Frequently Asked Questions: Control Devices

View frequently asked questions about EPA's 2024 final rule for oil and natural gas operations - control devices. On this page:

What is net heating value?

Net heating value (NHV) is the potential energy available in a fuel sample, which is an indicator of flare performance and combustion efficiency. More specifically, it is the total energy released when a substance undergoes complete combustion with oxygen under standard conditions (i.e., the amount of heat released when gas is burned). In the Final Rule, NHV is typically expressed in units of BTUs per standard cubic feet (scf).

What is the start date for completing the 14-day net heating value (NHV) demonstration for combustion devices/flares?

Under 40 CFR 60.8(a) (the General Provisions for New Source Performance Standards (NSPS), a source generally has 180 calendar days after startup to conduct performance (i.e., compliance) testing.

For NSPS OOOOb sources, affected facilities that were new, modified, or reconstructed after the supplemental proposal for this rule (published December 6, 2022), but before the final rule’s effective date of May 7, 2024, have 180 calendar days after the effective date of the rule to conduct performance (i.e., compliance) testing. For NSPS OOOOb sources that are new, modified or reconstructed after the final rule’s effective date of May 7, 2024, the applicable monitoring requirements (including the 14-day NHV sampling demonstration) must be completed within 180 calendar days after initial startup of the source. 

For the EG OOOOc model rule, designated facilities (those are facilities that commence construction, modification, or reconstruction on or before December 6, 2022), have 180 calendar days after the effective date of the state or Tribal plan to conduct performance (i.e., compliance) testing.

What test methods can be used to determine net heating value (NHV)?

For NHV sampling, there is no specific EPA Reference Method required to be used. The options and procedures that may be used to determine NHV are listed in §60.5417b(d)(8)(ii)(A)-(D) for NSPS OOOOb affected facilities and §60.5417c(d)(8)(ii)(A)-(D) for EG OOOOc designated facilities are as follows: 

What are the monitoring requirements for flares?

For flares, the net heating value (NHV) content of the fuel combusted, the maximum flare tip velocity, and the minimum inlet flow must be monitored (see NSPS OOOOb at §60.5412b(a)(3) and EG OOOOc at §60.5412c(a)(3)). 

NSPS OOOOb and EG OOOOc provide several options for determining the NHV content. These options consist of the following: 

Other methods and materials may be used. However, these alternative test methods are subject to Administrator approval as set forth in §60.8(b). 

The flare tip velocity monitoring requirements are specified in the General Provisions of Part 60 in §60.18(f)(4)-(6), where applicable, which prescribe either the use of EPA Reference Method 2, 2A, 2C, or 2D as appropriate or an equation approach for certain flare type categories. 

For NSPS OOOOb affected facilities, the inlet flow requirements are specified in §60.5412b(a)(3)(vi) and §60.5415b(f)(1)(vii)(B)(6), which are based upon the flare manufacturer’s recommendations. For EG OOOOc designated facilities, the inlet flow requirements are specified in §60.5412c(a)(3)(vi) and §60.5415c(e)(1)(vii)(B)(6), which are also based upon the flare manufacturer’s recommendations. 

What alternatives do owners/operators have for complying with NHV monitoring requirements for flares and enclosed combustion devices in 40 CFR § 60.5417b(d)(8)?

An owner/operator using a flare or enclosed combustion device that is subject to the NHV monitoring requirements in 40 C.F.R. § 60.5417b(d)(8) can choose to meet those requirements as follows:

(1) sample continuously for NHV with a monitoring device (of which there are several types, as noted above), see 40 C.F.R. § 60.5417b(d)(8)(ii), or

(2) conduct an initial performance test, consisting of either: (a) continuous NHV sampling for 14 consecutive days, plus ongoing (three samples every five years) sampling, or (b) a 14-day grab sample NHV demonstration, followed by a three-sample demonstration at five-year intervals, wherein the minimum collection time for each grab sample must be at least one hour. See 40 C.F.R. § 60.5417b(d)(8)(iii)(A). The Final Rule also allows for additional time to collect the requisite 28 samples where intermittent flow of the inlet gas makes collecting them within 14 days infeasible. See 40 C.F.R. § 60.5417b(d)(8)(iii)(A).

