Section 84.301 - Applicability to new and previously approved CCERs(a) Any CCER approval issued after April 9, 2012 must comply with the technical requirements of subpart O.(b) The continued manufacturing, labeling, and sale of closed-circuit apparatus previously approved under subpart H is authorized for units required for use in underground coal mines pursuant to 30 CFR 75.1714-1 .(c) Any manufacturer-requested modification to a device approved under the subpart H technical requirements must comply with the subpart H technical requirements and address an identified worker safety or health concern to be granted an extension of the NIOSH approval. Major modifications to the configuration that will result in a new approval must meet and be issued approvals under the requirements of this subpart O. 84 FR 16412 , Apr. 19, 2019