Method 2D
Measurement of Gas Volume Flow Rates in Small Pipes and Ducts
40 CFR Part 60, Appendix A-1
From the method — regulatory text
Sections 1.0 and 2.0 of Method 2D—Measurement of Gas Volume Flow Rates in Small Pipes and Ducts, as published at 40 CFR Part 60, Appendix A-1. Retrieved 10/07/2026. The full method is on the eCFR.
1.0 Scope and Application
1.1 This method is applicable for the determination of the volumetric flow rates of gas streams in small pipes and ducts. It can be applied to intermittent or variable gas flows only with particular caution.
1.2 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 All the gas flow in the pipe or duct is directed through a rotameter, orifice plate or similar device to measure flow rate or pressure drop. The device has been previously calibrated in a manner that insures its proper calibration for the gas being measured. Absolute temperature and pressure measurements are made to allow correction of volumetric flow rates to standard conditions.
EssentialRegs notes
Our plain-English reading of Method 2D. Not the method text.
What it measures
The volumetric flow rate of gas in a small pipe or duct, measured with a flow meter installed in the line or at its outlet and corrected to standard conditions.
How it works
A flow meter in the line reports the gas flow rate directly while the test runs. Readings are recorded along with the gas temperature and pressure at the meter. The flow rate is then corrected to standard conditions. The method sets requirements for the meter and its calibration.
Equipment
A gas flow meter such as a rotameter, orifice meter, turbine meter or similar device, with temperature and pressure measurement at the meter.
When a rule cites it
Flow measurement in small pipes, vent lines and low-flow gas streams during a performance test, where the stream is too small for a pitot traverse. It is used where a rule needs a flow rate for a vent or process line.
Notes for compliance staff
Method 2D is written for meters installed in small pipes and ducts and covers flow-rate meters such as rotameters and orifice meters; Method 2A is the direct gas volume meter method. Neither uses a pitot traverse, so the Method 1 traverse points do not apply. The meter calibration records belong in the test report.
Cited by
Provisions in the corpus whose text cites Method 2D. Subscribers land on the provision in the regulation reader; visitors see a preview of it (the GP05 sample opens in full).
Regulation 7
40 CFR Part 60 Subpart OOOO
40 CFR Part 60 Subpart OOOOa
40 CFR Part 60 Subpart OOOOb
40 CFR Part 60 Subpart OOOOc
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.