MEMORANDUM

Date: December 11, 2013

Subject: MACT-Allowable Emissions and Risks for the Acrylic and Modacrylic Fibers, 

Amino/Phenolic Resins, and Polycarbonate Production Source Categories

From: Lesley Stobert, EC/R Incorporated

To: Paula Hirtz, EPA/OAQPS/SPPD

Nick Parsons, EPA/OAQPS/SPPD

______________________________________________________________________________

The purpose of this memorandum is to present analyses related to “MACT-allowable” 

emissions levels and risks for the Acrylic and Modacrylic Fibers Production (AMF), 

Amino/Phenolic Resins Production (APR), and Polycarbonate Production (PC) source categories 

that are being addressed under EPA’s Risk and Technology Review (RTR) program. 

The RTR program is addressing the statutory requirements in section 112(f) and 

112(d)(6) of the Clean Air Act for federal air toxics regulations. The regulations are National 

Emission Standards for Hazardous Air Pollutants (NESHAP) contained in 40 CFR part 63. They 

are commonly referred to as Maximum Achievable Control Technology (MACT) standards. The 

emissions data being used for the RTR risk assessments for these categories consist of data 

representative of “actual” emission levels. In addition to the risks associated with these actual 

emission levels, EPA also considers the levels of HAP emissions that sources could emit and still 

be in compliance with the applicable MACT regulation. These emission levels are referred to as 

“MACT-allowable” emissions. The purpose of this memorandum is to discuss these MACTallowable emission levels and to relate the potential risks if facilities emitted at these levels.

This memorandum is organized as follows. Section 1 presents the estimated maximum 

risk levels based on the actual emission levels for each source category, and Section 2 discusses 

the basic approach to estimating the risks at the MACT-allowable levels. This is followed by a 

discussion of the estimation of the MACT-allowable emission level for each MACT standard in 

Section 3, particularly as it relates to the actual emission levels used in the risk assessments. This 

discussion is followed by a presentation of the estimated risks at these MACT-allowable levels.

1.0 Risk Levels Based on Actual Emissions

The estimated maximum inhalation risks for these source categories are summarized in 

Table 1. These risks are based on actual emission levels.
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Table 1. Summary of Estimated Inhalation Risks for the AMF, APR, and PC Production 

Based On Actual Emissions Levels

Source Category

Maximum individual 

cancer risk (in a 

million)1

Maximum chronic 

noncancer TOSHI2

Acrylic and Modacrylic Fibers Production 20 0.1

Amino/Phenolic Resins Production 9 0.2

Polycarbonate Production 0.3 0.04

1 Maximum individual excess lifetime cancer risk.

2 Maximum target organ specific hazard index (TOSHI). Target organ system represented by the TOSHI may vary 

across source categories. The maximum TOSHI is based on respiratory effects for the AMF, APR and PC source 

categories. 

2.0 Approach to Estimating Risks from MACT-Allowable Emission Levels

Detailed MACT-allowable emissions information is not available on an emission pointspecific level. Therefore, modeling was not conducted to estimate the risks from MACTallowable emission levels.

The basic approach to estimate the risks from MACT-allowable emission levels was to 

first estimate the relationship between the actual and MACT-allowable emission levels, and then 

to estimate the potential risk impacts from the differences between actual and MACT-allowable 

emissions. In general, the risk impact was assumed to be proportional to the difference in 

emission levels. For example, if MACT-allowable emissions were estimated to be three times as 

high as actual emissions, it was assumed that risks could be as much as three times as high as 

those estimated from the modeling conducted using actual emissions.

This assumption regarding the linear relationship between emissions and risks is 

generally reasonable for chronic cancer and noncancer risks. However, using this approach for 

acute risks would likely overestimate the impacts. The acute assessment already has numerous 

built in conservative assumptions. First, the acute assessment assumed a short-term emission rate 

up to 10 times that of the average longer term emission rate. Also, the maximum acute risks 

assume the simultaneous occurrence of independent factors that may vary greatly, such as hourly 

emissions rates, meteorology, and human activity patterns. In the assessment using actual 

emissions, EPA assumed that individuals remained for 1 hour at the point of maximum ambient 

concentration as determined by the co-occurrence of peak emissions and worst-case 

meteorological conditions. These assumptions would tend to overestimate actual exposures since 

it is unlikely that a person would be located at the point of maximum exposure during the time of 

worst-case impact. The addition of another factor to account for the MACT-allowable emissions 

level would further increase the conservativeness of the estimated MACT-allowable acute risks. 
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Therefore, this analysis does not discuss acute risks or estimate acute risks for the MACTallowable emissions level.

