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homebuilt fume hood

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Magpie - 13-4-2009 at 15:46

Since some members are having difficulty sourcing epoxy paint for their fume hoods or work surfaces I thought I would post these:

http://www.rustoleum.com/CBGProduct.asp?pid=116

http://www.armorpoxy.com/bath-and-kitchen/for-dummies-refini...

These products are available in the 1 quart size. I think I bought mine (Rust-Oleum) at Home Depot or possibly Lowe's. I used it to paint a plywood work surface before I built my hood. I can recommend it to anyone needing a small quantity of a 2-part epoxy paint.

I realize these products may only be available in the US, but hopefully similar products are available where you live.

For my hood I bought a gallon of 2-part epoxy paint from Sherwin-Williams, a paint dealer. The painted hood surfaces are as good as new after 3-4 years of use. The unpainted aluminum baffles, however, show battle scars from hot hydroxides.

[Edited on 14-4-2009 by Magpie]

EmmisonJ - 15-4-2009 at 11:26

i'm trying to think of ideas on how i can implement a sash.

my fume hood is just a wooden storage cabinet like this (no wheels)

i modified it so that i can put baffles in it (currently working on) and also modified it so that there is a shelf half-way through. below the shelf is storage for glass (tight on space) and above the shelf is the fume hood work area. so making a sash is kind of difficult because of the doors to the cabinet which i want to leave on there. i figured my only way of making a sash that works inside of this cabinet without interfering with the doors is one of two ways. either way, the glass will be held in place by using a sliding door lock. this is a great idea i saw someone else on here do in a fumehood post.

the first picture shows a side view of the first concept which i want to pursue but am unsure of how to realistically pull off the concept. basically the 3 squares where the sash is are representative of 3 glass panes, all lined up one in front of the other. the gap above the sash is for airflow coming in when the sash is closed. the first glass pane (closest to the outside) is immobile and no need to move, the second glass pane can move down its own height, the third glass pane can move down 2x its own height so that you get the effect of a closed glass sash. i'm unsure of how exactly to get the glass to do this.

the second picture shows that it would just be one long glass pane. there would be a slot cut out of the ceiling of the fumehood cabinet towards the front which allows the glass to slide up through this slot. this seems like it would work also but seems like it would be more unsightly when it's open because the glass would be almost 4' tall, in fact my ceiling may not even be tall enough to support the cabinet plus an additional 4' for this glass to go all the way up and the glass needs to go all the way up to fit tall pieces of glassware in it. so this may be do-able as a fallback, but i'd love to figure out how to somehow get the glass to work as in concept 1, with railing on the side or something to pull it off.

any ideas that may help?

[Edited on 15-4-2009 by EmmisonJ]

Lambda-Eyde - 1-8-2010 at 17:47

Hey guys, it's me again!

So, I've finally done some real work on the lab. The framework for the bench and fumehood is done with, and I'm refurbishing my fire-proof chemicals cabinet (read: removing rust and old paint). I've sent out some mails asking for prices on glue-laminated wood (got a factory a few tens of kms away from home) and laboratory faucets (Chinese. I'm not driving there). Still waiting for answers, though. I'll make a thread on my construction progress if anyone's interested (I love such threads myself!).

So, on to the fume hood. I'm about to put the ducting in place and I have a few questions about that. I'm going to use 100 mm (4") ducting, and there are two reasons for that: The fan I'm using (posted on page 4) has 100 mm in- and outlets, and I have quite a large supply of 100 mm PVC plumbing pipes and connectors lying around that I would like to put to a higher use.

Questions: Is 100 mm too small? Would there be any good in using 125 or 150 mm ducting even if the fan inlet is smaller? Also, I see that some of you object to the use of plastic ducting because of the fire danger. Does this also apply to the heavy duty pipes (~5 mm walls IIRC) I have? I can understand the concern with thin, flexible plastic ducting, but the problem should be non-existent with these pipes, right? When I need flexible ducting (about 3 m), should I go for aluminium ducting (what about acids?) or some plastic ducting designed for workshop vacuum systems? I have quite a few meters of the latter in my workshop, and it's quite tough. I don't know how it would stand up to long term solvent use, though.

And another problem: The vapors have to travel quite far from the hood to the fan, about two meters horizontally and three meters vertically. There will be two bends where I will use flexible ducting to make the bends as smooth as possible to not upset the flow. There is really no alternative to this route, as my parents would most likely kill me if I laid the ducting through our kitchen. Either that or they would die from some sudden leak in the ducting while I had some freak accident involving large amounts of chlorine in the hood.

And hey, there's more! I have two alternatives as to how I should connect the hood to the ducting: At the top of the hood or at the top of the right wall in the hood. I want to avoid the first one as it will introduce another, severe bend to the duct. Also, going for the second alternative allows me to make the hood slightly taller (10-20 cm). I can't see any problems with the second alternative if I have the baffles depicted in the picture integrated in the hood. Does any of the hood experts have any objections to this idea?

Here is a drawing of what my hood (hopefully) will look like:

The hood will be roughly 120 cm wide, I see that I forgot to include that in the drawing. The bench itself will be stainless steel (should I coat it?), the walls and ceiling will be made of drywall (fireproof), painted and epoxy coated. The baffles I don't know yet, but I'll probably get some aluminium plating and epoxy coat them as well if there's anything left after coating the walls.

The sash. I'm planning to have two layers: The inside glass and the outside plexiglass/acrylate/polycarbonate. Glass for chemical resistance (I'm not playing with fluorine anyways) and plastic to make it more mechanically durable. I really don't like the feel of all-glass sashes anyways, it feels like I can break it by lowering it too rapidly... Does anyone have any experience gluing large glass plates to large plastic plates? I bet it's not easy to do without any air bubbles or other deformities.

I will have to come up with some ingenious idea for the lowering mechanism. I have a fume hood at school featuring a system of weights and strings which I think I will copy (if I can make it work, that is). As you can see from the drawing, the sash is about 60 cm tall. In addition to that I will have about 40 cm of glass integrated into the hood. The reason the sash itself is relatively short is because there's only about two meters from the floor to the ceiling in my roof, so making it any longer would be pointless. I will leave about 10 cm of space for the airflow at the top of the hood.

I will also integrate a small sink and two gas outlets (vacuum and argon) in the hood if I can get a good deal from the faucets dealer I'm e-mailing. Pretty nifty, huh?

Phew, that's a huge wall of text I've made the last minutes. I hope you can bear with me and provide some feedback to my ideas. I'm counting on the experts here!

[Edited on 2-8-2010 by Lambda-Eyde]

Eclectic - 1-8-2010 at 23:22

You may want to try cement tile backer board instead of drywall. It should be a lot more resistant to liquids and mechanical damage.

