MEMORANDUM

SUBJECT: Chromium Emissions and Furnace Age 

DATE: August 14, 2014

FROM: Susan Fairchild

Office of Air Quality Planning and Standards

TO: Docket ID No. EPA-HQ-OAR-2010-1042

The EPA collected information on furnace age, refractory chromium content, and 

chromium emissions from each glass-melting furnace in the wool fiberglass industry 

(located at both major and area sources). The information was collected in two phases: a 

voluntary industry survey conducted in 2010 and a Section 114 information collection 

request sent out by EPA in 2012. After the results of the 2010 voluntary industry survey 

were obtained, source testing revealed high chromium emissions from a few furnaces. 

During this same time period, some companies rebuilt or repaired some glass-melting 

furnaces which resulted in reduced chromium emissions. For the 2012 Section 114 

information request, companies were required to provide information on the chromium 

content of their furnace refractories, furnace age, dates of furnace repairs and rebuilds, 

and conduct emissions testing on furnaces1at all facilities producing wool fiberglass. The 

data from both the 2010 and the 2012 collection efforts were compiled into a project 

database from which all analyses for the rule development were conducted. 

Most glass-melting furnaces with chromium emissions that exceed the proposed existing 

source emission limit (based on production throughput) are more than 10 years old, with

ages ranging from less than 1 year up to 23 years. The median age of furnaces among 

both major and area sources that exceed the limit is 12 years and the average age is 11 

years. The median age of furnaces that meet the chromium limit is 10 years and the 

average age is 8.5 years. We considered these data and without the ability to extract 

specific furnace design elements, note that furnaces emitting chromium at or below the 

limit are generally 2 to 3 years younger than the furnaces emitting chromium at levels 

exceeding the limit. Chart 1 (below) shows the compiled chromium compounds 

emissions data for gas-fired (oxyfuel and air-gas) glass-melting furnaces by age.

 

1 Every gas-fired furnace was required to be tested and every unique furnace at every facility was required to be 

tested regardless of whether it was electric or gas-fired.
Review of the furnace information and emissions test data show that serial testing was 

conducted at three furnaces in the industry: one series of four tests on the K2 furnace 

located at Certainteed facility in Kansas City, KS; and two series of tests conducted on 

the MT1 and MT2 furnaces at the Certainteed facility in Mountaintop, PA (these were 

tested over two different furnace campaigns).

The K2 furnace was constructed in 2002, began normal operations in 2003 and 

underwent testing in 2004, 2005, 2008, 2010, and 2011. The company applied by permit 

to increase their production rate at the K2 furnace in 2008, and the 2008 test was 

conducted to determine the PM and chromium emissions at the new production rate. 

Testing conducted in 2004-2008 sampled PM and total chromium compounds; testing 

conducted in 2010 and 2011 analyzed for both hexavalent chromium and total chromium 

compounds. The 2010 testing showed CrVI was 93% of the total chromium compounds 

emitted by the K2 furnace. Analytical problems2 with the 2011 test (including the loss of 

 

2 The 2011 testing was conducted properly, however the calculations done during the reporting phase were not 

correct, thus the reported numbers were incorrectly low. The corrected values presented by the test contractor 

were appropriate (and much higher than their original report). There remains the issue of discarded filters that 

were required under the method to be analyzed for hexavalent chromium; this step was not conducted and 

contributed to the low measured hexavalent emissions. While there appears to be no further reasons to discard 

the 2010 data (after corrections and assumptions of the level of hexavalent chromium that the discarded filter may 

have contained), the corrected 2011 report confirms emissions of the same order of magnitude, though slightly 

lower than the 2010 testing. This lower value may be attributed to the discarded filter.

10 11

11

7.5 10

7

10

12

12

12

<1

<1

8

-1E-04

1.2E-18

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

Air GasAir Gas

Oxy FuelOxy Fuel

Air Gas

Oxy FuelOxy FuelOxy FuelOxy Fuel

Oxy Fuel

Oxy FuelOxy Fuel

Oxy Fuel

lb Cr/ton

Chart 1. Chromium Emissions of Gas Fired Furnaces by Age

Old Test

Data

2012 Test

Data

6.00E-05 Area Sources

2

Major Sources
collected chromium compounds which were not analyzed as required by the method) 

influenced our decision to use only the 2010 test to quantify this source’s emissions of 

chromium. . This furnace is responsible for the highest measured hexavalent and total 

chromium emissions in the industry, as shown in Table 1 below.