3.0 Results of Analysis

a. Acrylic and Modacrylic Fibers Source Category

The AMF NESHAP addresses emissions from the following types of emission sources: 

(1) storage vessels used to store acrylonitrile, (2) continuous process vents, (3) fugitive emissions 

from spinning lines, (4) wastewater, and (5) equipment leaks. Table 2 summarizes the formats of 

the standards for these emission points.

Table 2. Formats of Standards for the AMF NESHAP

Emission Source Type Format of Primary Standard

Acrylonitrile Storage Tanks Performance Standard (% reduction) or Equipment 

Standards

Continuous Process Vents Performance Standard (% reduction)a

Spinning Lines (new facility or facility uses a 

spin dope produced from a solution 

polymerization process)

Performance Standard (% reduction)b

Equipment Leaks Work Practice Standards

Wastewater Equipment Standards, Performance Standard

a The NESHAP contains alternative standards to reduce emissions on a kg emissions/hour basis for hydrogen halides 

and halogens and to reduce total organic carbon based to a specified concentration 

b The NESHAP contains alternative standards to reduce emissions to a kg/Mg product basis or a specified spin dope 

concentration of acrylonitrile

The ability to estimate MACT-allowable emissions for specific emission points, or for 

specific emission point types, is largely dependent on the format of the standards. For work 

practice standards, there would be no difference between actual and MACT-allowable emissions 

for emission sources, provided the facility is not conducting additional work practices proven to 

reduce emissions beyond those required in the rule. We are not aware of any such situations at 

the one facility in this source category. Therefore, for equipment leaks, which are subject to work 

practice standards, we believe that the actual emission levels are a reasonable estimation of the 

levels allowed by the standard.

For wastewater emission sources, the regulation includes an assortment of equipment and 

performance standards. For equipment standards, the one source that is subject to the regulation 

is required to install specific equipment. Assuming that the equipment is maintained properly and 

is in good working condition (as required), there would not be a difference in the actual 

emissions level and the level allowed by the standard. In general, it is possible that sources could 

overcontrol emission sources subject to a performance standard. This would result in the actual 

emissions being lower than the MACT-allowable emissions. However, for wastewater sources, 

we are not aware of any such overcontrol. Therefore, we believe that the actual wastewater 

emission levels are a reasonable estimation of the levels allowed by the standard.
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For continuous process vents, which are subject to a performance standard, the sources 

could utilize control devices that achieve emissions reductions greater than the required 98 

percent reduction of acrylonitrile or 99 percent reduction in hydrogen halides and halogens. 

However, the continuous monitoring requirements of the rule result in situations where 

reductions at or above these required levels are required on a continuous basis. Specifically, the 

owner or operator is required to conduct performance tests to demonstrate initial compliance. 

During the test, they are required to monitor a specific parameter (e.g., temperature for a thermal 

incinerator). From the data collected during the test, they are required to calculate a parameter 

level (e.g., a minimum temperature) that is indicative of the control device performance achieved 

during the test. Ongoing compliance is then determined based on the continuous monitoring of 

this parameter as compared to the established level (e.g., if the incinerator temperature falls 

below the minimum temperature established during the test it would be an excursion). Therefore, 

if an incinerator was achieving a 99.5 percent emission reduction during the performance test, 

the temperature level established based on monitoring data collected during the test would be 

reflective of a 99.5 percent reduction. Thus, the performance level required by the rule would, in 

effect, be 99.5 percent. Because of these requirements, we assume that the actual emission levels 

are a reasonable estimation of MACT-allowable emissions for continuous process vents.

