RECOMMENDED SUBCATEGORIES FOR COLLECTION

Alternative 4

NAIMA urges EPA to subcategorize the bonded collection chambers. Section 112 of the Clean 

Air Act (“CAA”) authorizes EPA to “distinguish among classes, types, and sizes of sources 

within a category” in establishing MACT standards (CAA § 112 (d)(1)). EPA retains discretion 

in important respects in setting floors for MACT standards within the statutory framework to 

promulgate MACT standards that best serve the public interest. Specifically, Congress 

authorized EPA to subcategorize source categories based on classes, types, and sizes of sources, 

which will result in different floors for different categories. 59 Fed. Reg. 29,196, 29,200 (June 6, 

1994).

In other words, EPA’s authority to subcategorize is broad and discretionary. EPA’s criteria for 

subcategorization includes “air pollution control differences, process operation . . ., emissions 

characteristics, control device applicability and costs, safety, and opportunities for pollution 

prevention.”1 Therefore, NAIMA urges EPA to subcategorize the three bonded collection 

chambers based on variation in pollution control equipment. The subcategories would be

arranged as follows:

• Baghouse

- Industrial Insulation Group 

• Scrubber

- Rock Wool Manufacturing

• Screenhouse

- Thermafiber

Alternative 5

Based on the ability of EPA to subcategorize as discussed above, NAIMA urges EPA to 

subcategorize the three bonded collection chambers based on collection chamber design. 

Collection chamber design relates directly to possible binder emissions and control of the 

formaldehyde emissions. In fact, EPA has subcategorized when sources exhibit differences in 

operation, design, and size.2 Therefore, based on collection chamber design, NAIMA 

recommends the following subcategories:

• Drum

- Industrial Insulation Group

• Horizontal Screen

- Rock Wool Manufacturing

• Vertical Screen

- Thermafiber

 1

59 Fed. Reg. 26,429, 26,444 (May 20, 1994). 2

RTI International, Memorandum to EPA on MACT Floor Analysis, December 2003, p. 13.
2

Alternative 6

NAIMA urges EPA to subcategorize the collection chambers based on fiberization or spinner 

differences. When natural rock or iron ore blast furnace slag is melted in a cupola furnace or pot, 

this hot, viscous material is poured in a narrow stream onto one or more rapidly spinning wheels, 

which cast off droplets of molten material and creates fibers. As the material fiberizes, its 

surface may be coated with a binder material and/or de-dusting agent (e.g. mineral oil). The 

fiber then is collected and formed and deposited into the collection chamber. In the collection 

chamber, air, and in some cases a binder, is sprayed over the fibers. There are vertical and 

horizontal spinners which vary the velocity and direction in which the fiberized wool is 

deposited into the collection chamber, which, naturally, impact the emissions of formaldehyde. 

Based on the fiberization/spinner design, NAIMA recommends the following subcategories:

• Horizontal Spinner

- Rock Wool Manufacturing

- Thermafiber

• Vertical Spinners

- Industrial Insulation Group

RECOMMENDED SUBCATEGORIES FOR CARBONYL SULFIDE

Alternative 3

NAIMA urges EPA to subcategorize the industry based on permitted maximum melt rate:

• Greater than 9 tons per hour

- USG – Red Wing

- USG – Walworth 

• 6 to 9 tons per hour

- Industrial Insulation Group

- Rock Wool Manufacturing

- Thermafiber

• Less than 6 tons per hour

- Amerrock

- Isolatek International

The CAA grants the Administrator authority to “distinguish among classes, types, and sizes of 

sources within a category or sub-category.” Obviously, melt rate has important relevance to the 

size of the source and the economic feasibility of imposing additional costly controls. Therefore, 

melt rate provides a useful indication of the required difference among plants to justify 

subcategorization. The melt rate can effectively predict the level of emissions. In fact, the 

current Mineral Wool MACT Standard uses the hourly melt rate to determine compliance with 

the MACT standard. 64 Fed. Reg. 31,695, 31,698 (June 14, 1999). Therefore, NAIMA urges 

EPA to subcategorize the industry based on melt rate as indicated above.
3

Alternative 4

NAIMA urges EPA to subcategorize the industry based on bonded and unbonded.

During promulgation of the original MACT, the mineral wool industry was subcategorized into 

two groups: bonded and unbonded. In that the bonded and unbonded subcategories are already 

established by EPA, NAIMA will not go into detailed analysis of the difference between bonded 

and unbonded. NAIMA requests that these subcategories be retained. Although the differences 

between bonded and unbonded lines apply principally to the non-cupola portions of the line, 

EPA usually subcategorizes two or more sources within a category at the level of the entire 

source even though the sources may have some emission points in common. There is precedent 

for different subcategories for various production processes that have some emission points in 

common but are different with respect to other emission points.3 Therefore, subcategorizing the 

entire mineral wool industry into bonded and unbonded subcategories is totally appropriate. 

