Not all of them are terribly dangerous, but at least some of them are. Artifact of Doom: The DTI has an entire vault way out on the edge of the Sol system where they secretly squirrel away various temporal knick-knacks to prevent them from being accidentally or maliciously activated, in keeping with their strict policy of non-intervention.In Watching the Clock, the temporal duplicate of Picard from 'Time Squared' is explained as a result of the Manheim Effect from 'We'll Always Have Paris', and all the Mysterious Travellers From the Future in various Trek series are on one side or another of Star Trek: Enterprise's Temporal Cold War.
The Arc Welding is particularly notable in Forgotten History, which links all of Captain Kirk's time-travel experiences (in the Original Series and the animated series) to create the story of the DTI's origins and early activities.
