Publish Time: 2022-04-22 Origin: Site
The most important 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 pollutants in the experiment from spreading to the laboratory, use a fume hood near the pollution source. In the past, the number of fume hoods was small, and it was only used in experiments that were particularly harmful and dangerous and produced a lot of heat. The fume hood is only responsible for the auxiliary function of the test bench. Taking into account the improvement of the experimental environment, the experiments carried out on the experimental bench are gradually transferred to the fume hood, which requires the most suitable functions for the equipment to be used in the fume hood. 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 biggest purpose of using a fume hood is to discharge the harmful gas generated in the experiment and protect the health of the experimenter, that is to say, it must have a high degree of safety and superior operability.
(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 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 gas 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: In front of the fume hood, a non-slip glass window should be used to separate the inside and outside of the fume hood.
(4) Supplementary function: there should be a passage 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 usually 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 be installed with 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.
◆ Before the experiment starts, it must be confirmed that the fume hood should be in operation before the experiment operation can be carried out.
◆ Continue to run for at least 5 minutes before the end of the experiment before turning off the ventilator to discharge the residual gas in the pipeline. Consider installing an exhaust time delay device to ensure that the fan runs on a delayed basis.
◆ During the experiment, do not put any equipment within 150mm from the glass window. Large-scale experimental equipment should have sufficient space and should not affect the air flow. The front window should be closed as much as possible.