The subcategories would be the following:

• Bonded

- Industrial Insulation Group

- Rock Wool Manufacturing

- Thermafiber

• Unbonded

- Amerrock

- Isolatek International

- USG – Red Wing

- USG – Walworth

Alternative 5

NAIMA urges EPA to subcategorize the industry to reflect the diversity of the industry and the 

primary products it manufactures:

• Residential Loose-Fill

- Amerrock

• Ceiling Tiles

- USG – Red Wing

- USG – Walworth

• Fireproofing

- Isolatek International

• Commercial and Industrial

- Industrial Insulation Group

- Rock Wool Manufacturing

- Thermafiber

 3

EPA subdivided the source category for acrylonitrile butadiene styrene (“ABS”) into 5 subcategories based on 

different processes even though all had common emission points (60 Fed. Reg. 16,090-16,111 (March 29, 1995)).
4

The CAA allows grouping of facilities based on such broad terms as “class” and “type.” EPA 

specifically created different subcategories in the leather industry based on “types of leather 

products produced.”4

As suggested above, the subcategories based on product types also display a variety of 

differences. For example, the residential blowing wool produced by Amerrock uses no binder. 

Therefore, there are no formaldehyde emissions. Amerrock products are produced for the 

residential building market. Similarly, USG’s two plants are making unbonded products to 

produce ceiling tiles. While this product is ultimately bonded with non-phenolic binders, the 

binder is not applied at the manufacturing site. Ceiling tiles are produced largely for the 

commercial market.

Isolatek produces mineral wool for fire proofing products. The mineral wool is combined with 

other ingredients to create a spray applied for fire proofing of commercial and industrial 

facilities. Again, Isolatek uses no formaldehyde binders.

Commercial and industrial insulation is produced by Thermafiber, Industrial Insulation Group, 

and Rock Wool Manufacturing using formaldehyde binders.

Alternative 6

NAIMA urges EPA to subcategorize the industry based on raw material. This subcategorization 

would be based on predominant use of rock or slag. More than fifty percent use of rock or slag 

material would place the manufacturer in a particular subcategory. This subcategory could also 

be characterized as recycled (slag) and non-recycled (rock) plants. There are important 

differences between recycled and non-recycled plants with respect to raw materials, emissions, 

and products. The distinction between rock and slag plants is well recognized within the 

industry and in the scientific and technical literature, and therefore, subcategorization of rock and 

slag (recycled or non-recycled) plants would not be breaking new ground. The subcategorization 

would be as follows:

• Rock (Non-Recycled)

- Amerrock

- Industrial Insulation Group

• Slag (Recycled)

- Isolatek International

- Rock Wool Manufacturing

- Thermafiber

- USG – Red Wing

- USG – Walworth

 4

J. Michael Geers and Claudia M. O’Brien, “Basis and Rationale for Potential Subcategorization of Coal-fired 

Electric Utility Steam Generating Units,” March 8, 2002, p. 10 (http://www.epa.gov/ttn/atw/combust/utiltox/ 

9brh04.pdf).
5

Alternative 7

NAIMA urges EPA to subcategorize the industry based on use of air pollution control 

differences, specifically, use of an incinerator. EPA’s criteria for subcategorization includes “air 

pollution control differences, process operation . . ., emissions characteristics, control device 

applicability and costs, safety, and opportunities for pollution prevention.”5 Subcategorization 

based on existence of cupola incinerator controls and non-incinerator controls would be as 

follows:

• With Incinerator

- Industrial Insulation Group

- Thermafiber

- USG – Red Wing

- USG – Walworth

• Without Incinerator

- Amerrock

- Isolatek International

- Rock Wool Manufacturing

Alternative 8

NAIMA urges EPA to subcategorize the industry based on the age of the facility/cupola. The 

subcategories would be as follows:

• Prior to 1950

- Isolatek International

- Thermafiber

• 1951 – 1975

- Rock Wool Manufacturing

- USG – Walworth

• 1976 – Present

- Amerrock

- Industrial Insulation Group

- USG – Red Wing

Alternative 9

NAIMA urges EPA to subcategorize the industry based on cupola stack heights. The 

subcategories would be as follows:

• 150 feet and above

- Amerrock

- Industrial Insulation Group

- USG – Red Wing

 5

59 Fed. Reg. 26,429-26,444 (May 20, 1994).
6

• 100 to 150 feet

- Rock Wool Manufacturing

- USG – Walworth

• Below 100 Feet

- Isolatek International

- Thermafiber

RECOMMENDED SUBCATEGORIZATION FOR HYDROGEN FLUORIDE AND 

HYDROCHLORIC ACID

Alternative 4

NAIMA has recommended a variety of subcategorization options, including application of the 

existing bonded and unbonded subcategories to the entire source. If EPA sets a HF and HCl 

limit, NAIMA urges EPA to extend the bonded and unbonded subcategorization to the regulation 

of HF and HCl. Similarly, if any other subcategorizations are established for the mineral wool 

industry, NAIMA urges EPA to apply the subcategorization to the entire source, which would 

include the regulation of HF and HCl emissions.