After a short summer break, we’re excited to be back with our weekly newsletter! While many of you have been enjoying vacations and quality time with family (which is wonderful), we’ve been hard at work attending conferences and hosting workshops – even braving the heat in Phoenix. We also took our insights overseas to China, where we had some fascinating conversations.
One recurring theme at these events has been the use of face velocity as a metric for determining safe fume hood performance. My curiosity got the better of me, and I couldn’t resist digging deeper by asking the “5 Whys” (with a few “What Ifs” thrown in for good measure).
Why Face Velocity Might Be Leading Us Astray
It all started with a simple question: Why does ASHRAE 110 take just a 20-second reading for face velocity but a 300-second reading for SF6? Intrigued, I decided to conduct face velocity readings alongside the SF6 tests, and to put it bluntly, the results were eye-opening.
Take a look at this 300-second velocity reading. Depending on which 20-second window you choose, the numbers can vary dramatically. This led me to conduct more 300-second readings, and what I discovered was startling: average face velocity is almost useless as a metric. It barely tells us if air is flowing through the sash, let alone whether it’s flowing into or out of the hood – or worse, both.
There are fifteen 20-second interval readings in a 300 second test window. Where you view or capture any of those 20-second windows will give very different views or answers.
So what is the real face velocity?
I now have a much better understanding of the challenges in even determining an average face velocity. But here’s the kicker: it’s not really about face velocity at all. The real issue is containment. If a hood isn’t containing, regardless of its face velocity, it’s failing in its primary role as an exposure control device. Relying on average face velocity as a safety metric is risky, to say the least. You definitely wouldn’t want me testifying against you as an expert witness in an accident case.
It’s time to shift our focus from face velocity to containment. If a hood isn’t containing at safe levels, then it’s simply not performing its job. And if you’re not ready to make the necessary changes to ensure proper containment, you might as well shut the hood off and save the energy.
Let’s rethink how we approach fume hood safety. It’s time for a change.
True containment is determined by dynamic conditions in your lab. Realistic dynamic containment testing is challenging, we developed the Tri-Color system to provide a more accurate validation of containment in the conditions that exist in your lab..
If Tri-Color is of interest to you visit our Tri-Color website
Warmest regards from the entire Fume Hood Certified Team,
Chip Albright
Founder and President
Fume Hood Certified, LLC.
PO Box 71477
Phoenix, AZ 85050.
Email: Chip@fumehoodcertified.com
P.S. We will be doing the final Fume Hood Performance Workshop of this year Oct 2nd and 3rd This one will be another sellout. If you want to join this great group, act now.. For more information click here.
P.S.S. If you missed the earlier emails, many are posted here BLOG