US Lab/Equipment Sources

[jdanforth]

I’m building a new (proper) fume hood from acrylic. I need to get a suitable exhaust fan and was wondering where you guys got yours. I think Andy went here: http://www.plantitearth.com/

Suggestions?

My maximum opening size is 24×18 but the sash will fully close.

[Andy Stockton]

Yep – this is the page for the one I bought:

http://www.plantitearth.com/web-specials/hydrofarm-activeair-blower-fan.aspx

I got the 465 CFM model. It moves air at a good clip, but lets a lot of light in through the intakes. I have always been puzzled by the fact that it has two intakes, but only one of them is set up to take a 4″ diameter hose. The way I used it, that design didn’t matter, but if you were trying to pipe the air somewhere I think you would lose a lot of the rated airflow.

The blog I wrote about building the fume hood was here:

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

and the pictures are here:

http://www.thedaguerreotypist.com/tdg1/wordpress/gallery/?file=Fume_Hood/

[jgmotamedi]

I have been struggling with building fume hoods for a while, I recently bought a ‘real’ lab hood off craigslist, and can make a few quick suggestions. I will try to write something longer and post it in a day or so.

First, I would really go more than 465cfm. Maybe 700cfm? If you calculate how much you need, it usually is pretty low, in your case about 300cfm, but factor in that every foot of pipe and every 90 degree turn cut down the movement significantly. Also, I have found through lots of trial and even more error that the no-name fans (like you are probably thinking about buying from the garden stores) don’t live up to their rated cfm. I would recommend spending another $40 and buying a Dayton.

Second, consider putting the fan outside so it is pulling the air outside rather than pushing it. This will reduce the sound in your darkroom, but more importantly you wont have to worry about fan leakage, which seems to be a major problem with these little squirrel cages.

Lastly, TEST TEST TEST! Certainly buy a vaneometer (Dywer sells a functional cheap one), but also use smoke bombs. There is no predicting where leakage will be, and the easiest way of testing is using the colored smoke bombs. You can also make them yourself with saltpeter and sugar, but these tend to spit lots of flame, which might damage your nice acrylic hood.

[jgmotamedi]

Updated response: some thoughts and questions about venting and safety

I ran a few searches on the forum about ventilation, and notice that a number of people are using non-vented (i.e.; filtered) fume hoods. While I think in many circumstances these are fine, I am concerned about their use with mercury. There was an article in the Daguerreian Annual sometime back about Sandy Barrie, an Australian Daguerreotypist who poisoned himself with mercury because he didn’t change his filter frequently enough. Clearly human error may have played a factor here, but I do note that few (none?) mercury filters come with an end-of-life indicator, so it is really impossible to judge—short of elapsed time—when they need to be changed. I suspect that these non-vented fume hoods would be fine with iodine and bromine, since the strong chemical smell will quickly give away when the filters have started to fail.

My own set up employs two different fume hoods. One, in my basement darkroom, is used for sensitizing and another, in the studio (a rebuild garage) is used for mercury development as well as working with or mixing any of the sensitizers. I divided my set up this way for a few reasons; first and foremost, I didn’t want mercury in my house, and I also didn’t want to mix mercury and the sensitizers (they like to eat metal and my mercury pot is all metal, and also theoretically the sensitizers can contaminate an exposed plate before development).

The mercury fume hood is a real 4’ lab-grade fume hood which I found on Craigslist. It was unused and free for the pickup, but required finding three friends to lift it and borrowing a truck. I had to build a table to place it on, and then vent it through the ceiling and roof. It requires a 10” vent, which was surprisingly difficult to find. Since I would be using mercury and occasionally sensitizers in the hood, it couldn’t really be any sort of metal other than perhaps stainless steel, which was too expensive to even consider. I ended up buying 10 feet of 10” heavy duty RFH (rubber flexible hose) which is intended to vent corrosive fumes. I vented the fumes through the roof, attaching the 10” tube to a 5’ piece of 10” PVC sewer pipe I found in a dumpster. If I could do it over again I would probably have used 10” PVC sewer pipe for the whole thing.

