Date: November 6, 2014

To: Jeff Telander, EPA/OAQPS/SPPD

From: Gabrielle Raymond and Kristin Sroka, RTI International

Subject: Analysis of Potential Subcategories in the Clay Ceramics Source Category

I. Introduction

In accordance with section 112 of the Clean Air Act (CAA), the U.S. Environmental 

Protection Agency (EPA) established national emission standards for hazardous air pollutants 

(NESHAP) on May 16, 2003, for the clay ceramics manufacturing industry, specifically the 

sanitaryware and ceramic tile industry sectors. Sanitaryware includes plumbing and bathroom 

fixtures such as toilets and sinks. Ceramic tile is used to cover floors and walls. The NESHAP 

regulated emissions of hydrogen fluoride (HF), hydrogen chloride (HCl), and particulate matter 

(PM)—a surrogate for hazardous air pollutant (HAP) metals—from new and reconstructed kilns 

located at clay ceramics facilities. On March 13, 2007, the D.C. Circuit Court vacated the 

emission standards for clay ceramics manufacturing due to issues associated with the 

methodology used to determine the minimum regulatory “floors” for new and existing units.1

Therefore, the EPA is proposing new standards for clay ceramics manufacturing, including 

standards for HF, HCl, mercury (Hg), non-Hg HAP metals (specifically, the PM surrogate), and 

dioxins/furans.

The list of affected sources to be regulated has been expanded to include new and 

existing kilns, spray dryers (ceramic tile only), press dryers (floor tile only), and spray glaze 

operations. The facilities currently projected to be subject to the proposed NESHAP include 

three sanitaryware facilities. The ceramic tile facilities (including floor and wall tile facilities) 

have taken the necessary steps to become synthetic area sources (i.e., have obtained a federally 

enforceable limit reducing emissions below major source thresholds2

) and would not be subject 

to the major source clay ceramics NESHAP. The objective of this memo is to describe and 

document the determination of subcategories for clay ceramics sources.

 1 Sierra Club v. EPA, 479 F.3d 875 (D.C. Cir. 2007). 2 A major source of HAP is a facility that has the potential to emit 10 tons per year (tpy) or more of any single HAP 

or 25 tpy or more of any combination of HAP.
2

II. Subcategories Evaluated

Under CAA section 112(d)(1), the EPA has the discretion to “...distinguish among 

classes, types, and sizes of sources within a category or subcategory in establishing...” standards. 

As explained in the preamble to the proposed rule, there are three distinct sectors within the clay 

ceramics manufacturing industry, with differences in raw materials, processes, and final 

products: (1) ceramic floor tile; (2) ceramic wall tile; and (3) sanitaryware. For most sources 

within these industry sectors, the differences between source sizes, types, or emissions were not 

significant enough to warrant subcategories. The exception was the various types of glazing 

operations used at sanitaryware facilities; therefore, we examined the potential for subcategories 

of sanitaryware glazing operations.

III. Sanitaryware Glazing Operations

There are three different types of spray glaze applications used at sanitaryware facilities: 

manual, spray machine, and robot. Most manually operated spray booths are designed with a 

single spray gun to be handled by a single operator, although some can have more than one spray 

gun. Manual booths are typically used for application of glaze to a small number of pieces or 

when multiple glaze color changes are necessary. Spray machines have multiple fixed 

reciprocating spray guns with automated control. Ware is moved through these spray machines 

with a “chain-on-edge” conveyor system. Spray machines are typically used to apply a single 

glaze color to high volumes of ware. Finally, robot spray booths have a single robot fixed with a 

single spray gun for automatic application of glaze, resulting in the lowest glaze spray rate of the 

three types (Cassidy, 2013a).

In all cases, operators try to apply a specific amount of glaze to a piece so that it has 

proper glaze coverage when fired, regardless of the type of glazing operation used. The glaze 

transfer efficiency and the control device efficiency vary based on the type of booth, but the goal 

is to minimize the amount of glaze sprayed and maximize recovery of any excess glaze that is 

sprayed, which minimizes emissions as well as the cost of production (Cassidy, 2013b).

