Publish Time: 2022-03-02 Origin: Site
The fume hood can not only provide a good experimental environment for the laboratory, but also better ensure the personal safety of the experimental personnel. During the experiment, the fume hood plays the role of exhaust and ventilation, and discharges harmful gases to prevent the staff in the laboratory from being exposed to some toxic, pathogenic or unknown chemical substances or organic gases and particles, smoke, vapor, soot, dust and aerosols and other pollutants attack. Therefore, the fume hood is an essential part of the laboratory.
The fume hood is to protect the operator. It is sucked by the external exhaust system to maintain a certain suction surface wind speed of the front window of the fume hood, so that the aerosol pollution in the fume hood will not escape through the front window and protect the operator from Contamination from in vivo operations. Most of the exhaust air of the fume hood contains acid and alkali chemical components. The pipes, fans, valves, connectors and fasteners of the exhaust system need to pay more attention to anti-corrosion problems. Generally, the air ducts should be made of stainless steel.
The characteristic size of the fume hood is represented by its shape width. The size of the standard fume hood is 1.2m, 1.5m, and 1.8m. ). The air deflector on the back of the cabinet is divided into upper, middle and lower exhaust sections. The deflector can be adjusted according to the cold and hot operation in the cabinet and the density of the polluting aerosol to eliminate the dead angle of exhaust and limit the escape of pollution to the greatest extent. When the door of the fume hood is fully opened, the maximum height is 600~800mm, and the diameter of the exhaust port on the top of the fume hood is generally φ250mm.
Regarding the choice of the surface wind speed of the fume hood, the maximum surface wind speed recommended by the industry standard "Fume Hood" JB/T6412-1999 and "Laboratory Variable Air Volume Fume Hood" JG/T222-2007 are both 0.5m/s, and some people think that The face velocity should be increased according to the needs of the process operation. Relevant American associations and committees have done a lot of research and tests in this area, and the results are as follows:
American Association of Governmental Industrial Hygienists: A typical fume hood is that the operator stands in front of the fume hood and reaches into the interior of the fume hood to perform experimental operations. At this time, the airflow entering the fume hood will form a swirling airflow around the operator, which will cause the gas in the cabinet to overflow, and even rise along the operator's body to the breathing area. The higher the inlet wind speed, the stronger the swirling airflow formed. Therefore, things are not what people think, the higher the inlet wind speed, the better the airflow suppression effect. The higher inlet air speed will not increase or even worsen the airflow suppression effect of the fume hood while wasting energy consumption.
U.S. Occupational Safety and Health Administration: Under normal circumstances, the recommended inlet wind speed of the fume hood should be between 0.4~0.5m/s. For a few drugs with high toxicity or when the outside world has an adverse effect on the airflow suppression ability of the fume hood, the inlet wind speed can be 0.5~0.6m/s. However, the energy consumption of the fume hood is generally linear with the inlet wind speed. When the air inlet speed approaches or exceeds 0.75m/s, turbulence will be formed in the fume hood, thereby reducing the airflow suppression efficiency of the fume hood.
The research results show that when the surface wind speed of the fume hood reaches 0.6~0.75m/s, although almost all fume hoods can achieve efficient airflow suppression within this range, the effect is not essential compared to 05~0.6m/s Therefore, it is generally not recommended to use it. When the surface wind speed is greater than 0.75m/s, turbulence is caused in the fume hood, which greatly increases the possibility of toxic gas overflow in the cabinet. Therefore, the surface wind speed of the fume hood should not be greater than 0.75m/s.
The full exhaust type fume hood is the most widely used type at present. Its ventilation structure design is very reasonable. When the fume hood is exhausted, it can be well circulated in the cabinet. This type of exhaust is suitable for any experiment. In the room, and can more effectively and quickly discharge indoor harmful gases and substances.
The supplementary air fume hood is suitable for those laboratories that have requirements for indoor temperature. Since the temperature and humidity in some laboratories are constant, and in order to save heating, we can directly use this supplementary air fume hood. Structure, this design allows the fume hood itself to operate and circulate through the outside air.
Variable-type fume hoods are suitable for laboratories that require more wind speed, because this variable-type structure can better help us adjust the exhaust air volume.