Sciencemadness Discussion Board - DIY - Poor Mans Fume Hood - No Pics. Have it assembled within 1 hour of leaving the store.

DIY - Poor Mans Fume Hood - No Pics. Have it assembled within 1 hour of leaving the store.

FireLion3 - 23-7-2014 at 02:12

A fume hood, and why every amateur chemist should have one:

Anyone doing Organic Chemistry outside of a professional lab setting should have one of these, or something similar. There's no excuse really. If you own your house you don't want to be permanently embedding chemical smells into the foundation, and if you're renting an apartment, then you have no business permanently stinking up the place! Plus, this can save the amateur experimental chemists life if any reaction does something dangerously unexpected. The last thing you want is your house uncontrollably filling with toxic fumes with you frantically debating whether to call the fire department knowing you will have to deal with the police, prove your lab is legitimate, potentially lose valuable reagents as police insist on testing them, and even worse, if renting a place, getting evicted from your residence and possibly charged with some crime about violating some unknown local regulation you knew nothing about.

The Poor mans Fume Hood

This design can pretty much be built from a single trip to the hardware store, maybe under a few hundred bucks if you are lucky - the most expensive part being the fan itself. It is very easy to store, light weight, portable, and can basically sit atop any table. Building your own carbon filter will save you a lot of money to, to which you can find how-tos online.

I do not have any pictures for this yet, but the idea is very simple. This set up would contain no blast-barrier, but you could probably add one if you want. I got this idea when I realized having an air-scrubbed room is only good for keeping the inside air in, but does very little if you yourself do not want to be breathing in the inside air. Having an air scrubbed room is handy when the odors aren't particularily harmful, but you don't want them escaping... it does very little for when your reaction is producing hazardous lachrymator or worse! On that note, this is basically why I came up with this below design. Lachrymator's are no fun to be around, but are some very useful reagents, and with a fume hood, their utilization can actually become a realistic thing.

This concept does not include a activated charcoal filter, but you could build one pretty easily, or buy one. I suggesting building one unless you have a few hundred bucks to toss.

What you need:

1) A Rectangular Box/Storage container that you can cut, of suitable dimensions to where your equipment could fit under it set up. (you will be cutting out the front side). You can pick on up at almost any store for under $10.

1a) A large rectangular cardboard box would also work, but when doing any reactions under this, you would need your fan on always, because moisture, and other reagents, can corrode the box. Not much of a problem since it is very easily replaceable.... but also keep in mind a cardboard box is much more flammable, if god forbid any explosion were to occur.

1b) You may also use two cube shaped cardboard boxes, sides cut, and affixed together, since they are probably more common, but the above concerns about cardboard apply.

2) This is where most of your money goes. A GOOD fan will run you a couple hundred bucks, ducting roughly $10-30. A cheap fan can be had for under $100, but remember, you want as many CFM as you can get within your price range. A trip to your local garbage disposal place or even checking craigslist may yield you one for free. This fan should be capable of having ducting attached to it, somehow. Buy ducting as well. The fan I am using is made of plastic and capable of hitting 400 CFM, I got it from a gardening shop. It's light weight, quiet, and made of polyethylene so it should not react with most things. You can use a stainless steel fan, or even some lower metal, but if you do the latter, you will need to be sure your fan is pulling through your activated charcoal first, so as to avoid corrosion of the fan.

3) A Box Cutter or other sharp blade.

Putting it together

If you have all this stuff, it's pretty straight forward from here. Cut one of the long sides off the box. This will basically be what you work through. Flip the box around and cut a circular hole in the back, measured to fit your ducting somewhat snugly. If you cut the hole too big, you could probably affix the ducting with ductape, as long as there are no huge gaps and it stays in place. The hole does NOT have to be 100% air tight, and I will explain why.

How and why it is effective for containing most odors

This design does not have any blast glass or anything like that. With a okay fan turned on, pulling air from the back, air will always be entering in through the front. Any slight gaps near where the ducting is attached to the box won't matter, but if you seal them, air suction through the front will slightly increase, relative to the size of the hole you covered. Any fumes that arise from your reaction vessel will be pushed by the air entering in through the front and exit out through the back of the ducting. The only way fumes from your reaction will escape through the front is if your flask explodes, or if some other directional air current enters into the front from outside and is strong enough to mess with the pull of the fan.

arkoma - 23-7-2014 at 06:54

This google search turned up some seemingly good prices on ducted fans and carbon canisters.

