Fume hoods, biological safety cabinets, clean benches…What’s the difference?

Fume hoods, biological safety cabinets, clean benches…What’s the difference?


Fume hoods, biological safety cabi-        classes, each class has a specific        ous chemicals since these chemicals
nets and clean benches are three           purpose.  Class I BSCs protect the        would be recirculated into the room.  If
common laboratory ventilation de-         worker and the environment, but pro-       biological work requires a class II cabi-
vices designed to protect the worker      vides no protection to the experi-         net with chemical use, the air from that
and/or the experiment.  It is impor-       ment.  Ambient air is pulled from the     cabinet must be filtered then ex-
tant to know when each is necessary       working space into the cabinet and         hausted outside of the building through
and under which conditions each            across the experiment.  This ambient      permanent ducts.
should be used.                                air can introduce contaminants into
                                                       the experiment.  All the airflow is into   Class III BSCs protect the workers, the
Fume hoods are used to keep flam-         the cabinet, so the worker is pro-         environment and the experiments.  The
mable, toxic or odorous materials         tected from the experiment.  The air       cabinet is gas-tight with a non-opening
from entering the worker’s breathing       is passed through a HEPA filter, and      view window, and has rubber gloves
zone.  Fume hoods pull ambient air        then is exhausted; use of the filter       attached to ports in the cabinet that
out of the working area, into the fume     protects the workers and the environ-     allow for manipulation of materials in
hood and exhaust it outside the            ment from the exhaust.                    the cabinet.  Class III BSCs are typi-
building.  Gases, vapors and fumes                                                   cally used for the most hazardous bio-
generated inside the hood are ex-          Class II BSCs (the most common at         logical work; this level of hazardous
hausted along with all the moving air.     Ohio University) protect the workers,     biological work is not permitted at Ohio
Information about the proper use of       the environment and the experiment.        University so no class III BSCs are
fume hoods can be found at http://        Ambient air is pulled from the work        used. 
                                                                space into the cabinet, where the air
FumehoodSafetynewsletter.pdf.              is initially passed through a HEPA        A clean bench supplies particle free
Work with some highly hazardous           filter.  The filtered air is then passed   HEPA-filtered air to a product.  Clean
materials (such as air reactive            over the experiment being con-            benches are typically used to provide a
chemicals) may require more protec-        ducted. After passing over the ex-        dust and particle free air supply when
tion than offered by a fume hood;          periment, the air is again passed         working with some medical or elec-
contact EHS for more information.         through the HEPA filter.  Some of the      tronic devices. The ambient air is 
                                                      filtered air is used for the experiment    pulled into the cabinet and passed
Biological safety cabinets (BSCs) are      and some of the filtered air is ex-       through a HEPA filter.  The filtered air
primary containment devices for use        hausted. Class II BSCs can either         is passed over the experiment or de-
with biological materials.  For infor-     exhaust filtered air into the work        vices and exhausted directly onto the
mation on the correct use of BSCs,         space or exhaust the filtered air out-    worker.  Do not use biohazardous ma-
see the Ohio University Biosafety          side. Filtering only removes particles;   terials or chemicals in a clean bench
Manual       filtering does not remove vapors and       because contaminated air is directed
docs/Biosafety_Manual_2007.pdf.            gases.  Therefore, BSCs that ex-          towards the workers.
       BSCs are broken into three          haust the filtered air into the work-
 4                                                   space cannot be used with hazard-