A fume hood is indispensable among laboratory furniture. In the laboratory it serves to exhaust air and exchange air. Experiments produce all kinds of harmful gases, odours, moisture, and flammable, explosive and corrosive substances. To protect the user’s safety and prevent contaminants from spreading into the laboratory, a fume hood should be used near the source of contamination. In the past, few fume hoods were used — only for particularly harmful and dangerous gases and for experiments generating a great deal of heat — and the fume hood served only as an auxiliary to the bench.

In recent years, in order to improve the laboratory environment, experiments once carried out on the bench have gradually moved into the fume hood, which requires the hood to offer functions best suited to the equipment in use. In particular, most newly built laboratories require air conditioning, so the number of fume hoods to be used must be included in the air-conditioning plan at the preliminary design stage of the building. Because the fume hood occupies a very important position in a biochemical laboratory, the number of hoods in use has risen sharply, given the need to improve the laboratory environment, improve labour hygiene conditions and raise work efficiency.

Fume hoods are classified by exhaust method into three types: upper exhaust, lower exhaust, and simultaneous upper and lower exhaust. To ensure uniform air velocity in the working area, a fume hood for a cold process should use lower exhaust, one for a hot process should use upper exhaust, and for processes with unstable heat generation, exhaust openings can be provided both above and below, adjusting the ratio of upper and lower exhaust volume as the heat inside the hood changes, so as to obtain a uniform air velocity.

Fume hoods are also classified into three types by air intake method. Air entering from the room, circulating inside the hood and then discharged outdoors is called the full-exhaust type, which is a very widely used type.

By operating state, fume hoods can be classified as integral lower-open type, floor-standing type, two-sided type, three-sided glass type, bench-top type and connected type, as well as special fume hoods designed for radioactive experiments, synthesis experiments and perchloric acid experiments according to different experimental needs.

Safety is the greatest mission of a fume hood; using a fume hood in the laboratory is precisely to guarantee the user’s safety and prevent pollution of the surrounding environment.

When using a fume hood, pay attention to safety:

◆ Before starting an experiment, make sure the fume hood is running before carrying out any operation.

◆ At the end of the experiment, keep the hood running for at least 5 more minutes before switching off the fan, in order to discharge residual gas in the duct. An exhaust delay timer may also be installed to ensure the fan runs on.

◆ During experiments, do not place any equipment within 150 mm of the glass sash; large experimental equipment needs ample space and should not impede air flow; keep the front sash closed as far as possible during use.