IrC - 23-7-2014 at 11:12

From 27 to 200 bucks fans can be obtained which are very good for this purpose. Keep in mind the lower cost models are usually very loud and annoying. Redo wiring (as on fans with short cords/plugs) so switch is outside of area where any vapors either flammable or explosive will be for obvious reasons. I show Amazon links as most can buy from them virtually everywhere. I show 8" versions since this really is the best choice. 6" may work for you but far lower performance even if it is easier to construct and mount a dryer vent hood on the outside of your building (good idea for many reasons such as outside appearance, flapper valve to reduce chance windy days will fill your room with fumes when fan off, and so on). Do not even bother with anything smaller such as 4".

http://www.amazon.com/Inch-High-Velocity-Metal-Inline/dp/B00...

http://www.amazon.com/VenTech-DF8-Duct-Fan-400/dp/B005KMUHWY...

While cheap this VenTech is damned annoying, I say this from actual experience. However it will easily interface with ducting both rigid and flexible, and sucks a box of fumes very well.

http://www.amazon.com/VenTech-Inline-Exhaust-Blower-Centrifu...

More expensive but much more quiet and nearly double the 400 CFM of cheaper/louder models.

http://www.amazon.com/Hydrofarm-ACFB8-8-Inch-Line-Booster/dp...

Decent choice.

http://www.amazon.com/VenTech-Inline-Exhaust-blower-Scrubber...

With Carbon scrubber but build your installation so that cleaning-replacing filter easy and quick. Not a good idea to have a buildup of some chemical dangerous on it's own like peroxides, or in combination with whatever your next experiments will be. As always redo wiring so you have a switch mounted in safe area.

http://www.amazon.com/Metal-Wall-Damper-Screen-SDWVA/dp/B00B...

8" outside vent.

Typical 8" fan, loud as hell. Vent hood for outside decent and easily painted to match building. Yet another advantage is nosy neighbors may not think much about your setup with a vent hood like this. Assuming no jets of dense choking smoke is coming out of course.

Edit to add:

No doubt if you search you can find these things in plastic or mostly plastic if fumes reacting with metals is a concern.

[Edited on 7-23-2014 by IrC]

bob800 - 23-7-2014 at 11:27

It might work to a degree but you have not addressed any of the real issues in fume hood design... No baffling to direct airflow, no sash positioning scheme, no chemical resistance (plastic fan does not mean the motor is plastic*), or even face velocity calculations. I don't mean to be so negative but there are literally dozens of threads on here already that address these issues. You might find that with your activated charcoal filter, garden fan (CFM usually drops off with even slight air resistance for these), you are going to have a very slow face velocity, giving the fumes in the hood plenty of time to react with the non-ideal materials used.

*I see that you are hoping the activated charcoal will absorb all the fumes that pass through it. In reality corrosive acid fumes and the like are not going to be appreciably absorbed.

Here is an example of a good blower ($100 surplus) with a decent CFM/resistance curve. Note that the motor internals are separated from the airflow path.

[Edited on 23-7-2014 by bob800]

FireLion3 - 23-7-2014 at 13:28

Quote: Originally posted by bob800

It might work to a degree but you have not addressed any of the real issues in fume hood design... No baffling to direct airflow, no sash positioning scheme, no chemical resistance (plastic fan does not mean the motor is plastic*), or even face velocity calculations. I don't mean to be so negative but there are literally dozens of threads on here already that address these issues. You might find that with your activated charcoal filter, garden fan (CFM usually drops off with even slight air resistance for these), you are going to have a very slow face velocity, giving the fumes in the hood plenty of time to react with the non-ideal materials used.

*I see that you are hoping the activated charcoal will absorb all the fumes that pass through it. In reality corrosive acid fumes and the like are not going to be appreciably absorbed.

Here is an example of a good blower ($100 surplus) with a decent CFM/resistance curve. Note that the motor internals are separated from the airflow path.

[Edited on 23-7-2014 by bob800]

Yes but please keep in mind this is not a perfect complete idea. A partially functional fume hood is better than no fume hood at all. If a person is able to handle chemical reactions then they should be able to improve on their fume hood at they go along.

