United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-96/138 December 1996
EPA Project Summary
Evaluation of Styrene
Emissions from a Shower Stall/
Bathtub Manufacturing Facility
Larry Felix, Randy Merritt, and Ashley Williamson
Current EPA emission factors (AP-
42) for styrene emissions from the pro-
duction of polyester-resin-reinforced
plastic products represent a compos-
ite of spraying and post-spraying emis-
sions (from curing molds) from shower
stall/bathtub manufacturing plants that
use compressed-air-powered spray
guns to apply catalyzed styrene resins
to prepared molds. Because each step
of manufacture (gel coating, first-stage
spray lay-up, and second-stage spray
lay-up) creates large surface areas from
which volatile styrene monomer can
evaporate, non-spraying emissions can
constitute a large fraction of the sty-
rene emitted to the atmosphere. Thus,
it is of interest to quantify the level of
non-spraying styrene emissions char-
acteristic of this industry to validate
current emission factors for spraying,
as well as to develop emission factors
for emissions not directly related to a
spraying activity.
In this study, emissions were mea-
sured at a representative facility (Eljer
Plumbingware in Wilson, IMC) that
manufactures polyester-resin-rein-
forced shower stalls and bathtubs by
spraying styrene-based resins onto
molds in vented, open, spray booths.
Styrene emissions were characterized
for the three stages of manufacture by
measuring styrene concentrations at
the vents of spray booths used in each
part of the process. In addition, sty-
rene concentrations were measured at
each ventilation fan exhaust. Emission
levels were determined using EPA
Method 18 to obtain integrated emis-
sions samples and total hydrocarbon
analyzers to measure continuous emis-
sions levels during the EPA Method 18
sampling.
Analysis of the EPA Reference
Method data indicates that: (1) styrene
monomer is the only volatile organic
compound released in this process; (2)
overall, approximately 4% of all mate-
rial sprayed is lost to atmospheric emis-
sions as styrene (approximately 19%
of styrene sprayed); and (3) emissions
vary for each phase of manufacture,
with post-spraying emissions of sty-
rene (from curing molds) constituting a
large part, approximately 29%, of all
emissions.
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
Current EPA emission factors (AP-42)
for styrene emissions from the production
of polyester-resin-reinforced plastic prod-
ucts do not specifically account for post-
spraying emissions (from curing molds)
from shower stall/bathtub manufacturing
plants that use compressed-air-powered
spray guns to apply catalyzed styrene res-
ins to prepared molds. Because each step
of manufacture creates large surface ar-
eas from which volatile styrene monomer
can evaporate, post-spraying emissions
can constitute a large fraction of the sty-
rene emitted to the atmosphere. Thus, it
is of interest to quantify the level of spray-
ing and post-spraying styrene emissions
characteristic of this industry to validate
current emission factors for spraying, as
well as to develop emission factors for
post-spraying emissions.
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Shower stalls and bathtubs are among
the many products fabricated from liquid
polyester resin that have been extended
with various inorganic filler materials and
reinforced with glass fibers. These com-
posite materials are often referred to col-
lectively as fiberglass-reinforced plastic or
"fiberglass." Depending on the size, shape,
and intended use, any one of several
manufacturing processes can be used for
fabrication. For the manufacture of shower
stalls and bathtubs, the preferred tech-
nique is spray lay-up or sprayup. All of
these processes involve the application of
a liquid resin that is mixed with a catalyst
to initiate polymerization. In polymeriza-
tion, a liquid unsaturated polyester is cross-
linked with a vinyl-type monomer, usually
styrene, by the action of the catalyst. Com-
mon catalysts are organic peroxides, typi-
cally methyl ethyl ketone peroxide or ben-
zoyl peroxide. Resins may contain inhibi-
tors to avoid self-curing during resin stor-
age, and promoters to allow polymeriza-
tion to occur at lower temperatures.
In the production of fiberglass shower
stalls and bathtubs exhaust air from the
spray booths used for mold-coating and
plant ventilation air outlets represent the
major point sources of VOC emissions.
Thus, at a particular facility, the number of
manufacturing steps that involve the spray-
ing of styrene-based resins, the amount
of styrene sprayed in each step of manu-
facture, and the amount of styrene that is
volatilized during the spraying and curing
of molds determine the amount of styrene
emitted to the atmosphere.
This study was undertaken to quantify
styrene emission factors at a shower stall/
bathtub manufacturing plant determined
by the EPA to be a representative facility.
Once styrene emissions were measured,
the emissions measurements and raw
material usage data from the plant were
used to determine emission factors for
each phase in the manufacturing process.
