Magpie - 27-3-2015 at 09:53
A forum member asked me if I have ever had a fire in my hood, and if so, did I turn the fan off or leave it on.
I have had a phosphorus fire that nearly overwhelmed my powerful fan (~400 cfm). I left the fan ON as otherwise my garage would have been filled with
P2O5 smoke. It was a bit concerning to see white smoke billowing out of the vent in the peak of my garage, but otherwise not a fire risk. I was just
hoping the neighbors wouldn't see it and call the fire department. It lasted less than 1 minute.
On the other hand I've never had a solvent fire in my hood. I keep a dry chemical fire extinguisher and a bucket of sand handy, and I would quickly
use them. But would I leave the fan ON, or turn it OFF? On the one had you would want to move all that smoke out of your hood and lab. But on the
other hand the fan is feeding the fire fresh oxygen and potentially carrying the flame into the PVC ducting. I really haven't thought this through
very well.
What would you do, and why?
Sulaiman - 27-3-2015 at 10:18
1) change my trousers
2) close the hood if possible, preventing fresh oxygen and trapping the CO2
3) turn the fan off .... sucking flames up the vent may cause a wiring short so better if no power available.
4) tidy up and pretend it never happened 
Molecular Manipulations - 27-3-2015 at 10:31
For a solvent fire or any substance that burns to produce non-toxic gasses like carbon dioxide, water and nitrogen, I'd leave the fan off to keep it
from burning the fan, which is mostly plastic. If/when I have sulfur, phosphorus or something that burns to make a toxic oxide I'd leave/turn the fan
on. I've never had a bad fire in my hood (because I made it recently, and haven't really used it much). All my fires where before I had a hood, and
most where outside.
I did have one really bad fire, which started by itself while I was gone. It ruined at least $100 worth of reagents and left a lot of soot in my lab,
no equipment was destroyed though, because it happened in one of my chemical storage cabinets. To this day I don't know what started the fire, but I
think it may have been iodine trichloride (I2Cl6) because it a hole was burned through the plastic lid, and all of it was gone
because the glass cracked.
aga - 27-3-2015 at 13:37
The smart-ass reply would be :
Think things through, and arrange things so that an Uncontrolled fire was not possible.
I have not had an uncontrolled fire yet.
My attitude will likely change if i do.