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MEMORANDUM 

Date: June 18, 2015 

Subject: Wool Fiberglass RTR Ample Margin of Safety – Analysis and Controls for the Final 

 Amendments 

From: Susan Fairchild, EPA/OAQPS/SPPD/MMG 

To: EPA Air Docket EPA-HQ-OAR-2010-1042

I. Introduction 

The purpose of this memorandum is to present information used in the ample margin of safety 

analysis for the U.S. Environmental Protection Agency’s (EPA’s) residual risk review of the national 

emission standards for hazardous air pollutants (NESHAP) for the Wool Fiberglass Manufacturing 

Source Category (40 CFR part 63, subpart NNN) in accordance with section 112(f)(2) of the Clean 

Air Act (CAA). 

Wool fiberglass is produced by melting raw materials (silica sand, soda ash, borides, other 

minerals, and cullet) in a high temperature furnace and transferring the molten glass in a thin stream

to either a rotary spin (RS) or a flame attenuation (FA) line for fiber formation. If the end product is 

bonded wool fiberglass, the product must be coated with a binder. Some wool fiberglass facilities that

produce bonded wool fiberglass use a phenol-formaldehyde (PF) binder, but the industry has largely 

phased out the use of such binders in favor of non-HAP binding agents. Wool fiberglass products are 

primarily used as thermal and acoustical insulation for buildings, automobiles, aircraft, appliances, 

ductwork, and pipes. For more information on wool fiberglass manufacturing, see the preamble 

discussion in the November 25, 2011 proposal (76 FR 72776). 

Section 112(f)(2) of the CAA requires us to determine, for source categories subject to certain 

MACT standards, whether those emissions standards provide an ample margin of safety to protect 

public health. As specified in CAA section 112(f)(2)(A), if MACT standards that apply to a source 

category emitting a HAP that is “classified as a known, probable, or possible human carcinogen do 

not reduce lifetime excess cancer risks to the individual most exposed to emissions from a source in 

the category or subcategory to less than one-in-one million,’’ the EPA must promulgate residual risk 

standards for the source category (or subcategory) as necessary to provide an ample margin of safety 

to protect public health. Section 112(f)(2) of the CAA expressly preserves our use of the two-step 

process for developing standards to address any residual risk and our interpretation of “ample margin 

of safety” developed in the Benzene NESHAP. The first step in this process is the determination of 

acceptable risk. This determination “considers all health information, including risk estimation 

uncertainty, and includes a presumptive limit on MIR [cancer] of approximately 1-in-10 thousand 

[i.e., 100-in-1 million]’’ (54 FR 38045). In the second step of the process, the EPA sets the standard 

at a level that provides an ample margin of safety ‘‘in consideration of all health information, 

including the number of persons at risk levels higher than approximately 1-in-1 million, as well as 

other relevant factors, including costs and economic impacts, technological feasibility, and other 

factors relevant to each particular decision’’ (Id.).
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. The first step in this process is the determination of acceptable risk. Under this first step, 

Tthe EPA conducted two information collection requests (ICRs) that included all wool fiberglass 

facilities currently operating in the U.S. The first ICR was voluntary and allowed companies to 

perform HAP emissions testing on a subset of facility operations, if the facilities were able to 

demonstrate that the subset was representative of the untested subset. Emissions testing on bonded 

lines were conducted using EPA Method 318, for phenol, formaldehyde and methanol. Companies 

were also allowed to submit MACT-compliance testing (which is only for formaldehyde) with binder 

formula data on the phenol/formaldehyde and the methanol/formaldehyde ratios to estimate 

emissions of phenol and methanol. Emissions testing on the furnaces was conducted using EPA 

Method 5 for PM, Method 29 for total chromium compounds and Method 0061 to measure 

hexavalent chromium (in order to speciate the percentage of the total chromium that is emitted in the 

hexavalent state). The risk drivers for this source category are formaldehyde and hexavalent 

chromium. Test results were typically presented as three test runs and provided in units of mass of 

pollutant per mass of production (e.g., lbs of HAP/ton of glass pulled). 

