What are people using for fume hoods?

[phuphuphnik]

Not everyone can have a large lab hood installed in their house, what are some of the methods you use?

[Andy Stockton]

I made my own in an outbuilding – since I decided a while back that no matter how careful I am I don’t want mercury or bromine inside my house. Here is a post on my blog about it, and some links to pictures.

http://www.thedaguerreotypist.com/tdg1/wordpress/2008/10/12/infrastructure/

[drdag]

I was very lucky, I was given a fume cupboard on wheels(3 years old), (Like schools use) its 8 ft X 4 ft x 2 ft and has a hudge carbon filter. The college I was ttending used it for model painting. They moved it from one building to another and it stopped working. The college management said they would not spend money on an elctricain, so it ended up outside. I asked whether I could have it.I got it home and with 1/2 hr I had it working. (Someone up there wanted me to do this I think)

It is about £3000 new and is a current model. You cannot smell anything when it is running.

I know I am lucky, it is a shame that a college doesnt have the forsite to save these things.

I went back a while ago and the guy who gave it to me said they scrapped another one recently!

[jdanforth]

I built one out of 1/4″ acrylic. I’m using an 8″ inline blower mounted to the top and it seems to work pretty well. The vaneometer I bought on eBay is very useful for testing. I also got the opportunity to make some homemade smoke bombs to test it! Woot!

[dagist]

A precaution for anyone building or installing a fume hood.

It is important that your fume hood’s exhaust fan is mounted OUTSIDE your building (drawing the air out instead of pushing it out).

If no outside solution is feasible/practical, the fan can be carefully mounted into a wall of your work space that vents directly outside (without any ductwork), but the entire fan must be contained WITHIN the fume hood itself. This set-up is not ideal and does have some risk because dangerous fumes might get pushed into the space between your interior and exterior walls (where you cut the hole in your wall for the fan), thus finding their way back into your work space.

Never should your fan be mounted on top of your fume hood (sitting in the same environment that you breathe in), even if it is directly mounted to a wall that vents outside.

The reason for mounting your fan outside, is so that the entire fume hood exhaust system has a negative pressure within all of its components (including all ductwork) until it reaches the exterior of your building where it can then be safely exhausted into the atmosphere. All exhaust system ductwork within your work space must contain a negative pressure, which assures that no fumes can ever escape into your working environment because the fumes are being sucked out, not pushed out.

Mercury fumes aren’t entirely odorless (they can be smelled/detected in large enough concentrations), and an improperly installed exhaust fan could release enough low concentration (odorless) mercury fumes into your work environment that you would be slowly harming/killing yourself without ever knowing it.

Don’t let this information scare you away from making daguerreotypes, just take the proper precautions (mount your fan outside) and you will be able to safely practice the most amazingly life-like image-making-process photography has ever developed…..the daguerreotype.

Daguerreian Cheers,

Rob McElroy

Buffalo, NY

[phuphuphnik]

I was planning on using the Hg/Cl filters on a negative pressure box. Air flows into the box, and out the Mercury vapour filter. This way A) I don’t breathe it in, and B) It doesn’t get into the environment. I was looking at building a Sulfur mesh box to trap anything that got past the filter.

cheers,

chriso

 

[Andy Stockton]

Hi Rob – I was curious about your statement concerning mercury fumes in large enough concentrations being detectable. Is that from some experience on your part or did you run across some written reference you can point me to? I have read in so many places that mercury fumes are odorless that I was surprised by your statement. I’m always trying to learn more on this topic, so would appreciate any additional info you post.

I would add my “amen” to your statement about external fans being the way to go, since even heating/cooling pros have a hard time creating perfectly airtight ductwork, not to mention the issue of fan housing leakage.

I have also wondered about any kind of filter/trap approach that leaves the catchment apparatus inside the living space. It seems like no matter the plan you would always run the risk of trapped particles sitting there quietly off-gassing when the suction is turned off. I would also think it would be very difficult to determine when your filter is “full”.

I’ve adopted the “dilute in outside air” approach myself as the simplest safe method. I suppose it adds to the atmospheric load, but my contribution seems pretty small compared to the thousands of metric tons released worldwide from human and natural sources. even if I did filter, I would still be producing waste that would have to be taken care of somewhere. It’s a tough call, but I hope if people filter, they rig that part of the system outside their living space.

[dagist]

Andy,

In reference to your question about mercury fumes being detectable in large enough concentrations, you are correct that almost all the literature you come across will state that the fumes are odorless, but none of those references are referring to mercury at elevated temperatures (I’ve read at least three dozen different references from the early 1800s through the present). At room temperature, I would certainly agree that no odor can be detected.

