; and (ii) of the issuance of any such waiver, not later than 48 hours after such issuance. (B) Contents The head of an agency shall include in each notification under subparagraph (A)(ii) a detailed explanation of the reasons the waiver is necessary. (6) Definitions In this subsection: (A) Product carrier The term product carrier , with respect to a good, means a vessel constructed or adapted primarily to carry such good in bulk in the cargo spaces. (B) Head of an agency The term head of an agency means the head of an agency responsible for the administration of the navigation or vessel inspection laws, or an individual of such an agency delegated such responsibility. .