October 2012
7-29
7.6
Fume Hood Filtration and Wash-Down Systems
Particulate Filtration
If radioactive or biologically active materials or other hazardous particulates are pres-
ent, a particulate filter might be necessary. HEPA filters are often used for this pur-
pose. Proper procedures for changing filters should be taken into account to ensure
the safety of workers.
45
If considering a particulate filtration system instead of a wet
scrubber system, it’s important to evaluate the contaminant and concentration that
need to be removed to ensure that the hazard is fully abated. HEPA filters are often
only recommended for highly toxic particulates.
46
The fume hood filtration systems discussed above are summarized in Table 7-2.
Table 7-2. Fume Hood Filtration Systems
45
Ibid
.
Page 7.
46
National Research Council,
op. cit
.
Filtering
Mechanism
How Does It
Work?
How Is Contaminant
Removed?
Does It Use
Water?
What Are the
Special Considerations?
Wet
Scrubber
Packed bed system
that is wetted
with recirculated
scrubbing
liquor captures
contaminants from
air and releases
cleaned air.
Scrubbing liquor
with dissolved
contaminants is
blown down and the
liquor is periodically
replenished with
fresh water.
Yes
None
Inert
Adsorbents
Inert adsorbents
such as activated
carbon, activated
alumina, and
molecular
sieves, adsorb
contaminants.
Spent adsorbent
must be changed
or regenerated
regularly.
No
Adsorbent systems are not
effective in removing high
concentrations of contaminants
(
i.e., spills inside the hood).
These systems require a
consistent check on contaminant
concentrations and maintenance
of the adsorbent.
Chemically
Active
Adsorbents
Inert adsorbents
impregnated with
a strong oxidizer
such as potassium
permanganate
react with and
destroy organic
vapors.
Spent adsorbent
must be changed
or regenerated
regularly.
No
Adsorbent systems are not
effective in removing high
concentrations of contaminants
(
i.e., spills inside the hood).
These systems require a
consistent check on contaminant
concentrations and maintenance
of the adsorbent.
Particulate
Filtration
HEPA or other
filters remove
contaminants.
Filter must be
changed regularly.
No
This is useful for radioactive or
biologically active materials or
other hazardous particulates.
HEPA filters are often only
recommended for highly toxic
particulates.
