Fume hoods

In answer to Marian Blecker's enquiry, there are two main types of
fume hood, the built in variety with external exhaust/chimney stack
and the portable ductless fume unit with interchangeable filters and
a range of accessories to fit just about every budget.

To avoid the heartache of purchasing a system that turns out to be
incompatible with ones needs it is worth looking at the criteria
that may effect choice.

    1.  what chemicals will be used--certain types of chemicals will
        require stronger extraction fans and filters and may not be
        suitable for ductless systems. These chemicals may be
        filtered out in a ductless system however they can limit
        dramatically the retention capacity (lifespan) of the
        filter.

        As an indication a filter used with the likes of naphtha
        might last 9 months whereas ammonia used in the same filter
        system could reduce retention capacity and thereby lifespan
        to under a month.

        With filters ranging from $350 to $750 a piece one cannot
        afford to overlook this area.

    2.  what is the proposed concentration of the chemicals to be
        used--different concentrations and different groups of
        chemicals will effect filter saturation.

    3.  what procedures will be used for applying the
        chemicals--spraying as opposed to dipping or brushing on
        solutions will certainly effect choice of a filter, an
        application involving particulates may well require a
        stronger extraction system with thicker filters.

There are other things to consider like whether the cabinet will
take the size of material one may handle and whether one needs built
in lighting or supply functions but ultimately the type of unit you
opt for will depend upon the processes and chemicals handled.

The benefit of ductless systems to the smaller workshop with reduced
application needs cannot be denied. Ductless units can be taken down
after use and stored, they can be wheeled around the workshop to
different workstations, they can be removed altogether for assembly
in emergency work areas and they can even be expanded by joining up
additional units.

Built in units are permanent, they may well be bulky and most
certainly an expensive initial outlay. Unlike ductless units they
will not generally require replacement filters but they will come
with obtrusive external fittings which may not always fit in with
the external architecture. Plumbed in units will undoubtedly
though provide a much better level of extraction than might be
obtained with the ductless variety.

For almost a decade we have sold ductless systems to Conservation
units around the world, they are made by Erlab of France and I
believe now, also by Erlab in America. I will endeavour to provide
the list with an address in due course.

Mark Vine
Conservation Resources
England

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                  Conservation DistList Instance 9:26
                Distributed: Friday, September 15, 1995
                        Message Id: cdl-9-26-005
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