A blower assembly is configured to deliver a flow of breathable gas at a continuously positive pressure with respect to ambient air pressure to a patient interface in communication with an entrance to a patient's airways including at least an entrance of the patient's nares, while the patient is sleeping, to ameliorate sleep disordered breathing. The blower assembly includes a motor having a shaft that extends from opposite sides of the motor. The blower assembly also includes an impeller and a circuit board. The impeller is attached to the shaft on a first side of the motor and is structured to rotate in close proximity to a volute wall. The circuit board is configured to control power supplied to the motor and is configured to disable the motor when the impeller is closer than a predetermined distance from the volute wall.