1. Release function:
There should be a mechanism to absorb the harmful gas generated inside the fume hood by absorbing the gas outside the hood, so that it is diluted and discharged to the outside.
2. No backflow function:
It should have the function that the air flow generated by the exhaust fan inside the fume hood will not reverse the flow of harmful gases into the room from the inside of the fume hood. In order to ensure the realization of this function, it is the best way to connect a fume hood and a ventilator with a single pipe. It cannot be connected with a single pipe, and it is limited to the parallel connection of the same room on the same floor. The ventilator should be as far as possible. Installed at the end of the pipe (or at the top of the layer).
3. Isolation function:
There should be a non-slip glass window in front of the fume hood to separate the inside and outside of the fume hood.
4. Supplementary functions:
There should be a passage or alternative means for drawing air from outside the fume hood when the harmful gas is discharged.
5. Control wind speed function:
In order to prevent harmful gases from escaping in the fume hood, a certain suction speed is required. The factors that determine the intake speed of the fume hood are: the heat generated by the experimental content and the relationship with the number of air changes. Chief among them are the experimental content and the nature of the harmful substances. It is generally stipulated that the general non-toxic pollutants are 0.25-0.38m/s, the toxic or dangerous harmful substances are 0.4-0.5m/s, the highly toxic or a small amount of radioactivity is 0.5-0.6m/s, and the gaseous substances are 0.5-0.6m/s. 0.5m/s, granular material is 1m/s. In order to ensure such a wind speed, the exhaust fan should have the necessary static pressure, that is, the frictional resistance of the air when it passes through the ventilation duct. When determining the wind speed, we must also pay attention to the noise problem. When the air flows in the pipeline, the limit is 7-10m. If it exceeds 10m, noise will be generated. Usually, the noise limit value of the laboratory (indoor background noise level) is 70dBA. Reducing the wind speed will also reduce the noise. Considering the cost and construction of the pipeline, the power of the pipeline and the exhaust fan must be carefully selected.
6. Heat resistance and acid and alkali corrosion resistance:
Some of the fume hoods need to install electric furnaces, and some experiments produce a large amount of toxic and harmful gases such as acid and alkali, which are extremely corrosive. The countertop, lining board, side board and selected water nozzles and gas nozzles of the fume hood should have anti-corrosion function. Where strong acids such as sulfuric acid, nitric acid, and hydrofluoric acid are used in the semiconductor industry or in corrosive experiments, it is also required that the overall material of the fume hood must be resistant to acid and alkali, and must be made of stainless steel or PVC.