For acrylonitrile storage vessels, a facility may choose to either comply with a 95 or 98 

percent reduction performance standard, depending on the type of control device used, or to 

comply with equipment standards. As discussed above, it is reasonable to assume that the actual 

emissions from those sources complying with equipment standards are representative of the 

MACT-allowable emissions. If the facility complies using the performance standard, actual 

emissions reductions could be greater than the required reductions. The one operating facility 

uses a closed vent system routed to a combustion device for emissions reduction and is required 

to reduce emissions by 98 percent. The performance of this system is estimated to reduce 

emissions by over 98 percent. However, as discussed above for continuous process vents, the 

continuous monitoring requirements of the rule result in the situation where reduction at or above 

this level is required on a continuous basis. Because of these requirements, we assume that the 

actual emission levels are a reasonable estimation of MACT-allowable emissions for storage 

vessels.

The one facility in the source category is categorized as an “existing source” and has a 

fiber spinning line that uses a spin dope produced from a solution polymerization process. There 

are no emission reduction requirements for this type of spinning line at this type of facility. 

Therefore, the actual emission levels are the levels allowed by the standard.

In summary, the risks based on the “MACT-allowable” emissions levels are shown in 

Table 6 and are equal to the risks at the actual emissions levels for the AMF NESHAP.

b. Amino/Phenolic Resins Production

The APR NESHAP addresses emissions from the following types of emission sources: 

(1) storage tanks, (2) continuous process vents, (3) batch process vents, (4) heat exchange 

systems, and (5) equipment leaks. Table 3 summarizes the formats of the standards for these 

emission points.
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Table 3. Formats of Standards for the APR NESHAP

Emission Source Type Format of Primary Standard

Storage Tanks (new sources only) Equipment Standards, Performance Standards (% 

reduction), or Concentration Limit

Continuous Process Vents (new sources 

only) Performance Standard or Concentration Limit

Batch Process Vents Performance Standard or Concentration Limita

Heat Exchange Systems Work Practice Standards

Equipment Leaks Work Practice Standards

a The NESHAP contains an alternative standard to reduce emissions on a kg emissions/Mg product basis

For equipment leaks and heat exchange systems, which are subject to work practice 

standards, we are not aware of any facilities conducting additional work practices proven to 

reduce emissions beyond those required by the rule. Therefore, we believe the actual emission 

levels are a reasonable estimation of the levels allowed by the standards for this equipment.

For storage vessels and continuous process vents, all facilities identified as currently 

operating major sources subject to the APR MACT standards are existing sources. As existing 

sources have no control requirements for storage vessels and continuous process vents, actual 

emissions are equal to allowable emissions for these sources. 

For reactor batch process vents, organic HAP are required to be reduced by 83 percent at 

existing sources and 95 percent at new sources. For non-reactor batch process vents, across the 

collection of all non-reactor batch process vents within the affected source, organic HAP are 

required to be reduced by 62 percent at existing sources and 76 percent at new sources. All of the 

facilities included in the risk assessment for the source category were operating before the 

MACT standards for APR took effect and are therefore existing sources. For reactor batch 

process vents, the existing MACT floor is based on the arithmetic average of the control device 

performance of the top five facilities. It is likely that at least some facilities that needed to 

upgrade equipment to meet the MACT standard installed equipment that achieves greater than 83 

percent control, and according to the data gathered during the development of the MACT 

standards, this control level could be up to 95 percent. In these cases, 17 percent of organic HAP 

would be emitted at the MACT-allowable level, and it is possible that facilities are actually only 

emitting 5 percent (i.e., 95 percent emissions reduction). The maximum ratio of MACTallowable to actual emissions is therefore 17/5 = 3.4. For non-reactor batch process vents, the 

MACT standard is based on the overall control for all non-reactor batch vents, in which some 

may be controlled and others not controlled, but collectively achieve at least 62 percent control 

of organic emissions. While we do not have information on the post-MACT controls achieved 

across the non-reactor batch vents at APR facilities, to be conservative we assume that some 

achieve 76 percent control, which is the standard for new sources. In this case, 38 percent of 

organic HAP would be emitted at the MACT-allowable level, and it is possible that facilities are 

actually only emitting 24 percent (i.e., 76 percent emissions reduction). The maximum ratio of 

MACT-allowable to actual emissions is therefore 38/24 = 1.6. 

