PARTICULATE PENETRATION OF POROUS FOAM 565
TABLE II
Summary of 90 ppi porous foam tests
Filter face
Sampler Sampler Flow rate, —_velocity, Mean 50% Standard N
D diameter,mm ml/min cm/sec cut point, zm deviation,o _ replicates
1 40 200 26.4 45 0.17 3
2 40 200 26.4 4.5 0.06 3
3 40 200 26.4 45 0.08 3
1 40 250 33.0 42 0,06 2
2 40 250 33.0 42 0.05 3
3 4.0 250 33.0 40 0.14 5
1 40 300 39.6 3.8 0.04 3
2 40 300 39.6 3.9 0.05 3
3 40 300 39.6 3.7 0.10 3
4 63 630 33.7 43 0.04 3
4 63 760 40.7 40 0.22 3
4 63 970 51.9 35 0.27 4
5 12.0 2260 30.0 46 0.21 3
5 12.0 2730 36.3 40 0.17 4

To compare the penetration curves of the cyclone and the
experimental foam, the cyclone penetration was measured with
the same apparatus at 1.7 L/min. The cyclone penetration data
was fit using the functional form of the ISO penetration curve
as recommended by Soderholm®) and adjusting the function
parameters to give close agreement at approximately 4.0 um.
Figure 5 shows the fit of the cyclone data with the ISO func-
tion with adjusted parameters £’ = 1.25 replacing 2 = 1.5

and the coefficient (.11)d replacing (.06)d in the ISO respirable
definition. An equivalent alternative method, employed by Chen
etal.,' is an integrated lognormal distribution model.®) Chen
also stated that there is no suitable universal model for all cy-
clones currently available, Foam penetration data was then com-
pared to the derived equation to determine the closest match to
the cyclone penetration. Comparison of all the foam classifier
Penetration curves showed that the 4.0 mm tube operated at

48 T T T T T
Key

46 Tube! 4
& @ Tube2
E « Tube3
5 44 4
°
a L 4
© 42 }
8 }
2 407 7
8 i

3.8F } 4

3.6 L L 1 lL 1

190 210 230 250 270 290 310

FLOWRATE, mL/min

FIGURE 3
50 percent cut point results for three similar 4.0 mm samplers constructed and tested at flow rates of 200, 250, and 300 ml/min.
‘The standard error bars are shown.


568

4.

a

2

2

1.

12.

S.J. PAGE ET AL.

Bartley, D.L.; Chen, C.C.; Song, R.; Fischback, T.J.: Respirable
Aerosol Sampler Performance Testing. Am Ind Hyg J 55:1036—
1046 (1994).

Attfield, M.D.; Seixas, N.S.: Prevalence of Pneumoconiosis and
Its Relationship to Dust Exposure in a Cohort of U.S. Bituminous
Coal Miners and Ex-Miners. Am Ind Med 27:137-151 (1995).
Attfield, M.D.; Morring, K.: An Investigation into the Relationship
Between Coal Workers’ Pneumoconiosis and Dust Exposure in
USS. Coal Miners. Am Ind Hyg Assoc J 53(8):486~492 (1992).
Hurley, J.F.; Maclaren, W.M.: Dust-Related Risks of Radiological
Changes in Coal Miners Over a 40-year Working Life: Report on
Work Commissioned by NIOSH, Report No. TM/87/09. Institute
of Occupational Medicine, Edinburgh, Scotland (1987).

3. U.S. Congress. Federal Coal Mine Health and Safety Act of 1969.

Public Law 91-1173. (1969).

). Attfield, M.D.; Wagner, G.; Respiratory Disease in Coal Miners. In:

Environmental and Occupational Medicine. 2nd ed., Rom, W.N.,
Ed., pp. 325-344, Little, Brown and Company, Boston (1992).

). National Institute for Occupational Safety and Health (NIOSH):

Criteria for, a Recommended Standard—Occupational Exposure
to Respirable Coal Mine Dust, DHHS (NIOSH) Pub. No. 95-106.
NIOSH, Cincinnati, OH (1995).

