Regulations last checked for updates: Jan 31, 2025

Title 40 - Protection of Environment last revised: Nov 08, 2025
All TitlesTitle 40Chapter IPart 98Subpart WAppendix - Table W-4 to Subpart W of Part 98—Default Total Hydrocarbon Leaker Emission Factors
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Appendix - Table W-4 to Subpart W of Part 98—Default Total Hydrocarbon Leaker Emission Factors
Equipment components Emission factor
(scf total hydrocarbon/hour/component)
If you survey using Method 21 as specified in § 98.234(a)(2)(i) If you survey using Method 21 as specified in § 98.234(a)(2)(ii) If you survey using any of the methods in § 98.234(a)(1), (3), or (5)
Leaker Emission Factors—Onshore Natural Gas Processing, Onshore Natural Gas Transmission Compression—Compressor Components, Gas Service
Valve 114.849.5124.2
Connector5.593.589.13
Open-Ended Line17.2711.0728.2
Pressure Relief Valve39.6625.4264.8
Meter19.3312.3931.6
Other 24.12.636.70
Leaker Emission Factors—Onshore Natural Gas Processing, Onshore Natural Gas Transmission Compression—Non-Compressor Components, Gas Service
Valve 16.424.1210.5
Connector5.713.669.3
Open-Ended Line11.277.2218.4
Pressure Relief Valve2.011.293.28
Meter2.931.884.79
Other 24.12.636.70
Leaker Emission Factors—Underground Natural Gas Storage—Storage Station, Gas Service
Valve 114.849.5124.2
Connector (other)5.593.589.13
Open-Ended Line17.2711.0728.2
Pressure Relief Valve39.6625.4264.8
Meter and Instrument19.3312.3931.6
Other 24.12.636.70
Leaker Emission Factors—Underground Natural Gas Storage—Storage Wellheads, Gas Service
Valve 14.53.27.35
Connector (other than flanges)1.20.71.96
Flange3.82.06.21
Open-Ended Line2.51.74.08
Pressure Relief Valve4.12.56.70
Other 24.12.56.70

1 Valves include control valves, block valves and regulator valves.

2 Other includes any potential equipment leak emission point in gas service that is not specifically listed in this table, as specified in § 98.232(d)(7) for onshore natural gas processing, § 98.232(e)(8) for onshore natural gas transmission compression, and as specified in § 98.232(f)(6) and (8) for underground natural gas storage.

[89 FR 42325, May 14, 2024]
authority: 42 U.S.C. 7401-7671q.
source: 74 FR 56374, Oct. 30, 2009, unless otherwise noted.
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