Basic Documentation

Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 10
Term Definition Commentary
Fume Hood:
Baffle
Fume Hood:
California Hood
Fume Hood:
Containment
Fume Hood:
Face Opening
Fume Hood:
Face Velocity
Fume Hood:
Interior
Fume Hood:
Low Flow
Interior panel(s) on the rear wall of a fume hood that can be adjusted to direct the air
flowing through the fume hood interior for maximum effectiveness.
A fume hood with multiple or all sides being transparent and often with access to the
interior from two or more sides. It is often utilized when large distillation equipment is
required and in teaching labs when greater visibility is desired.
Keeping hazardous or unhealthy airborne substances such as fumes, gasses, smoke,
particulate, etc. from leaving the fume hood interior through the sash opening. Providing
containment of harmful airborne chemical substances so they can be removed by the
exhaust system is a fume hood’s primary function.
The fume hood opening at any given time (usually in the front) through which a user can
reach in and manipulate the chemicals and associated experimental apparatus.
The velocity or speed of the airflow moving into the fume hood, perpendicular to the
face opening, expressed in feet per minute (fpm) or meters per second (m/sec). This
airflow serves to prevent the user from being exposed to fumes emanating within the
fume hood interior. Since the actual velocity of the air is different throughout the overall
face opening, fume hood face velocity is always the average velocity
in the plane of the
fume hood face opening. The average face velocity must be within certain minimum and
maximum limits to provide proper user protection. (Also see the section on Fume
Hoods: Face Velocity.)
The internal volume within the fume hood’s sides, back, top, work surface, sash and the
internal exhaust plenum. The interior surfaces are normally lined with material that is
both chemically resistant and has a high resistance to combustion (that is, a flame
spread rating 25 or less in accordance with ASTM-E84).
A fume hood design that provides a means to reduce overall air consumption primarily
by utilizing a sash arrangement (See Fume Hood Sash) that reduces the maximum
attainable face opening. For instance, the same width of fume hood with horizontal
sliding sashes will require less total airflow (cfm) to maintain the same face velocity at
the maximum attainable face opening than the same width fume hood that has a single
vertical rising sash.
The nomenclature “California” is a carryover
from the initial versions of this specialized
type of fume hood design that were first
utilized in California.
The preferred way of determining fume hood
average face velocity is by first calculating the
fume hood’s face opening area in square feet
(or square meters). Next, the total fume hood
exhaust airflow in cubic feet per minute (or
liters per second) is measured. Lastly, the
total fume hood exhaust airflow is divided by
the face opening area to determine the
average face velocity in feet per minute (or
meters per second). For example, if a fume
hood had a face opening area of 8 square
feet and a total exhaust airflow of 800 cubic
feet per minute, the average face velocity
would be 800 cubic feet per minute ÷ 8
square feet which equals 100 feet per minute.
Note that fume hoods with multiple sashes
can have multiple face openings depending
upon the individual sash positions. The total
face open area then consists of a summation
of the individual sash face opening areas.