Situation 1:

• no ventilator
• closed windows
• open doors

Fresh air flows into the fire area through the lower part of the entrance door. This causes turbulences between the fresh air and the smoke layer.
In the upper area of the door smoke flows into the stairway which fills up with smoke progressively.
If windows are open in the fire area, smoke flows out of the builing.

Situation 2:

• no ventilator
• open windows
• open doors

Fresh air flows into the fire area through the lower part of the entrance door. This causes turbulences between the fresh air and the smoke layer.
In the upper area of the door smoke flows into the stairway which fills up with smoke progressively. Due to the less dense smoke there will be a chimney effect in the stairway.  
If windows are open in the fire area, smoke flows out of the builing.

Situation 3: 

• ventilator in front of the building
• closed windows in stairway
• open doors

Basically the same as situation 2, but there is more flow through the stairway and therefore less smoke.
If windows are open in the fire area, smoke flows out of the builing.

New: Smoke stopper - no ventilator: 

• no ventilator
• open windows
• open doors

Fresh air flows into the fire area through the lower part of the entrance door. Because the fresh air flow is forced to occur at floor level there is less turbulence. No smoke enters the stairway through the upper part of the door.
If windows are open in the fire area, smoke flows out of the builing.

New: Smoke Stopper and ventilator: 

• ventilator in front of the building
• open windows
• open doors

Basically the same as situation 2, but there is more flow through the stairway and therefore no smoke at all.
Again no turbulences in the entrance area to the fire compartment.