Selecting and using a fume hood

April 26, 2023 | Lab Furniture

Fume hoods are an essential part in laboratories as the local exhaust/containment device and one of the most reliable engineering controls. With proper installation, maintenance, and usage, a well-designed hood offers extensive protection to the user

Lab Manager offers the following considerations in choosing the right fume hood materials, specifications, and usage:

Fume Hood performance

A fume hood’s performance should be evaluated during installation and right before use to guarantee adequate face velocities and the absence of excessive turbulence. Assessing the performance against design specifications is crucial to ensure uniform airflow across the hood face and the total exhaust air volume. Evaluation of operator exposure is also important.

Successful hood performance is dependent on the face velocity of air entering the fume hood’s sash opening. The following factors affect the hood’s speed by:

  • cross-drafts created by the surrounding environment (movement of people, user’s presence, or hood and air currents from open windows and doors)

  • hood design

  • thermal loading

  • amount and location of equipment in the hood

Fume hood velocity

The exhaust flow rate pulled through the hood is controlled in most fume hood installations. This means that for a particular operation, the sash can be adjusted in order to obtain an optimal flow rate.

Basis for having a successful design of a fume hood is having a face velocity in the range of 60-120 ft/min. Too low a face velocity will not provide adequate exposure control while too high of a face velocity will increase turbulence and cause contaminants to escape.

Tip: Measuring worker exposure while the hood is being used for its intended purpose is the most effective method of evaluating hood performance and getting that optimum airflow rate.

Make-up air

Adequate supply of air, known as make-up air, is required to replenish the exhaust air otherwise the hoods will not be able to exhaust a sufficient volume of air to function properly as intended. 

 Work practices

 Adequate personnel training must be provided when using ventilation equipment. Here is a partial list of guidelines for same fume hood use:

  • Chemicals, equipment not used, or waste, should not be stored in the hood.

  • Chemical waste should not be disposed of by evaporation in a hood.

  • Heads should be kept outside of the fume hood. ‘Walking in’ in an operating hood is not advised.

  • Fume hood’s sash should be as low as possible or below the indicated operating height when in use.

  • Check airflow through the hood face periodically.

  • Rear hood exhaust slots should be free from blockages.

  • Combustibles or any material that restrict airflow should be kept out of the hood.

  • Perchloric acid in a fume hood not explicitly designed for this purpose should never be used. 

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