Smoke evacuation
Somewhere if i not mistaken I read that there is an interlocking mechanism automatically activated at 20 knots on one of the doors (i thought L1 or L4) that allowed the doors to be open in flight just a bit.
the metal bar prevent the door to blow open if the cabin is still a bit presurized. there is also a strap to the handle that prevent the total rotation into open position.
Anyone can confirm it?