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Halogenated substances are chemicals that have been engineered for a variety of industrial uses. Some are greenhouse gases with high global warming potentials (GWPs) as compared with carbon dioxide and, therefore, may have an effect on global climate disproportionate to the relatively small volumes emitted.

Emissions of halogenated substances can be classified into two groups. One group consists of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and other chlorine-containing gases whose phase-out is governed by the Montreal Protocol. The United Nations Framework Convention on Climate Change (UNFCCC) excludes from its provisions gases covered by the Montreal Protocol and, therefore, does not address CFCs and HCFCs.

The halogenated substances in the second group include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). These compounds are also potent greenhouse gases. In contrast to the chlorine-containing halogenated substances, these compounds do not destroy ozone, and as such are not governed by the Montreal Protocol.

Of particular interest to the electric power sector is SF6. Sulfur hexafluoride is used as an insulator for circuit breakers, switch gear, and other electrical equipment. The electric power industry uses roughly 80% of all SF6 produced worldwide. SF6 has a very high GWP – 23,900 times the warming effect of carbon dioxide per ton emitted. Therefore, even small amounts of SF6 emissions can constitute a significant carbon-equivalent emission tonnage.

Under ideal operating conditions, SF6 would remain contained within transmission and distribution equipment. In reality, however, SF6 is inadvertently emitted into the atmosphere during various stages of the equipment’s life cycle. Leaks generally increase as equipment ages. Fugitive emissions can escape through valve fittings and at joints between flanges and porcelain bushings. SF6 can be accidentally released at the time of equipment installation as well as during servicing.

In order to address this challenge, members of the electric power industry and EPA have come together in a collaborative effort to reduce SF6 emissions. In 1999, EPA created the “SF6 Emissions Reduction Partnership for Electric Power Systems” to help the electric power industry reduce its emissions of SF6. More than 70 electric utilities currently participate in EPA’s program.

Each year, the program’s participants have exceeded their goals for reducing SF6 emissions. According to EPA’s 2007 Annual Report, SF6 Partners in 2007 have collectively achieved a 64-percent decrease in emissions from the 1999 baseline year. Approximately 366,538 pounds of SF6, or the equivalent of 3.97 MMTCO2 emissions were avoided in 2007. Cumulatively (1999-2007), emissions avoided total 1,554,278 pounds or 16.85 MMTCO2e.

The SF6 emissions data reported to EPA were further analyzed to identify the trend in SF6 emissions reductions from the 2000-2002 base period used by Power Partners℠ and to update the estimated equivalent amount of CO2 emissions using the latest global warming potential equivalence factors. The results show that the power sector avoided a cumulative total of 3.4 million tons of CO2 emissions from the 2000-2002 base-period average through 2005. This is shown in the figure below:

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When Duquesne Light Company decommissioned its Carson Substation in Pennsylvania, the company paid careful attention to ensure the project was completed in an environmentally responsible manner. As part of the decommissioning process, the company worked with a vendor to recover and safely remove the SF6 gas. As a result, nearly 7,300 pounds of SF6 were removed, instead of being released in the atmosphere. This is equivalent to the CO2 emissions reductions realized from removing 17,000 cars from the road for one year.

As part of Exelon’s ComEd and PECO subsidiaries’ participation in the EPA Partnership, the companies set a joint SF6 goal in March 2006, committing to achieve a leak rate for SF6 of no more than 10 percent for 2006. To help achieve this goal, the companies provided additional training to substation personnel on the proper handling of SF6 gas to minimize leaks and revised SF6 handling procedures.

Great River Energy (GRE) reduced its 2005 SF6 emissions to half of its 1998 baseline of 3,335 pounds through additional employee awareness training; monitoring SF6 equipment for leaks; replacing old, large-volume equipment with smaller more efficient equipment; and investigating other available technologies.

Lower Colorado River Authority’s participation in EPA’s SF6 Emissions Reduction Partnership resulted in the reduction of 1,800 pounds of SF6 emissions in 2005 through circuit breaker replacements.

As part of MidAmerican Energy’s participation in EPA’s Partnership, the utility replaces at least three circuit breakers that leak SF6 each year. To date, 13 345-kV circuit breakers have been replaced, and SF6 emission rates have decreased from 23.9 percent in 2000 to 9.5 percent in 2005.

Since 1999, Northeast Utilities has reduced its SF6 emission rate by over 90 percent, a great achievement given that the utility has experienced significant transmission system growth during this period. These emission reductions were achieved in part through a dedicated equipment replacement program.

Public Utility District No. 1 of Douglas County, Washington has reduced emissions of SF6 through proper handling techniques, identification and elimination of leaks, and the replacement of equipment that do not meet specific leak rate thresholds. Douglas PUD successfully reduced its emission rate to zero in 2004 and continues to maintain zero emissions as of 2005.

Southern California Edison (SCE) received an EPA award for preventing nearly 110,000 pounds of SF6 emissions from entering the atmosphere from 1999 to 2005. This reduction is equivalent to removing 250,000 cars from the road for one year. Since joining the EPA partnership in 2001, SCE has reduced its SF6 emissions by 32 percent.

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Environmental Protection Agency, “Reducing SF6 Emissions Means Better Business for Utilities: PG&E Case Study”
http://www.epa.gov/electricpower-sf6/documents/pge_casestudy.pdf

The experience of PG&E can help other utilities in meeting their environmental and operational goals through cost-effective solutions to reduce SF6 loss.

Environmental Protection Agency, “SF6 Emissions Reduction Partnership for Electric Power Systems”
http://www.epa.gov/highgwp/electricpower-sf6/index.html

The SF6 Emission Reduction Partnership for Electric Power Systems is a collaborative effort between EPA and the electric power industry to identify and implement cost-effective solutions to reduce sulfur hexafluoride (SF6) emissions. Currently over 70 utilities participate in this EPA program.

Environmental Protection Agency, “SF6 Emissions Reductions Partnership for Electric Power Systems: 2007 Annual Report” (December 2008)
http://www.epa.gov/electricpower-sf6/documents/sf6_2007_ann_report.pdf

EPA’s annual report for the SF6 Emission Reduction Partnership for Electric Power Systems documents the Partnership’s progress in abating SF6 emissions through cost-effective practices and technologies. Cumulative SF6 emissions avoided by partners since 1999 are presented, as well as the latest results reported by partners for 2007.

Environmental Protection Agency, “SF6 Emissions Reporting Protocol” (spreadsheet)
http://www.epa.gov/highgwp/electricpower-sf6/documents/partnersf6reporting_eform.xls

This link will launch an Excel spreadsheet to assist in SF6 reporting to EPA's program. The Excel worksheet is based on the mass-balance method, and works by tracking and systematically accounting for all company uses of SF6 during the reporting year.

U.S. Department of Energy, Energy Information Administration, “Voluntary Reporting of Greenhouse Gases 2004”, Report #DOE/EIA-0608(2004), March 2006. Chapter 6: HFCs, PFCs, and Sulfur Hexafluoride”
http://www.eia.doe.gov/oiaf/1605/archive/vr04data/

In 2004, 33 entities reported on 59 projects that reduced emissions of HFCs, PFCs, and SF6. these projects claimed direct reductions of SF6 emissions that totaled over 7 million metric tons carbon dioxide equivalent. NOTE: EIA does not plan to produce a full version of the 2005 annual report on the 1605b Voluntary Reporting of Greenhouse Gases Program.  Budget considerations and the need to develop forms, instructions, and software under new guidelines prompted this decision.     

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