Here's the fume cupboard I've been working on. My aim is to make it such that I can safely handle chemicals including fuming mineral gasses, halogens,
and nitrogen / sulfur oxides. It's not intended to be explosion proof or to deal with extreme poisons like HCN (so please don't be too critical!).
The front is perspex and slides up and down. It can be held in a variety of set positions using the dowel pegs seen. The base is thick MDF, nice and
heavy so the cabinet won't topple over. The construction is otherwise screwed wood and board around a pine skeleton and any have been gaps sealed with
hot glue (or sticky felt in the case of the perspex front).
Those show the extraction system in greater detail. In the first picture is the top of the cupboard: the extraction hose is at the back, hidden by the
ply sheet (I hoped this arrangement with the ply would cause fumes to be sucked up over a wider area). Moving the air currently is a 240v 80mm metal
axial fan, nailed to a specially created hole in the garage wall .
I have a couple of things I'd like some help with:
In terms of fireproofing, do I need to buy special coating (expensive) or can I simply cover the inside with Al foil (cheap)? I'm not planning to do
thermite reactions in there but I might use a bunsen now and again.
I'm also going to change the fan as current airflow isn't satisfactory. The cabinet has about 0.2m^3 internal space and I can buy, at low cost, a 240v
fan on ebay with a CFM rating of about 75. This would move something like 125M^3 an hour. Will this suffice?
Does anyone have any other suggestions to improve effectiveness or safety?
Thanks in advance for the help,
Mossy. Picric-A - 2-11-2010 at 11:42
It looks like you wont get a lot of airflow through that small hose... certainly not enough that i would even think of using cyanide in it...
To improve it, buy a larger extractor fan with ~30cm diameter extractor tubing then add baffles.1281371269 - 2-11-2010 at 13:07
Not sure I can manage 30cm - for one, my parents might somewhat resent a 30cm diameter hole in the garage door.
On the other hand, I have just found this:
The 6'' version will extract, apparently, 305m^3 / hr which on par with some real cabinets whose specs I had a look at online, and I can get tubing
6'' ducting for it for about £1.40 / m.
Seems a very good compromise unless you think it definitely won't suffice?
Also could you possible explain what baffles are?Justin - 2-11-2010 at 14:39
The only problem with that motor is that the corrosive gases are gonna go right thru the motor and eat it up, the best ones are the ones with the
motor outside of the airstream. If you do you use a motor like that the best advice is to not let the gases get too the motor, use a gas bubbler to
scrub corrosive gases. I've seen some real nice squirrel cage fans with the motor sat outside of the airstream. Im planning on building a hood soon,
but your way ahead of me. Test your airflow, put a beaker with water and some dry ice, or a smoke bomb, cigarrete etc...metalresearcher - 2-11-2010 at 18:04
In terms of fireproofing, do I need to buy special coating (expensive) or can I simply cover the inside with Al foil (cheap)? I'm not planning to do
thermite reactions in there but I might use a bunsen now and again.
A good option is plasterboard or (better) Fermacell. I have the latter in my fumehood in which I even melt metals with a propane burner. Fermacell is light gray board of about 1cm thick which main purpose is fire
protection.
[Edited on 2010-11-3 by metalresearcher]1281371269 - 3-11-2010 at 10:21
Yeah that will be a problem...
On the other hand how do I set up a bubbler without radically reducing airflow?
How about an activated carbon filter?Picric-A - 3-11-2010 at 10:46
Baffles are 'wings' used to direct the flow of air out of the hood (outside) , basically making the hood more effective and it prevents the back-rush
of fumes out of the hood (towards the user) caused by turbulence.
If you are thinking of setting up an activated charcoal filter then you will need a much stronger fan as yes a lot of drag is caused by them. They can
be as simple as a PVC pipe filled with evenly packed activated charcol (pond grade is fine).
[Edited on 3-11-2010 by Picric-A]Justin - 3-11-2010 at 11:22
Yeah that will be a problem...
On the other hand how do I set up a bubbler without radically reducing airflow?
How about an activated carbon filter?
I wasn't talking about putting a bubbler in the air stream, an example: your distilling bromine in your hood, hook a tube from your vacuum adapter to
a beaker of base, doing your best to not let corrosive gases enter the airstream will do wonders for the durability of your hood, ya its kinda
backwards logic, if ya dont mind replacing the motor every once in a while and all the metal rusting to hell then let all the corrosive gases you want
go thru it. But a simple beaker of aq NaOH with a pasteur pipette bubbling your exit gases out of your distillation setup or whatever will prevent or
lessen corrosion issues1281371269 - 3-11-2010 at 15:26
Oh right, yeah that makes sense with the scrubbing gasses - I'll do my best to remember.
So I'm going to get the new fan I'll and plasterboard it (couldn't find any Fermacell): I'll keep you updated
Thanks for all the help FrickinA - 10-11-2010 at 15:48
I'm planning on building a fumehood out of an old wood cabinet and lining it with melamine. I decided to bring this old thread back up instead of
starting a new one, as there is some good info here already.
I'm wondering, where in the ventilation system do you recomend installing the fan? Inside the hood itself? somewhere in the middle of the hosing? or
on the very end?entropy51 - 10-11-2010 at 17:48
I'm planning on building a fumehood out of an old wood cabinet and lining it with melamine.
Melamine resin
gives off HCN when it burns, I do believe. Bare wood might be preferable and in my experience works just fine for this application. But then again,
I'm careful not to start fires in my hood.FrickinA - 11-11-2010 at 07:31
I did not know that, probably a good reason not to use...
So wood is okay against the usual fumes like HCl, NOx, possible halogen gasses, and acid fumes?
What about acid spills on the bare wood?entropy51 - 11-11-2010 at 09:10
One of the skills of a chemist is not to spill acids. Get a
plastic tray and transfer acids in the tray to catch small spills.
If your hood ventilation is adequate the gases you mention will not have time to damage the wood. There has been a lot of discussion of suitable
materials and coverings for fume hood surfaces in other threads.
.
