This is a 5 minute 3D face Velocity Profile
I hope this message finds you well. I wanted to bring to your attention an important issue regarding the assessment of fume hood safety metrics, specifically the reliance on average face velocity.
Above is a 5-minute face velocity reading taken from a single face velocity profile cell during an ASHRAE 110 SF6 containment test. This data consists of 300 points taken once per second over a 5-minute period. While the average face velocity was recorded at 102 feet per minute (fpm), the readings varied significantly, ranging from a minimum of 35 fpm to a maximum of 145 fpm.
The ASHRAE 110 standard call for a 20 second reading to determine an average. However, with this technique, you could derive an average anywhere from 35 fpm to 125 fpm based on which 20 seconds of data you selected.
What does this data truly reveal? It indicates considerable turbulence within the fume hood, leading to unstable airflows. This instability suggests a high probability of containment loss during the 5-minute period. Simply put, average face velocity is not a reliable metric for determining fume hood performance and safety.
A face velocity profile provides a more accurate prediction of containment. But to really see the hoods performance, and use face velocity as a indication of safety, it is crucial to conduct a 5-minute capture, displaying the average, minimum, and maximum face velocity for each cell. And hoods with a variation of more than +/- 10% of the average should be investigated further.
Remember it isn’t about face velocity it is about containment. As I point out in my presentations about 70% of hoods that perform poorly on a containment test have acceptable face velocities.
Consider this: would you certify a hood as safe based on such fluctuating data? In the event of an accident, under legal scrutiny, how would you justify the determination of the hood's safety? Especially when many standards acknowledge no direct correlation between face velocity and containment?
It's something worth serious consideration.
If this type of conversation is of interest to you, you might want to consider attending one of in-person fume hood performance workshops. For more information click here.
The ASHRAE 110 standard call for a 20 second reading to determine an average. However, with this technique, you could derive an average anywhere from 35 fpm to 125 fpm based on which 20 seconds of data you selected.
What does this data truly reveal? It indicates considerable turbulence within the fume hood, leading to unstable airflows. This instability suggests a high probability of containment loss during the 5-minute period. Simply put, average face velocity is not a reliable metric for determining fume hood performance and safety.
A face velocity profile provides a more accurate prediction of containment. But to really see the hoods performance, and use face velocity as a indication of safety, it is crucial to conduct a 5-minute capture, displaying the average, minimum, and maximum face velocity for each cell. And hoods with a variation of more than +/- 10% of the average should be investigated further.
Remember it isn’t about face velocity it is about containment. As I point out in my presentations about 70% of hoods that perform poorly on a containment test have acceptable face velocities.
Consider this: would you certify a hood as safe based on such fluctuating data? In the event of an accident, under legal scrutiny, how would you justify the determination of the hood's safety? Especially when many standards acknowledge no direct correlation between face velocity and containment?
It's something worth serious consideration.
If this type of conversation is of interest to you, you might want to consider attending one of in-person fume hood performance workshops. For more information click here.
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. It was once said in an ASHRAE 110 committee meeting, “We don’t design hoods to contain, we design them to perform well on the ASHRAE 110 tests”