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. ------- 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, ------- 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. ------- 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 ------- 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 BULK RATE POSTAGE & FEES PAID EPA PERMIT NO. G-35 EPA/600/SR-96/138 ------- |