A fume hood is an enclosed device that works to ensure the safety of lab personnel while working with hazardous materials by continuously delivering airflow away from the user. When used properly, fume hoods can prevent users and the environment from toxic gases, explosions, and spills.

Fume hoods are necessary when working with gases, vapors or dust that are hazardous in the event of exposure. They protect you from breathing in particles that can lodge in the lungs or enter the bloodstream.

As the most important appliance in a laboratory, fume hoods keep employees safe by removing harmful vapors and chemicals from the work area. The air they extract is then filtered by the building’s exhaust system before exiting the facility. That, right there, is the simple, two-sentence version of how a ducted fume hood works. But let’s dig a little deeper into how these devices function.

Fume hoods work by filtering the air to prevent the inhalation of toxic particles that can lodge in the lungs and cause serious health implications. 

Ducted fume hoods remove the air from the laboratory and disperse it into the atmosphere outside. Ductless fume hoods recirculate the air by filtering it before redistributing it back into the laboratory. 

Types of fume hoods include bench-top, floor-mounted, double-faced, and portable. The right type of fume hood you need will depend on what materials will be present in your lab, the amount of chemicals you work with, how often you will use the hood, and the kind of ductwork in your workspace. To determine the right fume hood for you, consider your laboratory layout, your budget, the scope of your project, and the chemicals you will be using.

Many factors are considered when pricing a fume hood. Prices differ greatly depending on the dimensions of the hood, special features, and add-ons. A fume hood that is made for work that may result in explosions will be priced much higher than one intended for spill containment. According to industry professionals, the “rule of thumb” is anywhere from $1,200 to $2,500 per linear foot. This means the cost of a 6 foot fume hood could fall anywhere from $7,200 to $15,000. 

A standard fume hood can be plugged into a 120-volt outlet while accommodations can be made for 240-volt outlets. Nearly all fume hoods, ducted and ductless, operate at a voltage that is safe for these outlets. However, it is always good to check the supply voltage for a fume hood, which can be found on the rating plate of each junction box.

To ensure that your fume hood continues to function properly, it must be tested upon installation and at least once a year. To obtain a certification, the fume hood must meet certain requirements. 

The sash refers to the front window or “door” of a fume hood. The glass window slides open and closed, allowing access to the workstation. The sash window provides both containment and protection from hazardous materials. The safety glass of the sash is designed to “spider” instead of shatter in the event of an explosion.

A fume hood is not designed to contain high-velocity releases of contaminants unless the sash is fully closed. If an explosion occurs when the sash is open, the glass and contents inside the hood will be spread around the laboratory, potentially harming other lab personnel.

It’s okay to have chemicals inside the fume hood when it is in use, but fume hoods are not designed to store chemicals for long periods of time.

In the case of an explosion, sashes are designed to “spider” instead of shatter, keeping those in the area safe from glass and chemicals. While they aren’t designed to handle every incident, a properly-installed fume hood will provide protection from small explosions and fires.

Biosafety cabinets are designed to provide a clean work environment and protection for personnel who create aerosols when working with infectious biological agents or toxins. A biosafety cabinet is appropriate when only small quantities of volatiles are present. If the amount is determined hazardous by a safety officer, then a fume hood is necessary. Most biosafety cabinets are not safe to use in place of a fume hood. 

There are two types of fume hood exhaust systems; Constant air volume (CAV) ventilation provides a constant flow of air, whether the sash is open or not. Some fume hoods have variable air volume (VAV) ventilation. These hoods vary the volume of air from the room that is exhausted while maintaining the face velocity at a predetermined level. 

Face velocity is a measurement of the speed at which air enters a fume hood’s face opening. It is generally recommended that a fume hood’s face velocity is between 0.3 m/s (60 fpm) and 0.5 m/s (100 fpm), however, it is best to check with local safety regulations before using a fume hood because variations exist by state and by use.

All fume hoods should have a coded certification or marking displaying the date of the last inspection.

The National Fire Protection Association recommends placing fume hoods at least 10 feet from any doorway and away from high-traffic areas, air supply diffusers, or windows. A fire or explosion could block a passageway and trap personnel in the lab. Also, any area that produces air currents or potential turbulence could affect the ability of the hood to capture and exhaust contaminants as designed

Like any equipment, fume hoods need regular cleaning to keep them in good condition. First, make sure that the cleaning agents will not react with the chemicals in the hood. 

• Polyglass Liner: Mild soap and water. 
• Sash Glass: Commercial glass cleaner. 
• Painted Steel Surfaces: Mild soap and water, ethyl alcohol or commercial glass cleaner. 
• Epoxy Liner and Worktops: Mild soap and water, solvent, or commercial glass cleaner. 
• Plumbing Fixtures: Fixtures are coated with a corrosive resistant coating. Mild soap or detergent only. Do not use an abrasive cleanser. 

If a fume hood fails a safety check or doesn’t pass a filtration efficiency test, it’s time to upgrade to a newer, safer hood.

The type of blower is directly related to the intended use of the fume hood. If the fume hood is used for venting non-toxic materials, an epoxy coated steel blower may be the best option. If the fume hood’s primary use is mixing acids, an acid-resistant blower made of PVC, polypropylene or fiberglass reinforced plastic may be the best option.