Ssr 2000 carbon filter fume cupboard.Advice required.

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Aog

Member
Joined
Aug 12, 2012
Messages
8
Hello all. Iv read a load on here with regards to fume hoods. Iv just purchased a clean air ltd fume hood. Model ssr 2000. It uses a pre filter and a 18kg activated carbon filter. It does cater for acid fumes.

Little bit lost as to the safety side of using the recirculating fume hood in my garage.

Other posts refer to the nox being scrubbed via activated carbon. I can't smell it. Perhaps I'm paranoid. I just don't want to gas myself or others.

Any advice would be great.
Ps the filters are new.

Many thanks in advance. Dave.
 
Shor once made a karat gold self contained refining unit that scrubbed through 2 packed clear plastic cylinders about 6" dia x 18" long. The first was filled with chunks of charcoal and the second with chunks of limestone in water. I saw this unit but never saw it operate. Since then, someone told me that the contact of the charcoal with the NOx gases could start a fire.

Maybe someone that knows could comment on this.
 
Carbon filters are a tricky thing. You have to be on top of them otherwise, all the sudden they stop working.

I have been using carbon filters in my salt water tanks since 1991. I have a schedule when to clean them, and because I have beneficial bacteria that live in my filter substrate, and in the carbon filter itself, I have to be very careful how much I wash at any given time, if I kill off too many bacteria, then my nitrites will rise because these particular bacteria convert nitrites into nitrates. As well the charcoal filter soaks up nitrites. Once it is saturated, it will no longer hold nitrites.

Charcoal will soak up all kinds of things, it's a wonderful material. However, no matter what your literature states, no matter what the salesman tells you, a carbon filter is not going to filter NOx. And even if the carbon, because it's so porous, retains some deposited Nitric/NOx, it is not converting it to anything else.

If you read EPA requirements for industry that creates NOx gases, they require the gases produced to be vented through a fume scrubber, either a catalytic or wet scrubber. If you tried to use a ductless fume scrubber with a carbon filter, you would be fined and for good reason. It just wouldn't work.

NOx is not one of those gases that can be filtered with media. The best thing to do if you are small scale and cannot afford a fume scrubber or build one is to vent at high CFM your NOx gas directly into the atmosphere so long as it's not putting your neighbors or animal/plant life in danger. On a home scale you are producing so little NOx that it isn't going to do any harm to the environment you can measure. Not unless you are doing large quantities. I am using a fume scrubber because I produce a lot of NOx. Otherwise I would probably be directly venting as well. If you do decide to vent outside your lab, just make sure you vent using as much airflow as you can afford. The more air mixed with the NOx gas as it develops, the better. Also the velocity of the exhaust can push it higher into the air, so as it falls it is more or less harmless. Remember NOx is heavy and wants to be close to the ground.

Anyway, just my two cents.

Scott
 
Thanks for the helpfull replys. I'm going to list it on eBay and swap for a vent to atmospher. Can't be to safe. Cheers.
 
I may be wrong but I think if the carbon filter is in contact with concentrated nitric acid fume's the carbon could become nitrated and thus much more combustible, possibly to the point of self ignition, depending on how the fume hood is used, if the fume exhaust was plastic this could be a flue fire that could burn down a building, this possibility of nitrated carbon material with the dust from the metals as oxides in the fumes and from dusting (from incineration and other processes) the metal oxides trapped by the filter, may increase its danger.

I would use fiber glass furnace filters, these will catch fine metals as dust particles, and these filters can be incinerated for recovery of trapped values, they will not catch fumes of acids any better than charcoal but also would not have the possibility to be nitrated like carbon can, (although these fiberglass filters should be changed when dirty or packed with dust from your lab, as this dust could also possibly become nitrated with nitric acid fumes).

As far as acidic fumes I cannot see any kind of air filter doing any good here, in fact the filter may just condense some of these fumes back into acids, the rest of these gases just passing through the filters.

Acidic fumes, scrubbing them would work, where I cannot see a filter (in a fume hood) helping with these, the filters are made to trap dust, charcoal is used to help eliminate the smell of some gases like smoke, by absorbing these smells, but for what gases and acids we use I feel they would not help at all, and could create more danger than good.
 
NobleMetalWorks said:
I am using a fume scrubber because I produce a lot of NOx. Otherwise I would probably be directly venting as well. If you do decide to vent outside your lab, just make sure you vent using as much airflow as you can afford. The more air mixed with the NOx gas as it develops, the better. Also the velocity of the exhaust can push it higher into the air, so as it falls it is more or less harmless. Remember NOx is heavy and wants to be close to the ground.

Anyway, just my two cents.

Scott


I see this post was five years ago but I'll give it a shot.

Did you make your scrubber or purchase it. Right now I am venting, but I would be willing to scrub it first just to avoid any possibility of neighbors catching a whiff.
 
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