Because it was not possible to determine whether an emissions point was a reactor batch 

process vent, a non-reactor batch process vent, or other type of emissions source in the NEI data 
6

available for this source category, we examined applying the larger of the two ratios, 3.4, to all 

organic HAP emissions associated with point (rather than fugitive) sources to be conservative. 

The maximum cancer risk associated with emissions from point sources is 3-in-1 million. The 

application of the factor of 3.4 to this value results in a maximum cancer risk at the MACTallowable emissions level of 10-in-1 million. The maximum TOSHI for the source category 

based on actual emissions is 0.2, and is due to emissions from a point source. The application of 

the factor of 3.4 applied to this TOSHI results in a TOSHI at the MACT-allowable emissions 

level of approximately 0.7. 

In summary, the risks based on the “MACT-allowable” emissions levels are shown in 

Table 6. The maximum individual cancer risk at the MACT-allowable emissions level is 10-in-1 

million and the maximum MACT-allowable TOSHI is 0.7 for the Amino/Phenolic Resins 

Production NESHAP.

c. Polycarbonate Production

The PC NESHAP addresses emissions from the following types of emission sources: (1) 

storage tanks, (2) process vents, (3) equipment leaks, and (4) wastewater. Table 4 summarizes 

the formats of the standards for these emission points.

Table 4. Formats of Standards for the PC NESHAP

Emission Source Type Format of Primary Standard

Storage Tanks Equipment Standards (Performance standard option 

available for certain sizes and vapor pressures)

Continuous and Batch Process Vents (for 

vent streams with TRE less than 2.7) Performance Standard (% reduction)a

Equipment Leaks Work Practice Standards

Wastewater Equipment Standards, Performance Standard

a The NESHAP contains alternative standards to reduce emissions on a kg emissions/hour basis for hydrogen halides 

and halogens and to reduce total organic carbon based to a specified concentration 

As in AMF, for equipment leaks, which are subject to work practice standards, we 

believe that the actual emission levels are a reasonable estimation of the levels allowed by the 

standard. We also believe that the actual emission levels are a reasonable estimation of the levels 

allowed by the standard for wastewater emission sources, which are regulated by equipment and 

performance standards.

For process vents, which are subject to a performance standard, the sources could utilize 

control devices that achieve reductions greater than the required 98 percent reduction of total 

organic HAP or 99 percent reduction in hydrogen halides and halogens. However, as discussed 

above for AMF process vents, the continuous monitoring requirements of the rule result in 

situations where reductions at or above these required levels are required on a continuous basis. 

Because of these requirements, we assume that the actual emission levels are a reasonable 

estimation of MACT-allowable emissions for process vents.
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For storage vessels, the requirements differ depending on the size of the tank and the 

vapor pressure of the stored material. The rule requires a 98 percent total organic HAP emissions 

reduction for tanks with capacities of 151 m3or more with a vapor pressure of 5.2 kilopascals 

(kPa) or greater. Those with a capacity between 75 and 151 m3and a vapor pressure of 76.6 kPa 

or more are required to achieve 95 percent total organic HAP emissions reductions, and those 

with a capacity between 75 and 151 m3and a vapor pressure between 27.6 and 76.6 kPa may 

either comply with a 95 percent reduction performance standard or comply with equipment 

standards. As discussed above, it is reasonable to assume that the actual emissions from those 

sources complying with equipment standards are representative of the MACT-allowable 

emissions. For facilities complying with performance standards, actual emissions reductions 

could be greater than the required reductions. While we believe it is likely that facilities control 

tanks to a greater degree than 95 percent, we are not aware of any situations where facilities are 

achieving significantly greater than 98 percent emissions reductions. In cases where storage 

vessels that are only required to achieve the 95 percent emissions reduction actually achieve 98 

percent emissions reduction, they would be emitting only 2 percent emissions while 5 percent 

would be emitted at the MACT-allowable level. The maximum ratio of MACT-allowable to 

actual emissions is therefore 5/2 = 2.5. 

