Ralph, Maybe the initial question should be to ask the chemist making the determination, specifically to define how the determination is being made and to what criteria.   If the determination is made upon limiting the maximum extraction quantity to not have a STEL, IDLH, etc., exposure scenario in case of an accident, I would be impressed and want to hire any graduate of that program!   However, if the determination is made based upon the chemists reliance upon odor threshold, designed ventilation system performance, instead of standard IH quantification, as used ventilation evaluation, etc., then we not only have a great deal of training/education to complete, but job security as well.      Bruce P..S.  The job security comment is due to the rapid turnover in undergraduate organic chemical labs and not meant to be detrimental in any way.  -----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 To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU 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 https://www.osha.gov/dts/chemicalsampling/data/CH_253450.html ) 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  ralph.stuart**At_Symbol_Here**keene.edu