My second fume hood is used only for iodine and bromine, and is a pretty simple affair, a 34 x 18 x 18” wooden box with 10 x 26” door. I vent everything with a 6” aluminum hose out the top. I will eventually replace the hose with PVC. The hose runs out of the house and joins with a 450 CFM squirrel cage blower which is screwed in place under my rear porch. The blower exhausts into a big (40lbs) activated charcoal filter from an indoor garden supply. My thinking being that activated charcoal will absorb bromine and the iodine fumes, and what it doesn’t absorb can be safely vented outside of the house. Any thoughts on using activated charcoal for absorbing halogens? Obviously it will have to be changed every year or so.

I tested the fume hoods first using one of the cheap Dwyer vaneometers, insuring that they measured at least 100cfm at all points of the entrance. I then tested with a few smoke-bombs (I used smoke-bombs I bought at a fireworks store, but they can also be made out of saltpeter and sugar. The problem with the homemade ones is that they tend to spit more fire) to make sure there were no leaks. I think the smoke-bomb test is very important because it allows you to examine all parts of your exhaust chain before putting odorless mercury there. I once built a fume hood with a friend, and before we used it we tested it with a smoke-bomb only to find out that his blower leaked out the side and would have re-circulated some of the fumes back into his darkroom. The leak was fixed with a quick weld and by moving the blower outside and turning it into a ‘sucker”. I have since learned my lesson and try to place (if at all possible) the blower outside the workspace. It is quieter that way too. This wasn’t possible with my commercial fume hood, which has a built in motor.

[Andy Stockton]

A few more notes on my home-made, built-in setup. Only the front face is plastic (a mixture of black ABS and clear Acrylic). The rest is plywood sealed with 2 coats of enamel paint. The front face can be adjusted by changing the size of the plastic panels (which are held on by magnetic seals). The opening I settled on after some experimentation is 14″x15.5″ and easily registers 150 LF and above on a Dwyer Vaneometer. I smoke tested it extensively and was even able to hold my smoke source two feet away from the work opening and have all the smoke pulled into the hood and exhausted. The fan is inside the fume hood, but vents directly to the outside with no intervening ductwork. There is a commercial charcoal “odor” filter on the intake with the 4″ flange. On the outside I have fastened some charcoal impregnated furnace filters over the exhaust. Both filters are in place only to control light leakage into the hood. I don’t actually like using the filters since I think they will trap mercury when I get to the point of using it. I have some designs for light traps in mind but have not had time to make them. I keep fresh mercury indicating powder inside the hood, and seal it shut when not in use. The one time I have transferred bromine in the hood, once the bottle was re-sealed I carefully took off my gas mask and had a sniff. I could detect no bromine odor at all inside my work area.

Long term I do worry about working with the sensitizers and the mercury in the same hood – related to the potential for cross contamination. I would be interested in any comments on how serious that problem is and how difficult to control.

[Mercury]

Hi Andy,

I wouldn’t worry too much about cross-contamination from sensitizers in the fume hood. The sensitizers are so volatile and reactive that they hate existing alone. If you are at all concerned after sensitizing in your hood, then place an open tray of non-detergent household ammonia in your hood for a few minutes, then turn the fan on. With the kind of airflow you’re talking about, you’d need to have an overwhelming and continuous source of free iodine or bromine in order to affect an exposed plate. Likewise with Hg. This is within my experience, of course. Happy dagging!

KN

[Andy Stockton]

Thanks Ken. Very helpful info. The rest of my life has put a lid on dagging for the moment, but I have been working on a number of small projects in preparation for my next attempts.

[Mercury]

Andy, don’tcha just hate it when the rest of your life comes barging in like that? I feel your pain, man.

I’ve been in a sort of similar pattern, and have held the rest of my life at bay by trying to learn a little something about galvanizing.

[jdanforth]

Thanks for the great feedback, folks! I assembled the four walls of the hood Monday night but I’m waiting on the right fan before I install the top. I figured it would be far easier to cut the vent hole *before* assembly than after!

I’ll look at a 700CFM+ fan. I got my Dwyer vaneometer in the mail on Monday (including the hilarious old photographs of people using it!) and can’t wait to experiment. I was planning several rounds of vaneometer tests and smoke tracer tests before proceeding with any kind of actual chemical work.

[Andy Stockton]

I will look forward to the pictures when you are up and running.

[Author]

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