United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-97/011 April 1997
&EPA Project Summary
Fractional Penetration of Paint
Overspray Arrestors
Charles H. Darvin
The report describes the develop-
ment of fractional penetration curves
for liquid droplet penetration of
overspray arrestors for discrete drop-
let diameters from 0.3 |jin to 10 |jm.
(NOTE: fine participate are particles
with diameters of 10 |jin or less.) These
data points were obtained for two con-
ditions: 1) for a clean arrestor and 2)
for an arrestor coated with paint. The
paint was applied to the arrestor by
spraying high solids baking enamel
from a spray gun directed at the paint
overspray arrestor with the air flowing
a face velocity of 120 fpm (0.61 mis).
Paint overspray arrestors tested can
be grouped into three generic designs.
This work demonstrated that, for the
conditions of the tests, the behavior of
the paint overspray arrestor is peculiar
to the design of the arrestor. The pro-
gram also defined the efficiency of the
test method used to define the frac-
tional penetration.
The results indicated that, with the
five different arrestor systems tested,
the 50% cutoff diameter (where at least
50% of the particles will be captured
by the arrestor) ranged from 3 to 7 |jm.
The two-stage polyester bag system
showed the smallest cutoff diameter at
approximately 3 |am. The inertia! sepa-
rator system designs exhibited the
greatest cutoff level at approximately 7
|jm.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory's Air Pollution
Prevention and Control Division, Re-
search Triangle Park, NC, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
A request for technical assistance was
received by EPA's Control Technology
Center (CTC) from the City of Philadel-
phia, PA, to evaluate the relative emis-
sions from various dry paint arrestors. A
study was initiated by the CTC to develop
the requested data. The results of the
initial study indicated that most dry arres-
tors operate at 90 to 99+ % arrestance -
based on a total weight capture basis.
However, it was also determined from
these studies that the capture of particles
less than 10 u.m in diameter (PM10) var-
ied significantly for different designs. This
suggested that, although the efficiency in
terms of total weight captured is high, the
capture efficiency for fine particulates could
be vastly different. This is because fine
particulates comprise only a small per-
centage of the total mass of paint
overspray, and thus their capture is not
significant in the total weight method.
Based on these findings, additional study
was commissioned by the CTC to evalu-
ate the fine particulate emissions (frac-
tional penetrations) of the various dry paint
overspray arrestor designs.
Fractional Penetration
A test protocol was developed to mea-
sure the fractional penetration of aerosol
droplets emitted (penetrating) through paint
overspray arrestors. Fractional penetration
is defined as the fraction of particles or
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droplets of a given size that avoid capture
when challenging an air cleaning device;
e.g., a filter or separator. Fractional pen-
etration is equal to 1 minus the capture
efficiency of the arrester. Capture efficiency
and fractional penetration are both func-
tions of the particle or droplet diameter.
The droplet diameter at which 50% of
the droplets penetrate the device (the re-
maining 50% are captured) is termed the
"cutoff diameter." The "cutoff diameter" is
only one of many descriptive criteria for
separation devices and is deemed appro-
priate to define paint overspray arrester
efficiency in the fine particulate PM10
range.
Research Test
The research was performed in a spe-
cially outfitted single pass wind tunnel that
allowed for spraying paint onto the paint
overspray arresters. The air flow was con-
trolled to provide a 120 fpm (0.61 m/s)
face velocity at the filter. The procedure
measured the droplets in discrete size
ranges both upstream and downstream of
the paint arrester. The ratio of downstream
concentration to upstream concentration
for each size range was determined as
the fractional penetration for that specific
range of particle or droplet diameter. The
fractional penetration of each paint
overspray arrester design tested for this
program was initially measured in a clean
condition, and then measured again after
being coated with a high solids baking
enamel.
The data quality objective (DQO) of the
project was quantification of fractional pen-
etration to within 0.1 at the 90% confi-
dence level over the particle size range
from 0.3 |im to 10 |im, and to resolve the
particle or droplet diameter plus or minus
20%, in an air flow velocity of 120 fpm at
the filter face. This DQO was met for
98.5% of the data.
The test procedure used during this pro-
gram was developed to permit an assess-
ment of the fine particulate capture capa-
bility of paint overspray arresters. It was
specifically developed to avoid the mea-
surement interference presented by a
weight efficiency method. This report gives
the procedure for performing the tests and
the results of testing five types of paint
overspray arresters.
Results
The five different paint overspray arres-
ters that were tested exhibited a range of
cutoff diameters from 3 |im to 7 |jm
The measurement of fractional penetra-
tion indicated that the PM10 penetration
varied widely between designs. The two-
stage polyester bag paint arrester showed
the smallest cutoff diameter of all systems
tested. This system achieved a 50% frac-
tional penetration at the 3 |im droplet di-
ameter.
Fiber-filter-based designs tended to main-
tain their fractional penetration after loading
with paint. The inertial-separator-based de-
signs maintained their fractional penetra-
tion after loading with paint, resulting in
cutoff diameters of greater than 6 urn.
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Charles H. Darvin (also the EPA Project Officer) is with the Air Pollution Prevention
and Control Division, National Risk Management Research Laboratory, Research
Triangle Park, NC 27711 (see below).
The complete report, entitled "Fractional Penetration of Paint Overspray Arresters,"
(Order No. PB97-147953; Cost: $28.00, subjectto change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/SR-97/011
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