Why Should A Fume Hood Sash Stay Lowered?

A lowered sash creates a physical barrier between the user and the work inside the hood. Depending on the design, sash position also affects airflow and the amount of conditioned air being exhausted.

Why Should Fume Hood Baffles Stay Clear?

Baffles direct air through the hood toward the exhaust path. Blocking them with materials or equipment can disturb airflow and reduce the hood's ability to capture contaminants.

What Is The Difference Between Constant-Volume And VAV Hoods?

A constant-volume hood exhausts a fixed amount of air. A VAV hood changes exhaust volume as the sash moves, so face velocity can remain more consistent while reducing total exhaust volume when the opening becomes smaller.

The Purpose Of A Fume Hood: How It Works With Lab Exhaust

Quick Summary

PSA Laboratory Furniture explains the purpose of a fume hood and how it works with a laboratory exhaust system to capture and remove hazardous airborne contaminants. The article also covers sash position, baffles, airflow, exhaust design, and planning considerations that influence hood performance.

Understanding the fume hood's purpose starts with its role as an engineering control. A chemical fume hood captures gases, vapors, and fumes and moves them away from the user.

In a ducted system, an exhaust fan draws contaminated air through connected ductwork and discharges it outside the building. Fume hoods are widely used as engineering controls to reduce laboratory exposure to hazardous materials.

The Purpose Of A Fume Hood: How It Works With Lab Exhaust

How A Fume Hood Moves Contaminated Air

A fume hood draws room air through its front opening and across the work area. Princeton explains that the exhaust fan pulls airborne contaminants into the hood and moves them through the duct system. This airflow helps prevent hazardous vapors and fumes from dispersing into the surrounding laboratory.

Several components work together to control this airflow. The sash at the front of the hood creates a partial barrier between the user and the experiment. Inside the enclosure, slots and baffles help direct air toward the exhaust path. The airfoil at the hood face also helps air enter more smoothly while reducing turbulence.

Why The Sash And Baffles Matter

The sash serves more than a viewing function. Its position changes the size of the hood opening and can affect airflow through the enclosure. Keeping the sash closed when it is not necessary to keep it open creates a physical barrier and can reduce energy consumption.

Baffles also need adequate clearance to function properly. Stored materials or large equipment can obstruct them and interfere with the exhaust path, which can reduce capture efficiency. Keeping materials away from these airflow paths helps the hood perform as designed.

Each hood should also have a flow monitor or alarm. If an alarm activates, work should stop, the sash should be closed, and the issue should be reported according to the facility's established procedures.

Constant Volume And Variable Air Volume Hoods

Princeton identifies two basic approaches to fume hood exhaust: constant volume and variable air volume.

A constant-volume hood pulls a fixed quantity of air. When its sash is lowered, the opening becomes smaller, so face velocity increases. Face velocity refers to the speed of air moving through the hood opening. A variable air volume, or VAV, hood changes exhaust volume as the sash moves. This helps maintain a more consistent face velocity while reducing total exhausted air when the sash is lowered.

PSA Laboratory Furniture offers several fume hood configurations, including airfoil bypass, high-performance, walk-in, variable air volume, perchloric acid, radioisotope, demonstration, thin wall, low bench, snorkel, and canopy models.

How The Hood Works With The Laboratory Exhaust System

The fume hood and laboratory exhaust system operate as a connected system. The hood captures contaminants at the work area, while the ductwork and exhaust fan move those contaminants away from the laboratory. If airflow is disrupted, the hood may not perform as intended. The exhaust connection, hood opening, sash position, and internal airflow path all contribute to effective containment.

For this reason, hood selection should be considered alongside the broader laboratory design. Hood placement, casework, work surfaces, equipment dimensions, and utility locations can all affect how the finished space functions. The planning process starts with a consultation, followed by drawings and revisions based on customer feedback.

Once the design is approved, a quotation is prepared, followed by coordination of ordering and shipping and, when selected, optional non-mechanical installation.

Plan Fume Hood Placement With The Entire Lab In Mind

The fume hood's purpose is closely tied to airflow, exhaust design, and user practices. A suitable hood also needs to fit the laboratory's layout and intended work.

At PSA Laboratory Furniture, we coordinate fume hoods with metal cabinets, countertops, sinks, fixtures, and other laboratory components. Our single point-of-contact project management helps customers move from layout discussions through design, ordering, shipping, and optional installation. This coordinated approach can make it easier to address equipment placement and laboratory furniture requirements within one project plan.

Frequently Asked Questions

The main purpose is to capture hazardous gases, vapors, and fumes at the work area and move them away from the user. In a ducted system, contaminated air travels through ductwork and is exhausted outside.