Issue Date 2/2021; Revised 4/2021
This site contains helpful information for the operation of your laboratory fume hood. For information on fume hood specifications for lab design, see Lab Design & Equipment > Fume Hood Specifications.
General Hood Information
Local exhaust ventilation is the one of the best engineering methods available to reduce the health hazard risk associated with the use of hazardous chemicals in the laboratory.
Fume hoods are used to prevent hazardous, offensive, or flammable gases and vapors from mixing with the general room air. A hood, especially with the sash down, also acts as a physical barrier between the laboratory workers and chemical reactions. The hood can also contain accidental spills of chemicals.
Note that laboratory fume hoods and biosafety cabinets, although similar in appearance, are extremely different devices. Biosafety cabinets are used for protection against exposure to biological materials and should not be used with chemicals unless specifically designed for this purpose. If you are uncertain about the type of hood or biosafety cabinet in your laboratory, check with your Principal Investigator or EHRS.
Check the SDS, appropriate Standard Operating Procedure, or chemical label for special ventilation requirements, such as:
Use with adequate ventilation
Use in a fume hood
Avoid inhalation of vapors
Provide local ventilation
If a fume hood is not available in your work space, contact EHRS before working with any hazardous chemicals.
To be effective, laboratory fume hoods must be installed and used correctly. The National Research Council in Prudent Practices for Handling Hazardous Chemicals in Laboratories; (1981) recommends that the following factors be remembered in the daily use of hoods:
Hoods should be considered as backup safety devices that can contain and exhaust toxic, offensive, or flammable materials, when the design of an experiment fails. Hoods should not be used as a means for disposing of chemicals. Thus, apparatus used in hoods should be fitted with condensers, traps, or scrubbers to contain and collect waste solvents or toxic vapors or dusts.
Hoods should be evaluated before use to ensure adequate face velocities (typically 80-100 fpm) and the absence of excessive turbulence. Further, some continuous monitoring device for adequate hood performance should be present and should be checked before each hood is used. If inadequate hood performance is suspected, it should be established that the hood is performing adequately before it is used. Call your building administrator to report inoperable hoods.
Except when adjustments of apparatus within the hood are being made, the hood should be kept closed: vertical sashes down and horizontal sashes closed. Sliding sashes should not be removed from horizontal sliding-sash hoods. Keeping the face opening of the hood small improves the overall performance of the hood.
The airflow pattern, and thus the performance of a hood, depends on such factors as placement of equipment in the hood, room drafts from open doors or windows, persons walking by, or even the presence of the user in front of the hood. For example, the placement of equipment in the hood can have a dramatic effect on its performance. Moving an apparatus 5-10 cm back from the front edge into the hood can reduce the vapor concentration at the user's face by 90%.
Hoods are not intended primarily for storage of chemicals. Materials stored in them should be kept to a minimum. Stored chemicals should not block vents or alter airflow patterns. Whenever possible, chemicals should be moved from hoods into cabinets for storage.
Solid objects and materials (such as paper) should not be permitted to enter the exhaust ducts of hoods as they can lodge in the ducts or fans and adversely affect their operation.
An emergency plan should always be prepared for the event of ventilation failure (power failure, for example) or other unexpected occurrence such as fire or explosion in the hood.
At Penn some hoods fume hoods are equipped with combination sashes, which include both a vertical-moving sash and also horizontal-sliding panels. These hoods are meant to be used in one of two ways:
1) With the vertical-moving sash raised to a position that is high enough to allow the researcher access to the materials in the hood, but low enough that the sash is protecting the researcher’s face and upper body.
2) With the vertical-moving sash completely down and one of the horizontal-sliding sash panels positioned directly in front of the researcher’s body. In this way, the researcher’s arms can reach around the panel to access the interior of the hood, while their entire body is shielded by the panel in front of them.