Method 2
Determination of Stack Gas Velocity and Volumetric Flow Rate (Type S Pitot Tube)
40 CFR Part 60, Appendix A-1
From the method — regulatory text
Sections 1.0 and 2.0 of Method 2—Determination of Stack Gas Velocity and Volumetric Flow Rate (Type S Pitot Tube), 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 average velocity and the volumetric flow rate of a gas stream.
1.2 This method is not applicable at measurement sites that fail to meet the criteria of Method 1, section 11.1. Also, the method cannot be used for direct measurement in cyclonic or swirling gas streams; section 11.4 of Method 1 shows how to determine cyclonic or swirling flow conditions. When unacceptable conditions exist, alternative procedures, subject to the approval of the Administrator, must be employed to produce accurate flow rate determinations. Examples of such alternative procedures are: (1) to install straightening vanes; (2) to calculate the total volumetric flow rate stoichiometrically, or (3) to move to another measurement site at which the flow is acceptable.
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 The average gas velocity in a stack is determined from the gas density and from measurement of the average velocity head with a Type S (Stausscheibe or reverse type) pitot tube.
EssentialRegs notes
Our plain-English reading of Method 2. Not the method text.
What it measures
The average velocity of the gas in a stack or duct and the volumetric flow rate of that gas, both at stack conditions and corrected to standard conditions.
How it works
A pitot tube is placed at each traverse point and measures the velocity pressure, the difference between the pressure of the gas moving into the tube and the static pressure in the stack. That reading, along with the gas temperature, the static and barometric pressures, and the molecular weight of the gas, gives the velocity at each point. The point velocities are averaged and multiplied by the cross-sectional area to give the flow rate. The traverse points come from Method 1.
Equipment
A Type S pitot tube with a differential pressure gauge, a temperature sensor, a barometer, and the means to determine static pressure. Gas composition and moisture come from Methods 3 and 4.
When a rule cites it
Performance tests that need a stack flow rate, to convert a concentration into a mass emission rate, and as the velocity measurement behind isokinetic particulate sampling. It is the standard flow method for stacks that meet the Method 1 site criteria.
Notes for compliance staff
Method 2 depends on Method 1 for the traverse points, on Method 3 for dry molecular weight and on Method 4 for moisture, so a report that cites Method 2 should include all four. It does not apply at a measurement site that fails the Method 1 flow criteria, such as one with cyclonic flow. Small pipes and vent lines are measured with Method 2A or 2D.
Cited by
Provisions in the corpus whose text cites Method 2. Subscribers land on the provision in the regulation reader; visitors see a preview of it (the GP05 sample opens in full).
Regulation 6
Regulation 26
Regulation 31
40 CFR Part 60 Subpart JJJJ
- Table 2 to Subpart JJJJ of Part 60 — Requirements for Performance Tests
40 CFR Part 60 Subpart OOOO
40 CFR Part 60 Subpart OOOOa
40 CFR Part 60 Subpart OOOOb
40 CFR Part 60 Subpart OOOOc
49 CFR Part 192
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.