ASHRAE Journal - June 2022 - 31

TECHNICAL FEATURE
escaping from the hood during
radiochemical experiments,
with a double vacuuming
system for personal protection.
Woodrow summarized different
institutions' recommended
values of face velocity to
maintain an acceptable hood
performance in her thesis, and
the details are shown in Table 1.14
A meta-analysis conducted
by Ahn, et al., revealed that
extremely low (<0.30 m/s
TABLE 1 Recommended fume hood face velocity values by different institutions.14
INSTITUTIONS
American Conference of Governmental Industrial Hygienists
National Institute for Occupational Safety and Health
U.S. Occupational Safety and Health Administration
National Fire Protection Association
U.S. Nuclear Regulatory Commission
Scientifi c Equipment and Furniture Association
American National Standards Institute
[<60 fpm]) or high (>0.76 m/s [>150 fpm]) face velocities
can signifi cantly reduce hood performance.
They found that increasing hood face velocity by
0.05 m/s (10 fpm) could reduce the hood failure ratio
(HFR) by 2%, although the relationship was not statistically
signifi cant.4 He and Guffey 6 investigated
fi ve levels of hood face velocity, and their experiments
indicated that there is an inverse relationship
between breathing zone leakage concentrations (Cbz)
and face velocities. While the highest Cbz value was
around 35 ppm under the lowest hood face velocity
(0.56 m/s [110 fpm]) and lowest cross-draft velocity
(0.07 m/s [14 fpm]), the lowest value of Cbz (approximately
0 ppm) occurred at the highest face velocity
(1.16 m/s [238 fpm]). According to research by Fuller
and Etchells, the face velocity can be as low as 0.31 m/s
(61 fpm) to maintain acceptable fume hood containment
performance if the operator follows the safety
procedure, and the cross-draft airfl ow velocity is less
than 30% of the average face velocity.15 These fi ndings
were verifi ed by Milcell, et al., in their later studies.16,17
Similarly, the American Conference of Governmental
Industrial Hygienists (ACGIH) warned that keeping
face velocities above 0.64 m/s (130 fpm) could lead to
excessive turbulence and consequently potential leakage
of contaminants as well as personal overexposure to
hazardous materials.18 The face velocity test results from
Tseng, et al., also confi rmed that lower face velocity
may not necessarily render poor hood containment
performance and may be capable of passing the criteria
recommended by ANSI/AIHA/ASSE Standard Z9.52012.9,19
In another study, Volin, et al., addressed the
importance of fume hood bypasses to the robustness of
the face velocity in constant air volume (CAV) systems.
RECOMMENDED FUME HOOD FACE VELOCITY (fpm)
60 - 100
100 - 1150
150 (for carcinogens only)
No specifi c requirements as long as the escape of fume
can be prevented
100 (for radioactive materials handling in medical
institutions); 150 (for operation with
enriched Uranium-235)
125 - 1150
100 - 1150
They found that the proper bypasses can support
a constant face velocity in the range of 0.48 m/s to
0.56 m/s (95 m/s to 110 fpm), and that there was no
signifi cant improvement in containment performance
with face velocities above 0.51 m/s (100 fpm).5
None of the studies mentioned previously review
the potential impact of various infl uential factors on
the robustness of face velocity. As mentioned earlier,
this article aims to further analyze these impacts
through fi eld experiments and comparative analysis.
Measurement and characterization of face velocity
under the infl uence of real operational factors could
facilitate a better understanding of fume hood
containment performance in the AU condition and
further guide investigation of the root cause of fume
hood containment failure. While this study involved
several predefi ned infl uential factors, the methodology
and process can be applied to examining potential
impacts on the robustness of face velocity for fume
hood containment performance evaluation of other
infl uential factors.
Materials and Methods
Field Experiments
Comprehensive face velocity measurement under the
infl uence of various factors in the AU condition (namely
thermal load, small and large inside clutter, tracer
gas emission rate) was conducted following ASHRAE
Standard 110-2016. The tracer gas containment test was
performed and provided supplementary information
on the various factors' infl uence on hood performance.
Finally, the impact of infl uential factors on fume hood
face velocity was characterized in terms of average and
variation values, as well as correlation with tracer gas
containment test results.
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