Lab Ventilation Hood

A lab ventilation hood, commonly known as a Fume Hood, is a critical piece of laboratory equipment designed to protect laboratory personnel from exposure to hazardous or unpleasant fumes, vapors, gases, and particulate matter generated during experiments or procedures.

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How a Fume Hood Works

A fume hood functions by creating a contained workspace and establishing a continuous, controlled airflow that sweeps air and contaminants away from the user and exhausts them safely, usually outdoors.

 

 

 

• Enclosure and Sash: It consists of an enclosure with a movable front window called the sash. The sash acts as a physical barrier between the worker and the experiment.

• Airflow: Air from the laboratory room is drawn into the hood through the opening created by the sash. This inward flow prevents contaminants generated inside the hood from escaping into the lab.

• Containment: The hazardous materials are captured and contained within the hood's workspace. Internal baffles direct the airflow toward the exhaust ports.

• Exhaust System: A fan, typically located on the roof of the building, pulls the contaminated air through ductwork and expels it to the atmosphere, often at a high velocity to ensure safe dispersion.

• Face Velocity: The speed of the air entering the hood through the sash opening (face velocity) is crucial for containment, typically maintained within a specific range (e.g., 80–120 feet per minute) to ensure effectiveness without creating disruptive turbulence.

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Types of Ventilation Hoods

There are several types of ventilation hoods, each designed for specific applications and safety needs:

Type of Hood	Description & Primary Function	Key Features
Ducted Fume Hood (Chemical Fume Hood)	The most common type; draws air from the lab and exhausts it outside after passing through ductwork.	Used for general chemistry, volatile or toxic chemicals.
Ductless Fume Hood (Recirculating)	Uses carbon or HEPA filters to remove contaminants from the air and then recirculates the filtered air back into the laboratory.	Mobile, lower installation cost, but filter must be compatible with the specific chemicals used. Not suitable for highly toxic materials.
Variable Air Volume (VAV)	Adjusts the exhaust flow rate based on the sash position to maintain a constant face velocity.	Energy efficient, as less air is exhausted when the sash is lowered.
Constant Air Volume (CAV)	Exhausts a constant volume of air regardless of the sash position.	Simple design, but less energy efficient than VAV.
Perchloric Acid Hood	Specifically designed for heating perchloric acid. Includes a wash-down system in the hood and ductwork to prevent the accumulation of shock-sensitive perchlorate crystals.	Constructed with materials resistant to corrosion (often stainless steel).
Radioisotope Hood	Designed for handling radioactive materials.	Constructed with seamless, coved stainless steel and may include lead shielding or specialized filters.
Canopy Hood	Wall-mounted or suspended hood without a sash.	Designed to vent non-toxic vapors, heat, and steam from equipment like ovens or autoclaves. Does not provide personnel protection from hazardous fumes.

Best Practices for Safe Use

Following proper work practices is essential for the effective function and safety of a fume hood:

• Sash Position: Keep the sash as low as possible (typically at or below the designated operating height) when working. Completely close the sash when the hood is unattended.

• Work Area: Conduct all work and place equipment at least 6 inches inside the hood face to ensure proper containment. Avoid blocking the rear baffle slots.

• Keep it Clear: Do not use the hood for long-term storage of chemicals or equipment, as this obstructs airflow and reduces efficiency.

• Avoid Turbulence: Do not make rapid movements in front of the hood or use fans nearby, as this can disrupt the protective airflow. Keep lab doors and windows closed.

• Pre-Check: Always check the airflow indicator (like a gauge or monitor) before starting work to confirm the hood is operating correctly.