These are all issues worth considering. If you read the post you would see I suggested using a carbon filter before the fan, so that corrosive fumes do not get pulled through the fan first. When you are working on a limited budget here, you would hope that you can construct a perfect design, but with limited budget's things will be far from perfect. Parts may need to be monitored and replaced periodically, but having fumes absorbed the majority of the time is better than laying on the floor coughing up blood and unable to reach the phone to call for help. Having a fume hood, especially one like this, really gives no reason for a person to do a reaction on a large scale that they have not done on a small scale before. They should be at least relatively aware of what is going on in the reaction they are doing. If they're doing something involving acid fumes.

Excessive CFM's actually don't matter as much you would might think as long as the physical design is proper. Even the slightest bit of air flow from a fan pulling air out will be enough to stop the majority of odors and fumes evolving from the reaction from escaping through the front, assuming you have nothing blowing air out inside the box.

Even if your box is around 12-20 cubic feet, even the weakest inline fan rated for 50 cfm will do the task of keeping a lot of fumes from escaping. More CFM Is clearly ideal, but being realistic here, a cheap fume hood is better than no fume hood. I had a 400 CFM fan set up to a 800+ cubic feet room, and having it on high was enough to keep a constant air flow coming in through the door to prevent any odors from escaping the room, and the fan was not even positioned at the back. The result of this was that the room had a negative pressure, even standing near the door opening you could feel constant air coming in. Worth mentioning that having a fan on inside the room can blow air out through the door, as I experienced! Though when you get down to brass tax, you would be surprised how even the slightest bit of negative pressure in an enclosure can keep a lot of gases from escaping.

Activated Charcoal can absorb corrosive acid fumes and a lot of other chemicals that it does not directly react with, but this absorption method is more about having enough charcoal in the way. When I was selecting my filter set up, I called 3 different air filter manufacturering companies whom all suggested that for acid fumes, specifically Hydrohalide acid fumes, a activated charcoal was most suggest, and/or an additional hepa filter on top of that.

This design can be no doubt improved upon. I strongly advice a person work on attaching some sort of sash that hangs over the front and leaves air opening at the bottom. Painters plastic can be purchased at any hardware store, and easily cut to side. You cut this to size and attach it to your box, and you can pretty effortlessly lift it up and put it atop the box when you need to work, and then bring it back down when you really need to ensure fumes are kept in. Though, this of course will provide minimal protection from a flask explosion - for that you would need something sturdier than painters plastic.

bob800 - 23-7-2014 at 16:30

FireLion3,

You have obviously done a lot of research on this that was not apparent to me initially. I am just concerned because you mention the use of acid fumes, lachrymators, etc in the hood. In this case I would strongly suggest doing some calculations to ensure that you're moving enough air through the system.

You may not need much ducting, and thus not experience much friction in your system, but others who read this thread may. I would be concerned in their case if they thought any garden-variety blower would be suitable (haha pun not intended). Remember that the CFM rating of a blower is stated at 0" of friction in the system. That is NEVER going to be the case in the real world.

I would recommend doing a search for fume hood design, or at least view this thread https://www.sciencemadness.org/whisper/viewthread.php?tid=14.... The calculations are laid out here. IIRC a face velocity of 1 foot/second is generally the standard value, where V= cfm of fan / ( 60 * area of opening in square feet).

If you use 400CFM in the equation you will probably get a very fast face velocity with plenty of flow like you said. However, even if you don't use much ducting, the charcoal filter is going to have an IMMENSE impact on the actual CFM. You can see the drop-off on the blower link I listed... that is a good blower with a good CFM/friction curve, much better than any garden fan.

I use that blower in my hood (2.5' square) with no ducting, and I initially placed a thin kitchen-exhaust type filter onto the blower hole. The face velocity immediately dropped to a level where significant amounts of fumes escaped. Even with the baffling I recently installed I doubt it would work.

"Excessive CFM's actually don't matter as much you would might think as long as the physical design is proper."

Without baffling or any airflow resistance calculations, and using a blower which (I assume) places the motor in the air-stream, I would not say the "physical design is proper".

You know more about activated charcoal filters than I do... but I would be surprised if you could find one that can both absorb many mL's of acid and yet maintain airflow with your fan (the 400CFM is irrelevant without specifying friction).

