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culating air. There is a speed control located
in the light canopy.
Tum it clockwise until you have the
desired airflow. If the airflow cannot be
maintained, it will be necessary to replace
the HEP A filters. (See "Replacing the HEPA
Filters' later in this section.)
. WARNING!
When the light canopy is lowered, some
electrical parts are exposed. Do
not
perfonn
, :his
work unless you are a trained electrician
or. electronic teclmician;
,
Filter Media and Seal Leak Tests
When preparing your cabinet for use after
shipment, and then at prescribed intervals
throughout its working life, you will need to
verify that the filters have maintained their
integrity. This is done by probe-testing the filter
faces and seals.
The equipment you will need includes:
•
An aerosol photometer. The instmment
should sample air at a flow rate of 1 CFM.
•
A D.O.!'. generator with Laskin nozzle(s).
Liquid dioctylphthalate (D.O.P.),
dioctylsebacate or
a
comparable substance is
aerosolized by flowing through the nozzle(s).
When generated with Laskin type nozzle(s),
the mean droplet size of the aerosol is 99
percent less than
0.3
microns.
Here is the procedure:
1
..
it according to the manufach1rer's
instructions.
2.
Position the D,O.P. generator so as to
introduce air generated srnoke into the area
upstream of the filter.
1.
1Vfeasure the tlpstrearn concentration of
D.O.P.
WARNING!
Do not do this unless the unit has been
properly decontaminated.
20
4.
Holding the photometer probe about one
inch from the filter face with the diffuser
removed on the downstream side, scan the
entire surface area and perimeter (filter
gasket frame area) in slightly overlapping
strokes at a traverse rate of not more than ten
feet per minute. Repeat at
90
degrees to the
first scan pattern.
5.
Eliminate leaks in the gasket frame area by
re-tightening the filter gasket.
6.
An HEPA filter
i.s
considered acceptable
when all significant leaks have been sealed.
Airflow Smoke Pattern Test
To check for the direction of air movement, use
a smoke generator and trace along the front access
opening on the inside of the cabinet. Observe that
no smoke is escaping from the work area.
In order to be sure that room air is not entering
the work area, trace along the outside of the front
access opening. Observe that no smoke
penetrates farther into the cabinet than the front
perforated grille.
Cabinet Integrity Test
The purpose of this test is to detennine that the
cabinet welds and gasketed seams are free of
detectable leaks.
1.
Decontaminate the cabinet if it has been used.
2.
Seal off the exhaust filter port. This may be
done by instal1ing
a
gasketed panel over the
opening using the stods on the filter box
flange. An alternative is to tape a piece of
cardboard or plastic over the opening.
3.
Disconnect the electricity and then remove
the two nuts holding the canopy clips at the
top of the canopy. Let the canopv pivot
down. Disconi1ect the electrical plugs inside
on e;Kh end. Disconnect the restraints and
hlnges. Lift the canopy up
2Lrtd
off.
4.
Lm,\.rer the vieVv'Screen untiJ lt is cornp ietely
closed.
5.
Remove the top viewscreen tracks by
removing the
tvvo
cap nuts at the top of each
track, then puJJ.ing upward on each track.
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