Subject to RCW 49.46.170, the director, to the extent necessary in order to prevent curtailment of opportunities for employment, shall by regulations provide for (1) the employment of learners, of apprentices, and of messengers employed primarily in delivering letters and messages, under special certificates issued pursuant to regulations of the director, at such wages lower than the minimum wage applicable under RCW 49.46.020 and subject to such limitations as to time, number, proportion, and length of service as the director shall prescribe, and (2) the employment of individuals whose earning capacity is impaired by a disability, under special certificates issued by the director, at such wages lower than the minimum wage applicable under RCW 49.46.020 and for such period as shall be fixed in such certificates.