Magpie - 2-8-2010 at 07:21

Your design incorporates a variable opening height of 20 to 60 cm. That's a 3 fold range of area. Therefore you can get a 3 fold range of face velocity. That's why I promote a fixed opening area as in my hood design, previously provided. But in practice you will likely use only a limited range of sash openings so the face velocity changes may not be an big issue. Use of a bunsen burner is an example where you don't want a lot of change in face velocity.

Your blower flow is about 500cfm (units I can visualize). This should be good but you haven't provided the fan curve, ie, against what flow resistance can the blower deliver this flow.

If the blower outlet is 100cm then it won't do much good to increase the duct size. You effectively would have a restricting orifice right at the blower.

Overall, I think you are on the right track. But I would feel much more comfortable if I could see a fan curve.

Look into buying a window. This would save you a lot of trouble.

watson.fawkes - 2-8-2010 at 10:10

Quote: Originally posted by Magpie

If the blower outlet is 100cm then it won't do much good to increase the duct size. You effectively would have a restricting orifice right at the blower.

A single restriction like that is just some constant static head loss. If the length of the duct is long, that creates an additional head loss. It's perfectly fine to enlarge a duct for lower losses if it makes the system work better. Having said that, unless the duct run gets on the long side, considerations other than friction loss will likely predominate. Take a look at this nomogram. The difference between 4" and 6" (100 mm and 150 mm, say) is about an order of magnitude. If the total loss is close to zero, this difference may not matter. As always, it's a trade-off between cost of a heftier blower vs. cost of bigger ducts.

peach - 2-8-2010 at 10:11

EmmisonJ, how's about sliding or hinging the sash horizontally?

[EDIT] CAN WE PLEASE MERGE AND STICKY THE FUME HOOD QUESTIONS? YOU GUYS WILL NAIL REPEAT QUESTIONS IN THE ASS, LET ALONE THOSE COMING FROM NEW THREADS, AND YET THIS ONE IS HERE ALL THE TIME. IT'S DILUTING THE INFORMATION AND CLOGGING THE FORUM. STICKY IT. I'D ALSO RECOMMEND A STICKY FOR VACUUM AND HOTPLATE QUESTIONS. [/all caps]

[Edited on 2-8-2010 by peach]

watson.fawkes - 2-8-2010 at 10:22

Quote: Originally posted by Lambda-Eyde

Is 100 mm too small? [...] When I need flexible ducting (about 3 m), should I go for aluminium ducting (what about acids?) or some plastic ducting designed for workshop vacuum systems? [...] The vapors have to travel quite far from the hood to the fan, about two meters horizontally and three meters vertically. There will be two bends where I will use flexible ducting to make the bends as smooth as possible to not upset the flow.

As in my just-previous post, whether 100 mm is too small depends on your fan, the length of the run, and your target flow rate.

The static loss from flexible corrugated pipe is quite large, something like an order of magnitude more than smooth pipe of the same diameter. Keep the bends short and you'll be OK. Better yet, go get "wide sweep" fittings. With some care, large radius bends in PVC can be achieved with a hot air gun and some fixtures and/or assistance. (I must admit I've never done it with anything as large as 100 mm.)

PVC should be just fine for a home lab as long as your not running solvent vapors up the chimney constantly. Some solvent will absorb into the plastic. It will then desorb with fresh air. So if you use PVC pipe, purge the duct work when you're done with it each time.

Corrugated duct is typically made with vinyl plastic, which I'd worry about more, both because it's thin and it seems to be more subject to solvent attack. As long as it's on the inlet side of the fan, though, any failure creates another inlet, not a new outlet for hood fumes. Nevertheless, if you use it, keep it in sight so that you can inspect it.

A side outlet from the hood should be fine if you're using baffles. The baffles will do a lot to distribute the flow sideways across the width of the hood.

Lambda-Eyde - 2-8-2010 at 11:41

Quote: Originally posted by Magpie

Your design incorporates a variable opening height of 20 to 60 cm. That's a 3 fold range of area. Therefore you can get a 3 fold range of face velocity. That's why I promote a fixed opening area as in my hood design, previously provided. But in practice you will likely use only a limited range of sash openings so the face velocity changes may not be an big issue. Use of a bunsen burner is an example where you don't want a lot of change in face velocity.

Thanks for the advice. I think I will go for my version as I like to have the opportunity to have a large shield between myself and the hood. I guess it's a psychological thing.

I'll have it in the back of my head when using burners.

Quote: Originally posted by Magpie

Your blower flow is about 500cfm (units I can visualize). This should be good but you haven't provided the fan curve, ie, against what flow resistance can the blower deliver this flow.

If the blower outlet is 100cm then it won't do much good to increase the duct size. You effectively would have a restricting orifice right at the blower.

Overall, I think you are on the right track. But I would feel much more comfortable if I could see a fan curve.

Look into buying a window. This would save you a lot of trouble.

I've been looking for a fan curve but it's proving to be difficult - I don't even know what the brand name is! However, I have the exact same blower in my workshop and I may have the papers that came with it lying around somewhere. If I find it I might be able to find a fan curve. Would it be a good idea to exchange the radial blade for some other configuration? Seems like I would need a blower capable of delivering an acceptable flow rate at quite a high pressure drop - see below.

I have a few windows where I will scavenge the glass needed, if the sheets are large enough. Unfortunately I think they're under 120 cm wide. Cutting such large sheets would also be a problem. I'll visit some glass suppliers to inquire about plexiglass and probably normal glass if my windows are too small.
"Save me some trouble"? There's no such thing as trouble, only experience waiting to be earned.

Quote: Originally posted by watson.fawkes

There's about 5 meters of ducting - would there be any point in swapping about two of those meters of 4" ducting with 5" or 6"? (100, 125, 150 mm) Ducting isn't that expensive, I could probably even use all 5" or 6" ducting from the hood to the fan. But I would like to use some of the piping I have laying around.

Quote: Originally posted by watson.fawkes

Take a look at this nomogram. The difference between 4" and 6" (100 mm and 150 mm, say) is about an order of magnitude. If the total loss is close to zero, this difference may not matter. As always, it's a trade-off between cost of a heftier blower vs. cost of bigger ducts.

Heck - a 500 cfm blower with 4" ducting is off the charts!

For about 5 meters of ducting that corresponds to about 2" of H<sub>2</sub>O. And that doesn't account for the corrugated duct and the bends in the system. That's no good. However, looking at the nomogram, using a 6" duct reduces the pressure drop to 0,33" of H<sub>2</sub>O, quite a difference! But again, that doesn't account for the corrugated ducting and now the problem of the 4" inlet/outlet comes into play. Does anyone dare to make a qualified guess as to how much it will interfere?

