Once the train has cleared the tunnel, the door closes again and the fans operate for 20 to 30 minutes with maximum power to clear the tunnel of exhaust before the next train passes through. In the opposite direction, the door opens when the train is within . The fans are powered by two 800-horsepower electric motors, clearing the air through the of tunnel within 20 minutes. Present-day train crews carry portable respirators for use in the event of a fan failure or a train stalling inside the tunnel. In addition, there are emergency/safety stations spaced apart, depending on the location within the tunnel, that provide additional air tanks and equipment to be used in the event of a ventilation/other failure.