U.S. Department of Labor: Report of the Secretary of Labors’ Ad-
visory Committee on the Elimination of Pneumoconiosis Among
Coal Mine Workers, recommendations 8 and 17. Department of
Labor, Washington, D.C. (October 1996).

Cantrell, B.K,; Williams, K.L,; Stein, S.W, etal.: Continuous Res-
pirable Mine Dust Monitor Development. Proc. of the 6th Intea-
tional Mine Ventilation Congress, pp. 11-17. Littleton, CO, SME
Inc. (1997).

|. Lehocky, A.H.; Williams, P.L.: Comparison of Respirable Sam-

plers to Direct-Reading Real-Time Aerosol Monitors for Measur-
ing Coal Dust. J Appl Ind Hyg 57:1013-1018 (1996).

}. Tsao, C.J.; Shih, T.S.; Lin, J.D: Laboratory Testing of Three Direct

Reading Dust Monitors. J Appl Ind Hyg 57:577-563 (1996).

}. Dobroski, H. Jr.; Tuchman, D.P.;Vinson, R.P.: Differential Pres-

sure as a Means of Estimating Respirable Dust Mass on Collected
Filters. Proc Appl Ind Hyg (1995).

16.

20.

21.

24,

25.

26.

27.

28.

Volkwein, J.C.; Schoeneman, A.L.; Page, S.J.: Laboratory Evalua-
tion of Pressure Differential-Based Respirable Dust Detector Tube,
ACGIH Applied Workshop, Occupational & Environmental Expo-
sure Assessment, Chapel Hill, NC, Feb. 23-24, 1998 (1998).

. Chen, C-C.; Lai, C-Y.; Shieh, T-S.; Yeh, W-Y.: Development of

Respirable Aerosol Samplers Using Porous Foams. Am Ind Hyg
Assoc J 59:766-773 (1998).

. Aitken, R.J.; Vincent, J.H.; Mark, D.: Application of Porous Foams

as Size Selectors for Biologically Relevant Samples. Appl Occup
Env Hyg 8(4):363-369 (1993).

Liden, G.; Gudmundsson, A.: Optimization of a Cyclone to the
1993 International Sampling Convention for Respirable Dust. Appl
Occup Environ Hyg 11:1398-1408 (1996).

Kenny, L.C.; Thompson, J.: Characterisation of Porous Foam Size
Selectors Using Polydisperse Aerosols. Proc. 9th Annual Confer-
ence of Aerosol Soc., 104-109 (Apr 1995).

Baron, P.A.: Calibration and Use of the Aerodynamic Particle Sizer
(APS 3300). Aer Sci & Tech 5:55-67 (1986).

Griffiths, W.D.; Iles, P.J.; Vaughan, N.P: The Behavior of Liquid
Droplet Aerosols in an APS 3300. J Aero Sci 6:921-930 (1986).

. Bowman, J.D.; Bartley, D.L.; Breuer, G.M.; et al.: Accuracy Cri-

teria Recommended for the Certification of Gravimetric Coal
‘Mine Dust Samplers, NTIS Publication No. 85-222446, NIOSH,
Cincinnati, Ohio (1984).

Vincent, J.H.; Aitken, RJ.; Mark D.: Porous Plastic Foam Filtra-
tion Media: Penetration Characteristics and Applications in Particle
Size-Selective Sampling. J Aero Sci 7:929-944 (1993).

Gibson H.; Vincent, J. H.: The Penetration of Dust Through Porous
Foam Filter Media. Ann Occup Hyg 24:205-215 (1981).

Wake, D.; Brown, R.C.: Filtration of Monodisperse Aerosols and
Polydisperse Dusts by Porous Foam Filters. J Aero Sci 22(6):693~
706 (1991).

Hinds, W.C.: Aerosol Technology, Properties, Behavior, and Mea-
surement of Airborne Particles, p. 118. John Wiley & Sons, New
York (1982).

