## Sample/Velocity Traverses (Traverse Points)

This 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 where the effluent stream is flowing in a known direction is selected, and 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.

It is important to determine exactly where in the stack to collect samples before diving into the analytical methods. EPA Method 1 is how the stack tester:

● selects an appropriate sampling location,

● determines the required number of sampling points, and

● calculates the location of the sampling points within the duct.

With a circular stack, in an ideal situation, test ports would be located at least 8 diameters from any upstream flow disturbance, and at least 2 diameters from any downstream disturbance or stack exit. A sample is collected at points along two perpendicular axes. Each point is located such that the cross-section ring that it represents has an area equal to all of the other cross-section rings.

In a rectangular duct, the sample points are set up in a grid configuration. Keep in mind that sampling locations that are increasingly far away from the ideal 8-and-2 diameters situation require increasing numbers of sample points.

For more information, please visit the EPA's Method 1 Webpage.