Gorilla trekking is considered very safe. Dangerous incidents are virtually unheard of. Visitors are taken to habituated gorilla troops by experienced park rangers. These gorillas see people every day and they've learned that people are no threat to them. They mostly ignore humans although young gorillas might sometimes show some curiosity.
Mountain gorillas are, in essence, gentle giants. They show little aggression toward each other and their overall vibe is very peaceful.