30. Notwithstanding section 29, shoring is not required for:(1) an excavation or a trench:(a) made in solid rock;
(b) where no worker is required to descend into it;
(2) walls where there is no danger of landslides and whose slope is less than 45º starting at 1.2 m (3.9 ft) from the bottom;
(3) walls whose slope presents no danger of landslides and for which an engineer certifies that it is not necessary to provide support, because of the slope, the nature of the soil and its stability; a copy of the engineer’s certification shall be kept at the mine site.