The main function of the Laboratory 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 to protect the user's safety. To prevent the spread of contaminants in the laboratory to the laboratory and to use Laboratory Fume Hoods near the sources of pollution. In the past, the number of tables used in the Laboratory Fume Hoods was relatively small, and they were only used in particularly harmful and dangerous gases and experiments that produced large amounts of heat. The Laboratory Fume Hood is only responsible for the auxiliary functions of the lab bench. Taking into account the improvement of the experimental environment, the experiments carried out on the experimental bench were gradually transferred to the Laboratory Fume Hood, which required the most suitable function for the equipment in the Laboratory Fume Hood. In particular, most newly-built laboratories require air conditioning. Therefore, the number of Laboratory Fume Hoods to be used must be included in the air conditioning system plan during the preliminary design phase of the building. Because the Laboratory Fume Hood occupies a very important position in the biochemical laboratory, considering the improvement of the laboratory environment, improvement of labor hygiene conditions, and improvement of work efficiency, the use of Laboratory Fume Hoods has dramatically increased. Followed by the ventilation ducts, piping, wiring, exhaust, etc. have become an important task of laboratory construction.
The main purpose of using the Laboratory Fume Hood is to discharge the harmful gases produced in the experiment and protect the health of the experimental personnel, that is, to have a high degree of safety and superior operability. This requires that the Laboratory Fume Hood should have the following functions:
(1) Release function: It should have means for absorbing the harmful gas generated inside the Laboratory Fume Hood to absorb the gas outside the cabinet, and dilute it to exclude the outdoor one.
(2) No backflow function: The air flow generated by the exhaust fan inside the Laboratory Fume Hood shall have the function of preventing harmful gases from flowing into the room from inside the Laboratory Fume Hood. To ensure the realization of this function, it is best to connect a Laboratory Fume Hood with a fan with a single pipe. It cannot be connected with a single pipe. It is also limited to the same room with the same room and the fan can be connected as much as possible. Installed at the end of the pipe (or at the top of the floor).
(3) Isolation function: Separate the inside and outside of the Laboratory Fume Hood with a non-sliding glass window in front of the Laboratory Fume Hood.
(4) Supplementary function: There should be a channel or an alternative device for sucking in air from outside the Laboratory Fume Hood when harmful gases are discharged.
(5) Control of wind speed function: In order to prevent harmful gases in the Laboratory Fume Hood from escaping, a certain suction speed is required. The factors that determine the suction speed of the Laboratory Fume Hood's air intake are: the amount of heat generated by the experiment content and the relationship with the number of air changes. The main thing is the nature of the experiment and the nature of the pest. It is generally stipulated that generally non-toxic pollutants are 0.25-0.38 m/s, toxic or dangerous pests are 0.4-0.5 m/s, highly toxic or slightly radioactive is 0.5-0.6 m/s, and gaseous substances are 0.5m/s, granular 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, you must also pay attention to the noise problem. When the air flows through the pipe, it is limited to 7-10 m. If the air exceeds 10 m, noise will be generated. Generally, the noise limit of the laboratory (indoor noise level) is 70 dBA. Reducing the wind speed will also reduce noise. Taking into account the funding and construction issues of the pipeline, the power of the pipeline and exhaust fan must be carefully selected.
(6) Heat and acid and alkali corrosion resistance: Some of the Laboratory Fume Hoods need to be equipped with electric furnaces. Some experiments produce a lot of toxic and harmful gases such as acids and alkalis that are extremely corrosive. The countertops, liners, side plates, and optional nozzles and nozzles of Laboratory Fume Hoods shall have anti-corrosion function. The use of strong acids such as sulfuric acid, nitric acid, and hydrofluoric acid in the semiconductor industry or in corrosive experiments also requires that the entire material of the Laboratory Fume Hood must be acid and alkali resistant, and must be made of stainless steel or PVC.