Low/No Budget Ventilation Hood

I am setting up a community darkroom, trying to get by with all donated and improvised equipment. So far, the results have been outstanding, and we have managed to get a lot.

As far as ventilation goes, we have a fan and ducting already set up, but I am stuck on creating a ventilator for the sink.. I have read in other posts that the best way to vent is directly behind the sink, but short of buying a low profile vent hood, I am stuck on how to do this.

I am putting this out there to hope that APUG members might have some improvised options that would bypass the necessity of this purchase.

Thanks, Dan

Well without seeing your room setup, why not run some ductwork up the wall behind your sink and connect it to your exhaust fan ductwork, assuming your fan and ductwork are for exhaust, not air supply. Or look for a used kitchen fan hood.

Yes, exactly! The problem is that I am trying to design a good end for the ducting, that is a good 'hood' that will draw from the back of the sink...

D.

I've been using a broan multi room fan. It has mutiple outlets and I have one just above each tray. These come from electrical supply houses and might be worth a call to see if they have a bruised one they might be willing to donate. You can go on the Broan site to see what size would fit your needs

Ventilation hood? What is this for? I didn't know any photochemicals had vapors harmful enough to need ventilation. Am I going to die?

I took a different approach. I have my fan blowing in though a filter on one end of the sink and the exhaust on the other end of the sink. Positive pressure ventilation does wonders to keep the dust down. Also, I didn't want a hood above the sink because I wanted safelights there. It works well for me even when using strong and hot selenium.

If I were to make a hood, I'd just build what I needed from 1/4 in. plywood.

BetterSense said:

Ventilation hood? What is this for? I didn't know any photochemicals had vapors harmful enough to need ventilation. Am I going to die?

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No, but you'll stink of fixer. The university darkroom use to have lousy ventilation. I'd be in there all night, not even noticing the smell of fixer (becoming so use to it), but returning home, my girlfriend would wrinkle her nose and could smell it on me (love me , love fixer, I guess!)

Standard stop bath and fixer are acidic...those with asthma are more sensitive to acid fumes.

And sepia toning might be a bit much -- though one's nose stops reconizing sulfur dioxide after awhile. That what kills oilmen...their noses become insensitive to it and they die, not knowing that they are breathing mostly sulfur dioxide.

Instead of a hood, a large plastic pipe laid across the back of the sink, with hortizontal slits cut into it does a good job. Fresh air passes by one's head, passes over the trays and into the pipe. Hoods are okay, but if one has one's head over the trays, then the fumes go right past one's head...and that is like having no ventilation at all.

Vaughn

PS...Mark -- Someone else who uses hot selenium toner! I use to use it at 100 to 120F when I was silver printing, but at 1:16. Portriga Rapid for 30 seconds [drained for 15 sec) then put into the rinse tray] gave me a consistant perfect color change. Got rid of the greenish tinge and moved it to a red-brown...without going to the more purplish tone. Ah...the good old days!

Well here in western Canada, forced air heating is the "standard", so it is easy to head off to the store and buy premade sheet metal bits just for this purpose. Depending on the width of your sink, the vertical riser should terminate in an inverted T fitting with arms extending sideways to each end of the sink. Here I would buy 6" diameter floor boots for 2x16" registers for each arm. Looks like a 24" long 6" diameter tapered sheet metal tube with 2x16 flanged slots that are lengthwise in it.

Dan,
I sulphide tone all my prints. So I know about ventilation. For my darkroom I have a standard exhaust fan, the kind you would use for a bathroom in a residential home, (don't know the cfm, but could look it up), and a flexible 6" hose, which I can position about 18 inches above the toning tray. No hood or anything else, just the hose. The hose is a bit in the way as I work, but that's where it needs to be. It works great! I keep the fan running for 30 minutes after I have finished toning.
Stefan

Vaughn said:

And sepia toning might be a bit much -- though one's nose stops reconizing sulfur dioxide after awhile. That what kills oilmen...their noses become insensitive to it and they die, not knowing that they are breathing mostly sulfur dioxide.

Vaughn

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Hey Vaughn, you got it mixed up. Hydrogen sulphide (H2S - rotten egg) not sulphur dioxide (SO2, like the acrid odor that hits you between the back of your throat and the nasal maze that you get with sulphured dried apricots, among other things).

