OIL & GAS EQUIPMENT | Updated May 2026 | 10 min read
What You’ll Learn in This Guide
- The complete EPA flare monitoring rule landscape 40 CFR 60.18, OOOOa, OOOOb, and OOOOc
- What each rule requires of operators and how the rules layer on a single facility
- The 98% Destruction and Removal Efficiency requirement and how it applies to different flare types
- What continuous parametric monitoring instrumentation OOOOb requires
- Performance testing requirements using EPA Methods 18, 25A, and 25B
- Recordkeeping, retention, and CEDRI reporting obligations
- How the IRA methane fee interacts with EPA flare monitoring rules
EPA’s flare monitoring rule structure layered significantly between 1990 and 2026. What started as 40 CFR 60.18 general flare requirements grew through Subparts OOOO and OOOOa, and reached current form with 40 CFR 60 Subpart OOOOb (new and modified affected facilities) and Subpart OOOOc (existing affected facilities). For operators trying to make sense of which rule applies to which facility and what each requires, the layered structure is genuinely confusing. This guide walks through the complete rule set so operators, project engineers, and compliance staff can plan accurately rather than reacting to ambiguity.
Hero Process Solutions, founded in 2011 and headquartered in Kellyville, Oklahoma with operations in Midland, Texas, manufactures industrial flare systems, vapor combustors, and emission control equipment for upstream production, midstream gas processing, refining, and petrochemical customers. All Hero products are designed for EPA OOOOb / OOOOc compliance and shipped with the monitoring instrumentation, documentation, and field commissioning support needed to satisfy the rules out of the box.
DIRECT ANSWER: EPA’s flare monitoring rule landscape consists of four layered rules. 40 CFR 60.18 (1990s) sets baseline general flare requirements including 5-minute-per-2-hour visible emission limits and minimum heating value thresholds. Subparts OOOO (2012) and OOOOa (2016) set the original New Source Performance Standards for oil and gas affected facilities. Subpart OOOOb (2024) raises requirements on new, reconstructed, and modified affected facilities 98% Destruction and Removal Efficiency, continuous parametric monitoring, annual performance testing, and CEDRI reporting. Subpart OOOOc (2024) extends the same emission guidelines to existing affected facilities through state plans. Operators need to understand which rules apply to which equipment and how the requirements layer on a single facility.
1. The Four Layered EPA Flare Monitoring Rules
40 CFR 60.18 General Flare Requirements (Foundation Rule)
40 CFR 60.18 is the foundation flare rule. It applies broadly to flares used as control devices across many EPA New Source Performance Standards categories. Key requirements include visible emissions limited to no more than 5 minutes during any consecutive 2-hour period, minimum heating value of the inlet gas (200 Btu/scf for steam-assist and air-assist flares, 300 Btu/scf for non-assisted flares), maximum exit velocity limits at the tip, and continuous pilot flame requirements.
40 CFR 60.18 still applies broadly today as the baseline operating standard. Compliance with the visible emissions, heating value, exit velocity, and pilot requirements is the floor that more specific rules build on.
Subpart OOOO and OOOOa Original Oil and Gas NSPS
40 CFR 60 Subpart OOOO (2012) was the original New Source Performance Standard for crude oil and natural gas production, processing, transmission, and distribution facilities. Subpart OOOOa (2016) updated and expanded OOOO’s requirements. Both rules required 95% destruction efficiency on affected flares plus operator self-monitoring and recordkeeping.
OOOO and OOOOa are partially superseded by OOOOb for new and modified affected facilities, but legacy facilities subject to OOOOa retain those requirements unless modifications trigger OOOOb applicability.
Subpart OOOOb New, Reconstructed, and Modified Affected Facilities (2024)
40 CFR 60 Subpart OOOOb is the current New Source Performance Standard for affected facilities constructed, reconstructed, or modified after December 6, 2022. The rule applies to well sites, gathering and boosting stations, natural gas processing plants, certain compressor stations, and certain associated equipment.
