ASTM F25-68(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: F 25 – 68 (Reapproved 1999)
Standard Test Method for
Sizing and Counting Airborne Particulate Contamination in
Clean Rooms and Other Dust-Controlled Areas Designed for
Electronic and Similar Applications
This standard is issued under the fixed designation F 25; 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 aid of a vacuum. The number of sampling points is propor-
tional to the floor area of the enclosure to be checked. The
1.1 This test method covers counting and sizing airborne
apparatus and facilities required are typical of a laboratory for
particulate matter 5 μm and larger. The sampling areas are
the study of microparticle contamination. The operator must
specifically those with contamination levels typical of clean
have adequate basic training in microscopy and the techniques
rooms (white and gray rooms) and dust-controlled areas
of particle sizing and counting.
designed for electronic work. It is not a test method for dust
counting in which isokinetic sampling is a factor (Appendix
4. Apparatus
X1).
4.1 Filter Holder, aerosol open type having an effective
1.2 The values stated in inch-pound units are to be regarded
filtering area of 960 6 25 mm .
as the standard. The values given in parentheses are for
4.2 Vacuum Pump, capable of producing a vacuum of 500
information only.
torr (500 mm Hg) while pumping at a rate of 10 L/min.
1.3 This standard does not purport to address all of the
4.3 Flowmeter, calibrated and having a capacity in excess of
safety concerns, if any, associated with its use. It is the
10 L/min, or a limiting orifice, calibrated with the pump, filter
responsibility of the user of this standard to establish appro-
holder, and filter used for this method at a flow rate of 10 6 0.5
priate safety and health practices and determine the applica-
L/min. Ensure visually that the orifice is free of restricting
bility of regulatory limitations prior to use.
matter before each test.
NOTE 1—Information is included relative to modifications to the referee
4.4 Membrane Filters, black, 0.80-μm mean pore size,
techniques which will make the test method more suitable for specific
47-mm diameter with imprinted grid squares having sides 3.10
routine monitoring, such as described in Appendix X4.
6 0.08 mm. Pressure drop across the filter used shall be no
greater than 50 torr for an air flow rate of 1 L/min·cm .
2. Terminology
4.5 Glass Microscope Slides, 50 by 75 mm, or 47-mm
2.1 Definitions of Terms Specific to This Standard:
plastic disposable petri dishes.
2.1.1 Major Projected Dimension of a particle is desig-
4.6 Forceps, with unserrated tips.
nated as the particle size.
4.7 Binocular Microscope, (Fig. 1) with ocular-objective
2.1.2 Standard Unit of Length for sizing purposes is the
combinations to obtain 40 to 453 and 90 to 1503 magnifica-
micrometer, μm, which is 0.001 mm or 0.000 04 in. Only
tions. Latter objective shall have numerical aperture of 0.15
particles with a measurable length greater than 5 μm are to be
min.
counted.
2.1.3 Fiber is considered a particle, no distinction being
The following apparatus, or equivalent, is satisfactory for this test method;
made with respect to length to width ratios.
except where mentioned otherwise, the part numbers refer to equipment available
from Millipore Filter Corporation, Bedford, MA.
3. Summary of Test Method
(1) Filter holder, Millipore XX50 047 10; or Gelman 1200 A with 1207 Adapter
3.1 The test method is based on the microscopical exami-
available from Gelman Instrument Co., Chelsea, MI.
(2) Limiting Orifice, XX50 000 00.
nation of particles impinged upon a membrane filter with the
(3) Filter, AA Black Grid, 0.80 μm.
(4) Forceps, XX62 000 06,
(5) Check Slide Photographic, XX50 000 50 or equivalent,
This test method is under the jurisdiction of ASTM Committee E21 on Space (6) Aerosol Monitors, Type MABG037A0, and
Simulation and Applications of Space Technology and is the direct responsibility of (7) Adapter, XX62 000 04.
Subcommittee E21.05 on Contamination. Microscopes such as Bausch & Lomb No. TBV-5, Series C; American Optical
Current edition approved Aug. 15, 1968. Published October 1968. Originally Co. X2BUHBW, Leitz SM 0.4.4S 25/81; and Zeiss: Model KF 124–212 (with
published as F 25 – 63. Last previous edition F 25 – 66 T. accessories): or equivalent, have been found satisfactory for this purpose.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F 25 – 68 (1999)
2 2
150 ft (13.9 m ). Sample at 1, 2, 3, 4, and 5 for areas up to
2 2 2
1000 ft (92.9 m ). For areas larger than 1000 ft , increase
sampling by four locations per 1000 ft . If desired, for an
average room dust count, a single sample may be taken for 5 ⁄2
min at each of the five designated sampling points.
