The portable smoke blocker prevents the spread of smoke and heat in not affected areas of burning buildings. With the easily operated tension lever the portable smoke blocker can be fast installed into a door or entrance opening. The door to the affected area can be opened now and the fire fighters can enter the room behind for their operations without the spread of smoke and heat in the building. The stairways can be ventilated with positive pressure ventilation without streaming in of additional smoke from the burning areas. Escape routes for the residents and retreat ways for the fire fighters stay smoke-free. It is possible for the security backup to stay close to the attacking fire fighters. The time for the rescue operation in case of a breathing protection emergency is considerable reduced. Dangerous situations through smoke and heat spread are effectively minimized or avoided. When the smoke stopper is inserted to a door frame the fire fighters can enter the burning room without any problems.