The ICR responses from all the facilities were compiled in the project database and included 

information on each facility, process, process equipment, control equipment, costs, and HAP 

emissions. The second ICR requested specific information about furnaces and required that all 

facilities that had not submitted chromium and hexavalent chromium (Cr6+) test data conduct and 

submit Method 29 and Method 0061 testing. The EPA then used all available data (which is a 

combination of both new and existing test data) to populate the wool fiberglass residual risk modeling 

file. The risk assessment, which evaluated both actual and MACT-allowable emissions, can be found 

in the October 2014 Draft Residual Risk Assessment for the Mineral Wool Production and Wool 

Fiberglass Manufacturing Source Categories in Support of the June 2015 Final Rule in the dDocket. 

Generally, if risks are found to exceed 100-in-1 million, we consider this unacceptable and act to 

reduce risk to acceptable levels by requiring emission reductions of the pollutants responsible for the 

risk (i.e., the ‘risk drivers’). If risk is found to be below 100-in-1 million, we consider risk to be

acceptable; for the wool fiberglass manufacturing source category, risks were found acceptable at 20-

in-1 million. 

 The second step of sSection 112(f)(2) provides for an ample margin of safety (AMOS) to 

protect public health. In this step of the process, the EPA sets the standard at a level that provides an 

ample margin of safety “in consideration of all health information, including the number of persons at

risk levels higher than approximately 1-in-1 million, as well as other relevant factors, including costs 

and economic impacts, technological feasibility, and other factors relevant to each particular 

decision.” For the AMOS determination, the EPA searched for technologies and associated costs 

reviewed the industry and the technical literature to determine if cost-effective means are available 

that would further reduce emissions of hexavalent chromium or formaldehyde. The data search 

included similar sources both within and outside the source category for technologies that would 

reduce these emissions. Because the industry was in the process of eliminating the use of 

formaldehyde using non-HAP binders, and had already reduced formaldehyde emissions by up to 95 

percent of the MACT levels, EPA considered this raw material substitution already underway as an 

appropriate strategy to further reduce risk from formaldehyde. The EPA focused risk reduction 

efforts on technologies that would further reduce emissions of chromium emissions, especially Cr6+. 

 Similar process associated with Cr6+ emissions within three industries were found: chromium 

electroplating, the metallurgical industry and the electric utility industry. The costs of control 
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technologies for those industries were evaluated, and two technologies (reducing the operational life 

cycle for specific process equipment and installation of sodium hydroxide [NaOH] scrubbers) were 

found to have reasonable cost effectiveness in terms of dollars per pound of pollutant removed. The 

wool fiberglass glass-melting furnace process parameters were compared to those in the chromium 

electroplating, metallurgical and electric utility industries. These technologies were evaluated, taking 

into consideration costs, energy, safety and other relevant factors (such as adverse environmental 

effects) to determine whether risk, although acceptable, could be further reduced to meet a level 

achieving an AMOS, using the available cost effective emission reduction approaches and that these 

emission reduction approaches are transferable to the furnace operations.1

 

II. Identification of Subpart NNN Risk Driver HAP and Processes 

The November 2011, February 2013, and October 2014 draft residual risk assessments were 

based on actual emissions currently emitted by industry and are summarized as follows: 

2011 proposal risk results  MIR = 40 (formaldehyde*, Cr6+) 

(based on actual emissions) 11,641 people exposed to cancer risk >10-in-1 million 

 849,000 people exposed to cancer risk >1-in-1 million 

 HI = 0.2 (formaldehyde) 

 HQ = 30 (formaldehyde – based on REL) 

 Cancer incidence = 0.05 (52% formaldehyde, 47% Cr

6+) 

2013 proposal risk results  MIR = 20 (formaldehyde); 

(based on actual emissions) 1,800 people exposed to cancer risk >10-in-1 million 

 650,000 people exposed to cancer risk >1-in-1 million 

 HI = 0.2 (formaldehyde) 

 HQ = 30 (formaldehyde – based on REL) 

 Cancer incidence = 0.04 (64% formaldehyde, 35% Cr

6+) 

2014 proposal risk results  MIR = 20 (formaldehyde and Cr6+); 

(based on actual emissions) 6,900 people exposed to cancer risk >10-in-1 million 

 1,200,000 people exposed to cancer risk >1-in-1 million 

 HI = 0.2 (formaldehyde) 

 HQ = 30 (formaldehyde – based on REL) 

 Cancer incidence = 0.04 (64% formaldehyde, 35% Cr

6+) 

The EPA also analyzed post-MACT risks based on the proposed limits in the 2014 supplemental 

proposal. Below is a summary of the results of the post-MACT risk assessment and details of the 

analysis can be found in the October 2014 Draft Residual Risk Assessment for the Mineral Wool 

Production and Wool Fiberglass Manufacturing Source Categories.

