The control tower at Tulsa International Airport remains closed today following an incident Wednesday night when a number of controllers experienced impaired breathing and nausea. The field is currently being operated as a non-controlled airport using only Runway 18L/36R, with personnel in the TUL Tracon delivering some ATC services. The FAA expects a mobile control tower to be operating at TUL by late tomorrow afternoon. The initial airport arrival rate while the field is non-controlled has been set at 20 aircraft per hour, but is expected to rise to 32 once the mobile facility is operating.