ASTM F91-70(1996)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 91 – 70 (Reapproved 1996)
Standard Practice for
Testing for Leaks in the Filters Associated With Laminar
Flow Clean Rooms and Clean Work Stations by Use of a
Condensation Nuclei Detector
This standard is issued under the fixed designation F 91; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope small areas at the filter surface and the joints at the filter edges.
The HEPA filter effluent normally shows a low nuclei count
1.1 This practice covers the testing of the integrity of
(<100 particles/cm ). When a leaking filter area is encountered,
high-efficiency particulate air (HEPA) filters installed in lami-
an increase of at least ten-fold in the particle count is noticed
nar flow clean rooms of the ceiling to floor or wall to wall type,
within the 2-s response time of the nuclei counter.
and laminar flow clean work stations. The recommended
practice may be used to detect faults or voids in the filter media
4. Apparatus
itself or in the joints between the filter and the room or work
2,3
4.1 Condensation Nuclei Counter.
station structure. The determination of filter media efficiency is
3 1
4.2 Plastic Tubing, ⁄8 in. (9.5 mm) in outside diameter; ⁄4
not within the scope of this practice.
in. (6.5 mm) in inside diameter; of suitable length, not to
1.2 The values stated in inch-pound units are to be regarded
exceed 5 ft. (1.5 m).
as the standard. The values given in parentheses are for
4.3 Glass Laboratory Funnel, 50 mm in outside diameter, 7
information only.
mm in stem diameter, 80 mm over-all length.
1.3 This standard may involve hazardous materials, opera-
4.4 Double-Pole Single-Throw Relay, 115 V, 8 A.
tions, and equipment. This standard does not purport to
address all of the safety problems associated with its use. It is
5. Preparation for Test
the responsibility of the user of this standard to establish
5.1 Assemble the apparatus by slipping one end of the
appropriate safety and health practices and determine the
plastic hose over the funnel stem, and the other end over the
applicability of regulatory limitations prior to use.
nuclei counter input nipple.
5.2 Turn on the electrical supply to the nuclei counter and
2. Terminology
allow 30 min warm up time with the input tube sampling the
2.1 Definitions:
effluent from a HEPA filter.
2.1.1 condensation nuclei—particles within the size range
5.3 Measure the nuclei concentration at the intake to the
from 0.001 to 0.1-μm radius.
HEPA filter. A concentration of less than 1000 particles/cm
2.1.2 HEPA filter—high-efficiency particulate air filter.
indicates a concentration insufficient for conveniently detecting
2.1.3 laminar flow—airflow in which the air confined within
leaks in the filter or its gaskets.
the walls of a room or a smaller work station moves as an
5.3.1 In the event that a nuclei concentration of less than
isovelocity front along parallel flow lines.
1000 particles/cm occurs when sampling a clean work station,
2.1.4 leak—a gap or void in the filter media, or in the
move the work station into a room having a less clean ambient
associated gaskets, which permits unfiltered room air to pen-
such as a room not supplied with filtered air.
etrate the clean room or clean work station.
5.3.2 In the event that the intake nuclei concentration of less
3. Summary of Practice than 1000 particles/cm occurs in a laminar flow room of the
ceiling to floor or wall to wall type, make the filter leak test at
3.1 This recommended practice takes advantage of the fact
a time when the room is operating on a full work schedule with
that a HEPA filter retains a high percentage of the condensation
the maximum number of occupants.
nuclei found in ordinary room air. In this recommended
5.3.3 Should the nuclei concentration level of the input air
practice a nuclei counting apparatus is arranged to sample
fail to reach 1000 nuclei/cm after executing steps 5.3.1 or
5.3.2, set up a nuclei generator using a DPST relay (see 4.4).
This practice is under the jurisdict
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