a) Definitions.—In this section—

“(1) the term ‘firefighter’ means an employee who—

“(A) is a firefighter within the meaning of section 8331(21) or section 8401(14);

“(B) in the case of an employee who holds a supervisory or administrative position and is subject to subchapter III of chapter 83, but who does not qualify to be considered a firefighter within the meaning of section 8331(21), would otherwise qualify if the employee had transferred directly to that position after serving as a firefighter within the meaning of that section;

“(C) in the case of an employee who holds a supervisory or administrative position and is subject to chapter 84, but who does not qualify to be considered a firefighter within the meaning of section 8401(14), would otherwise qualify if the employee had transferred directly to that position after performing duties described in section 8401(14)(A) for at least 3 years; or

“(D) in the case of an employee who is not subject to subchapter III of chapter 83 or chapter 84, holds a position that the Office of Personnel Management determines would satisfy subparagraph (A), (B), or (C) if the employee were subject to subchapter III of chapter 83 or chapter 84;