Basic Documentation

Technology Report
February, 2004
Siemens Industry, Inc. Page 1 of 6
Fume Hood Face Velocity
Can it Ensure Safe Containment?
This paper examines the controversy that
sometimes arises regarding whether fume hood face
velocity is indicative of safe fume containment.
Face Velocity Requirements
For many years, fume hood manufacturers,
laboratory safety standards
1
and safety
professionals have maintained that a face velocity of
about 100 fpm was generally required for adequate
fume containment and thus safe fume hood use.
The California State Occupational Safety and Health
Administration (CAL-OSHA) mandated 100 fpm as
the minimum average face velocity with a minimum
of 70 fpm at any point in the sash opening. The U.S.
Federal OSHA is less stringent and recommends a
face velocity from 60 through 100 fpm. In short,
there are many references as to what a fume hood’s
face velocity should be.
More recently, many experienced and renowned
fume hood safety professionals have stated that
having the recommended fume hood face velocity is
no guarantee that a given fume hood will provide
adequate fume containment and user safety. And,
newer editions of laboratory safety standards
contain extensive warnings against using face
velocity as the sole criteria for safe fume hood
operation.
2
Individuals who have wide-ranging
experience in fume hood containment testing,
especially with the ASHRAE 110 tracer gas test, will
frequently cite their own test results as evidence
1. American National Standard for Laboratory Ventilation
ANSI/AIHA Z9.5, 3.3.1: Design face velocities for laboratory
chemical hoods in the range of 80
 100 fpm (0.41  0.51m/s)
will provide adequate face velocity for a majority of chemical
hoods.
2. American National Standard for Laboratory Ventilation
ANSI/AIHA Z9.5, 3.3.1: In one published study,
approximately 17% of the hoods tested using the method
(ASHRAE 110 test method) had "acceptable" face velocities
in the range of 80
 120 fpm, but failed the tracer gas
containment and exceeded the ACGIH recommended
control level of 0.1 ppm. (Smith and Crooks, 1996).
against equating adequate face velocity with
adequate fume containment.
The Designer’s Dilemma
If fume hood face velocity cannot be used as a
criterion for safety, how can a laboratory facility
ventilation system be designed to ensure a safe
work environment for laboratory users? Experienced
designers know that a laboratory ventilation system
design must accommodate the room and fume hood
airflow requirements. Designers often say that a
laboratory room’s ventilation requirements are
primarily driven by the air consumption of the room’s
fume hoods. Since fume hood air consumption is
directly related to face velocity, it follows that the
laboratory ventilation system design is then driven
by the face velocity of the fume hoods.
Face Velocity Controversy
If a fume hood manufacturer has determined what
level of face velocity provides good containment as
a result of properly conducted ASHRAE 110 tracer
gas containment tests, why can’t that face velocity
be indicative of proper fume containment? The
answer is that while a fume hood manufacturer may
have conscientiously performed ASHRAE 110 tests,
the test conditions will invariably not be the same as
the actual laboratory room conditions where the
fume hood is ultimately used. These include:
 Room Airflow–Laboratory rooms are subject to
high makeup airflow rates, especially if the room
has multiple fume hoods. And, high room airflow
rates can often result in appreciable air currents
within the rooms. Research has established that
room air currents (termed cross currents) can be
very detrimental to effective fume hood
containment. Even relatively low air currents
passing in front of a fume hood with an open
sash, can draw fumes out from the hood interior.
Thus, horizontal, vertical, or even angular room
air currents all pose the potential for
Document No. 1
49-989