Use of recirculated air curtains inside ventilated rooms for the isolation of transient contaminant

•A recirculated air curtain was arranged inside a room for transient zonal isolation.•Air curtain was installed on the basis of existing mixed ventilation in the room.•Isolation initially increased and then decreased as discharge velocity increased.•Air curtain performed better when the air was recirculated from the floor below it.•Reducing protected area did not significantly improve regional protection capacity.