Using Optical Gas Imaging to Comply with OOOOa Regulations


In June 2017, new regulations from the Environmental Protection Agency (EPA) for the monitoring of natural gas compressor stations went into effect. The new rule, “Oil and Natural Gas Sector: Emission Standards for New, Reconstructed, and Modified Sources,” which EPA labels as Subpart OOOOa to 40 CFR Part 60, is widely referred to as Quad OA. The rules require quarterly checks for methane leaks at any compressor station that has been newly constructed or modified since September 2015. Under the regulation, compressor stations have the option of performing the required monitoring using Method 21, an older approach that uses a “sniffer” to detect the presence of hydrocarbon gases, or using optical gas imaging with an IR camera, the more modern option, which has been designated by the EPA as the “best system of emission reduction.”

Optical gas imaging uses spectral filtering to target the infrared wavelengths absorbed by the gas, letting the user visualize otherwise invisible gas leaking from pipes and equipment. This approach provides distinct advantages over Method 21. For example, whereas Method 21 only reports the concentration of methane in the air at the spot where the test is performed but cannot provide any information about the rate or direction in which the gas is flowing, optical gas imaging allows inspectors to actually see where the gas is coming from, making leaks easier to find and repair. In addition, optical gas imaging saves considerable time by allowing the inspector to survey a whole scene from a particular vantage point rather than requiring physical contact, one by one, with every potential leak source, represented by every pipe seam, joint and valve.


While the EPA’s concern with respect to the monitoring of natural gas compressor stations is the reduction of emissions of methane, a potent greenhouse gas, experience began to suggest that regular testing using optical gas imaging might save companies money and improve worker safety, as well. Montrose conducted a study to explore whether implementing these new quarterly checks for the purpose of complying with EPA rules would also deliver financial- and safety-related benefits when performed using optical gas imaging.


During the four quarters of 2017 and the first quarter of 2018, Montrose performed a total of 224 inspections at 104 facilities, housing an average of 2.4 compressors per facility, in nine different states owned by five compressor companies. Each monitoring event was carried out by a technician with at least 1,000 hours of experience in optical gas imaging, using a FLIR GF320 camera in high-sensitivity mode with a spectrally filtered indium antimonide detector and resolution of 320 by 240 pixels. Over the five-quarter period, inspectors discovered a total of 1,977 leaks, 65% of which were of low severity, 32% of which were of medium severity, and 3% of which were of high severity. The smallest leak discovered measured only 0.01 cfm, while the largest was 7.85 cfm, where each cfm of escaped gas corresponds to a cost of roughly $1,600 per year. Over all 104 facilities, a total of more than $360,000 worth of gas was saved annually as a result of the discovery of these leaks by optical gas imaging. In addition, of all the leaks found, 22 were identified as potential safety hazards, with seven of those being high hazards and three considered extreme. Finally, the emissions reduction benefit was the discovery of a total amount of methane equivalent to 59,000 metric tonnes of carbon dioxide per year. In short, optical gas imaging not only enables compressor companies meet regulatory requirements, it also saves them money and makes their facilities safer.


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