Of all the greenhouse gasses contributing to climate change, none is more potent than sulfur hexafluoride (SF₆). It may be lesser known, but SF₆ is 23,500 times more effective at trapping heat than its carbon-rich counterpart, carbon dioxide (CO₂). It’s been used to fill tennis balls, insulate soundproof windows, and even provide the cushioning in Nike’s Air Max shoes, however the majority of SF₆ is used in the power sector, providing critical insulating properties for high-voltage equipment.

Since the majority of SF₆ emissions in the U.S. are attributed to electricity transmission and distribution, policymakers can effectively reduce the production of this gas through regulations in the power sector. There are limited examples of state-level SF₆ regulations, although as we continue to expand electricity infrastructure, it’s critical that we avoid locking in additional emissions of this high-potency greenhouse gas. Through improved technologies and industry practices, many SF₆ emissions can be greatly reduced or avoided altogether.

In this policy explainer for our Dashboard Digest article series, we’ll dive deeper into the sources of SF₆ emissions and how states can help reduce them.

What is Sulfur Hexafluoride (SF₆) and Why is it Important?

While sulfur hexafluoride (SF₆) can occur naturally, the vast majority of SF₆ in our atmosphere was made by humans. It was first formulated in 1901 by French chemist, Henri Moissan, who won the Nobel Prize in Chemistry for the first isolation of fluorine. SF₆ is odorless, nontoxic, stable, and it can hold an electric charge, making it extremely useful in electrical applications.

Today, it’s most commonly used to insulate high voltage equipment in transmission and distribution power systems by quenching, or extinguishing, the arc that’s formed when an energized circuit breaker is opened. Although SF₆ is used in other industries, approximately 75 percent of all SF₆ emissions in the U.S. were attributed to the power sector in 2021. To a lesser extent, SF₆ is also currently used in the manufacturing of electronics and semiconductors, and the production of metals like magnesium.

It’s estimated that SF₆ only contributes around 0.8 percent of global CO₂e emissions, however because it’s such a potent greenhouse gas, any potential reductions are important to address. Plus, research suggests this figure could be an underestimate. Many utilities are not required to report SF₆ emissions to the Environmental Protection Agency (EPA), meaning we may not have an accurate picture of how high they really are. However, the EPA recently revised the way it estimates SF₆ emissions from non-reporting facilities. In the past, their SF₆ emissions reductions were estimated to follow the same trend as the facilities that were required to report to the EPA. The new calculation assumes that non-reporting facilities may not have decreased their emissions by quite as much. This change by the EPA could serve as an example to help other governments better track their own emissions.

Reporting is also not just a U.S. problem: one study found that current inventories of SF₆ emissions only account for half of the total concentration of global SF₆ found in the atmosphere. This means that we know that a significant amount of SF₆ emissions are going unreported, we just don’t know where they’re coming from. It’s crucial that we gain a deeper understanding of where SF₆ leaks are occurring in order to stop them.

How States Can Mitigate SF₆ Emissions

There are three basic approaches to managing SF₆ emissions: 1) implementing reporting requirements, 2) establishing responsible SF₆-use practices, and 3) phasing down of SF₆ equipment.

Reporting Requirements

One of the simplest ways regulators can reduce SF₆ emissions is to implement reporting requirements. The EPA’s Greenhouse Gas Reporting Program requires companies to report large sources of emissions. In the past, if the equipment’s listed SF₆ capacity was under 17,280 pounds, utilities would not be required to report any emissions. This year, the EPA expanded the definition for which utilities would be required to report their emissions. The new EPA rules replace this threshold with a total CO2e estimate — meaning companies with emissions greater than or equal to 25,000 metric tons (MT) CO2e must report any SF₆ (and other) emissions. This will help create a more accurate estimate of the total SF₆ emissions in the U.S.

Some states across the U.S. have their own SF₆ reporting requirements. In Washington, electric power entities that import or deliver electricity must report emissions that are greater than or equal to 10,000 MT CO2e per year. In Oregon, all investor-owned utilities and electricity service suppliers must report SF₆ emissions. Often, these state requirements are part of a broader effort to reduce emissions of all greenhouse gasses.

Responsible SF₆ Use

When utilities are unable to implement alternative technologies in their equipment, it’s important that they’re responsibly managing how they use existing SF₆. State regulators can work with utilities to encourage responsible SF₆ use through best practices and policies in a way that’s cost-effective and mutually beneficial. The federal government has been doing this for decades and states can learn from their success.

In 1999, the EPA established the SF₆ Emission Reduction Partnership for Electric Power Systems, a collaborative effort between utilities and the federal government to identify, recommend, and implement cost-effective solutions that mitigate SF₆ emissions. According to the EPA, the Partnership has slashed SF₆ emissions in the U.S. by 80 percent since 1990 levels.

The Partnership has identified the following best practices for the industry to reduce SF₆ emissions:

• Establish a lifecycle approach for SF₆ management
• Establish procedures for gas inventory, accounting, and tracking
• Ensure good management of SF₆ acquisitions and gas inventory
• Train employees annually in SF₆ handling and in using the necessary equipment
• Recycle SF₆ gas at equipment servicing or disposal
• Implement leak detection and repair strategies
• Upgrade equipment to reduce SF₆ use and leaks
• Decommission equipment properly

Phasing Down SF₆ Equipment

States can also implement solutions to phase down the use of SF₆ in gas-insulated equipment through emissions limits and utilization restrictions. This helps increase demand for alternative technologies including those utilizing less potent gasses and clean vacuum-insulated switchgear (a key component of power systems that protects and isolates electrical equipment). For example, a proposed regulation in New York sets a retirement timeline for SF₆ equipment and a ban on acquisition after designated phase-out dates. Starting in 2025, owners of SF₆ gas insulated equipment will be required to maintain an inventory of their equipment and the phase-down will occur through 2033. The New York Department of Environmental Conservation is expected to issue final SF₆ regulations later this year.

State Examples

California

California’s Regulation for Reducing Sulfur Hexafluoride Emissions from Gas Insulated Switchgear took effect in 2011. It was codified in the same part of the law as the California Air Resources Board’s (CARB) mandatory greenhouse gas reporting and cap-and-trade regulations. California’s rule applies to all owners of SF₆-insulated switchgear and set an annual maximum rate of SF₆ emissions, starting at 10 percent in 2011 and reduced by one percent each year until 2020. From 2020 on, the maximum SF₆ emissions rate cannot exceed one percent for any owners of SF₆-insulated switchgear.

In 2022, the CARB introduced new regulatory amendments to phase out the use of SF₆ in gas-insulated equipment starting in 2025. The new regulations restrict utilities from purchasing SF₆ equipment after certain dates, require new emissions limits, set reporting requirements, and maintain gas-insulated equipment inventories.

Massachusetts

Massachusetts has a regulation that applies to any company or municipality located in the state that owns, leases, operates, or controls SF₆-containing equipment. The state set a maximum annual SF₆ leak rate of one percent, and requires owners to maintain their equipment in accordance with industry standards to reduce leakage of SF₆. Any owners that exceed this leak rate must inform the Massachusetts Department of Environmental Protection and describe how they will reduce this rate in the future. The regulation also requires that any SF₆-containing equipment that is removed must be securely stored, re-used, recycled, or properly disposed of.