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How Does a Fume Hood Work?

Grainger Editorial Staff

The fumes chemicals emit can quickly make the air unbreathable. A fume hood helps prevent exposure to toxic vapors so people can stay safe when working with chemicals. 

What Is a Fume Hood?

A fume hood is a piece of laboratory equipment designed to minimize a person's exposure to hazardous chemicals. The fume hood draws away harmful vapors so lab employees can work with chemicals without the risk of accidental exposure. The air is extracted from the fume hood and filtered to remove dangerous vapors, and then either exhausted outside of the building or recirculated back into the lab. 

How Does a Fume Hood Work?

The fume hood works by using a sash (a window that opens or closes to protect the user) to contain the vapor and keep it away from the user’s face or to prevent it from drifting out into the rest of the laboratory. Blowers draw in air from the room, through a filter or number of filters within the fume hood and towards an exhaust area. 

According to Labconco, to safely work in a fume hood, keep all work at least six inches away from the plane of the sash. This will ensure fumes are pulled away from the user. Also, make sure the hood sash remains closed as much as possible and keep the hood slots and baffles free of any obstructions by containers or equipment. Never place your head inside the fume hood when working with chemicals.

The airflow will differ depending on the type of hood you use. For a constant air volume (CAV) hood, the fan has only one speed, providing a stable and continuous airflow. A variable air volume (VAV) hood allows users to adjust the velocity of the exhaust for added versatility, while reduced air volume (RAV) hoods offer lower airflow performance, making them ideal for working with less harmful compounds.   

Different Types of Fume Hoods

Every lab is unique. That’s why fume hoods come in a wide variety of sizes and functionalities so that you can find one that fits your exact needs. When comparing fume hoods, here are some of the different types to consider:

  • Ducted fume hoods: A ducted fume hood connects to your building’s HVAC system, which then carries the air outside. When choosing a ducted fume hood, it will be necessary to work with your building’s infrastructure team to ensure the ventilation system can provide the required volume of air to ventilate the hood properly. Because the ducted fume hood is connected to your duct system, keep in mind that you may have limited options as to where you can place the unit. 
  • Ductless fume hoods: A ductless fume hood is a freestanding unit that does not require your building’s HVAC system. Instead, the hood uses a carbon-based filter to absorb fumes and vapors. The filtered air then recirculates back into the workspace. A secondary particulate-trapping HEPA filter can be added after the carbon filter to provide exhaust air suitable for cleanroom applications. Unlike a ducted fume hood, a ductless fume hood can be placed anywhere and easily moved. 
  • Light-duty hoods: These smaller, basic hoods are used to vent non-toxic materials such as heat, steam, odors and smoke. 
  • Specialized hoods: There are several fume hoods available for specialty applications. Acid digestion hoods are built with chemical-resistant materials to avoid corrosion, while radioisotope hoods are built out of stainless steel to prevent the absorption of radioactive materials. For educational settings, full-view hoods have transparent backs and sides for enhanced visibility when conducting demonstrations or monitoring students, along with multiple openings so students can work from both sides of the hood.

When selecting a fume hood, consider the volumes and types of chemicals you most often work with and how often you work with them, along with the size of the equipment you need to use in your work. This can help you determine the size and capabilities you’ll need in a fume hood to ensure it’s the right fit for both your workspace and your people. Now that you know more about how a fume hood works, you can pick one for your facility.

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.


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