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?

Never seen or heard of anything like what you speak of on all Boeing, Douglas and most Airbus jet aircraft.

Most unlikely. The aircraft I have flown pressurise themselves to -200' when take-off power is set. This is all handled by the pressurisation controller. All of the doors remain locked at all times.

As above stated this is called pre-pressurisation, set to clean the doors up, at this point the D/P on the cabin (even .5dpsi) would make just about impossible for a human to open a door.

Such a feature neither exists on Dash or Fokker aircraft.

The Dash 8 has a manually controllable 3rd outflow valve in the forward pressure bulkhead (in addition to the two on the aft bulkhead) that can be used to flush smoke out of the cockpit in case of need.