RE: Fume hood

From: Best, Dianne ^lt;[email protected]>
Date: 10/31/05-07:27:10 AM Z
Message-id: <51ABFBF1DF07AA4384B3E1BCC0A93C7801DC2E53@MHMAIL03.hydro.mb.ca>

Ether is VERY explosive! According to the MSDS, it has a lower explosive
limit of 0.9% - that's scary!
 
Ether compounds (collodion) was the only reason for doing the fume hood
so the hood was designed for high air flow and a spark-proof exhaust.
 
The fan is a "duct fan" from a local surplus/discount mechanical store
(Princess Auto) that cost about $45.00 It is built with a shaded pole
motor (no brushes or commutator) and runs a steel shaft in bronze
bushings so it is absolutely spark-proof. The only hazard from the motor
would be if the coil overheats (which it shouldn't) or if the plastic
fan blades build up a static charge when the humidity gets really low
(mid winter). I even soldered all the wire connections before putting
Marettes over them - just extra insurance against sparks!
 
The ductwork is all galvanized steel and is electrically grounded. From
the hood to the fan chamber is a short length of 4" - the whole system
was originally 4" but I had to change the fan to 6" to get enough air
flow. From the fan to the outside is all 6" galvanized. The exterior
portion is a simple snorkel - two 90 degree elbows so the exhaust is
pointed to the ground and out of the rain - with a fiberglass window
screen over the end to keep bugs out. The pipes and elbows are all
painted flat black on the inside to stop light reflecting down into the
darkroom.
 
I designed the system so that the fan sits in the outer window plate and
blows air up the snorkel. The rest of the system sees a vacuum created
by the fan. This ensures that any air leaks in the system are drawing
air from inside the house, not blowing explosive fumes into the
darkroom.
 
350 CFM is probably over-kill for this fume hood but I'd rather loose a
little heat in the winter than risk reaching that 0.9% lower explosive
limit with the ether!
 
Dianne
Received on Mon Oct 31 07:27:30 2005

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