Quote: Originally posted by watson.fawkes

The static loss from flexible corrugated pipe is quite large, something like an order of magnitude more than smooth pipe of the same diameter. Keep the bends short and you'll be OK. Better yet, go get "wide sweep" fittings. With some care, large radius bends in PVC can be achieved with a hot air gun and some fixtures and/or assistance. (I must admit I've never done it with anything as large as 100 mm.)

PVC should be just fine for a home lab as long as your not running solvent vapors up the chimney constantly. Some solvent will absorb into the plastic. It will then desorb with fresh air. So if you use PVC pipe, purge the duct work when you're done with it each time.

Corrugated duct is typically made with vinyl plastic, which I'd worry about more, both because it's thin and it seems to be more subject to solvent attack. As long as it's on the inlet side of the fan, though, any failure creates another inlet, not a new outlet for hood fumes. Nevertheless, if you use it, keep it in sight so that you can inspect it.

A side outlet from the hood should be fine if you're using baffles. The baffles will do a lot to distribute the flow sideways across the width of the hood.

When you say "corrugated duct", I take it you're referring to aluminium ducting with plastic coating? Then plan is to use it only on the inlet side of the fan as you say, I have thought about that problem. I'm considering using the heavy-duty flexible plastic ducting I mentioned earlier, but it seems like I can only get 4". Looking at the monogram and some other fan curves I'm leaning more towards 5" or 6", whichever I can get. 2" of pressure drop is quite a lot and will affect the flow severly.
What's a "wide sweep fitting"? I tried googling without much luck. Is it just a big bend instead of a sharp bend? I most likely won't buy it anyways, as the prices for any adapters and fittings are ridiculous. For the bends I'll use the flexible ducting as it will allow me to make the bends exactly as I want them at a fraction of the price.

Bending 100 mm PVC pipes with 5 mm walls seem like an ambitious project - I don't think I'll even try.

Also, the ducting has to go through two walls and a floor on the inlet side, so rigid pieces will be hard to implement there. I want to use the 100 mm PVC pipes for the three meter vertical part, which is a straight line.

Seems like I'm going to put the inlet on the side of the hood, with the proper baffles installed.

EmmisionJ: I'll look into those cement boards. I'd like to use plaster though, as I have some already plus it's dirt cheap. Adding enough epoxy solves everything, right?

Also, I second Peach's statement.

Thanks for the advice guys, it is greatly appreciated. I can't wait to start the real construction.

Magpie - 2-8-2010 at 12:30

Quote: Originally posted by Lambda-Eyde

I think I will go for my version as I like to have the opportunity to have a large shield between myself and the hood. I guess it's a psychological thing.

I think you are misunderstanding me. Understanding the concept of a fixed open area with sliding sash seems to be difficult, and not just for you. If I am mistaken, please accept my apology.

With my hood design I can have the sash all the way pulled down and still have the "fixed open area." With this design the face velocity never changes, regardless of the position of the sash. My 450cfm blower always sees a constant air flow. That's what's removing the noxious gases, after all. If you completely close your hood no air will flow and the noxious gases will just sit there.

Now when the sash is in the all-the-way down position, the open area above the sash does increase in area. But this is well above my head so I'm not really worried about it. In between my face and the experimental apparatus is a double glazed window of tempered glass.

If you buy a 120cm wide x 150cm high window with only one sash (120cm wide x 75cm high, a special order) you will have a PVC frame ready to go. Now if you are looking forward to constructing this dimensionally demanding cabinetry, with counter weights, then best wishes.

Lambda-Eyde - 2-8-2010 at 13:21

No, I understand you. It's my formulation in the above post that's too poor, sorry.

With my current design (which is not so easy to see in the drawing) There will be a permanent 10 cm opening at the top, and a 10 cm opening at the bottom when the movable sash is pulled all the way down. Although it doesn't ensure a constant flow it ensures (hopefully) sufficient air intake. When the sash is pulled all the way down the idea is to have full protection (glass) between me and the contents of the fume hood.

Does the benefits of the constant flow design outweigh the added security of an extra piece of glass?

watson.fawkes - 2-8-2010 at 14:59

Quote: Originally posted by Lambda-Eyde

Does the benefits of the constant flow design outweigh the added security of an extra piece of glass?

The missing piece is the way of slowing down the flow when the sash is down. The term of art I've seen used most often is VAV = variable air volume. You can get this with an adjustable speed fan, an inline damper, or an extra, switchable inlet in parallel with the hood.

A wide sweep bend is indeed just a big bend instead of a sharp one. If a sharp bend has a bend radius of 2x the duct radius, a wide sweep will be more like 4x-6x. "Wide sweep" is the term of art in the USA, I'm certain that they're called something else elsewhere (not merely translated).

For more accurate computations of static loss, there are a number of loss calculators online than showed up with a Google search for "duct loss". Before trying to use one, make a schematic of your system, annotated with dimensions.

The static loss from changing duct sizes depends on the geometry. A butt joint with no transition incurs a fair amount of loss (primarily from turbulence). Taper transitions have far less loss. Again, the cost of fittings is a trade-off with the size of your fan.

Magpie - 2-8-2010 at 16:25

I think you do understand "constant flow" design.

My typical "sash down" working height on the lower opening is ~22cm. This allows me to work with my gloved hands while still providing full face and upper body protection by the sash.

So I think you are going to be good as long as your face velocity is appropriate (~ 0.3m/s) at about 22cm of lower opening height.

Lambda-Eyde - 2-8-2010 at 17:42

Watson: Thanks for the tip, I found a calculator and I've played with it quite a bit now. Quite some depressing results, though: depending on the variables I get anything from 0,9" to 8".

Seems like five meters of 4" ducting is out of the question - and I absolutely have to find a fan curve.

peach - 2-8-2010 at 20:30

Quote: Originally posted by watson.fawkes

You can get this with an adjustable speed fan, an inline damper, or an extra, switchable inlet in parallel with the hood.

I was going to say this as well, control the flow rate from the other end to make the sash open area more flexible.

I'm not sure, but I don't think a light dimmer will be too happy attached to a fan, due to light bulbs being resistive elements and the motor an inductive / capacitive load.

[Edited on 3-8-2010 by peach]

cnidocyte - 22-8-2010 at 08:15

The cheapest sparkless fans I can find have a capacity of about 200cubic metres/hour (120 cubic feet per minute) )which isn't too bad but not the best. Would putting 2 of these side by side double that capacity? If so would it be best to space between apart or install them right beside each other?

