50 USC 2013 - Participants in CIARDS system

(a) Designation of participants 
The Director may from time to time designate employees of the Agency who shall be entitled to participate in the system. Employees so designated who elect to participate in the system are referred to in this chapter as participants.
(b) Qualifying service 
Designation of employees under this section may be made only from among employees of the Agency who have completed at least 5 years of qualifying service. For purposes of this chapter, qualifying service is service in the Agency performed in carrying out duties that are determined by the Director
(1) to be in support of Agency activities abroad hazardous to life or health; or
(2) to be so specialized because of security requirements as to be clearly distinguishable from normal government employment.

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(c) Election of employee to be participant 

(1) Permanence of election 
An employee of the Agency who elects to accept designation as a participant in the system shall remain a participant of the system for the duration of that individuals employment with the Agency.
(2) Irrevocability of election 
Such an election shall be irrevocable except as and to the extent provided in section 2151 (d) of this title.
(3) Election not subject to approval 
An election under this section is not subject to review or approval by the Director.