Controlled Environments spoke to Scott Alexander, an Advanced Certification Technician with AGAPE Instruments Service, about why fume hoods are needed in cleanrooms. AGAPE performs independent field testing,
certification, and repairs of air filtration and air
particulate control devices.
Controlled Environments (CE): What is the
importance of fume hood exhaust monitoring?
Scott Alexander (SA): It is crucial to have calibrated
exhaust monitors on fume hoods for personnel protection. If working with hazardous, volatile, or corrosive
material without sufficient airflow, the results could be
deadly. Most exhaust monitors have an audible and
visual alarm. If the air flow has dropped to calibrated
levels, this could expose personnel to harmful material.
Another way that the alarm can be used in a
cleanroom is to help monitor the pressure. In many
cases the pressure in a controlled environment is
very important to keep regulated. If inconsistent
variation is noticed in the fume hood monitor there
may also be a problem with the pressure in the area.
This scenario can only be accomplished with monitors that give a digital velocity read out.
CE: What are the different kinds of fume hoods
available for cleanrooms?
SA: For starters, there are two different air flow valve
set ups. The first being a variable air volume (VAV),
meaning it can be programmed to adjust the air
velocity depending on where the sash height is or
can regulate the velocity to a set flow no matter what
the sash height is. Second is a constant volume valve
(CV), meaning the valve is set to a specific velocity
at a specific sash height and that is how the hood is
designed to be worked in. If the sash is raised past
the set point the velocity will then drop. If the sash is
lowered the velocity will increase.
Most of the variations consist of size or material.
There are many different materials including but not
limited to old coated wooden units, stainless (coated or
raw), and different polymer materials to be used with
acid and other volatile chemicals. I have seen them as
small as 2-ft. wide and as large as 10-ft. wide walk-in
Fume hoods can also have different kinds of sash
opening setups. There are vertical, horizontal, combination, and walk-in sash designs.
In some cases manufacturers have outfitted their
fume hoods with supply HEPA filters that are above
the work surface and supply the work area with
CE: What is the regular maintenance process like
for fume hoods?
SA: The regular maintenance process usually consist
of an annual or semiannual certification. The certification then consists of a velocity test with a thermal
anemometer at predetermined points depending on the
size of the sash opening. Followed by calibration of the
alarm and smoke visualization test to prove the direction of the air flow and containment of the smoke. On
top of the certification there is usually a PM schedule
in place to check the blower motor belt. This work is
usually done by the facility personal and the frequency
is usually determined by the facility procedures.
CE: How often should fume hood exhaust moni-
toring systems/equipment be replaced?
SA: Replacement of a fume hood monitor is necessary when the system no longer functions or does
not calibrate properly.
CE: What do cleanroom facility managers need to
keep in mind when selecting a fume hood exhaust
SA: The main things to keep in mind when selecting
an exhaust monitoring system is to think about how
much data you would like to receive. Some monitors
only give an audible and visual light alarm when a
set percentage of velocity drop is detected. Others
give an actual readout of the velocity. Some customers will require the velocity read out for documentation or trending reasons. I would highly suggest not
getting a monitor that does not at least give you an
audible and visual alarm of some kind.
Scott Alexander is an Advanced Certification
Technician with Controlled Environment Certification
Services Inc. (a STERIS Corp. Company), doing business
as AGAPE Instruments Service, in Cincinnati, Ohio.
The Basics of Fume Hood