Method 1A

Sample and Velocity Traverses for Stationary Sources With Small Stacks or Ducts

40 CFR Part 60, Appendix A-1

From the method — regulatory text

Sections 1.0 and 2.0 of Method 1A—Sample and Velocity Traverses for Stationary Sources With Small Stacks or 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 Measured Parameters. The purpose of the method is to provide guidance for the selection of sampling ports and traverse points at which sampling for air pollutants will be performed pursuant to regulations set forth in this part.

1.2 Applicability. The applicability and principle of this method are identical to Method 1, except its applicability is limited to stacks or ducts. This method is applicable to flowing gas streams in ducts, stacks, and flues of less than about 0.30 meter (12 in.) in diameter, or 0.071 m² (113 in.²) in cross-sectional area, but equal to or greater than about 0.10 meter (4 in.) in diameter, or 0.0081 m² (12.57 in.²) in cross-sectional area. This method cannot be used when the flow is cyclonic or swirling.

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 method is designed to aid in the representative measurement of pollutant emissions and/or total volumetric flow rate from a stationary source. A measurement site or a pair of measurement sites where the effluent stream is flowing in a known direction is (are) selected. The cross-section of the stack is divided into a number of equal areas. Traverse points are then located within each of these equal areas.

2.2 In these small diameter stacks or ducts, the conventional Method 5 stack assembly (consisting of a Type S pitot tube attached to a sampling probe, equipped with a nozzle and thermocouple) blocks a significant portion of the cross-section of the duct and causes inaccurate measurements. Therefore, for particulate matter (PM) sampling in small stacks or ducts, the gas velocity is measured using a standard pitot tube downstream of the actual emission sampling site. The straight run of duct between the PM sampling and velocity measurement sites allows the flow profile, temporarily disturbed by the presence of the sampling probe, to redevelop and stabilize.

EssentialRegs notes

Our plain-English reading of Method 1A. Not the method text.

What it measures

Where to sample, and at how many points across the cross-section, in stacks and ducts that are too small for the Method 1 procedure.

How it works

Method 1A does the same job as Method 1 for small stacks and ducts. It sets the criteria for a suitable measurement site and fixes the traverse points across the cross-section. It exists because the probe and the Method 1 point layout would block too much of a small cross-section and disturb the flow being measured.

Equipment

No analytical instrument. A tape measure or similar tool for the stack dimensions and the sampling ports installed in the stack wall.

When a rule cites it

Performance tests on small stacks and ducts, as the traverse method that goes with a small-duct velocity method. It is invoked where a rule requires a velocity or flow measurement and the stack is below the size range of Method 1.

Notes for compliance staff

Whether a stack falls under Method 1 or Method 1A is decided by its size, so the test plan should state the stack dimensions.

Cited by

Provisions in the corpus whose text cites Method 1A. 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 IIII

Table 7 to Subpart IIII of Part 60 — Requirements for Performance Tests for Stationary CI ICE With a Displacement of ≥30 Liters per Cylinder

40 CFR Part 60 Subpart JJJJ

Table 2 to Subpart JJJJ of Part 60 — Requirements for Performance Tests

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.