The 6-point function of the fume hood

The main function of the fume hood is the exhaust function. In the chemical laboratory, various harmful gases, odors, moisture and flammable, explosive and corrosive substances are generated during the experimental operation. In order to protect the safety of users, To prevent the contaminants in the experiment from spreading to the laboratory, a fume hood should be used near the pollution source. In the past, the number of fume hoods used was small, and it was only used in experiments with particularly harmful and dangerous gases and large amounts of heat. The fume hood is only responsible for the auxiliary function of the test bench.
 
In recent years, taking into account the improvement of the experimental environment, the experiments carried out on the experimental bench have been gradually transferred to the fume hood, which requires that the fume hood should have functions suitable for the use of equipment. In particular, most of the newly built laboratories require air conditioning, so the number of fume hoods used should be included in the plan of the air conditioning system in the preliminary design stage of the building. Since the fume hood occupies a very important position in the biochemical laboratory, the number of fume hoods has increased dramatically in terms of improving the laboratory environment, improving labor hygiene conditions, and improving work efficiency. Followed by the ventilation ducts, piping, wiring, exhaust, etc. have become important issues in laboratory construction.
 
The purpose of using a fume hood is to discharge the harmful gases generated in the experiment and protect the health of the experimenters, that is to say, to have a high degree of safety and superior operability, which requires the fume hood to have the following functions:
 
(1) Release function: There should be a mechanism to absorb the harmful gas generated inside the fume hood by absorbing the gas outside the cabinet, so that it can be diluted and discharged to the outside.
 
(2) Non-reverse flow function: It should have the function that the airflow 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 a good method 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 installed as much as possible. at the end of the pipe (or at the top of the layer).
 
(3) Isolation function: In front of the fume hood, a non-sliding glass window should be used to separate the inside and outside of the fume hood.
 
(4) Supplementary function: There should be a channel or an alternative device for inhaling air from outside the fume hood when the harmful gas is discharged.
 
(5) Function of controlling wind speed: 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 when the air 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 be installed with electric furnaces, and some experiments produce a large amount of toxic and harmful gases such as acid and alkali, which are highly corrosive. The countertop, lining board, side board and selected water nozzles and gas nozzles of the fume hood should have anti-corrosion function. In the semiconductor industry or in corrosive experiments where strong acids such as sulfuric acid and nitric acid are used, 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.