* "Two in, two out" refers to the rule that firefighters never enter a building or other IDLH situation alone but go in as a pair. Two go in and two come out; also, the two in can refer to the two who enter the building while a backup team of two remains outside the building ready to enter if needed. | * "Two in, two out" refers to the rule that firefighters never enter a building or other IDLH situation alone but go in as a pair. Two go in and two come out; also, the two in can refer to the two who enter the building while a backup team of two remains outside the building ready to enter if needed. |