OOOOb raises the destruction efficiency standard from 95% to 98% for flares used as control devices, requires continuous parametric monitoring of pilot flame presence and combustion zone activity, requires annual performance testing, and mandates reporting through EPA’s Compliance and Emissions Data Reporting Interface (CEDRI). Visit our EPA OOOOb compliance resource for the full requirements.
Subpart OOOOc Emission Guidelines for Existing Affected Facilities (2024)
40 CFR 60 Subpart OOOOc extends OOOOb-style requirements to existing affected facilities (those constructed before December 6, 2022). OOOOc operates through state implementation plans rather than direct EPA enforcement. States submit plans showing how they will achieve the EPA-set emission guidelines, and existing facility operators comply through the state plan’s requirements.
Implementation timelines vary by state. Operators with existing facilities should track their state’s OOOOc plan submission and approval timeline to understand when OOOOc requirements take effect locally.
2. How the Rules Layer on a Single Facility
| Facility Type | Applicable Rules | Key Requirements |
|---|---|---|
| New well site constructed after Dec 6, 2022 | 40 CFR 60.18 + OOOOb | 98% DRE, continuous monitoring, annual testing, CEDRI reporting |
| Existing well site (pre-Dec 6, 2022) | 40 CFR 60.18 + OOOOa + OOOOc (when state plan effective) | OOOOa baseline now; OOOOc-driven upgrades coming via state plans |
| Modified existing well site (after Dec 6, 2022) | 40 CFR 60.18 + OOOOb | Modifications trigger OOOOb applicability |
| Refinery flare (not OOOO-affected) | 40 CFR 60.18 + Subpart Ja | Subpart Ja applies to petroleum refineries with refinery-specific rules |
| Petrochemical flare | 40 CFR 60.18 + relevant MACT | HON, MON, or other source-specific MACT rules apply |
The layered structure means a single facility can be subject to multiple rules simultaneously, and compliance documentation must address each applicable rule. The starting point is identifying which rules apply, then working through each rule’s specific requirements.
3. The 98% Destruction and Removal Efficiency Requirement
OOOOb’s 98% Destruction and Removal Efficiency requirement applies to flares used as control devices for affected facilities. The 98% standard is up from the 95% threshold under OOOOa and represents the most consequential change in OOOOb for flare operators.
98% DRE must be maintained across the full operating range, not just at peak design flow. This requirement directly affects flare selection air-assisted flares need VFD blower control to hold 98% DRE during turndown, sonic flares need pressure profile management to maintain choked-flow conditions, gas-assisted flares need composition-based variable assist control to avoid wasting fuel gas while maintaining DRE on heavier streams.
For more on how each flare technology achieves 98% DRE under OOOOb, see our companion articles on air-assisted flare OOOOb compliance, gas-assisted flare fuel gas optimization, and sonic flare sizing.
KEY INSIGHT: 98% DRE is not a snapshot standard it must be maintained, monitored, and documented across all operating conditions. A flare that passes its initial OOOOb performance test at peak flow and then operates at 90% DRE during routine turndown is non-compliant. The selection and design must satisfy 98% across the full operating envelope, not just the test condition.
4. Continuous Parametric Monitoring Requirements
OOOOb requires continuous monitoring of three flare operating parameters during all periods of waste-gas flow. Each parameter has specific instrumentation and logging requirements.
Pilot flame presence must be verified continuously, typically using a redundant thermocouple and ionization-rod arrangement at the pilot. For ignition systems without continuous pilots (battery/solar spark systems on low flow flares), combustion-zone verification during waste-gas flow substitutes for pilot monitoring.
Combustion zone presence (main flame) must be verified during waste-gas flow using video flame monitor, combustion-zone thermocouple, or flame ionization detector.