Magpie - 22-8-2010 at 08:42

I can't speak from experience about two fans in parallel, but I have read that it can produce an oscillatory effect, ie, a push-pull oscillation. This is the result of the two fans not being in perfect balance with respect to each other and the resistance they "see." To mitigate this I would place them in as nearly a symmetrical position as possible. Perhaps others know more about this.

peach - 22-8-2010 at 09:05

This was a big deal in WW2 for the multiprop bombers. If the engines weren't in sync, they'd produce a pulsing noise like two strings on an instrument nearly in tune with each other; which us brits could actually hear from miles across the channel using spiffing big concrete 'ears' with a guy sat in the middle reading the paper, having a cup of tea.

It's also how a pulse jet works, resonant oscillation.

If they're both the same make of fan, I doubt it's going to be much of an issue. One will likely carry slightly more load than the other, but not a lot else.

I also doubt your fan needs to be truly sparkless in the first place. A centrifugal is already pretty good in that the motor is separate from the airflow, unlike a lot of axials.

Get that scrubber on thar though! Right against the hood.

I'll be posting some photos in the 'tour my lab' thread demonstrating what things like hydrogen chloride gas do to 'stainless'. It's pretty, but not necessarily what you want to happen, and it happens overnight.

Edit: If you check out the wiki article on ground glass, you can have a sneak preview of the effects and you'll see marmalade has made another internet appearance, along with some clips that have come into contact with trace quantities of hydrogen chloride.

Scroll to keck clips

[Edited on 23-8-2010 by peach]

cnidocyte - 22-8-2010 at 12:34

Bilge blowers can be bought for around $25 and since they're designed for extracting petrol fumes, they are completely sparkless. They have decent capacity too. The 3 inch fans have a capacity of around 200m^3/h but I saw a site selling 4 inchers with a capacity of 350m^3/h. Not bad at all for $35. Bilge blowers are inline fans, centrifugial fans would be better for placing on the roof of a hood but in my case, its far more practical to mount the fan on one of the walls of the hood.

Formply for bench and/or fume hood?

Gearhead_Shem_Tov - 28-8-2010 at 18:12

I'm looking at getting a sheet of formply (a.k.a. hard face) plywood to build my lab bench & fume hood (and maybe a chemical storage cabinet).

Formply is used for making concrete forms and is exterior-grade plywood with a phenolic coating on the outer hardwood plies. I reckon since phenolic has pretty good chemical resistance properties that it should work well, at least for a bench top. The phenolic layer is quite thin, less than half a millimetre, so I would probably put ceramic tiles down inside the fume hood to take the brunt of any spillage.

I can pick up a brand new 1200 x 2400 x 17 sheet locally for $64AU or a surplus "second" sheet for about $45AU.

Has anyone tried this stuff? It's quite a bit more expensive than cement board, but heaps stronger.

-Bobby

spong - 2-9-2010 at 21:57

I was looking in the tip shop today for an old fridge to use the compressor from and I found this and thought it could be modified a little to make a fumehood, I then realized it was a fridge and has a compressor in it

Does it look like it could be relatively easily modified to turn into a fumehood? I like the fact that it's stainless steel and pretty much airtight (provided I put the doors back on and fix a few broken seals) and has the glass on the front. It's $15 and they don't sell ordinary fridges there so I'll be buying it either way.

Here's the compressor:

cnidocyte - 3-9-2010 at 15:06

^^ My god you got that for $15? There are probably all sorts of alternative uses for that fridge. Whats a tip shop? I can't really say if that would make a good fume hood. I'd try and cut a rectangle out with a glass cutter, then attach a plexiglass flap.

spong - 3-9-2010 at 15:41

Yeah its a shop at the tip (dump) where they collect anything of use and sell it. It's great, I got 2 hotplates for $2 they have some pretty interesting stuff there at times.

cnidocyte - 4-9-2010 at 09:57

I tested my fumehood out today for the first time, I gave it a blast of the fire extinguisher but unfortunately it only extracted about 80% of the dust cloud. Reducing the area of the opening should take care of that though. Smaller opening, greater face velocity. Not gonna have much space to get my arms in there though.

entropy51 - 4-9-2010 at 11:19

A blast from a fire extinguisher is not a very realistic simulation of chemistry, or at least non-runaway chemistry.

Use a few pieces of dry ice in beakers and flasks of water to generate vapor clouds for testing the exhaust. By adding more small pieces of dry ice you can increase the rate of cloud formation and see at what point some of it begins to escape the hood.

peach - 4-9-2010 at 12:30

{edit x 2}By dust, I'm assuming you mean powder

The powder will be too heavy for the fan to pick up in the same way as it will fumes. It's designed to blanket puddles of things on fire (I used one of these to put my brother out when he set his feet on fire and ended up dancing around the garden - one of the funniest things I've seen). Fortunately, he did suffer some long lasting burns, so he's learnt his lesson now.

I'd expect it to work quite a bit better with something closer to a fume.

An even simpler suggestion, set fire to something. Petrol / oils / liquid lighter fuels / xylene / toluene (both gloss paint thinners) / hexanes will produce a cloud of visible smoke / soot, light solvents like ethanol, methanol, acetone, acetate etc won't. An acetylene / MAPP torch with the oxygen turned off will, a propane / butane / NG torch won't.

The hardware / plumbing stores nearby will likely sell smoke bomb pellets / matches for testing flues. You'll get lots of thick, pretty smoke and they smell nice too. Practical joke stores may sell them cheaper.

Although my 'Mr Shiterlot Sugar' didn't do a lot to it's unknowing target. Looks like I'll have to upgrade to genuine pharmaceutical capacity for a good yield.

{edit}Hopefully you still have some fire extinguisher left if you're going with the on fire route. Things that produce plumes of black smoke generally.... dislike? water.

[Edited on 4-9-2010 by peach]

Magpie - 4-9-2010 at 15:37

Open a bottle of conc HCl, or better yet conc ammonium hydroxide, in your hood. If you don't smell anything while standing in front of your hood it would seem it's doing an adequate job.

cnidocyte - 9-9-2010 at 07:38

I tested out my hood with a smoke bomb twice, the first time it worked well but the 2nd time the smoke bomb was near the opening and at least half of the smoke came out. I increase the face velocity somehow. I still haven't sealed up all the holes and cracks, that will definitely increase it a bit.

peach - 9-9-2010 at 08:19

Have you got some baffling in there?

The baffles, and which ones you open / close, are important in controlling where all the air is sucking from and going to. It could be that the stream is just bypassing the smoke, and that it's actually fine, just not flowing where you want it.

