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Sciencemadness Discussion Board » Engineering and Equipment » Reagents and Apparatus Acquisition » DIY Fume hood

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Cognition

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posted on 23-11-2015 at 05:45

DIY Fume hood

Hi, I'm taking my first steps in hobby chemistry; although I've worked professionally (sometimes unprofessionally) in a lab for many years.

A likely area of interest will be polyurethanes which will mean handling isocyanates so I will need to construct a fume hood on a limited budget. I'm thinking of buying a cheap second-hand kitchen cupboard (or similar), replacing the doors with a transparent polycarbonate sash and fitting a small shower extractor fan (see pic).

The construction is unlikely to be wholly air-tight. Does anybody know if a small shower extractor fan is likely to do the job in this arrangement?

I intend to wear an isocyanate monitoring badge so I should be aware of any leaks once I start working but I'd like to have some idea of success before I spend the time and effort.

I'm guessing some of you have built fume hoods in the past so any advice is appreciated (e.g. fire extinguisher and other requirements).

ae235.jpg - 7kB

aga

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posted on 23-11-2015 at 08:09

Cognition

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posted on 23-11-2015 at 14:19

Thanks for the links aga. I did a search for 'fume hood' before posting but found so many irrelevant results.

I like your construction and it's similar to what I was thinking for myself. I think I will use something more powerful than a pc fan however as I'll be working with isocyanates so I need to be extra careful.

The LED lighting is worth considering at a little extra cost. Did you use glass panel for the sash? I think I will use a polycarbonate greenhouse panel - shatter proof and much lighter.

aga

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posted on 23-11-2015 at 14:27

Polycarbonate sounds like a better plan, so long as you're not going to use nasty stuff that dissolves/reacts with polycarbonates.

The search feature on this site basically doesn't work.

All those links i found on google, using this magic formula :

site: sciencemadness.org [whatever-i-wanted-to-know]

That brings up just about EVERYTHING you would wish to know about a chemical-related question.

What will you do if the isocyanate badge says 'Dead' ?

Also, what if the lab catches on fire ? Bucket of water on hand and a fire extinguisher.

Get some Plans in place if you're going to start messing with dead-ing compounds.

E.g. at least inform someone you're about to attempt a deadly systhesis, and inform them of the precautions to take whilst approaching the corpse.

I have no knowledge of isocyanates, so am probably over-reacting.

chemrox

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posted on 23-11-2015 at 15:10

I'm not sure about the bathroom fan although I've seen diy hoods that used computer fans. You could test it: buy some cigarettes and smoke them while you're running anything that could release HCN. If you smell almond extract bail and get a better fan. I bought a hood for the price of shipping but since my lab is on rented facilities it had to be installed by HVAC folks. Also I wanted better ventilation so the hood installation tied in with the exhaust fan installation. The roof is flat and doesn't support much weight so the fan had to go on the exterior wall. It's a killer fan which lets me handle toxic solvents anywhere in the lab. The whole project cost me $2400. In spite of the high air exchange rate I keep a mask nearby. I have filters for fine particles like silica and organic vapor filters that also capture chlorine and HCN. I recommend having a mask as well as safety glasses.

"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)

Dr.Bob

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posted on 23-11-2015 at 17:09

The isocyanates used in most polyurathane chemistry are far less nasty than smaller MW ones, like methyl and ethyl. Most are bis(isocyanonato)benzenes or xylenes. We used them in an open undergraduate lab and they sell them as Gorilla Glue. Not that you want to breathe them, but they are not very volatile. I presume that you are mixing them with various amounts of diols and triols and other modifiers? Most of those are also not too volatile.

So a good bath or kitchen fan should work OK if that is what you are doing. If you are making the isocyanates yourself (normally done with phosgene or its equivalents), then you need to do a much better job with professional hoods and special equipment. I have done that some, and don't miss it at all.

Cognition

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posted on 24-11-2015 at 12:55

I agree Dr Bob; most isocyanates (HCN) used commercially are trimers or prepolymers thus have low vapour pressure and are harmless at ambient temperatures. PPE is recommended only when the HCN is atomised from a spray gun.

In my case I intend reacting HCN with diols and polyols. As these reactions proceed at ambient temperature there should not be a significant hazard. However I may also wish to synth allophanates; formed from one mole of a mono-functional alcohol with two moles isocyanate. In order to progress this reaction to completion it requires temperature >100 C. And this is where my concern lies.

I wish I could afford chemrox's lab but I can't. Instead I shall proceed with caution. An isocyanate monitoring badge will turn red way before levels of HCN become dangerous so this is my early warning to shut the reaction down and get the hell out of the room.

It's very good advice from aga to have a plan of action for the worst case scenario. In actual fact breathing in isocyanate is unlikely to kill you but it can sensitise your lungs. I happen to know a colleague who became sensitised to HCN - it turned his life upside down. He can barely walk outside his house if there is pollen in the air. If someone uses aerosol deodorant he starts chocking for breath. Unfortunately I think he will be like that for the rest of his life - he's in his early forties.

You may ask; why don't I take on a less dangerous project. I think when you have that spark of inspiration, that one truly inventive idea then you owe it to yourself to pursue the possibility. It may not work but I'd hate to say that I never tried.

aga

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posted on 24-11-2015 at 13:16

It is Excellent that you are thinking this through and asking for advice.

I have the expectation that you will perform the synthsis and survive, then post the results in this thread with some photos of before/after.

Get 2 badges.

One near your breathing holes and the other off-body, between you and the reaction, somewhere you can see/check it easily and frequently.

If that one goes red, shut down heating then run away, then check the one you're wearing.

I usually use this arrangement

[Edited on 24-11-2015 by aga]

Sciencemadness Discussion Board » Engineering and Equipment » Reagents and Apparatus Acquisition » DIY Fume hood