(a) Finding and declaration of fact. The following occupations in excavation operations are particularly hazardous for the employment of persons between 16 and 18 years of age:

(1) Excavating, working in, or backfilling (refilling) trenches, except (i) manually excavating or manually backfilling trenches that do not exceed four feet in depth at any point, or (ii) working in trenches that do not exceed four feet in depth at any point.

(2) Excavating for buildings or other structures or working in such excavations, except: (i) Manually excavating to a depth not exceeding four feet below any ground surface adjoining the excavation, or (ii) working in an excavation not exceeding such depth, or (iii) working in an excavation where the side walls are shored or sloped to the angle of repose.

(3) Working within tunnels prior to the completion of all driving and shoring operations.

(4) Working within shafts prior to the completion of all sinking and shoring operations.

(b) Exemptions. This section shall not apply to the employment of apprentices or student-learners under the conditions prescribed in § 570.50 (b) and (c).