{People ramble on about the technicalities of fume control all the time, and lots of people have their own opinions or ways of doing things. But a universal constant is that the thing producing fumes needs to be about 6" or so AWAY from the opening. It really wants to be towards the back, near the baffles. If your smoke bomb was near the opening, that may be why. You're also supposed to stand back from the opening, as your body will create dead airspace in front of you. I work with corrosive, blistering gases quite frequently, I still don't understand the urge to stand directly in front of the hood, why you'd need to or why you'd even need to be tweaking the sash all the time. If you need to constantly play with the gear, you're doing something wrong. Shut it over, bugger off for a cup of tea. As per the solvent still rooms in universities. The still rooms on curly arrow's page, at Cambridge in their chemistry department, actually have "CLOSE THE SASH!" sticky taped to them}

[Edited on 9-9-2010 by peach]

cnidocyte - 9-9-2010 at 10:25

Quote:

Quote: Originally posted by peach

Have you got some baffling in there?

The baffles, and which ones you open / close, are important in controlling where all the air is sucking from and going to. It could be that the stream is just bypassing the smoke, and that it's actually fine, just not flowing where you want it.

I don't actually know what baffles are yet. I've read a few definitions but I really need a picture to see what they are. If I put the smoke bomb at the back of the hood, the fan will extract all of the smoke.

Also there is not just 1 passageway for air to flow in this lab, as you can see here

the shelf space underneath the hood is open to the outside so thats an alternative route for air flow. I can easily seal that up so that the only input route is the door.

metalresearcher - 9-9-2010 at 11:47

I recently moved to a new home in which I dedicated one room as my silversmithing room and lab including a fumehood.

More pictures:

http://www.metallab.net/fumehood2.php

fumehood-finished.jpg - 39kB

[Edited on 2010-9-9 by metalresearcher]

peach - 9-9-2010 at 11:53

The baffle is simply a sheet of wood, metal, plastic, whatever you prefer, at the back of the cupboard. It covers the intake to the fan. Imagine just walling off the fan intake area. Then there's a few horizontal slits in it from the top to the bottom.

There's usually one right up at the top, then one about where a beaker or flask would be if it was sat on a plate, then one right at the bottom.

The idea is that they;

a.) Stop the air for scooting round and through the cupboard without sweeping the fumes up with them, but forcing the fan to suck a kind of virtual wall of air towards the back of the cupboard

b.) Some gases are lighter than air, some are heavier, sometimes there's a beaker spewing them off. The baffles mean the person doing the coughing can open the top one, or the bottom one, or whatever combination they want to suck the fumes away where they're pooling up. It's just like a hose on a vacuum cleaner really, or one of those fume things on a flexible light stand that electronics guys put over their boards as they do the soldering. To put the sucking where it needs sucking. The heat of a roasting hotplate can sometimes carry heavier than air gases up.

It doesn't need to be complicated, and experimenting will work as well or better than spending weeks trying to do it on paper (too many variables).

Again, some people differ on how they do it;

The big slits at the back are to create a wall moving away from the front, the fan is sucking from behind there.

Another method using sheets

They're doing a lot of chatting about the topic, here <-------

[Edited on 9-9-2010 by peach]

cnidocyte - 11-9-2010 at 11:09

Nice one peach. That explains it. Shit if I'd known about this I wouldn't have put my fan right in the center of the depth of the hood. Ah well I can always move it.

peach - 11-9-2010 at 11:13

No need matey, just make the top angled baffle reach further forward so it covers the intake.

Further back would be little better, but that means sawing more holes and patching the originals.

spong - 16-4-2011 at 22:39

I finally got started on my fumehood today, I'm using a dust extractor fan and the shop fridge I posted upthread. I still have to make the sash and baffles but even with nothing on the front it works great for sucking smoke out, even smoke from KNO3/sugar didn't make it outside the hood.
The hood:

The blower:

There are still some holes I have to seal on the blower, I burned a bunch of toluene in the hood with the fan running so the soot would collect around the holes, this is much easier than putting something smelly in the hood and trying to smell for the holes.
Soot around hole:

GreenD - 17-4-2011 at 10:50

If anyone lives in the upper midwest of the states I know a place where you can buy a professional lab fume hood for <500$

Fans

Studentsmi - 4-6-2011 at 02:26

I know some people are having trouble locating fans with the external motors, maybe this will help.

http://www.axair-fans.co.uk/products/centrifugal-fans/plasti...

Rgds

digitalemu - 7-6-2011 at 09:43

If you are looking for something compact, a furnace inducer blower could be used. Most fit within 12"x12" amount of space.

Thor - 13-6-2011 at 07:02

My first post, so I decided to share some pictures of my recently completed fume hood.

The construction consists of an outer shell of wood, and an inner shell of PVC. The PVC was chosen mainly because I had a lot left over from a previous project. It is reasonably fire proof, and according to a compatibility table, is corrosion proof to nearly everything except certain solvents (mainly esters). The base has been tiled, to make more durable to spills.

The baffle system is also made from PVC sheet, the design copied from Magpie's informative pictures. I also copied his front sash, by using a commercial double glazed sash window. The hood has an interior space of roughly 1m wide by 1m high and a depth of approx 0.7m.

The fan is unfortunately an in-line centrifugal model (squirrel cage fans don't seem to have the same availability in Europe), capable of moving 600m3 of air per hour. With careful absorption of nasty gases, I expect it to withstand at least for a while. A small fluorescent tube gives interior lighting from a glass panel bonded to the roof.

With the exception of the fan and the window (which was got at a discount price), the whole hood has been constructed from recycled material, so did not cost too much to build, however makes it far from perfect.

Magpie - 13-6-2011 at 09:50

Very nice, Thor. I was curious about your face velocity, so assuming a window height of 0.5m I calculated a face velocity of 1.09 ft/s. This, I feel, is quite adequate (I think mine is 1 ft/s).

Just out of curiosity what is the ID of your ducting, and where did you place the outlet of your duct from the building?

Also, if your fan motor is directly exposed to duct flow I would be very wary of handling flammable solvents. Ordinarily it would probably be safe due to the high dilution with air, but if you spilled a 100mL of ether I wouldn't want to be around to see what happens!

Thor - 13-6-2011 at 10:34

Thank you Magpie! And that sound's about right for the face velocity, I did the calculation very quickly after I sourced the window unit. Building round about the window limited the design somewhat, but the price of the unit was too good to pass by. My allotted lab space in the garage is very small, so I make do.

