Beliefs about face velocities have certainly evolved over the years. First we learned that more isn't necessarily better and in recent years we learned that less isn't necessarily worse either.
The latest edition of the Canadian Standards Association Z316.5-15 Fume Hoods and Associated Exhaust Systems recognizes that face velocity alone is not a reliable determinant of hood performance and, depending on the conditions of use, a wide range may be acceptable. Here's a brief table that summarizes what it says:
Face velocity range
>.75 m/s (> 150 fpm)
0.65 - 0.75 m/s (120 - 150 fpm)
Potential for turbulence. High cost.
0.5 - 0.6 m/s (100-120 fpm)
Effective but costly
0.4 - 0.5 m/s (80 -100 fpm)
Effective and cost effective
0.3 - 0.4 m/s (60 - 80 fpm)
Effective under ideal conditions
< 0.3 (<60 fpm) standard hood
< 0.3 (< 60 fpm) high performance hood
Performance tests critical.
I hope you find this helpful.
Wayne Wood | Director, Environmental Health and Safety -Directeur, Sante´, securite´ et environnement|McGill University | 3610 rue McTavish Street, 4th floor | Montreal, Quebec, Canada, H3A 1Y2 | Tel: (514) 398-2391
100 fpm is the standard for us. But, we do have some at 80 fpm if they pass a qualitative test with either smoke or dry ice in warm water.
Check out the CHAS website for some resources from the Fume Hood Design Workshop that was held a couple of years ago. It's under the Technical Resources tab.
SEFA 1 was updated in 2010.
As far at the sash height, we go with 18 inches with a stop installed. I've heard of others going as low as 14". We've considered this. But, we have too many people who are really tall. The comfortable working height is different for everyone and 18", with instruction to keep the sash between you and your work, seems the most flexible.
Laboratory Ventilation Specialist
Department of Environmental Health and Safety
By a quick show of hands, what face velocity do all of you consider as an acceptable velocity for certifying standard chemical fume hoods in academic and research labs? OSHA is pretty vague on the issue (must provide adequate ventilation [1910.1450(e)(3)(iii)]). Appendix A (non-mandatory) references Prudent Practices, where 80-100 is standard, up to 120 is okay for high hazard (no containment benefit proven) and 60fpm may be okay for low flow, specially designed hoods.
Before getting into too much detail, I am curious as to what all of you are considering as passing at 18in sash height, and what you are considering as failing.
Brandon S. Chance, M.S., CCHO
Associate Director of Environmental Health and Safety
Office of Risk Management
Southern Methodist University
PO Box 750231 | Dallas, TX 75275-0231
T) 214.768.2430 | M) 469-978-8664
" - our job in safety is to make the task happen, SAFELY; not to interfere with the work - " Neal Langerman
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