In addition, the regulations allow owners/operators to request the use of alternative monitoring or alternative test methods in order to demonstrate compliance. If you are interested in requesting approval of an alternative monitoring plan or alternative test method, contact your appropriate delegated state (or local) authority responsible for implementing the Final Rule, or if not delegated, the appropriate EPA regional office. See the EPA Process Manual for Responding to Requests Concerning Applicability and Compliance Requirements of Certain Clean Air Act Stationary Source Programs.

Alternative Monitoring

Per 40 C.F.R. § 60.5417b(d), owners/operators may “request approval from the Administrator to monitor different operating parameters than those specified in paragraphs (d)(1) through (8) of this section in accordance with § 60.13(i).”

Depending on the nature of a particular request, it may be appropriate for owners/operators who wish to use an alternative monitoring plan (AMP) in light of, for example, the one-hour sampling requirement for the initial performance test in 40 C.F.R. § 60.5417b(d)(8)(iii) due to intermittent flow in the gas stream, to request an AMP for an alternative fuel sampling strategy pursuant to § 60.13(i).  An AMP may also be used to propose alternative sampling location(s), provided that the alternative sampling location(s) is representative of the NHV content of the fuel gas vented to the flare or ECD.

Alternative Test Methods

Per 40 C.F.R. § 60.5412b(d), in order to “demonstrate that a flare or enclosed combustion device reduces methane and VOC in the gases vented to the device by 95.0 percent by weight or greater, as outlined in § 60.8(b), [an owner or operator] may submit a request for an alternative test method.”

Owners/operators may request to use “shorter sampling times and smaller sample volumes when necessitated by process variables or other factors,” see 40 CFR § 60.8(b)(5), or “an existing reference method with minor changes in methodology.” See 40 C.F.R. § 60.8(b)(1).

Depending on the nature of a particular request, it may be appropriate for owners or operators who wish to request to use a shorter sampling time than, for example, the one-hour sampling requirement in 40 C.F.R. § 60.5417b(d)(8)(iii), due to intermittent flow in the gas stream, to request use of an alternate test method pursuant to 40 CFR § 60.8(b)(5).

Owners/operators can also request to use an “equivalent method” pursuant to 40 CFR § 60.8(b)(2), or “an alternative method the results of which [the Administrator] has determined to be adequate for indicating whether a specific source is in compliance” pursuant to 40 CFR § 60.8(b)(3). EPA is currently accepting and reviewing applications for alternative (ALT) test methods for NHV monitoring in the oil and natural gas sector.  Approved alternative test methods for NHV monitoring in the oil and gas sector can be found at this EPA website: Broadly Applicable Approved Alternative Test Methods.  

More information about submitting a request for an alternative test method is available in EPA’s guideline document for alternative test method requests.

Are premix air assist flares covered by NSPS OOOOb and EG OOOOc?

Yes, NSPS OOOOb and EG OOOOc addresses premix air assist flares. The requirements for this flare type are located in §60.5417b and §60.5417c, which are referred to as air-assisted flares that use premix assist air. 

Are the manufacturer performance-tested enclosed combustors that are reviewed by the EPA and listed at Performance Testing for Combustion Control Devices - Manufacturers’ Performance Test exempt from the requirement to determine the gas net heating value (NHV) listed in NSPS OOOOb sections 60.5412b and 60.5417b?

The combustion control devices listed in the EPA’s “Manufacturers Performance Test” table are not exempt from the NHV sampling requirements in NSPS Subpart OOOOb, §60.5412b and §60.5417b. While the listed sources are exempt from having to perform initial performance testing for total organic compounds (TOC) (see §60.5413b(a)(7)), the NHV demonstration must still be performed. 

When will EPA be updating its “Manufacturer’s Performance Test” list for the final rule combustion control devices, and where will it be posted?

The Manufacturer-Tested Combustion Control Devices list (or Combustion Control Devices subject to 40 CFR Part 60, NSPS subparts OOOO, OOOOa, OOOOb, and EG OOOOc and 40 CFR Part 63, NESHAP subparts HH and HHH) is posted here (opens in new window).  

The most recent update to this list was made on April 11, 2024. The current version of the list will always be available at the link above. 

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Last updated on September 19, 2024