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MEMORANDUM

Date: March 5, 2013

Subject: Technical Basis for Separate Chromium Emission Limits for Wool 

Fiberglass Glass-Melting Furnaces

To: Susan Fairchild, OAQPS

I. BACKGROUND 

In the 1999 Wool Fiberglass Manufacturing NESHAP (subpart NNN), EPA, EPA promulgated 

emission limits for PM (0.5 lb PM per ton of glass pulled) as a surrogate for non-mercury metal 

HAP emitted from glass-melting furnaces. The rationale for this surrogacy is that the metal HAP 

are contained (in trace amounts) in the PM, and that the PM control devices remove non-mercury 

metal HAP with the same efficiency as they remove total PM. Therefore, a limit on PM also 

creates equivalent control of the non mercury metal HAP. See National Lime v. EPA, 233 F.3d at 

639 (use of PM as a surrogate for metal HAP is reasonable under these circumstances).

II. TECHNICAL BASIS FOR SETTING CHROMIUM LIMITS

We continue to believe that PM is an appropriate surrogate for non-mercury metal HAP for all 

types of glass-melting furnaces at wool fiberglass manufacturing facilities. The EPA may use a 

surrogate to regulate HAP if there is reasonable basis to do so. We have used PM as a surrogate 

to regulate non-mercury metal HAP becauseHAP because: “(1) HAP metals are invariably 

present . . . in PM;” (2) “PM Control technology indiscriminately captures HAP metals along 

with other particulates;” and (3) “PM control is the only means by which facilities achieve 

reduction in HAP metal emissions.” National Lime v. EPA, 233 F.3d at 639. We have also 

always reasoned that “[i]f HAP metals are invariably present in ...PM, then even if the ratio of 

metals to PM is small and variable, or simply unknown, PM is a reasonable surrogate for the 

metals-assuming ... that PM control technology indiscriminately captures HAP metals along with 

other particulates.” Id. Additionally, we believe that PM controls are still effective for chromium 

emissions at the same efficiency as total PM and other metal HAP. However, we believe that in 

the case of gas-fired furnaces a separate chromium limit is also necessary to provide for 

additional removal of chromium than provided by PM control alone. This control would be 

provided by a polishing NaOH scrubber following primary PM control, which scrubber would 
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selectively remove chromium (i.e. remove chromium preferentially to removal of other metal 

HAP). .

In general, the PM emissions from glass-melting furnaces result from the entrainment of small 

particles of the raw material feed in the exhaust gas. The feed materials going into the furnace 

contain trace amounts of chromium and other HAP metals. Therefore, the resulting PM also 

contains HAP metals (including chromium) in trace amounts. However, there is also a second 

particulate source which is the refractory above the glass melt line of the furnace, which, for gasfired furnaces is both chromium-rich and can become entrained in furnace emissions. 

Specifically, due to the chemical and thermal properties of the gases, a corrosive environment 

exists within a gas-fired furnace. This causes erosion of the refractory lining of the furnace, 

which releases chromium-bearing refractory particles into the furnace exhaust gas as PM. 

Though all furnaces are lined with chromium refractories at and below the glass melt line, gasfired furnaces may construct the entire furnace (crown, sidewalls, front and back walls, 

forehearth, etc.) from chromium refractories. This chromium refractory does not contain 

chromium in merely trace amounts; rather, chromium compounds make up a significant portion

(over 94%) of the refractory composition above the glass melt line1

. This results in gas-fired 

furnaces emitting particulate that contains chromium in larger amounts than that of electric 

furnaces. Based on PM and chromium emissions test data collected from industry for 

development of the proposed rule, chromium constitutes an average of 0.96 percent of PM 

emissions for gas-fired furnaces, which is 13 times higher than the average for electric furnaces 

(0.07 percent of PM emissions are chromium). 2

As an example, if a furnace is emitting 100 pounds per year (lb/yr) of uncontrolled PM and has a 

99.9 percent efficient control device; assume that total metal HAP are about 1 percent of the 

uncontrolled PM, and chromium makes up 10 percent of the metal HAP. Controlled PM 

emissions would be 0.10 lb/yr of PM, and controlled chromium emissions would be 0.0001 lb/yr. 

However, if the 100 lb/yr of PM came from the chrome refractory located above the glass melt 

line of a gas-fired furnace, the chromium content might be as high as 50 percent of the PM. This 

would result in the same level of controlled PM emissions, 0.10 lb/yr, but controlled chromium 

emissions of 0.05 lb/yr. This is a 500 fold increase in chromium emissions but no increase in 

total PM emissions.

Because chromium compounds are a significant component of the refractory used above the 

glass melt line in gas-fired furnaces, a greater potential for chromium emissions exists, which is 

not associated with a commensurate increase in emissions of other HAP metals. 

Emissions test data for glass-melting furnaces at gas-fired wool fiberglass manufacturing 

facilities indicated that the phenomena discussed above can result in emissions levels of 

chromium up to 50 lb/year, and in one case as high as 540 lb/year from gas-fired furnaces, while 

 1 See the 114 responses from all wool fiberglass manufacturers on furnace design, construction, and refractory 

composition. Also, see product specification statements from St. Gobain, in references.

2 See the Modeling File in the Docket for this rule.
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emissions from electric furnaces at similar PM emissions levels are below 5 lb/year. Table 2 

shows a comparison of the average and maximum total chromium emissions between electric 

and gas-fired glass-melting furnaces. Chromium has been identified by EPA as one of the urban 

air toxics based on its prevalence and toxicity in urban areas (see EPA’s Urban Air Toxics 

Strategy, published 64 FR 38705 (July 19, 1999).)

Table 2. Average Annual Total Chromium Emissions for Glass-melting Furnaces1

Average Chromium 

Emissions per 

Furnace (lb/yr)

Maximum Chromium 

Emissions from a 

Furnace (lb/yr)

Electric 

Furnaces 0.38 1.7

Gas-fired 

Furnaces 42 540

1. Based on furnaces for which PM and chromium emissions testing was submitted

Chromium can be controlled preferentially through use of aof a packed bed sodium hydroxide 

(NaOH) scrubber. However, this type of control is not effective in reducing PM emissions. Thus, 

a PM limit alone would not adequately control chromium (as just illustrated) and would be a 

poor match for the control technology on which the proposed chromium limit is based. Since the 

control technology would not capture PM indiscriminately with chromium (see 233 F. 3d at 

369). 

In lieu of setting both a PM and chromium limit, we also considered setting a chromium limit 

alone. However, the PM limit is the most effective means of assuring control of the other HAP 

metals, since that control is predicated on performance of a primary control device which 

controls HAP metals indiscriminately. Moreover, for all the reasons noted above (i.e. the fact 

that the PM controls are still effective, but the chromium content of the particulate is increased) 

we believe it would be difficult to improve the efficiency of the PM controls to meet a chromium 

limit based on GACT.
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References

1. High Performance Refractories: Chromium Oxide. Saint-Gobain Product Specification Sheet in 

Ceramic Materials. Saint-Gobain.com, 2013.

2. SEFPRO. Saint-Gobain Product Specification Sheet for Refractories for the Glass Industry. SaintGobain.com, 2013.

3. Project Database for Development of the Wool Fiberglass Manufacturing RTR and Area Source Rules.