This guide is for utility, generating-station, substation, and SF6 compliance teams. It covers how OGI works, how to inspect safely, what the technology can't tell you, and what to do after a confirmed leak.
One caveat up front: OGI finds and localizes leaks. It doesn't replace electrical safety procedures, OEM instructions, or the measurement and reporting methods your program requires.
Key Takeaways
- An SF6-capable OGI camera images infrared absorption in a gas-specific band; a general thermal camera may not see SF6.
- Remote imaging can help locate a leaking component from a standoff distance, when site procedures allow.
- Wind, temperature contrast, rain, fog, background, and operator skill all affect visibility.
- A confirmed plume calls for documentation, confirmation or measurement, and a qualified repair plan.
What Is Optical Gas Imaging for SF6 Leak Detection?
OGI is infrared imaging that uses a spectral filter aligned to a target gas's absorption band. SF6 absorbs part of the infrared radiation passing through it. The camera sees the difference between the plume and its background, then processes it into a visible plume on the display, as described in an EPA-hosted paper.
Camera configurations differ
No single wavelength applies to every camera. Published FLIR specifications show the variation:
| Camera | Detector and SF6 band | Published sensitivity |
|---|---|---|
| FLIR GF306 | Cooled QWIP, 10.3-10.7 µm | <0.3 ppm-m at ΔT 10 °C, 1 m |
| FLIR GF77 with HR filter | Uncooled microbolometer, 9.5-12 µm | <1 ppm-m at ΔT 10 °C, 1 m |
The GF306 is a legacy model that FLIR lists as discontinued. Always check the datasheet for the exact camera and lens you plan to use.
OGI versus a thermal camera
An ordinary thermal camera displays temperature differences. An OGI system is configured to visualize a target gas's absorption. The GF77, for example, has a separate radiometric temperature mode and a distinct SF6 filter configuration.
A camera built for methane or other hydrocarbons shouldn't be assumed to see SF6.
What you get, and what you don't
An image tells you whether a plume is present, which way it moves, and the likely source area on the equipment.
It doesn't give you a leak rate. The sensitivities above are in ppm-m (concentration integrated along the optical path) under stated test conditions. They aren't grams per hour. An OGI scan also doesn't prove that an inspection satisfies every applicable reporting requirement.
Why SF6 Leak Detection Matters in US Substations
EPA describes SF6 as an insulating and arc-quenching gas used for current interruption in electrical equipment. Losing it reduces insulation and interrupting performance.
Reliability
In one GE breaker manual, falling gas pressure triggers an alarm and the need for a top-up. Below the minimum functional pressure, that breaker configuration may lock in position or open automatically. Setpoints vary by equipment, so check the OEM documentation.
Typical leak points, according to EPA and EPRI, include:
- Flanges and gaskets
- Fittings, valves, and pipe connections
- Bushings
- Gas mechanisms and density-monitor interfaces
- Tanks, castings, and enclosure joints
An older EPA study of more than 2,300 breakers installed 1998-2002 estimated weighted-average annual leak rates of 0.2% to 2.5%. That's a historical population, not a current fleet benchmark.
Environmental and regulatory weight
EPA gives SF6 a 100-year global warming potential of 23,500 and an atmospheric lifetime above 1,000 years. EPA also reports that electrical transmission and distribution equipment accounted for roughly 67% of US SF6 emissions in 2022, per its SF6 basics page.
Several rules may apply to your facility:
- 40 CFR Part 98 Subpart DD covers SF6 use in electrical transmission and distribution equipment. Applicability generally depends on emissions of at least 25,000 metric tons CO2e per year.
- GHGRP rules are under reconsideration, and deadlines have shifted. Check the current eCFR and EPA notices.
- California's CARB regulation phases out new SF6-insulated equipment by voltage class and sets annual emission limits for existing equipment.
EPA's voluntary SF6 partnership is no longer active, though its archived resources remain useful. Transmission & Distribution Services (TDS) notes that EPA inspection questions often ask whether a utility documents its SF6 leaks and has an action plan to repair them.
Why localize early
Visual localization helps crews prioritize repairs, plan access or outages, and avoid searching an entire GIS or breaker assembly. Treat that benefit as practical rather than quantified; authoritative US estimates of time or cost saved are hard to find.
How to Perform an SF6 OGI Inspection
Plan and control safety first
Before anyone picks up the camera:
- Identify the equipment and gas compartments, and review drawings and OEM instructions.
- Confirm approach boundaries. OSHA's arc flash fact sheet separates shock boundaries from arc-flash boundaries, and both depend on voltage, task, and equipment condition.
- Confirm that only qualified personnel will be involved.
- Decide whether the scan can happen with the equipment energized.
Remote imaging reduces the need to approach a suspected leak. It doesn't remove arc-flash, shock, pressure, switching, or site-access hazards.
Check conditions
Visibility drops when thermal contrast is weak, the plume is small relative to the pixels, distance grows, the background is cluttered, or wind disperses the gas. Note these before you scan:
- Wind direction and speed
- Rain or fog
- Temperature difference between gas and background
- Obstructions and viewing angle
- Focus and lens selection
Use the manufacturer's operating limits. For reference, the G306 datasheet lists -20 to 40 °C with the 14.5° lens, and the GF77 lists -15 to 50 °C.
Scan systematically
- Start with the whole enclosure or compartment.
- Move to known sealing interfaces and fittings.
