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 the user, Prevent the spread of pollutants in the laboratory to the laboratory. Use a fume hood near the source of pollution. 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 functions of the test bench. Considering the improvement of the experimental environment, the experiments carried out on the test bench were gradually transferred to the fume hood, which required the function of the equipment to be used in the fume hood. In particular, most newly built laboratories require air conditioning, so the number of fume hoods to be used in the initial design phase of the building is included in the air conditioning system plan. 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 the sanitary conditions, and improving work efficiency. It is followed by ventilation ducts, piping, wiring, and exhausting, which have become important topics in laboratory construction.
The purpose of using the fume hood is to discharge the harmful gases generated in the experiment and protect the health of the experimenter, 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: The mechanism for absorbing the harmful gas generated inside the fume hood to absorb the gas outside the cabinet should be diluted to exclude the outdoor unit.
(2) Non-backflow function: It should have the function of the airflow generated by the exhaust fan inside the fume hood to prevent harmful gas from flowing 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 with a single pipe with a single ventilator. It cannot be connected by a single pipe. It is also limited to the same room in the same floor. The ventilator can be installed as much as possible. At the end of the pipe (or at the top of the layer).
(3) Isolation function: The inside of the fume hood should be separated by a non-sliding glass window.
(4) Supplementary function: There shall be a passage or alternative means for drawing in air from outside the fume hood when harmful gases are exhausted.
(5) Control wind speed function: In order to prevent the harmful gas in the fume hood from escaping, a certain suction speed is required. The factors that determine the suction speed of the air inlet of the fume hood are: the heat generated by the experimental content and the relationship with the number of air changes. The main ones are the experimental content and the nature of the harmful substances. Generally, the generally non-toxic pollutants are 0.25-0.38 m/s, the toxic or dangerous pollutants are 0.4-0.5 m/s, highly toxic or a small amount of radioactivity is 0.5-0.6 m/s, and the gas is 0.5m/s, granules are 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 as it passes through the ventilation duct. When determining the wind speed, you must also pay attention to the noise problem. When the air flows through the pipeline, it is limited to 7-10m. If it exceeds 10m, noise will be generated. Generally, the noise limit of the laboratory (indoor background noise level) is 70dBA, and the pipe cut area will be increased. Reducing the wind speed also reduces noise. Considering the cost of the pipeline and construction problems, the power of the pipeline and the exhaust fan must be carefully selected.
(6) Heat-resistance and acid-alkali corrosion resistance: There are some electric furnaces in the fume hood, and some experiments produce a large amount of toxic and harmful gases such as acid and alkali, which are extremely corrosive. The countertops, linings, side panels and selected water nozzles and air nozzles of the fume hood should have anti-corrosion function. In the semiconductor industry or corrosive experiments using strong acid such as sulfuric acid, nitric acid, hydrofluoric acid, etc., the overall material of the fume hood must be resistant to acid and alkali, and must be made of stainless steel or PVC material.