# Has any one used a ductless fume hood?



## Bizness4you (Jan 25, 2012)

I am looking at a ductless fume hood with the acid cartridge filters that you change out. I was just wondering if anyone has used a set up like this, or bad idea? Thanks for the input.


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## Smack (Jan 26, 2012)

I would not use one of them, I have looked at them but no way man...too many unforseens. The risks are just too high.


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## Noxx (Jan 29, 2012)

I doubt that the acid cartridges can catch NOx...


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## NobleMetalWorks (Mar 31, 2012)

I have been looking at hoods, for about 3 months now. I called many places that sell new hoods because I wanted to understand my options before I even attempted to purchase any hood, used or new. This is what I discovered.

Ductless hoods depend upon chemical filtration. The problem with chemical filtration, regardless if it would work for NOx or not, is that once it becomes saturated with anything it stops working, charcoal filters work because they absorb. If you are doing anything that creates steam, guess what? You are going to render your filter useless very fast.

Not to mention that the filters will not filter NOx. If you do find one let me know, because I would like to use those filters in a respirator, but so far as I can tell, in all the information I have read and the sales people I have spoken with, they will not filter NOx.

Talking about sales people, most of them have no clue. Some will tell you that "THEIR" filtering system will work with acids. You have to ask them what happens when the filter is filtering steam, ask them what happens once the filter is saturated and your unit starts pumping out noxious toxic gas. Remember, these units recycle air, they don't pump it away from your work area unless you install the fan and ducting.

Ideally you want a hood that is made of acid resistant material, such as Polypropylene, or coated with an acid resistant epoxy or enamel. As far as moving the NOx or other gases away from your work area, the very least you must do in order to enjoy some safety is to pipe the air and outgas from your reactions away from your work area so that it isn't polluting the air you are breathing, and do so using an acid resistant fan otherwise your fan will stop working in a relatively short amount of time. If you are doing this at home you could affect your neighbors or animals by doing this. I chose to build a scrubber because I not only want to move the gas from my work area, but I want to be responsible about re-introducing the gas into my neighborhood environment.

Like with anything you should do a lot of investigating and reading on your own, and ask questions like here. Sales people are almost always going to sell you their system because it's "better" than anyone else, I had one salesperson tell me that if I didn't buy his ductless system with their special filters ($1,000 + a pop) that I would end up killing myself. I only gave you my own thoughts, I am sure there are people here that know far more and would be better equipped to point you in the right direction.

Read this to get a better understanding about fume hoods.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=54&t=12641

I have to say this, you are doing the right thing asking in the forum before you buy anything!


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## nickvc (Apr 1, 2012)

I believe there are some decent almost ductless hoods available but they tend to be quite large and won't handle large volumes, they have internal scrubbers but need to be vented outside in my opinion. New they aren't cheap and have definite limitations, you wouldn't want to be dissolving 10 kilos of material at a time in them but would be fine with smaller quantities, the scrubbing medium would require regular attention I'm fairly sure to make it effective.
All in all you would be better off building your own and add the scrubber you need and venting it off, more work but cheaper and it can be built to your needs not to the limitations of a ready made unit.


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## Photobacterium (Apr 1, 2012)

Smack said:


> I would not use one of them, I have looked at them but no way man...too many unforseens. The risks are just too high.



a specific filter/fume hood for a specific reaction - MAYBE.

but for the many varieties of reactions that most GRF'ers do - with varieties of acids and varieties of ore ?!

i think my own small set-up has enough different reactions going on that it would take an experienced chemist busy for a week analyzing them all.


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## NobleMetalWorks (Apr 1, 2012)

Photobacterium said:


> Smack said:
> 
> 
> > I would not use one of them, I have looked at them but no way man...too many unforseens. The risks are just too high.



a specific filter/fume hood for a specific reaction - MAYBE.

but for the many varieties of reactions that most GRF'ers do - with varieties of acids and varieties of ore ?!

i think my own small set-up has enough different reactions going on that it would take an experienced chemist busy for a week analyzing them all.[/quote

I am not sure what your comment is referring to, but since I have been looking for the past three months I'll try to explain about different hoods.