Table1. Certainteed K2 Furnace chromium emission testing.

Year K2 Chromium emissions at 

permitted production rate, pounds 

per year

2004 <5

2005 30

2008 114

2010 540

The second series of tests were conducted at the Certainteed facility in Mountaintop, PA. 

The ESP outlet controlling the MT1 and MT2 furnaces was first tested in 1991 and 1995. 

The test conducted in 1991 showed emissions at 10.5 lb/year. Four years later, the same 

furnace showed that chromium emissions had doubled. That furnace was then rebuilt and 

retested. The second set of chromium emission tests were then conducted on the rebuilt 

furnace in 1998 and 2003. These two tests measured chromium emissions at 4.9 lb/year 

and 5.3 lb/year, respectively. Chromium emissions doubled over four years in the first 

furnace campaign, and increased an average of less than 2% per year over the second 

furnace campaign, an increase that is not statistically significant. While the two different 

test sets show increasing chromium emissions with furnace age, they also show that other 

factors, potentially including differences in furnace designs, chromium content of 

refractories, and internal furnace chemistry as a result of the wool fiberglass raw material 

composition, may account for significant differences in chromium emissions.

Table 2. Serial testing of unaltered furnaces.

Incremental Total Chromium Emissions from Oxy-Fuel Furnaces (lb/yr)

Furnace K2 MT1 MT1

First test emissions (lb/yr) <5 10.5 4.9

Last test emissions (lb/yr) 540 20.9 5.3

Time Period 6 yrs 4 yrs 5 yrs

Annual Incremental Emission 

Rate (%/yr)

1,473 50 <2

Annual Incremental Emission 

Rate (lb/yr)

72.8 2.6 <0.1
Other Factors Influencing Chromium Emissions

The rate of chromium emissions is influenced by the size of the furnace, chromium 

content of the refractories, position within the furnace, available boron from the glass 

melt, chemistry of the melt, and glass pull rate. Changes in these factors can reduce or 

increase the rate of chromium emissions from wool fiberglass furnaces. 

Most of the furnace design and operating parameters as well as the glass chemistry are 

proprietary to each company and held in strict confidence, making them largely unknown 

for regulatory development. We obtained information in our Section 114 information 

collection from all wool fiberglass companies on furnace age, first construction date, and 

most recent rebuild dates. Section 114 furnace construction data and industry statements 

2,3 obtained after submittal of the Section 114 information collection and during site visits 

indicate the following:

 all gas-fired wool fiberglass furnaces are constructed using high chromium refractories,

 chromium refractories are chiefly responsible for the higher chromium emissions

 the use of chromium refractories in the construction of gas-fired furnaces is an essential 

component of the wool fiberglass manufacturing process.

Gas-fired furnaces typically operate around 2,800◦ F and oxyfuel furnaces operate 

between 3,500 and 4,000◦ F. Borides, which are used in the wool fiberglass formulation 

for attenuation of the fibers during the production process, introduce a highly corrosive 

and reactive component to the wool fiberglass furnace chemistry. Both the temperature 

and corrosivity of the furnace environment cause wear on the inside of the furnace lining. 

Wool fiberglass gas-fired furnaces are constructed using refractories that are high in 

chromium to withstand both the thermal and chemical demands of the interior of the wool 

fiberglass furnace. 

The refractory materials typically include oxides of silica, magnesium, alumina and two 

types of chromium-bearing materials: Cr2O3 (from the chromium-bearing ores chromite 

and magnesiochromite) and Cr3O4 (chromic oxide, a pigment).The increasing chromium 

emission rate with refractory wear is substantiated by industry studies, published papers 

symposia and other sources available in the technical literature. 

5,6,7,8,14

Based on the available information, chromium emissions increase with furnace age, and 

may increase exponentially for certain furnace designs and glass formulations. However, 

we are not at this time able to predict chromium emission rate due to the absence of 

complete data on the many influencing factors. 

Mechanism of Chromium Emissions
The refractory bricks and blocks are installed having even and level smooth sides. Over 

the life of the furnace, the hot furnace gases react with any available oxides (including 

those in the refractory materials), causing degradation of the refractory materials. The 

refractory wear pattern is semi-spherical. As the corrosive gases of the wool fiberglass 

furnace continue to erode the refractory lining over the life of the furnace, the spherical 

wear pattern is enlarged.