5.5 Locations are approximate. Location 1 is the area center,
18 and 28 are centers of triangles on respective bases. Locations
2, 3, 4, and 5 are half distances from center to respective
corners on area diagonals, as shown in the sampling plan.
6. Preparation of Apparatus
6.1 Before sampling, remove dirt and dust from the filter
holder by washing in a free-rinsing detergent, ketone-free
isopropyl alcohol and submicron-filtered reagent grade petro-
leum ether (boiling range 30 to 60°C) or trichloromonofluo-
romethane or trichlorotrifluoroethane.
6.2 Maintain the laboratory equipment and area used for
counting and sizing the airborne particulate in a condition of
cleanliness paralleling or superior to the area sampled. Plastic
microscope hoods have proven satisfactory as covering in the
FIG. 1 Suitable Microscope: Inclined Binocular Body; Mechanical
absence of a laboratory.
Stage; Triple Nosepiece; Ocular-Objective Combination to Obtain
40 to 453 and 90 to 1503 Magnification
6.3 Personnel performing sizing and counting operations
shall be equipped with garments consistent with good practice.
6.4 Clean and prepare microscope slides and petri dishes for
4.8 Normal Counter, (2 gang) or equivalent.
preserving the membrane filter and specimen. Lens tissue
4.9 Microscope Lamp, 6 V, 5 A, high-intensity.
properly used is satisfactory for this operation.
4.10 Ocular Micrometer Scale, 5-mm linear scale with 100
6.5 Handle hazardous chemicals used in the method with
divisions.
recognized precautions.
4.11 Stage Micrometer, standard 0.01- to 0.1-mm scale.
6.6 Establish a background count on membrane filters by
4.12 Standard Counting Specimens.
examining each filter used for referee purposes. Examination at
5. Sampling (Fig. 2)
40 to 503 magnifications through the microscope will reveal
low or high background count.
5.1 The airborne particles shall be collected with the aid of
6.7 Make a background count (Note 2), following micro-
a vacuum source on a membrane filter of 960-mm effective
scopical methods outlined in this method, upon any filter with
filtering area. The filter surface must be vertical with respect to
a contamination level approximating 10% or greater of the
the floor. For an inplant method of sampling using aerosol
estimated test sample (Note 3). This count will be subtracted
monitors, see Appendix X4.
from the total count (P ) obtained in 8.1 for each size range.
5.2 The standard sample for this test method shall be 10 t
6.8 Place acceptable filters in clean petri dishes and cover.
ft (283 L). For inplant procedure, the sample size may be
Identify dishes for test use.
adjusted for specific conditions.
5.3 The sample shall be taken at waist level (36 to 40 in.
NOTE 2—For routine work a background count on two filters per box of
(0.9 to 1.0 m)) from the floor) or at bench level unless the area
100 is adequate under present rigid production methods.
NOTE 3—If the background count is estimated to be greater than 10 %
is limited. Sampling points shall be as designated on the
3 3
of the total count from a 10-ft (0.3-m ) specimen, a larger sample (15 or
sampling plan in Appendix X2. The number of samples for
3 3
20-ft (0.4 or 0.6 m ) volume) may be used to eliminate background count
averaging is a function of the floor area of the space being
procedure.
sampled (see 5.4). These sampling locations give a statistical
average for the entire room. It is recommended that areas of
7. Procedure
critical operations also be monitored for closer control of these
7.1 With the aid of laboratory pressure tubing of rubber or
specific areas.
plastic, connect the filter holder to the vacuum train which
5.4 The sample shall be taken at the respective locations
includes the filter holder, and either or both a limiting orifice of
illustrated on the sampling plan in Appendix X2. Sample at 1
10 L/min (Fig. 3) or a flowmeter having a capacity of 10 L/min,
for areas of cabinet size. Sample at 18 and 28 for areas less than
and a source of vacuum (vented outside sampling area or
filtered to prevent contamination of the area samples) (Fig. 2).
4 7.2 With clean unserrated forceps, carefully remove the
The Veeder Root counter has been found satisfactory for this purpose.
membrane filter from the petri dish and place, with grid side
The AO Spencer Universal, or equivalent, lamp has been found satisfactory for
this purpose.
up, on the screen support of the filter holder (Fig. 4). Twist the
Bausch & Lomb No. 31-16-01, or equivalent, scale has been found satisfactory
locking ring in place to secure the filter.
of this purpose.
