Method 21
Determination of Volatile Organic Compound Leaks
40 CFR Part 60, Appendix A-7
From the method — regulatory text
Sections 1.0 and 2.0 of Method 21—Determination of Volatile Organic Compound Leaks, as published at 40 CFR Part 60, Appendix A-7. Retrieved 10/07/2026. The full method is on the eCFR.
1.0 Scope and Application
1.1 Analytes.
| Analyte | CAS No. |
|---|---|
| Volatile Organic Compounds (VOC) | No CAS number assigned. |
1.2 Scope. This method is applicable for the determination of VOC leaks from process equipment. These sources include, but are not limited to, valves, flanges and other connections, pumps and compressors, pressure relief devices, process drains, open-ended valves, pump and compressor seal system degassing vents, accumulator vessel vents, agitator seals, and access door seals.
1.3 Data Quality Objectives. Adherence to the requirements of this method will enhance the quality of the data obtained from air pollutant sampling methods.
2.0 Summary of Method
2.1 A portable instrument is used to detect VOC leaks from individual sources. The instrument detector type is not specified, but it must meet the specifications and performance criteria contained in section 6.0. A leak definition concentration based on a reference compound is specified in each applicable regulation. This method is intended to locate and classify leaks only, and is not to be used as a direct measure of mass emission rate from individual sources.
EssentialRegs notes
Our plain-English reading of Method 21. Not the method text.
What it measures
Whether a piece of equipment — a valve, pump seal, flange, connector, open-ended line or similar component — is leaking volatile organic compounds, by reading the concentration at the component's surface against a leak definition set by the rule.
How it works
A portable organic vapor analyzer is calibrated with a reference gas, then its probe is moved slowly over the places a component can leak, held at the interface where leakage would emerge. The highest reading, in parts per million as the calibration compound, is compared with the leak definition in the applicable rule. The method sets how the instrument must perform and how it is calibrated and used; the number that counts as a leak comes from the rule that invokes the method, not from Method 21 itself.
Equipment
A portable hydrocarbon analyzer meeting the method's response-time, calibration-precision and response-factor requirements, such as a flame ionization or photoionization detector, with calibration gases.
When a rule cites it
Leak detection and repair programs for equipment in volatile organic compound service, and the monitoring that follows a repair to confirm the leak is gone. Rules that allow optical gas imaging as an alternative usually still name Method 21 as the reference approach or as the confirmation method.
Notes for compliance staff
Method 21 is a screening procedure — it identifies leaking components, it does not measure how much is being emitted. Each rule that invokes it defines its own leak threshold, so the same reading can be a leak under one rule and not under another. Method 22 is a different method for visible emissions and is often cited alongside Method 21 in flare and fugitive requirements.
Cited by
Provisions in the corpus whose text cites Method 21. Subscribers land on the provision in the regulation reader; visitors see a preview of it (the GP05 sample opens in full).
Regulation 7
- I.B.3.
- I.J.1.d.
- I.J.2.b.(ii).
- I.K.2.f.
- I.L.4.a.
- I.L.4.d.
- I.L.8.
- II.A.2.
- II.E.6.a.
- II.E.6.b.
- II.E.6.e.
- II.E.6.f.
- II.E.6.f.(i).
- II.E.6.f.(ii).
- II.E.6.g.
- II.E.6.g.(i).
- II.E.6.g.(ii).
- II.E.7.b.(i).(B).
- II.E.8.d.
- II.I.2.c.(i).(B).
- II.I.2.c.(ii).(D).
- II.I.2.g.(i).(B).
- II.I.2.g.(i).(C).(1).
- II.I.2.g.(i).(D).(1).
- II.I.2.g.(i).(E).
- II.I.2.g.(i).(F).
- II.I.2.g.(i).(G).
- II.I.2.h.(ii).(B).(1).
- II.I.2.h.(ii).(B).(2).
- II.I.2.h.(iv).
- II.J.1.c.(i).(C).
- II.K.1.b.(i).(C).
- IV.A.1.
- N.
- P.
- HH.
APCD General Permit GP09
APCD General Permit GP10
40 CFR Part 60 Subpart OOOO
