Method 2A
Direct Measurement of Gas Volume Through Pipes and Small Ducts
40 CFR Part 60, Appendix A-1
From the method — regulatory text
Sections 1.0 and 2.0 of Method 2A—Direct Measurement of Gas Volume Through Pipes and Small 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 gas flow rates in pipes and small ducts, either in-line or at exhaust positions, within the temperature range of 0 to 50 °C (32 to 122 °F).
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 A gas volume meter is used to measure gas volume directly. Temperature and pressure measurements are made to allow correction of the volume to standard conditions.
EssentialRegs notes
Our plain-English reading of Method 2A. Not the method text.
What it measures
The total volume of gas that passes through a pipe or small duct over a test period, and from it the flow rate, corrected to standard conditions.
How it works
A gas volume meter is installed in the line, or at its outlet, and the meter totalizer is read at the start and end of the test period. The difference is the actual volume of gas, which is divided by the elapsed time for a flow rate. Gas temperature and pressure are recorded at the meter so the volume can be corrected to standard conditions.
Equipment
A gas volume meter, such as a positive displacement or turbine meter, with temperature and pressure measurement at the meter, and a stopwatch or timer.
When a rule cites it
Flow measurement in small pipes, vent lines and low-flow gas streams where a pitot traverse is not practical. It is used where a rule needs the gas volume or flow rate during a performance test of a small line.
Notes for compliance staff
Method 2A reads a meter in the line. It does not traverse the cross-section and does not use a pitot tube, so Method 1 is not needed. Method 2D covers meters that read a flow rate directly, such as rotameters and orifice meters, rather than a totalized volume.
Cited by
Provisions in the corpus whose text cites Method 2A. Subscribers land on the provision in the regulation reader; visitors see a preview of it (the GP05 sample opens in full).
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.