 

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 See the following memoranda available in docket EPA-HQ-OAR-2010-1042: Control Cost 

Evaluation for Glass-Melting Furnaces, Section 112(d)(6) Technology Review for Wool Fiberglass 

NESHAP, and Development of Background Information on Area Source Emissions Limit - 

Determination of GACT for Wool Fiberglass Furnaces at Area Sources).
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Post-MACT estimated risk results  MIR = 5 

0 people exposed to cancer risk >10-in-1 million 

 21,000 people exposed to cancer risk >1-in-1 million 

HI = 0.3 

 HQ = 7 

 

Following the publication of the November 2014 supplemental proposal, we did not receive 

new actual emissions data and we did not have to revise our estimate of actual emissions from wool 

fiberglass manufacturing facilities. Therefore, we did not re-assess the risks from actual emissions for 

wool fiberglass manufacturing facilities. The MIR based on actual emissions remains at 20-in-1 

million with the acute noncancer HQ remaining at 30 for the REL and 1 for the AEGL–1 

(formaldehyde). The maximum chronic non-cancer TOSHI value based on actual emissions is 0.1 

with emissions of formaldehyde dominating those impacts, indicating no significant potential for 

chronic noncancer impacts. 

However, Wwe conducted a new assessment of the risks remaining after implementation of 

the final rule revisions. The risk assessment took into account the change in the chromium 

compounds emission limit for gas-fired glass-melting furnaces from 0.00006 to 0.00025 pounds of 

chromium per ton of glass pulled and the actual MACT-allowable emissions of formaldehyde, 

methanol or phenol from RS lines. The MIR for cancer after implementation of the RTR could be up 

to 60-in-1 million and is driven primarily by the MACT-allowable formaldehyde emissions with 

chromium emissions as a secondary risk driver. These post-RTR risks were determined to be 

acceptable. We used actual emissions from RS lines for the assessment of the risks remaining after 

implementation of the final standards because, as we noted in section V.H of the preamble to the final

rule, the EPA is not establishing limits under CAA sections 112(d)(2) and (3) for RS lines at this 

time. We believe that the data that we relied on in proposing the RS standards are not sufficiently 

related to current operations or emissions from RS bonded lines and we have issued a CAA section 

114 ICR to wool fiberglass facilities to obtain updated formaldehyde, methanol, and phenol 

emissions and process data for RS manufacturing lines. We will analyze the ICR data and evaluate 

RTR limits for RS lines at wool fiberglass manufacturing facilities at a future date. 

Additionally, based on comments received in response to the November 2014 supplemental 

proposal that indicated that a newly-rebuilt furnace, which we believe is the likely compliance 

technology, might not be able to demonstrate compliance with the proposed chromium emission 

limit. We re-evaluated the proposed total chromium limit and conducted an assessment of the risk 

attributable to all HAP for each facility and determined that increasing the chromium compound 

emission limit from 0.00006 to 0.00025 pounds total chromium per ton of glass pulled has a minimal 

effect on the post-RTR risks because these risks are largely driven by formaldehyde emissions. 

Specifically, at the chromium compounds emission limit of 0.00025 pounds total chromium per ton 

of glass pulled, the MIR due to only chromium emissions for the source category is 3-in-1 million; 

whereas, the MIR due to only the MACT-allowable formaldehyde post-RTR emissions for the source 

category is 60-in-1 million. As noted above, these post-RTR risks were determined to be acceptable. 

It is important to note that, even though risks are acceptable, the health risks from Cr6+ emissions 

from wool fiberglass manufacturing facilities could be much higher in the future without a chromium 

compounds emission limit. To capture this scenario, we conducted an auxiliary risk analysis in which 

we assumed all wool fiberglass furnaces emitted Cr6+ at the same rate as the highest-emitting furnace. 

