Omg
I m sorry to have generated such much suspicious !!!!!!
Let me re frase the question
Above which speed the mechanical interlock door Bar ( if any) automatically is inserted to prevent the total opening of the door in flight if necessary to evacuate the smoke if any ?
I read it somewhere 20 kts or I may have fabricate it into my ram memory....thank you BOAC for observing the facts..I appreciated and peacefully go back to sleep.