From: Robert Haugen <haugenengineering**At_Symbol_Here**YAHOO.COM>
Subject: Re: [DCHAS-L] High performance hoods
Date: June 27, 2012 8:13:56 PM EDT
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: <1B4D1665F78352429F7714A6540EB03629429F34**At_Symbol_Here**>

As you note, Ralph, most issues are not related to hood containment if face velocities are properly set per manufacturers' and end users' recommendations.
Some more relevant issues are:
1)  Air changes in lab.  Unless special detection and flushing technology is present, a small number of HE hoods in a lab may not produce enough air changes to promptly clear a lab proper from accidental spill vapors.  Also, lab thermostatic and humidity control may become issues.
2)  Low lab air changes may also produce an excessive thermal gradient from ceiling to floor.
3)  Errors in setting hood flows become more significant when nominal flow is a lower number. 
+ 10 FPM is fairly inoccuous at 100 FPM (+10%), but downright serious at 60 FPM (+18%).
4)  Solvents tend not to be problems as long as duct concentrations can never exceed 10% of the LEL.
I have had other experiences with HE hoods and would be glad to elaborate for any members wishing more detail.
Dr. Bob Haugen

From: Ralph B Stuart <rstuart**At_Symbol_Here**CORNELL.EDU>
Sent: Wednesday, June 27, 2012 10:47 AM
Subject: Re: [DCHAS-L] High performance hoods

>  Does anyone have experience with such hoods and have they found them to be acceptable for use with common solvents. Are there any downsides to their use?

I have seen demonstrations of them that indicate that they work as well as more traditional hoods in terms of containment. Aerodynamically, there's nothing particularly magic about 100 fpm, so I believe that a well designed hood should be able to provide the same protection at 80 fpm and don't forsee any operational downsides. Some jurisdictions have regulators who need to be convinced of this, though.

Maybe someone with more direct experience of the lower flow hoods knows of other challenges they present?

- Ralph

Ralph Stuart CIH
Laboratory Ventilation Specialist
Department of Environmental Health and Safety
Cornell University


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