The ID of the exhaust tubing is 150mm, I had a choice of this or a 200mm outlet on the fan, however I wasn't comfortable knocking a bigger hole through the wall. The tube exits on the outside wall, the layout of the land outside means its quite high up, and i'm fortunate to be quite far away from the neighbours. I did consider directing the exhaust straight up through the ceiling, but it would have been rather obvious looking and a lot more work getting the roof sealed again.

A quick inspection of the fan, showed it to be a magnetic type induction motor. It seemed reasonably sealed from the airflow path. With that type of motor, there should be no sparking, unless its excessively worn. I am however aware of the risk though, and will need to be very careful. Getting a squirrel cage fan seems to be next to impossible here, It would have more than doubled the cost of the project. For the moment, I will be conducting quite simple experiments, as its a totally different ball game experimenting at home, compared to the labs at university.

SecretSquirrel - 17-6-2011 at 01:57

Outstanding work, Thor! May I ask what king of locking mechanism you used on the door to keep it open/prevent it from falling freely?

Thor - 17-6-2011 at 04:49

Secret Squirrel: Thank you! The window is a commercially produced double glazed sash unit. Like one you would buy for your house. The mechanism is a counterbalance system, and is fully integrated into the window frame. The window sits at whatever height you set it at. One could build such a sash, but it would increase the complexity of the build quite a bit.

[Edited on 17-6-2011 by Thor]

Chordate - 24-9-2011 at 01:12

Dredging up this here old thread, cause I had an idear and wanted to knock it off some of you more hvac minded individuals..

My current workspace has a blower rated for 6000 cfm on the top of it blowing directly into the room. I recently tried running power to it and discovered it works quite well. Well enough to slam doors just by plugging the thing in.

Its not corrosion resistant, and it's inline, but because it is such a burly blower I was thinking I might just seal the place up, run a duct straight out the wall from the back of the fume cupboard, and install a vent with a baffle above the door to control overall flow to the building. Basically just using the fume hood as a window and keeping the place under positive pressure.

I think my biggest challenge is actually going to be making the duct small enough to provide enough back pressure such that my face volume won't be counterproductive. That and baffling. I'm having some trouble figuring out the best way to calculate this. My fist "duct" is basically directly from the blower into an 8000 cubic foot room, my second would be the opening of the hood, and my third the outlet to outside. How do I calculate the necessary amount of back pressure on the outlet to ensure I don't knock over any glassware with this beast?

Any input/resources?

DJF90 - 24-9-2011 at 04:18

I'd suggest replacing any glazing with polycarbonate or perspex sheet of appropriate thickness.

watson.fawkes - 28-9-2011 at 02:42

Quote: Originally posted by Chordate

I think my biggest challenge is actually going to be making the duct small enough to provide enough back pressure such that my face volume won't be counterproductive. That and baffling. I'm having some trouble figuring out the best way to calculate this. My fist "duct" is basically directly from the blower into an 8000 cubic foot room, my second would be the opening of the hood, and my third the outlet to outside. How do I calculate the necessary amount of back pressure on the outlet to ensure I don't knock over any glassware with this beast?

Trying to calculate this doesn't seem like the short path to success. Rather than calculating the duct resistance to find the right face velocity, just measure it and adjust the back pressure empirically. All you need is an anemometer. There are hand-held units available for less than $50 that should be adequate. You could mount the anemometer permanently into the enclosure to ensure that your operating parameters don't change.

I should mention that the other way to moderate the face velocity is to create an alternate path for air flow. Opening a door will do this (one of the reasons to continuously monitor the velocity), but so will making another exhaust duct with a damper. Opening this damper will lower the face velocity, just as opening the damper on the outlet of the hood will.

Neil - 29-9-2011 at 07:03

Throwing this out there;

If you use a lot of organics; do not use polycarbonate. It will crystallize and shatter with time and exposure.

Ranger blower fan

Steve_hi - 29-9-2011 at 16:03

I'm in the process of building a fume hood on a tight budget "cheap" I was wondering if I could use this blower fan I took out of my 89 ranger the squirrel cage is about 3 x 6 inch
I was hoping it would be strong enough because I like the idea of being able to have variable speed so when i dont need a lot of suction I wont be blowing out all the heat of the basement in the winter. and if the power should go out it will still be able to run off the battery which I intend to have powering it as well as a DC transformer

[img]C:\Users\Steve\Pictures\2011-09-29\2.jpg[/img]

[Edited on 30-9-2011 by Steve_hi]

overload - 29-9-2011 at 19:40

Quote: Originally posted by Steve_hi

I'm in the process of building a fume hood on a tight budget "cheap" I was wondering if I could use this blower fan I took out of my 98 ranger the squirrel cage is about 3 x 6 inch
I was hoping it would be strong enough because I like the idea of being able to have variable speed so when i dont need a lot of suction I wont be blowing out all the heat of the basement in the winter. and if the power should go out it will still be able to run off the battery which I intend to have powering it as well as a DC transformer

You should just buy a new sparkless motor that way you will only have to worry about the power going out instead of both the power going out and the motor going out. You said this motor has been used quite a bit right?

Steve_hi - 30-9-2011 at 01:21

Actually I didnt say but considering it is a 89 and not 98 as I originally posted and the fact that this is canada and the heater is on 9 months of the year I guess we could say it was used a lot. A sparkless dc motor where could i get such a thing that would fit with this fan. but It is the volume of air I'm wondering about. I can't find any data on the volume that a vehicle fan puts out but I connected it to a battery and it seems quite strong

watson.fawkes - 30-9-2011 at 03:35

Quote: Originally posted by watson.fawkes

Opening this damper will lower the face velocity, just as opening the damper on the outlet of the hood will.

Oh, the typos. This sentence should read as follows, with one important word change:

"Opening this damper will lower the face velocity, just as closing the damper on the outlet of the hood will."

Neil - 30-9-2011 at 04:58

I modded a computer power supply to run tandem engine room exhaust blowers from a local boating store. Each blower is rated to 230CFM and were something like 30$ each - which is significantly cheaper then a bathroom or range hood fan blower with the same CFM. (To get 460 cfm with bathroom fans I was looking at having to spend 300$ or more)

These blowers are explosion proof and can be for only a few more dollars, water proof. I got the idea from the other fume hood thread.

Alternative?

Kiwichemicali - 12-4-2013 at 00:04

What do you think of an extraction arm as an alternative to a fume hood for a hobby chemist?

Kiwi

<img src="http://www.cleanairco.com/public/images/products/extractionarms/alsident/026%20100%20CR.jpg" width="300" />

[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: reduced image size(s)]

[Edited on 7/12/13 by bfesser]

CaptainOfSmug - 12-4-2013 at 09:37

I think that would work just fine. I use something similar except I have my fan connected to ducting with a carbon scrubber attached. I like it more than a fume hood in some respects because I can simply move the duct attached to some rails on the ceiling over where I'm currently experimenting.

hyfalcon - 12-7-2013 at 10:51

Just picked up 3 of these PSC blowers. I pad less than $100.00 shipped on an offer. First piece of the puzzle for a fume hood.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=26122...

