shouldn't pose any serious danger to the public or planet. If it was truly a concern then I don't think we'd be hearing all about the dangers mBH's and stranglets.
Or maybe I should move this to the conspiracy theory discussions!
mBHs and stranglet dangers are just an easily debunked distraction to prevent us learning they could cut a hole through the planet!!!