John aka jjs:

I think you miss the point, so let me be more specific.  There is a big
difference between dust/static control and scrubbers, and I cannot agree
with what seems a repudiation of dust and static as a danger. Dust/static
actions capture the bad guys and pitch them outside.  Scrubbers capture
chemical bad guys and neutralize them for safe disposal.

Elimination of dust and static is easy and bring immediate results in the
home darkroom. It is also cheap to control. Keep humidity up in winter to
reduce static.  Keep the darkroom under positive pressure and filter
incoming air with a cheap furnace filter.  Put an exhaust fan above the
chemical trays. Use tongs.   Tape the edges of ceiling panels to trap
fiberglass particles. There have been frequent instances on this newsgroup
and in my photo club where dust was a problem and the solutions discussed.

OTOH scrubbing chemicals is technically difficult and costly. Air scrubbers
have in common with good darkroom ventilation the capture of fumes, but
beyond that the similarity ends.   In large part, scrubbers benefit the
outside atmosphere only.  They need to capture a significant quantity to
compare with what is emitted from many common sources like industrial paint
booths.  They need a revenue stream to pay for the system. The quantities in
darkrooms are trivial to the outside air quality. The darkroom quantities
are like peeing in the ocean. Who could measure it?  So, the benefit inside
the darkroom is ZERO.

Regards,

PSsquare

Dan,  If you vent inside, then humidity will be a problem.  For the most
part the air traversing the scrubber becomes saturated with water vapor.  It
would act as a humidifier unless some means are used to dry out the air.
Hence a dehumidifier.  Most dehumidifiers that are commercially available
use the refrigeration process to condense the water out of the air.  This
will make the expense of installation and operation increase significantly
(it'll drive the electrical bill through the roof).  Otherwise you must vent
to the outside.  And if you do vent outside, due to the airflow, this air
must be drawn from somewhere and you're back to providing filtered air into
the darkroom.  The scrubber liquor (I wonder if that's the correct use of
that word for this purpose, but who knows) still must be disposed of so you
are not reducing the chemical disposal and environmental issue

Now, I'm all for ecological darkroom use.  However, _I_ do not believe the
particulate or emissive vapors are of significant quantity from the home
darkroom enthusiast to warrant the expense of a scrubber.  A good cross
ventilation system with one or more blowers would provide the best - and
cheapest - method of maintaining a healthy and fume free darkroom.

For those looking for good, cheap and efficient filters for your darkroom
needs, don't overlook the pleated paper filters available in the Auto Parts
store.  Some diesel engines use good size ones, they're practically a HEPA
filter and cost about $10.00.  I used one in a home made negative drying
cabinet...