Sample and Velocity Traverse Points – USEPA Method 1

USEPA Method 1 provides guidance for the selection of sampling ports and traverse points at which sampling for air pollutants will be performed.  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.
 
The requirements of this method must be considered before construction of a new facility from which emissions are to be measured; failure to do so may require subsequent alterations to the stack or deviation from the standard procedure.  Cases involving variants are subject to approval by the Administrator.
 
This method is applicable to gas streams flowing in ducts, stacks, and flues.  It cannot be used when:

• the flow is cyclonic or swirling,
• a stack is smaller than 0.30 meter (12 in.) in diameter,
• a stack is smaller than 0.071 m2 (113 in.2) in cross-sectional area. 

Two procedures for determining cyclonic flow are presented in Method 1:  a simplified procedure, and an alternative measurement site procedure.  The magnitude of cyclonic flow of effluent gas in a stack or duct is the only parameter quantitatively measured in the simplified procedure.  The simplified procedure cannot be used when the measurement site is less than two stack or duct diameters downstream or less than a half diameter upstream from a flow disturbance.  In these cases, the alternative measurement site procedure, which involves traversing the source with a directional flow-sensing probe (3D Probe), must be used to measure the pitch and yaw angles of the gas flow at 40 or more traverse points.  The resultant angle is then calculated and compared to acceptable criteria for mean and standard deviation.