Okla. Stat. tit. 40, § 141.8

A. The chief boiler inspector shall employ deputy inspectors, subject to approval of the Commissioner of Labor, who shall be responsible to the chief boiler inspector and who shall have at the time of appointment a valid commission issued in accordance with the constitution and bylaws of the National Board of Boiler and Pressure Vessel Inspectors. B. The deputy inspectors may at the Commissioner's discretion be appointed in a trainee status provided the trainees successfully complete the examination as defined in Section 141.10 of this title and receive a valid National Board Commission within twenty-four (24) months after appointment.