Release function: There should be a way to absorb the harmful gases generated inside the fume hood and discharge them to the outside after dilution. Isolation function: there should be a non-sliding glass window behind the fume hood to separate the upper and lower part of the fume hood. Heat-resistant and acid and alkali corrosion-resistant function: some fume hoods need to be installed with electric furnaces, and some experiments produce a lot of acid and alkali and other toxic and harmful gases, which are highly corrosive. Fume hood countertops, lining boards, side panels and the selection of water and gas nozzles should have anti-corrosion features. Semiconductor industry or corrosive experiments in the use of sulfuric acid, nitric acid, hydrofluoric acid and other strong acids, but also requires the fume hood of the overall material must be acid and alkali resistance, must use stainless steel, PVC or all-steel.
No backflow function: should have the function of exhausting the airflow generated by the exhaust fan within the fume hood to prevent harmful gases from flowing into the room from the outside of the fume hood. In order to ensure the realization of this function, it is a good method to connect a fume cupboard and a ventilation fan with a single pipe. It is not possible to connect single pipes and is limited to parallel use within the same room on the same floor. Whenever possible, the ventilator should be installed at the end of the duct or on the roof of the building to remove the waste outside.
Supplementary function: There should be a channel or alternative device for drawing air from outside the fume hood when harmful gases are exhausted.
Function to control air speed: In order to prevent harmful gases from escaping from the fume hood, a certain inhalation speed is required. The elements that determine the inhalation speed of the fume hood intake air are: the heat generated by the content of the experiment and the relationship with the number of air changes. The main ones are the content of the experiment and the nature of the harmful substances. It is usually stipulated that the general non-toxic pollutants are 0.25-0.38m/s, toxic or dangerous harmful substances are 0.4-0.5 m/s, highly toxic or a small amount of radioactivity is 0.5-0.6m/s, gaseous substances are 0.5m/s, and particulate matter is 1m/s. In order to ensure such air speeds, the exhaust fan should have the necessary static pressure, i.e. the frictional resistance of the air as it passes through the ventilation duct. Determine the wind speed must also pay attention to the noise problem, through the air flow in the pipe to 7-10m as a limit, more than 10m will produce noise, usually laboratory (indoor background noise level) noise limit value of 70dBA, increase the pipe cut area will reduce the wind speed, but also to reduce the noise, taking into account the pipeline of the funds and construction problems, must carefully select the pipeline and exhaust fan power. Considering the cost of ducting and construction problems, the power of ducting and exhaust fan must be carefully selected.