Bartley, D.L.; Breuer, G.M.: Analysis and Optimization of the Per-
formance of the 10 mm Cyclone. Am Ind Hyg Assoc J 43:520-528
(1982).



564

in size distribution during the sampler test. In some instances,
one of the two reference size distributions showed instability.
‘When this occurred, only the one stable reference size distribu-
tion was used. Visual examination of the sampler test, in com-
parison to other sampler tests, was sufficient to establish whether
or not the aerosol was stable during the test. If instability was
detected, the entire set was discarded.

For the cyclone penetration only two valid replications were
made. However, the low replicate variance in the foam cut point
determinations as well as previous reports”) which show the
inter-cyclone variability to be between two and five percent rel-
ative standard deviation allows for confidence in the measured
cyclone cut point. Also, subsequent gravimetric comparison of
the cyclone with the optimum foam dosimeter testing showed
good agreement.('

Data Analysis

The APS accumulated particle count data in discrete chan-
nels covering a range from 0.5 1m to 14.9 um particle size. Due
to the small number of counts in channels below 1.0 um and
above 6.3 zm, only the 26 channels between these size values
were used. Additionally, this size range was considered to be an
appropriate range for comparison to 10 mm cyclone penetration
data. Error per channel due to phantom particle counts caused
by coincidence was estimated to be less than 0.1 percent for
channels below 4.4 um particle size. In the size range between
4.4 and 5.8 ym this error increased up to 4.2 percent. At and
above 6.3 jzm, count error often exceeded 20 percent. These es-
timates were made by averaging the APS count data in channel
sizes above 10 um, where the aerosol generator was very un-
likely to generate particles, and dividing this average value by
the particle count for each channel between 1.0 um and above
6.3 wm. Because this error was typically less than 0.1 percent
in the approximate region of interest (4 zm), the error was not
subtracted from each channel. Adjusting the data would only
improve the polynomial fit in the size range above 5.5 um.

The sampler penetration as a function of aerodynamic size
was calculated by dividing the sampler aerosol distribution by
the reference distribution, channel by channel. The median cut
point of each sampler was determined by fitting a polynomial
function to the penetration curve. The fits were efficient (R? >
0.98) and allowed prediction of the aerodynamic particle size at
50 percent penetration. Although a sigmoidal-type curve would
provide a better fit to the penetration data over the entire size
range tested, the functional form used is not important to ob-
tain an estimate of the 50 percent cutpoint so long as the fit is
reasonable over the region of interest.

Particulate penetration through foam was determined semi-
empirically by Vincent et al.,2 using data from Gibson and
Vincent®5) and Wake and Brown) and others. The Vincent
model describes the particle penetration P to be:

inp == [54.365 +3891NTM] 1]
f

S.J. PAGE ET AL,

where

the foam thickness,
dy = the equivalent fiber diameter of the porous foam.

The equivalent fiber diameter d, has been empirically related
to foam porosity p, at the Health and Safety Executive of the
United Kingdom to be:

dy = (0.009633 p,)"!716, 12]

S,, the inertial parameter, and N,, the gravitational parameter,
are defined as:

d.vgU
18ndy

_ Ge¥8
Mea 1870 8)

1,

where

d,, = the aerodynamic diameter,
y = the density of water,
7 = the viscosity of air,
U = the velocity of air through the foam, and
g = the acceleration due to gravity.

RESULTS AND DISCUSSION

‘Table II summarizes the test results of the 90 ppi foam sam-
plers over arange of flow rates from 200 to 2730 ml/min. Figure 3
shows the results of the three similar 4.0 mm tubes tested at flow
rates of 200, 250, and 300 ml/min. As would be expected, the
50 percent cut point is seen to decrease with increasing flow rate,
presumably due to impaction effects. Overall, the relationship
between cut point and flow rate appears somewhat non-linear
as would be expected for an asymptotic approach to a limiting
value of the cut point due to particle impaction since subsequent
increases in flow rate must produce smaller changes in the cut
point. Inertial impaction theory states that the cut point varies
directly as the square root of the Stokes number and, therefore,
inversely as the square root of the volumetric flow rate.2” The
variability of the cut points between the three tubes, as well as
the replicate variability for each tube, was small in comparison
to the effect due to the flow rate.

