From: Harry J. Elston <helston**At_Symbol_Here**MIDWESTCHEMSAFETY.COM>
Subject: Re: [DCHAS-L] Microwave Digestion
Date: Fri, 31 Aug 2018 07:58:05 -0500
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Message-ID: CAJ2hcfcJwXjF4gGzK_pDSQBWQ+TfCnHbn89A74DMr4qo+HxdDg**At_Symbol_Here**


I have done about a half-gazillion microwave digestions of various organic and inorganic products for radiochemistry use. Here's a very short list of what you may want to consider:

1) Use ONLY laboratory type microwave systems. These have vessels that have integrated pressure relief systems in them and are nearly-infinitely programmable for digestion time/temperature/pressure.
2) NEVER use flammable solvents in a microwave system. Never. Don't think you can walk the razor's edge here - you cannot. Do not ever consider it.
3) Venting must be done to a properly operating laboratory chemical hood that vents outside. Do not vent them into a "ductless hood." (That was a huge question in Ask Dr. Safety in Boston).
4) Scrubbers are available but we didn't use them. Under normal conditions the vapor content is low. Under upset conditions (e.g. you over-pressurize your reaction vessels) you'll probably overwhelm the manufacturer's scrubber anyway. <--This is experience talking here. I did this with milk/nitric acid/hydrogen peroxide. It was, literally, a hot mess.

We used, what I consider to be the best system available: A MARS system from CEM. The models have changed over the years, but their system remains top notch with integrated safety features to detect and over-pressure and over-temperature conditions, pressure relief sensing with auto shut-down etc. Clearly this is "opinion" as there are several lab-grade systems available. Full disclosure - I don't get a penny from CEM.

If you want to talk more off-line, contact me.


On Fri, Aug 31, 2018 at 5:08 AM Andrew Pham <andrew**At_Symbol_Here**> wrote:
Hi all,

I had brought this up at Ask Dr. Safety, and I wanted to follow up on the query. My laboratory is working on installing a microwave digester, and the manufacturer seems to suggest that venting the exhaust in a ductless fume hood would be okay. I am emphasizing that this would not be okay, but construction costs and city regulations on venting outside the building are causing a lot of obstacles in getting this digester installed. We will mostly be digesting with nitric acid, which should exhaust NO2 gas.

The main question is a) is it absolutely necessary to vent into a ducted fume hood, and b) if the exhaust is to be piped outside, should we install a series of scrubbers as well? The city may be concerned about venting gases to a mixed-zone industrial/residential neighborhood.



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Harry J. Elston, Ph.D., CIH
Company Information
Twitter: **At_Symbol_Here**MidwestChemSafe
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