FireLion3 - 23-7-2014 at 17:11

Currently for my main tent I am using about 8 feet of ducting for a 400 CFM fan. For most rooms it is generally recommended that the fan be able to scrub the room once every 3 minutes, but this, in my opinion, is too slow for a fume hood. A 3 foot wide hood, 2 feet deep, and 2 feet tall, is only 12 cubic feet. Some of the smallest fans you find at the hardware store, for example a 4 inch inline booster, may start at 50 CFM. This could be "adequate" for a hood, but as always, more is better.

You are correct, there is not a huge need for large quantities of ducting. Like you said, more ducting = more friction, and the carbon filter itself also adds friction, though, if you are pulling through a suitable filter, a good amount of the fumes will be absorbed and you can blow this wherever you please. If possible it would be ideal to blow it outside but I do not suggest this if you live around other houses even if you are confident about the carbons ability.

Though, it is surprising how effective a ton of activated charcoal can be. Prior, I was using a store-bought carbon filter, and it weighed nearly 30lbs. When I attached my fan to it, and stood at the other end of the ducting where the filtered air was being blown out, the intensity of the air was comparable to one of those electric-air hand dryers you see in public restrooms.

Luckily actived carbon is cheap, you can get bags of granulated charcoal capable of absorbing thousands of cubic feet, for nearly $100 for a 55 lb bag. Cheaper smaller quantities can be gotten at pet stores. A homeade filter might only require a few pounds of carbon, but the more, the better. A home chemist would, like anything involving chemistry, have to experiment with the amount of carbon they can use without slowing down their fan too much.

Quote:

Without baffling or any airflow resistance calculations, and using a blower which (I assume) places the motor in the air-stream, I would not say the "physical design is proper".

You know more about activated charcoal filters than I do... but I would be surprised if you could find one that can both absorb many mL's of acid and yet maintain airflow with your fan (the 400CFM is irrelevant without specifying friction).

The great thing about activated carbon is that it is ridiculously cheap at $100 for a 55 lb bag, replacing it isn't a problem. Unless you're running an industrial size lab generating excessive fumes, most chemists should not have an issue with how often they need to replace it. A very good and cheap carbon filter can be built from PVC piping, that can allow for easy carbon swapping and easy attaching to the ducting.

And to state the obvious:

Any DIY-experimental chemist would obviously need to experiment on a safe level first before doing anything serious. For example, I didn't do ANYTHING in my tent or my hood until I tried safe things inside them that generated odors.

I let cigerettes burn in my tent/hood, scented candles, stink bombs, smoke bombs. Lighting a smoke bomb in your hood as a test can allow you to get a very good idea on just how capable your fan is at capturing fumes. Dry ice + water as well. Most organic reactions aren't going to generate profuse smoke like that unless something goes seriously wrong. The advantage of testing with safe items like these is it can enable you to fix any problems before they are seriously needing attention.

Pre-Testing is essential before using it for anything serious, but this goes for anything.

Magpie - 24-7-2014 at 07:25

Quote: Originally posted by FireLion3

For most rooms it is generally recommended that the fan be able to scrub the room once every 3 minutes.

This may be appropriate for a grow room but how is it relevant to a lab? Your goal should be to keep the vapors from ever escaping into the lab. You do this with adequate hood face velocity.

FireLion3 - 24-7-2014 at 19:41

Quote: Originally posted by Magpie

Quote: Originally posted by FireLion3

For most rooms it is generally recommended that the fan be able to scrub the room once every 3 minutes.

This may be appropriate for a grow room but how is it relevant to a lab? Your goal should be to keep the vapors from ever escaping into the lab. You do this with adequate hood face velocity.

Did you notice you snipped off the last part of my sentence and added your own period? Here is the full sentence:

Quote:

For most rooms it is generally recommended that the fan be able to scrub the room once every 3 minutes, but this, in my opinion, is too slow for a fume hood.

You are absolutely correct though, and I would strive for much faster than once per 3 minutes for any fume hood. Though it is important to keep in mind that when dealing with any gasses, even the slightest movement of air can effect them. If a amateur chemist is constructing a fume hood on a very limited budget, a low-quality fan that will prevent all fumes from escaping, but at a slow rate, is better than having no fume hood at all. Even the slightest negative pressure in an enclose can be successful in stopping 100% of the fumes that evolve from a flask, as long as those fumes are not moving magically outwards with their own force, and as long as the flask has not exploded outwards.