The results of the auxiliary risk analysis showed that, at the assumed emission rate, four facilities 
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would have MIR cancer risks greater than 100-in-1 million. The results of the risk assessment are 

presented in more detail in the final residual risk memorandum titled “Residual Risk Assessment for 

the Mineral Wool Production and Wool Fiberglass Manufacturing Source Categories in Support of 

the June 2015 Final Rule”, which can be found in Docket ID No. EPA-HQ-OAR-2010-1042. 

 

Risk Uncertainties 

Although every effort was made to identify all the relevant facilities and emission points, as 

well as to develop accurate estimates of the annual emission rates for all relevant HAP, the 

uncertainties in our emission inventory likely dominate the uncertainties in our exposure modeling 

estimates. The chronic ambient modeling uncertainties are considered relatively small in comparison, 

since we are using EPA’s refined local dispersion model with site-specific parameters and reasonably 

representative meteorology. If anything, the population exposure estimates are biased high by not 

accounting for short- or long-term population mobility, and by neglecting processes like deposition, 

plume depletion, and atmospheric degradation. Additionally, estimates of the maximum individual 

risk (MIR) contain uncertainty, because they are derived at census block centroid locations rather 

than actual residences. This uncertainty is known to create potential underestimates and overestimates

of the actual MIR values for individual facilities, but, overall, it is not thought to have a significant 

impact on the estimated MIR for a source category. 

The acute screening results were purposely biased high, considering that they depend upon 

the joint occurrence of independent factors, such as hourly emissions rates, meteorology and human 

activity patterns. Furthermore, in cases where multiple acute threshold values are considered 

scientifically acceptable, we have chosen the most conservative of these threshold values, erring on 

the side of overestimating potential health risks from acute exposures. In the cases where these results 

indicated the potential for exceeding short-term health thresholds, we have refined our assessment by 

developing a better understanding of the geography of the facility relative to potential exposure 

locations.

Additional discussion of uncertainties in our risk analysis can be found in Section 5 of the 

final risk assessment document titled “Residual Risk Assessment for the Mineral Wool Production 

and Wool Fiberglass Manufacturing Source Categories in Support of the June 2015 Final Rule”, 

which can be found in the rulemaking docket.

III. Ample Margin of Safety Analysis 

The main risk drivers for the wool fiberglass source category were formaldehyde and Cr6+

emissions. Formaldehyde emissions are associated with the production of bonded wool fiberglass 

products that use PF binders and many facilities are continuing to switch their binders and have 

reduced or eliminated formaldehyde emissions. 

Formaldehyde Emissions from Manufacturing Lines 

As noted in the preamble to the November 25, 2011 proposal (76 FR 72777-72778), most 

facilities have phased out the use of PF binders on bonded lines, and as a result, the wool fiberglass

manufacturing industry has significantly reduced or eliminated formaldehyde emissions. Based on 

the most recent information provided by industry, we estimate that two facilities have 13 bonded FA 

manufacturing lines and all of the FA lines are in compliance with the emission limits in the final 

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rule. Therefore, additional controls are not needed for existing FA lines. The most recent information

provided by industry indicates that four companies operate 5 RS bonded lines on which a PF binder is 

used. 

As noted in Section II of this memorandum, we are not establishing limits under CAA 

sections 112(d)(2) and (3) for RS lines in the final action because we believe that the data that we 

relied on in proposing the RS standards are not sufficiently related to current operations or emissions 

from RS bonded lines. The EPA has issued a CAA section 114 ICR to wool fiberglass facilities to 

obtain updated formaldehyde, methanol, and phenol emissions and process data for RS 

manufacturing lines and we will analyze the ICR data and evaluate RTR limits for RS lines at a 

future date. We believe that deferring the standards for RS lines, under CAA sections 112(d)(2) and 

(3), does not impact the risk assessment conducted under CAA section 112(f)(2) because the risk 

assessment was based on test data of actual emissions of formaldehyde from all the facilities that 

manufacture wool fiberglass.

As discussed above, sources that use RS lines have been phasing out the use of formaldehyde, 

but, at the time we conducted the risk assessment, we did not know which lines and facilities were 

formaldehyde-free. We therefore, included the available actual emissions from the RS bonded lines. 