It is when mercury is heated that the concentrated vapors can sometimes be detected. Here’s a quote from an 1854 homeopathic journal, “Mercury, for instance, is inodorous. But this does not hinder its volatility, which is so great that it can be distilled at a moderately elevated temperature. We know from accidents which are occasioned every day among the workman who, by their business, are exposed to mercurial emanations, that, although almost without any smell, mercury is nevertheless one of the most frightful poisons with which we are acquainted.”

The reference “almost without any smell” above – concurs with my own experience, where I once made the mistake of forgetting to remove the protective rain-cap on the exhaust fan I installed on the outside of my van. The fan was running properly (so I thought because I could hear it) but no actual air was being drawn out of the portable fume hood because I had left the fan’s rain-cap on. When I returned to my van to process the on-location daguerreotype I had just exposed, I opened the van door and climbed inside. With my very first breath, I could detect a very-faint slightly-sweet odor that seemed to just tickle/irritate the back of my throat. I knew something was amiss and quickly got out of the van, whereby I discovered the rain-cap still in place, preventing the air from being exhasted/drawn out. It was the smell that clued me in, and I will of course never make that mistake again.

Here in the USA, our government’s Occupational Safety and Health Administration (OSHA) guidelines for mercury vapor says “No information is available on the appearance or odor of mercury vapor.” Because heated mercury vapors can be so toxic to all living things, it is no wonder that there are no recent accounts of what it actually smells like when heated.

Cheers,

Rob McElroy

Buffalo, NY

[Andy Stockton]

Thanks for the very interesting reply Rob. I suppose that hot mercury is one smell we never want to experience, but it is certainly something to remember. If I’m ever working with mercury and notice an unusual odor I will evacuate first and ask questions later.

[daniel]

I just scored this fume hood on craigslist. It is 48inches wide, has a built in drain and made stainless steel. It came with an 8 inch pbm pabst inline centrifugal fan with a plastic impellar rated at 530 cfm. Would the the fan be OK to use for venting out mercury and halogen fumes? The motor is pretty well sealed and the lead wire looks to be very well insulated from the air being sucked out. any advice would be very appreciated.

thanks all,

Dan in Seattle

 

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[Kaden Kratzer]

Hi folks,

I have a question. So far I have been unsuccessful in finding an HVAC professional willing to install the necessary duct system to connect the fume hood I have to the duct area coming from inside the house to the outdoors. My question is in regards as to what type of material should the ducts be made of since it may corrode the metal duct already installed. Any ideas anyone?

[jgmotamedi]

PVC green waste-grade PVC pipe comes in large sizes (6″ to 12″). Rubberized flexible hose (RFH) is meant for exhausting chemicals which comes in a variety of widths. Both are relatively expensive, and neither will resist long term direct contact to bromine, but both should last for many many years without worry for our purposes. Obviously aluminum is out, as is most metal duct work. I would think fiberglass should be OK, but I never found any for purchase.

[Kaden Kratzer]

Thanks Jason. I just found an HVAC Company that will install the PVC pipe from inside the darkroom to the outside of the house next week at a somewhat reasonable price. 🙂

 

[dagist]

My fume hood is exhausted through 6″ PVC sewer pipe, which is the common white PVC, not green like some brands. It is easily procured at any professional plumbing supply house here in the US. It has works extremely well for over 20 years and provides plenty of air flow for my home made hood.

Do not try to save money by using anything smaller than 6″-diameter pipe because it will reduce the airflow considerably and may not provide adequate suction if your fan motor has been properly installed outside (not inside) your building , preferably on the roof.

Cheers,

Rob McElroy

Buffalo, NY

[newone2010]

Safty is the first important thing.My wife told me again and again.I will rebuild my fume box and other things.

[Kaden Kratzer]

Thanks for the advice everyone. I actually had 4″ PVC installed. I tested it and the airflow looks just fine. Also fact after checking into it the white 6″ PVC vs what the HVAC company installed, I found the white PVC to be of lesser quality and cheaper.

 

Here are some images of my temporary set up.:

 

 

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[jgmotamedi]

With a small demonstration hood, like you have, the 4″ might be ok, but it probably won’t handle a larger hood.

More importantly, why does it look like your exhaust is going down once outside of the house? Or is the image upside down? It should go UP, right?

[Kaden Kratzer]

Thanks for the question Jason. Right above the duct in the 1st floor there are massive windows. Hence the duct goes down and connects to a fantec unit and then climbs up to avoid the windows.

No straight upwards line was possible, although that would have been an elegant solution.

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