To estimate the impacts on emissions and risks considering storage tank MACTallowable emissions, several assumptions were made for the polycarbonate production source 

category. In the NEI data for this source category, it was not possible to determine whether an 

emission point was a storage tank or another type of emissions source. Based on data available 

for another chemical production source category, polyvinyl chloride production (PVC), the 

percentage of total PVC emissions that were attributed to storage vessels was approximately 0.2 

percent.aFor organic chemical production facilities that contributed data for the Hazardous 

Organic NESHAP (HON) residual risk analysis, the percentage of total HON emissions that 

were attributed to controlled storage vessels was approximately 5 percent.b Based on this 

information, to be conservative, we have assumed that 5 percent of the total polycarbonate 

production emissions are from storage tanks. In addition, while some storage tanks already are 

required to meet the 98 percent control efficiency standards, we do not have information on the 

number of tanks or the emissions of tanks required to meet the 98 percent or 95 percent control 

standards. To be conservative, we assumed all storage tanks are required to meet the 95 percent 

control efficiency standards but are actually reducing emissions by 98 percent. Location of the 

storage tanks is another factor that may affect risk results, where an increase in tank emissions in 

closer proximity to residences could increase risk more than tanks located further from 

residences. However, as the NEI data for this source category does not include different locations 

for the different emissions sources for three of the four facilities and only includes two locations 

for the other facility, we assume that the emissions at the given locations are due to all the 

emissions sources. Therefore, we have assumed that 5 percent of the emissions at these locations 

are from storage tanks. To consider storage tank MACT-allowable emissions, we have multiplied 

 

a

“Costs and Emission Reductions of the Proposed Standards for the Polyvinyl Chloride and Copolymers (PVC) 

Production Source Category.” Memorandum from Eastern Research Group, Inc. to Jodi Howard, U.S. 

Environmental Protection Agency. April 13, 2011. (Docket item no. EPA-HQ-OAR-2002-0037-0097).

b EC/R Incorporated. Synthetic Organic Chemical Manufacturing Industry – Residual Risk Assessment. Prepared for 

the U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards. September 2005. (Docket 

item no. EPA-HQ-OAR-2005-0475-0108 (Appendix G)).
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these actual emissions by 2.5 as shown in Table 5 below. This equates to a 7.5 percent increase 

in total emissions for each facility.

Table 5. Polycarbonate Production Actual and Estimated Allowable Emissions 

Facility

Total Actual 

PC 

Emissions 

(TPY)

Assumed 

Actual 

Storage 

Vessel 

Emissions

Storage 

Vessels 

Actual to 

Allowable 

Multiplication 

Factor

Assumed 

Allowable 

Storage 

Vessel 

Emissions

Total 

Allowable 

PC 

Emissions 

(TPY)

Dow –

Freeport, TX 7.9 0.4 2.5 1 8.5

Bayer –

Baytown, TX 0.40 0.02 2.5 0.05 0.43

Sabic –

Burkville, AL 170.9 8.5 2.5 21.3 183.7

Sabic – Mt. 

Vernon, IN 151.2 7.6 2.5 19 162.6

The resulting risks based on the application of the organic HAP ratio of 2.5 for storage 

vessels (a 7.5 percent increase in total emissions for each facility) is shown in the “MACTallowable” level risks shown in Table 6.

Table 6. Summary of Estimated Inhalation Risks for the AMF, APR, and PC Based On 

MACT-Allowable Emissions Levels

Actual MACT-Allowable

Source Category

Maximum 

individual 

cancer risk (in a 

million)

Maximum 

chronic 

noncancer 

TOSHI

Maximum 

individual 

cancer risk (in a 

million)

Maximum 

chronic 

noncancer 

TOSHI

Acrylic and Modacrylic Fibers 

Production 20 0.1 20 0.1

Amino/Phenolic Resins Production 9 0.2 10 0.7

Polycarbonate Production 0.3 0.04 0.3* 0.04*

* Allowable risks appear unchanged from actual risks because the slight risk increase (7.5 percent) did not cause a 

change in the presentation of risks with one significant digit