Continuous Emissions Monitoring 101: In-Facility Leak Detection Sensor Networks (LDSN)

June 20, 2024—

Leak Detection and Repair (LDAR) is a work practice designed to identify leaking equipment so that Volatile Organic Compound (VOC) emissions can be reduced through repairs. LDAR regulations require monitoring at specified, regular intervals to determine whether or not equipment is leaking. Method 21, promulgated in 1981, uses a portable instrument to detect methane and VOC leaks from individual sources (PID or FID). Optical Gas Imaging (OGI) is an Alternative Work Practice (AWP) promulgated in 2008 designed to identify leaking equipment at regular intervals using thermal infrared radiation to detect gasses.

In February of 2023, the EPA announced  the approval of the first alternative means of emission limitation (AMEL) which allows the use of a Leak Detection Sensor Network (LDSN) along with a Detection Response Framework (DRF). The introduction of LDSNs in the environmental regulatory landscape marks a significant advancement in the approach to controlling VOC emissions, particularly within the oil and gas sector. LDSNs have the potential to replace or enhance traditional methods of leak detection and monitoring within the oil and gas sector such as OGI and Method 21. LDSN approval provides an innovative, automated, and comprehensive means of providing LDAR compliance.

LDSN At A Glance

Benefits of LDSNs

Leak Detection Sensor Networks use real-time sensors strategically deployed across industrial facilities to monitor for in-facility leaks 24/7. The autonomous nature of LDSNs allows for swift alert notifications to LDAR technicians, enabling prompt and efficient repairs.

Upon reaching a notification threshold, a Potential Source Location (PSL) window is assigned, triggering a DRF-guided response from LDAR personnel to investigate and identify the emission source. The identified source is measured using calibrated Method 21 equipment (or OGI) to document peak concentration values and initiate repair procedures. All leak-related information is then recorded in a mobile device for regulatory, operational, and quality assurance purposes, streamlining the operation of the LDSN.


LDSNs offer an efficient and proactive approach to emissions management, minimizing environmental impact and ensuring operational integrity. Understanding LDSNs is crucial to deciding which approach to use in controlling your facility’s emissions.

Emissions Reductions: LDSNs are equipped with automated detection capabilities and can trigger alerts when emissions exceed thresholds. This automated approach enhances the speed of response times resulting in drastically lower fugitive emissions. Using an environmental data platform such as Montrose’s Sensible EDP allows companies to view all of their sensor data in a single dashboard across computers, tablets, and mobile devices.

Process Safety: LDSNs ensure prompt leak detection and immediate response to enhance safety practices while meeting regulatory requirements. By eliminating the need for personnel to conduct potentially hazardous Method 21 or OGI inspections, LDSNs contribute to a safer working environment. Additionally, the comprehensive coverage of LDSNs reduces the facility's vulnerability to leaks, enhancing overall safety and regulatory adherence.

Continuous Monitoring: Methane emissions pose particular difficulties in quantification due to their often-unpredictable nature, stemming from events like leaks, equipment malfunctions, or third-party damage, which can vary widely in terms of quantity, duration, and frequency across industries. LDSNs provide continuous, real-time monitoring of emissions, offering immediate response to potential leaks.

Cost Reductions: While there are initial setup costs for LDSNs t, their continuous monitoring capabilities can lead to long-term savings compared to periodic inspections required by Method 21 and OGI. These savings include reduced manpower requirements, recovery of “lost” product, proactive risk mitigation, and minimized litigation expenses.

Comprehensive Coverage:  LDSNs cover a wide area and multiple points simultaneously, ensuring a comprehensive and efficient monitoring system. Method 21 and OGI inspections may be more localized and time-consuming, potentially missing emissions sources in other areas.


Best Practices to Consider

Forward Thinking Emissions Monitoring

As organizations adopt LDSNs as a forward-thinking method for emissions monitoring, it becomes crucial to implement best practices. Here are some to keep in mind to maximize your LDSN’s performance:

Strategic Sensor Placement: Carefully position sensors in critical areas within the facility to maximize coverage and ensure the detection of potential leak sources.

Regular Calibration: Conduct regular calibration of sensors to maintain accuracy and reliability in detecting emissions.

Adherence to Regulatory Standards: Stay informed about evolving regulatory standards and ensure that LDSN configurations and practices align with the latest requirements. This proactive approach helps organizations adapt to changing compliance landscapes.

Documentation and Reporting: Maintain detailed records of LDSN data, including detection events, responses, and corrective actions. Accurate documentation is essential for regulatory reporting, internal audits, and demonstrating compliance.

Periodic System Audits: Conduct periodic audits of the entire LDSN system to identify and address any issues promptly. Regular assessments help optimize system performance and identify areas for improvement.


Additional Considerations

Voluntary Sustainability Initiatives

  • Oil & Gas Methane Partnership 2.0 (OGMP 2.0): OGMP 2.0 is a partnership among oil and gas companies, international organizations, governments, and NGOs aiming to improve methane emissions reporting. It provides a comprehensive framework for measuring emissions across all value chain segments, aiding emission reduction efforts, and enabling stakeholders to assess performance accurately.

    An LDSN may also be integrated into voluntary sustainability initiatives such as OGMP 2.0. Oil and gas operators who participate in OGMP 2.0 commit to achieving a near-zero methane intensity. The pathway to achieving the target emissions intensity starts with an accurate quantification of actual methane emissions in order to help identify the best path to cost-effective emission mitigation. Gold standard is achieved when (1) a site has compared source-level emissions with site-level emissions measurements and demonstrates a thorough understanding of site emissions, and (2) methane emissions intensity targets are aligned with OGMP 2.0 objectives. [Read more about OGMP.]

  • A LDSN could be integrated into a robust OGMP 2.0 program in two ways:

Source-Level Emissions Quantification:

If paired with a quantification technology, a LDSN may be used to quickly identify leaks that could then be quantified. Source-level emissions could be calculated using the measured emission rate and an accurate leak time. [Read more about quantification]

If paired with representative site-specific emission factors, a LDSN could be used to accurately identify the actual leak time for use in emissions estimates.

Methane Emissions Mitigation

LDSNs offer continuous monitoring for in-facility leaks, operating 24/7. Their autonomous nature enables swift alert notifications to LDAR technicians, facilitating prompt and efficient repairs, lower methane emissions, and lower methane intensities that align with OGMP 2.0 targets.

  • Sensible EDP Software

  • Detect, Pinpoint and Monitor Leaks

  • Montrose Environmental Group's Sensible EDP and its cutting-edge LDSN redefine the standard for leak detection and repair. Using C1D2 sensors, our LDSN continuously monitors facility leaks in real time, swiftly alerting LDAR technicians upon detection for prompt and efficient repairs.
  • The Sensible EDP LDSN system automatically detects and locates emission sources within monitored process units, using VOC concentration, wind speed, and wind direction. Montrose can deploy methane and total VOC sensors to address upstream, midstream, and downstream oil and gas facilities. Immediate alerts and alarms notify the LDAR team of high-level emissions, enhancing safety measures within the existing facility systems. Routine emissions are communicated over time, with repeated concentration peaks under varying wind directions, building confidence in emission event identification.

Contact us to learn more about leak detection sensor networks at or visit our website at Ready to see the platform? Use the form below to schedule a demo with one of our experts today.