Overview of SF6 Emissions and What Can Be Done to Reduce Them

Before we begin talking about SF₆ emissions, let’s get a better understanding of Sulfur hexafluoride. SF₆ is an inert, manmade gas composed of one Sulphur and six fluoride atoms. It is odorless, colorless, and chemically inert. It is also non-flammable and has a higher density than air. The high density of SF₆ gas makes it vibrate more slowly across your vocal cords, so when it’s inhaled, your voice will sound very low and deep. Though the pure gas is non-toxic, it can irritate the lungs and vocal cords. Additionally, SF₆ can contain dangerous acid vapors and cause serious health risks if inhaled, so please don’t try at home. Finally, as you’ll learn in a bit, SF₆ emissions (even from a balloon) should be avoided at all costs.

SF₆ has an extremely stable molecular structure, requiring a high temperature (up to 500^oC ) to break its bonds. Even if the bonds are broken during, say, an arcing event, SF₆ will mostly recombine. You can read more about SF₆ gas and its properties here. These properties make it an excellent dielectric and its high thermal conductivity make it more effective than air, nitrogen, or other dielectrics at dissipating heat. SF₆ has been used as a dielectric in gas-insulated substations and switchgear since the 1950s.

That all sounds pretty good, right? Well, the same properties that make SF₆ such a perfect dielectric also make it the most potent greenhouse gas. SF₆ emissions are serious because SF₆ gas is 22,800 times more effective at trapping infrared radiation over a 100-year period than the more famous greenhouse gas, CO2. Although SF₆ emissions make up a small proportion of greenhouse gases found in the atmosphere, controlling SF₆ emissions is so important because of its lifespan of 3,200 years. Even a small amount emitted into the atmosphere has a significant impact on climate change.

SF₆ Emissions by Sector

In order to reduce SF₆ emissions, we must learn what industries are the main users and emitters of SF₆ gas. SF₆ is used in various industries, including the manufacture of electronics and semiconductors, the production of magnesium, and medical applications such as eye surgery. The largest proportion of SF₆ emissions by sector goes to the Transmission & Distribution industry. It is estimated that the T&D industry uses around 80% of the SF₆ gas manufactured and is therefore responsible for a large majority of the SF₆ emissions found in our atmosphere. In fact, the EPA estimates that around 71% of all SF₆ emissions in the United States are attributed to the electrical transmission and distribution industry.

The Most Common Causes of High SF₆ Emissions

• Virgin SF₆ Gas: One of the causes of SF₆ emissions in the T&D industry stems from the sourcing of the gas. The production of virgin SF₆ gas is a known source of emissions and must be imported from countries that have not banned its manufacture, such as parts of Eastern Europe and China.

• Faulty or Leaking Gas Insulated Equipment (GIE): Properly maintained SF₆ GIE has a lifespan of more than 30-40 years. Overtime, GIE can become compromised and begin to leak SF₆ gas into the atmosphere.
• Improper SF₆ Gas Handling Methods: Our late CEO, Lukas Rothlisberger, used to say that our industry does not have an SF₆ gas problem but rather an SF₆ gas HANDLING Problem. While it cannot be disputed that SF₆ gas is a potent greenhouse gas, there should be little to no emissions to the atmosphere when proper steps are taken during gas handling.
• GIE Nameplate Inaccuracy and “Phantom Emissions”: With emission reporting now being mandatory for many SF₆ users, reports of nameplate discrepancies have become quite common.  Across the industry both SF₆ users and regulatory agencies alike are faced with the difficulty of trying to gather accurate data. When the nameplate capacity of the breaker is incorrect, this can result in either negative or “phantom emissions”. For example, if the actual value is 300 lbs and the nameplate is 280 lbs, there will be a negative emission of 20 lbs. Conversely, if the true value is 280 lbs and the nameplate is 300 lbs, there will be a “phanotom emission” of 20 lbs.

Tips for Reducing and Controlling SF₆ Emissions

Regulatory agencies such as the Environmental Protection Agency (EPA) and the California Air and Resources Board (CARB) have begun imposing regulations on SF₆ gas and to reduce SF₆ emissions. Whether or not your company is affected, you can start taking steps to reduce emissions, which will save your company money and help the environment. Below are some basic tips on how to reduce SF₆ emissions:

1. Invest in Training: Well-trained technicians are the first line of defense against SF₆ emissions. There is no substitute for knowing how to properly operate SF₆ gas handling equipment.  According to the EPA, “Employees involved in handling gas should be specifically trained in SF₆ handling and using equipment for performing this task on a routine basis (e.g., annual refresher training)”. DILO offers both virtual and in-person SF₆ Safety and Handling Training to help keep your staff up to date on best practices and the latest regulations.

2. Utilize Zero-Emission Gas Handling Equipment: Using the right tools for the job is half the battle. Be sure that you’re using appropriate leak detection equipment in the field and consider a room monitor system for indoor Gas Insulated Substation (GIS) applications. Utilize a measuring device that has an internal recovery feature or is compatible with a recovery bag to avoid venting SF₆ to the atmosphere during testing. It’s also important to use the correct size and type of recovery unit for the volume of SF₆ gas you’re working with. Our SF₆ Time Calculation App can help you determine which gas cart is suitable for your application.

3. Choose Reconditioned SF₆ Gas: As mentioned earlier, sourcing virgin SF₆ gas contributes to SF₆ emissions. Luckily, SF₆ gas that has been reconditioned to meet or exceed IEEE standards can be used in place of virgin gas in applications for the T&D industry. Another bonus is that sourcing reconditioned SF₆ is usually much less expensive than purchasing virgin gas. DILO team members have written a few articles on reconditioned SF₆ gas if you’d like more information. It’s important that you select a vendor who conducts 3^rd party testing to verify that the gas has been reconditioned to meet or exceed IEEE standards, thereby making it safe to use in Gas Insulated Equipment (GIE).

4. Recover to Blank-Off Pressure: Be sure to reach the lowest level of vacuum or blank-off pressure possible during SF₆ gas recovery. If the amount of gas in GIE is reduced to atmospheric pressure, a startling 20% of residual gas is left inside. This creates a high potential for an SF₆ emission.

5. Verify Nameplate Capacity: Check the OEM’s manual or nameplate for accurate SF₆ capacity information. Overfilling GIE can result in SF₆ emissions by engaging the pressure relief valve. Using a mass flow meter or cylinder weight scale to track SF₆ gas movements is also helpful and can prevent any errors that may result in “phantom emissions”.  Ensure that your mass flow meter is capable of measuring liquid SF₆ gas. We have an excellent white paper, SF₆ Nameplate Inaccuracies and their Impact on Greenhouse Gas Reporting, that covers this topic in more detail.

6. Use Proper Fittings and Adapters:  Ensure fittings used for connection to GIE and other accessories (manifolds, analyzers, cylinders, etc.) are leak tested. Refrain from using threaded connections, which are prone to leak over time. Metal to metal sealing technology is best for SF₆ gas handling.

The above is not an exhaustive list- we could spend all day writing and talking about ways to reduce SF₆ emissions and still have more to say. For a more in-depth experience, we suggest you check out our SF₆ Safety and Handling Trainings. We can even come to your facility to train your entire team on how to reduce SF₆ emissions. Please contact us if you have any questions or receive more information on custom training at your facility.