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To: Susan Fairchild, EPA From: Dave Reeves, RTI

Project Files Date: October 15, 2014

Re: Wool Fiberglass RTR Ample Margin of Safety – Analysis and Proposed Controls

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, borite, 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 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 preamble 

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

Section 112(f)(2) of the CAA refers to a two-step process for developing standards to address 

residual risk. The first step in this process is the determination of acceptable risk. Under this first step

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

currently operating in the US. 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. 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 test data conduct and submit Method 29 and Method 061 testing. 

The EPA then used a combination of new and existing test data to populate the wool fiberglass residual 

risk modeling file. The risk assessment which evaluated both actual and 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 the Docket. 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 Section 112(f)(2) provides for an ample margin of safety (AMOS) to

protect public health. For the AMOS determination, a search was conducted outside the source 

category for technologies that would reduce chromium emissions, especially hexavalent chromium. 

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

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

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II. Identification of Subpart NNN Risk Driver HAPs 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*, Cr+6)

(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 Cr+6); 

(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.

Post-MACT estimated risk results MIR = 5 

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

 

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

HI = 0.3 

HQ = 7 

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.

III. Ample Margin of Safety Analysis

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

hexavalent chromium emissions. Formaldehyde emissions are associated with the production of 

bonded wool fiberglass products that use phenol-formaldehyde binders. Chromium emissions, 

including hexavalent chromium (Cr+6), are associated with glass-melting furnaces and the 

degradation of chromium refractories in the furnace. Most, if not all glass-melting furnaces are lined 

with high-chrome 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 Cr+6 emissions. We 

considered several process alternatives and control options for reducing chromium emissions from 

glass-melting furnaces which are summarized in Table 1.
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Table 1. Summary of Options Considered for Wool Fiberglass Ample Margin of Safety Analysis.

Option Feasibility Assumptions Annualized 

Cost ($M)

Total Chromium 

Reduction, lb/yr

Replace high-Cr 

refractories in gasfired furnaces with 

non-chromium 

refractories1

Furnace operating 

temperatures and corrosive 

properties of glass melt 

composition require highly 

resistive materials. High 

potential for industrial 

accidents. Considered 

infeasible. 

$10M per rebuild 

every 4 years 

(versus every 10 

years)

2.5M 100%

More frequent 

furnace rebuilds

(every 4 years)

Cost prohibitive because of 

material and labor. 

$10M per rebuild 

every 4 years 

(versus every 10

years)

2.5M 464 lb/yr

(for 3 furnaces)

More frequent 

furnace rebuilds 

(every ~7 years)

Feasible and cost effective 

based on net present value 

approach. 

$10M per rebuild 

every 7 years 

(versus every 10 

years)

0.64M 464 lb/yr

(for 3 furnaces)

Different furnace 

types

Electric furnaces are less 

economical, have less 

capacity, and require more 

frequent rebuilds than 

oxyfuel, but are preferred for 

production of certain niche 

markets

Electric furnaces 

could replace oxyfuel furnaces in 

capacity. 

--- 90% 

Different furnace 

designs

New designs being 

developed/evaluated for 

large oxy fuel furnaces.

-- --- ---

Add-on controls for 

furnace exhausts2

Some Cr emitted as vapor 

not in PM; NaOH scrubbers 

used for chromium 

electroplating, metallurgical 

applications, and in the

electric utility industry for 

Cr+6

See Control Cost 

Evaluation for 

Glass-Melting 

Furnaces 

memorandum

Range 

between 

212K -695K

155 lb Cr/yr (per 

furnace)

Different raw 

materials - including 

cullet

Technically feasible, but 

reducing recycled glass 

(cullet)  more costly

No test data on 

contribution of Cr 

from raw materials

--- ---

Lower furnace 

operating temp (to 

reduce Cr+6 

formation)

Infeasible. High temperature 

achieves low viscosity 

needed for molten glass to 

be spun or attenuated.

No test data on 

Cr+6 emissions at 

lower temps

--- ---

1See reports on New Thermal Shock-Resistant Dense Zircon and Dense Chromic Ozide Refractories and Bacor High 

Chromium Refractories available in the docket. 

2See Control Cost Evaluation for Glass-Melting Furnaces memorandum available in the docket. 

Several potential measures or options for reducing formaldehyde emissions from bonded lines 

were evaluated. First, the EPA reviewed current controls found on bonded lines and found that all 

were equipped with HAP controls (i.e., incinerator, RTO, or scrubber) and, as stated in the 

technology review memo, no new technologies (beyond those already in place) were found. The EPA 
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also evaluated the use of non-HAP binders in the wool fiberglass manufacturing industry to decrease 

HAP emissions. Recent information from industry stakeholders show that most facilities have phased 

out the use of formaldehyde on bonded lines, and of the facilities that have not completely phased it 

out, one or two production lines among several continue to operate using formaldehyde based 

binders. As a result, the wool fiberglass manufacturing industry has significantly reduced or 

eliminated formaldehyde emissions. 

Most facilities currently have thermal oxidizers available for use on the bonded lines. 

According to their ICR responses, those facilities currently not meeting the proposed phenol, 

formaldehyde and methanol emission limits selectively operate thermal oxidizers (or scrubbers) to 

meet the existing MACT limits (formaldehyde). These types of control are also effective in reducing 

methanol and phenol emissions. Therefore, there are no additional capital costs to comply with the 

proposed formaldehyde/phenol/methanol emission limits and we estimated operation and 

maintenance (O & M) costs for a thermal oxidizer at each facility to be $125,000 annually. We 

identified eight manufacturing lines with emission rates above the proposed emission limits and 

estimate that approximately 123 tons of organic HAP would be reduced annually at major sources. 

Only a small percentage of these formaldehyde emission reductions are associated with the high(er) 

risk facilities identified in the draft risk analysis. However, for three facilities the reductions in 

formaldehyde emissions ranged from 62 to 77 percent and resulted in the total facility risk to be less 

than 1-in-1 million.

IV. Conclusions

The health risks associated with formaldehyde emissions from wool fiberglass bonded 

manufacturing lines and Cr+6 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 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 Cr+6 emissions are reduced to comply 

with the proposed emission limits, then the resulting MIR is reduced to 5-in-1 million. Considering 

cost and technical feasibility, reducing the operational life of the gas-fired furnaces from 10 years to 7 

years was identified as the most feasible option for increasing the ample margin of safety for wool 

fiberglass manufacturing facilities.