Sometimes it is required that a fan is able to operate at elevated temperatures continuously, or when there are particles or hazardous gases within the air stream that would damage a motor if it was unprotected. Bifurcated fans split the airflow around a motor tunnel which means that the motor is held outside of the airstream and therefore does not get exposed to what the air stream is carrying. Bifurcated fans are used as kitchen hood extract fans, keeping the motors protected from grease and elevated temperatures, also bifurcated fans are also used in industrial processes where air temperatures are continuously high (foundries for example) or where acids or abrasive particles are common in the airflow.