1: Act 1 Part 1, terminal room
2: Act 1 Part 2, through the flaming truck
3: Act 2 Part 1, inside lift control room
4: Act 2 Part 2, in the left starter room with the barrel
5: Act 3 Part 3, in the bottom of the circular room
6: Act 4 Part 2, behind first pillar
7: Available from the start