- "Do you guys remember when the reveille bell rang at the exact moment the dome in Shelter 41 collapsed? It was exactly at 0600... almost like cause and effect. The bell rang and woke everyone up a split second before they died. As a boy, I remember thinking: 'That's so unfair.'"
- ―Philip Pearson
Shelter 41 is a bunker in the future housing a portion of humanity. It will eventually be built in a mountain range along the former United States-Canada border. The Faction originated among the survivors here. Notably, Grant MacLaren and the core team come from a version of the future in which Shelter 41 was destroyed and therefore the Faction never existed.
In the first season finale, Trevor Holden describes the collapse of the bunker as an inevitable result of design flaws, claimed that "the weight of the ice" was too much for the structure to bear. Grace and Ellis (along with the Faction) come from a version of the future where the collapse didn't occur. It is not explained why Shelter 41 survived - the environmental conditions could have been less dire or the structure could have been designed properly.
Philip Pearson mentions in the episode titled Room 101 that the shelters were designed to house 10,000 people and were filled to double capacity.