(EN) A safety device for the air in a room has an intake air channel for supplying outside air to the room. A device for air treatment is provided. A detector for air contaminants is arranged in the intake air channel. A safety closure with a drive is arranged in the air intake channel and has an open position and a closed position for airtightly closing the intake air channel or an inlet of the device for air treatment that is arranged downstream of the safety closure. An exhaust air channel is connected to the room and the device for air treatment. When the safety closure is in the open position, a partial recirculating operation occurs. When the safety closure is in the closed position, a complete recirculating operation is present. The device for air treatment, the detector, and the drive are connected to a control device.