Rationale For Chromium Compounds From Wool Fiberglass Manufacturing

We are regulating chromium compounds as a ‘brick issue’ in the NESHAP. Although the 1999 rule used PM as a 

surrogate for HAP metals, we believe certain forms of chromium compounds (chromic oxides) have volatile 

characteristics in the furnace process and are emitted more readily than the other HAP metals present in the PM 

of the furnace emissions. Therefore we question whether PM is an appropriate surrogate for the HAP chromium 

compounds from this source category, but we have no reason to believe that PM is not an appropriate surrogate 

for other HAP metals from furnace processes. We are therefore proposing emission limits for chromium 

compounds in the RTR.

Furthermore, we make no distinction between furnaces at area sources and those at major sources. We are 

therefore proposing to regulate furnace emissions at wool fiberglass area sources in the same way that we 

regulate furnaces at major sources in this source category. We are listing the area source category “wool 

fiberglass manufacturing” for regulation under this proposed rule.

The risk assessment concluded that the MIR for wool fiberglass is 40-in-one million. We recognize uncertainties 

inherent in the risk assessment methodology in the preamble to the proposed rule. When risks are between 1-in 

one-million and 100-in-one million, we generally consider other factors in our determination of whether the 

risks are acceptable and present an ample margin of safety. Because glass furnaces must be rebuilt every 7-10 

years, and because one facility emits 840 lb of hexavalent chromium per year due to furnace construction using 

high chrome refractories, we examined what the risks would be if all wool fiberglass furnaces rebuilt their 

furnaces using high chrome refractories and as a result emitted at this level. We found under this hypothetical 

scenario that the risks would be 900 in one million from one facility and over 100 in one million from 7 other 

facilities. 

We believe industry has a strong economic incentive to rebuild glass furnaces using high chrome refractories 

because this practice extends furnace life almost two-fold. Therefore, a furnace constructed of high chrome 

refractories would have to be rebuilt every 14-20 years instead of 7-10 years. The cost of rebuilding a furnace 

lies mostly in the labor to rebuild, and not so much in the materials themselves. This practice costs and 

additional 15% over the use of conventional refractories for furnace rebuilds.

Moreover, because most of the industry has phased out the use of formaldehyde-based binders in their 

manufacturing processes, sources that were once major are now area sources. We have some information 

indicating that all but 2 facilities are area sources. While we encourage and applaud the ‘green’ choice across 

the industry to phase out sources of HAP, we are also concerned that in the near future, furnaces at both area 

and major sources may choose to rebuild their furnaces using high chrome refractories. Although this does not 

change the risk assessment results in the RTR, the hypothetical scenario and the economic incentives presented 

by high chrome refractories inform our finding of a threat of adverse health effect for the area source finding. 

We do not fully understand the properties and all of the different types of chrome compounds that may be 

emitted from wool fiberglass furnaces at this time. We plan to issue 114 letters to the wool fiberglass industry to 

gather additional information on refractory composition and complete chrome and hexavalent chromium 

emission testing.