[Edited on 12-7-2013 by hyfalcon]

PeeWee2000 - 12-7-2013 at 12:51

Heres my craigslist found 15$ 3/4 HP furnace blower mounted in the window next to my lab table. I just screwed it to the window and sealed i up with plastic sheeting and duct tape

. I cant say its safe for playing around with toxic fumes and such but its proven to be enough to keep explosive vapors (e.g. Diethyl Ether) from building up. Does an excellent job of keeping me cool with all my safety stuff on too!

Building a fume hood

Upsilon - 13-10-2013 at 15:45

As many people before me have probably figured out, it seems rather useless to spend $1000+ on something that wouldn't be very difficult to build yourself. Anyway, I'm trying to build my own fume hood, and I was wondering if anyone had any tips. I am planning on making the main structure out of wood, with aluminum sheeting to line the interior to prevent the whole thing from burning down. Over the aluminum would just be some cheap replaceable plastic sheeting to prevent corrosion of the aluminum. Also, does anyone know of a fairly cheap fan that can move a lot of air? I'm just asking for tips from people who have done this before.

Dariusrussell - 13-10-2013 at 16:35

There are many many many...many many threads on this. Do a search next time.
As for your design, it seems fine, I would suggest you do a spray on enamel or epoxy in lieu of the plastic sheeting. I assume your going to use very thin aluminium, I would suggest backing it with 1/8th in MDF/Plywood/Particleboard so that you can mount things to it.

As for the fan, You want a squirrel cage blower. Its preferable to have one where the motor is on a belt, but at the very least use one with the motol not built into the fan. I also suggest that you spray all parts of the system in an epoxy/enamel spray to prevent corrosion.

http://bit.ly/190UNMo, I'm lazy heres the google search

Gooferking Science - 13-10-2013 at 17:01

I have a four part tutorial on making a fume hood on my youtube channel. The link to my channel is in my signature. The total cost is about $150. I have used the hood many times and it seems to work perfectly.

bfesser - 2-1-2014 at 10:12

Admittedly not suited to all tasks, but I like the simplicity of this design. I think I'll try building one.
<iframe sandbox width="560" height="315" src="//www.youtube-nocookie.com/embed/Enfzy_NyeXs?start=7&end=189" frameborder="0" allowfullscreen></iframe>

[Edited on 2.1.14 by bfesser]

subsecret - 4-1-2014 at 15:49

This is a very interesting fume hood design that I found...It's got a Venturi-type arrangement.
http://www.youtube.com/watch?v=-4oQU-SyYZY

My fume hood (I understand that this is crappy) is a wooden box with a bathroom exhaust fan connected to the top. It exhausts through a good length of 4 inch dryer exhaust hose, which is connected to a board shoved in the window and held via a dryer termination (with flaps). The fan moves about 50CFM (not much at all, I understand), and the face velocity is very low. I plan to connect an inline fan between the end of the dryer hose and the wall termination, creating negative pressure along the entire length of the exhaust system (no chance of fumes escaping). This would work in series with the bathroom exhaust fan, though it may be removed entirely. After testing with ammonium chloride fumes, it's very rewarding to see a thin cloud forming outside the basement window.

I may ask my brother if I can use his massive cage fan for a new design. It's termination is a 6 inch round duct, and it pulls a lot of air. The only problem with it is that the motor is placed inside the fan drum, though it is sealed entirely (I assume that cooling slots were not necessary because of the massive amount of airflow).

nanobot-dnp - 7-1-2014 at 21:46

Dont forget that it's not just all about the amount of air your fan can pull. You also need to bring the same amount of air into the room.

[Edited on 8-1-2014 by nanobot-dnp]

Making My Fume Hood

Jmap science - 25-1-2014 at 07:44

Yesterday I started on my fume hood. I am going to put it on my desk and the duct fan goes from the hood to outside. It is 30" deep, 36" high, and at the top there is a plexiglass face shield.There is a Led light in it and also a plug and gas connections, it has a small shelf in it.

I am going to use it for things like making benzene or diethyl ether to flash powder. do you think there is any other thing I need to add to it?

[Edited on 25-1-2014 by Jmap science]

TheChemiKid - 25-1-2014 at 09:26

Maybe you could add a vacuum connection if you have a pump.

bigmol - 2-3-2014 at 10:10

Like many commercial labs I dont have a fume hood instead the whole lab is treated as a fume hood with a large exhaust fan and crossflow ventillation. The whole lab air change is only a few minutes.
If there was anything to bad I would use a glove box under a slight vacuum

subsecret - 19-12-2014 at 20:27

Sorry to post in such an old thread, but I just got an idea for a cheap, somewhat chemically-inert fume hood fan.

I just bought one of these online: http://www.amazon.com/Diversitech-625-AF6-Round-Duct-Fan/dp/...

To make an externally-driven fan, the motor and blade of the fan would be removed, and the blade would be mounted to a longer steel shaft using epoxy glue. Next, the empty fan housing would be sealed to a metal tee fitting, so that the fan attaches to one opening of the top of the "T." A flat stovepipe cap with a hole in it to accept the extended shaft would be attached directly opposite the fan housing, and the blade with the extended shaft would be passed through the original motor mount and the hole in the cap, so that it protrudes from the outside of the cap. A plastic bearing (possibly with an oil wick) could be made to prevent the shaft from abrading. Next, the motor would be attached to the outside of the cap with pieces of wood, and the shaft would be attached with a piece of tight-fitting PVC tubing or a setscrew connector.

This way, the motor is not exposed to fumes, and most of the system can be under negative pressure to prevent leaks.

Hellafunt - 19-12-2014 at 22:03

since this thread is resurrected from the deep sleep, maybe i could ask a question. ive been working on my fume hood for a few weeks, and its almost finished. im excited. it is made of 1/4" plywood with a frame of wooden slats taken from an old futon. it has a used window in the front, and ive purchased a dayton blower fan for it. im about 75% finished building it, but i still have not decided on lighting.
ive read through what i think is all the fume hood posts on the site, and ive come across very little about lighting the fume hood. ive seen mention of explosion proof lighting, some talk of mounting lights on the outside shining through the sash to the inside, and ive considered using battery operated LEDs. My computer is very old and ive been unable to open a lot of the photos people have posted of their DIY hoods. the imageshack pics are some that i can NOT access. anyway, any brilliant (ha!) ideas?