Considering that the foam plugs were cut and inserted into
the glass tubes, there is the possibility that nonuniformity of the
plugs and slight compression on insertion into the tube could
affect the penetration characteristics of the classifier tubes. If
such variations were important, they would manifest themselves
in changes of the perimeter- to-surface area ratio. Figure 4 shows
the 50 percent cut point variation with foam face velocity for
tube diameters of 4.0, 6.3, and 12 mm. Differences in 50 percent
cut point at equivalent face velocities were insignificant. This
suggests that the primary collection is inertial impaction within
the foam and not wall losses or sedimentation.


566 S.J. PAGE ET AL.

5 T T T T T
E i |
a y=-0.04x+576
Bat |
&
E
2
Ost Key 4
PS @ 4.0mm Tube
8 = 6.3mm Tube

12mm Tube
2 i i 1 1 =e
25 30 35 40 45 50 55

FACE VELOCITY, cm/sec
FIGURE 4

50 percent cut point results for 4.0, 6.3, and 12 mm tubes constructed and tested at flow rates of 200, 250, and 300 ml/min. The

standard error bars are shown.

250 ml/min provided the closest’match to the cyclone pen-
etration. Figure 6 shows a typical representation (one out of
ten tests using three different 4.0 mm tubes at 250 ml/min) of
this comparison. Although the foam classifier shows a some-
what lower penetration below 3 ym, the comparison appears
reasonable.

‘The theoretical particulate penetration of the foam used in this
study was determined using Equations 1-3, the experimental
flow rate of 250 ml/min, and a measured pore size of 86 ppi
determined by Foam-X Corporation. The resulting aerodynamic
dso was calculated to be 3.8 zm. This compares favorably to the
experimentally measured aerodynamic dsp of 4.0 um.

rae T T T T T T
- - 3 Wttene Key ]
3 ° $3 8 @ 1.74/min cyclone data
é 80F 8 © Functional approximation 7
3
B eo | ¢ |
2 60F 7
i}
5 | ¢ ]
4of — Etficiency= o5 s1ta)[t- erttx2)] |
3 | X= dold/T) 24.25 pm % ]
& And 321.25
B27 st(a)0.5(140-e4) 8 '
< $ 1
a
! i 1 n 1 t fir
ce) 1 2 3 4 5 6 7

AERODYNAMIC DIAMETER (d), ym

FIGURE 5

Approximation of the 10 mm nylon cyclone tested by the functional form of the ISO respirable definition, using modified
parameters © = 1.25 replacing X = 1.5 and the coefficient (.11)d replacing (.06)d in the ISO respirable definition.


Particulate Penetration of Porous Foam Used
as a Low Flow Rate Respirable Dust Size Classifier

Steven J. Page,! Jon C. Volkwein,! Paul A. Baron,? and Gregory J. Deye”

| Public Health Service, Centers for Disease Control, National Institute for Occupational Safety
and Health, Pittsburgh, Pennsylvania; *Public Health Service, Centers for Disease Control,
National Institute for Occupational Safety and Health, Cincinnati, Ohio

Porous foam has been used as a material for classification
of particulate matter into various size fractions. The pene-
tration characteristics of a nominal 90 pores per inch porous
foam were studied at various flow rates, face velocities, and
foam plug diameters and compared to the aerosol penetra-
tion of a 10 mm Dorr Oliver cyclone operated at 1.7 L/min,
Poly-dispersed triethanolamine spheres were classified thr-
ough porous foam plugs and the resulting penetration was
determined using an aerodynamic particle sizer. Results
showed that for a given plug diameter, as face velocity in-
creased from 26 to 39 cm/sec, the 50 percent cut point de-
creased from 4.5 to 3.8 zm. Furthermore, as the diameter
of the plug increased from 4 to 12 mm, the 50 percent cut
points were similar to other plug diameters at equivalent
face velocities, The best match to the 1.7 L/min cyclone pen-
etration characteristics occurred at a flow rate of 250 ml/min
through a 25 mm by 4 mm diameter section of 90 pore per
inch foam. Because of the need to provide short-term or real-
time estimates of worker respirable dust exposure, porous
foam may be a viable classification media for a low flow rate,
disposable respirable dust sampler for use in the coal mining
industry.