The volume of a sphere is calculated as: 

V =

4

3

∏r3

The volume of a hemisphere is half that of a sphere, or:

V = (

4

3

∏r3) / 2 

As the corrosive gases of the wool fiberglass furnace continue to erode the refractory 

lining over the life of the furnace, the spherical wear pattern is enlarged. Thus, as the 

furnace interior is continually corroded/eroded in semispherical manner, the surface area 

exposed to the corrosive environment enlarges exponentially. We believe this 

phenomenon is the reason that the chromium emissions for the K2 furnace increased 

exponentially over time and is illustrated by the K2 emissions testing in Table 1. 

Consequently, we believe that chromium emission rates for gas-fired furnaces have the 

potential to increase exponentially over time. 

We considered whether the known principles of refractory degradation could be applied 

to the life expectancy of the furnace to determine at what point the chromium emissions 

would be expected to approach the chromium emission limit. However, the data are 

insufficient at this time for development of a predictive pattern of anticipated future 

chromium emissions. We proposed in both November 25, 2011 and the April 15, 2013 

Federal Register for the Wool Fiberglass RTR and Area Source Rules that owner / 

operators of Wool Fiberglass furnaces would be required to conduct chromium testing 

periodically. Future compliance emissions testing compiled from wool fiberglass 

facilities may add to the existing data to improve our understanding of the correlation 

between increasing furnace age and accelerated chromium.
References

1. Section 114 and ICR Responses. Dataset for the Wool Fiberglass RTR and Area Source 

Rule. U.S. Environmental Protection Agency, Office of Air Quality Planning and 

Standards. CBI file. 2013.

2. Industry- EPA Meetings. March 19, 2012; August 31, 2011; November 16, 2011.

3. Wool fiberglass manufacturer’s facility site visits to Certainteed and Owens-Corning U.S. 

sites. CBI Office project number 481, USEPA/OAQPS/SPPD. December 2012. 

4. Saint-Gobain Ceramic Materials. Chromium Oxides. Saint-Gobain Websites, 2012.

5. “Formation of hexavalent chromium by reaction between slag and magnesite-chrome 

refractory”. Lee, Y., Nasaralla, C.L. Metallurgical and Materials Transactions, B: 

Process Metallurgy and Materials Processing Sciences. Vol 29: 2. April 1998.

6. Corrosion of Chromium Rich Oxide Refractories in Molten Waste Glasses. Gan, Hao; 

Lu, Xiaodong; Buechele, Andrew C.; Paul, M. Catherine; and Pegg, Ian L. Catholic 

Univ. America, for U.S. Dept. of Energy. March 2002.

7. Compressive Creep and Thermophysical Performance of Refractory Materials. Ferber, 

M.K.; Weresczak, A.A.; Hemrick, J.G. Oak Ridge Nat’l. Lab. for U.S. Dept. of Energy. 

Energy Efficiency and Renewable Energy. Document No. ORNL/TM-2005/134. June 

2006. Contract No. DE-AC05-00OR22725.

8. “Hexavalent chromium in refractories”. Khoroshavin, L.B.; Deryabin, V.A.; Perepelitsyn, 

V.A.; and Lapteva, T.N. Refractories and Industrial Ceramics. Vol. 34. No. 9-10. Pp. 

457-462. 1993. 

9. “NYS Governor’s Awards for Pollution Prevention-Owens Corning, Delmar Plant”. 

Dept. of Env. Cons. NY State Press Release. Jan 30. 2013.

10. Oxygen-Enhanced Combustion. Chapter 7. “Glass”. Eleazer, P.B. and Hoke, B.C., Jr. pp. 

215-236. 1988. Ed. Baukal, Charles E.

11. Refractory Insulation and Fire Brick. Glass Furnace. Refractory Insulation and Fire Brick 

Website, 2012.

12. Saint-Gobain SEFPRO. Sintered High Chromium Oxide. Saint-Gobain websites, 2012.

13. Refractories for Industrial Processing: Opportunities for Improved Energy Efficiency. 

Hemrick, James G.; Hayden H. Wayne; Angelini, Peter; Moore, Robert E.; and Headrick, 

William L. for Oak Ridge Nat’l. Labs. January 2005.

14. “Environmental Issues Affecting Raw Material Selection”. GMIC Workshop, Columbus, 

OH. Oct 20, 2011. Ross, Philip C. www.GlassIndustryConsulting.com.