Chemical fume hood guide for laboratory designers.
A properly functioning fume hood is one of the most important pieces
of laboratory safety equipment. A chemical fume hood can protect
workers from inhaling chemical fumes by constantly pulling contaminated
air into the hood and exhausting it out of the building. It can also
protect users in case of a fire or explosion by helping to physically
contain the event.
A conventional fume hood is designed with an adjustable sash that can be
raised and lowered in front of the user's face. These traditional
fume hoods use constant air volume (CAV) exhaust fans, which exhaust air
from the hood at a constant rate, regardless of sash height. This
simple design can result in unacceptably high air velocities at the face
of the fume hood when the front sash is lowered and nearly closed.
The most common fume hood is the constant volume conventional hood.
This hood is enclosed on three sides, and has a sash that slides in the
front. The sash can go up or down, which determines the hood's
performance and face velocity.
A conventional bypass fume hood is an improved design, featuring a
protected, secondary air intake above the sash face area. This air
intake gradually opens as the sash is lowered, thereby limiting the
velocity of air flowing under the sash into the hood. This allows
for a consistent removal of air from the lab.
A constant volume auxiliary air hood allows outside air — also
called "auxiliary air," to come in directly in front of the sash, but
outside the hood. This auxiliary air is different than the air in
the room. These types of hoods are most often used in laboratories
that don't have a quantity of room air sufficient for the operation of
the fume hoods.
A radioisotope hood is a type of constant volume air hood that is designed
for ease of cleaning. Because they are often used with radioactive
materials, the liners are designed so they can't be penetrated by these
materials, and the base is strong enough to support heavy shielding
bricks. Special HEPA air filters are used on these hoods to collect radioactive
A variable air volume (VAV) fume hood can sense the sash position, and
adjust the volume of air exhausted through the hood accordingly.
These fume hoods can virtually eliminate the excess face velocity and
air turbulence problems associated with CAV hoods. These hoods are
generally quite energy-efficient.
In some situations, where environmental concerns or government regulations
dictate, ductless fume hoods or fume hood scrubbers may be appropriate
A ductless fume hood often incorporates replaceable charcoal and
HEPA filters to remove a variety of air contaminants around a laboratory
workstation, and release the cleaner exhausted air indoors. These
aren't connected to any exhaust system, but are designed to absorb
certain chemical fumes.
A fume hood scrubber reduces the emission of water soluble vapors
and contaminants into the atmosphere by intercepting them with a liquid
spray. Perchloric acid hoods come equipped with sprayers that wash
away accumulated matter.
Other specialized types of fume hoods include distillation hoods,
canopy hoods, downdraft hoods, and elephant trunks.
A distillation hood is any kind of general hood that has a greater
interior height, so that it may accommodate larger apparatuses.
A California hood is a type of distillation hood that has either vertical
or horizontal sashes in the front and back. Another type of
distillation hood is the walk-in hood, which is mounted on the floor
and allows for large objects or equipment to be placed inside.
When heat and steam needs to be drawn away, canopy hoods, which can
be placed over large pieces of equipment like ovens, are frequently
used. Slot hoods draw air via slots in their side walls, and are
frequently used with sinks.
Downdraft hoods are a popular choice when it comes to exhausting
heavy materials, such as powder or dust. These particles are drawn
through a perforated surface and then exhausted.
Elephant trunks are flexible ducts designed to catch discharge from
instruments that produce vapors or odors.
Laboratory fume hoods are often the primary control device when using
toxic and flammable chemicals in a laboratory. It is important
for lab personnel to understand how chemical fume hoods operate so they
can use them correctly and avoid undue exposure to hazardous materials.
When designing a laboratory hood system, it is important to consider
the application and operating conditions as well as air flow requirements,
environmental regulations, and maintenance issues.
The size of the hood will usually depend upon the size of the
workspace. The most common hood sizes range from 3 to 6 feet
wide, but specialized fume hoods can be up to 8 feet wide.
Custom-sized hoods are also available. The hood sash, and whether
it opens horizontally, vertically, or both, will also depend on the use
of the fume hood. Hood linings vary according to what kind of
chemicals and other substances they will be exposed to.
Because the whole purpose of the hood is to ensure that operators are safe
from chemicals and other contaminants, the correct fume hoods must be used
according to specifications. There are different fume hoods for
different situations, and using a sub-optimal fume hood can negate the
reason for using it in the first place.
This laboratory hoods
page provides another perspective on fume hood designs and applications.
This supplier of fume containment solutions specializes
in application solutions for the laboratory environment.
They manufacture a series of ductless fume hoods and laminar flow hoods
designed to protect lab workers from toxic vapors, gases, fumes and particles. www.AirCleanSystems.com
Laboratory Equipment Manufacturers (LEM) manufactures quality
laboratory products including the "Eliminator" line of laboratory fume hoods
for the laboratory and chemical fume hood industry. www.FumeHood.net
Terra manufactures a comprehensive line of exhaust fume hoods,
including benchtop and free-standing models. Options include
HEPA/ULPA filtration modules, chemical vapor filters, ionizers and air
flow meters. www.TerraUniversal.com
This extensive article about chemical fume hoods includes information
concerning their uses, safe operating procedures, design styles, and function monitoring.
Published by the Department of Environmental Health & Safety at the University of Louisville. www.Louisville.edu