Date: Fri, 29 Apr 2005 09:03:05 EDT
Reply-To: ACTSNYC**At_Symbol_Here**CS.COM
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: ACTSNYC**At_Symbol_Here**CS.COM
Subject: Re: Ductless fume hoods policy?
Comments: To: rstuart**At_Symbol_Here**
Has anyone developed policies for when the use of ductless fume hoods
is appropriate?
For example, ductless fumehoods are ok for pouring of not more than
5/50/500 ml of acetone.
We generally discourage them, but inquiring minds want to know...
- Ralph

That was a brilliant question!  It must be brilliant because its something I
already asked and have been working on for several months---and not getting
too far.

Here's the problems:  First there are several types of treated activated
carbon.  Some are good at adsorbing solvents, some formaldehyde, some for amines
and ammonia, etc.

Assuming you are only interested in using common solvents in your hood, you
have to find out how well each solvent is adsorbed.   They are not all equally

And then there is the humidity.  All these carbon filters would prefer to
adsorb water vapor so humidity decreases their efficiency by huge amounts.

All this is not mentioned in the advertisements for these products.  Instead,
they give you a length of service time in months or years for "typical" use
and that is just a crock since everyone works differently in both the chemistry
biz and the art biz.

So I got in contact with a company that wants me to endorse their product.  I
don't usually do this, but the way I explained it to them is that if they
could get enough data from the suppliers of their carbon filters about the
adsorption of common solvents at various relative humidities, I would figure out
"fail-safe" recommendations for the amount of these various solvents they could
use in that hood or in the room with that air purifier.

And that's exactly the question you asked--because clearly, that is the
information we need.

The company has given me some data on trichloroethylene (TCE) because that
apparently is the solvent they use for testing the organic vapor carbon filters.
  Now, damn, that is not a solvent we often use, but the data shows the
steady drop with humidity.  The chart only goes to 80% relative humidity, but it
almost looks as if 100% humidity would just about finish the filter!!!  And what
if you were boiling water in the hood as part of the process?   Hmmmmm.

The chart they gave me, however, is hard to interpret because they don't
provide the protocols for the testing, but it looks like we are in the range of
under 5% of the weight for absorption.  In other words, a 100# filter could
only be expected to hold 5 # of TCE at 80% humidity.

They also provided a chart from somewhere that lists various solvents and
other substances with 4 ratings from good capture to not recommended: #4 high
capacity,  #3 satisfactory capacity, #2 borderline, and #1 not recommended.   TCE
is listed as #4 high capacity.  Your acetone is listed as #3 satisfactory
capacity, meaning that it would not be adsorbed as well.  So now we are looking
at an even lower percentage by weight absorption--but this amount can't be
determined from the very limited data I have.

However, this data CLEARLY shows the filter industry KNOWS what percentage by
weight these various filters will hold of various solvents and chemicals.
Maybe it is available somewhere, but I just don't know where.  But at the very
least, a bunch of us should get together and try to find it or get the filter
manufacturers to give it to us.

My plan is to concentrate on the data at 80% humidity as a worst case
situation with the caveat that if the humidity goes above this and the filter is
full, it will probably kick solvent back out and be a danger to users.  Then we
should look at the w/w% absorption of the various solvents, and convert them
with their specific gravities to provide volume recommendations for the use of
various solvents.

Since I provided this interpretation of the data for the company, I have not
heard from them.  I expect, they see the handwriting on the wall.  I would
only be recommending these filters for really low solvent use which would hurt
their business.  However, there are uses for which a hood that could capture 500
ml  of a particular solvent would be very useful.

Anyone out there have any ideas or data?????

Monona Rossol, M.S., M.F.A.,
industrial hygienist
Arts, Crafts & Theater Safety, Inc.
Safety Officer,
United Scenic Artist's, Local 829
International Alliance of Theatrical Stage Employes (IATSE)
181 Thompson St., #23
New York NY 10012-2586     212/777-0062
In a message dated 4/29/05 12:23:49 AM Eastern Daylight Time, rstuart**At_Symbol_Here**
> Ralph Stuart, CIH
> Environmental Safety Manager
> University of Vermont
> Environmental Safety Facility
> 667 Spear St.
> Burlington, VT   05405
> rstuart**At_Symbol_Here**
> fax: (802)656-5407

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