Keywords Porous Foam, Dust, Sampling

Prolonged exposure to airborne respirable coal dust is re-
sponsible for coal workers’ pneumoconiosis (CWP). Respirable
dust, although historically defined in various ways, is qualita-
tively defined as that fraction of particle size which is capable
of penetrating to the alveolar lung region. The current accepted
definition of respirable dust recommended for industrial hygiene
practice is the ACGIH/CEN/ISO convention."!:2-3) However, the
U.S. coal mining industry is regulated by the Mine Safety and

‘This article is not subject to U.S. copyright laws.

Health Administration (MSHA) for respirable dust using the
10 mm nylon cyclone operated at 2.0 L/min as a particulate
size classifier. When the 10 mm nylon cyclone is operated at
the recommended flow rate of 1.7 L/min, the agreement with
the ACGIH/CEN/ISO convention is improved but still possesses
a steeper slope in the penetration characteristic. Therefore, this
device does not correspond to the ACGIH/CEN/ISO convention
at either flow rate.

Health research studies have identified that the severity of
CWP is directly related to the amount of dust exposure and the
coal rank.5-”) Because the passage of the 2.0 mg/m? TWA (time-
weighted average) exposure limit dust standard in the Federal
Coal Mine Health and Safety Act of 1969,®) average dust levels
were reduced from over 6 mg/m? to current levels just under the
2.0 mg/m? standard.

The National Institute for Occupational Safety and Health
(NIOSH) has recently determined through their Coal Worker's
X-ray Surveillance Program that coal miners continue to have
an elevated risk for CWP under the current 2.0 mg/m? dust
standard and recommended a 1.0 mg/m? dust standard to reduce
the prevalence of CWP." In view of this finding, it becomes
increasingly important to adequately monitor the miner exposure
in a timely manner.

In the Report of the Secretary of Labor’s Advisory Commit-
tee on the Elimination of Pneumoconiosis Among Coal Mine
Workers,"") several recommendations deal with the develop-
ment of continuous respirable dust monitors to help protect the
workers’ health. In addition, the NIOSH Criteria Document”
lists improved sampling devices as a research need pertinent to
coal miner respiratory health and prevention of disease. Sev-
eral approaches are being taken to address these needs. These
studies include, but are not limited to (1) a machine-mounted res-
pirable dust monitor, ) (2) light scattering dust monitors,“>:'4)
and (3) pressure drop evaluation of filter media‘) as well as
other novel techniques. One of the principle goals of each of
these efforts has been to identify or develop an instrument that
will give short-term or real-time measurements of worker dust
exposure.

561


PARTICULATE PENETRATION OF POROUS FOAM 567
100 T T T T T T
L Key 4
?

z > 00-52 7 © 250mL/min, 4mm sampler
is 80F 00° @1.7L/min cyclone 4
3s ft ° ;
we
ira
Ww 6oF 4
3
= fF 3 4
ir
2 40+ ° 4
s) °

- So 4
$ 20 ° .
a
a a o 4

l 1 1 1 1 3 Sig
0 1 2 3 4 5 6 7

AERODYNAMIC DIAMETER (d), pm

FIGURE 6
Comparison of the 4 mm tube with 90 ppi foam classifier operated at a flow rate of 250 ml/min with the 1.7 L/min nylon cyclone
penetration function determined in Figure 5.

