The fume hood is the main safety equipment in the laboratory. Most of the experiments are completed in the fume hood. The fume hood is a special form of closed hood, and the operation process of harmful substances is completely carried out in the hood. The fume hood is generally equipped with opening and closing operation holes and observation holes. Negative pressure is formed in the fume hood by exhausting air, so as to prevent harmful substances from escaping due to mechanical equipment disturbance, chemical reaction or heat source heat pressure, and indoor transverse airflow interference.

According to the difference of harmful gas density and air density, there are many forms of fume hood. Different forms of fume hood are applied in different places. The main forms of the fume hood include: the upper exhaust fume hood, the lower exhaust fume hood, and the upper and lower combined exhaust fume hood. At the same time, there are energy-saving air supply type fume hood.

The cover wind speed of the fume hood is the main technical index to measure the performance of the fume hood. It refers to the average inlet wind speed at the opening sliding door of the fume hood. The selection criteria of the wind speed of the hood cover are: not only the harmful gas can not escape from the cabinet, but also the turbulence in the fume hood should be avoided.

The high wind speed of the cover can lead to the air flow disorder in the space above the working table in the exhaust cabinet. Pollutants may accumulate in a corner of the cabinet, and may blow out the flame, which will damage the ongoing test. Too low wind speed of the cover will inevitably cause the escape of pollutants and endanger the safety of the test personnel.

For toxic or dangerous harmful substances, the wind speed on the operating mask of the fume hood is generally 0.4 ~ 0.5m/s. The exhaust air volume of the fume hood is calculated according to formula (1) [1]:






For the general laboratory fume hood, when considering the interference air flow in the room and the uneven suction velocity at the operating port of the fume hood, the opening area should be taken as the opening area with large volume of operating ports.






It can be seen from the above formula that for the traditional fume hood without regulating system, when the operating door is fully opened, the cover wind speed of 0.4 ~ 0.5m/s can be met. When the operating door is half opened or fully closed, the wind speed of the operating face will be greater than the design value, which will affect the experimental operation and exhaust effect.