Laboratory Fume Hood Basics. What is a Fume Hood? Why are they important? And How do they work?

What is the purpose of the fume hood?

A laboratory fume hood is a ventilated enclosure used in laboratories to safely contain and remove hazardous fumes, vapors, gases, and airborne chemicals produced during experiments or procedures. It works by drawing air into the hood and exhausting it through a ventilation system, preventing harmful substances from being released into the laboratory environment. Fume hoods typically have a movable sash or window, which can be adjusted to provide access to the workspace while ensuring safe airflow. They are essential for protecting laboratory personnel from exposure to potentially harmful airborne contaminants.

Why is it important to have a fume hood?

Having a fume hood in a laboratory is important for several key reasons:

1. Safety: Fume hoods protect laboratory workers from exposure to harmful chemicals, toxic fumes, vapors, gases, and particulates that could be released during experiments or processes. This is critical for preventing respiratory issues, chemical burns, and other health hazards.
2. Containment: They effectively contain hazardous substances, preventing their spread into the general laboratory space. This helps minimize the risk of accidents and exposure to both laboratory workers and others in the building.
3. Ventilation: Fume hoods ensure that the air inside the hood is continuously exchanged and filtered, removing harmful contaminants from the environment and maintaining clean air for the researcher. This is particularly vital when working with volatile or toxic substances.
4. Chemical Handling: Some chemicals release toxic gases or vapors when exposed to air, heated, or mixed with other substances. Fume hoods help manage and mitigate the risks associated with such reactions, ensuring safe chemical handling.
5. Compliance: Many safety regulations and guidelines, such as those from OSHA (Occupational Safety and Health Administration) and ANSI (American National Standards Institute), require the use of fume hoods in laboratories that work with hazardous materials. Compliance with these regulations helps ensure safe working conditions.

Overall, fume hoods are a critical safety feature in any laboratory, ensuring the protection of researchers, the environment, and the integrity of experiments.

How does a fume hood work?

A fume hood works by creating a controlled airflow that captures and exhausts harmful fumes, vapors, and gases from the laboratory environment. Here’s a breakdown of how it operates:

1. Airflow Design

• Sash or Window: The fume hood has a front window (called a sash) that can be raised or lowered. This allows access to the interior of the hood while controlling the volume of air entering.
• Air Inlet: Air is drawn into the hood through the open sash as it moves from the laboratory room into the hood's interior. This airflow is typically directed from the front to the back of the hood.

2. Capture and Containment

• Airflow Movement: The air drawn in helps to capture and contain any hazardous substances, such as chemical fumes or vapors, generated within the hood. The air moves towards the back of the hood, where it enters the exhaust system.
• Containment of Dangerous Materials: The hood is designed to prevent contaminants from escaping into the lab space. This containment is essential for worker safety.

3. Exhaust System

• Exhaust Fan: Once the air enters the fume hood, it is sucked through the exhaust system by a fan. This fan moves the contaminated air outside the building or into a specialized filtration system.
• Ductwork: The air is typically funneled through ductwork that leads to the exterior of the building, where it is released safely. In some cases, fume hoods may use filters (like HEPA or activated carbon) to remove hazardous substances before exhaust.

4. Airflow Speed (Face Velocity)

• The speed of the incoming air is crucial for ensuring safe containment. A typical fume hood maintains an airspeed (called face velocity) of around 80–120 feet per minute (fpm) to ensure that harmful fumes are properly captured and not allowed to escape into the lab.

5. User Safety and Adjustment

• Adjusting the Sash: Users can adjust the sash height based on their needs. A lower sash height ensures optimal airflow and containment. Keeping the sash at an appropriate height is important for maintaining safe conditions in the lab.
• Continuous Ventilation: A well-functioning fume hood provides continuous ventilation, even when not in use, to maintain a safe working environment.

In short, a fume hood works by drawing contaminated air into its enclosure and safely expelling it outside the building, preventing harmful substances from contaminating the laboratory air and protecting those working in the lab.