Assessment of personal respirable dust exposure is an impor-
tant step in eliminating many dust-related occupational illnesses
and diseases. One method of eliminating occupational dust dis-
eases by reducing worker dust exposure is effective monitor-
ing with immediate feedback of exposure results to workers.
However, analysis of the filter obtained from the conventional
gravimetric sampler method used in coal mining takes several
weeks to process before results are reported to the mine. As
stated earlier, one of the recommendations of the Report of the
Secretary of Labor’s advisory committee was to develop an in-
strument that will give short-term or real-time measurements of
worker dust exposure. The concept of the dust dosimeter was
developed to provide an inexpensive, short-term measurement
of the cumulative personal dust exposure of a worker during a
shift, but not intended to be a replacement or substitute of the
current approved dust sampler used to determine compliance
with federal regulations. The results of the presently described
work demonstrates that a low flow rate configuration of porous
foam can reasonably pattern the penetration of the 10 mm ny-
lon cyclone which is currently used for measuring respirable
coal mine dust exposure. Because of this, the porous foam can
be used as a respirable particulate classifier in a low cost, dis-
posable dust dosimeter configuration currently under develop-
ment.

CONCLUSIONS

A small-diameter tube with 90 ppi foam and 250 ml/min flow
rate at a face velocity of 33 cm/sec yields a 50 percentcut pointof
4 wm and may possibly be used as a classifier of respirable dust.
This configuration has been found to approximate the 10 mm
nylon cyclone particulate penetration at 1.7 L/min. Cut point
variation with foam face velocity in different tube sizes was not
significant. Laboratory tests for tube diameters of 4.0, 6.3, and
12 mm suggest that the primary collection mechanism of the
detector tube is inertial impaction within the foam and not wall
losses or sedimentation.

REFERENCES

1, American Conference of Governmental Industrial Hygienists
(ACGIH): Threshold Limit Values for Chemical Substances
and Physical Agents and Biological Exposure Indices. ACGIH,
Cincinnati, OH (1999).

2. International Standards Organization (ISO): Air Quality-Particle
Size Fraction Definitions for Health-Related Sampling. Draft Int.
Standards ISO Tech. Rpt., ISO/TR 7708-1983 (E), ISO, Geneva
(1993).

. Soderholm, S.C.: Proposed International Conventions for Particle
Size-Selective Sampling. Ann Occup Hyg 33(3):301-320 (1989).

»


562

A dust dosimeter concept study using the pressure drop
method was evaluated for feasibility." Because the new dust
dosimeter was to operate at a flow rate of about 250 ml/min, a
respirable classification device such as the 10 mm cyclone that
operates at 1.7 or 2.0 L/min could not be used. An integral part
of the dosimeter is a section of porous foam that provides an
approximate respirable classification of airborne dust. Chen et
al."7) evaluated various porous foam combinations of pore den-
sity and thickness in the same face velocity range as the present
study, 25-50 cm/s. However, because the diameters were large,
being on the order of 25 mm, the flow rates were approximately
10 L/min. Chen’s recommendation was that the sampler could be
miniaturized for smaller sampling flow rates to fit the capacity of
personal sampling pumps. The present study involves miniatur-
ization to a significantly smaller flow rate. Also, because porous
foams have been demonstrated by Aitken“® to be respirable
classifiers at approximately 2.0 L/min and have numerous ad-
vantages, they appeared to be a viable choice for a 250 ml/min
flow rate sampler. However, it is important to have well-defined
foam porosities (in the present context, uniform compression of
foam) from sampler to sampler and this variability should be
determined.

Specifically, to match the 10 mm nylon cyclone classification
as used by MSHA, the classifier required must (1) provide nearly
100 percent filtration of particles greater than 7 xm equivalent
aerodynamic diameter (EAD), (2) allow a percentage penetra-
tion of respirable particle sizes, and (3) not provide a significant
Pressure restriction, either initially or during sample collection.
These characteristics are also those usually associated with low-
efficiency filters. The porous foam classification technique takes
advantage of the typical disadvantage of virtually all dust filtra-
tion concepts—a decreasing collection efficiency for particle
sizes below 10 jzm. The objective of this work is to evaluate
the particulate penetration of porous foam for application as a
size selective device within an inexpensive, disposable, short-
term respirable dust measurement device which approximates
the 10 mm nylon cyclone penetration operated at a flow rate of
1.7 L/min.

