From: "R Alton Simpson (asimpson)"
Date: April 8, 2009 9:01:42 AM EDT (CA) To: Ralph Stuart Subject: FW: [DCHAS-L] Class lab fume hoods? We still provide a small fume hood for each pair of students in teaching labs; we also provide a few 4 to 6 foot hoods in the lab for unusual tasks that need more room. These small hoods are ducted bench top units that are quite adequate for the work, but use much less space and air volume than a normal fume hood. The small hoods do pass the ASHRAE 110 test. Al Alton Simpson, CHMM, NRCC-CHO Director, Environmental Health and Safety The University of Memphis 216 Browning Hall Memphis, TN 38152-3340 (901) 678-4672 fax (901) 678-4673 http://ehs.memphis.edu ==== =0CFrom: ACTSNYC**At_Symbol_Here**cs.com Date: April 8, 2009 9:10:18 AM EDT (CA) To: ecgrants**At_Symbol_Here**uvm.edu Subject: Re: [DCHAS-L] 12 Re: [DCHAS-L] Class lab fume hoods? >In our Organic labs we currently have bench top hoods for each student pair, as well as two larger hoods in each lab. We are having one lab updated over the summer and installing island workbenches. One hood will hang over each island and be accessible from all sides so that two pairs can work under it. Then we will have 3 larger hoods with sashes in the lab also, and one will be handicap accessible. The only further comment I would have would be on this entry. This type of canopy overhead hood violates the ACGIH industrial ventilation principles and will not be effective for vapors and gases emitted by evaporation or release at room temperature or below. Canopy overhead hoods are only proper for very hot processes which will drive emissions up into the hood's capture area which is only a few inches from the face of the hood. Emissions from the types of chemical procedures in most labs are only effectively captured by enclosure such as the standard fume hood provides. Monona Rossol, M.S., M.F.A., industrial hygienist Arts, Crafts &Theater Safety, Inc. and Safety Officer, United Scenic Artist's, Local USA829 International Alliance of Theatrical Stage Employes (IATSE) 181 Thompson St., #23 New York NY 10012-2586 212/777-0062 artscraftstheatersafety.org === =0CFrom: "DAVID KATZ" Date: April 8, 2009 10:40:59 AM EDT (CA) Subject: Re: [DCHAS-L] 12 Re: [DCHAS-L] Class lab fume hoods? Hi Ralph, Some interesting responses to your inquiry. Here are some of my experiences. Currently, I work at Pima Community College in Tucson. I have been here for 6 years. We have 3 chemistry labs with hoods along one long side of the room. Two labs have 2 long 8 to 10 foot hoods with no pull down sashes. There is a small 4 foot hood in the center that does have a pull-down sash that we use for waste materials generated during lab classes. The thrid lab has 5 6-foot hoods along with a smaller hood like the other labs. The hoods have simply one-setting, on or off. To the best of my knowledge, they do not pull any make-up air from outside to compensate for the negative pressure in the room. I have no data on number of air exchanges per hour in the labs. Each hood has at least one small sink in it along with gas jets. We generally do not use the sinks, except for the lab reserved for organic experiments, so they show the effects of non-use. We do use the gas jets occasionally, but usually use hot plates or other electrical sources for heating. These labs are over 25 years old. The hoods have not been well maintained over the years and, after having hoods in one lab non-operational for a week, I have recently insisted on starting a monthly check of the hoods in addition to visual checks by facuilty and our lab specialist. Overall, these have been adequate for most of the work we do in our labs. I have been very instrumental in getting our faculty to go to smaller scale experiments and eliminating those experiments that produce too many fumes. The hoods are in dire need of an upgrade, but I know our heating/air conditioning system could not handle the load of more efficient hoods. I keep asking about a new science building rather than replacement of our hoods. Since the hoods should be on continuously, they should be able to be powered down to a lower setting when the lab is not in use or when we are lecturing in the lab. They should pull make-up air from outside to reduce some of the strain of the heating/air conditioning system. In 1980, we designed new labs at the Community College of Philadelphia. We wanted at least 6 5-foot hoods per lab with exhaust canopies over each work area. The big problem was that the negative pressure would he too high. We did end up with 6 hoods per room and that was adequate for our classes, but did produce quite a bit of negative pressure, even with make-up air being pulled into the hood from outside. These hoods had two settings,"low and high". All the hoods were equipped with a small sink, water, gas, compressed air, and vacuum. The labs had about 8 air exchanges per hour. We were quite pleased with the hood set-up in each lab. I did work for 5 years at a small college where there was only one, poorly functional hood in the lab along with poor ventilation. I had to rethink all our experiments to adjust for those conditions. Organic chem did not fare as well so we needed open doors and exhaust fans. Thankfully, there was only one incident with an organic student getting ill from fumes and that was settled without any legal litigation. That college eventually built a new science building, but that was after I left. I cannot envision a chemistry lab without hoods. They are useful just in speeding up water evaporation for some experiments. One of the major factors to be considered is not just the number of hoods per lab, but the experiments being performed in each lab. I would suggest that the experiments be reviewed and updated for smaller scale and to reduce fumes where possible. Plan the hoods for current and anticipated student use, more hoods for organic and upper level labs, less hoods for introductory labs. Remember to have a determination of the number of air exchanges per lab per hour (no one mentioned that in your compilation of answers) Portable hoods do serve a purpose, but have very limited application - I only recommend them for something such as an instrument room where we may be doing final preparation of samples for instrumental analysis. I prefer students working in groups of two, most of my colleagues allow groups of four (so some sit around mainly observing rather than working). That will also affect the need for hood space. Energy efficiency is also a major consideration. Make sure that the company you work with has experience with both academic and industrial lab construction. The heating and air conditioning people should also be involved. I hope my comments help. David _________________________________________________________________________ David A. Katz Chemist, Educator, Expert Demonstrator, Science Communicator, and Consultant Programs and workshops for teachers, schools, museums, and the public 133 N. Desert Stream Dr. * Tucson, AZ 85745-2277 * USA voice/fax: (520) 624-2207 * email: dakatz45**At_Symbol_Here**msn.com Visit my web site: http://www.chymist.com _________________________________________________________________________
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