Ray-tracing software has proven to be a valuable and powerful tool to predict community noise from industrial facilities. Accurate predictions are necessary to select the noise reductions needed to meet regulations and/or project noise limits, and then to determine individual equipment noise limits, select add-on noise controls, and confirm the plant will comply with its noise limits. Although ray-tracing and similar image-source software packages have proven to be powerful, they have many limitations. To use ray-tracing software effectively to model community or in-plant noise, the user needs to understand those limitations. How the software handles barriers is considered the most significant limitation. Further, ray tracing does not adequately predict levels when the wavelength of sound is comparable to dimensions of objects in the transmission path, when diffuse reflections occur, or when sound is scattered and transmitted by equipment and piping. The empirical methodology (ISO 9613-2) used to predict outdoor propagation, including ground effects, also imposes limitations. This paper identifies and discusses many of the more important limitations of ray-tracing software for predicting community noise. Examples are given. Commercially available software is identified, but no attempt is made to compare available packages.
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