Basically you have a bypass hood or velocity hood made out of whatever materials to be resistant to specific types of material or work performed under the hood. If you build a hood and your design isn't correct you can actually cause a venturi affect in your hood, which could potentially be dangerous to whoever is in the area, imagine NOx swirling around in the hood. Velocity hoods, when used with an air meter in my opinion, is a fairly safe method of being able to work under the hood, while still enjoying the protection of hood face flow, and it can be adjusted by raising or lowering the sash. What you are looking for is constant face velocity, the air moving past the face of the hood into whatever system you have, filter, exhaust, scrubber or some combination of.

Self enclosed hoods with filters are generally meant for only specific applications, such as something that is dusty, if you are dealing with dry chemicals only, this may be your choice, and it could be said to be an acid resistant hood, and a salesperson would may tell you that hood is okay for dealing with acid, however not the outgas created by chemical reactions. See the problem here?

I have yet to come across a ductless hood that could be used for our applications. The reason is two fold, we create steam during the AR process when the beaker is warmed to increase the effectiveness of the AR, and when evaporating, etc. This will quickly render most filters in-op. The other problem is that you cannot filter NOx with a normal chemical filter, usually, those filters are geared towards dealing with the salts, dust, etc and not gasses such as NOx.

So hoods are built with specific needs in mind, and yes, they are made to deal specifically with gases produced by chemical reactions. And some go as far to even list the types of reactions that they deal with. After all, a hood is not only used for mixing, they are used as large positive air flow reaction chambers. The entire point of a hood is to contain your reaction.

There are bio hoods, fume hoods, acid fume hoods, acid resistant fume hoods, smoke fume hoods (for welding or a restaurant) and the list goes on and on and on. I had one sales person try to sell me a perchloric acid hood stating how dangerous perchloric acid is, and how if the hood can deal with that acid, surely it could deal with NOx. He was wrong, perchloric is an explosive acid, so the hood is made out of almost entirely, stainless steel with blast proof sash. Although stainless steel is resistant to acid, it's still not idea to use AR inside a stainless steel hood, not to mention the affects on the stainless steel over the long term. So in this case, you have a hood designed for a specific acid, yet it cannot be adapted to be used for our applications, unless you spend a lot of money cladding it in poly.

If you are getting advice or direction from a sales person you have to make sure they know what they are talking about. Hamilton was able to give me some really good information, and a few others as well. Hoods are designed for specific applications, they are even custom made for specific applications, I had one company offer to spec out a hood for my needs, any of them will they do all the time.

I opted for acid resistant hoods that I can easily adapt for my own applications. Two of them came from a biotech company that went belly up. So I am going to use a hood that was originally intended for the biotech industry. I called and spoke with an engineer at the company that made the hood to make sure I could adapt it for my needs, they will even sell me some parts I can replace with parts better suited to my needs. So not only are hoods made for specific reasons, but some can also be adapted for use for other things.

You can pimp your hood (if this turns into a reality show I want credit for saying it here first)

Anyway, without boring anyone more, hoods are made for general purpose or for really specific purposes depending on the application.


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## grainsofgold (Jul 8, 2012)

We have two at work. In the casting room to suck up smoke from the burnour oven- Works fairly well. 

I would not want to use one for acids involved in refining- Better to be safe with a regular fume hood in my opinion.


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## qst42know (Jul 12, 2012)

At some point any cartridge system will cease to be effective. The odds are good during a reaction, gradually poisoning your work space air. 

At what point do you evacuate the area? 

Hopefully before you do irreparable harm but then how would you know?


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## Palladium (Jul 12, 2012)

Even with a fume hood things can get hairy at times. I made a rookie mistake the other day and just had to have me a whiff of So2. I still can't taste right. :shock:


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