Maybe it takes a winemaker to know (I do that) or someone who walked to school as a kid in Tacoma WA (I did that). In Tacoma, we got H2S when the wind was blowing one way from the kraft paper mill, and SO2 when it blew from the other way from the Asarco copper smelter (of course, that isn't ALL we got. Arsenic anyone?). Quite different odors. Highly unpleasant both, but I think the H2S would give you headaches, make you nauseous, but the SO2 is deadly in large enough concentrations and as you say, I believe it damages the sense of smell. NASTY STUFF.

When you open a bottle of wine, this is why you let it "breath" - Potassium metabisulphite or Sodium sulphite is used to kill bad things. In dissolving, it produces SO2 which goes into solution acting as a preservative, just as sodium sulphite does in our developers. When you open the bottle, the gas comes out of the wine. Tastes much better when it's gone!

Had you been in Eureka/Arcata in the '50's/60's, you would have had plenty of H2S, because, I believe, there was at least one paper mill there. In paper making, they use sulphuric acid, at high temperatures, to "digest" the wood fiber.

For a long time I had a fan blowing air into the darkroom (part of the wall heater) and a darkroom light tight fan above the sink that sucked the air out. I could get a regular wind tunnel in there, which was handy if I was processing cibachromes, toning, etc. I'm planning a new darkroom now - most likely in a trailer, because I don't think I will have a permanent residence. I'm glad to have found this thread. Good stuff here.

BetterSense said:

Ventilation hood? What is this for? I didn't know any photochemicals had vapors harmful enough to need ventilation. Am I going to die?

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Do you mix from powders? If you do, you better think again!

Ask any marijuana smoker, or tobacco smoker for that matter, how efficient the lungs are in introducing chemicals into the blood. From the lungs, the chemicals go direct to your brain. Doesn't that sound like fun?

Chemicals in aqueous solution aren't so bad, but when you open that bag of dektol, and pour it in the water, what do you think that white stuff that goes into the air is?

If you should spill a bit of water on the floor, and a bit of chemical on the floor, they probably look the same. When the water evaporates, except for a small amount of mineral content which is left there, it is gone. When the chemical evaporates, the water is gone. The chemical is still there. We walk through it. In doing so, we grind it up into really fine powder, which gets into the air. We breath it. If it was fixer, and we breathe enough of it, when we die and are cremated, our ashes might be worth fifteen cents or so. But when we are living, we are living with heavy metal in our system.

Don't be casual about ventilation. Please.

Thanks all for your responses!

Bob, I like the idea of the heating ducting, although it does seem to require a bit of cash. Your described item seems to have the perfect shape. Vaughn- your idea is perfect, it is just that I am having a bit of trouble imagining the proper design for the tube and how it would be connected and the spacing of the slits. Stefan, your idea, although a bit too improvised for a public lab, underlines the need for the ventilation to be directed at the spot where the fumes are produced. It is more efficient and effective this way by far.

Bowzart- your response reminds me that not all chemical worries are fume-related. The white crystals that are left anywhere chemicals dry are perhaps the most dangerous of all, and wouldn't be dealt with by a simple ventilation system over the sink. I would imagine that the crystalline structure of these chemicals could be damaging to the lungs on their own, as inhaled 'sharps'. Hmmm, I'm starting to freak myself out a bit...

Dan

I have positive vent system (Intake fan, out-take vent).
The venting behind and along the sink length is a piece of 4" pvc I drilled 1/2 inch holes in. With the positive pressure, all holes draw equally. With an exhaust type (draw air out via fan), I'd change it a bit.

A couple of suggestions.

First, an arrangement in which you force air into the darkroom, and then forcibly extract it near the sink is most efficient. Second best is to force air in, and then let it flow out based only on positive pressure. Both do a good job of controlling dust. The third option - forcibly extracting air - requires that air come into the darkroom via whatever paths it can find, and that usually increases the dust control problem.

Second, I recall seeing some articles in either PopPhoto or Peterson's way back in the day in which they suggested installing an exhaust pipe at the back of the sink with small vents along the edge facing the trays. The argument was that this would do a better job of picking up fumes from trays than having a single vent either behind the sink or at one end.