Testing was carried out at Eljer
Plumbingware, Wilson, NC, and was part
of a larger effort that also involved the
evaluation of a pilot-scale liquid chemical
scrubber for styrene removal. Styrene
emissions measurements were originally
scheduled for the week of June 14, 1993,
and the liquid chemical scrubber evalua-
tion was originally scheduled for the fol-
lowing week. Because the plant was op-
erating on a 4-day production week dur-
ing this time (Monday through Thursday),
instead of the 5-day production week that
had been expected, emissions testing had
to be extended through Monday, June 21,
1993, to obtain a suitable set of emissions
data. A full day of testing could not be
carried out on Monday because portions
of that day had to be devoted to preparing
for the upcoming liquid chemical scrubber
evaluation.
Section 2 of the full project report con-
tains a detailed description of the facility
and sampling locations. Detailed descrip-
tions of the sampling methodology are
presented in Section 3 and the results of
this evaluation along with a discussion of
these results are presented in Section 4.
The quality assurance and quality con-
trol measures taken during this evalua-
tion, as well as the results of these mea-
sures, are contained in the Quality Con-
trol Evaluation Report as Appendix A. This
project summary briefly addresses the
methodology and emission rate conclu-
sions from the study. More detailed infor-
mation can be obtained from the report
sections described above.
Two methods were used to measure
styrene emissions. A heated Tedlar™ bag
sampler was used to obtain an integrated
sample of the contaminated air exiting a
representative point in each process ex-
haust vent. Concurrently, styrene emis-
sions were measured on a continuous ba-
sis using a total hydrocarbon (THC) ana-
lyzer equipped with flame ionization de-
tectors. Sample times ranged from 40 to
45 minutes, typically the time required to
spray eight to ten molds. Sample times
were dictated by the plant production rate
and the time available for sampling during
a particular period of spraying.
Table 1 presents average styrene emis-
sions as a function of the area sprayed,
the total mass that was sprayed, and the
total amount of styrene that was sprayed.
Styrene emissions based on measure-
ments with the THC analyzers were gen-
erally greater than those determined by
Method 18. This result is somewhat unex-
pected because one might suspect that
some styrene would be lost in the long
heated sampling lines used to convey the
ventilation air samples to the THC analyz-
ers. Apparently, that was not the case for
these measurements. However, as Table
1 shows, within the uncertainty of the data,
styrene emissions as determined from
THC data and from Method 18 data do
overlap. It should be emphasized that be-
cause of the lack of multiple measure-
ments, no uncertainty could be determined
for styrene emissions not captured by
spray booth exhaust fans (based on THC
analyzer data). Therefore, the uncertain-
ties in Table 1 are minimum values. The
lack of multiple measurements for such
emissions is especially unfortunate be-
cause styrene emissions not captured by
active spray booth exhaust fans are one
of the largest sources of styrene emis-
sions.
Research conducted subsequent to the
above analysis of test results has also
shown differences between EPA Method
18 measurements of styrene emissions
and those using THC analyzers. How-
ever, the reason for these differences
remains the subject of research. It has
been suggested that in the Method 18
procedure styrene can polymerize be-
fore analysis and may also have a very
low vapor pressure at stack or instru-
ment conditions. Both of these condi-
tions would result in a lower measure-
ment for styrene.
Although it is not specifically noted in
AP-42, it is reasonable to assume that
styrene emission factors cited in this stan-
dard for polyester resin plastics products
fabrication include emissions not captured
by active spray booths. Thus, in order to
compare the results obtained in this study
with those cited in AP-42, it is necessary
to apportion non-spray booth emissions
to those parts of the process associated
with spraying operations: gel coating, lay-
up, and back-up. When such an appor-
tionment is carried out, with the data
obtained at Eljer, the following emission
factors are obtained:
• Gel Coat - 47.5% of the styrene
sprayed in that phase of manufac-
ture
• Lay-Up - 20.0% of the styrene
sprayed in that phase of manufac-
ture
• Back-Up - 12.1% of the styrene
sprayed in that phase of manufac-
ture
These data suggest that spray booth
emissions are higher than those cited in
AP-42 for gel coating and spray lay-up.
AP-42 cites a value from 26% to 35% of
styrene monomer being emitted for gel
coat that contains no vapor suppressing
additives (as was the case at Eljer). Like-
wise, these results show that when non-
spraying emissions are apportioned to
each part of the manufacturing process
nearly 48% of the styrene in the gel coat
mix is lost to the atmosphere.
