; (iv) consider the effects and risks of exposure to hydrogen cyanide from multiple sources and in combination with exposure to other pollutants; and (v) consider the best available science, including as provided by the National Academy of Sciences. (C) Regulation (i) Initial regulation (I) Deadline The Administrator shall promulgate the initial regulation required under subparagraph (A) not later than 2 years after the date of enactment of this paragraph. (II) Compliance date The compliance date for the initial regulation required under subparagraph (A) shall be not later than 3 years after the date of enactment of this paragraph. (ii) Public hearings Before finalizing a regulation (or revision thereof) required under subparagraph (A), the Administrator shall hold at least 2 public hearings in communities exposed to air pollution from petroleum refineries. (D) Savings clause Nothing in this paragraph shall be interpreted to preclude or deny the right of the Administrator or any State or political subdivision thereof to adopt or enforce emission standards, monitoring, or other requirements that are more stringent than the requirements herein. .