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Author: Subject: Question about fume hoods.
itb2003
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[*] posted on 25-1-2013 at 22:32
Question about fume hoods.


I have a few questions mostly about fume hoods I might need to make another topic for some of them.


-I saw some posts on DIY fume hoods here and I was curious what the holes at the very top of the sash are for and/or are they even needed? I'm guessing this is used to direct airflow.

-I was also curious about the very end of the fume hood where the exhaust comes out...it looks like people use a stack high in the air to let out there exhaust although it looks like some of the diy ones use horizontal outlets...I was curious is this done with carcinogenic materials also? Or are there scrubbers or does it become so dilute in the air it doesn't matter?

-How do you make your sash air tight? Or does it matter since the air will be going in anyway?

-I found a big motor around 720cfm but its 8inches and my exaust will be 6inches with probably 3 90degree bends in it....will this make it push much less feet per minute with those loads and by how much?...or does this one require experimentation or maybey I should just get the 6inch fan?

-Last question...I was reading some posts about people describing the smell of benzene lol isn't this carcinogenic?? Maybey a little isn't harmful or is it cumulative like radiation? Not that I will try to smell it lol.
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vmelkon
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[*] posted on 26-1-2013 at 14:56


Don't know about your fume hood.
Benzene is a known carcinogen but like other carcinogens, it depends on exposure (amount and time length). Benzene is something that is added to gasoline in certain countries, so most likely, we are all smellers of that sweet smell.
http://www.cancer.org/cancer/cancercauses/othercarcinogens/i...

[Edited on 26-1-2013 by vmelkon]
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itb2003
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[*] posted on 4-2-2013 at 03:06


Wow interesting it looks like benzene is used in lots more than I knew about.

Here's a picture I got off the forum to clarify more about one of the questions I had. There's the sash and then above it there seems to be openings for air I've seen on a lot of diy drawings for hoods this way...is that needed and why?

I figured out the motor question allready, you would just add a motors seperate from your main motor with its own seperate ducts to add more cfm.

Also if you know the answers to the rest of my questions below that would be awesome : )

bla.bmp - 1011kB
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itb2003
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[*] posted on 4-2-2013 at 04:16


I think I finally figured out another of my questions..the slots at the top are bypass slots so the fume hood can sustain constant face velocity instead of increasing velocity when you close the sash...I think I would just vary motor speed though...
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blogfast25
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[*] posted on 4-2-2013 at 09:03


Quote: Originally posted by chemrox  
The opening at the top is also good for evacuating the lab when the hood door is closed. I run all my ventilation through the hood.


There's a thread on homemade fumehoods sowhere here. I wish someone would dig it up...




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chemrox
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[*] posted on 4-2-2013 at 10:42


The opening at the top is also good for evacuating the lab when the hood door is closed. I change air every 2 min through the hood. Before the hood I had a glove box with a disposable filter. Small hoods with filters are fairly common. But I have chlorinated solvents in the lab and bromine, SOCl2 and PCl3 in the hood. I generate HCl in there as well. Having a hood almost completes my lab. I would like even more space. It would be nice to have a dedicated area for the Parr reactor. The vacuum cart gets in the way sometimes and I could use running water on both walls. But all in all it works pretty well. It's just that I like to have 2 or 3 synths going at a time.



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Magpie
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[*] posted on 4-2-2013 at 13:14


Quote: Originally posted by blogfast25  

There's a thread on homemade fumehoods sowhere here. I wish someone would dig it up...


Here's one:

http://www.sciencemadness.org/talk/viewthread.php?tid=11145




The single most important condition for a successful synthesis is good mixing - Nicodem
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itb2003
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[*] posted on 4-2-2013 at 13:22


Yes that's the thread I read on diy fume hoods but I didn't find all the answers I was looking for in there..


I just have two more questions that haven't been answered yet although I think I have the answers to them...however I would like it if someone could confirm what I think.


-I was also curious about the very end of the fume hood where the exhaust comes out...it looks like people use a stack high in the air to let out there exhaust although it looks like some of the diy ones use horizontal outlets...I was curious is this done with carcinogenic materials also? Or are there scrubbers or does it become so dilute in the air it doesn't matter? I'm guessing all chemicals are just vented out the top though with no filtration necessary...in a lab setting anyway....guessing industrial would be different?

-How do you make your sash air tight? Or does it matter since the air will be going in anyway? I'm guessing this doesn't matter at all...except maybey lower face velocity by the tiniest fraction.





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[*] posted on 4-2-2013 at 13:42


Quote: Originally posted by itb2003  

-I was also curious about the very end of the fume hood where the exhaust comes out...it looks like people use a stack high in the air to let out there exhaust although it looks like some of the diy ones use horizontal outlets..


Use either method. Which one would you like your neighbors looking at?

Quote: Originally posted by itb2003  

....guessing industrial would be different?


correct

Quote: Originally posted by itb2003  

-How do you make your sash air tight? Or does it matter since the air will be going in anyway? I'm guessing this doesn't matter at all...except maybey lower face velocity by the tiniest fraction.


correct




The single most important condition for a successful synthesis is good mixing - Nicodem
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