We believe that this would be the kind of uncertainty in emissions datasets used for risk assessments 

that we discussed in our November 2011 proposal. In that proposal, we explained that there are 

inherent uncertainties and potential for bias in all risk assessments, such as uncertainty in emissions 

datasets (i.e., accuracy of emission values that vary depending on the source of the data, the degree to 

which data are incomplete or missing, the degree to which assumptions made to complete the datasets 

are inaccurate, error in estimating values and other factors). We concluded that despite these 

uncertainties, we believed that our approach, which uses conservative tools and assumptions, ensures 

that our decision is health-protective (76 FR 72783-84). Additionally, because we believe that actual 

formaldehyde emissions would be less than indicated by the emissions test data on which the risk 

assessment was based (due to the continuing phase out of PF binders), we continue to believe that the 

risk assessment as it relates to formaldehyde is a conservative overstatement of risk and that our 

decision to finalize the emission limits for existing, reconstructed, and new FA lines, as proposed in

2014, remains health-protective. We note that even though formaldehyde is the driver for the MIR 

and we are not finalizing emission limits for RS lines in this action, the post-RTR MIR is equivalent 

to the MACT-allowable MIR at 60 in-a-million 

Chromium Emissions from Gas-fired Glass-Melting Furnaces

Chromium emissions, including Cr6+, are associated with gas-fired glass-melting furnaces and 

the degradation of chromium refractories in the furnace. Chromium compounds emissions are a 

secondary risk driver to formaldehyde, and the current baseline risk is 7-in-1 million. Most, if not all 

gas-fired glass-melting furnaces are lined with high-chromium refractory materials to withstand the 

extreme temperatures and highly corrosive gases released in the melting process to manufacture wool 

fiberglass. Due to the extreme operating conditions, the refractories erode over time (i.e., 3 to 10 

years – depending on furnace type and design) and are believed to be the source of most of the 

chromium and Cr6+ emissions. The memorandum “Mechanisms of Chromium Emissions From Wool 

Fiberglass Glass-Melting Furnaces,” which is available in docket EPA-HQ-OAR-2010-1042, 

presents a more in-depth discussion of chromium emissions from gas-fired glass-melting furnaces. 

As discussed in the memorandum for the ample margin of safety to support the November 13, 

2014 proposal (Wool Fiberglass RTR Ample Margin of Safety – Analysis and Proposed 

Formatted: Indent: First line: 0.5"

Formatted: Indent: First line: 0.5"
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Controls, EPA-HQ-OAR-2010-1042-0334), we considered several process alternatives and control 

options for reducing chromium emissions from gas-fired glass-melting furnaces. As discussed in the 

preamble to the November 13, 2014 proposal (79 FR 68021-68022), we initially proposed in 2011 

that both the furnace rebuild and the addition of a NaOH scrubber were cost effective options for 

reducing chromium emissions. At that time, we surmised that a wool fiberglass manufacturer would 

choose non-chromium refractories with which to rebuild the furnace. We have since learned from 

industry that the use of high-chromium refractories is needed to withstand the high internal 

temperature, reactivity, corrosivity, and erosivity of the gas-fired glass-melting furnace environment. 

Consequently, we considered the early replacement of the high-chromium refractory before high 

levels of chromium emissions are released as the refractory degrades as the most likely approach that 

wool fiberglass manufacturers will take to reduce chromium emissions from gas-fired glass-melting 

furnaces. 

IV. Conclusions 

The health risks associated with formaldehyde emissions from wool fiberglass bonded 

manufacturing lines and Cr6+ emissions from glass-melting furnaces were reviewed. Both of these 

HAP-emitting processes were the focus of the ample margin of safety analysis because control 

measures and raw material substitution options applied to these processes offer the greatest potential

for risk reduction. Industry stakeholders have told us that many facilities are continuing to switch 

their binders and have reduced or eliminated formaldehyde emissions. If formaldehyde and Cr6+ are 

emitted at the level of the final emission limits, then the resulting MIR could be as high as 60-in-1 

million based on MACT-allowable formaldehyde emissions, which we determined is are acceptable. 

Considering cost and technical feasibility, replacing the high-chromium refractory before degradation 

results in elevated chromium emissions from reducing the operational life of the gas-fired furnaces 

from 10 years to 7 years was identified as the most feasible option for increasing providing anthe

ample margin of safety for wool fiberglass manufacturing facilities. 

Commented [DG1]: Winifred, we deleted Table 1 since it is 

already discussed in the AMOS memo for the 2014 proposal