Vent-gas flow rate must be measured at the relief header inlet using Coriolis, ultrasonic, or similar flow meter with accuracy sufficient for the air-to-gas ratio control loop on assisted flares.
Data must be logged at intervals frequent enough to detect deviations typically 15 seconds to 1 minute and retained for five years.
5. Annual Performance Testing Under EPA Methods 18, 25A, and 25B
Initial and annual performance tests demonstrate that the flare actually achieves 98% DRE under operating conditions. The test methodology depends on inlet stream composition.
EPA Method 18 (gas chromatography) speciates the vent-gas inlet stream to identify hydrocarbon components and concentrations. Method 18 is used to establish the inlet carbon mass flow.
EPA Methods 25A and 25B measure total hydrocarbon emissions at the flare outlet. Method 25A uses flame ionization detection; Method 25B uses non-dispersive infrared. The choice depends on stream composition and laboratory capability.
DRE is calculated as the percentage of inlet vent-gas carbon destroyed in the combustion zone. Sample ports for outlet hydrocarbon measurement must be located in compliance with EPA Method 1 a requirement that affects flare stack design from day one and is difficult to retrofit if missed at fabrication.
6. Recordkeeping, Retention, and CEDRI Reporting
OOOOb compliance documentation must be retained for five years and must be available to EPA on request. Required documentation includes the design specification, initial performance test report, all continuous parametric monitoring data, all annual recertification test reports, all flame-loss or deviation events with timestamps and root causes, and maintenance and calibration records for monitoring instrumentation.
Reports are submitted electronically through EPA’s Compliance and Emissions Data Reporting Interface (CEDRI) on the schedule set in the facility’s compliance plan. Routine reports are typically annual. Deviation reports must be submitted within 30 days of the event.
7. How the IRA Methane Fee Interacts with EPA Rules
The Inflation Reduction Act of 2022 established a methane emissions fee on large oil and gas facilities exceeding methane emission thresholds. The fee operates separately from EPA OOOOb but interacts with it.
The IRA fee applies to methane emissions above a facility-specific threshold. Uncombusted methane from flaring counts toward the fee threshold. A flare operating at 98% DRE (the OOOOb requirement) still vents 2% of inlet methane, which is now a regulatory cost on top of any environmental concerns.
The fee phases in at $900 per metric ton of methane in 2024, rising to $1,500 per metric ton in 2026 and beyond. For affected facilities, the fee creates economic pressure to reduce flaring (via flare gas recovery systems) on top of OOOOb’s compliance pressure.
8. Compliance Documentation Strategy
For OOOOb-affected facilities, the most effective compliance documentation strategy treats all four rule layers as a single integrated system rather than separate compliance files.
One unified flare compliance file per device includes the 40 CFR 60.18 baseline operating documentation, the OOOOb-specific design, monitoring, and testing documentation, OOOOa references for any facility transitioning from older NSPS, and state OOOOc plan compliance documentation when applicable. Cross-references between the layers make audit response straightforward.
The unified file should be updated continuously not just at annual testing or audit triggers. Continuous monitoring data feeds into the file daily; deviation events get root cause analysis and documentation within 30 days; annual testing reports get added on test completion. Hero’s field services team helps customers structure and maintain this documentation.
9. Common EPA Flare Monitoring Compliance Mistakes
| Mistake | Why It Hurts | Fix |
|---|---|---|
| Treating OOOOb 98% DRE as a snapshot test rather than continuous standard | Initial test passes, routine operation fails the rule | Design and monitor across the full operating envelope |
| Single-point pilot monitoring instead of redundant sensing | Single-failure deviation events become the norm | Specify redundant thermocouple and ionization rod from start |
| Sample ports retrofitted after fabrication | Ports often fail EPA Method 1 location criteria | Locate sample ports during stack fabrication |
| Data logged at intervals too sparse to detect deviations | Cannot demonstrate continuous compliance | Log at 15-second to 1-minute intervals minimum |
| Treating OOOOa and OOOOb as exclusive instead of layered | Modifications transition older facilities into OOOOb but compliance files stay on OOOOa template | Track modification dates and update applicable rule set |
| Ignoring state OOOOc plan implementation timeline | Late awareness of state plan effective date triggers rushed compliance work | Track state OOOOc plan submission and approval status |
Article Summary
- EPA’s flare monitoring rule structure consists of four layered rules: 40 CFR 60.18, OOOO/OOOOa, OOOOb, and OOOOc.
