# Fume hood vs full room ventilation



## abaddown (May 27, 2014)

I have two 12 liter borosilicate round bottom boiling flasks that I intend to use for the refining of gold with aqua regia (gold extracted from e-scrap via other processes and karat scrap). I intend to mount a reflux condenser on each and draw any fumes through a series of scrubbing vessels with a vacuum pump that draws approximately, 1 cfm. 

My question, however, is what to do to combat trace fumes that may manage to escape my apparatus. I've been scouring the internet for data on proper lab grade full room ventilation for trace fumes and none of the papers I've found seem to come to any concrete conclusions. I was thinking I would mount a couple thousand cfm worth of blowers venting the room's atmosphere and call it a day, but I'd like to be more precise. A fume hood strikes me as an inappropriate measure for this sort of situation...why build a fume hood for large closed systems when you can just vent the whole room to negate any trace fumes? The room is approximately 700 cf. I also have access to a supplied air respirator and a full body Tychem F suit, but I would rather not allow vapors to accumulate in my lab for obvious reasons.

In short, why not turn my entire lab into one big fume hood...so to speak. If anyone has an idea of the calculations involved, please advise. I have 4metals's spreadsheet for calculating the cfm requirements of a fume hood and the resultant scrubber size, but I am not sure how this applies to an entire room.


Thanks.


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## 4metals (May 27, 2014)

1 CFM through a vacuum pump is small for 2 reactors to be scrubbed well. How are you drawing the vacuum? A mechanical vacuum pump will be short lived. 

The only reason for a hood is to vent out the emissions that escape scrubbing. For example, when dispensing acids and pouring same into reaction vessels. Those whiffs of chemical that come from this can be efficiently evacuated from a hood and all of the smell will not be noticed by the operator in front of the hood. With the proper sized hood and blower you can work in the room without all of the suits and respirators you have and not be exposed to any odors. 

The fumes from the refining still need to be fed through a scrubber. A properly sized scrubber can be used to evacuate reactions either inside a hood or outside the hood. If you are bent on using the entire room as a hood, please remember the corrosive nature of even a small quantity of acid fume. All of the surfaces of the room, the walls and the ceiling and the sealed and coated floor should be smooth and have no exposed unprotected metal. I hope this room is not going to be in your house.


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## abaddown (May 27, 2014)

4metals said:


> 1 CFM through a vacuum pump is small for 2 reactors to be scrubbed well. How are you drawing the vacuum? A mechanical vacuum pump will be short lived.


You bring up a good point, 4metals. It's a nice Buchi brand ptfe diaphragm vacuum pump I got for $50 and refurbished, I would hate to have to keep replacing the valves and diaphragms. I will look further into your posts on venturi scrubbers on here.




4metals said:


> The only reason for a hood is to vent out the emissions that escape scrubbing. For example, when dispensing acids and pouring same into reaction vessels. Those whiffs of chemical that come from this can be efficiently evacuated from a hood and all of the smell will not be noticed by the operator in front of the hood. With the proper sized hood and blower you can work in the room without all of the suits and respirators you have and not be exposed to any odors.


I think you have swayed me toward building a hood. I just realized having a hood would allow others to safely enter my lab without masks, if need be. Multiple supplied air lines have a tendency to get tangled together. Far more convenient and professional.




4metals said:


> The fumes from the refining still need to be fed through a scrubber. A properly sized scrubber can be used to evacuate reactions either inside a hood or outside the hood. If you are bent on using the entire room as a hood, please remember the corrosive nature of even a small quantity of acid fume. All of the surfaces of the room, the walls and the ceiling and the sealed and coated floor should be smooth and have no exposed unprotected metal. I hope this room is not going to be in your house.


The room is entirely sealed off from the house with FRP paneling on the walls and ceilings. No vents, except to the outside. Rather strange, but this is the way it was when I bought it.



Thanks for the suggestions. As they say, if it ain't broke, don't fix it.


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## butcher (May 28, 2014)

When using a fume hood, you will have to let air into the lab, as the fume hood exhaust cannot suck air from a closed hood or room, with this opening letting this fresh air into the room on the opposite side of the room, the fume hood will also be pulling air out of the room and through the hood, as fresh air from outside enters the room, giving your lab fresh air changes as the hood is in operation.

Many of the acidic gases and fumes can be heavier than air (they can sink to the floor), keep this in mind with your hood and with working in your lab.


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## Clneal2003 (Jul 8, 2014)

Oh my! I just checked out wet scrubbers! Those thing look expensive! I'm small scale winging everything the first time I try it. I've yet to use nitric as it looks like it takes fumes and smells to a whole new level. I've gotten by so far just working outside when I'm able. Could I get by with a good industrial fan pointing up from the floor towards a fume hood in my shed along with the shed door being open? Is the nitric fumes way worse than hcl CL? I'm sure with the mall batches I make a simple fume hood would work for that... It's the nitric that's unknown to me.

Keep in mind that so far usually 100ml HCL and 50ml Bleach is enough to digest my small batches. I plan on getting more and more gold though I seriously plan on increasing my activity and professionalism is in this hobby. The wife and kids tend to leave me alone when I'm in the yard covered from head to tow wearing safety goggles and rubber gloves :lol:


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## Shark (Jul 8, 2014)

On small batch's take a look at this. I started with something along these lines and still use it at times. 

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=17396


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## Clneal2003 (Jul 8, 2014)

Shark said:


> On small batch's take a look at this. I started with something along these lines and still use it at times.
> 
> http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=17396



Noob Q. When it comes to that water you use as a filter... Does that then take on solution like properties? Can you just dump that filter water in the yard or down the toilet? I'm guessing not and that over time the becomes more and more like the solutions it filtered.


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