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Fugitive emissions are those that do not pass through vents, stacks, or other openings that are designed to vent emissions. Knowing if an emission is fugitive or non-fugitive is important for permitting, because non-fugitive emissions are always counted to determine if a source exceeds major source thresholds, while only certain fugitive emissions are counted.
EPA says that emissions that are actually collected are not fugitive emissions. For example, when a source is subject to a national standard that requires emissions collections, those emissions are not considered to be fugitive.
Where emissions are not actually collected at a particular site, the question of whether the emissions are fugitive or nonfugitive is made on a case-by-case basis by the permitting authority. EPA has stated that if other sources are using a certain kind of collection technology, then it presumes collection of emissions from a similar pollutant emitting activity is reasonable, even if that activity is located within a different source category.