As might be expected AP-42 makes no
distinction between styrene emissions from
lay-up booths or from back-up booths,
and indicates that with vapor suppressing
additives in the mix, from 3% to 9% of the
styrene sprayed in this operation is emit-
ted. If vapor-suppressing additives are not
added to the mix, emissions rise to from
9% to 13% of the styrene sprayed. At
Eljer, vapor suppressants are added to
the lay-up and back-up mix. However,
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Table 1. Styrene Emissions for Each Part of the Manufacturing Process
(a) Styrene Emissions per Unit Area of Mold Sprayed
THC Analyzer
EPA Method 18
Emissions from:
Gel Coat Booths
Lay-Up Booths
Back-Up Booths
Non-Spray Booth Emissions
All Emissions
Styrene (g/m2)
110.5
116.0
68.7
83.7
378.9
Pop. Std. Dev. (g/m2)
21.2
43.1
3.8
N/A
48.1*
Styrene (g/m2)
69.5
85.5
51.9
83.7
290.6
Pop. Std. Dev. (g/m2)
26.4
28.3
12.6
N/A
40.7*
(b) Percent of Total Mass Used in Each Stage of Manufacture That Was Emitted as Styrene
THC Analyzer
EPA Method 18
Emissions from:
Gel Coat Booths
Lay-Up Booths
Back-Up Booths
Non-Spray Booth Emissions
All Emissions
Styrene (%)
14.3
3.4
2.4
1.2
5.4
Rel. Std. Dev. (%)
2.7
1.3
1.5
N/A
0.7*
Sytrene (%)
9.0
2.5
1.8
1.2
4.2
Rel. Std. Dev. (%)
3.4
0.8
0.4
N/A
0.6*
c) Percent of Styrene Used in Each Stage of Manufacture That Was Emitted
THC Analyzer
EPA Method 18
Emissions from:
Gel Coat Booths
Lay-Up Booths
Back-Up Booths
Non-Spray Booth Emissions
All Emissions
Styrene (%)
44.4
16.1
11.4
5.3
24.2
Rel. Std. Dev.
8.5
6.0
0.6
N/A
3.3*
Styrene (
27.9
11.9
8.6
5.3
18.6
Rel. Std. Dev. (%)
10.6
3.9
2.1
N/A
2.8*
'Minimum estimate. Assumes each process independent with no contribution from the non-spraying emissions component.
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the levels of styrene emissions measured
there suggest that the emissions levels
are probably higher than what AP-42 cites
as typical for non-vapor suppressed emis-
sions, particularly for the lay-up phase of
manufacture. Thus, results calculated ac-
cording to the above apportioning proce-
dure show that styrene emissions to the
atmosphere averaged 20% of the styrene
sprayed in the lay-up booths and 12% of
the styrene sprayed in the single back-up
booth.
These generally higher-than-expected
emission levels may be due, at least in
part, to the nature of the process. At the
Eljer facility (determined by the EPA to be
a representative facility) molds that have
been sprayed are frequently left near the
mouths of spray booths where spraying is
in progress. Hence, styrene evolved from
a curing mold can be captured by an
adjacent spray booth. While this practice
is not common in the gel coat booths
(because of limited space in front of the
booths at the Eljer facility), this practice is
an integral part of the manufacturing pro-
cess for the latter two stages of spraying.
In fact, at any one time, it is common for
as many 15 molds to be in various stages
of manufacture in the general vicinity of
the lay-up and back-up booths. Also, molds
are generally left in a lay-up booth be-
tween sprayings where the surface of the
mold is rolled flat. In AP-42 it is noted
that styrene emissions are increased by
such manual rolling.
Finally, AP-42 provides no separate es-
timate of styrene emissions not captured
by spray booths. While such emissions
are certainly a function of ventilation sys-
tem design and the specific equipment at
a given facility, at Eljer it was found that
6% of all the styrene sprayed exits the
facility through openings other than spray
booth exhausts. As noted in Table 2, this
corresponds to from 22 to 29% (depend-
ing on the measurement method) of all
styrene emitted to the atmosphere; thus,
styrene emissions not captured by spray
booths represent a source of styrene emis-
sions as great as (or possibly greater than)
styrene emissions associated with any one
of the spraying operations.
Table 2. Distribution of Styrene Emissions from Each Part of the Manufacturing Process, Including Styrene Emissions Not Captured by Spray Booths
Date
From THC Analyzer Measurements
Gel Back-
Coat Lay-Up Up Non- All
Booths Booths Booths Spraying Sources
From Method 18 Measurements
Gel Back-
Coat Lay-Up Up Non-
Booths Booths Booths Spraying
All
Sources
6/15/93
6/16/93
6/17/93
Average
29.9
29.2
29.2
29.4
30.2
30.5
30.6
30.5
17.9
18.1
18.2
18.0
22.0
22.2
22.0
22.1
100.0
100.0
100.0
100.0
24.5
24.0
24.0
24.2
29.1
29.3
29.5
29.3
17.6
17.8
17.9
17.7
28.8
28.9
28.6
28.8
100.0
100.0
100.0
100.0
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Larry Felix, Randy Merritt, and Ashley Williamson are with Southern Research
Institute, Birmingham, AL 35255.
Bobby E. Daniel is the EPA Project Officer (see below).
The complete report, entitled "Evaluation ofStyrene Emissions from a Shower Stall/
Bathtub Manufacturing Facility,"(Order No. PB97-125439; Cost: $21.50, subject to
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
Official Business
Penalty for Private Use $300
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EPA
PERMIT NO. G-35
EPA/600/SR-96/138
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