1 Answer

Researched from wikipedia.

As I understand it, many 3rd class passengers were immigrants. The barriers segregating 3rd class were designed to keep the immigrants in a confined area until they could be processed at Ellis Island. If there weren't any barriers it would have been much easier for 3rd class passengers to avoid the immigration process by debarking with 1st and 2nd class passengers and disappearing into the streets of New York City. With barriers in place, however, they could be processed in an orderly and secure fashion.

The barriers were meant for immigration control, not to keep 3rd class passengers from reaching the boat deck and competing with the upper class passengers for lifeboat seats, although that was the unintended result of having so many passageways blocked.

When the order came to board the lifeboats, the 1st and 2nd class passengers were closest to the boat deck and thus got most of the available seats. For a long time (until all but just a couple of boats had been lowered), few realized that Titanic would actually sink, and that the sinking would happen before rescue ships arrived on the scene. Thus 3rd class passengers were milling about peacefully on their deck until realization suddenly hit that Titanic was doomed.

By the point 3rd class passengers (and most of the rest of the passengers for that matter) knew what was happening, only a couple of lifeboats remained. And because many of the 3rd classers still remained on the third class deck, when that frightening realization finally set in and panic spread, many of them went to the closest possible exits only to find them barred (but those had been barred all along to keep 3rd class segregated for the reasons set forth above).

There were evacuation routes for third class that were open and many third class passengers made it out sooner or later. But the barriers that many had encountered at first only made them that much more desperate and added fuel to the raging fire of panic.