40 CFR Part 60 Subpart OOOOa
- § 60.5371a(a)(3)(iv)
- § 60.5397a(a)
- § 60.5397a(c)(2)
- § 60.5397a(c)(8)
- § 60.5397a(c)(8)(i)
- § 60.5397a(c)(8)(ii) — Procedures for conducting surveys
- § 60.5397a(c)(8)(iii) — Procedures for calibration
- § 60.5397a(c)(8)(iii)(A)
- § 60.5397a(d)(2)
- § 60.5397a(h)(4)(i)
- § 60.5397a(h)(4)(iii)
- § 60.5397a(h)(4)(iii)(A)
- § 60.5397a(h)(4)(iii)(B)
- § 60.5399a(g)
- § 60.5399a(h)
- § 60.5399a(i)
- § 60.5399a(j)
- § 60.5399a(k)
- § 60.5399a(l)
- § 60.5399a(m)
- § 60.5401a(g)
- § 60.5416a(b)(1)
- § 60.5416a(b)(2)
- § 60.5416a(b)(3)
- § 60.5416a(b)(5)
- § 60.5416a(b)(6)(i)
- § 60.5420a(c)(6)(ii)
- § 60.5420a(c)(15)(i)(E)
- § 60.5420a(c)(15)(i)(I)(3)
40 CFR Part 60 Subpart OOOOb
- § 60.5371b(d)(2)(v)
- § 60.5386b(a)(2) — Method 21
- § 60.5397b(c)(2)
- § 60.5397b(c)(8)
- § 60.5397b(c)(8)(i)
- § 60.5397b(c)(8)(ii) — Procedures for conducting surveys
- § 60.5397b(c)(8)(iii) — Procedures for calibration
- § 60.5397b(c)(8)(iii)(A)
- § 60.5397b(c)(8)(iv)
- § 60.5397b(d)(2)
- § 60.5397b(f)(2)
- § 60.5397b(g)(1)(iii)(B)
- § 60.5397b(g)(1)(iv)(F)
- § 60.5397b(g)(1)(v)(B)
- § 60.5397b(g)(1)(vi)
- § 60.5397b(g)(2)
- § 60.5397b(g)(3)
- § 60.5397b(h)(1)(ii)
- § 60.5397b(h)(4)(i)
- § 60.5397b(h)(4)(iii)
- § 60.5397b(h)(4)(iii)(A)
- § 60.5397b(h)(4)(iii)(B)
- § 60.5397b(h)(4)(v)
- § 60.5398b(b)(5)(ii)(A)
- § 60.5398b(b)(5)(ii)(B)
- § 60.5398b(b)(5)(iii)(A)
- § 60.5398b(b)(5)(iii)(B)(1)
- § 60.5398b(b)(5)(iv)(A)
- § 60.5398b(b)(5)(iv)(B)(1)
- § 60.5400b(c)(1)
- § 60.5400b(d)(1)
- § 60.5401b(d)(1)
- § 60.5402b(b)(2)
- § 60.5403b(b)(1)
- § 60.5403b(b)(1)(iii)
- § 60.5403b(b)(2)
- § 60.5403b(b)(2)(i)
- § 60.5403b(c)(2)
- § 60.5416b(b)(1)(i)
- § 60.5416b(b)(1)(ii)
- § 60.5416b(b)(1)(iii)
- § 60.5416b(b)(4) — Method 21 application
- § 60.5416b(b)(4)(i)
- § 60.5416b(b)(4)(ii)
- § 60.5416b(b)(4)(iv)
- § 60.5416b(b)(4)(v)(A)
- § 60.5420b(c)(8)(i)
- § 60.5420b(c)(8)(ii)
- § 60.5420b(c)(9)(i) — A record of each cover inspection
- § 60.5420b(c)(9)(ii)
+8 more provisions in 40 CFR Part 60 Subpart OOOOb cite Method 21. Show allShow fewer
- § 60.5420b(c)(14)(v)(E)
- § 60.5420b(c)(14)(v)(I)(3)
- § 60.5421b(b)(4)
- § 60.5421b(b)(5)
- § 60.5421b(b)(9)
- § 60.5421b(b)(9)(v)
- § 60.5421b(b)(11)(iv)(A)
- § 60.5430b — What definitions apply to this subpart?
40 CFR Part 60 Subpart OOOOc
- § 60.5388c(a)(2)(v)
- § 60.5397c(c)(2)
- § 60.5397c(c)(8)
- § 60.5397c(c)(8)(i)
- § 60.5397c(c)(8)(ii) — Procedures for conducting surveys
- § 60.5397c(c)(8)(iii) — Procedures for calibration
- § 60.5397c(c)(8)(iii)(A)
- § 60.5397c(c)(8)(iv)
- § 60.5397c(d)(2)
- § 60.5397c(f)(2)
- § 60.5397c(g)(1)(iii)(B)
- § 60.5397c(g)(1)(iv)(F)
- § 60.5397c(g)(1)(v)(B)
- § 60.5397c(g)(1)(vi)
- § 60.5397c(g)(2)
- § 60.5397c(g)(3)
- § 60.5397c(h)(1)(ii)
- § 60.5397c(h)(4)(i)
- § 60.5397c(h)(4)(iii)
- § 60.5397c(h)(4)(iii)(A)
- § 60.5397c(h)(4)(iii)(B)
- § 60.5397c(h)(4)(v)
- § 60.5398c(b)(5)(ii)(A)
- § 60.5398c(b)(5)(ii)(B)
- § 60.5398c(b)(5)(iii)(A)
- § 60.5398c(b)(5)(iii)(B)(1)
- § 60.5398c(b)(5)(iv)(A)
- § 60.5398c(b)(5)(iv)(B)(1)
- § 60.5400c(c)(1)
- § 60.5400c(d)(1)
- § 60.5401c(d)(1)
- § 60.5402c(b)(2)
- § 60.5405c(a)(2) — Method 21
- § 60.5406c(b)(1)
- § 60.5406c(b)(1)(iii)
- § 60.5406c(b)(2)
- § 60.5406c(b)(2)(i)
- § 60.5406c(c)(2)
- § 60.5416c(b)(1)(i)
- § 60.5416c(b)(1)(ii)
- § 60.5416c(b)(1)(iii)
- § 60.5416c(b)(4) — Method 21 inspection
- § 60.5416c(b)(4)(i)
- § 60.5416c(b)(4)(ii)
- § 60.5416c(b)(4)(iv)
- § 60.5416c(b)(4)(v)(A)
- § 60.5420c(c)(7)(i)
- § 60.5420c(c)(7)(ii)
- § 60.5420c(c)(8)(i) — A record of each cover inspection
- § 60.5420c(c)(8)(ii)
+8 more provisions in 40 CFR Part 60 Subpart OOOOc cite Method 21. Show allShow fewer
- § 60.5420c(c)(13)(v)(E)
- § 60.5420c(c)(13)(v)(I)(3)
- § 60.5421c(b)(4)
- § 60.5421c(b)(5)
- § 60.5421c(b)(9)
- § 60.5421c(b)(9)(v)
- § 60.5421c(b)(11)(iv)(A)
- § 60.5430c — What definitions apply to this subpart?
The sections marked as regulatory text above are reproduced from the CFR. Everything under ‘EssentialRegs notes’ is our reference copy, not the method. The method as published in the CFR controls.