US HB161

Amends Clean Air Act sections 111, 169, and 171 to narrow the definition of "modification" that triggers New Source Review permitting requirements for stationary pollution sources

Establishes that a change only constitutes a modification if the maximum hourly emission rate after the change exceeds the maximum hourly rate achievable during any hour in the preceding 10-year period

Exempts changes designed to reduce pollution per unit of production or to improve facility safety and reliability from being classified as modifications, unless the EPA Administrator determines the increased hourly emission rate would cause adverse health or environmental effects

Excludes changes at major emitting facilities from "construction" and "modification" definitions if they do not result in a significant emissions increase in annual actual emissions

Includes a rule of construction ensuring the amendments do not newly classify any changes as modifications that were not already treated as such before enactment