In one memorable scene from the classic 1997 movie Titanic, third-class passengers are locked below deck as the ship sinks. According to the BBC, some of these gates were indeed locked during the ship's voyage.
However, this was not meant to prevent people from reaching lifeboats in the event of a disaster, but instead to follow American immigration laws — as officials worried about the potential spread of disease.
Nevertheless, the result was the same. Passengers in third-class were forced to navigate a trickier pathway to reach the boat deck, and there were no lifeboats stored in the third-class sections of the ship. And so those in third-class had a much lower survival rate than those in second or first.