(a) All disaster service workers shall, before they enter upon the duties of their employment, take and subscribe to the oath or affirmation required by this chapter.
(b) In the case of intermittent, temporary, emergency or successive employments, then in the discretion of the employing agency, an oath taken and subscribed as required by this chapter shall be effective for the purposes of this chapter for all successive periods of employment which commence within one calendar year from the date of that subscription.
(c) Notwithstanding subdivision (b), the oath taken and subscribed by a person who is a member of an emergency organization sanctioned by a state agency or an accredited disaster council, whose members are duly enrolled or registered with the Office of Emergency Services, or any accredited disaster council of any political subdivision, shall be effective for the period the person remains a member with that organization.