When the temperature of the hazardous material is lower than the surrounding air temperature, it is called a cold process fume hood. The movement of airflow when the cold process fume hood uses upper exhaust. The inhalation velocity at the upper part of the working hole is 150% of the average flow rate, while the lower part is only 60% of the average flow rate, harmful gases will escape the lower part. In order to improve this situation, the cabinet should be added to the baffle, the exhaust vent is located in the lower part of the fume hood.