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Author: Subject: Avoiding Explosions with Fumehood's Inline Fan -Spark Hazard
LuckyWinner
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[*] posted on 18-7-2020 at 01:50
Avoiding Explosions with Fumehood's Inline Fan -Spark Hazard


Ive been reading about lab safety recently.

hcl fumes can corrode metallic parts...

diethyl ether and similar chemicals can be ingnited by
sparks that may form in any non explosion proof electronic devices.

in the fumehood this could be an inline fan.
in my case its a IP44 isolated inline fan with its housing made out of PP with 30% glassfiber.


I guess a venturi principle fumehood only works with industrial fans.
to quote magpie
Quote:

Before I gave up and bought a blower I did try to build an air driven jet suction device based on the venturi principle as used in an aspirator. This was suggested in Ammen's book on refinining of precious metals. But he only gave a crude sketch, no details. In the 3rd picture of mine (above) you will see a number of PVC pipe pieces by the cabinets. Those are from my experimentation in this area using my old household electric furnace blower as motive air. I did manage to create some vacuum (0.5"H2O) but the system was not nearly sufficient to move the large volume of air needed for a fume hood (my blower draws 400-500 cfm @ 0.75"H2O pressure drop). Commercial jets are available that are commonly used at construction sites for their portability and ease of setup. The only utility needed is a source of high pressure air (~90-120psi, IIRC). They move a lot of air. They are also, I understand, quite noisy.





I know best practice is to keep all fumes inside the glassware and neutralize them once they leave the glass but how to improve the flowhood design with a regular inline fan
to minimize danger if there are any explosive volatile chemicals around...
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Tsjerk
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[*] posted on 18-7-2020 at 02:05


I wouldn't worry too much about explosive vapors, as long as you have an air flow going the vapors will be very diluted and far below the explosive limit.

For a homemade fumehood you can aim for a less than perfect airflow, just make sure the fan is a bit over powered.

[Edited on 18-7-2020 by Tsjerk]
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JJay
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[*] posted on 18-7-2020 at 02:20


Most ventilation fans that are intended for removing fumes are designed to keep the motor outside of the airflow. I've seen axial ventiation fans that were rated for explosive vapors that used shielded motors, but they were several decades old. A belt-driven centrifugal fan is probably what you're looking for.
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Mush
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[*] posted on 18-7-2020 at 13:17


A regular inline fan is not designed for explosive vapors. I was thinking to use that too but I dropped the idea.
https://intrinsicallysafestore.com/intrinsically-safe-fan-vs...

https://www.casals.com/en/products/industrial-ventilation/at...

Maybe a blower? The motor is outside of the airflow like JJay mentioned. It looks promising.

CY063 Electric Air Blower,Centrifugal fan,Mini blower,Mini fan ,high qulitity, low price Cooling fan 230V/13W
https://www.aliexpress.com/item/4000109095258.html?spm=a2g0o...

This one looks even better:
CY112 Electric Air Blower Centrifugal fan Mini blower Mini fan high qulitity 60W
https://www.aliexpress.com/item/4000199990393.html?spm=a2g0o...
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CouchHatter
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[*] posted on 18-7-2020 at 17:13


Although not applicable for ductwork and a true in-line fan, I got around exposing mine to vapors by putting a 2-gallon grout bucket around it after cutting slots for the mounts. You don't have to worry about this if you get a single intake blower like Mush linked.

hoodmotor.jpg - 127kB
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draculic acid69
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[*] posted on 18-7-2020 at 17:56


A simple inline boat fan can handle flammable vapours and is mostly plastic or metal sealed in plastic.
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Fyndium
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[*] posted on 21-7-2020 at 00:33


Look for duct fans used in cannabis growing. They are efficient, silent, made of plastic and speed can be adjusted. It is also easy to attach active carbon filter to it. I have been using one for long.
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zed
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[*] posted on 10-8-2020 at 02:58


I've had buddies that did it. Big fan, big window. But, maybe not Ether.

Keep your eyes out for a squirrel-cage blower. It's a better way to go.

I once bought one, at a Goodwill Surplus store, for five bucks. Worked fine.
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macckone
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[*] posted on 10-8-2020 at 07:43


Most blower motors will be 'sparkless' since they are induction (often shaded pole).
They don't have brushes.
The good news is that the 'grow' blowers are designed for high humidity and are pretty corrosion resistant.
HCl fumes don't aggressively attack copper but the coils are covered with a plastic coating to insulate them.
The primary point of failure is in the blades and bearings.
Plastic blades can soften with exposure to solvents.
Capacitor start motors often have a relay or other contacts that can spark.

As I have noted in other threads, 'sparkless' does not mean explosion proof.
Explosion proof fans also contain explosions when they happen and act as a firestop.
Cheap fans won't do that except by accident.

Ideally flammable gas is kept below the LEL (typically between 1 and 5% depending on substance).
Flammable gasses tend to be more of a problem than liquids simply because the liquids have to become vapor at a sufficient rate to overwhelm the ventilation system. This is more likely to happen with the sash fully closed without an alternative air entry.

[Edited on 10-8-2020 by macckone]
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Fyndium
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[*] posted on 10-8-2020 at 08:12


I would restrict all corrosive and flammable fumes by limiting air contact to a minimum and using only closed vessels and setups that contain it. Major part of exposure is when pouring or transferring reactants.

A bigger issue could be the odors, a thing that goes mostly undiscussed, but I have noticed that many chemicals can have a very strong and pervasive smell that not only can be disturbing, but it also clings to all the clothing and equipment and can annoy your co-inhabitants or even neighbors and has a potential to cause misunderstandings. While activated carbon has limited to low ability to absorb flammable fumes, it is on the other hand extremely efficient at removing odors.
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macckone
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[*] posted on 10-8-2020 at 08:51


I second fyndium's comment on odors.
I am currently building a fume hood simply for that reason.
Any reaction that can go through a scrubber should.
And fumes that you might not consider bad can be bad to housemates and neighbors.
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[*] posted on 10-8-2020 at 09:30


Only and single reason I've ever gotten complaint on - and several times so - is the smell of what I'm doing.

Acetic acid? Yuck! What the hell is that reek?
Toluene and other aromatics? Did you moron spill the thinner again?
Benzyl chloride? Oh god...

The phenylacetaldehyde experiment literally made the whole region around my workspace smell of it, and I really got triggered of that smell in a negative light eventually when I realized how badly it clinged into everything. Especially all fabrics and even plastics seem to just absorb it and keep it forever. My backpack, which was only on my lab for a short period, had so intense smell I had to hang it outdoors for a couple of days to get rid of most of it. Thank god the smell isn't actually bad on it's own, but the clinginess of it is surprising. Ironically, no one complained about that smell, though.

I actually ordered an ozone generator to eliminate odors. After I'm done, I let it run for a few hours and then leave the space sit without ventilation until I return. It should be a near surgical method to remove these type of odors because they tend to easily oxidize even on their own. I also have an UVC light which I could hang in the fume hood, it generates ozone in situ.
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