Ductless fume hoods, sometimes called carbon-filtered enclosures or
filtered fume hoods, are self-contained, filtered laboratory
enclosures that remove hazardous fumes, vapors and particles from
the laboratory. Unlike traditional fume hoods, installation costs
are very low and no ductwork is required. Therefore, many people
think selecting one is a good choice when they first learn of them.
There are some important things to consider before making the final
decision to purchase a ductless fume hood. Take these aspects into
thorough consideration to be confident that a ductless fume hood is
the right choice for your laboratory and your applications:
1. Is your general application appropriate for a ductless fume
hood? Although there are different classes of ductless and filtered
fume hoods, some hoods still limit applications that can be
performed in them. Some ductless fume hoods should only be used
light-duty or process-specific fume hoods. Other filtered fume
hoods can be used for a wide range of chemicals, but keep in mind
that larger chemical volumes will always shorten filter life. This
means that: A limited number of different chemicals should be used.
No extreme heating should be carried out in the hood, i.e. acid
digestion applications. Modest chemical volumes should be used,
around 500 mls or less per chemical. Moderate chemical exposure
times should be maintained. If your application does not meet these
parameters, a standard ducted fume hood is likely the best option
for maximum safety and economical feasibility. If you do not know
what chemicals will be used in the future, or you have a very long
list of chemicals, the application would best be performed in a
ducted fume hood. At this point you should discuss your application
with a Fume Hood Specialist to confirm which kind of fume hood is
primarily recommended.
2. Will the chemicals involved in your application be effectively
filtered with the available carbon filters? Typically, ductless
hoods will be outfitted with chemical specific filters. Specific
filter types increase chemical trapping capacity for different
chemical families; however, some chemicals cannot be safely
filtered or aren’t filtered effectively enough to allow ductless
hoods to be a financially viable option. Filtered fume hoods can
filter out acids, bases, and solvents with one filter type,
however, there are still some chemicals (low molecular weight
solvents) that will not be effectively filtered. To filter various
chemical groups, GCC offers seven different types of carbon filters
for use in our ductless fume hoods: HEPA (High Efficiency
Particulate Air) Filter: a 99.99% efficient particulate filter for
chemical powders and particulates Organic Carbon Filter: Activated
carbon to chemically adsorb organic vapors Acid-Sulfur Carbon
Filter: Impregnated carbon to neutralize Acids and Sulfur
containing compounds Ammonia-Amine Carbon Filter: Impregnated
carbon to neutralize ammonia/amine compounds Formaldehyde Carbon
Filter: Impregnated carbon to neutralize formaldehyde Mixed Bed
Carbon Filter: 60 % Impregnated carbon to neutralize acids and
sulfur containing compounds (20%), Ammonia and amine compounds
(20%), formaldehyde containing compounds (20%) and 40% activated
carbon for organics Radioisotope Carbon Filter: Impregnated carbon
to neutralize radioisotopes GCC Carbon Filters: a comprehensive
filter type for use in our Filtered fume hoods.
3 If all of the chemicals involved in your application match one of
these filter types, it is a good sign that your application will be
suitable for use with a ductless fume hood; however, there are some
chemical exceptions with each filter type. For instance, some
organics (such as methanol) are very volatile, light weight, and
are not effectively adsorbed on the organic filter. Whereas some
acids (like perchloric acid) present special hazards and should be
used in a specialized fume hood. The best way to determine if your
chemicals are compatible with the filter types offered is to
request a Chemical Assessment from our Chemical Specialists. They
will review your application to help you determine if it is
suitable, make appropriate equipment and filter recommendations,
and provide you with any necessary precautions. 4 In some cases,
you may be able to determine the correct filter type using our
Chemical Guide for Ductless Hoods. Remember, though, the Guide is
not an approved list of chemicals; you and your safety officer must
ultimately determine which chemicals, quantities and filters ensure
your personal safety.
