Ben Sandilands, in
this article refers to the flight deck roof top hatch in the ATR being used as an emergency exit for ditchings. The article also refers to a similar hatch in the DH8 (does the -400 have one?).
As best I can recall from my DH8 EPs days, some 13 years ago, the flight deck hatch wasn't considered an "emergency exit", more for the evacuation of tech crew if the flight deck door was jammed/blocked shut.
I wonder if things have changed?