Laboratory Fume Hoods
Fume hoods are chemical containment devices used to control chemical emissions (and resulting exposures). The emission is controlled by enclosing and containing the emission in the hood.
To provide adequate control of the emissions, a fume hood must provide an average face velocity of 100 feet per minute. Air velocities exceeding 150 feet per minute (fpm) and below 80 fpm can cause eddy currents. The eddy currents can release the chemical emissions into the laboratory and expose individuals without warning.
Found mainly in the Physical Science Laboratory Building (PSLB), auxiliary air hoods were developed to reduce energy consumption.
They function by supplying outside air near the top and front of the hood face. This is to prevent the conditioned laboratory air from being exhausted through the hood.
Auxiliary air hoods do not exhaust the ambient laboratory air. Do not rely on these hoods to be a source of exhaust ventilation ambient laboratory air.
How to use a Fume Hood
- Position the sash to be in line with the 100 feet per minute arrow located on the side of the hood. The arrow is located were proper air flow velocities are achieved at the hood’s face.
- Set up work at least six inches from the face opening. This will avoid turbulence at the sash edge and provide greater protection.
- Separate and elevate each instrument. Use blocks or racks to elevate equipment one to two inches off the hood deck surface so that air can easily flow around all apparatus with no disruption.
- Lower sash to optimum height. The sash will then act as a physical barrier in the event of an unplanned incident in the hood.
- Keep hood storage to an absolute minimum. Keep only items needed for ongoing operation inside the hood. Excess materials in the hood disrupt airflow and can act as a barrier or cause airflow to bounce back across the face of the hood. Keep the back bottom slot clear at all times as it serves as an exhaust port for fumes and heat generated near the surface.
- Minimize foot traffic near and around the hood. A person walking past the hood can create competing air currents. Other cross drafts should be eliminated such as open doors or fans. Use extreme caution with ignition sources inside a fume hood. Ignition sources such as electrical connections and equipment, hot plates, controllers, and open flame will ignite flammable vapors or explosive particles from materials being used in the hood. All electrical equipment used inside a fume hood must be designed or certified as intrinsically safe unless it can be absolutely established (and enforced) that flammable or explosive materials will not be used in a particular hood.
- Never put your head inside a hood while operations are in progress. The plan of the sash is the imaginary boundary that should not be crossed except to set up or dismantle equipment.
- Clean up spills as soon as possible.
- Do not dismantle or modify the physical structure or exhaust system without consulting Environmental Health and Safety first. Modifications can result in a decrease in air flow and could make the hood less protective.
Laboratory Fume Hood Components and Functions
- Airfoil: found along the bottom and sometimes edges, airfoils streamline airflow into the hood preventing turbulent eddies at the face that can carry vapors out of the hood. Bottom airfoils also provide a space for room airflow when the sash is completely closed.
- Baffles: movable or adjustable petitions used to create slotted openings along the back of the hood body. Baffles help to keep a uniform airflow across the face of the hood, which eliminates dead spots and optimizes capture efficiency.
- Sash: a movable, see through barrier that closes or opens the face of the hood
- Work Surface: generally a laboratory bench top. The area under the hood where apparatus and equipment is placed.