Date: Wed, 8 Apr 2009 14:50:25 -0400
Reply-To: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
Subject: 3 more on class lab fume hoods

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.


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

=0CFrom: ACTSNYC**At_Symbol_Here**
Date: April 8, 2009 9:10:18 AM EDT (CA)
To: ecgrants**At_Symbol_Here**
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  

Monona Rossol, M.S., M.F.A.,
industrial hygienist
Arts, Crafts &Theater Safety, Inc.
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

=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  

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 A. Katz
   Chemist, Educator, Expert Demonstrator, Science Communicator, and  
   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**
            Visit my web site:


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