How airflow is affected in a chemical fume hood: transcript

Key points

• Fume hoods capture and exhaust chemical vapors and airborne particulates, and air flow can be interrupted, altered or changed by different factors.
• Work at least 6 inches from the front, because chemicals and objects near the opening may leak out and cause loss of containment.
• Keep the sash at the certification mark and raise or lower it slowly, since quick movement disturbs airflow.
• Large equipment should be elevated so air can flow underneath it, and abrupt movements can create turbulence.
• A person walking past an open hood creates vortices faster than about 250 feet per minute that can pull contaminants out of the hood.
• Place materials inside before starting, move arms slowly and perpendicular to the hood face, and install hoods away from doors, fans and air diffusers in low traffic areas.

Chapters

1. 0:08How air flows in a fume hood
2. 0:43Placement of chemicals and sash height
3. 1:16Sash movement, equipment and turbulence
4. 1:56Walking past the hood and vortices
5. 2:26Working practices and hood location

Full transcript

0:08There are several types of chemical fume hoods that provide protection and help capture and exhaust chemical vapors in airborne particulates. However, all types work on similar principles. Air flow in a chemical fume hood can be interrupted, altered, and changed by different factors. Air flows into the hood capturing and containing contaminants, preventing them from escaping into the laboratory room. The smoke shown here provides visual demonstration of how air flows in a fume hood.

0:43Many conditions can affect the efficiency and safe operation of a fume hood. Chemicals closer to the front of the hood are more likely to leak from the hood. Operate at least 6 inches from the front. The placement of objects close to the front opening may result in leakage and loss of containment. Sash height is important for maintaining proper air flow and to keep those working in it and around it safe.

1:16When working in the hood, the sash should be at the certification mark. Raising and lowering the sash should be done slowly. Moving the sash quickly can disturb the airflow and result in leakage. Large equipment inside the hood can obstruct the airflow and may allow vapors to escape into the lab. Equipment should be elevated to allow air to flow under it so the proper fume hood airflow patterns will be maintained. Abrupt movements can cause turbulence allowing vapors to escape.

1:56For example, most people walk at a velocity of approximately 250 feet per minute, about 3 miles per hour. Wakes or vortices form behind a person who is walking and the velocities in these vortices exceed 250 feet per minute. When a person walks in front of an open fume hood, the vortices can overcome the fume hood face velocity and pull contaminants out of the fume hood.

2:26Into the vortex and into the laboratory. Place equipment and materials inside the hood before work begins. If you do need to move your arms out of the hood, move them slowly and perpendicular to the hood face. The location of the hood is important too. It should be away from doors, fans, or ceiling air supply diffusers. The fume hood should be installed in a low traffic area.

Source and licence

Recording: File:Chemical Fume Hood - How Airflow is Affected.webm by Centers for Disease Control and Prevention (2018-08-22), via Wikimedia Commons. Licence: Public domain.

The transcript is machine speech-to-text by the TidyTools Audio & video transcriber; the summary, key points and chapters were written by Claude from that transcript. Both may contain errors: check the recording before quoting it.