7-28
October 2012
7.6
Fume Hood Filtration and Wash-Down Systems
Figure 7-4. Fume HoodWet Scrubber
Other Gas-Phase Filtration
Besides wet scrubbers, there are two other basic types of gas-phase filtration systems
for fume hoods: inert adsorbents and chemically active adsorbents, which do not
require water use. Inert adsorbents include activated carbon, activated alumina, and
molecular sieves. Chemically active adsorbents are simply inert adsorbents impreg-
nated with a strong oxidizer, such as potassium permanganate, that react with and
destroy the organic vapors.
42
Because contaminants build up in the adsorbent and can be desorbed if the concen-
tration is too high or if the adsorbent has a higher affinity for another contaminant,
the adsorbent must be changed or regenerated regularly. Adsorbent systems are
not effective in removing high concentrations of contaminants (i.e., spills inside the
hood). Since these systems require a consistent check on contaminant concentra-
tions and maintenance of the adsorbent, these factors should be taken into account
when evaluating alternatives to fume hood wet scrubber systems, keeping in mind
the contaminant and concentration that needs to be removed to ensure that the
hazard is fully abated.
43,44
Make-Up
Water
Supply
Chemical
Supply
Blowdown Recirculation
Pump
Liquid Flow Air Flow
Packing
Spray Manifold
Mist Eliminator
Air From
Fume
Hood
Scrubbing
Liquor
Sump
Clean Air Out to
Exhaust System
42
Ibid
.
Page 6.
43
National Research Council, et al. 1995.
Prudent Practices in the Laboratory—Handling and Disposal of Chemicals
.
Washington, DC: National Academy Press. Page
188.
44
Hitchings, Dale T.,
op. cit.
,
Pages 6-7.
