Hoods and Fume Hoods

The purpose of a localized extraction system is to capture the contaminant as close as possible to the point where it was generated, the contaminant source, preventing it from spreading to the general laboratory environment. It consists of four basic elements:

a. Bell: it is the part of the system through which the pollutants are effectively captured.

b. Duct: place through which the contaminant-laden exhaust air circulates to the fan.

c. Scrubber: an air treatment/purification system from which, when the concentration, hazardousness or other characteristics of the

and with a view to protecting the atmospheric environment, it provides for the installation of an extraction system


d. Fan: mechanism that provides the energy necessary for the air to circulate through the hood, duct, and the

The system will be able to operate at a set flow rate and overcome the pressure drop of the system.

Any localized extraction system requires a design and operating characteristics that allow the contaminant to be entrained at the necessary velocity, its conveyance through the installation at an adequate flow rate and a fan that provides this flow rate while overcoming the pressure drop offered by the installation as a whole.

A localized extraction system is considered to be working properly when in the vicinity of the source from which it is intended to capture the pollutant emitted, its concentration is at the level that had been foreseen.

Localized exhaust systems have a number of advantages over dilution ventilation.

Various localized extraction devices are found in the laboratory: fume hoods, bench-top fume hoods, with or without filtering and connection to the outside, hoods for dissipating heat from instruments and removing fumes and vapors, and mobile extraction points. Fume hoods differ from other extraction devices in that they include an enclosure.