They also made a point of noting that placing the vent ABOVE the sink is not good - because your face (and nose) would be directly in the path that fumes must take between the trays and the sink. They recommended placing that vent pipe just above the level of the trays.

The recommended solution was a length of PVC or ABS pipe installed at the back of the sink just above the tray level, with a series of holes bored in the pipe facing the trays. To make this a forced air system, use a length of plastic ducting to connect this pipe to a fan to draw air out of the darkroom.

Radio Shack carries some computer-style 'muffin fans' that are perfect for building a ventilation system - most commercial exhaust fans are very noisy, but the fans from Radio Shack are exceptionally quiet, especially if they are installed outside the darkroom and connected to air inlet or exhaust vents via flexible plastic ducting - the kind used for bathroom air extractors.

Monophoto said:

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Radio Shack carries some computer-style 'muffin fans' that are perfect for building a ventilation system - most commercial exhaust fans are very noisy, but the fans from Radio Shack are exceptionally quiet, especially if they are installed outside the darkroom and connected to air inlet or exhaust vents via flexible plastic ducting - the kind used for bathroom air extractors.

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The 120 volt AC versions of these fans are harder to find; I don't know whether Radio Shack has them or not. The 12v DC version is what computers use, at least as far as I know. I have a 120 v fan plugged into a variac in my studio, aimed at the gas fireplace to help distribute heat. It is great to be able to adjust the speed.

bowzart said:

The 120 volt AC versions of these fans are harder to find; I don't know whether Radio Shack has them or not.

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I've bought several 120v AC units at Radio Shack, but it's true that they carry a wider line of low voltage DC models.

My son the geek tells me that the presence of a Radio Shack store is evidence that a community is civilized.

Monophoto said:

...
My son the geek tells me that the presence of a Radio Shack store is evidence that a community is civilized.

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I think he's right. Here in our town we actually have one that is wholly owned by the proprietor! That means that there is someone around most of the time who might actually know something!

The big (4, 5, or maybe 6" diameter ?) thin wall PVC pipes can be got from Home Depot or the local hardware store etc. and are cheap enough to duct your exhaust fumes from behind the trays for near nothing.

There are sections with perforations along the side so that you can have a section sucking up darkroom air along it's length, as well as unperforated sections that merely convey the gases to their destination.

bowzart said:

Hey Vaughn, you got it mixed up...
Had you been in Eureka/Arcata in the '50's/60's, you would have had plenty of H2S, because, I believe, there was at least one paper mill there.

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Thanks...It did not sound right as I was typing...but that did not stop me from blowing it, again.

Both pulp mills were in full operation when I arrived here in '72. In Arcata we could when a storm was coming because we could smell the pulp mills from across the Bay. One closed down years ago, and the other changed over to a non-chlorine process...much less stinky, but is closed down for the moment and looking for a new owner. People are keeping their fingers crossed we need the jobs and our water bills will go sharply if the mill not working (our water infrastructure was designed for the massive amount of water the two mills use to use -- the cost of maintaining that infrastructure will be passed to household users without the existing mill paying their bill).

Vaughn

Thanks for all your responses! CBG pretty much pegged what we're going to end up doing, with the aid of positive pressure from a second fan we have lying around...

Vaughn, as late as 1990, we could smell the pulp mills as far north as Trinidad (20+ miles north of the mills) as a sure sign of rain. With the dry year we're having, maybe we can use all the extra water the pulp mills aren't using to supplement the rainfall. Maybe I could use some of those PVC pipes with holes for the job...hmmmm.

Dan

BetterSense said:

Ventilation hood? What is this for? I didn't know any photochemicals had vapors harmful enough to need ventilation. Am I going to die?

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Yes we all are, It's just a question of when.

BetterSense said:

Ventilation hood? What is this for? I didn't know any
photochemicals had vapors harmful enough to need
ventilation. Am I going to die?

Click to expand...

I've not had an odorous fume since chucking
acid stop and acid fix. Sulfites in fixer will emit
sulfur dioxide upon acidification. Sodium sulfide
will likewise emit hydrogen sulfide, the more so
as it's solution becomes more acidic. Same for
selenium. Hydrogen selenide is EXTREMELY
TOXIC. Dan