7.3 When in the sampling area, place the filter holder in a
Bausch & Lomb No. 31-16-99, or equivalent, micrometer has been found
satisfactory for this purpose. horizontal position (filter surface vertical) 36 to 40 in. (91 to
F 25 – 68 (1999)
micrometer) for each magnification (Fig. 5). (A whipple disk
similarly calibrated is satisfactory for many inplant investiga-
tions.)
7.5.2 Knowing the subdivisions of the stage micrometer
(top), the divisions of the measuring eyepiece (bottom) may be
sized from it (Fig. 5).
NOTE 4—Example—Stage micrometer 100 μm per major division, 10
μm per minor division; 100 divisions of the measuring eyepiece subtend
1050 μm, one division of the measuring eyepiece = 10.5 μm.
7.5.3 Place the microscope slide or petri dish containing the
specimen under the microscope. The petri dish cover must be
removed.
7.5.4 Adjust the microscope lamp intensity and direct it on
the specimen from an oblique position to obtain the maximum
FIG. 3 Inserting a Typical Orifice
definition for sizing and counting. High intensity illumination
is a critical requirement.
7.5.5 Use a magnification of approximately 453 for count-
ing particles 50 μm or larger and approximately 1003 for
particles smaller than 50 μm. (Greater magnification may be
advantageous for examination to identify particles.)
NOTE 5—Analysis for particles in the 0.5- to 5.0-μm size range may be
achieved by using transmitted light techniques, after rendering the white
filter transparent by placing the filter on immersion oil of refractive index
1.515. A magnification of at least 5003 is required. For transmitted light
microscopy, a white filter must be used (instead of black filter) since only
the white filter can be rendered transparent with immersion oil. If a
smaller pore size filter is used, the flowmeter and limiting orifice will
require calibration with filter holder and filter in place.
7.5.6 Particles should be counted and tabulated in two size
FIG. 4 Placing the Filter on a Typical Screen Support
ranges: particles greater than 50 μm and particles 5 to 50 μm.
Particles smaller than 5 μm are not to be counted by this
method. The size of a particle is determined by its greatest
projected dimension. Fibers are counted as particles.
7.6 Method of Counting Particles:
7.6.1 Adjust the microscopic focus and lamp position so
that maximum clarity of filter surface and particle definition is
obtained.
7.6.2 With the lower magnification (approximately 453)
count the entire effective filter area for particles larger than 50
μm. Use a manual counter for this purpose.
7.6.3 At the higher magnification, estimate the number of
particles in the 5- to 50-μm range over the effective filtering
area by scanning one unit area. If the total number of particles
in this range is estimated to be less than 500, count the number
of particles in this range also over the entire effective filtering
FIG. 2 Typical Air Sampling-Filtration Apparatus
area. If the number is greater, the counting procedure in 7.7
applies.
7.6.4 The largest projected dimension of the particle deter-
102 mm) from the floor level for purposes of sampling. Apply
mines the size category of the particle.
the vacuum and adjust to a flow of 10 L/min. When using the
7.7 Statistical Particle Counting:
orifice, no adjustment is necessary. However, the pump should
7.7.1 When the estimated number of particles over the
be checked with the manometer to ensure its ability to maintain
effective filtering area in the 5- to 50-μm range exceeds 500,
a vacuum of 500 torr (500 mm Hg) or better while sampling.
the method entails the selection of a unit area for statistical
7.4 The filter should be removed from the holder with
counting, counting all particles in the unit area which are in the
forceps and placed between clean microscope slides or in a
5- to 50-μm range, and then similarly counting additional unit
clean petri dish for transport to the microscope counting area.
areas in accordance with the counting plan of Fig. 6 until the
7.5 Microscopical Analysis:
following statistical requirement is met:
7.5.1 Place the ocular micrometer in one eyepiece. Using a
stage micrometer, calibrate the measuring eyepiece (ocular F 3 N 5.500 (1)
n t
F 25 – 68 (1999)
FIG. 5 Calibrating the Measuring Eyepiece
where:
F = number of grid squares or unit areas counted and
n
N = total number of particles counted in F areas.
t n
7.7.2 After establishing with low-magnification examina-
tion that particle distribution on the filter is uniform, for the
referee method, use the counting plan as shown in Fig. 6.
Count a number of grid squares or unit areas within different
grid squares as indicated in the counting plan of Fig. 7 until the
statistical requirements of 7.7.1 are met.
NOTE 6—An alternative test method for statistical particle counting is
presented as Appendix X3.
7.7.3 Select unit areas for counting so that the average total
number of particles in a unit area does not exceed 50 particles.
FIG. 6 Double-Diameter Counting Plan (Shaded Area Used)
(See Fig. 7 for alter
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