What is the function of a fume hood?

A fume hood is an essential part of laboratory equipment. In the laboratory, it plays the role of exhaust and ventilation, and the selection of the appropriate fume hood is particularly important for the health of laboratory staff.

One. The structure and material of the fume hood

The structure of the fume hood is of the upper and lower type, and there are exhaust holes at the top of it, which can install fans; There are deflectors, circuit control touch switches, power sockets, etc. in the upper cabinet; The perspective window is made of tempered glass, which can be moved up and down or left and right; The lower cabinet adopts the style of experimental side table, with a table top and a cabinet below; The countertop can be fitted with small drinking glasses and faucets.

There are many materials to choose from, the common ones are all-steel, PP structure, stainless steel, fiberglass, etc. Its countertop materials mainly include solid core physical and chemical boards, ceramics, epoxy resin boards, etc.

Two. The main function of a fume hood

The most important function of the fume hood is the exhaust function, in the chemical laboratory, various harmful gases are produced during the experimental operation, in order to protect the safety of users, to prevent the spread of pollutants in the experiment to the laboratory, the fume hood will be used.

That is to say, the fume hood must have high safety and operability, which requires the fume hood to have the following functions:

1. Release the function

There should be a mechanism to absorb the harmful gases generated inside the fume hood by absorbing the gas outside the cabinet, so that it can be diluted and eliminated outside.

2. No backflow function

It should have the function of not reversing the flow of harmful gases from the inside of the fume hood by the air flow generated by the exhaust fan inside the fume hood. To ensure this function, it is best to connect a fume hood to a ventilator with a single duct. If it cannot be connected by a single pipe, it can only be connected in the same room on the same floor, and the ventilator can be installed at the end of the pipe as much as possible.

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. Supplemental features

There should be a passage or alternative device for drawing air from outside the fume hood when the harmful gas is discharged.

5. Control wind speed function

(1) In order to prevent the escape of harmful gases in the fume hood, a certain inhalation speed is required. The factors that determine the suction speed of the inlet air in the fume hood are: the heat generated by the experimental content and the relationship with the number of air exchanges. The main ones are the content of the experiment and the nature of the harmful substance. Under normal circumstances, 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 small amount of radioactivity is 0.5-0.6m/s, the gaseous matter is 0.5m/s, and the particulate matter is 1m/s.

(2) 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 passing through the ventilation duct. When determining the wind speed, it is also necessary to pay attention to the noise problem, when the air flows in the pipe, it is limited to 7-10m, and more than 10m will produce noise, usually the noise limit value of the laboratory (indoor background noise level) is 70dBA, and increasing the pipe section will reduce the wind speed, which will reduce the noise. Considering the cost and construction of the pipeline, the power of the pipeline and exhaust fan must be carefully selected.