What Exactly is the "Maximum Permissible Noise Level?"

A key component of assessing potential noise impacts or designing acceptable acoustical conditions in external areas is identifying and understanding whatever applicable noise laws, ordinances, regulations and standards may be in place for a particular location or jurisdiction. However, in many cases, the appropriate limit to apply, or what metric or descriptor to use, may be anything but clear and is often left open to interpretation. This is especially true in the case of such ambiguous phrases as "maximum permissible noise level" without any further detail regarding the actual values to be measured and presented. In this paper, the authors review several examples of local and regional noise regulations, some better defined than others, in an effort to better understand the most common or appropriate usage of such expressions.