| About This Archive | | DCHAS-L 2005 Index | | DCHAS-L Yearly Index | |
Check out Safety Emporium for your N95, N99, and face shield needs.
|
Previous by Date: Subject: Re: Ductless fume hoods policy? Date: Fri, 29 Apr 2005 09:03:05 EDT Author: ACTSNYC**At_Symbol_Here**CS.COM |
Next by Date: Subject: Peroxides within empty containers. Date: Fri, 29 Apr 2005 12:38:21 -0500 Author: Kent Candee |
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 ACTSNYC**At_Symbol_Here**CS.COM 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 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 adsorbed. 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. and 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 artscraftstheatersafety.org SNIP In a message dated 4/29/05 12:23:49 AM Eastern Daylight Time, rstuart**At_Symbol_Here**uvm.edu writes: > Ralph Stuart, CIH > Environmental Safety Manager > University of Vermont > Environmental Safety Facility > 667 Spear St. > Burlington, VT 05405 > > rstuart**At_Symbol_Here**uvm.edu > fax: (802)656-5407 > > >
Previous post | Top of Page | Next post