OM0295
Rev 2 September 2020
Page 59 of 103
7.6 HEPA Filter Leak Test
In order to check filter and filter seal integrity, the HEPA filter media and seals must be directly accessible, by the measuring
instrument. The challenge material (i.e. PAO) should be supplied over the supply inlet for the supply filter and in the rear
center of the workzone over the intake slots for the exhaust filter. The upstream challenge port for each filter is located on
top of the cabinet.
7.6.1 Supply Filter
The diffuser plate placed below the HEPA to protect the filter during normal usage may be removed as follows:
The diffuser is secured to the cabinet shell by #1/4-20 acorn nuts located immediately behind the front viewing
window. After removing the fasteners, drop the front of the diffuser plate several inches and pull forward gently.
Note that the diffuser is purposely a tight fit - it is held to the back wall of the cabinet interior by a light push - fit
with projecting studs.
7.6.2 Exhaust Filter
The exhaust filter is checked using a gross leak method, since the exhaust filter is not easily scanned when
connected to an exhaust system. It may be leak tested by drilling a hole in the duct at a downstream location that
will produce a well-mixed aerosol and inserting the sampling probe with rigid extension tubing through hole.
NOTE:
To avoid the window high alarm during the filter integrity check, it is desirable to enter into the
calibration/Service/sensor setup/calibrate downflow sensor menu.
NOTE:
If the upstream challenge port is deemed contaminated and not accessible, use both downflow and
exhaust volume for determining challenge concentrations. Use following area information below with
average downflow velocity and spot-check exhaust velocities as measured to determine volume (CFM)
(CMH). Use exhaust volume as given.
Model Size
*Supply Area (ft
2
)(m
2
)
Exhaust Volume CFM (CMH)
400
7.81(.725)
740 (1257)
600
11.85 (1.101)
1122 (1906)
* Measured 4 inches (102mm) above the bottom edge of the window.
Laskin Nozzle Concentration Formula
# Nozzles x 135 CFM x 100 ug/L
Challenge
Downflow (CFM) + Exhaust (CFM)
Concentration (ug/L)
# Nozzles x 229 CMH x 100 ug/L
Challenge
Downflow (CMH) + Exhaust (CMH)
Concentration (ug/L)
=
=
Summary of Contents for LabGard NU-560-400
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