Date: Fri, 29 Apr 2005 10:49:04 -0500
Reply-To: Bob Peck <eagles-rest**At_Symbol_Here**CHARTER.NET>
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: Bob Peck <eagles-rest**At_Symbol_Here**CHARTER.NET>
Subject: Re: Ductless fume hoods policy?
Comments: To: ACTSNYC**At_Symbol_Here**CS.COM
In-Reply-To: <159.503313c1.2fa38a89**At_Symbol_Here**>
I think my previous reply only went to Ralph.  So I'm adding it here.
To share my point of reference, I was previously Director, S&IH
Schering-Plough Corporation and a Corporate IH with Monsanto having
responsibility for research labs and manufacturing operations.  While at
Monsanto I published in the AIHA Journal (Aug.,1982?) on Freon 12 lab
hood performance test methods that provided data for the ACGIH Hood
Performance Standard proposed by Kaplan and Knutson.  We did not allow
lab hood exhaust back to the room in either company except for HEAP
filtered hoods from dust weighing operations only.  Even in those cases
if there was a lab hood in the room and we needed more hood space, we
frequently directed the exhausted to the back inside the adjacent hood.
HEAP filter hoods can come with pressure differential breakthrough
indicators and that is the only kind we bought.  You might also refer to
various standards on exhaust air recirculation that require continue
monitoring with alarm for toxic materials and end of service life
indicators for adsorbent beds.  Also keep in mind that charcoal adsorbs
different solvents at different rates and some solvents can be desorbed
before saturation by others which the charcoal has a greater affinity
for.  OSHA carefully regulates air purifying respirators for compounds
like formaldehyde and forbids them for methylene chloride for some of
these same reasons. My original response follows:

Unless you are using an absorbent bed with a service life indicator
specific to the liquid/vapor being used, a ductless hood should only be
used for dusts that don't sublime.  Use of any volatile material with
this type hood should be gauged by room air changes, with the
understanding that you are contaminating the room air by the process you
run.  That is generally a very bad idea from a personnel exposure point
of view!

Bob Peck
Eagle's Rest Consulting Services, LLC
Sunrise Beach, MO

-----Original Message-----
From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**LIST.UVM.EDU] On Behalf Of
Sent: Friday, April 29, 2005 8:03 AM
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: Re: [DCHAS-L] Ductless fume hoods policy?

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
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,
have to find out how well each solvent is adsorbed.   They are not all

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

All this is not mentioned in the advertisements for these products.
they give you a length of service time in months or years for "typical"
and that is just a crock since everyone works differently in both the
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
could get enough data from the suppliers of their carbon filters about
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
apparently is the solvent they use for testing the organic vapor carbon
  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
only be expected to hold 5 # of TCE at 80% humidity.

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