- Scan from several angles and against different backgrounds.
- Follow any plume back toward its source without touching the equipment.
Interpret what you see
Watch plume movement and note whether the emission is intermittent or continuous. Be skeptical of hot equipment, airflow, and busy backgrounds. Published SF6 sources don't give a definitive list of false-positive artifacts, so verify by changing position or background and repeating the scan before treating a leak as confirmed.
Record each finding
- Asset and compartment or component
- Date, time, weather, and viewing conditions
- Camera model and filter
- Images or video
- Apparent source, urgency, and recommended action
- Follow-up measurement
EPA recommends equipment inventories, leak-history records, regular leak detection, and testing before and after repair.
Confirm and quantify
When you need a number, a compliance record, or repair acceptance, pair OGI with a handheld detector, analyzer, pressure or density trend, or another approved leak-rate method.
OGI Compared With Other SF6 Leak Detection Methods
| Method | What it tells you |
|---|---|
| OGI | Visual plume and source location at a distance |
| Handheld ionization detector | Local detector response (one DILO model specifies 5 g SF6/year sensitivity) |
| Handheld NDIR detector | Concentration in air (one DILO model claims 3 g/year) |
| Soap or bubble test | Leakage at an accessible joint by contact |
| Pressure/density monitor | Possible gas loss; no location |
| Ultrasonic | High-frequency sound from turbulent flow; vendor material isn't SF6-switchgear validated |
| Gas analyzer or recovery weighing | Gas quality or quantity moved; no location |
EPA reports that OGI can find minor chronic leaks missed by soap-and-water or halogen detectors. TDS's own survey work relies on infrared scanning because wind, noise, and survey thoroughness can undermine traditional methods.
When OGI fits best
- Screening many components quickly
- Locating a source on energized equipment, when permitted
- Checking hard-to-reach areas from a distance
- Documenting the plume on video
When to combine methods
Add another method for leak-rate quantification, regulatory records, very small leaks, enclosed spaces, blocked line of sight, or conditions outside the camera's specification. No controlled head-to-head SF6 comparison is publicly available.
Buy, rent, or hire
Options include buying a camera, renting one, or hiring a qualified inspection provider. FLIR and rental listings for the G306 are quote-only, and public price ranges for cameras, calibration, and services are hard to pin down. Training costs vary as well; one provider has listed $2,200 for an OGI I course, so treat that figure as outdated and request current quotes.
What to Do After Confirming an SF6 Leak
Build the decision path
- Protect personnel and equipment.
- Classify the finding by operational and environmental urgency.
- Consult OEM and site procedures.
- Decide whether continued operation is acceptable.
- Schedule repair or outage work.
EPA recommends prioritizing repairs by leak findings, following proper SF6 recovery practices, and testing before and after repair.
Repair options
Common repair paths include gasket or seal replacement, recovery and recharge, clamps, and injected sealant. EPRI's 2013 update documents one case comparing a five-day, $20,000 re-gasketing outage with a one-day, $21,000 clamp-and-sealant repair. It also reports mixed durability for some approaches.
Those are historical cases, not guarantees. Any method needs OEM procedures and equipment-specific engineering review.
Where TDS fits
TDS is a substation leak-sealing specialist. Its technicians work exclusively in substations, using low-pressure, cured-in-place gasket methods on SF6-filled circuit breakers and GIS systems. These can avoid traditional disassembly when conditions allow.
Key advantages include:
- Free equipment surveys covering location, repair price, and method
- OSHA-certified technicians
- Many repairs completed with apparatus energized and in service, when access doesn't require getting close to energized components
- A four-year leak-seal warranty
- No charge for sample repair work if TDS can't fix the leak
TDS says it must find the exact leak source before proposing a repair method. Some jobs still need an outage for safe clearance, which TDS describes as switching out and grounding the equipment.
Verify and record
After repair, repeat the OGI scan or a complementary test. Log the repair and any SF6 recovered or added, update maintenance and emissions records, and set a follow-up interval based on site procedures.
Subpart DD reporting covers equipment capacities, gas quantities acquired, returned, and recycled, and supporting calculations. General GHGRP records are kept three years after submission, and five years for verification-software records. Confirm current requirements in the eCFR.
Frequently Asked Questions
How much does an OGI camera cost?
Price varies with detector type, SF6 filter, cooled or uncooled design, lenses, software, calibration, and support. FLIR purchase and rental listings are quote-only, so request current quotes.
What type of camera can detect gas leaks?
A gas-specific OGI camera can visualize selected gases such as SF6. A standard thermal camera isn't automatically suitable, so match the camera's filter and specification to the gas.
How far away can a thermal camera see?
There's no universal distance. It depends on lens, leak size, concentration, background contrast, weather, and line of sight. FLIR's sensitivities are tested at 1 m; an EPA-hosted presentation shows a breaker filmed at about 40 ft as a demonstration only.
What is optical gas imaging?
OGI is infrared imaging that turns gas-specific absorption and background contrast into a visible plume. It lets an operator locate a leak without relying only on a point measurement.
What is IR imaging used for?
Ordinary infrared thermography shows temperature patterns. Gas-specific OGI visualizes selected gas emissions. Both are used in electrical, industrial, environmental, and maintenance inspections.
What is SF6 used for in switchgear?
SF6 insulates and helps quench arcs when breakers interrupt current. Keeping it contained supports reliability and emissions management.