It goes without saying that if a chemist is working with a reaction that evolves a lot of vapors and they must be intimately having their hands near it at all times, then they should aim for the best fan they can afford. I would get the best fan one can afford even if they didn't have this exact scenario.

It is better to be safe than sorry, but I think it is important to keep in mind that a lot of people who come on this forum do not work in professionally equipped labs and are on very limited budgets. A partially effective fume hood is 100% more effective than a non-existent fume hood.

ave369 - 27-9-2015 at 11:38

I have a Russian brick stove. It already has a built-in (unfanned) fume hood for removing smoke from the combustion chamber (it works on firewood and produces a lot of smoke). It has a lid-shaped valve for opening and closing the smoke passage. So my idea is putting a fan where the lid should be, and the Russian stove will work as a fume hood!

aga - 27-9-2015 at 15:42

Surely the Perfect Poor Man's Fume Cupboard is simply being Upwind and Outside on a moderately windy day ?

[Edited on 28-9-2015 by aga]

ave369 - 27-9-2015 at 23:34

Quote: Originally posted by aga

Surely the Perfect Poor Man's Fume Cupboard is simply being Upwing and Outside on a moderately windy day ?

It's only perfect when the temperature outside is above zero.

MrHomeScientist - 28-9-2015 at 12:04

The one issue these threads never address is Where The Fumes Go. I'm perfectly capable of building a box with a sash, fan, and ducts, but where does the ducting lead? I'm not really prepared to punch a hole in my roof, and going out a window seems like an invitation for fumes to waft back in if the seal isn't perfect. If you have a DIY hood, where does your ducting lead?

196 - 28-9-2015 at 19:55

I have my ducting leading to a piece of plywood that I cut to the size of my window, so I just put it in the frame when running the hood and it seams reasonably sealed. Along with the continuous blowing of the fan out the end of the duct, nothing really seems to try to get back in.

Magpie - 29-9-2015 at 08:41

Quote: Originally posted by MrHomeScientist

The one issue these threads never address is Where The Fumes Go. I'm perfectly capable of building a box with a sash, fan, and ducts, but where does the ducting lead? I'm not really prepared to punch a hole in my roof, and going out a window seems like an invitation for fumes to waft back in if the seal isn't perfect. If you have a DIY hood, where does your ducting lead?

Clearly the effluent from your hood needs to be vented to the outside atmosphere as high up as practical. How one does this varies with the case at hand.

In my case I vented it through the existing louvered grill in my garage attic peak. This puts it about 12 feet above ground level. I explained this in my description of my hood construction. I also advised Jor about this. He punched a hole in his tile roof.

I punched a hole in my plywood/asphalt shingle roof to provide a vent for my gas hot water heater. It's really not a big deal and could easily be reversed if I change plans later.

aga - 29-9-2015 at 13:01

Fume disposal depends on the Fumes you're producing.

If it's Seriously Lethal gas then extreme measures are warranted.

Personally my fume hood simply throws any gasses outside of my shed.

The Wind Direction is rather important as the shed is very small, although it is literally in the middle of nowhere (i.e. unpopulated).

For things like NO i have a gas mask out and ready in the case the wind changes.

Clearly this is inadequate for routine handling of seriously toxic gasses, but then again, i'm just an amateur and not in the habit of making those daily.

One advantage is that i built it, know what went in there, and have at least a clue what is in there as a residue, and am in control of when the fan gets changed etc.

If you need to use an Alien fume cupboard (non-Lizard) always ask about how it works, what it has handled before, as any residues may react catastrophically with whatever exotic gasses you are keen to produce : explosions in the ducting have already happened to people.

Whatever the construction of the fume cupboard, always remember it's limitations, and have a backup plan.

Magpie - 29-9-2015 at 13:26

Quote: Originally posted by aga

Whatever the construction of the fume cupboard, always remember it's limitations, and have a backup plan.

Turn and run away!

https://www.youtube.com/watch?v=QM9Bynjh2Lk

NedsHead - 4-10-2015 at 05:05

I acquired this extraction fan today, the fume cupboard it was attached to was really too small to be of any practical use so I did a deal and bought the top section, now I just need to build a box to put under it