There is no standardized federal, state or local methodology for assessing noise impact from major industrial facilities and power plants in the U.S. The U.S. EPA “Levels” document guideline of DNL = 55 dBA is sometimes used as a de facto standard, but is misapplied more often than not. Thirteen states promulgate noise emission standards for industrial sources. Of these, eight issue “maximum-emission” levels and five ublish “ambient-based” standards. Levels deemed “acceptable” for permitting purposes for an identical project in the thirteen states can vary by 17 dBA or more, and the rest of the states consider noise a local issue. This paper reviews and critiques in-use assessment methods and develops a method called the Noise Perception Index (NPI) that is based on core thresholds and methods used for decades in the states using ambient-based assessment procedures. The intent is to develop a uniform and relatively simple method to predict true community perception over the long range course of the installation. Spectral imbalance and tonal character are accounted for as are adverse cumulative effects inherent in ambient-based methods. It is believed that the developed NPI assessment method is fair and reasonable for both the community and the project owner since the core method has been validated from years of application throughout the U.S.