- 40 CFR 60.18 sets baseline general flare requirements including 5-minute-per-2-hour visible emissions, minimum heating value, exit velocity, and continuous pilot.
- OOOO and OOOOa were the original oil and gas NSPS, partially superseded by OOOOb for new/modified facilities.
- OOOOb (2024) requires 98% DRE, continuous parametric monitoring, annual performance testing, and CEDRI reporting for new, reconstructed, and modified affected facilities.
- OOOOc (2024) extends OOOOb-style requirements to existing affected facilities through state implementation plans.
- 98% DRE must be maintained across the full operating range, not just at initial performance test conditions.
- Performance testing uses EPA Method 18 (vent-gas inlet) and Methods 25A/25B (flare outlet) with sample ports compliant with EPA Method 1.
- The IRA methane emissions fee creates additional economic pressure on top of OOOOb compliance for affected facilities.
Frequently Asked Questions
What is 40 CFR 60.18?
40 CFR 60.18 is the foundational EPA flare rule setting baseline general flare requirements. Key provisions include visible emissions limited to no more than 5 minutes during any consecutive 2-hour period, minimum inlet gas heating value (200 Btu/scf for steam/air-assist, 300 Btu/scf for non-assisted), maximum exit velocity limits at the tip, and continuous pilot flame requirements. 60.18 still applies broadly today as the baseline operating standard.
What does EPA OOOOb require?
40 CFR 60 Subpart OOOOb applies to oil and natural gas affected facilities constructed, reconstructed, or modified after December 6, 2022. It requires 98% Destruction and Removal Efficiency on flares used as control devices, continuous parametric monitoring of pilot and combustion zone, annual performance testing using EPA Methods 18, 25A, or 25B, five-year recordkeeping, and reporting through EPA’s CEDRI portal.
How is OOOOc different from OOOOb?
OOOOb applies directly to new, reconstructed, and modified affected facilities through federal EPA enforcement. OOOOc extends similar emission guidelines to existing affected facilities (those constructed before December 6, 2022) but operates through state implementation plans rather than direct federal enforcement. States submit plans showing how they will achieve the EPA-set emission guidelines, and existing facility operators comply through the state plan’s requirements.
What test methods does OOOOb require?
Initial and annual performance tests use EPA Method 18 (gas chromatography to speciate the vent-gas inlet stream) and Methods 25A or 25B (to measure total hydrocarbons at the flare outlet). DRE is calculated as the percentage of inlet vent-gas carbon destroyed in the combustion zone. Sample ports for outlet measurement must be located in compliance with EPA Method 1.
How long must OOOOb records be retained?
OOOOb compliance documentation must be retained for five years and made available to EPA on request. Required documentation includes design specification, initial and annual performance test reports, continuous parametric monitoring data, deviation events with root cause analysis, and maintenance and calibration records. Routine reports are submitted electronically through CEDRI annually; deviation reports must be submitted within 30 days of the event.
How does the IRA methane fee interact with EPA flare monitoring rules?
The IRA methane fee applies separately from OOOOb but creates additional economic pressure on the same operators. Uncombusted methane from flaring (typically 2% of inlet for a 98% DRE flare) counts toward the IRA fee threshold. The fee phases in at $900 per metric ton of methane in 2024, rising to $1,500 per metric ton in 2026 and beyond, creating economic pressure to reduce flaring via flare gas recovery systems on top of OOOOb’s compliance pressure.
