From: Rita Kay Calhoun <r.calhoun**At_Symbol_Here**MOREHEADSTATE.EDU>
Subject: Re: [DCHAS-L] Benchtop Methylene Chloride Use in Undergraduate OChem labs
Date: Tue, 18 Nov 2014 14:33:27 +0000
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: 081D54673FDDB347BC1F77943BC7C7FA3E0C04DD**At_Symbol_Here**
In-Reply-To <073439EC-C2A5-4F7E-BD07-1DB775124C54**At_Symbol_Here**>

Back in the days before "efficiency" was tied to, and for some became synonymous with, cost efficiency, to say a hood was efficient simply meant that it worked really well to remove vapors. Therefore, working in an "efficient fume hood" meant you were safe from exposure to the volatiles being used.


-----Original Message-----
From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of Stuart, Ralph
Sent: Tuesday, November 18, 2014 6:46 AM
Subject: Re: [DCHAS-L] Benchtop Methylene Chloride Use in Undergraduate OChem labs

>As many OChem labs lack adequate fume hoods, many colleges do these
>extractions at the bench,

My first response doesn't answer the overall question directly, but is about a question that I've been wondering about. What do chemists mean when they say "adequate fume hoods". Is it a question of the number available for the number of work stations desired? Or is it a question of fume hood performance?

One reason I ask is that I've seen peer reviewed papers that direct someone trying to replicate the procedure in an "efficient fume hood" for safety reasons. I'm not clear what that means; from a safety point of view, to fulfill their safety function, fume hoods should capture fugitive chemical vapors released and efficiency isn't part of the safety picture. I'd like to understand the chemists' perspective on fume hoods better.

To more directly answer the question, the industrial hygiene approach to the overall question is that measuring the concentration of methylene chloride in the air during the work and comparing it to an appropriate exposure limit (take your pick from ) should help determine whether the lab facility is up to work being conducted in it. When you look at that link, you'll see why that is a trick answer...

- Ralph

Ralph Stuart, CIH, CCHO
Chemical Hygiene Officer
Keene State College


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