Table 1 describes the differences in operation between the types of sanitaryware spray 

glaze application.
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Table 1. Characteristics of Various Types of Sanitaryware Glazing Operationsa

Manual Spray Machineb Robot

How spray gun 

controlled

Manual (operated by 

human operator)

Automatic, reciprocating 

from fixed location. Spray 

gun does not move at all, 

fixed.

Automatic, mounted on 

robot arm with high level 

of mobility. Arm moves 

like a human arm.

Number of spray guns One spray gun per 

station per booth

10-20 fixed reciprocating 

spray guns per booth

One spray gun per booth 

How ware moved Manual set up Automatically moved on 

“chain-on-edge” conveyor 

system

Manual set up

Ware volume Low. Dependent on ware 

shape; often used when 

multiple glaze color 

changes are necessary.

High. Typically used when 

all products will be the 

same color.

Low. Dependent on ware 

shape.

Number of pieces able to 

spray at a time

1 to 2 6 to 7 1

Glaze application rate Low High Low

a Information provided by Kohler Co. (Cassidy, 2013a: Cassidy, 2013b).

b Also referred to as “chain-on-edge” or “COE,” as that is the term used to describe the conveyor system for the ware.

The emission profiles from any spray booth are a function of glaze spray transfer 

efficiency and control device efficiency. As noted above, these parameters will vary depending 

on the type of glazing operation, so we evaluated the available test data to determine if there 

were significant differences in emissions rates for these glazing operations. Table 2 shows the 

sanitaryware glazing operations test data available to the EPA, including emission factors, which 

were calculated from the emissions data and the rate at which the glaze was sprayed. More 

details about the test data can be found in the memorandum Test Data Used in Clay Ceramics 

Proposed Rule (Raymond, 2014).
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Table 2, Sanitaryware Glazing Operations Test Data

Facility 

ID APCD Typea New-Source ID

Glazing 

Operation Type

Glaze 

Spray 

Rate 

(tph)

PM 

(lb/ton of 

glaze 

sprayed)

KOHL-TX Baffles, Water Curtain SO3/SO4 Manual 0.128 3.33

KOHL-SC No Baffles, Water 

Curtain

LBM Manual 0.066 16.62

KOHL-TX Baffles, Water Weir EO13 (EPN013-

Manual SB)

Manual 0.079 22.84

KOHL-TX Baffles, Water Weir EO14 (EPN014-Bowl 

SM 1)

Spray Machine 

(COE)

0.331 1.95

KOHL-SC Baffles, Water Curtain BBM Spray Machine 

(COE)

0.232 6.53

KOHL-SC Baffles, Water Curtain NTM Spray Machine 

(COE)

0.090 9.32

KOHL-TX Baffles, Water Curtain SR1 (EPN 104-1P) Robot 0.073 1.32

KOHL-TX Baffles, Water Curtain SR5 (EPN251-Robot) Robot 0.100 3.26

KOHL-SC Baffles, Water Curtain Robot 3 Robot 0.084 6.28

KOHL-WI Baffles, Water Curtain P18-Q24/S18 Robot 0.059 6.84

Average – Manual 0.091 14.26

Average – Spray Machine 0.22 5.93

Average – Robot 0.079 4.42

a A baffle with a water curtain or water weir is a common air pollution control device (APCD) used on sanitaryware 

spray glaze booths, particularly spray machine and robot booths. The baffles collect most of the solid particles in 

the excess glaze, which can be scraped off and reused. Keeping these solids from reaching the water curtain or 

water weir device prolongs the life of the water in the device and minimizes water use and wastewater generation.

The differences in operating characteristics in Table 1 and the differences between the 

glaze spray rates and emission rates in Table 2 for manual, spray machine, and robot glaze spray 

applications are significant enough to support three subcategories of sanitaryware glazing 

operations.

IV. References

Cassidy, M. 2013a. “RE: Glaze spray booth PM emissions” E-mail and attachment from Michael 

Cassidy, Kohler Co., to Jeff Telander, EPA. January 29, 2013.

Cassidy, M. 2013b. “RE: Chain on edge vs robot spray booths.” E-mail from Michael Cassidy, 

Kohler Co., to Sharon Nizich, EPA. June 20, 2013.

Raymond, G. 2014. Test Data Used in Clay Ceramics Proposed Rule. Memorandum from 

Gabrielle Raymond, RTI International, to Jeff Telander, EPA/OAQPS/SPPD. November 6, 

2014.