[Edited on 20-12-2014 by Hellafunt]

subsecret - 19-12-2014 at 22:37

You could simply buy some Chinese LEDs and solder them up in parallel, and put the string inside a clear piece of tubing. It may not be explosion proof, but it's easily replaceable.

Magpie - 20-12-2014 at 12:22

This is what I did for lighting. Ie, two 4 ft, 40w fluorescent lamps mounted on a piece of glass silicone caulked to the hood roof:

hood side view - resized.bmp - 664kB

The lighting is good. See thread "Tour My Lab" for more info.

[Edited on 20-12-2014 by Magpie]

Hellafunt - 20-12-2014 at 14:56

thanks awesomeness, magpie. magpie, your fume hood has been an inspiration for me, however, my fume hood needs to be portable, i need to drag it out when i want to use it. i need to keep it as light as possible, it is already getting pretty heavy. i like the LED idea.

Lambda-Eyde - 30-12-2014 at 01:00

Any thoughts on mounting the fan intake on the bottom of the hood? I've realized that I have no choice but to place the fan under the hood, as the ceiling height in my lab is only 2.1 meters. How would you make proper baffles? Obviously you wouldn't want a spill to end up inside your fan. Something like a double set of baffles (Edit: s/sash/set of baffles/), like below, maybe? How do you prevent standstill near the ceiling (since air moves both in and out near the bottom)? While still making sure that you're sucking dense vapors and gases out, instead of letting them flow out the sash? Splitting the intake into channels that go further up? How does one accomplish this without losing fan pressure which will already be hurt by three 90° bends after the fan?

Code:


│ ││
│ ││
│  │
│ ││
│ │     <--
│ └───────
 |
 V

Also, making space for a 4" duct at the base of the hood means sacrificing a lot of valuable space. Are there any obvious disadvantages to doing a 4" round to, say, 20-30 x 5 cm square transition at the opening?

Quote: Originally posted by Hellafunt

thanks awesomeness, magpie. magpie, your fume hood has been an inspiration for me, however, my fume hood needs to be portable, i need to drag it out when i want to use it. i need to keep it as light as possible, it is already getting pretty heavy. i like the LED idea.

Just buy a complete LED strip instead of bothering with soldering. They can be bought complete with transformers (which you of course want to mount on the outside) for very cheap at DealExtreme, among other places.

[Edited on 30-12-2014 by Lambda-Eyde]

[Edited on 30-12-2014 by Lambda-Eyde]

Magpie - 30-12-2014 at 10:43

Quote: Originally posted by Lambda-Eyde

Any thoughts on mounting the fan intake on the bottom of the hood?

I think it could be done - with proper design.

Quote: Originally posted by Lambda-Eyde

How would you make proper baffles?

Your sketch is on the right track I think. By proper sizing of the baffle openings you can direct flow to give an even sweep over the hood working areas.

Quote: Originally posted by Lambda-Eyde

Obviously you wouldn't want a spill to end up inside your fan.

If you mount the outlet a few inches above the hood floor this would not be a concern.

Quote: Originally posted by Lambda-Eyde

How do you prevent standstill near the ceiling ...?

By having an opening at the top of the back wall through use of a baffle, as you have shown. This opening would be something like 2" x 48", assuming a 48" wide hood.

Quote: Originally posted by Lambda-Eyde

How does one accomplish this without losing fan pressure which will already be hurt by three 90° bends after the fan?

That's going to be the real challenge. You have to have a fan with a characteristic curve (delta P vs flow rate) that will give you adequate flow to provide the hood face velocity of ~1 ft/s.

You are severely hampered right from the start with a small duct size like 4" diameter (A=12.6 in^2). The 25cm x 5cm duct size would be significantly better (20 in^2), even with the square corners.

FYI my duct diameter is 8". This gives 4X the area of a 4" duct.

Quote: Originally posted by Lambda-Eyde

See above comment.

Hellafunt - 7-3-2015 at 20:43

im very excited to report, that after 4-5 months of stopping and starting, working and procrastinating, my fume hood is essentially finished. id like to thank you guys , i gleaned so much info from this forum, i wouldnt have been able to do it otherwise. My friend Dave did the work that required skill.
ill try to get some pictures up. it is a little different than most because it is not a permanent install. I live in a 450 Square foot studio, and im a renter. but it is not a plastic flimsy box made up of tupperware. its made from .25" plywood, it has the corners and edges reinforced with aluminum, and a dayton blower. and a used window in the front. and baffles in the back.
tonight we did a tester. i had a coffee filter that had been used to filter some homemade KClO3. i sprinkled it with sugar, and then broke up some sticky KNO3 and sugar smoke bomb on top. we lit it and the box filled with smoke and i got nervous. but i flipped the switch, and damn, it worked. im excited! tomorrow, i get to make some nitric acid without holding my breath!

[Edited on 8-3-2015 by Hellafunt]

subsecret - 8-3-2015 at 20:20

What about a perforated tabletop with an intake plenum underneath?

Zombie - 8-3-2015 at 20:43

The only issue I see with that is you need to contain spills if equipment fractures or falls over.

I was thinking along the same lines at one point.

It's actually safest to have the air draw everything away from you via a front opening.

My New Fume Hood

Metacelsus - 15-3-2015 at 16:17

I finally finished my fume hood!

The fan and duct supplies I got from a local surplus store (Ax-Man, for anyone in the area) for a remarkably good price. The most expensive part was the acrylic glass, which I hope lasts for a decent amount of time.

Yes, I am using part of a yogurt container as an adapter.

Photo on 3-15-15 at 7.10 PM #2.jpg - 255kB

Photo on 3-15-15 at 7.10 PM #3.jpg - 273kB

Zombie - 15-3-2015 at 16:50

Impressive Cheddite!

What size is that? About 4' x 4'?

I especially like the outside baffle. I had to settle for a spring loaded "flap" type. Like the old school kitchen type. I never thought of a baffle.

radiance88 - 15-3-2015 at 16:53

Wow Cheddite. Looking great there.

Shouldn't the fan be at the end of your exhaust vent though rather than in the beginning? So in the case that somehow your tubing springs a leak, you aren't pushing the fume back into the room. If your fan is at the end, even with a minor leak the bad fumes should still go in the right direction.

Metacelsus - 15-3-2015 at 17:14

Yeah, I thought about putting the fan at the end, but there would have been problems with hooking the ducting up to the fan intake. The ducting goes much more easily on the outlet.

The size is 3 feet high by 4 feet wide by 2 feet deep.

[Edited on 16-3-2015 by Cheddite Cheese]

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