Osmium Plasma Coater Model OPC-60N
Why fume hood operation is probably "over kill"
The automatic response of virtually anyone familiar with the properties of
osmium tetroxide is that any aspect of its use should be done in a chemical
fume hood. However, in this instance, we believe this recommendation might
very well be over kill.
For one thing, the system, being completely automatic, has a programming
such that it is impossible for vapors of osmium tetroxide to get out into
the environment of the system. For one thing, the osmium tetroxide, once
loaded into the reservoir (which should be done in a fume hood), can not be
introduced into the unit until the vacuum has dropped below a certain preset
level. And once introduced into the system, and the coating done, the
chamber can not be vented until the various gas lines are again evacuated
and all traces of the tetroxide eliminated. Then and only then can the
chamber be vented to atmosphere and opened.
So it is just not possible for vapors to exit the unit through the open
chamber.
What happens to the osmium tetroxide once it enters the vacuum system?
Osmium tetroxide is one of the strongest oxidizers known. And as a result,
just about anything it contacts is oxidized and as a consequence, the osmium
itself is reduced, directly in fact to the dioxide, OsO2, a fairly innocuous
and harmless substance. With time there can be some osmium dioxide built up
on the inside of the vacuum line.
Our own sense is that we have never found evidence that any tetroxide ever
makes it to the hot pump oil of the rotary vane pump. But if by some chance
it did, it would then surely be instantly reduced to the dioxide.
The only thing that could exist the rotary vane pump would a osmium dioxide
colloidal size particles but they would be trapped by the oil mist filter.
And sitting on top of the oil mist filter is the "osmium filter". We felt
we needed something more, but we have come to learn it is all psychological.
If there was any active tetroxide getting that far, surely it would turn
black the filter media of this final filter. We have had the same "osmium
filter" operating on our demo units for nearly three years and it is just as
white as the day it was installed the first time. Of course we know how
fast that white paper would turn black if there was in fact any tetroxide
getting that far. And of course there is not any getting that far.
We do however recommend that the rotary vane pump ultimately be vented to
the outside, not because of any concern about osmium vapors but out of a
desire to keep down the level of hydrocarbons generally in the close
confines of the laboratory.
So officially we say, yes, run it in a fume hood, but we really don't
think that it is necessary to do that.
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