Sciencemadness Discussion Board

Fume hood ventilation. Need advice.

Mixe - 29-11-2021 at 12:06

I'm (finally) building a fumehood in my garage. I have a decent metal box fan, with large diameter in- and outlet and good airflow. But its metal. I've seen what the fumes from boiling sulphuric acid does to metal, so I'm not sure how long it will last. Or what the condensated and accumulated products lining it will do together eventually ...

What are the do's and dont's when it comes to fumehood ventilation? How did you solve it? Is it enough to spraypaint the metal fan with some kind of teflon paint? How should the ventilation pipes be constructed? What about filter(s), what kind, how expensive?

Or am I overcomplicating it? From the constructions shared on Youtube and alike it looks like I am ...

[Edited on 2021-11-29 by Mixe]

Oxy - 29-11-2021 at 13:45

I've simply used a fume duct ventilator from hardware store which is made from a polymer. I don't know what is that to be honest but it's strong enough to survive acids of all kind, solvents and other nasty and corrosive things (PVC probably). The pipes are made from PVC (not 100% sure) and I have no problems with that at all.
The only time I was worried was when I was working with a lot of diethyl ether and was afraid that it might blow up as the fan is not explosion proof. But I probably didn't produce enough fumes and nothing bad has happened. The hood and ventilation system prove their effectiveness and safety to some extent. I wouldn't definitely evaporate diethyl ether or gasoline to open air but for just normal work it seems good enough.

teodor - 29-11-2021 at 15:08

Mixe, I think you overcomplicating it.

Surely, all metal parts are corroded by acid fumes but it doesn't mean they stop working.

Axial fans have a good airflow only when there is no resistance. Air pipe + fume hood makes them poor performers and one day you will wish to replace a fan for a centrifugal one. I think this day will come long before the fan will corrode enough.

Try to build your fume hood with components you have and then you will see how to improve it.

Mixe - 30-11-2021 at 23:22

It's not primarily the corrosion that worries me. If the fan corrodes and stop working thats a bitch, but ok. It's the accumulation of residues I'm worrying about. I'll have to manufacture my own base chemicals, after all, so for example I'll be boiling off and distilling both nitric acid and SA. The combined residue of these within the ventilation system would produce a nitrating mixture, no? Just as an example. Then there's the question of directly explosive or flammable fumes and the motor of the fan.

I'm ok with corrosion or far-from-perfect ventilation in a functional aspect, I'm just not ok with starting fires or blowing myself up.

teodor - 1-12-2021 at 03:21

Mixe, start trying. I don't think nitric acid fumes can create explosive residue in your ventilation. Also because they will not stay there. They will react with the metal or will go out.
I am aware only of perchloric acid that can build explosive residue in a ventilation system. Also don't try to evaporate any flammable solvents, use only a distillation setup for that.
Probably other people can share their experiences but I am not aware of the danger of evaporating nitric acid in a fume hood.
I personally put an open concentrated ammonia solution to minimize the effect of acid fumes on the metal parts & pipes etc. Ammonium nitrate or chloride is much easier to wash out than metal oxides.
Also, I try to minimize evaporating of acid in open beakers, I use it only when doing small-scale experiments like the qualitative analysis.
For everything else, I usually use a distillation setup.

[Edited on 1-12-2021 by teodor]

Mixe - 1-12-2021 at 10:18

OK, thanks. I'm hard at work building it. I only wanted to bounce some thoughts about safety I had. Very reassuring. I'll post an update when the fume hood's starting to take form!

macckone - 2-12-2021 at 21:52

I am rebuilding my fume hood after a flammable accident.
The previous hood did its job and contained the flames and liquid.
The fan melted somewhat but was mostly in one piece as the fire extinguisher did the job.

I previously used an inline fan for hydroponic ventilation.
They are generally made of pvc or polyethyene, neither of which is going to be attacked by a nitrating mix at any appreciable rate at close to room temperature.
They also have an epoxy coating on the wires and are brushless induction motors.
I am looking at using a scrubber set up with the new fume hood.