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Subject: Fume hoods

Fume hoods

From: Geoffrey I. Brown <gibrown>
Date: Thursday, December 7, 1995
Becky Ryder <rjryde01 [at] ukcc__uky__edu> writes

>conservation lab will be included in the new building....
>The Construction Manager and Health/Safety Officer have
>questioned our need for a fume hood. They are suggesting that an
>exhaust canopy that is open on the sides and front might be adequate
>for use with the chemicals for stain reduction and tape removal.

I can appreciate your situation regarding whether a fume hood or
canopy is more appropriate for your new conservation lab.  It might
be instructive to examine air flow characteristics first to
determine if a canopy can provide the standard 100 fpm flow and if
so, what the consequent costs of exhaust fan, building air make-up
equipment, etc. will be.  A fume hood has a much more limited
aperture and air requirement than a canopy of equal area and flow

The canopy would undoubtedly be more convenient, but in order to
safely remove highly volatile vapors, the support equipment that is
not visible will probably cost 2-3 times what it would for a hood.
I expect that the cost of a hood enclosure is about twice that of a
well-designed canopy of the same area.

Another concern is the draft created around these devices.  If you
are flushing huge amounts of air through the lab, it might be quite
problematic for other activities as well as very noisy.  Fume hoods
are available in designs that use ducted make-up air and so do not
require nearly as much ambient air to operate properly.

You might also ask your architects to examine the long-term energy
requirements of the different systems.  If you are using a canopy
which will require very high volumes of air, not only will the
air-handling equipment cost increase relative to a fume hood, but
the long term costs of treating (heating & cooling) such a high
volume of air might exceed the initially higher cost of a hood
within a very short time period. This energy demand is not a fixed
one-time factor, but a continually increasing operating cost.

Although I am not a paper or book conservator, I would think that it
is impossible to predict what chemicals might be required in the
future for as-yet undiscovered treatments, even if your presently
predicted usage is limited to materials of low volatility and low
toxicity.  Retrofitting for fume hoods is extremely expensive and
disruptive, and would probably cost several times what it will cost
at this time.

Future safety is a continual concern.  What is the possibility that
your staff will use chemicals for which the canopy is not sufficient
protection?  Even occasional use of this sort poses significant
health risks and consequent institutional liability.

In summary, I recommend a fume hood of adequate size and air flow.
A canopy might be considered for very specific operations and
specific chemicals, provided that these are of high enough volume to
justify the second installation.  It is very important to be
generous with the hood size, because even the occasional object that
is too big for the hood will tempt (or require) people to work
unprotected in the open.  In my lab, I have a side take-off on the
fume hood duct that allows me to hook up a 6" flexible duct for
occasional out-of-hood work.  Hood performance is nearly the same
with the side duct open or closed, so safe performance is not
compromised by this arrangement.

I would be happy to discuss these issues with you or your technical
people by e-mail or telephone.  Good luck.

Geoffrey Brown
Curator of Conservation
Kelsey Museum
University of Michigan

                  Conservation DistList Instance 9:48
                 Distributed: Monday, December 11, 1995
                        Message Id: cdl-9-48-001
Received on Thursday, 7 December, 1995

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