40 CFR § 51.906 - Redesignation to nonattainment following initial designations for the 8-hour NAAQS.
---
identifier: "/us/cfr/t40/s51.906"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 51.906 - Redesignation to nonattainment following initial designations for the 8-hour NAAQS."
title_number: 40
title_name: "Protection of Environment"
section_number: "51.906"
section_name: "Redesignation to nonattainment following initial designations for the 8-hour NAAQS."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "C"
subchapter_name: "AIR PROGRAMS"
part_number: "51"
part_name: "REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF IMPLEMENTATION PLANS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "23 U.S.C. 101; 42 U.S.C. 7401-7671q."
regulatory_source: "36 FR 22398, Nov. 25, 1971, unless otherwise noted."
cfr_part: "51"
---
# 51.906 Redesignation to nonattainment following initial designations for the 8-hour NAAQS.
For any area that is initially designated attainment or unclassifiable for the 8-hour NAAQS and that is subsequently redesignated to nonattainment for the 8-hour ozone NAAQS, any absolute, fixed date applicable in connection with the requirements of this part is extended by a period of time equal to the length of time between the effective date of the initial designation for the 8-hour NAAQS and the effective date of redesignation, except as otherwise provided in this subpart.
[70 FR 71700, Nov. 29, 2005]