Depends on type, certainly.
Friend of mine died at BOS many years ago on a PanAmerican 707 freighter due to a dangerous goods fire aft, and they had to open the sliding cockpit window to
try to see the instruments, the smoke was so thick.
This helped a bit, but not in time, sadly...the airplane crashed just short of the runway.
Investigation later proved improperly packed acid set the packing material (also not approved) on fire after the package tipped over....
big fines for the shipping company and (I think) jail time for two execs of same.
Gotta know your type, folks....when it all goes pear-shaped.
I guess the packs are turned off to avoid some sort of pressure surge ?!
More than likely to get the window open in the first place.