MEMORANDUM 

Date: June 18, 2015 

Subject: Mineral Wool RTR Ample Margin of Safety – Analysis and Proposed Controls 

 

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

 

To: EPA Air Docket EPA-HQ-OAR-2010-1041 

I. Introduction 

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

safety (AMOS) 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 Mineral 

Wool Production (40 CFR part 63, subpart DDD) in accordance with section 112(f)(2) of the 

Clean Air Act (CAA). 

Mineral wool is an insulation product which is made by melting layers of minerals and 

mineral products such as rock, slag, glass cullet and coke in a cupola, fiberizing the molten 

mineral, collecting the fiber as a layer that can be cut and formed into various products for fire 

protection and noise attenuation in commercial, institutional and industrial buildings. When a 

binder is used, it is applied at the fiberization process. The three process lines in the mineral 

wool industry that manufacture a bonded product use a phenol/formaldehyde-based binder which 

is cured to harden, providing structural strength. The mineral wool building products must meet 

rigid product safety specifications. For more information on the mineral wool production 

process, see preamble discussion in the November 25, 2011 proposal (76 FR 72775). 

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 the EPA conducted an information collection request (ICR) that included all mineral 

wool production facilities currently operating in the US. The 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). 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 EPA then used the test data to populate the mineral wool 

residual risk modeling file. The final risk assessment which evaluated both actual and MACT 

allowable emissions can be found in the document titled Residual Risk Assessment for the Mineral 

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

2015 Final Rule 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 mineral wool production 

source category, risks were found acceptable at 10-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, the EPA again considers all of the health 

risks and other health information considered in the acceptability determination. Beyond that 

information, additional factors relating to the appropriate level of control are also considered, 

including costs and economic impacts of controls, technological feasibility, uncertainties and any 

other relevant factors. Considering all of these factors, the agency will establish the standard at a 

level that provides an ample margin of safety to protect the public health, as required by CAA 

section 112(f). The EPA proposed in the April 15, 2013 Federal Register that risks from the 

mineral wool production source category are acceptable at 10-in-1 million (78 FR 22370). 

Details of the analysis can be found in the document titled Residual Risk Assessment for the 

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

June 2015 Final Rule. For the ample margin of safety determination, the EPA referred to the 

conclusions from the technology review (see docket item EPA-HQ-OAR-2010-1041-0111) 

performed for CAA section 112(d)(6) that no technologies (beyond those already in place) were 

identified for reducing HAP emissions from mineral wood production processes and that the 

proposed subpart DDD standards protect public health with an ample margin of safety. 

II. Identification of Subpart DDD Risk Driver HAPs and Processes 

The risk assessment identified the one mineral wool facility with the highest risk of an 

MIR of 10-in-1 million due to emissions of formaldehyde. Approximately 1 person was 

estimated to have cancer risk greater than or equal to 10-in-1 million and 11,600 people at cancer 

risks above 1-in-1 million as a result of emissions. The assessment estimated chronic non cancer 

risks (HI) at 0.1 and a maximum acute hazard quotient (HQ) of 20. Formaldehyde was also the 

driver for both HQ and HI. Three of the seven mineral wool facilities emit the majority of 

formaldehyde emissions from bonded lines (that is, the production of bonded products which 

involve the application of a HAP-based binder, typically composed of a phenol-formaldehyde 

resin). The specific processes of a bonded mineral wool production line that emit formaldehyde 

are curing and collection. Therefore, the ample margin of safety analysis discussed for the 

remainder of this memorandum focuses on this risk-driver HAP and the curing and collection 

processes. 

III. Ample Margin of Safety Analysis 

Several potential measures or options for reducing formaldehyde emissions from bonded 

lines were evaluated. Current controls at curing and forming operations on bonded lines were 

reviewed. All bonded lines are equipped with HAP controls (i.e., incinerator, RTO, or scrubber) 

and, as stated in the technology review memo (docket item EPA-HQ-OAR-2010-1041-0111), no 

new technologies (beyond those already in place) were found. 

A pollution prevention option (the use of non-HAP binders) was considered, but it was 

found that product (performance) specifications of mineral wool products made this option 

technically infeasible. 

The original Mineral Wool NESHAP did not regulate the collection chamber of bonded 

lines. Emissions from the collection process and controls were evaluated. Most collection 
processes are routed to a mechanical filter for PM control. The cost estimates for installation of 

additional HAP controls at the collection process were evaluated and it was found that controls 

capable of handling the high volume air flows characteristic of most collection processes would 

be cost prohibitive. A cost estimate for an incinerator large enough to handle this air flow in the 

exhaust of the collection chamber was $1.8 million, with an additional estimated $0.4 million for 

a pre-filter and exhaust stack. Annual operating and maintenance expenses were estimated at 

$1.1 million. Assuming addition of incineration to the collection process would control 

formaldehyde emissions by 98 percent, an estimated industry-wide reduction in formaldehyde is 

less than 1 ton per year. This results in an insignificant impact on risk reductions. 

In general, incinerators and oxidizers are most effective on high concentration organic 

compounds. When VOC (including formaldehyde) are in dilute quantity, combustion efficiency 

is greatly reduced which could result in lower formaldehyde reductions than current operations. 

The potential re-routing exhaust from the collection process through existing incineration or 

other control equipment was considered. It was found that existing facilities do not have 

equipment with sufficient capacity to handle the additional flow and pollutant loading of the 

collection chamber and therefore this option would not be technically feasible (see Section 

112(d)(6) Technology Review for Mineral Wool NESHAP, docket item EPA-HQ-OAR-2010-

1041-0111). Table 1 summarizes the above information for the AMOS options that were 

considered. 

 
Table 1. Options Considered for the Mineral Wool Ample Margin of Safety Analysis. 

Option Feasibility Annualized Cost 

($M) 

Formaldehyde 

Reduction (ton/yr) 

Phaseout of PhenolFormaldehyde Binders Infeasible- building 

product safety 

specifications 

--- --- 

Add on RTO to 

baghouse 

High air flow reduces 

effectiveness of RTO, 

increases cost 

$1.1M <1 

Reroute 

curing/collection 

exhaust to cupola 

Infeasible – existing 

equipment does not have 

additional air flow capacity 

--- --- 

Of the seven existing mineral wool production facilities, three operate bonded lines in 

association with the collection processes, which have been termed ‘combined collection and 

curing’. Each of the combined collection and curing designs (e.g., drum, vertical, and 

horizontal) were reviewed, and due to significant differences between each process design, 

emission limits for phenol, formaldehyde and methanol were proposed under these three 

subcategories according to design (see Revised Technical Approach for Mineral Wool MACT 

Floor Calculations dated September 26, 2014 in docket EPA-HQ-OAR-2010-1041). 

IV. Conclusions 

The health risks associated with formaldehyde emissions from curing, forming, and 

collection processes at bonded lines were reviewed. These formaldehyde-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. Considering cost and technical 

feasibility, no feasible options for increasing the ample margin of safety were identified for 

mineral wool production facilities.