EXPERIMENTAL METHODS

Materials

The tests used nominal 90 ppi (pore per inch) foam (PCF
Foam Corporation of America, Hamilton, Ohio) plugs approxi-
mately 25 mm in length. Pore sizes were measured by Foam-X
Corporation (Eddystone, Pennsylvania) using both microscopy
and pressure measurements. Plugs of diameter 4, 6.3, and 12mm
were mounted in glass tubes. Figure 1 shows the specific tube
configuration for testing the 4.0 mm foam plugs. Larger tube
diameters 6.3 and 12 mm were used without the 4 mm insert to
hold the large diameter foam sections. Three similar tubes were
constructed with the 4.0 mm foam to estimate the inter-sampler
variability.

S.J. PAGE ET AL.

>~—

43 mm

'

To APS

FIGURE 1
Construction of the 90 pores per inch (ppi) foam particle
classifier used to obtain a respirable size fraction.

Procedures

‘The porous foam and 10-mm nylon cyclone sampler penetra-
tion curves were measured using the sampler exposure system
shown in Figure 2. The aerosol was generated from an ultrasonic
nebulizer (Sonotek, Poughkeepsie, New York) that was fed a so-
lution of triethanolamine (TEA) in isopropanol from a syringe
pump. The nominal droplet size from the nebulizer was 30 um
with a geometric standard deviation (GSD) = 1.3. The final
droplet median aerodynamic diameter of approximately 4 zm
was selected by using a dilution of 4 g/L of TEA in isopropanol.
This centered the mode at the sample cutpoint to optimize sta-
tistical precision in this range. The droplets were transported to
the collection chamber for further mixing and dilution.

The sampler penetration was measured with an Aerosol Parti-
cle Sizer (APS3300, TSI, St. Paul, Minnesota), the use of which


PARTICULATE PENETRATION OF POROUS FOAM 563
15 L/m
To compressed
laboratory <— air
vacuum
To aye
i——— -~ Aerodynamic — triethanolamine
Particle in isopropanol
Sizer 3300
Sonotek
ultrasonic nebulizer
Blank 7 — Test foam at 6.6 watts
=——
TM -— Fiow
straightener
Foam air
inlet
Sample chamber Particle generation
chamber
FIGURE 2

Laboratory apparatus used to generate the test aerosol.

has been adequately described previously."7!*~ The APS cal-
ibration was checked using monodisperse latex particles (Bangs
Laboratories, Inc., Fishers, Indiana). Size measurements of some
oil droplets were found to be incorrect for the APS because of
droplet distortion in the high acceleration sensor region of the
APS."!:22) TEA was chosen for the penetration measurements
because its high viscosity would reduce distortion. Measurement
of TEA droplets generated with a vibrating orifice monodis-
perse aerosol generator (Model VOMAG, TSI, Inc., St. Paul,
Minnesota) suggested that TEA droplet distortion did not occur
and accurate particle size measurements could be made with this
material. Measurements of the TEA polydisperse test aerosol us-

ing impactors of known cutpoints (Table I) showed agreement
with the APS, suggesting that errors due to either droplet dis-
tortion or otherwise did not occur. The ultrasonic nebulizer thus
produced spherical particles within a stable size distribution with
controllable median size.

The size distributions used to determine the porous foam pen-
etration were measured alternately using tubes with and without
(blank reference measurement) the foam material. The size dis-
tributions used to determine the cyclone penetration were mea-
sured in the same manner. The reference distributions before
and after each sampler test were averaged channel-by-channel of
APS counts, where possible, to reduce bias due to small changes

TABLE I
Classifier data obtained to verify aerosol particle sizer (APS) calibration
50% cut 50% cut

Flow rate point, zm, point, um,

Test material Classifier mi/min measured _ calculated
Triethanolamine —Impactor #1 760 27 2.7
Triethanolamine —Impactor #2 200 2.9 29
Triethanolamine Cyclone 1700 4.0 40