101 Basics Of Fume Wood

A fume hood is a ventilated enclosure that captures and removes gases, vapors, and fumes from the work area. An exhaust fan on the roof of the laboratory building draws in air and airborne contaminants through connected ductwork and exhausts them to the atmosphere. Click here to find out fume hood price Malaysia here.

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A typical fume hood in a Princeton University laboratory has a movable front sash and an interior baffle. The sash may move vertically, horizontally, or a combination of the two depending on its design and provides some protection to the hood user by acting as a barrier between the worker and the experiment.

The hood’s slots and baffles direct the air and, in many cases, can be adjusted to provide the most even flow. It is critical to keep the baffles clear of debris caused by excessive material storage or equipment, as this has a significant impact on the exhaust path within the hood and, as a result, the efficiency of hood capture. The airfoil, a bevelled frame around the hood face that eliminates sharp curves to reduce turbulence, allows for even air flow into the hood.

There are two basic types of fume wood: 

  1. Constant volume
  • where the exhaust flow rate or amount of air drawn through the hood is constant When the sash is lowered and the cross-sectional area of the hood opening decreases in this configuration, the velocity of airflow (face velocity) through the hood increases proportionally. As a result, as the sash is lowered, the velocity of air at the hood face increases.
  1. Variable air volume
  • where the exhaust flow rate or the amount of air drawn through the hood varies as the sash is raised or lowered to maintain a constant face velocity As a result, when the sash is lowered and the cross-sectional area of the hood opening decreases, the velocity of air flow (face velocity) through the hood remains constant, resulting in a reduction in total air volume exhausted.
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A properly used and functioning fume hood exhausts hazardous gases, dusts, mists, and vapors from a confined space, protecting workers from inhalation exposure.

A biological safety cabinet looks like a fume hood but is intended for work with pathogens (infectious microorganisms) or materials contaminated with pathogens that require a specific biosafety level.

Biosafety cabinets (BSCs) protect the user, the environment, and the material, whereas fume hoods protect the user and others in the workspace. A fume hood, for example, normally exhausts a toxic chemical to a roof stack, where it is diluted to such a low concentration that it is unlikely to harm anyone. In contrast, even if diluted, releasing a pathogen such as Ebola or coronavirus into the environment would be extremely dangerous, so biosafety cabinets are equipped with HEPA filters to remove biological material. Biological safety cabinets may be unsafe to use with toxic chemicals unless the filtered air is exhausted outside the lab/work space. At least one report has been made public. 

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Fume hoods are not intended to be storage containers unless specifically designated. Incompatible materials and/or hazardous wastes stored in fume hoods have resulted in numerous accidents, many of which have resulted in death or injury. Here’s an example of a fume hood fire/explosion caused by such carelessness.