No, we do not put our microwave system in the hood.
1100 ft/min is the velocity through the fan. Do keep in mind that the same flow in ft3/min (volume/min flow) in a larger diameter hose or in a larger area such as the inside of the microwave will be a smaller linear velocity number than in the fan or in a smaller tube, but still meet intended specs when the door is closed. Did you get 0 ft/min with the door open?
R. Steven Pappas, Ph.D.
Team Lead, Tobacco Inorganics Group
Centers for Disease Control & Prevention
4770 Buford Highway, NE
M.S. F44, Building 110
Atlanta, GA 30341-3717, USA
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). [mailto:[log in to unmask]] On Behalf Of Derek
Sent: Tuesday, March 21, 2017 1:32 PM
To: [log in to unmask]
Subject: Microwave digestion system question
I have some questions regarding microwave digestion systems. We have a Mars 6 microwave system and recently we noticed that our exhaust line close to the ceiling that is made of metal, the spot weld started to corrode, which led to small drips of nitric acid dripping onto the counter top. Our fix to this will be to put in an all plastic system (the original idea of using metal was not mine but facilities). I have a few questions, does anyone have any type of cold trap to catch the acid vapors as they are released to the exhaust system. I also noticed that the fan on the back of the system pulls about 1100 ft/min, we have a 40 sample carousel and when I took a measurement from the top of the carousel where the vessels would be venting closest to the fan this number decreased to about 230 ft/min. I then took a measurement near the door furthest away from the fan and this number actually decreased down to 0 ft/min. Now with a 40 sample carousel only about 3 tubes at any point in time will have 230 ft/min exhaust, leading potential for vapors to escape out the microwave door. There is no rubber gasket around that door so I have my doubts that the door is air tight when the door is closed. I have been working in the room before where I would smell nitric acid, I do think this is a flaw on this particular system regarding the ventilation. Does anyone keep their microwave system in the hood? Keeping the microwave in the hood would minimize expose to acid vapor.
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