Chemical hood

What characterises a chemical fume hood is an extraction system that, by taking air through the front working opening, produces a flow of air generated and maintained by an electric fan.
At first glance, chemical fume hoods all look the same, but in reality, the differences are many and not always easy to understand.

Chemical fume hoods can be distinguished between:

outdoor ducted (or conventional)
recirculating (non-conventional)

Outdoor ducted hoods

Outdoor ducted chemical fume hoods consist of a cabin, an extraction duct and an electric fan. Pollutants are ducted to the outside with a filter system or without.
The electric fan can be found either inside or outside the laboratory.
These types of chemical fume hoods can be with a constant volume of expelled air (variable speed, CAV) or with variable volume (VAV), so that the air speed can be kept constant without depending on the height of the front opening. They can have a double rear wall for air intake or none at all. There are also chemical extraction hoods that have special equipment depending on the type of application they are intended for, e.g. hoods for perchloric acid, flouridic acid, etc.

Recirculating air fume hood

Recirculating air chemical fume hoods have small dimensions; all elements of the chemical fume hood are enclosed in a single body. Their shape allows them to be placed either on the bench or on the floor.
The work surface is located inside a transparent cabinet placed at the front, which can be opened and is connected to the purification and suction system.
In this type of chemical fume hood the air is purified of toxic vapours by absorption during the solid phase, the electric fan sucks the air through a bed of absorbent substances, which purify it and retain the pollutants by chemical or physical absorption.

The air is then purified and then sucked into the cabinet.

Efficacy of the chemical fume hood

The frontal velocity of the incoming air determines the extraction effectiveness of chemical fume hoods, this is located in the free section positioned between the bottom of the sliding panel frame and the underside of the worktop.

Useful links:

Chemical cap Chemical cap Chemical cap